The Downwind Turn -killed Two Here

[Texas Buzzard]

Last summer a pilot working for the Border Patrol was killed during a low altitude downwind turn near here.
Last night 3 were killed in a helicopter crash in the Laguna Madre South of Corpus Christi, Texas.

In both cases the wind was blowing at a rate of 25 to 35 mph.

About 7 years ago there was a conversation/debate in RCM (mag) about the effects of the downwind turn on RC aircraft. This debate went on for several months. Various types contributed to the debate.

Just a week ago my adult son lost a small prop jet which had a wing loading of close to 12 oz/sq ft. He was about to land w/ half power headed downwind in a 10 to 15 mph wind. He made a tight aileron turn to the left when the nose dropped, it rolled left and from 20 feet altitude he couldn't recover. The Park Jet hit vertically crushing the nose.

We know the K.E. (and momentum) of the small Park Jet is significantly less than a 7 pound glow ship, thus making the electrics more susceptible to the FATAL DOWNWIND TURN- right?

I've been flying bigger glow powered ships for over 30 years and have noticed the effects of making a tight downwind turn - a loss of speed and altitude. It's common for winds blow here at 10 to 20mph during the day.

*** In RCM some college professors w/ a private pilots license + full-scale instructors continually talked about K.E., relative velocities, etc.

Can any of the readers talk about the FATAL DOWNWIND TURN?
We are NOT talking about a wide sweeping turn - we are talking about a TIGHT TURN while moving DOWNWIND.

[Rodney]

The plane is flying in an air mass. It could not care less whether it is flying down wind or up wind and will behave the same in any direction if the air speed is constant. What confuses many RC pilots is that they relate the airplane speed to ground speed and slow down to much (lose airspeed) when they make that downwind turn as they feel the plane is moving to fast and cut the power still more to decrease the ground speed and stall the plane out by losing air speed.

[N74463]

Oh no, it's back. It's the myth that refuses to die. No amount of vector diagrams can kill it. No explanation of the actual physics involved can drive it back to its lair. It's the dreaded DOWNWIND TURN!!!
Run, I tell you, run for your lives!!

::Runs from room, screaming...::

Joe

[Speed is Life]

>>>>"""Last summer a pilot working for the Border Patrol was killed during a low altitude downwind turn near here.
Last night 3 were killed in a helicopter crash in the Laguna Madre South of Corpus Christi, Texas.

In both cases the wind was blowing at a rate of 25 to 35 mph."""
>>>>>>

I guarantee that NTSB and/or FAA have NEVER heard of a "killer downwind turn". Aside from mechanical failure there is only poor piloting and/or lack of situational awareness that caused those crashes not some mythical "wind effect".

[CloudyIFR]

It's a myth, it doesn't happen and can't.

You're talking about ground speed versus indicated and/or true airspeed that the plane sees.

I can't believe this topic keeps rearing it's ugly head.

Curtis
Montana
6000 hr Commercial Pilot.

[podavis]

So maybe people are going too slow to make the turn because they misjudge the true airspeed due to the velocity added by the tailwind?

[nmasters]

Last summer a pilot working for the Border Patrol was killed during a low altitude downwind turn near here...

In both cases the wind was blowing at a rate of 25 to 35 mph.

Pilot error. He failed to watch his airspeed

[Dan Baldwin]

Last night 3 were killed in a helicopter crash in the Laguna Madre South of Corpus Christi, Texas.

In both cases the wind was blowing at a rate of 25 to 35 mph.
Helicopters don't stall, so it seems unlikely that anybody could attribute that crash to the "Killer downwind turn".



Just a week ago my adult son lost a small prop jet which had a wing loading of close to 12 oz/sq ft. He was about to land w/ half power headed downwind in a 10 to 15 mph wind. He made a tight aileron turn to the left when the nose dropped, it rolled left and from 20 feet altitude he couldn't recover. The Park Jet hit vertically crushing the nose.
That was an upwind turn, not a downwind turn.


Once an RC airplane gets above it's stall speed and leaves the ground, it's only tie to the ground is the pilot, but that relationship can cause the "killer downwind turn". In high winds the airplane will speed up considerably relative to the pilot when it turns downwind, so the normal response is to pull back on the stick, sometimes causing a stall. It can take quite a bit of stick time flying in high winds to suppress that tendency.

Dan

[JetPlaneFlyer]

Yep... I'll add another supporting voice to the 'aint no such thing as a downwind turn' argument.

'Wind' is relative to a ground datum only. Once the model leaves the ground it travels with the moving air mass and the wind you feel while standing on the ground has no effect on it.

[N9DP]

Those of us who are private pilots (or even Commercials and ATPs ) recognize the scenario. In a full size plane we have this little gauge called the ASI – the air speed indicator. It keeps us from stalling out when turning downwind to base, and much more frequently, base to final. I’m not aware of the “downwind” turn as being nearly the killer that the base-to-final turn is.

But our RC models lack such an instantaneous readout of airspeed. So we rely on ground speed. If the wind speed is 15 mph we need to fly the downwind leg 15 mph faster than we would in calm air. This seems too fast. We adjust the ground speed to what we are accustomed to in calmer air and our margin above stall speed narrows.

You describe a “tight aileron” turn. Could you comment on the bank angle? By aileron turn, do you mean uncoordinated, that is, aileron-only, without rudder input?

A 60 degree coordinated turn causes the airplane to weigh twice as much, so stall speed is increased by 40%. Combined with an already too slow air speed due to our improper interpretation of the fast ground speed, the model stalls.

When the air speed falls to below stall speed, the model stalls. The wing doesn’t care how much kinetic energy the model has, whether the engine is electric, gas or no engine at all; it doesn’t care about relative speeds (which are, however, getting the pilot into trouble!). The wing only knows the angle of attack is too great for the present conditions and it stalls.

There is considerable misunderstanding about stalls in the landing pattern, sadly among full scale pilots who should know better, and have a stall warning horn and ASI to keep them out of trouble. So it’s no wonder we RC pilots have problems with this critical phase of flight as well.

I think I’ve managed to say in several hundred words what several others so succinctly pointed out with far fewer words in their messages.

Good landings,

Dennis

[Speed is Life]

N9DP,
Very nicely stated.
-Mike

[Gary Warner]

It's back... Okay, who's going to email Myth Busters to finally put this one to rest. :rolleyes:

[Texas Buzzard]

Later today I heard the report that last night's helicopter crash, at first glance could from the radio conversation of the pilot and the EMS which was on Padre Island, there was a directional shift in the direction of the wind. I have seen the wind shift from SE to directly N when a Norther hits down here in South Texas.

The same night a 70 passenger jet landed very hot in a turbulent crosswind. I talked to a neighbor who was on that plane. He said the plane was really rocking from side to side when they came down through the clouds. Weather reports said the wind here was 25 gusting to 40 mph. That was SOP for a crosswind,i.e., lower upwind wind wing a bit and play with the rudder to stay on line in a crosswind.

But my primary reason for posting this was to stimulate and possibly make us more aware of how the RC plane handles when turning quickly from downwind in a 180 and back into the wind.

How many of you have flown a 7 to 8 lb RC in winds over 15 mph?.... Then have the same pilots flown a 14 oz. Electric plane in the same 15 mph + wind?

If some of you do have experience with a 7 lb RC and also a <1 lb RC did you notice a difference?

Back in my initial post in this thread I wrote,"Can any of the readers talk about the FATAL DOWNWIND TURN?
We are NOT talking about a wide sweeping turn - we are talking about a TIGHT TURN while moving DOWNWIND.

As you can see I am talking about a tight turn. One poster asked if the rudder was coordinating the turn. NO, in a Park Jet like ny son was flying it cannot use rudder control. It has no rudder.

If some of you have sailed a small boat like a HobieCat 16 in 20 mph winds then later sailed in a 30 ft. heavy sailboat, then you certainly noticed a big difference in how they handled. The small (16 ft) Hobie bounces around much more than the 200 lb sailboat.

You guys a much like the guys who fly in my club. When faced with an unusual topic - each guy has a ready answer even tho' he might not really know much about the question. My guys (20 of them)would probably fall into 3 different groups. RC guys are very opinionated and independant - right?

For those of you who dispute the "downwind turn syndrome" ( YES THAT IS IN THE LITERATURE OF THE FAA)

Four of you posters fall into the "There ain't no such thing" group : see posts # 3, 4, , 5 and 9. Posters # 7 & 8 (NMasters and Dan Baldwin ) showed some experience with the topic. N9DP says he is a private pilot. (I too was a private pilot who let his license lapse 4 years ago ( eyes). I took my private in a 7AC Champ.

So if any of you think a light plane will handle in gusty & high winds when making a tight 180 left turn will be effected the very same as a Boeing 747 ; explane why this is true.

Addendum: The Border Patrol pilot's accident was ruled pilot error. Furthermore spectator said," he was following illegal aliens in Mesquite country. He was headed North in a wind of maybe 30 mph from the South. He suddenly banked left (steep????what does that mean??) Then the plane rolled to it's right and went into a spin down low. He crashed while spinning to his right.

As a student pilot my ex-USAF instructor had me practice stalls from a climbing left turn. The 7AC has no "stall warning" device. The 7AC would stall and FALL OFF TO THE RIGHT. It's easy to recover if you stick the nose down and add some power - catch it quick - right?Can any of the readers talk about the FATAL DOWNWIND TURN?

We are NOT talking about a wide sweeping turn - we are talking about a TIGHT TURN while moving DOWNWIND.

[Speed is Life]

[QUOTE #Buzzard........(snip).............."topic - each guy has a ready answer even tho' he might not really know much about the question".......(snip)........."group : see posts # 3, 4, , 5 and 9. Posters # 7 & 8 (NMasters and Dan Baldwin ) showed some experience with the topic."
[QUOTE]

What a bunch of condescending Bull........highly likely that quite a few of us that have posted have MORE experience than your over inflated self esteem can imagine. Just that we likely didn't build rockets back in the Eisenhower Administration or whatever you claim to have done.
And, just what class standing did you get out of UPT/Air Cadets if you even graduated? Nah, I don't care.

This thread sounds like a really bored person trying to get attention.

I'm outta here :censored: -and Buzzard is on my ignore list.


-Mike

[mlbco]

I'm attaching the text of an article I'm writing for a hang gliding magazine on this subject. I apologize that the figures aren't finished, but maybe the words will give you some idea of what is happening when turning near the ground in a steady wind. This article does not address turbulence, gusts, wind gradients, etc.. The main reason I wrote it is to help solve the exact conflict that is occurring here:

1) The academics claim there is no problem, just watch your airspeed.
2) The practitioners know there is a problem because other sensory cues confuse the situation.

The unfortunate result of these discussions is a lot of name calling and no useful rules to fly by that reduce accidents. In my article I try to show how the visual cues and flight planning (from a hang glider pilot's perspective) must be re-assessed to fly safely near the ground in wind. RC pilots can adapt these results and also learn to be safer.

The bottom line is that downwind turns are a danger and people need to know why and how to deal with them. The academic answers rarely provide this information.

