Flying in the wind

[mrblucor]

Hello RCGroup members,
I was flying in the wind today. In fact I was the only one flying. I've read in our clubs newsletter that a light foamy can't fly in the wind. HA! I say. I fly my foamy's in the wind all the time. So after a few flight today, I was told that light foamys could fly in the wind, but heavy 50cc size plane can't. Well, which is it????

My theory is that it has to do with wing loading and control authority. Heavy wing loading won't be as much affected by wind as a lightly loaded plane. Control authority is needed to compensate or fight back against the wind and wind gusts.

Does anyone have facts to back or dismiss my theory??

JB

[Montag DP]

Any plane can fly in the wind. You just have to be careful of those downwind turns because they'll cause your plane to stall as it loses airspeed. :rolleyes:

(That was sarcastic unless the smiley didn't give it away.)

Seriously though, I more or less agree with your conclusions. There are some other considerations as well such as size and thrust which also make a difference.

Dan

[mrblucor]

I agree, power is a good thing. All my planes have ample power.

I think wing loading is key. Larger planes tend to have higher wing loading.

JB

[phat23]

Any of my planes WILL fly in the wind.

My 6lb World Models Super Stunts 40 flys in the wind and is fun to fly.

My 10oz E-Flite Jenny flys in the wind, too. Fun to fly in the wind? NO.

[Brandano]

Any airplane will fly in the wind, as long as the wind is slower than the airplane's maximum speed. Oh, well, the airplane will fly in it anyway, but it will quickly fly backward out of range, followed by any object not securely tied to the ground included the pilot...

[Cory]

As an almost exclusively slope flyer with only two electric planes, I don't have much trouble flying park flyers in the wind, unless I fly near a obstacle on the ground that causes nasty turbulence, or as mentioned before, if the wind is blowing faster than the plane can fly. Gettting around on the downwind side of the elementary school is a bad idea. Might be able to DS the school with a different plane, but not with my Slowstick or light weight EDF jet.

[ADB2]

Hi,
I think gliders in general require ballast to get a higher wing loading, to be able to fly in stronger wind. It seems to me that powered aircraft are slightly different.
I found out after flying my very lightly loaded Owl-RT Depron 3D trainer on a windy day that all I really needed to be able to fly it in the wind was pitch speed (i.e. power), and of course you also need to pay attention when turning downwind.
Here is a video of it: http://www.rcgroups.com/forums/showthread.php?t=940944
Wing loading is 16g/dm2 (5.2oz./sq.ft.). Wing cube loading is 3.75.

[Brandano]

Gliders need ballast because the only motive power available to them is gravity. A powered plane will actually fly faster if it's kept lighter, because it will achieve enough lift to maintain altitude at a lower AOA, and this will in turn result in lower drag and higher speed for the same thrust

[mrblucor]

I find flying in the wind is pretty straight forward. Landing in the wind is another story. Close to the ground the wind is less predictable. I find it will move my plane in unpredictable ways. Large control authority helps in that you can fight back when a wind gust pushes the plane. A heavily wing loaded plane seems to be less effected by these wind gusts.

Stall speed is another consideration. What if the plane's stall speed is 18 mph and the winds are blowing 20? A higher wing loading means a higher stall speed. and therefore, the wind speed with respect to the stall speed is less and should have less effect.

JB

[Montag DP]

Stall speed is another consideration. What if the plane's stall speed is 18 mph and the winds are blowing 20? A higher wing loading means a higher stall speed. and therefore, the wind speed with respect to the stall speed is less and should have less effect.

JBIt wouldn't make a difference unless you get a sudden gust. Remember stall speed is relative to the air, not the ground.

[ndb8fxe]

I find flying in the wind is pretty straight forward. Landing in the wind is another story. Close to the ground the wind is less predictable. I find it will move my plane in unpredictable ways. Large control authority helps in that you can fight back when a wind gust pushes the plane. A heavily wing loaded plane seems to be less effected by these wind gusts.

Stall speed is another consideration. What if the plane's stall speed is 18 mph and the winds are blowing 20? A higher wing loading means a higher stall speed. and therefore, the wind speed with respect to the stall speed is less and should have less effect.

JB

In this case you could land the plane going 2mph groundspeed backwards.

If a plane can fly when it's calm It can fly in any wind. The problem with wind is that it usually come with gusts which can make the airplane difficult to control and if you are close to the ground ie. landing there may not be time to react. When people crash and the wind is blowing it's usually a mental problem ie. being scared/nervous that causes the crash not the wind itself.

Wind 90% of the time blows out of the east. Most flyer get very comfortable landing in that direction. When the wind turns the runway around the garbage cans quickly fill up due to people not being comfortable landing in the opposite direction. There are no obsacles, it's just making a pattern in a different direction.

Personally I'll fly(ugly stik .40) in winds up to 25knots with little problem.

[DT56]

Airplanes actually fly because of wind.

The airplane, model or full scale, makes it's own wind with forward speed and doesn't care how fast or which direction the naturally occurring wind blows.
Full scale aircraft fly in hurricanes and jetstream winds approaching 200 MPH. Slope soaring modelers fly in winds of over 50 MPH and some of their models are designed to fly their best in such conditions. The naturally occurring wind only becomes a problem when relating the aircraft flight to the ground. (That's why they are called airplanes and not groundplanes)

The real problem with flight in windy conditions is the turbulence near the ground, especially when landing. The only "safe" solution is the method used in full scale, which is to add extra speed to account for variations in airspeed caused by the gusts. Easier said than done sometimes, though I admit it's generally easier in full scale than RC for me. The practical maximum wind strength at ground level for full scale flight will be considerably less than the stall speed of the airplane. Most RC airplanes aren't limited to such a low figure, because they can be hand launched into the more consistent wind a couple of yards above the ground. You still have to land the RC model in those conditions, but just knowing it's not your "bacon" on the line if you auger in on approach helps.

[mrblucor]

I agree, it's near the ground that things get interesting. Take two Cessna 182's, if one has a 24" wingspan and the other has a 96" wingspan, if the wing loading is the same on both planes, then the stall speed should be the same. I would say either plane would be effected equally by 10 mph gust. So the size of the plane shouldn't matter. I think a 182 with higher wing loading would be less effected by the same 10 mph gust regardless of actual size. "All planes fly on wind", that's true. The higher wing loaded plane will have to generate more thrust with its prop to fly. Therefore, a higher percentage of the total wind the plane sees is from its prop rather than the 10 mph gust. This leads me to believe that it would be less effected by the gust.

JB

[vintage1]

I agree, it's near the ground that things get interesting. Take two Cessna 182's, if one has a 24" wingspan and the other has a 96" wingspan, if the wing loading is the same on both planes, then the stall speed should be the same. I would say either plane would be effected equally by 10 mph gust. So the size of the plane shouldn't matter. I think a 182 with higher wing loading would be less effected by the same 10 mph gust regardless of actual size. "All planes fly on wind", that's true. The higher wing loaded plane will have to generate more thrust with its prop to fly. Therefore, a higher percentage of the total wind the plane sees is from its prop rather than the 10 mph gust. This leads me to believe that it would be less effected by the gust.

JB

A little knowledge....

Now try MAKING a 96" span model with the same wing loading as a 24" one. :p

I haven't seen any Boeing 747s coming to land at my feet at 8mph either ;)

[Brandano]

Incidentally, planes are made to land close to the stall speed to make the shortest possible landing run, but they don't HAVE to. Especially if they are a taildragger design, you can just fly them to a rolling landing in the wind. If the wind is faster than the plane's stall speed you can just land it vertically.

[BMatthews]

Wind flying is more about skill than any aerodynamics or construction details. One of my best days of sailplane flying was with a relatively lightly loaded but not "gasbag" class glider in a howling wind that saw only myself and the guy with the F3B ship flying. I had a highly stressfull but exciting 20 or so minute flight of dynamic soaring. The dynamic aspect being from using the gusts and shear effects similar to the slope dynamic soaring so much more common recently. But this was flat land and only used the increases and decreases. It still sticks in my mind from 20 years ago it was so demanding and exciting. I really should go out storm flying more often.

Anyhow. Yes for windy flying you CAN fly a lightweight puff of a plane but a little loading can really help steady it. But go TOO heavy and you'll find it gets doggy to respond when you're near the stall but can't tell because it seems to be going so fast downwind already.