Steve Morris
---------------------------------------------------------
(Long article attached here)



Downwind Turns: What Your Instructor Never Told You

Steve Morris


Introduction
How an aircraft behaves when turning downwind has often resulted in heated arguments amongst pilots, instructors, and scientists who often have conflicting ideas on the physics of this maneuver. A carefully study of the various arguments from a scientific perspective shows that the theories which satisfy the laws of physics all tell the same story for this maneuver, but the interpretation of these results still leads to pilot confusion and accidents. This article will not attempt to revive these age old arguments (many of which use incorrect physical aurguments) but instead will try to explain what a pilot needs to know to stay out of trouble when flying near the terrain in wind. The situation we are most concerned with is the influence of a steady wind on the way we maneuver near the terrain. The influence of wind gradients and turbulence from thermals or rotors are very important when flying near the terrain, but will not be considered here since they do not change the basic issues we hope to explain.

It can be mathematically proven using Newton’s laws of motion or conservation of energy principles that:

The rate of descent of a gliding aircraft turning at fixed airspeed and bank angle will not be affected by the amount of wind or the direction it is blowing from.

This statement is the same as saying that when the air mass is in uniform motion and you are maneuvering relative to the air (i.e. fixed airspeed and bank angle) the aircraft feels no influence from the steady motion of the air mass. Of course, your trajectory over ground is distorted by the wind (figure 1), but if you ignore the ground and just fly relative to the air the wind has no influence. Flying in the wind can be problematic when we focus on the ground as a visual reference or when we want to maneuver relative to obstacles on the ground to avoid colliding with them. In these critical cases the influence of the wind on our motion over the ground can confuse us and result in piloting errors that can be fatal. The old adage that a steady wind can’t affect a turning aircraft is irrelevant when you are concerned with terrain obstacles in the environment. Instead, the pilot needs to know exactly how wind affects his or her perception of motion over the ground and how he or she should maneuver the glider to safely control their flight path. Unfortunately, this topic is rarely taught to students because it is tricky to explain, yet when we fly we need to deal with it at the most critical phases of our flight; launch, landing, and soaring near terrain.

Beginner pilots are more susceptible to the dangers of flying downwind near the terrain because most of their training takes place flying upwind and away from the hill. The first time they fly towards the hill or directly downwind, they may not be adequately prepared for what they will see and feel. Many accidents occur regularly because of confusing perceptions when flying near terrain in a moving air mass and it is important to study this problem in the “classroom” so that we can be prepared when we encounter it in the air.

What is a Downwind Turn?
A downwind turn occurs when the velocity of the aircraft (with respect to the ground) changes from 90 degrees crosswind, to straight downwind, and then 90 degrees crosswind again, but now heading in the opposite direction from which the glider originally started (figure 2). The remaining portion of the 360 degree turn that restores the aircraft to its original heading is called an upwind turn. Please note that the downwind turn is defined by the heading angle of the velocity vector over the ground (not relative to the air) and that the aircraft will be crabbed into the wind at the beginning and end of the downwind turn maneuver. I’ve chosen this definition of a downwind turn because it defines the region where extra care must be taken to avoid perceptual confusion or stalling of the glider. Some may prefer to think of a turn from straight downwind to straight upwind as a downwind turn but, as we shall soon see, many of the confusing effects caused by the wind cancel out during this portion of maneuver.

Turning with fixed bank angle in a steady wind

Figure 3 shows the ground path of a glider flying a 360 degree turn at a fixed bank angle in a steady wind equal to ½ the glider’s airspeed (both wind and airspeed are assumed constant). The portion of this maneuver that meets our definition of a downwind turn is highlighted in red and the upwind portion is shown in blue. The triangles drawn along the path show the position of the glider at equal time intervals and from this one can gain a sense of the velocity over the ground during the maneuver. Keep in mind that the motion of the glider relative to the air is a perfect circle for this fixed bank angle maneuver and therefore figure 3 shows the distortion of the path over the ground due to a steady wind.

If you study figure 3 closely you should be able to verify these conclusions.

Fixed bank angle turn in wind
1) The amount of time spent in the downwind portion of the turn is longer than spent in the upwind portion.
2) The rate at which the glider’s velocity vector changes heading (relative to the ground) is lower on the downwind portion of the turn than the upwind portion.

Considering the pilot’s perspective, we can reduce these conclusions to an even simpler result. If you’re flying straight downwind and bank for a turn, it will feel like you aren’t turning very fast relative to obstacles on the ground. It will actually take longer to get your velocity over the ground to change direction than if you performed the same turn while flying directly upwind. This is an important thing to know if you’re trying to avoid trees or a hillside! Most glider pilots spend little of their flight time heading straight downwind near the terrain and don’t get to study this phenomenon much. What we experience most often is the opposite effect, i.e. turning with a strong headwind, where we experience an enhanced sense of maneuverability relative to the terrain. Anyone who has soared a ridge in strong wind knows that only a slight deviation in heading is needed for the glider to make a big change in direction relative to the ridge. If the wind speed is nearly equal to your flight speed, you need barely move the nose relative to the horizon and like magic your traversing 90 degrees down the ridge! Move the nose a few degrees the other way and you traversing the opposite direction along the ridge, or 180 degrees of heading change in your ground velocity. Unfortunately, the opposite effect occurs when we have our nose pointed straight downwind and now we need to swing the nose of the glider more than 90 degrees in order to get our velocity over the ground to change 90 degrees. This overlooked effect is responsible for many accidents where pilots hit the terrain, not knowing why the glider “felt like it stopped turning”. Beginners are especially susceptible to confusion when turning from straight downwind flight because they have almost all of their flying experience has been with the nose into the wind which enhances the sensation of maneuverability.


Turning with fixed radius over the ground in a steady wind
Now imagine that we choose to fly a perfect circle relative to the ground instead of the air. This is the scenario we find ourselves in when we want to avoid the hill or other obstructions. Let me stress that you should always plan your flight to avoid being in this situation and this article is not encouraging pilots to fly downwind close to the terrain. It is useful, however, to study the ground-fixed radius maneuver as a basic element of all maneuvers which avoid the terrain when flying in wind.

Assuming constant airspeed, we can solve for the bank angle required to maintain constant turn radius (as seen from the ground). Figure 4 shows the resulting trajectory and figures 5&6 show the bank angle and g forces during the maneuver. The red portion is the downwind turn and the blue is the upwind, based on our previously mentioned definitions. I’ve drawn a cliff directly downwind of the circle to be representative of the situation pilot’s sometimes find themselves in when soaring.

This maneuver feels quite different to the pilot than flying a constant bank angle 360 in the wind. The downwind portion of the turn happens quickly and at much greater bank angle and ‘g’ force than the upwind portion. The glider feels like its “whipping” around the downwind side of the turn and then un-banking to crawl along the upwind segment. The pilot’s motion over the ground is also quite different. Instead of drifting a large distance downwind, the glider carves a perfect circle over the ground and changes direction most quickly on the downwind portion of the maneuver, exactly opposite of the constant bank angle case! Here are a few more important observations for the maneuver:

Fixed ground radius turn in wind
1) The amount of time spent in the upwind portion of the turn is longer than spent in the downwind portion.
2) The rate at which the glider’s velocity vector changes heading (relative to the ground) is lower on the upwind portion of the turn than the downwind portion.
3) Maximum bank angle (and ‘g’) occurs when the gliders ground velocity vector is pointed straight downwind
4) This maneuver takes longer to complete than fixed a bank angle 360 of the same radius and airspeed.


In a constant radius turn over the ground, the glider spends a lot of time at low bank angle on the upwind portion of the turn and experienced pilots will use the slow portion of the upwind segment to gauge the wind and to establish proper clearance from the terrain before turning in and “whipping it around” on the downwind side. Turning in or banking too soon will sacrifice terrain clearance and lead to disaster. The “whipping” portion of the turn requires aggressive pilot action, precise control and timing. If the wind speed is ½ the airspeed of the glider, the maximum bank angle required will be over 45 degrees while on the upwind portion the glider is banked less than 10 degrees. The maximum bank angle occurs when the glider is flying straight downwind (i.e. directly at the cliff in figure 4) and not when the glider is parallel to the cliff. An experienced pilot can perform this maneuver in a very fluid motion, often masking the skill and timing necessary to get it right. If he or she banks too soon (or not enough), the circle will distort and possibly intersect the terrain. Many beginners can understand this aspect of the maneuver, but they often forget to reduce the bank angle on the upwind portion which is vital for establishing clearance from the hill and for setting up the downwind turn. Beginners may also have little familiarity with steep-banked turns and the phenomenon of high-speed stall, often entering the maneuver with too little airspeed to safely pull ‘g’ on the downwind side.


What your instructor never told you

So far we have studied two types of 360 deg turns in wind; fixed bank angle and fixed radius over the ground. These maneuvers are the basic pieces of the downwind turn puzzle and show us why downwind turns feel different when we are near the terrain. Now let’s consider an approach into a confined landing area with a hill and trees on the downwind side and a significant breeze blowing. A standard landing approach would consist of a downwind, base, and final approach leg, but this field is so small that only a downwind and final will be possible. An experienced pilot would fly the downwind leg with excess speed and initiate an aggressive high-bank turn at the downwind end of the field (with appropriate terrain clearance), leveling out with enough room upwind to land inside the field. At the beginning of the 180 deg onto final, the pilot knows that initially he or she will experience a slow turn rate w.r.t. the ground and this is why a high bank angle is needed. As the glider comes around past 90 degrees from straight downwind, it will have a higher turn rate over the ground as it encounters a headwind and the pilot reduces the bank angle accordingly. The excess airspeed at the beginning of the maneuver is needed to avoid a high-g stall during the downwind portion of the turn.

A less experienced pilot in the same situation might do things in a disastrously different manner. While flying downwind the terrain appears to be moving quickly so the pilot subconsciously slows to a lower airspeed to keep the visual cues looking the same. At the downwind end of the field a moderate, constant bank angle turn is initiated and the glider slowly comes around while drifting downwind off the edge of the field. Even though it is banked up, the glider doesn’t feel like its turning because the scenery isn’t rotating as fast as the pilot expects for this bank angle and speed. In these crucial moments the glider’s ground track is pushed towards the trees by the wind and the lack of sufficient bank angle. Sensory overload occurs because the “bad” things are happening fast: the trees are getting closer, the glider feels “funny”, like it won’t turn. The pilot may freeze at the controls in a state of brain-lock or push out to accelerate the turn and stall into the trees because the airspeed is already low.

Each year many accidents like this occur and they are often blamed on the pilot’s inability to maintain airspeed while turning, when in fact the root cause is a lack of familiarity with downwind flight techniques near the terrain. Here are some key points to remember:

Important points to remember

1) When flying straight downwind a glider has a slower turn rate w.r.t. the ground and will take longer to change heading. This can confuse the inexperienced pilot and lead to “brain-lock” or the sensation that the glider won’t turn when flying downwind.
2) Carry extra airspeed when flying downwind and be prepared to turn aggressively with high bank angle to avoid terrain. Understand and avoid high speed stalls when turning aggressively.
3) A properly executed aggressive downwind turn will feel like you are whipping through the turn, where as a turn with lower bank angle and airspeed will seem to take forever and cause you to drift far downwind.
4) If you are 360’ing near terrain your maximum bank angle will occur when the glider is flying directly downwind. Reducing bank angle on the upwind side of the 360 is essential to “open up the circle”, establishing terrain clearance and giving the pilot time to prepare for the downwind “whip”.


To better appreciate the effects of wind on turning maneuvers it is best to practice 360 degree turns about a point fixed with plenty of terrain clearance and altitude. You should have a minimum of 500 ft. altitude and 500 ft. terrain clearance on all sides of the maneuver. Try to execute a fixed radius circle about a point on the ground and notice how the bank angle and turn rate change. Practice increasing your airspeed after flying directly upwind and then roll the glider so that the maximum bank angle occurs when straight downwind. Remember to reduce the bank angle smoothly so that when you are flying directly upwind the glider is almost level. Use this portion of the turn to relax, gauge your drift, and prepare for the downwind “whip”.

When you are soaring, do not maneuver downwind close to the terrain if you can avoid it. For example, fly linked 180’s when thermalling near the hill instead of 360’s until you have sufficient altitude. Every time you begin a landing approach, mentally prepare yourself for the turn from downwind to base, since this turn must be started early and requires more bank angle to avoid drifting off course. If you are making a 180 onto final and the field is restricted, carry extra airspeed and prepare to execute the downwind “whip” onto final.

[Dan Baldwin]

I too am a private pilot with about 135 hours in Cessna 150s, 152s, 172s, cherokees, a bonanza, a champ, and a sailplane. I have done many upwind turns, and downwind turns (1000s?) and I have never seen the airspeed indicator move unless I did something to change it, like changing flaps, elevator, or power. Yes, a high bank angle turn while close to stall can cause the airplane to stall, but it has nothing to do with a "downwind turn", in fact it is an upwind turn. It's called an approach to landing stall, and as N9DP states, the most likely place for it to occur is the turn from base to final, since that is generally where the plane is slowest, and if the pilot overshoots base, he may be tempted to use a high bank angle.

I also flew slope for many years. I flew very heavy planes, and very light planes in high winds, and none of them dropped out of the sky when I turned downwind.

Now gusts are a completely different matter. Many crashes of light planes and jets have been cause by wind shear, which is a rapid change in wind velocity. A plane might be flying into a 15 knot head wind, fly through the microburst that is creating that headwind, and end up with a 15 know tailwind. He has suddenly lost 30 knots of airspeed. Again, that has nothing to do with the "downwind turn syndrome".

A tight turn at low speed can cause a stall, but as your son found out, Buzzard, it doesn't matter if it's an upwind, downwind, or crosswind, turn.



Back in my initial post in this thread I wrote,"Can any of the readers talk about the FATAL DOWNWIND TURN?
We are NOT talking about a wide sweeping turn - we are talking about a TIGHT TURN while moving DOWNWIND.

As you can see I am talking about a tight turn. One poster asked if the rudder was coordinating the turn. NO, in a Park Jet like ny son was flying it cannot use rudder control. It has no rudder.

For those of you who dispute the "downwind turn syndrome" ( YES THAT IS IN THE LITERATURE OF THE FAA)
Can you post a link to that literature?





So if any of you think a light plane will handle in gusty & high winds when making a tight 180 left turn will be effected the very same as a Boeing 747 ; explane why this is true.


We are NOT talking about a wide sweeping turn - we are talking about a TIGHT TURN while moving DOWNWIND.
No, light planes don't handle the same as Boeing 747s. Does that have some relevance to this discussion?

What you seem to be describing is an upwind turn. A downwind turn is a turn to downwind.

Dan

[vintage1]

So maybe people are going too slow to make the turn because they misjudge the true airspeed due to the velocity added by the tailwind?

Of course they are, but try telling them that!

Oh no, they werent going too slowly, it was a DOWNWIND TURN!! :rolleyes:

Actually, I've piled in just as many on upwind turns, but no one wants to hear about it.

When you start life with free flight, you get to understand a lot more about how a plane flies without dumb thumbs trying to make it do what it can't.

It seems that it turns real smooth into wind, and then rips away dowwind, and takes an age to come around..but its the same time in seconds, it just looks so slow because its travelling downwind.

Of course when you get on the sticks and are as dumb as some posters here, you try and yank it round in a hurry, and of course it tipstalls or plain speed stalls and falls out of the sky.

Birds don't make those mistakes tho. Nor do full size pilots.

Turbulence can catch you out either way. My last crash was simply a slow speed approach into wind..which picked up a little, raised the nose and then dropped way, leaving the plane to tip stall in from 12 ft. Smashed the nose.

It was the DREADED UPWIND APPROACH. Nothing to do with me me being silly and not carrying more throttle and more down on the approach... :rolleyes:

[Gary Warner]

For those of you who dispute the "downwind turn syndrome" ( YES THAT IS IN THE LITERATURE OF THE FAA)
I think the word "syndrome" about sums it up. It's an issue between the ears. Otherwise I think it would be best described as a phenomenon, not a syndrome.

22 year "practitioner" pilot.

...Ahh nuts! I got sucked in again! :p

[vintage1]

Actaully its called 'denial' or 'transference' Or possibly 'simplistic explanations of slightly more complex things'.

People note something happening, and firstly deny it's their problem, then transfer it to something else to escape blame for it, and finally prop the whole shaky edifice up with pseudo science that just about fools enough people to make them feel better.

[Dan Baldwin]

Actaully its called 'denial' or 'transference' Or possibly 'simplistic explanations of slightly more complex things'.

People note something happening, and firstly deny it's their problem, then transfer it to something else to escape blame for it, and finally prop the whole shaky edifice up with pseudo science that just about fools enough people to make them feel better.

It's always good to find some reason for our crash other than our dumb thumbs. When I crash, I turn toward the pits and yell "Okay, who turned on?". :D

Dan

[Gary Warner]

Actaully its called 'denial' or 'transference' Or possibly 'simplistic explanations of slightly more complex things'.

People note something happening, and firstly deny it's their problem, then transfer it to something else to escape blame for it, and finally prop the whole shaky edifice up with pseudo science that just about fools enough people to make them feel better.
Psychology 101

[Dan Baldwin]

...Ahh nuts! I got sucked in again! :p

Ya know, sometimes you have to respond, even though you don't want to. It's a force that's too great to resist. Don't fight it man! You're only human!

By the way, I did a search for "downwind turn syndrome", and "downwind turns syndrome" on faa.gov, and I got no hits. I'm still waiting for the link.


Dan

[JetPlaneFlyer]

It's an issue between the ears.

Gary,
You summed up in a sentence what would have taken me a page to write :D

Its the modelling equivalent of the computer acronym 'PEBKAC' (Problem Exists Between Keyboard And Chair)

[Gary Warner]

By the way, I did a search for "downwind turn syndrome", and "downwind turns syndrome" on faa.gov, and I got no hits. I'm still waiting for the link.
Dan

I did find this link (http://www.faa.gov/about/office_org/field_offices/fsdo/lnk/local_more/plane_talk/media/jun04.pdf). See page 5

Part of the text:
This downwind turn is not dangerous because
of a loss of lift but due to an illusionary
difference. When at a low altitude flying
into the wind, when a pilot turns downwind,
the pilot senses an increase in
speed. He mistakenly interprets this as an
increase in airspeed and not groundspeed.
Since he thinks that his airspeed has increased,
he subconsciously increases his
pitch causing the airspeed to decay. If airspeed
decays too much, the pilot risks a
possible stall.

[Texas Buzzard]

I too am a private pilot with about 135 hours in Cessna 150s, 152s, 172s, cherokees, a bonanza, a champ, and a sailplane. I have done many upwind turns, and downwind turns (1000s?) and I have never seen the airspeed indicator move unless I did something to change it, like changing flaps, elevator, or power. Yes, a high bank angle turn while close to stall can cause the airplane to stall, but it has nothing to do with a "downwind turn", in fact it is an upwind turn. It's called an approach to landing stall, and as N9DP states, the most likely place for it to occur is the turn from base to final, since that is generally where the plane is slowest, and if the pilot overshoots base, he may be tempted to use a high bank angle.

I also flew slope for many years. I flew very heavy planes, and very light planes in high winds, and none of them dropped out of the sky when I turned downwind

Now gusts are a completely different matter. Many crashes of light planes and jets have been cause by wind shear, which is a rapid change in wind velocity. A plane might be flying into a 15 knot head wind, fly through the microburst that is creating that headwind, and end up with a 15 know tailwind. He has suddenly lost 30 knots of airspeed. Again, that has nothing to do with the "downwind turn syndrome".

A tight turn at low speed can cause a stall, but as your son found out, Buzzard, it doesn't matter if it's an upwind, downwind, or crosswind, turn.


Can you post a link to that literature? NO I CANT. I am repeating my ex-UASF instructor.



No, light planes don't handle the same as Boeing 747s. Does that have some relevance to this discussion? YES I THINK IT DOES. That Border Patrol pilot was flying a Cassna 182, which is a light plane when compared to a 747. Ha,Ha of course. The reason I mentioned it is this: If a 747 is flying in a parcel of air at cruise speed his K.E. & Momentum is very significant. A body in motion tends to remain in motion and will change direction or speed only if a force acts upon it - ( Newton ). The K.E. of a 747 is much larger than that of a 182 if both are moving at the same speed ( yes at the same speed - for comparison sake). With all that K.E. stored in a 747 it will not be acted on significantly by a 35 mph wind when he turns into it - Right?

Now consider an Aeronca Champ. TOWT about 800 lbs. While flying cruise speed his K.E. is minute compared to the 747. Right? Won't the Champ be affected more by turning into the wind?

You and I know that the lift of our wing decreases as we increase a bank. If I remember correctly a wing in a 60 degree bank has a vertical vector of lift much less than when wings are level. That is a fact. So if the Border Patrol pilot was in a 60 degree bank flying slowly as they do when observing illegal aliens ( I have seen them) and on top of that he was flying in a 35 mph wind. So when he made the steep banl to do a 180 and ended up facing the wind - don't you think he would stall....I have done this very thing but at about 1500 ft up. The plane will stall and roll to the right. It is very surprising when you first do it. But a spin will result unless corective action is taken.
The above is from personal experience.

So when I wrote, "Downwind turn" I was talking about a steep turn and a tight turn ( we were asking the wing to give more lift - and the plane said NO.
Now that I have more completely described this "downwind turn" maybe you'd have a comment. I value your input & thanks.

What you seem to be describing is an upwind turn. A downwind turn is a turn to downwind.

Dan
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
You and I know that the lift of our wing decreases as we increase a bank. If I remember correctly a wing in a 60 degree bank has a vertical vector of lift much less than when wings are level. That is a fact. So if the Border Patrol pilot was in a 60 degree bank flying slowly as they do when observing illegal aliens ( I have seen them) and on top of that he was flying in a 35 mph wind. So when he made the steep bank to do a 180 and ended up facing the wind - don't you think he would stall....I have done this very thing but at about 1500 ft up. The plane will stall and roll to the right. It is very surprising when you first do it. But a spin will result unless corective action is taken.
The above is from personal experience.