So learn to use the feedback on how the model is responding to your inputs. If it is slow and listless to respond you're near the stall regardless of how fast it seems to be going for ground speed. If it's snappy and flicky moreso than normal then it's flying fast through the air even if it's standing still or barely crawling in terms of ground speed.

Landings are a special treat. Maintain a solid nose down where you know the angle is enough to generate a mild dive with secure airspeed. But don't point it down TOO much or you'll find it being blown downwind. You want a fast glide and no more. The idea is to learn what that angle of the fuselage is in calm air and THEN use it in the wind. Don't flare too early but do avoid the sudden "prang". Just level it in the air about 1 to 1.5 feet from the ground and then let the speed bleed off and the model settle. Windy days are not the time to be going for the tail dragging three pointer. Just wheel it on smoothly as the speed falls. If you flare too early and then let it settle through the last 3 feet the wind shear effect will bite you and the last foot or two will be a stalled drop in.

Be ready with small but decisive control corrections. Wind near the ground is full of oddball rotors and other effects. You need to correct for disturbances but not OVER correct. Much of this comes from flying in progressively windier weather.

A really heavy model will appear to fly better in the wind but when it comes to landing it can surprise you with sudden stalls. I like to fly solid performers in the higher winds that are neither heavy and not fun to fly normally nor my old timers that are light and thermal capable. The general fun to fly sport models are just right. But I would likely not enjoy wind flying with 3D capable models since they are so light and have so much area. The models themselves would do fine thanks to all the control authourity but with that much wing area and being so comparatively light they'd be kicking around a lot.

[vintage1]

Steady wind is one problem, you can fly a light model in a steady wind OK.

Its turbulence that makes them dance around.

That's when a model with a bit more inertia and a natural faster landing speed helps.

[mrblucor]

I fly at a field that is dominated by large scale gas driven 3Dtype planes. They see my small electrics as a nuisance and not 'real' RC planes. I was told that larger planes fly better. I was told my lightweight electrics coundn't fly in the wind. I was also told at one time that my electrics were too slow and couldn't fly with the 'regular' RC planes.

I take pride in my airplanes. I work hard to build them light, strong, true and powerful. Most of my planes have wide flight envelopes like 5:1. I cut my teeth early flying small foamies in the wind. I got to the point where I could fly as long as my top speed was greater than the wind speed.

Last Sunday I arrived at the field with 5 planes. Some real floaters like a Cessna 172 44' WS from Hobby Lobby, a Super Miss II also from Hobby Lobby. These planes are light, really light. They'll thermal in the smallest of updrafts. Five large scale gas planes were assembled on the flight line. They were waiting for the winds to die down. I took the Super Miss up and flew for about half an hour, till I got tired of looking up. I hardly used any battery at all. When I got in, I said "it's not too windy. If I can fly this light thing, then you can certianly fly your larger planes". I was then told that the wings on the large scale planes are too big for the wind. I said "it's the wing loading that counts, not the wing span.

The Super miss has 397 square inches of wing and weighs in at 32oz for a wing loading of 11.63oz/square foot. The power plant is 150 Watts WOT. A typical 50cc size 3D plane has 1450 square inches of wing and the lightest weight in it's range is 16 lbs. That's a wing loading of 25.6 oz/square foot. With that wing loading and 2:1 power and large control surfaces, shouldn't it be able to fly better in gusty winds?

JB

[DT56]

I fly at a field that is dominated by large scale gas driven 3Dtype planes. They see my small electrics as a nuisance and not 'real' RC planes. I was told that larger planes fly better. I was told my lightweight electrics coundn't fly in the wind. I was also told at one time that my electrics were too slow and couldn't fly with the 'regular' RC planes.

I take pride in my airplanes. I work hard to build them light, strong, true and powerful. Most of my planes have wide flight envelopes like 5:1. I cut my teeth early flying small foamies in the wind. I got to the point where I could fly as long as my top speed was greater than the wind speed.

Last Sunday I arrived at the field with 5 planes. Some real floaters like a Cessna 172 44' WS from Hobby Lobby, a Super Miss II also from Hobby Lobby. These planes are light, really light. They'll thermal in the smallest of updrafts. Five large scale gas planes were assembled on the flight line. They were waiting for the winds to die down. I took the Super Miss up and flew for about half an hour, till I got tired of looking up. I hardly used any battery at all. When I got in, I said "it's not too windy. If I can fly this light thing, then you can certianly fly your larger planes". I was then told that the wings on the large scale planes are too big for the wind. I said "it's the wing loading that counts, not the wing span.

The Super miss has 397 square inches of wing and weighs in at 32oz for a wing loading of 11.63oz/square foot. The power plant is 150 Watts WOT. A typical 50cc size 3D plane has 1450 square inches of wing and the lightest weight in it's range is 16 lbs. That's a wing loading of 25.6 oz/square foot. With that wing loading and 2:1 power and large control surfaces, shouldn't it be able to fly better in gusty winds?

JB

One shouldn't discount the "investment" factor of not only money, but sometimes considerable building time, of larger models. I'd risk an inexpensive ARF in conditions I wouldn't consider flying a more valuable model in.

Wing Cube Loading is considered by many to be a more reliable comparison tool than Wing Loading. Here's a link to a Wing Cube Loading Calculator.

http://www.ef-uk.net/data/wcl.htm

[mrblucor]

I can understand the cost in both time and money. Electric isn't cheap. I spend a lot of time building my models, even the ARF's. That may be a factor, but that was not what was said. I maintain that a plane with heavier wing loading is easier to fly in the wind as long as it has ample power and control authority.

Can you tell me what wing cube loading is and why it's a better method to calculate how a plane will fly.

JB

[flyingwing12]

Any plane can fly in the wind. You just have to be careful of those downwind turns because they'll cause your plane to stall as it loses airspeed. :rolleyes:

(That was sarcastic unless the smiley didn't give it away.)

Seriously though, I more or less agree with your conclusions. There are some other considerations as well such as size and thrust which also make a difference.

Dan
Well Dan, no need to be sarcastic, because your correct. a turn into the wind will give you loft and keep you airborne. but turn downwind and your plane will drop and possibly crash

[Cory]

Why is it, then, that when I make a downwind turn with a sloper in winds as high as 55 mph, the only thing that happens is that the plane moves downwind toward the hill really fast and I have to turn quicker, unless I'm trying to DS and want to get on the back side? I can't recall ever stalling when doing that, or seeing any of my friends stall in a downwind turn either. Hmmm.....must be lucky..... :)

[ADB2]

Why is it, then, that when I make a downwind turn with a sloper in winds as high as 55 mph, the only thing that happens is that the plane moves downwind toward the hill really fast and I have to turn quicker, unless I'm trying to DS and want to get on the back side? I can't recall ever stalling when doing that, or seeing any of my friends stall in a downwind turn either. Hmmm.....must be lucky..... :)
I am a newbie at RC flying, but from my little experience I have noticed I tend to fly my foam 3D trainer slightly differently through turns, compared to my V-shaped slope soaring motorless flying wing.
The flying wing tends to fly at a slowly changing airspeed which is always above stall speed; there's no prop and the airframe itself is somewhat low drag, compared to my foam 3D trainer. On my foam 3D trainer I use the throttle constantly and airspeed changes from 0 to high speed constantly, going through stall speed both when accelerating and decelerating.
So yes, I always tend to be careful in downwind turns with my foam 3D trainer.

[Brandano]

There's extensive literature and discussion history about the "dreaded downwind turn". It boils down to this: the plane doesn't care. The pilot tends to fly relative to the ground and not relative to the air and smashes the plane. Gliders are less affected because the pilot has no direct control over the thrust. Any thread starting to discuss the "downwind turn" in Modeling Science ought to be automatically locked before religious wars start.

[mrblucor]

When I started this thread, I was wondering what makes a plane more stable in the wind. Landing in the wind seems to be the hardest part because of unpredictable nature of wind gusts near the ground. Some planes get bounced around more than others. I've seen planes come in on landing approach that look rock solid in winds that make my foamies look like they're traveling through white water rapids.

I think power and control authority help on any plane. I also think that a plane with higher wing loading is less effected by wind gusts because the prop is doing more work. I think of the prop as creating controlled wind. The higher the percentage of controlled wind Vs gusty wind, the more control you will have on your plane. It seems to me that a 10 mph wind pushing on a plane with a wing loading of 12.5oz/sq foot Vs a plane with 25oz/sq foot will have about twice the effect. Is this correct? Am I even close?