No, light planes don't handle the same as Boeing 747s. Does that have some relevance to this discussion? YES I THINK IT DOES. That Border Patrol pilot was flying a Cassna 182, which is a light plane when compared to a 747. Ha,Ha of course. The reason I mentioned it is this: If a 747 is flying in a parcel of air at cruise speed his K.E. & Momentum is very significant. A body in motion tends to remain in motion and will change direction or speed only if a force acts upon it - ( Newton ). The K.E. of a 747 is much larger than that of a 182 if both are moving at the same speed ( yes at the same speed - for comparison sake). With all that K.E. stored in a 747 it will not be acted on significantly by a 35 mph wind when he turns into it - Right?

Now consider an Aeronca Champ. TOWT about 800 lbs. While flying cruise speed his K.E. is minute compared to the 747. Right? Won't the Champ be affected more by turning into the wind?

I guess that dead B.P. pilot was concentrating on the ground to notice hid airspeed.

[mlbco]

It seems that it turns real smooth into wind, and then rips away dowwind, and takes an age to come around..but its the same time in seconds, it just looks so slow because its travelling downwind.

Vintage1,

If you look at the heading of the velocity vector relative to the ground the downwind portion of the turn does take longer than the upwind portion. The compass heading changes at a constant rate, but not so for the velocity heading w.r.t. the ground. This is important to note because for fixed bank angle it will take longer to change course and avoid obstacles on the ground. This is one of the subtle and often overlooked points that I tried to bring out in my article posted previously. The opposite effect (which is easier to understand) occurs when ridge soaring in high winds: a small change in compass heading gives a big change in velocity heading over the ground. This makes upwind turns feel "good" and authoritative to the earth fixed flier. Downwind turns are just the opposite.

Steve

[slipstick]

So when he made the steep bank to do a 180 and ended up facing the wind - don't you think he would stall.
If you end up facing into the wind that's a turn UPWIND not downwind. And all the usual downwind turn "logic" (using the term very loosely) insists that when you turn upwind, because the wind is now blowing towards your wings, it will help you by providing more lift. Obviously it didn't because what you have described is a stall caused by excessive bank with insufficient altitude for recovery. Unfortunately people have died from doing that upwind, downwind or even in a flat calm.

Steve

[MarkusN]

I think mlbco makes a good point here: Yes, it is a problem between the ears, but it is caused by our senses that fool us and are not adapted to the situation, and no amount of training can completely avoid it. So we need to be aware of it, especially in situation where we have to fly relative to the ground such as in a landing pattern or when avoiding obstacles.

Another thing that has not been touched yet is wind shear. When starting into the wind and then turning downwind one may indeed experience a sudden increase of the tailwind component due to the climb angle bringing us into higher winds, or simply turbulence (wind speed is not very constant in the boundary layer over the ground.)

[biber]

There are lots of people with lots of sticktime in various fullsize airplanes, who are getting more or less safely up
and back down for years and yet don't know how the physics of what they are doing would work.

You have to practice and learn to do the right things, to be safe.
The understanding of the underlying physics does help, but is obviously not required, to operate an airplane safely.

The part that is regularly anoing me is, that a big part of the fairly experienced pilots and even instructors
have some seriously flawed concepts of flight physics in mind, that they won't ever put down.
Even worse, they will continue to spread their misconceptions of physics.

Sometimes I think, you'd be able to make a talented monkey learn to fly safely or even with virtuosity.
But don't let him design an airplane!

However, the cool thing about this board is, you meet lots of people that do have it right and have already added to this thread.

biber, stepping off the soapbox

[vintage1]

absolutely right, and its why pilots are taught to make a big circuit to downwind, and turn into finals a fairly long way out. So they don't have to make turns near the ground that might confuse them.

That transfer of attention from instruments to ground is always a tricky one in a wind.

It is not required that the pilot understands the physics, merely that he knows a fixed set of rules that will allow safe operation. But like all 'rules that are for the obedience of fools, and the gudance of wise men', knowing what is really happening gives a good pilot a considerable edge.

[Tom Harper]

"My last crash was simply a slow speed approach into wind..which picked up a little, raised the nose and then dropped way, leaving the plane to tip stall in from 12 ft. Smashed the nose." (Vintage)

Had you been headed downwind you would have experienced loss of control and a loss of lift.

In a steady flow of air there is no change in flight dynamics with a change in heading.

A gust presents a different set of conditions.

[biber]

From experience and theory gusts are pretty much random in amount and direction.
So different set of conditions, but not relevant to the issue discussed here.

biber

[Tom Harper]

Biber,

I believe that is not the case. I measured the prevailing wind at our flying field and found that it was a series of gusts rather than a steady flow. The literature describes gusts as having a 1-cos profile. That is true to the extent that a gust slowly builds then rolls off to a constant rate. However, gusts often build and fade in steps.

I believe this is relevant to the issue here. Many 'downwind turn' incidents are a matter of pilot error. However, many are simply a matter of a gust causing the situation observed by Vintage.

I had a similar experience last week with my LT-40. It was coming in dead stick in the direction of the prevailing wind. A gust caused loss of control and decrease in lift. No crash but the effect was obvious.

[Texas Buzzard]

I don't want to beat a dead horse. I do want to give you guys the last word though.

May I insert a bit more information? From my point of view this last senario is my best explanation of HOW TO ACHIEVE A BAD ENDING WHEN MAKING A DOWNWIND TURN. REMEMBER THE TURN IS VERY TIGHT ( SMALL RADIUS ).

Here it is: You are flying either something like a piper Tripacer (full scale) or a high winged RC ( not a floater but one of wing loading of 16 oz/sq ft or more)
It would apply to War Birds too.

O.K., the wind is about 20 mph gusting to 25 mph. You want to make a 180 degree turn quickly.
You are headed downwind at 15% above stalling speed. Your turn is initiated with ailerons ( w/ rudder to compensate adverse yaw - or just stay off the rudder if you want ). [ With the small electrics we are controlling with throttle, ailerons & elevator - no rudder ]

The plane is banked between 30 & 40 degrees to the left and you pull in a bit of UP elevator to swing the bird around as you want to do a 180. To prevent losss of altitude you begin a climbing turn ( slightly - just a tad.) :rolleyes:

In this manuver THE RIGHT AILERON IN DOWN. THIS IS GIVING THE RIGHT WING A MUCH MORE POSITIVE INCIDENCE THAN THE LEFT WING.

Which wing will stall first? :confused:

The right wing will stall first - In A Turn The relative STALLING SPEED GOES UP ! So The right wing STALLS. THERE IS AN ABRUPT ROLL TO THE RIGHT & THIS USUALLY CAUSES THE PLANE TO SPIN.

So finally, the plane thinks it's in a climbing turn to the left. Then when stalling speed is reached the plane rolls to the right ( rt. wing at a higher incidence - eh?) So the spin is to the right.
Where I fly near the Gulf Coast in Texas the winds start about 8 AM. On a typical day the wind is 12 to 20 mph, this week we had winds 24 hr/day of 15 to 30 mph. I took up sailing about 10 years ago because the wind bent the palm trees every day for a month one summer. :) :rolleyes: :rolleyes: :cool:

[Jurgen Heilig]

...
It's the dreaded DOWNWIND TURN!!!
Run, I tell you, run for your lives!!
...

Amazing that this thing comes back again and again - and it is older than the airplane on the conveyor belt.

:) Jürgen

[JetPlaneFlyer]

Buzzard,
The situation you describe could very well result in a stall but this is simply because you attempted a tight turn while flying close to stall speed... Its got absolutely nothing to do with wind direction ;)

[MarkusN]

I believe this is relevant to the issue here. Many 'downwind turn' incidents are a matter of pilot error. However, many are simply a matter of a gust causing the situation observed by Vintage.
That is why in gusty conditions you are instructed to land a full scale airplane at + 1/2 Vw over the normal approach speed, which is already at 10% above stall of the fully loaded plane. Rules for a fool to obey...

[MarkusN]

and it is older than the airplane on the conveyor belt.
Oh, right! It's about time to start one of those again. Or not start it, as it were, because, amazingly enough, that is the result.

(If you consider wheel inertia, that is.)

[Dan Baldwin]

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
You and I know that the lift of our wing decreases as we increase a bank. If I remember correctly a wing in a 60 degree bank has a vertical vector of lift much less than when wings are level. That is a fact. So if the Border Patrol pilot was in a 60 degree bank flying slowly as they do when observing illegal aliens ( I have seen them) and on top of that he was flying in a 35 mph wind. So when he made the steep bank to do a 180 and ended up facing the wind - don't you think he would stall....I have done this very thing but at about 1500 ft up.

A bank willl ABSOLUTELY increase the stall speed of an airplane. I don't think anybody is disputing that. If a plane that is near stall already enters a steep bank, it will stall, but it doesn't matter if it's turning upwind, downwind, or is flying in calm conditions. We have already covered the fact that the pilot may bank more steeply because of what he sees on the ground. The only facts that are in dispute as far as I'm concerned is wether or not a plane will stall strictly because it turns in a particular direction with respect to the wind. Most people believe that a downwind turn will cause a stall. For some reason you believe that an upwind turn will cause a stall.



Now consider an Aeronca Champ. TOWT about 800 lbs. While flying cruise speed his K.E. is minute compared to the 747. Right? Won't the Champ be affected more by turning into the wind?

I guess that dead B.P. pilot was concentrating on the ground to notice hid airspeed.No, the champ is not affected at all by turning into the wind, although the pilot may be. Obviously, a pilot can lose track of airspeed due to watching what's happening on the ground.


Dan

[podavis]

You are headed downwind at 15% above stalling speed. Your turn is initiated with ailerons .... The plane is banked between 30 & 40 degrees to the left and you pull in a bit of UP elevator to swing the bird around as you want to do a 180. To prevent losss of altitude you begin a climbing turn ...
In this manuver THE RIGHT AILERON IN DOWN. THIS IS GIVING THE RIGHT WING A MUCH MORE POSITIVE INCIDENCE THAN THE LEFT WING....
... In A Turn The relative STALLING SPEED GOES UP....


I may be remembering it wrong but I recall from Scott Stoops book the inside wing stalls first because it's going slower. I would expect that even though the right wing may be at a higher effective incidence angle it's because it's airfoil is heavily modified by the aileron acting like a flap which should knock its stall speed back down, whereas the opposite is true for the left (inside of turn) wing with the aileron up. I'm going to have another look at The Book.

[podavis]

...Turbulence can catch you out either way. My last crash was simply a slow speed approach into wind..which picked up a little, raised the nose and then dropped way, leaving the plane to tip stall in from 12 ft. Smashed the nose.

Turbulance could be a topic of more discussion given all the park fliers. I have it spades where I fly, it makes my planes dance like St Elmo's fire.

[Gary Warner]

A bank willl ABSOLUTELY increase the stall speed of an airplane. I don't think anybody is disputing that. If a plane that is near stall already enters a steep bank, it will stall, but it doesn't matter if it's turning upwind, downwind, or is flying in calm conditions.

Just as a matter of crossing T's and dotting I's, it's the angle of attack at any attitude or any speed that causes a stall. A steep 'falling' bank (read: no extra up elevator applied) will not increase the angle of attack. That said, I think we all (with a few exceptions) understood that this remark of yours included maintaining altitude in the bank, where the stall speed will increase.

[Dan Baldwin]

Just as a matter of crossing T's and dotting I's, it's the angle of attack at any attitude or any speed that causes a stall. A steep 'falling' bank (read: no extra up elevator applied) will not increase the angle of attack. That said, I think we all (with a few exceptions) understood that this remark of yours included maintaining altitude in the bank, where the stall speed will increase.

100% agree.

Dan

[Texas Buzzard]

Imagine this: You are flying a lightly loaded plane (wingloading), its a full scale or a model....you decide to execute a 180 degree turn as fast as you can.

You are to turn to the left. Your right aileron goes down and the left aileron goes up. This means the air "sees" the two wings to be at a different attitude. The right wing has a greater angle of attack. Right?

Then you pull in some up elevator to maitain altitude. Throttle setting isn;t changed. You are trying to maintain aprox. a 35 degree bank.

That wing when banked will have a higher stall speed IF YOU TRY TO HOLD ALTITUDE. Right? Which wing will stall first?

Yes the right wing will stall first. The plane will roll to the right. If you hold up elevator you will stall, while falling off to the right. Right?

The first time I was shown this I was surprised to roll to the right when stalled.

BUT, the right aileron being down gave the right wing a more positive attitude so it stalled FIRST.

I surely am enjoying reading ALL these posts. And Vintage-1. I too started with Free Flight & Gliders - before easy and convenient RC equip. was available.........have you read the book "STICK & RUDDER"? By a German Pilot.

[biber]

Once the bank is established and you start to yank it around, do you still have left stick applied if it's a left turn?
I don't, it's rather slightly the other way around for me.
The very most of all fullsize gliders I know (that's about 30 different types of all ages and sizes)
do have the habit to dive in to the circle in turns when stalling, or just mush around without diving to any side.
And they do that regardless of any wind, regardless where you are pointing at that moment.
Of yourse the yaw string is always centered or very slightly outward of the turn.

From what I've seen and heard of the book 'Rudder & Stick' it's really good,
but I can't believe, that your statements are quoted correctly from the book.

biber

[JetPlaneFlyer]

Buzzard,
I do tend to agree with you that (assuming you are holding 'into the turn' aileron) the outer wing will probably stall first in a turn. Biber also makes a good point that once a turn is initiated a little counter turn aileron is required on some aircraft.

The argument posed earlier by Podavis that the inner wing is flying slower so will stall earlier is fundamentally flawed because stall is not directly related to airspeed. An airfoil stalls when it reaches a certain angle of attack, airspeed makes little difference (Re number changes accepted). Just because the inner wing is going slower does not mean it's operating at a higher angle of attack so it does not mean it will stall first.

Of course none of this stuff has anything to do with the topic of the thread :rolleyes:

Steve

[biber]

In addition, to all previously mentioned points, if you deflect a controlsurface on a wing, the local AoA where that wingportion
will stall might differ from the flush surface case aswell as the Cl_max will differ.
Further, any rollrate present will change the local AoA too, so it's not always that easy to determine how close to stall any of the wing portions is.
You can calculate that, but need some info on the wings geometric data.
AVL combined with Xfoil or windtunneldata can do that calculations and (i suppose even more conveniently) XFLR5.
For rough guesses some general knowledge on airfoils combined with some trigonometrics will do.

biber

[vintage1]

A steep 'falling' bank (read: no extra up elevator applied) will not increase the angle of attack. That said, I think we all (with a few exceptions) understood that this remark of yours included maintaining altitude in the bank, where the stall speed will increase.

I thought and decided it will, because it reduces the effective wing area.

I.e. the lift vector is no longer upwards, but canted over. So it needs more of it to keep te vertical component equal to the weight.

To maintain a constant heading in the bank will then require that some lateral force is generated..typically by use of opposite rudder and the engine thrust or the fuselage side area.

So unless the plane is allowed to fall, any bank angle means an increase in stall speed.

Couple that with the fact that a long winged e.g.sailplane in a tight turn can have the inner wing going very slowly indeed, and you can see the reasons why washout works ...

WWII fighters learnt to pull as many G's as they could stand, and take the plane right to the edge of a high speed stall..if you are pulling 6-7g that is teh efecitive 'weight' of the plane as far as the wing is concerned. When the gs are suuch that the plane's stall speed approaches its maxiumum speed, you are in the regime of 'thats as much load as we can ever impose on the airframe'

Until you do a high speed dive of course ;)


As far as outboard alerons go, the problem is not the use of aileron to get into the bank..thats fine. It's the use of down aileron on the inner slower moving wing to get OUT of the bank. That can EASILY stall that wing. And almost certainly will partly stall it leading to excessive drag and 'adverse yaw'





.

[Texas Buzzard]

Without builtin differential ailerons do show adverse yaw in slower training types. And surely the wing with the aileron in the down position is flying at a greater angle of attack ensuring that it stalls first. Don't you agree?

Here are some entries under "downwind turn" and related topics.
November 4, 2006 edition
Steve Seibel
steve at aeroexperiments.org
www.aeroexperiments.org

Here are some examples from published literature and other sources. Some pertain to full-scale, piloted aircraft and some pertain to radio-controlled models.

Source: "West Wings Hunter" by Curtis Matikow. Radio Control Jet International magazine, issue 80 (October/November 2006), pp. 28-30. Quote: "After a 150 foot take-off run, she was off and climbing, but rather slowly...as soon as I turned downwind, I knew I was in trouble. With the modest power of the motor, the extra drag and weight of the landing gear I had made up, and the 30 mph tailwind, I was unable to keep altitude downwind. I ended up in the bushes at the edge of the runway..."

Source: "Electric Jet Airplane Design" by Ian Monty. Quiet Flyer magazine, v.11, issue 08 (August 2006), pp. 24-27. Quote: "When turning onto the downwind leg of a landing pattern, always be ready to add a little extra power."

Source: Certified Flight Instructor (and recent graduate of Embry-Riddle Aeronautical University) giving me a biennial flight review in a Cessna 172 at Corvallis Oregon, spring 2005. Quote: "Let's do the stall flying into the wind--the wing will stall at the same airspeed flying in either direction, but it will take more altitude to recover if we are flying downwind. It's like the difference between taking off into the wind and taking off with a tailwind."

Recall again that in the related article on this website entitled "Downwind turns ARE 'different'!", we noted that IF there is a significant wind gradient in the usual direction (wind increasing with height), then an aircraft actually extracts energy from the wind gradient (leading to a decrease in sink rate) when descending WITH the wind, and loses energy to the wind gradient (leading to an increase in sink rate) when descending INTO the wind! Yet many of the pilots quoted above appear to be describing the opposite phenomenon. It certainly appears that in many of these cases these pilots are unconsciously moving the control stick aft and decreasing the airspeed to a value well below the optimum airspeed, and simultaneously increasing the angle-of-attack to a value well above the optimum angle-of-attack, when flying with a high groundspeed, i.e. when flying with a tailwind.
For more, see these related articles on the Aeroexperiments website:

Brain teasers for those who believe that downwind turns are "different"

Downwind turns ARE "different"!--this is a bit of a "disclaimer" for the "Brain teasers for those who believe that downwind turns are 'different'"!
And for still more, see these articles from the "Ask J and D" feature of the "DJAerotech" website:

some interesting notes on wind shear

And for still more, see these articles:

Challenging the wind by Martin Hepperle-- an interesting little article on the best strategy for flying in wind during a pylon race
Copyright © 2004 aeroexperiments.org

[Texas Buzzard]

Buzzard,
I do tend to agree with you that (assuming you are holding 'into the turn' aileron) the outer wing will probably stall first in a turn. Biber also makes a good point that once a turn is initiated a little counter turn aileron is required on some aircraft.

The argument posed earlier by Podavis that the inner wing is flying slower so will stall earlier is fundamentally flawed because stall is not directly related to airspeed. An airfoil stalls when it reaches a certain angle of attack, airspeed makes little difference (Re number changes accepted). Just because the inner wing is going slower does not mean it's operating at a higher angle of attack so it does not mean it will stall first.

Of course none of this stuff has anything to do with the topic of the thread :rolleyes:

Steve

DITTO JPF

[MarkusN]

Source: Certified Flight Instructor (and recent graduate of Embry-Riddle Aeronautical University) giving me a biennial flight review in a Cessna 172 at Corvallis Oregon, spring 2005. Quote: "Let's do the stall flying into the wind--the wing will stall at the same airspeed flying in either direction, but it will take more altitude to recover if we are flying downwind. It's like the difference between taking off into the wind and taking off with a tailwind."
Sorry, but that's complete and utter bull. It's exactly the case Biber was ranting about.

Wndshear, I agree. that can add some interesting effects during climb or descent.

[Dan Baldwin]

Sorry, but that's complete and utter bull. It's exactly the case Biber was ranting about.

Wndshear, I agree. that can add some interesting effects during climb or descent.

Since the plane is traveling faster downwind, it will take more GROUND to recover, but no more altitude.

Obviously, wind is very important to pylon racers, and they would treat a downwind turn differently than they would an upwind turn, because they using ground references for their turns.

Wind shear is real, wind gradients are real, high speed stalls are real (and different planes react differently to high speed stall), wind gusts can cause a plane to stall, and the pilot may very well be affected by visual cues on the downwind turn, but the plane is not. Buzzard, if you have actually flown full size aircraft, you know that this is true.

Dan

[N9DP]

Source: Certified Flight Instructor (and recent graduate of Embry-Riddle Aeronautical University) giving me a biennial flight review in a Cessna 172 at Corvallis Oregon, spring 2005. Quote: "Let's do the stall flying into the wind--the wing will stall at the same airspeed flying in either direction, but it will take more altitude to recover if we are flying downwind. It's like the difference between taking off into the wind and taking off with a tailwind."



Here’s what my friend Steve says:
_____________
Dennis,

It might take more distance to recover but not more altitude! The stall occurs at the same angle of attack either with a headwind or tailwind. Recovery uses the same amount of altitude. The only reason an aircraft can take off earlier into a headwind is that the airflow is measured against groundspeed just before liftoff. Once in the air the wing responds to relative wind with the only possible exception of windshear. This is not unlike a boat in a strong current, no matter how fast the boat appears to be going as viewed from the shore if it is not being propelled on its own it will have no rudder authority. Clear as mud.

Steve

CFII Embry-Riddle Class 0f 1979
_______________

In addition to being a “double i”, my good friend Steve is a senior ATP captain, check pilot, and fellow RC pilot. He is always willing to help his neighbor private pilots become safer pilots. Its guys like him that make the aviation community great.