JB

[Cory]

In a steady wind, the wind will have the same effect on the two planes. In a gust, you're right, the higher wing loading plane will react more slowly to the gusts.

While weight makes a difference, there are other factors, too. Obstructions that cause turbulence, such as trees and buildings make a big difference. Pilot experience has a lot to do with it. That's actually why I brought up slope soaring. Slopers are used to compensating for the difference in ground track caused by the wind. New slopers have to get used to this. All fast slopers are not heavy. I have a Speedo Thermo that weighs only 13 ozs. with a 48" wingspan. I've flown it in 25 mph low turbulance winds without problem.

[BMatthews]

It reacts more slowly but once moving due to a gust it takes more to correct.

I have to say that while I'm a fan of "lighter is righter" for truly turbulent wind conditions I do prefer models with a touch more heft. But go TOO far in that direction and the windy weather response suffers as well. A model that is a good solid performer but not 3D light in mild to moderate weather is going to be my choice for stormy days as well. As with so many things there's a happy middle ground.

Something like a Great Planes Sportster is a nice calm day model but without the lightness that makes it a 3D style stunter. But this same Sportster will do just fine on all but the most brutal days. A heavier model may punch through the weather better (although I think that is arguable) but it'll suffer so much on normal weather days that it won't be much fun to fly.

[Brandano]

planes with higher wing loading have a steadier flight in gusty wind, but are more prone to be affected by windshear since they take longer to catch up to the wind . This is not always a good thing.

[ndb8fxe]

planes with higher wing loading have a steadier flight in gusty wind, but are more prone to be affected by windshear since they take longer to catch up to the wind . This is not always a good thing.

Yes not a good thing if you are flying with little margin to stall speed, however it will fly smoother as long as a comfortable margin is kept.

[Texas Buzzard]

There's extensive literature and discussion history about the "dreaded downwind turn". It boils down to this: the plane doesn't care. The pilot tends to fly relative to the ground and not relative to the air and smashes the plane. Gliders are less affected because the pilot has no direct control over the thrust. Any thread starting to discuss the "downwind turn" in Modeling Science ought to be automatically locked before religious wars start.
.................................................. .........................................
About six months ago I posted that a Border Patrol piloy was killed while circling some illegal aliens in a 30 mile per hour wind. Tell him that there is no such thing as "A Fatal Downwind Turn". It was said by the athorities that he was in a 40 degree bank and was concentrating on the people on the ground when it happened.

Some say "the plane doesn't know it is flying in a wind - that's true, planes don't have brains, but they do have Kinetic Energy. As the plane turns into the wind when coming out of a downwind turn it's Kinetic Energy becomes to little to sustain lift - thus a stall occurs unles the pilot points the nose down or in the case of a power plane he adds thrust.

For an excellent explanation written in simple language which tells you how an airplane flies read "STICK & RUDDER" by Wolfgang Langewiesche. An excellent book for a student pilot. BTW, I held a Private Pilot's Lic for 20 years.

[Brandano]

The pilot was killed because he was circling a fixed spot on the ground, and not paying attention to windspeed. If there is a wind you can't fly an exact circle and expect to keep a steady turn, you have to adjust for the wind constantly. Had he been flying instrumentally and without looking at the ground he'd still be flying now. Anyone's death is a tragedy, but you can't blame the plane or the weather for what is essentially a pilot error.

[JetPlaneFlyer]

As the plane turns into the wind when coming out of a downwind turn it's Kinetic Energy becomes to little to sustain lift - thus a stall occurs unles the pilot points the nose down or in the case of a power plane he adds thrust.
.

:censored: Lets not start this one again pleeeesssse.

Take it to the original thread on the same subject: http://www.rcgroups.com/forums/showthread.php?t=814242&highlight=downwind+turn+killed

I'd lose the will to live if we have to attempt to explain the physics of inertial reference frames yet again (clearly it did not sink in last time so no point trying again anyway):rolleyes:

Steve

[ndb8fxe]

The pilot was killed because he was circling a fixed spot on the ground, and not paying attention to windspeed. If there is a wind you can't fly an exact circle and expect to keep a steady turn, you have to adjust for the wind constantly. Had he been flying instrumentally and without looking at the ground he'd still be flying now. Anyone's death is a tragedy, but you can't blame the plane or the weather for what is essentially a pilot error.

With the exception of a sudden change of speed and direction (wind shear) a plane does not and will not lose lift due to a turn in relation to direction of wind. Given a power setting any normal turn will not result in a change in airspeed due to wind direction. Now if you are slow and trying to orbit an object the turn downwind is likely to try to "push" you off location which will result in the pilot trying to increase bank angle. This bank angle will cause a higher g loading which in turn will increase stall speed. Given the same conditions, ie bank, altitude, power setting the plane would stall reguardless of wind direction.

To test this is to take an airplane and keeping a constant power setting and make constant bank 360 turns. Initally the airspeed (reguardless of direction) will decrease a few knots, but the remainder of the turn the airspeed will be constant througout the turns.

[Bg~]

For an excellent explanation written in simple language which tells you how an airplane flies read "STICK & RUDDER" by Wolfgang Langewiesche

Nowhere in that book is the downwind turn myth supported. In fact, pages 105-107 make the case against your 'downwind turn'. Allow me to quote page 107:

Why are we required to do spins, chandelles, and so on upwind? The reason is not that to do them down wind or cross wind is dangerous or difficult; but doing them upwind keeps students from getting lost while concentrating on the maneuver.

[funfly2]

If you watch the video below carefully you'd notice that the glider lost abruptly altitude entering into spin just when its tail pointed towards the wind:

http://youtube.com/watch?v=_xCct8cDtyk

Just like some "experts" here, the pilot assumed that the glider was moving in a "steady state" carried by "a sea of air" and therefore kept turning it down the wind instead of uppwind.
Probably got stuck in some inertial frame of reference...
:cool:

[Montag DP]

If you watch the video below carefully you'd notice that the glider lost abruptly altitude entering into spin just when its tail pointed towards the wind:

Just like some "experts" here, the pilot assumed that the glider was moving in a "steady state" carried by "a sea of air" and therefore banked it down the wind instead of uppwind... just got stuck in some inertial frame of reference.
:cool:No one is denying that downwind turns can be a problem when trying to land. However, the issue is that the pilot is lining up based on objects that are on the ground, which are not traveling at the same speed and direction as the wind. As the pilot turns downwind, the plane is carried farther by the wind than it would have moved if there were no wind, so to compensate he banks too hard and stalls.

The reason the pilot loses airspeed and stalls is because he banks too hard, not because he is turning downwind. If he was cruising along leisurely at 2000 feet instead of trying to land, he would not have made the same mistake.

[funfly2]

No one is denying that downwind turns can be a problem when trying to land. However, the issue is that the pilot is lining up based on objects that are on the ground, which are not traveling at the same speed and direction as the wind. As the pilot turns downwind, the plane is carried farther by the wind than it would have moved if there were no wind, so to compensate he banks too hard and stalls.The pilot was an instructor, so you mean that he didn't bother about the instruments on board?
I don't buy it.


The reason the pilot loses airspeed and stalls is because he banks too hard, not because he is turning downwind. If he was cruising along leisurely at 2000 feet instead of trying to land, he would not have made the same mistake. The glider would not stall if the pilot had turned to the left instead of to the right.

[JetPlaneFlyer]

Funfly, we have been here before with the same video... the pilot pulled too tight a turn when flying too slow and too low... end of story.

[funfly2]

Funfly, we have been here before with the same video... the pilot pulled too tight a turn when flying too slow and too low... end of story.End of story maybe for those who have drawn the wrong conclusion.

The pilot did not pulled too tight.

The plane entered into spin when it got wind from behind.

[JetPlaneFlyer]

For those who have drawn the wrong conclusion maybe.
The pilot did not pulled too tight.
The plane entered into spin when it got wind from behind.
I give up :rolleyes:

[Brandano]

The reason not to land in favor of wind is because the landing speed relative to the ground goes up, and so does the landing distance. That glider clip looks like an aborted takeoff, probably a cable break. The pilot just aimed at the runway head, and stalled. He should have aimed to land further down the runway, but perhaps there wasn't enough space.