It seems a bit incongruous to me that this thread should persist in “Modeling Science:
Physics, Aerodynamics, Engineering, Circuitry, and other scientific discussions". Frankly, I find more trolling than science in the discussion. But it does present a fascinating case study of human interactions via the internet – better than watching “Survivor” [grin].

Good landings,

Dennis

[funfly2]

Could the dreadful downwind turn have killed this one too?
http://www.liveleak.com/view?i=c53_1174480506

[ciurpita]

at least for me, the only time this has been a problem is when i'm fairly close to the ground (~20ft), making a very high banked turn (>60) with an 8' wingspan, and it's fairly windy out (>15k)

after reading some articles in RCSD, i began thinking that the problem was related to the wind gradient close to the ground.

[funfly2]

I must say that most of you have been unfair towards Texas Buzzard.

He has indeed a point here.

Most of you are just ignoring inertia, yes I repeat: inertia.

Suppose a plane is flying against strong wind, having plenty of airspeed but almost zero ground speed.
Now you make a sudden 180 deg turn, so the plane suddenly gets a strong tailwind; it_will_take_certain_time (due to inertia) until the plane gets enough airspeed downwind, which may be long enough to cause stall.

:)

[biber]

You don't do fullsize gliding, do you?

Please take a ride and try yourself.

Inertia is the very reason, why steep turns require more lift from the wing than straight forward flight.

You don't see any variations in airspeed during the tightest turns in any wind, except for what you steer yourself and gusts,
where the speed varies pretty much randomly regardless of the direction your pointing at.

biber, who has done a turn or two

[JetPlaneFlyer]

Funfly2,
You need to brush up on physics ;)
You are relating aircraft inertia to a ground datum, but an aircraft 'sees' only it's inertia in relation to the air around it. The aircraft does not 'care' how fast the earth is moving by below it becuse it has no 'connection' to it. The aircraft inertia relative to the ground is only significant when the aircraft actually comes into contact with the ground.

If you think this is wrong think about the fact the the earth is revolving at a velocity at the equator of around 1040 mph, do you notice any difference when you move east compared to moving west?.... I know I dont :rolleyes: .
Also the earth is revolving around the sun at about 60,000 mph ... do you 'feel' this?

If you still thgink that inertia makes a difference have a read of the brain teasers on this page: http://www.aeroexperiments.org/brainteasers.shtml

[vintage1]

Or to put it simply. All Newtonian mechanics applies to relative velocities, there is no absolute velocity because no absolute linear inertial frame exists.

There is an absolute inertial frame of acceleration though. A fact which if pursued would have led Newton to relativity theory.

Inertai applies to changes in momentum. There is no concept of absolute momentum in Newtonian mehanics.

Perhaps we need a new thread 'Basic physics and mechanics' before we get on to arguing these issues.

[funfly2]

You don't do fullsize gliding, do you?

Please take a ride and try yourself.

Inertia is the very reason, why steep turns require more lift from the wing than straight forward flight.
Yes, and so what?!



You don't see any variations in airspeed during the tightest turns in any wind, except for what you steer yourself and gusts, where the speed varies pretty much randomly regardless of the direction your pointing at.

biber, who has done a turn or two
Oh boy, you made my point!

Now, what are gusts? What is wind-shear?
They're nothing but sudden changes in wind force and/or direction, which, if your plane can't follow them to a certain extent, it may mean you're in trouble!




Funfly2,
You need to brush up on physics
You are relating aircraft inertia to a ground datum, but an aircraft 'sees' only it's inertia in relation to the air around it. The aircraft does not 'care' how fast the earth is moving by below it becuse it has no 'connection' to it. The aircraft inertia relative to the ground is only significant when the aircraft actually comes into contact with the ground.

Now it's getting funny.

All objects resist changes in their state of motion, no matter if they are on earth or in the air.
All objects have this tendency - they have inertia.
The tendency of an object to resist changes in its state of motion varies with its mass.
Mass is that quantity which is solely dependent upon the inertia of an object.
The more mass an object has, the more inertia it has.
A more massive object has a greater tendency to resist changes in its state of motion.

That has nothing to do with the wind. An object's inertia is just related to its mass!

Have you ever travelled on a balloon?
Well, you seldom feel any wind up there on a balloon until the wind force or direction suddenly changes, then you feel the wind until the balloon has reached the new airspeed or the new wind direction.
How long it will take depends on the balloon's inertia and on how fast the wind changes as well as on the magnitude of the change.

:)

[eflightray]

This thread brings back memories.

In my younger days I used to fly free flight models, glider and rubber powered. The strange thing was they would gently climb away and start to circle, then fall out of the sky. No one anywhere in the world could ever get a free flight model to actually do a complete circle if there was any wind. The clubs 'expert' explained that it was "the dreaded down wind turn, it eventually wiped out the Pterodactyl", and "would be impossible for a plane to do circle in a wind until radio control is invented and a ground pilot can control the turn".

Luckily radio control came along shortly afterwards and......gasp in amazement!, we could do down wind turns, admittedly after lots of crashes and explanations of what we were doing wrong.

Sadly it would appear that there are so few 'experts' left in the world that the 'dreaded down wind turn' is starting to reappear and is crashing planes without warning.

It looks like the outcome for the future of model flight is to only fly on calm days.

(OUCH!, just bit my tongue in my cheek). :rolleyes:

[JetPlaneFlyer]

Funfly2,

You are quite right, i should have more correctly used the term 'momentum' instead of 'inertia' in my previous post, my mistake...
I think it was Galileo that first stated that's it's impossible to tell a stationary object from a moving one unless you have a point of reference to compare it against... What reference point you pick is up to you. Why is the surface of the earth at the point you happen to be standing any better point of reference to a flying aircraft than, say, the earth's core or maybe the sun? None of these points have any physical contact with the aircraft... The air that surrounds the aircraft is surely the most logical reference to use when considering an aircrafts movement though the air?

Momentum is proportional to velocity and velocity is a 'vector' quantity... i.e velocity has a direction. If you look at change in velocity (and hence change momentum) of an aircraft flying at 50mph northward (no wind) then doing a 180 Deg turn. Lets say for the sake of argument that northward direction is positive and southward vector is negative... The change in velocity (and hence momentum) is the difference between 50mph north (positive) to 50mph south (negative) = 100mph

Now look at the same aircraft still flying at 50mph northward but now into into a 50 mph headwind... It's velocity 0mph. It does a 180 Deg turn and it's velocity is then 100mph south (negative)
So change in velocity (and hence momentum) is the difference between 0 and -100 mph = 100mph

You can hopefully see from the above that the change in momentum of the aircraft is independant of wind :)

Steve

[biber]

Funfly2, if you had experience in fullsize airplanes you would know, that there is no way to determine the wind direction without seeing the ground, just from measuring accelleration.
If your statement would be true, then it would be possible to determine the wind without seeing the ground.

biber

[Thomas B]

Anyone who ignores wind gradients (wind speed vs distance above ground) in the landing pattern and assumes that the air mass is that perfect uniform set of air all moving at one speed is certainly a little more likely to crash as they turn in a decent.

The old rule of thumb of adding half the wind speed to your approach speed helps, but you can still get bit by a gust from your aft quarter or a lull from your front quarter at an inopportune time as you turn base and final to land.

The inertia/momentum argument holds some water, as it takes a bit finite time to accelerate/decelerate objects in relation to their frame of reference.

I have a few hundred hours in both full scale sailplanes and light planes and recall a few times where only instant attention to the stick (and throttle if you have it) prevented a stall in the pattern as I was turning, as the wind gradient changed wind speed in a big way with altitude changes.

In a couple of those cases, if the full scale sailplane had been in free flight with no one at the controls to correct the airspeed, it would have stalled and crashed.

One can say that in all cases like this, the accident was due to the pilot failing to maintain adequate airspeed just like you can say that in the end, the cause of death is always heart failure...:)

Usually, the truth is a little more complicated.

The steady state air mass is great for discusion, but rarely exisits in real life. What matters is the action of the hugely imperfect air mass near the ground, where variations in it can combine with lack of time to correct problems to put people in trouble.

[Thomas B]

Funfly2, if you had experience in fullsize airplanes you would know, that there is no way to determine the wind direction without seeing the ground, just from measuring accelleration.
If your statement would be true, then it would be possible to determine the wind without seeing the ground.

biber

That is not precisely true. It is true in a steady state air mass, but not in a dynamic air mass.

All else being held steady..power if you have it, controls, descent proile: a gust from the rear of the aircraft will momentarily lower indicated airspeed and a gust from the front will momentarily increase indicated airpseed. If you were in fog (for some silly reason) and unable to see the ground, you could still sense these changes and the direction that they are coming in, if they are large enough. The smaller and and lighter and draggier and slow the aircraft, the more the effect is noticable

I never had any trouble simply feeling or hearing these effects in the old 2-33 trainer and 1-26 sailplanes that I flew. I do think a guy in a modern glass slipper is a bit more removed from the feeling/hearing of the gust effects on the glider, since they are lots more slippery.

This all matters much more in very slow aircraft like vintage sailplanes and lightplanes and some of our models that are flying at small multiples of typical wind and gust speeds near the ground than is does on larger aircraft that are flying at larger multiples of typical wind and gust speeds near the ground.

I have no doubt that most "downwind turn" acccidents are due to the illusion of plenty of airspeed supplied by the fast moving ground reference, but sometimes there is a little more to the story.

[biber]

Wind gradients are usually encountered when ascending or descending through a rather narrow wind shear layer.
That can be close to the ground or at any altitude where temperature gradient inversion occurs.
That's indeed more complicated and if you take it to that level, then the donwind turn is an inappropriate oversimplification of the issue.

Edit:
Gusts do not have only one possible direction.
You seem to claim, that gusts only can have the same direction as the general wind has.
And that' just not true.
You will find not only gusts of the sort 'sudden increase in wind velocity' but also 'sudden change of direction' and sudden 'lack of wind velocity'.
The gust coming from rear, that takes away from you some precious airspeed can come at you any time and on any heading.

biber

[Thomas B]

Wind gradients are usually encountered when ascending or descending through a rather narrow wind shear layer.
That can be close to the ground or at any altitude where temperature gradient inversion occurs.
That's indeed more complicated and if you take it to that level, then the donwind turn is an inappropriate oversimplification of the issue.

biber

The "downwind turn" that kills people and wrecks models happens close to the ground, as does the wind gradients and gust effects that I am talking about...thus, this is precisely on topic...:)

Wind gradients and gust effects at altitude whern you are cruising and not turning to land close to the ground are not as hard to deal with and the steady state air mass model is much more applicable.

[Thomas B]

Wind gradients are usually encountered when ascending or descending through a rather narrow wind shear layer.
That can be close to the ground or at any altitude where temperature gradient inversion occurs.
That's indeed more complicated and if you take it to that level, then the donwind turn is an inappropriate oversimplification of the issue.

Edit:
Gusts do not have only one possible direction.
You seem to claim, that gusts only can have the same direction as the general wind has.
And that' just not true.
You will find not only gusts of the sort 'sudden increase in wind velocity' but also 'sudden change of direction' and sudden 'lack of wind velocity'.
The gust coming from rear, that takes away from you some precious airspeed can come at you any time and on any heading.

biber

Note that I mention gusts from any and all directions. Also, as another poster mentioned, wind speed and direction is the average velocity of all the chaos that is happening in the atmosphere.

Most gusts and lulls will be related to the prevalent wind direction and not happening at random from any direction on the compass.

[biber]

Ok, if you narrow it down to the particular case of low level with considerable wind gradient then that's fair enough.
But it's important not to mix up the terms 'wind' and 'wind gradient'.

biber

[Thomas B]

Ok, if you narrow it down to the particular case of low level with considerable wind gradient then that's fair enough.
But it's important not to mix up the terms 'wind' and 'wind gradient'.

biber

The wind gradient as you encounter it consists of the local (micro) wind effects at your location above the ground at the moment you are there, so wind and wind gradient do get discussed at the same time.

The wind gradient is the set of localized wind velocities charted to their height above ground and relaitive directions.

Another way to get bit in a sailplane with the wind gradient is to have a strong wind velocity change over the relative vertical height of ypur wings when in a large amount of bank. If if is something like 8-10 knots less over your lower wing than the upper wing, things can get dicey.

[MarkusN]

I never had any trouble simply feeling or hearing these effects in the old 2-33 trainer and 1-26 sailplanes that I flew. I do think a guy in a modern glass slipper is a bit more removed from the feeling/hearing of the gust effects on the glider, since they are lots more slippery.Good ol' 'seat of the pants' flying. It's still viable, and when themalling can supplement the vario a great deal (also in a slippery carbon ship) It is, however, essential that you also have visual cues to give you a steady reference. The bad thing is that human senses are awful at keeping track of all acceleration loads an thus can't give you a steady reference as to 'what's up.'

I once read a statistic how much time you have left to live if you lose sight of the ground and horizon in a VFR-equipped plane. I don't rememer the exact figure, but IIRC it's less than a minute on average.

[JetPlaneFlyer]

Does this talk of wind gradient and gusts not confuse the topic of the thread?... We all know that wind gradient and gusts are 'real' and do have an effect on any aircraft, no one is contesting this.
However these things are not really what this thread is about... are they :confused:

[biber]

I meant the relationship of wind gradient beeing the wind vector differentiated by the altitude.
About this way: wind gradient = d wind / d altitude

biber

[Thomas B]

Does this talk of wind gradient and gusts not confuse the topic of the thread?... We all know that wind gradient and gusts are 'real' and do have an effect on any aircraft, no one is contesting this.
However these things are not really what this thread is about... are they :confused:

"Downwind turn" crashes happen near the ground, when aircraft are slowed to the pattern speed and preparing to land.

Wind gradients and gusts created by upwind terrain effects also happen near the ground, due to the aerodynamic drag of the ground and ground features on the local moving air masses.

They are certainly linked.

No, it does not apply to the theoretical steady state air mass with an aircraft turning in it..that is true enough, but does not fully cover what is being discussed and observed here.

[Thomas B]

Good ol' 'seat of the pants' flying. It's still viable, and when themalling can supplement the vario a great deal (also in a slippery carbon ship) It is, however, essential that you also have visual cues to give you a steady reference. The bad thing is that human senses are awful at keeping track of all acceleration loads an thus can't give you a steady reference as to 'what's up.'

I once read a statistic how much time you have left to live if you lose sight of the ground and horizon in a VFR-equipped plane. I don't rememer the exact figure, but IIRC it's less than a minute on average.

Vertical thermal bumps in the seat of the pants are universal to both types of sailplanes, but I was talking about horizontal wind gust caused momentary airspeed changes in gliders and lower performance sailplanes that already had some built in headwind...:)

Certainly not talking about flying IFR with less than needle, ball and airspeed, but there is certainly some feel involved in wind gust effects over the airframe when flying at low speeds.

It is a given that a human cannot keep up with all acceleration changes felt, but some can be noticed as they occur.

Pilots in the old days always knew that if the wind in the wires noise lessened, they were flying more slowly, reguardless of how fast the ground was going by.

Perhaps a aural reminder of airspeed at all times (rather like a vario) in the typical lightplane would help out the VFR pilot as he is in the pattern preparing to land...might help during a crucial moment when the eye might be momentarily fooled by the ground racing past and the eye is away from the airspeed indicator, looking for traffic or at the field........

A backup based on another sense that is not as momentarily overloaded in and out the cockpit as your personal eyeballs can get.

However, pilots stall land gear up with the gear horn blairing in their ears, so nothing is mistake proof.

[JetPlaneFlyer]

"Downwind turn" crashes happen near the ground, when aircraft are slowed to the pattern speed and preparing to land.

Wind gradients and ground induced gusts also happen near the ground, due to the aerodynamic drag of the ground on the local moving air masses.



Wind gradient and gusts dont effect an aircraft any more in a 'downwind turn' than in any other part of their flight pattern, in fact wind shear is more likely to be a problem in the final approach... And you can turn 'downwind' at any altitude.
I really dont see the direct connection. In my opinion it's just confusing the thread :(

[Thomas B]

Wind gradient and gusts dont effect an aircraft any more in a 'downwind turn' than in any other part of their flight pattern, in fact wind shear is more likely to be a problem in the final approach... And you can turn 'downwind' at any altitude.
I really dont see the direct connection. In my opinion it's just confusing the thread :(

I must beg to disagree.

Wind gradient effects typically happen close the the ground. And we are talking about "downwind turns" close enough to the ground to sometimes cause a crash if the pilot does not handle things properly.

Gusts are typically more prevalent close to the ground and the ones closer to the ground are often caused by surface discontinuities upwind.

Thus, these effects are present at the type of events we are talking about.

I agree that when you have a large smooth air mass all moving at one speed across the ground at higher altitudes that airspeed is unaffected by the wind. That is a no brainer.

However, the crashes that sometimes occur with models and light planes when turning near the ground are not occurring in that perfect air mass.

Sometimes the crashes are certainly caused by not adding enough airpseed to deal with the wind and gust effects. And sometimes, when the conditions are just right, a strong wind graident effect or a rear quartering gust catches an aircraft that has some extra speed on, but not enough to deal with the gust that arrives and robs airflow over the wing.

A typical light plane or sailplane cannot accelerate instantly if airspeed is suddenly lost...all you can do is unload the wing with down elevator to avoid a stall, add power if you can, and try to accelerate and hope to recover.

Sometimes the wind effects of a microburst (another unique wind effect that matters close to the ground) are such that no normal light aircraft (even an airliner) has enough acceleration to escape it. The wind certainly is affecting airspeed in those cases, since the air is not a uniform mass.

[vintage1]

Wind shear is most likely to crash when coming upwind or turning into wind, as the model is travelling slowly wrt the ground and when it gets into still air near the ground, or in fact dips a wing into slower air, it will pile in.

Wind shear helps you during the downwind phase...the model acquires airspeed as it gets near the ground.

So you are set to disprove the downiwnd turn thesis if you persist with wind shear as your argument.

As far as rolling turbulence goes - well you get up and downdraughts, gusts and lulls pretty much in equal quantities, in the direction of the wind..and across teh wind if there arevertical obstacles like trees or buildings..you are as likley to have issues coming up wind as down, or even going cross wind..

Admit it. The 'downwind' turn is nothing more than brain failure on the part of the pilot who thinks that groundspeed means airspeed. It doesn't, never has, and never will. In wind you FLY the airplane well above stall speed, or you are an idiot. I've been there, done that, and learnt to be smarter.


EOS.

[Thomas B]

Wind shear helps you during the downwind phase...the model acquires airspeed as it gets near the ground.

..............................

As far as rolling turbulence goes - well you get up and downdraughts, gusts and lulls pretty much in equal quantities, in the direction of the wind..and across teh wind if there arevertical obstacles like trees or buildings..you are as likley to have issues coming up wind as down, or even going cross wind..

EOS.

True enough in some and perhaps most circumstances...but you can also get gusts from the rear quarter that momentarily take away the advantages gained from descending into the area of lower wind velocity, especially if you are slowing up a little to land. If the gust is enough and from the wrong direction, it can contribute to getting bit.

How about the type of wind gradient you get from a microburst, where the velocity of the wind relative to the ground increases the CLOSER you get to the ground? Combine this effect with the downward motion of the air mass from the microburst at higher altitudes forcing you closer to the ground and the wind gradient is not a help. Granted, this is fairly rare and rarely a factor in an R/C model crash, but it has certainly killed people in full scale aircraft.

if you get equal gusts and lulls, the wind would average out at about half the max velocity of the gusts.

The real point is that the perfect air mass used in the typical discussion about downwind turns does not exist, especially at pattern altitude.

Let's talk about sharp wind gradients that occur over a small change in altitude and havng an aircraft bank and turn 180 degrees from upwind to downwind so that the higher wing half is still in the higher wind above the shear and the lower wing half is in the slower wind below the shear. the differing wind effects and airspeed on each wing panel can certainly cause some interesting fun....:)

Let's not forget the crosswind to downwind turn, the other type of downwind turn...these are not as typically low and slow as the downwind to base turn, but they can still offer up some interesting effects due to the wind gradient and gust effects, as well.

I have seen some very low powered R/C models basicially have to land out of a low crosswind to downwind turn as they could not stay in the air long enough or descend enough or add power to accelerate to match the speed of a little wind velocity increase across the rear quarter, caused by a bit of a gust as they turn...downwind...:)

And I have seen what you mentioned in an earlier post, a lull causing a loss of airspeed on short final. However, lulls like that are typically easier to handle as you are not turning at the same time.

[eflightray]

Getting back to model aircraft and pilots.

Ignoring my own advice of many years, "don't turn back into wind if going down wind low and dead stick", I tried and failed, which resulted in the loss of a model to a classic 'woops it stopped flying and fell out the sky'.

The point I'd like to make which is very RC related is, what do most people do if the model appears to be coming down steeper than you expected?...........usually bend the Tx stick back giving full up.
And what does full up elevator do to the speed of a model in these circumstances?.........usually slow it down even more just as you are already approaching a stall.

So from experience and observation I would say some of the down wind crashes can be put down to the automatic reaction of a RC pilot trying to save a model by giving the wrong control and making the situation worse.

If we learn by our mistakes, why do I still make so many? :D

[jkettu]

The point I'd like to make which is very RC related is, what do most people do if the model appears to be coming down steeper than you expected?...........usually bend the Tx stick back giving full up.
And what does full up elevator do to the speed of a model in these circumstances?.........usually slow it down even more just as you are already approaching a stall.And that's why everybody should learn to fly with a glider. This will teach you that whenever you seem to be having problems, nose down will help.

[biber]

Thomas B, if you say, the down wind turn problem is due to wind gradient,
then a descending path is required which will steal some of your airspeed when you're heading downwind.
But there's no turn needed at all to get a stall due to the gradient.
So you'd better call it for what it is and it's nothing to do with turns.
The turn is not the particular problem, nor is its contribution required.
Same goes for gusts, they can steel airspeed, but not only in turns.
If you don't increase your speed for tight heavy banked turns, then its your fault.
Then you accept your margin to stall to decrease.
But don't complain about the possible ugly outcome.

biber

[Dan Baldwin]

Thomas, I don't think I've ever seen anyone argue that wind gradients, wind shear, and gusts cannot cause airplanes to crash. What I and others have been arguing against is the idea that a plane will stall because of the downwind turn. There are many people who believe as Funfly2 does, including some of the people I fly with.