[funfly2]

The reason not to land in favor of wind is because the landing speed relative to the ground goes up, and so does the landing distance. That glider clip looks like an aborted takeoff, probably a cable break. The pilot just aimed at the runway head, and stalled. He should have aimed to land further down the runway, but perhaps there wasn't enough space.That might be the reason why the pilot chose that flight path, but I've said it before and say it again:

The glider would not stall if the pilot had turned to the left instead of to the right.

[Brandano]

in that situation, since takeoff is in the direction of the wind, what side you choose to turn on doesn't matter. He wouldn't have crashed if he had kept the nose down and left the spoilers closed. Here's how it's done properly: http://www.youtube.com/watch?v=H3VMdarklVo

[JetPlaneFlyer]

I dont appear to be able to explain the physics in a way that certain folk can understand so I've coppied and pasted this from another site. Funfly; please read it, analyse the mathematics, then tell us that the plane stalled because it turned downwind:

.....The fallacy comes because it *seems* like the inertia of the airplane will resist the acceleration required to maintain airspeed in the downwind turn, and that the airplane requires more acceleration to maintain airspeed in the downwind turn. This fallacy is seductive, because on the face of it is *seems* so *right* and I can certainly see the appeal of that line of thinking. The trouble is, it is just a fallacy, the aircraft turning "downwind" accelerates at the identical rate as the airplane turning at the same turn rate in still air. Let’s take all the "seems like", "common sense tells you" and other fuzzy thinking out of the equation and analyze what is actually happening, using numbers. It’s not hard to do.


Acceleration is defined as change in velocity per unit of time. So what is the required acceleration?

Take an airplane flying first directly north at 50 knots, then turning at standard rate, constant altitude and airspeed turn 180 degrees to directly south..

We’ll consider only north/south winds, so we need only consider north/south acceleration. East west acceleration becomes irrelevant.

So, what is the acceleration when this is done in still air? Immediately before the turn, the velocity is 50 knots north, and immediately after the turn the velocity is 50 knots south, so the velocity change is 100 knots (168.8 ft/sec). The change takes place in exactly one minute, so the average north-south acceleration during the turn is 100 knots/minute , or 2.81 ft/sec./sec


Ok, now what happens when we make the same turn in a wind? Lets say we have a 25 knot wind out of the north. Now, I’ll consider the groundspeed here, because that is what causes the erroneous perception. In reality, it’s only the airspeed that matters, but the results won’t change if you consider the groundspeed correctly.

What is the groundspeed before the turn? 25 knots north
After the turn? 75 knots south
Net change in goundspeed? 100 knots (The velocity difference between 25 knots one way and 75 knots the opposite direction is 100 knots or 168.8 ft/sec)

Time to turn 180 degrees in a standard rate turn? 1 minute.

Average acceleration ? 100 knots per minutes or 2.81 ft/sec/sec. The average acceleration through the turn, after you add a wind, is identical, right out to however many decimal places you want to carry it out to.

OK, how about a really big wind, surely if we use enough wind the airplane will have to accelerate faster to keep flying speed right? Well let’s take a look. Let’s say we had a 200 knot wind out of the north.

Groundspeed before the turn 150 knots south (50 knots in a 200 knot head wind).
Groundspeed after the turn 250 knots south. (50 knots plus a 200 knot tail wind)
Change in groundspeed 100 knots (168.8 ft/sec)
Time to turn 180 degrees in a standard rate turn? Still 1 minute.

Average acceleration needed to maintain 50 kt. airspeed? Still 100 knots in one minute, or 2.81 ft/sec/sec.

I know what some of you are thinking. You’re saying, well a standard rate turn isn’t a much of a turn, it’s such a gradual turn that the airplane has enough time to accelerate downwind, you need a faster turn to get the "wind blowing backward over your wing causing you to fall out of the sky" effect.

OK, let’s use a faster turn, see how that changes things. Lets use a 45 degree bank. Lets say that our airplane can bank 45 degrees at 50 knots without stalling, and that it has sufficient power to circle indefinitely at 45 degrees bank and 50 knots in a level turn without loosing airspeed. And lets further say that 50 kt is hte slowest this airplane can fly in a 45 degree bank, 49.5 knots and it falls out of the sky. 45 degrees bank at 50 knots will give a turn rate of approximately 22 degrees per second (from the chart on pg. 179 of Aerodynamics for Naval Aviators) That means that the 180 degree turn will take about 8.2 seconds.

So what is the acceleration in still air?

50 knots north to 50 knots south is still a change of 100 knots. The 180 degree turn now takes 8.2 seconds, so the average acceleration needed is 100 knots/8.2 seconds, or 20.6 ft/sec/sec.

Now, let’s see what the acceleration is in the dreaded downwind turn. Let’s skip right to a really big wind and not piddle around with insignificant 25 knot winds. Let’s use the same 200 knot north wind we used before with a standard rate turn.

Groundspeed before the turn? 150 knots south
Groundspeed after the turn? Must be 250 knots south, 249.4 knots across the ground (49.5 kt. airspeed) and the airplane stalls
Total velocity change required. 100 knots (168.8 ft/sec)
Time for velocity change 8.2 seconds
Average acceleration needed to maintain 50 kt airspeed? 168.8/8.2 = 20.6 ft/sec/sec

Huh, turns out even in a really steep bank, really low airspeed, high turn rate and ridiculously huge wind, the acceleration needed to maintain airspeed in the turn with a 200 kt. wind is identical to the same turn in still air.

And that is where the rubber meets the road. All the downwind turn theories depend on "inertia causing the airplane to not accelerate fast enough to maintain airspeed" with the fundamental flawed belief that the acceleration *must* be greater if you turn downwind or you lose airspeed.

However, when you actually analyze what the required acceleration is, by taking the velocity before, the velocity after, and the time of the turn, (change in velocity divided by time is the only valid way you can consider acceleration, because that is the definition of acceleration) we find that the wind makes absolutely no difference in the acceleration required through the turn in order to come out the other side with 50 knots of airspeed.


Now some of you are probably thinking, yes but that is the *average* acceleration, the acceleration varies during the turn. Well, yes, the acceleration in hte north/south direction does vary, but just like the *average* acceleration remains identical out the nth decimal place, regardless of the wind, so does the acceleration at any particular point during the turn. Think about it, the acceleration during the turn changes significantly, but the *average* acceleration remains the same? Not likely. For those of you who are unswayed by the unlikeness of that, we can take a more analytical look at the situation.

Yes, it is true that the acceleration during the turn changes, more specifically, the acceleration in the North/South direction (which is what we’re interested in) changes, the total acceleration during a constant turn remains the same. The north south component of the acceleration will be greatest at the 90 degree point of the turn and the least at the 0 degree and 180 degree points in the turn. So lets look at the point where the acceleration is the greatest, that’s where we’ll fall out of the sky right?

First off, what is the lateral (across the ground) acceleration? Well, it we stick with the 45 degree bank, the lateral acceleration is conveniently, 1 g , or 32.2 ft/sec/sec. I see some of you saying, no, a 45 degree turn is more than 1 g, well yes and no. It gives a "load factor factor" of 1.414 but that’s 1 g of gravity vertically and 1 g of horizontal acceleration, add Pythagorean theorem and that gives you 1.414 g aligned with your butt in the seat. So, 1 g lateral acceleration for a 45 degree banked turn. Now in a zero wind situation, what is our groundspeed (or airspeed, no difference if there’s no wind) at the exact 90 degree point in the turn? Zero, right? That’s the precise point when our groundspeed (and airspeed) is reversing from just a little in the north direction to just a little in the south direction. And right at the reversal, north/south groundspeed (and airspeed) is zero. So let’s examine that one second bracketing the precise 90 degree point. One half second after the reversal, the north/south groundspeed is 16.1 ft sec (9.5 knots) to the south, Acceleration is 32.2 ft/sec/sec, and we’ve accelerated at that rate for 1 half second from zero north/south groundspeed, (32.2 * 0.5 = 16.1 ft/sec). Similarly, at one half second before the 90 degree point the north/south groundspeed (and airspeed) is 9.5 knots in the north direction. So in that second the groundspeed and airspeed changes from 16.1 ft/sec (9.5 kt.) north to 16.1 ft/sec (9.5 kt) south for a total velocity change of 32.2 ft/sec in one second which is an acceleration of 32.2 ft/sec/sec or one g.