I must say that most of you have been unfair towards Texas Buzzard.

He has indeed a point here.

Most of you are just ignoring inertia, yes I repeat: inertia.

Suppose a plane is flying against strong wind, having plenty of airspeed but almost zero ground speed.
Now you make a sudden 180 deg turn, so the plane suddenly gets a strong tailwind; it_will_take_certain_time (due to inertia) until the plane gets enough airspeed downwind, which may be long enough to cause stall.

:)


Dan

[N9DP]

You don't do fullsize gliding, do you?

Please take a ride and try yourself.

biber, who has done a turn or two

While I encourage all my fellow RC pilots to get some time in a glider or powered plane to experience the joy of flight, don’t for a microsecond think that a full-size plane pilot skills carry over to models! The is no surer way to destroy an RC plane than to hand the transmitter over to a licensed pilot in the mistaken belief that if he can fly the full-size jobs he can fly your model!

A few months back some friends of mine were at the local hobby shop and they were at the Real Flight kiosk unsuccessfully trying to fly planes on the simulator. They each managed about 5 seconds of flight before crashing. The two ATPs had upwards of 70,000 logged hours between them.

A little kid, maybe eight, asked if he could “show them how to fly”. His dad apologetically lifted him up so he could reach the sticks, and the kid proceeded to fly the simulator plane with skill. My buddies slinked away.

For the record, I’ve recently dialed in 25 mph winds into Real Flight 3.5 and made oodles of down-wind, cross-wind and up-wind turns close to the ground with nary a hint of a stall. Most of the planes I choose fly in the sim are unable to penetrate that wind velocity, but they fly “backwards” fine wrt their ground reference.

Good landings,

Dennis

[Thomas B]

If you make a downwind turn and crash during it due to a wind gradient effect across the span of the wing or a gust effect, you still crashed in a downwind turn....;)

I have seen some low performance RC models that are climbing slow after takeoff that make make a gentle 180 turn downwind at a certain altitude that seems to correspond with the spot where the wind graident makes a sharp shange, giving the climbing model a gust of wind from the aft quarter during the climbling turn.....another kind of downwind turn being effected by the non uniform air mass.

Here is a video of a sailplane getting bit by flying too slow when turning to land downwind, after a low level winch line break. Assuming there were not better landing options upwind, he was stuck in an ugly corner.

Note the full wind sock....pointed the wrong way. The right wing stalled and the aircraft rolled over...due to low speed and probable wind gradient effects with the wing panels likely in air masses of different speeds (unavoidable due to the low level winch line break and again assuming there was a very good reason not to land straight ahead into the wind)

All else being equal...would he have stalled if the air had been calm? Yes, he appears to be flying a little too slowly, but I predict he would not have crashed in calm conditions.


http://www.youtube.com/watch?v=_xCct8cDtyk&mode=related&search=

[biber]

All else being equal...would he have stalled if the air had been calm? Yes, he appears to be flying a little too slowly, but I predict he would not have crashed in calm conditions.I'd not dare to predict that.
To slow is still to slow.

Dennis, I wouldn't ever claim that full size experience can replace model experience.
But you can't suppose it to be the other way around aswell.
Some things are not easy experience without sitting in the plane.

biber

[N9DP]

[QUOTE=Thomas B]
Here is a video of a sailplane getting bit by flying too slow when turning to land downwind, after a low level winch line break. Assuming there were not better landing options upwind, he was stuck in an ugly corner.
[QUOTE]

A sad finish to an aborted winch launch. I’d bet the NTSB would rule this one as pilot error. Thanks for the video,

I don’t see any hints of wind gusts or wind shear. The sock is at about 14 kts extension (almost fully extended) and perfectly steady during the period it is in view – no fluttering that would signal gusts. A sleek sailplane like that one can handle winds of much higher speed with ease.

The plane never makes any abrupt movements. It looks like the pilot commanded a turn while low to the ground and traded precious stall margin and control for an ill-conceived attempt to land in the grass instead of the weeds. I don’t see any clearly-defined stall break. It appears to me that the plane may have lost altitude in the turn and simply crashed due to maneuvering too slow and close to the ground. When the wing tip caught the ground it was all over.

The first order of business in a situation like this -- low and slow -- is to level the wings using rudder and ailerons. At the start of the video it looked as if the pilot had sufficient air speed to land straight ahead, under control, in a stabilized, albeit ungraceful, landing. Turning was a very bad idea. There is no black box so we’ll never know for sure what happened or if the tragic loss of that beautiful bird could have been prevented. However, a crash with wings level is nearly always better than cart wheeling.

There is a full-size plane analogy that applies in a situation like this: When you lose an engine on take off (or experience a tow-line break), you land straight ahead. You don’t try to turn back. Land with the wings level. Single-engine planes have a better track record than twins in that regard. Save for professionals who practice engine outs regularly, the average light twin pilot cannot handle an engine out on takeoff, self-feathering props and generous single-engine performance notwithstanding.

Good landings,

Dennis

[Dan Baldwin]

There is a full-size plane analogy that applies in a situation like this: When you lose an engine on take off (or experience a tow-line break), you land straight ahead. You don’t try to turn back. Land with the wings level. Single-engine planes have a better track record than twins in that regard. Save for professionals who practice engine outs regularly, the average light twin pilot cannot handle an engine out on takeoff, self-feathering props and generous single-engine performance notwithstanding.

Good landings,

Dennis

That reminds me of something I read once. If you experience an engine failure on takeoff at night, turn on the landing light so you can see where you will land. If you don't like what you see, turn the light back off.

Dan

[JetPlaneFlyer]

No one can say for 100% sure but in my opinion the wind or the 'fatal downwind turn' had nothing to do with that crash. There was no sign of gusts and when turning downwind and descending windshear would heve been in his favour.
He turned too tight while flying too slow and too low.... simple as that.... He would have crashed regardless of if the turn was upwind, downwind or crosswind.

[Thomas B]

Interesting that the windsock streams a little straighter right after the impact...a wind change occured...might not be a very large one, though.

No one can say for certain if the aircraft was in a wind gradient or not, but not, but it is certainly a good possibility, given the conditions.

The wind gradient would help once the entire aircraft was in it and below the shift line and wings level, but with the higher wing in the faster airmass and the lower wing dipped into the slower one, as a gust comes through, conditions are far from the steady state air mass argued as part of the case against the classic downwind turn.

[N9DP]

I Googled “wind gradient” and was immediately led to the that great internet resource, Wikipedia, “The Free Encyclopedia”. Is this a case where you get what you pay for?

There were some useful formulae, but alas, no exponential coefficients given, so I couldn’t compute the wind gradient for a 14 kt wind over smooth terrain. I already knew the functional dependence, and just wanted some quantitative help.

Wikipedia cautioned “Wind gradient is also a hazard for aircraft making steep turns near the ground.” Wow! While this wisdom is doubless true, so is the fact that *any* maneuvering close to the ground is hazardous in the extreme.

Once upon a time I found formulae for the wind gradient function near (< 10 m) of the ground. Sadly I didn’t bookmark it. If anyone has the link, please let me know.

Good landings,

Dennis

[vintage1]

Well I dio know that I took a plane out to fly one evening..thinking the wind had dropped..so it had at ground level, but about 30 feet up it was blowing 10-15mph.

Smooth gradient all the way. IIRC the 'windpseed' on the weather maps was around 20mph.

[Thomas B]

The terms wind shear and wind gradient have both been tossed around here.

A shear is not a uniform gradient. It is a discontinuity in the airmass with a more abrupt change.

I got a call from an R/C glider buddy on Sunday. They were high starting some pretty decent molded sailplanes (winch was down).

Their flying site had a very sharp shear about 30-40 feet up of about 15 knots or so, if not more.

They would launch the sailplanes, which would proceed up the highstart normally until they got to the wind shear, at which point the models would be inmmediately blown directly downwind, still attached to the highstart, until the models were 30-40 feet behind the point where they were launched. Winds of about 10-12 knots on the ground and more than double that just above the field at the 30-40 foot mark. The launch then continued normally and the sailplanes were massy enough to do well in the strong wind.

Descending after the flight, they were careful to not park and hover their way down through the known steep gradient/shear zone and be caught out by the sudden loss of a headwind.

That was not a gradual gradient. I have seen the basic formula somewhere and it is reasonable, if you agree with the assumptions that the terrain upwind is uniform and that there are not conflicting air masses mixing it up over your location.

[N9DP]

By wind gradient I refer to the normal wind profile varying from 0 at the ground to a quasi-asymptotic level at around 30 to 40 feet. As we go higher the normal atmospheric wind profile kicks in. A good model is

V(z) = Vg x (Z/Zg)^^(1/a),

Where V(z) = speed of the wind at height z
Vg = wind speed at height Zg, and
a = a constant

a is a function of the rms roughness of the surrounding terrain, and is the constant I can’t seem to find anywhere.

I need a for smooth terrain.

I’ve encountered wind shear in my Skyhawk many times. In all cases the plane landing ahead of me, the tower, or ATIS gave me a heads up, like “Be advised, last plane lost 10 knots airspeed on short final”. That gets my attention, and in goes the throttle! I’ve also seen wind socks at opposite ends of a 3500 foot strip pointing 180 degrees apart. Wind shear, here we come.

I not skilled enough to fly my RC planes in winds greater than about 10 kts, and wind shear does not usually occur with surface winds of that magnitude. Maybe that will keep me safe.

Good landings,

Dennis

[eflightray]

Why don't we just put it down to, 'Gravity pulls greater on a profile view than on a plan view'.

Oh and don't forget the B52 video, that proves it was gravity, not wind shear, wind gradient, up wind, down wind, cross wind or even flatulence. Gravity wins when you stop pedaling.

[kristianb]

eflightray, you are on the right track here!
Flying in Sweden, I occasionally experience gravity shear! :)
vbr KristianB

[N9DP]

eflightray, you are on the right track here!
Flying in Sweden, I occasionally experience gravity shear! :)
vbr KristianB

I would urge you to carefully document the gravity shear. You will for sure win a Nobel Prize (Nobelpriset) in Physics. And you will only have to travel to Stockholm to receive it. Think of all the RC goodies you can buy with the prize money!

Good landings,

Dennis

[kristianb]

Yeah Dennis,
Good thinking!
But to be honest I´m into this hobby for the joy it gives, not for the money...
The latest time I entered a downwind turn discussion someone also told me that I´m in the race for a nobel prize!
For the last crash I´m a bit unsure if it was caused by gravity shear or just plain brain flutter!
Thanks for the positive comment!
KristianB

[Julez]

I find this conclusive.

[JetPlaneFlyer]

I find this conclusive.
But the aircraft in the video was turning downwind... so according to the diagram you attached wind gradient would have been in his favour ;)