Well what if we throw a wind in there? Again, we’ll use the 200 knot wind because that ought to magnify any small effects. So, in a 200 kt wind out of the north, what is the airplane’s north/south groundspeed at the exact 90 degree point? As we saw in the still wind case the north south airspeed goes to zero, so the groundspeed must be 200 kt. (337.6 ft/sec) to the south. A half second before the 90 degree point, groundspeed is 190.5 kts. (321.5 ft/sec) south (200 knots wind to the south plus 9.5 knots airspeed to the north = 190.5 knots to the south) one half second after the 90 degree point the groundspeed is 209.5 kt (353.6 ft/sec) to the south (200 knots wind to the south plus 9.5 knots airspeed to the south = 209.5). So, over that one second centered on the 90 degree point in the turn the north/south groundspeed goes from 190.5 knots south to 209.5 knots south, a change of 19 knots (32 ft/second) in one second when is 32 ft/second/second, which is the same acceleration we had in the no wind condition.


I could go on, and do the same analysis for the 45 and 135 degree points for the turn, or any other point, but the math will start to get complicated, and the answer will always be the same. A constant, unaccelerated wind will not change the acceleration of the plane in the turn, one iota, nor will it change the acceleration required to maintain airspeed as you turn down wind.

[Cory]

Every time the downwind turn comes up, I feel like the discussion needs to be transferred to the "Life, the Universe, and Politics" forum. Shouldn't be this way because the facts are obvious, but some of these guys seem to defend their "dreaded downwind turn" view more vehemently than they would argue their religions or political viewpoints.

[funfly2]

in that situation, since takeoff is in the direction of the wind, what side you choose to turn on doesn't matter. I am not focusing on why the pilot turned back, but on the fact that if the pilot after turning to the right had changed the course to the left [into the wind] with the same bank angle, the glider would not stall.



He wouldn't have crashed if he had kept the nose down and left the spoilers closed. Here's how it's done properly: The spoilers opened AFTER the plane entered into spin. Could have been a panic manoeuvre.

[funfly2]

JetPlaneFlyer,
I guess that the pilot of that crashed glider has read the same text you have posted. The results were rather dramatic.

Every time the downwind turn comes up, I feel like the discussion needs to be transferred to the "Life, the Universe, and Politics" forum. Shouldn't be this way because the facts are obvious, but some of these guys seem to defend their "dreaded downwind turn" view more vehemently than they would argue their religions or political viewpoints.The same assumption should be applied to those who believe that the plane is always flying in a "steady state" carried by "a sea of air" no matter how you turn it...

[Brandano]

Given sufficient altitude and the proper distance from the field you can bring the glider down safely. You need (and you get!) the same amonut of energy to get the glider down from the same height, irrespective of how much distance it covers horizontally. In several countries fighter pilots are trained on gliders in order to learn proper energy management, and how to trust the instruments more than their eyes even when close to the ground.
[edit]: I think the description of this book says it all: http://www.stormingmedia.us/20/2068/A206863.html

[sixty9mustang]

When I started this thread, I was wondering what makes a plane more stable in the wind. Landing in the wind seems to be the hardest part because of unpredictable nature of wind gusts near the ground. Some planes get bounced around more than others. I've seen planes come in on landing approach that look rock solid in winds that make my foamies look like they're traveling through white water rapids.

I think power and control authority help on any plane. I also think that a plane with higher wing loading is less effected by wind gusts because the prop is doing more work. I think of the prop as creating controlled wind. The higher the percentage of controlled wind Vs gusty wind, the more control you will have on your plane. It seems to me that a 10 mph wind pushing on a plane with a wing loading of 12.5oz/sq foot Vs a plane with 25oz/sq foot will have about twice the effect. Is this correct? Am I even close?

JB

JB
Yes to a degree you are correct. Don't forget about the design of the aircraft, some are designed to fly in wind.
There are two factors that have been left out. Any slope pilot knows that any plane will fly in wind, that is what they do. Most any pilot knows that any plane will fly in wind. Here is the kicker not every pilot can fly in the wind. :D , and not that they can't, either they won't or they don't have enough experience to do so. Even those that do have tough times in the wrong conditions.
With that said, higher wing loading will handle wind better than lower wing loadings, heavier mass needs more lift. The other thing you need to factor in is the REYNOLDS numbers of flight. Remember an aircraft can be small (like your park flyer or large like the 3D aircraft you talk about), but an air molecule remains the same size no matter what. Now you can also say that in colder air the air is denser than in hotter air( less distance between molecules as they get hotter because they become more active), and this also has an effect on how aircraft perform. A bigger aircraft can carry a larger wing loading than a smaller aircraft based on Reynolds numbers and sciences that I have no knowledge of/don't have enough time figure out.
With gliders we fly in winds we are comfortable with, like most pilots should. If someone flying a large 3D model is not comfortable flying in any wind, he shouldn't, but he should not state that it is the models fault. I fly a 21.5 oz(10.5 oz/sq ft wing loading) 60 inch sailplane in winds varying from 8-45mph and am very comfortable with it. It is all about knowing your limitations and the models.

In the end, if you can successfully fly your aircraft in the wind, enjoy the free airspace and let everyone else watch. Their loss :p .
I'd look up Reynolds numbers on the internet, and try to find a website that explains them in depth if you want to know more about the sciences of flight. It will lead you into a world of great expanse.

Chip

[DT56]

http://www.glider.org/SafetyCorner/FrankDocuments/Skids03-02.htm

It appears to me that the accident was the result of a skidding turn on final.

The pilot can cause it to happen in a headwind, downwind or zero wind. The great distance between tips on a glider wing mean considerable difference in speed in a turn. In a skid, the pilot aggravates that difference by forcing the inside tip to actually move aft of the outside tip.

A slip on the other hand is generally regarded as safe, as it moves the inside wing tip forward of the outside tip. Since the initial recovery from a slip is a skid, one should "ease" out of a slip when at an altitude that precludes recovery from a spin.

The problem can be avoided by heeding the most basic instrument onboard the glider, the yaw string.

DT56

No, I didn't stay at a Holiday Inn Express last night, but I am a full scale glider pilot.

[sixty9mustang]

http://www.glider.org/SafetyCorner/FrankDocuments/Skids03-02.htm

It appears to me that the accident was the result of a skidding turn on final.

The pilot can cause it to happen in a headwind, downwind or zero wind. The great distance between tips on a glider wing mean considerable difference in speed in a turn. In a skid, the pilot aggravates that difference by forcing the inside tip to actually move aft of the outside tip.

A slip on the other hand is generally regarded as safe, as it moves the inside wing tip forward of the outside tip. Since the initial recovery from a slip is a skid, one should "ease" out of a slip when at an altitude that precludes recovery from a spin.

The problem can be avoided by heeding the most basic instrument onboard the glider, the yaw string.

DT56

No, I didn't stay at a Holiday Inn Express last night, but I am a full scale glider pilot.
DT
Nice article/good read..

Thanks
Chip

[DT56]

Your welcome Chip!

That's just one of many great articles by Jayne and Frank Reid of Bermuda High Soaring, in Lancaster, South Carolina.

http://www.glider.org/

DT56

[ndb8fxe]

double post

[ndb8fxe]

The difference in this is that the "downwind turn" discussion is scientific and can be proven in real numbers, while the meaning of life etc. are not.

The fact remains that the turn downwind is only detrimental when the pilot is using ground clues to judge his airspeed. This is how we can turn with the stall warning screaming while demonstrating Vmca in training. Try doing it low to the ground and using ground references to guage airspeed and you'd be in trouble.

[mrblucor]

Chip,
Thank you very much for your thoughtfull post. You are 100% correct in saying the pilot should be comfortable with the wind they are flying in. I knew it wasn't the models fault, but didn't have the knowledge to back it up.

I think bigger models fly better. They seem to be a lot smoother in the air than the little ones. Maybe this has to do with the reynolds number being larger for larger aircraft. I also think they can fly better in gusty winds because of their larger wing loading. So if I were to compare two Extra 300's, one 16 oz and the other 16 lbs, (thrust to weight ratio the same), I would say the larger one would handle the wind better because of it's higher wing loading and possibly its high reynolds number.

JB

[kevinhines]

Hello RCGroup members,
I was flying in the wind today. In fact I was the only one flying. I've read in our clubs newsletter that a light foamy can't fly in the wind. HA! I say. I fly my foamy's in the wind all the time. So after a few flight today, I was told that light foamys could fly in the wind, but heavy 50cc size plane can't. Well, which is it????

My theory is that it has to do with wing loading and control authority. Heavy wing loading won't be as much affected by wind as a lightly loaded plane. Control authority is needed to compensate or fight back against the wind and wind gusts.

Does anyone have facts to back or dismiss my theory??

JBJB, I suspect you are right about wingloading being the key parameter in how aircraft are pushed around by gusts.

I believe that when a gust blows against an aircraft's wing area, the change in force applied to the wing is proportional to the wing area. And per Newton's laws of motion, F=ma, (i.e., force = mass x acceleration), so the acceleration, a, is equal to the force divided by the mass of the plane.

So if a gust produces a force proportional to the wing area, and the acceleration due to the gust is proportional to the force divided by the plane's mass, that means that the acceleration is proportional to the wingarea divided by the mass of the plane... thus, the acceleration o fthe aircraft due to a gust is inversely proportional to the wingloading.

Does that make sense?

That's my understanding of the relationship between wingloading and an aircraft being pushed around (accelerated) by gusts.

Thanks for starting this thread!
Kevin

[DT56]

I can understand the cost in both time and money. Electric isn't cheap. I spend a lot of time building my models, even the ARF's. That may be a factor, but that was not what was said. I maintain that a plane with heavier wing loading is easier to fly in the wind as long as it has ample power and control authority.

Can you tell me what wing cube loading is and why it's a better method to calculate how a plane will fly.

JB

Cubic Wing Loading is an empirical formula that takes into account the affect of aircraft size on wing loading. As a general rule, larger aircraft can handle higher wing loading than smaller aircraft. Cubic wing loading = weight of aircraft in ounces divided by the wing area in square feet to the power of 3/2.

Cubic Loading links:

http://www.stefanv.com/rcstuff/qf200407.html

http://www.emfso.org/electric_flight_articles_weight.asp

http://findarticles.com/p/articles/mi_qa3819/is_199712/ai_n8772261

[funfly2]

http://www.glider.org/SafetyCorner/FrankDocuments/Skids03-02.htm

It appears to me that the accident was the result of a skidding turn on final.

The pilot can cause it to happen in a headwind, downwind or zero wind. The great distance between tips on a glider wing mean considerable difference in speed in a turn. In a skid, the pilot aggravates that difference by forcing the inside tip to actually move aft of the outside tip.

A slip on the other hand is generally regarded as safe, as it moves the inside wing tip forward of the outside tip. Since the initial recovery from a slip is a skid, one should "ease" out of a slip when at an altitude that precludes recovery from a spin.

The problem can be avoided by heeding the most basic instrument onboard the glider, the yaw string.
I know it's quite possible to land downwind provided you have enough airspeed (the ground speed would just be higher than normal), but in this case, despite the pilot kept nose down to gain airspeed, he didn't make it because the plane was too low and turning downwind.
I do also know that stall may occur and it often occurs headwind, but you'll increase the stall risk dramatically if you bank downwind at low airspeed.

In such a circumstance you'd rather bank into the wind and save your butt.

The pilot was an instructor and therefore should know how to read the airspeed, unfortunately he must have also learnt the same nonsense as some others in these forum.

[JetPlaneFlyer]

JetPlaneFlyer,
I guess that the pilot of that crashed glider has read the same text you have posted. The results were rather dramatic.


Rather than glib dismissal of the text I posted please read it and comment on the validity of the actual physics. If you can spot a flaw then say so... if you cant then surely you must accept that it's correct, even if it does disagree with your intuition (on which your entire argument is based)?

[funfly2]

Rather than glib dismissal of the text I posted please read it and comment on the validity of the actual physics. If you can spot a flaw then say so... if you cant then surely you must accept that it's correct, even if it does disagree with your intuition (on which your entire argument is based)?
I stopped reading further your post when I read following:


So, what is the acceleration when this is done in still air? Immediately before the turn, the velocity is 50 knots north, and immediately after the turn the velocity is 50 knots south, so the velocity change is 100 knots (168.8 ft/sec). The change takes place in exactly one minute, so the average north-south acceleration during the turn is 100 knots/minute , or 2.81 ft/sec./sec
...
I just don't agree with that.

[Brandano]

Unfortunately that's a fact, and when facts don't agree with you you have to question your beliefs, otherwise you are basing your opinion on faith alone.

[JetPlaneFlyer]

I just don't agree with that.

Let me get this straight...You dont agree that acceleration = change in velocity divided by time taken :eek:

Then how do you define acceleration?

[funfly2]

Let me get this straight...You dont agree that acceleration = change in velocity divided by time taken :eek:

Then how do you define acceleration?If it took one minute for a plane flying at 50 knots to turn 180 degrees, how could the plane get an acceleration of 100 knots/minute?
So, if the plane kept flying in circles would it keep accelerating at 100 knots/min...?
But wasn't the plane already flying at the speed of 50 knots in still air?

Or maybe you meant Radial Acceleration... but that's a different calculation with a completely different result...
:cool:



So, what is the acceleration when this is done in still air? Immediately before the turn, the velocity is 50 knots north, and immediately after the turn the velocity is 50 knots south, so the velocity change is 100 knots (168.8 ft/sec). The change takes place in exactly one minute, so the average north-south acceleration during the turn is 100 knots/minute , or 2.81 ft/sec./sec
...
The reasoning in that text is flawed and therefore the rest is based on a false premise, but I know the internet is infected with tons of junk... and in absence of light, darkness prevails...
:rolleyes:

[Montag DP]

I know it's quite possible to land downwind provided you have enough airspeed (the ground speed would just be higher than normal), but in this case, despite the pilot kept nose down to gain airspeed, he didn't make it because the plane was too low and turning downwind.
I do also know that stall may occur and it often occurs headwind, but you'll increase the stall risk dramatically if you bank downwind at low airspeed.

In such a circumstance you'd rather bank into the wind and save your butt.

The pilot was an instructor and therefore should know how to read the airspeed, unfortunately he must have also learnt the same nonsense as some others in these forum.So you're saying that, in a downwind turn, a plane loses airspeed. Correct? That means it loses kinetic energy relative to the air.

So where does this kinetic energy go? Does it get lost to friction? Maybe it gets changed into potential energy somehow? Certainly it can't just disappear.

[funfly2]

So you're saying that, in a downwind turn, a plane loses airspeed. Correct? That means it loses kinetic energy relative to the air.

So where does this kinetic energy go? Does it get lost to friction? Maybe it gets changed into potential energy somehow? Certainly it can't just disappear.As you might know energy doesn't disappear, but just changes its form, in this case part of kinetic energy is changed into potential energy as the plane still has its mass and [hopefully] still has some altitude left...

[Cory]

As you might know energy doesn't disappear, but just changes its form, in this case part of kinetic energy is changed into potential energy as the plane still has its mass and [hopefully] still has some altitude left...

So......if the kinetic energy changes to potential energy..........help me with this.........yer sayin' the plane climbs when ya turn downwind?! Now yer contradicting yerself! :confused:

[Montag DP]

As you might know energy doesn't disappear, but just changes its form, in this case part of kinetic energy is changed into potential energy as the plane still has its mass and [hopefully] still has some altitude left...Haha ok, that's great to know. If I ever need to gain some altitude I'll just turn downwind. Glad you clarified that for me. :D

[JetPlaneFlyer]

If it took one minute for a plane flying at 50 knots to turn 180 degrees, how could the plane get an acceleration of 100 knots/minute?


Because acceleration is defined as a change in VELOCITY over time and velocity is a VECTOR quantity... ie it has DIRECTION in addition to magnitude (unlike speed which has only magnitude).

If the plane was flying north at 50knots, and lets call north the positive(+) vector... and it turns 180 deg then it's now flying south (still at 50knots), which being opposite to north must be the negative (-) vector direction.

Acceleration is change in velocity over time taken and the difference between +50 and -50 is 100. So if the turn took one minute then yes, the average acceleration is indeed 100 knots per minute.

This is basic 'schoolboy' physics... check it out in any school physics text book or on any internet site.

[funfly2]

So......if the kinetic energy changes to potential energy..........help me with this.........yer sayin' the plane climbs when ya turn downwind?! Now yer contradicting yerself! :confused:Tell us when did I write that the plane climbs downwind???
You'd better read what I've written before posting your comments.

[funfly2]

Haha ok, that's great to know. If I ever need to gain some altitude I'll just turn downwind. Glad you clarified that for me. :D
Hey, I never said that the plane climbs downwind, I said that if it has some altitude left after turning downwind.

[Cory]

But you did say that the kinetic energy is changed into potential energy. Do you understand the difference?

Potential Energy: the energy stored in an object due to its position. A raised object will have potential energy. Potential energy is dependant on the mass and height of an object.

Kinetic Energy: the energy of an object due to its motion. Kinetic energy depends on the mass and velocity of an object.

If you convert kinetic energy into potential energy, you gain height.

[funfly2]

Because acceleration is defined as a change in VELOCITY over time and velocity is a VECTOR quantity... ie it has DIRECTION in addition to magnitude (unlike speed which has only magnitude).

If the plane was flying north at 50knots, and lets call north the positive(+) vector... and it turns 180 deg then it's now flying south (still at 50knots), which being opposite to north must be the negative (-) vector direction.

Acceleration is change in velocity over time taken and the difference between +50 and -50 is 100. So if the turn took one minute then yes, the average acceleration is indeed 100 knots per minute.

This is basic 'schoolboy' physics... check it out in any school physics text book or on any internet site.You are wrong: +50 -50 = 0.
Anyway, your case is about circular motion where you get a Radial Acceleration that is not even close to your 100 knots/min and by the way you've expressed acceleration wrong too, since the time should be squared.
For example, a = 300m/s^2.

But even if you try to apply your flawed reasoning, tell us what the acceleration would be if the plane just turned 90 deg?
Or tell us what the acceleration would be if the plane turned 360 deg?
:p

[funfly2]

But you did say that the kinetic energy is changed into potential energy. Do you understand the difference?

Potential Energy: the energy stored in an object due to its position. A raised object will have potential energy. Potential energy is dependant on the mass and height of an object.

Kinetic Energy: the energy of an object due to its motion. Kinetic energy depends on the mass and velocity of an object.

If you convert kinetic energy into potential energy, you gain height.Ok, let me say it in other words:
As long as the plane has altitude there's a potential energy related to the ground + kinetic energy related to the ground (if there's ground speed) + kinetic energy related to the air (if there's airspeed).
When you turn downwind there's an instantaneous reduction of airspeed and an increase of ground speed so the kinetic energy related to the air decreases while the kinetic energy related to the ground increases.

[Cory]

You're absolutely correct that the kinetic energy relative to the ground changes when you turn in wind. Your kinetic energy relative to Mars will also change, but it doesn't matter. The plane is flying relative to the air mass.

But there's not an instantaneous reduction in airspeed. (unless you are turning so tight that your creating a lot of drag, but that happens even if there's no wind. In a gentle turn the increased drag will be slight) I have a private pilot's license and got about half way through my instrument rating. I spent many hours flying with a hood on my head so that I saw nothing but the instrument panel. I flew lots of racetrack holding patterns and procedure turns on windy days. I did not see a reduction of airspeed when I turned downwind. Of course, that's because that while flying a standard rate turn the plane is flying relative to the airmass and doesn't care what the ground is doing. Keeping the eyes inside the plane is also great assurance that one doesn't get confused and start flying relative to the ground.

When I was flying VFR and practicing turns around a point, the potential for a stall was higher when the plane was flying directly downwind because this is the tightest banked portion of a constant ground track turn in wind. Common practice for student pilots is to try to fly nice round ground tracks around a country road intersection. If you are flying a round ground track, you will cross each road perpendicularly. When you don't quite compensate for the wind correctly, you will cross a road at a non 90 degree angle. This gives the pilot input on the strength of the winds. He then must increase bank angle to tighten up the turn. In order to maintain a constant altitude the pilot must also "pull". This increases the angle of attack, thus increasing the lift coeficient, "g" forces, and drag. The increase in drag will slow the plane down. The "accelerated" stall speed will be higher than the normal stall speed. If the pilot lets his plane slow down too much he will experience an "accelerated" stall. I used to do turns around a point at up to a 60 degree bank. In order to maintain airspeed while maintaining altitude I had to increase the throttle setting. This is where pilots get into trouble. If they lose awareness of airspeed and forget that stall speed is higher in a turn, they can stall the plane. Accelerated stalls often result in a spin for a variety of reasons that I won't get into here. If you do this while too low, you die.

Do you know what the hardest part of piloting a real airplane is? Most people who haven't done it wouldn't guess right. The hardest part is not the physical coordination used to make the plane do what you want. In fact, it's common for light aircraft pilots to fly landing approaches left handed because the throttle is in the middle and they sit on the left side. The hardest part of flying is time and information management. It you haven't developed a good, consistent radial scan of the instrument panel it's easy to lose track of things like altitude, heading, rate of climb, turn coordination, pitch attitude, bank angle, and often most deadly, of airspeed.

Translate this over to RC where you don't have any precise knowledge of airspeed but are in reality just flying by how the plane appears to be traveling. This makes it really hard to know how close you are to your stall speed. What I have found that works is this; I balance and trim my gliders so that the plane does not climb much at all when it accelerates in a dive. I also check for how much "push" it takes to fly inverted. When the CG is back enough that it almost flies upside down without pushing, and when it can go into a several hundred yard dive without pulling up much at all, the plane is trimmed. A common mistake for glider pilots is to pull back on the stick to keep altitude. Often a better approach is to let the plane descend and accelerate to a more efficient flying speed, then gently pull back to climb, while retaining as much airspeed as possible. After learning this lesson, a good pilot will also learn how much to "pull" to maintain altitude in a turn. This pretty much becomes habit after a while. Now, here's where this applies to the downwind turn. Let's say that my plane takes a pull of about 1/8 inch on the transmitter stick to keep it's altitude in still air. If you are flying in wind you must realize that if you pull this same amount regardless of whether you are turning upwind or downwind, your plane will maintain altitude and exit the turn with the same airspeed. However, the ground track and ground speed will be considerably different. The problem comes when you try to make identical ground tracks without realizing that you are bleeding of airspeed.

[JetPlaneFlyer]

You are wrong: +50 -50 = 0.
Anyway, your case is about circular motion where you get a Radial Acceleration that is not even close to your 100 knots/min and by the way you've expressed acceleration wrong too, since the time should be squared.
For example, a = 300m/s^2.


I did not say +50 minus 50.. i said the DIFFERENCE between the two figures, or +50 minus -50 (two minuses make a plus). If you think the numeric difference between -50 and +50 is really zero then you are well behind my 8 year old child in understanding of basic addition.
The units are not wrong.. a knot is a measure of speed, unlike the 'm' in 300m/s^2 which is a measure of distance. That's where the second 's' value comes in, to turn 'm' into a measure of speed, its not needed in knots per minute because knots is already a measure of speed.

Anyway.. All this has been gone over in tedious detail in the original thread and you are still convinced that your intuition is correct and nothing i can say is going to change your mind so I'll leave it at that, this is eating up my model building time.

Steve

[funfly2]

I did not say +50 minus 50.. i said the DIFFERENCE between the two figures, or +50 minus -50 (two minuses make a plus). If you think the numeric difference between -50 and +50 is really zero then you are well behind my 8 year old child in understanding of basic addition.
The units are not wrong.. a knot is a measure of speed, unlike the 'm' in 300m/s^2 which is a measure of distance. That's where the second 's' value comes in, to turn 'm' into a measure of speed, its not needed in knots per minute because knots is already a measure of speed.

Anyway.. All this has been gone over in tedious detail in the original thread and you are still convinced that your intuition is correct and nothing i can say is going to change your mind so I'll leave it at that, this is eating up my model building time.

SteveYou can't calculate the acceleration of a body moving at constant speed in circular motion by just taking the difference between +50 knots and -50 knots.

If the plane was initially flying at 50 knots and "got an acceleration of 100 knots/min" as you say, then after one minute it would have a speed of 150 knots…

But again: your case is about circular motion where you get a Radial Acceleration, which is not even close to your 100 knots/min.

And you still didn't answer what the acceleration would be if the plane just had turned 90 deg or if it had turned 360 deg according to your "math".
:rolleyes:

[funfly2]

...
But there's not an instantaneous reduction in airspeed. (unless you are turning so tight that your creating a lot of drag, but that happens even if there's no wind. In a gentle turn the increased drag will be slight) I have a private pilot's license and got about half way through my instrument rating. I spent many hours flying with a hood on my head so that I saw nothing but the instrument panel. I flew lots of racetrack holding patterns and procedure turns on windy days. I did not see a reduction of airspeed when I turned downwind. Of course, that's because that while flying a standard rate turn the plane is flying relative to the airmass and doesn't care what the ground is doing. Keeping the eyes inside the plane is also great assurance that one doesn't get confused and start flying relative to the ground.
...
The amount of airspeed reduction when turning downwind (and hence the preception of it) depends on how quick you turn AND how strong the wind is related to your airspeed at the moment of the turn.

If you turn with a relatively wide radius at an initial airspeed much greater than the actual wind speed, you barely notice any difference.

BUT, if you are flying crosswind near your stall speed close to the ground, you'd better turn upwind rather than downwind if you want to preserve your life and the life of somebody else who might suffer the consequences of your manouvre...

Check out the video clip again carefully, the pilot was an instructor who surely knows about airspeed stuff...

http://youtube.com/watch?v=_xCct8cDtyk

[JetPlaneFlyer]

You can't calculate the acceleration of a body by just taking the difference between +50 knots and -50 knots.
If the plane was initially flying at 50 knots and "got an acceleration of 100 knots/min" as you say, then after one minute it would have a speed of 150 knots…

But again: your case is about circular motion where you get a Radial Acceleration that is not even close to your 100 knots/min.

And you still didn't answer what the acceleration would be if the plane just had turned 90 deg or if it had turned 360 deg according to your "math".


My last word in this thread...

Acceleration like velocity is a vector quantity i.e. it has a direction. In the example we are talking about the acceleration is in the opposite direction to the original northerly direction of travel (which is why the model ends up going South)... So the acceleration is taken away from the original velocity, not added to it.

To answer your other points..
A 360 deg turn produces an AVERAGE acceleration of zero... that's because the accelerations during the turn are in opposing directions so exactly cancel each other out. The average acceleration 'must' be zero because the model is flying at the same speed and direction before and after the 'event'. (This is not to say the instantaneous acceleration during the manoeuvre is zero, clearly not, if you want to calculate that then it's the product of velocity squared divided by radius of turn.
If you struggle with this concept consider a case where you go 100m north at 5m/s, turn round and go 100m back to your start point at 5m/s. What is your average velocity?... Answer: Average velocity is zero (average speed however is 5mph)

the case of a 90deg turn is a little more complex because the vectors are not in the same line. You need a vector diagram to properly describe this one but the answer is Sq. Root (50^2 + 50^2) = 70.7

look at this site: http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/circles/u6l1b.html
Try the questions ... do you get them right?

[Cory]

Check out the video clip again carefully, the pilot was an instructor who surely knows about airspeed stuff...
Obviously didn't pay attention to what he should have known.

[funfly2]

My last word in this thread...

Acceleration like velocity is a vector quantity i.e. it has a direction. In the example we are talking about the acceleration is in the opposite direction to the original northerly direction of travel (which is why the model ends up going South)... So the acceleration is taken away from the original velocity, not added to it.
So if you have two equal vectors with an angle of 180 deg between them, they just cancel each other out, the result is zero.



...
If you struggle with this concept consider a case where you go 100m north at 5m/s, turn round and go 100m back to your start point at 5m/s. What is your average velocity?... Answer: Average velocity is zero (average speed however is 5mph)
According to that definition your plane heading north after turning 180 deg has actually moved to a point on the west or on the east (depending on whether it turned left or right) while pointed to the south…

So, if the speed of the circular movement was 50 knots and it took one minute to turn half the circle, the length of the half perimeter of the circle was 0.833 of a mile…
So, if you divide the perimeter by pi you'll get the diameter = 0.53 of a mile, which is the distance from the initial point.
The velocity = distance / time = 31.8 knots

That's less than the initial speed 50 knots…
:rolleyes:

[vintage1]

Rcgroups have an ignore list.

Its really useful to avoid wasting time in the way shown in the pictogram in the previous post. :cool:

[funfly2]

Obviously didn't pay attention to what he should have known.The pilot knew that the plane had to have enough airspeed, and he also knew that's possible to land downwind, that's why he kept diving all the way back.
And he did it well until the point when the plane got a greater wind speed from behind than its airspeed and entered the spin.

Yes, it was pilot error because the plane was near the stall speed while he kept turning into downwind.

[ADB2]

Hmmm, guys, I think funfly2 was pretty clear and if you are trying to misrepresent what he wrote, well, I am not quite OK with that.
Basically this argument is getting people into two camps:
Camp1 says you don't have to watch out for downwind turns any more than you should watch out when turning into the wind, coz the plane couldn't care less about the wind, since it is moving in the wind itself. The basic assumption here is that the pilot will maintain a constant (absolute) airspeed while turning.
Camp2 says you should watch out for downwind turns, coz for any imaginable reason the plane's airspeed can drop (and the pilot may not be concentrating on airspeed at that point), and you get a stall and crash (and you die if you are inside the plane).
Both camps are right but I am with Camp2.

[vintage1]

No. Camp1 says the plane doesn't care, and any spurious analysis about what happens and why won't help, unless the pilot realises that he is moving relative to the airmass and the plane.

Camp2 invents loads of spurious physics and maths to prove why he cant do mental vector transformations, and fly a plane in wind, and thereby avoids taking responsibility for his perceptions, and blames it all on pseudo science.

Both camps agree that flying a plane in wind is tricky. The first camp says its because of the illusion of airspeed due to excessive groundspeed, the second says the airspeed actually changes without pilot input, and that's the problem.

Generally Camp 2 are those who haven't understood vector mathematics. And dont see why they should, either.

All I have to say, finally, is those that use science to explain things, should do so scientifically. You cant have your cake and eat it too. That way lies Creationism. An illusion of science with all the strictures firmly removed to fool the gullible.

[ADB2]

You mean that sine and cosine thingy? ;)
Yeah, I have a hard time doing "mental vector transformations" when I am flying an RC model. :)
And I am still with Camp2 as far as watching for downwind turns is concerned. Anything goes as long as I don't crash my RC model. Can't say for sure about real planes but I think when your life is on the line anything goes too. :)

Ok, now the obvious that everybody has stated many times and most people will agree with: it's very hard to judge airspeed in a strong wind, whether in the case of flying an RC model, or as a pilot in a real airplane. Specially when turning downwind.

[Brandano]

free flight models are trimmed to fly circles. They don't care whether they are turning into the wind or away from it, their altitude isn't affected. they drift downwind with time, and therefore don't fly exact circles over the ground. Pilots don't seem to be able to do this as effectively as a pilotless, trimmed plane

[funfly2]

Hmmm, guys, I think funfly2 was pretty clear and if you are trying to misrepresent what he wrote, well, I am not quite OK with that.
Basically this argument is getting people into two camps:
Camp1 says you don't have to watch out for downwind turns any more than you should watch out when turning into the wind, coz the plane couldn't care less about the wind, since it is moving in the wind itself. The basic assumption here is that the pilot will maintain a constant (absolute) airspeed while turning.
Camp2 says you should watch out for downwind turns, coz for any imaginable reason the plane's airspeed can drop (and the pilot may not be concentrating on airspeed at that point), and you get a stall and crash (and you die if you are inside the plane).
Both camps are right but I am with Camp2.Thanks ADB2, it seems impossible to keep a meaningful discussion with some of these guys here.

I've never excluded the fact that a pilot who keeps using the ground as reference may get mislead by the higher ground speed when flying downwind.

But that's not the full story, because if one thinks that as long as he/she just keeps staring at the airspeed meter there would be no danger, sooner or later something like what is shown in that video may happen… suddenly the airspeed disappears while the ground is always waiting below.

[ADB2]

free flight models are trimmed to fly circles. They don't care whether they are turning into the wind or away from it, their altitude isn't affected. they drift downwind with time, and therefore don't fly exact circles over the ground. Pilots don't seem to be able to do this as effectively as a pilotless, trimmed plane
Exactly. Also free flight models fly at a rather constant airspeed. And they don't care about being carried away by the wind.

Pilots generally want to go somewhere and land on the landing strip, so they are controlling the airplane with respect to the ground.

[ADB2]

Thanks ADB2, it seems impossible to keep a meaningful discussion with some of these guys here.

I've never excluded the fact that a pilot who keeps using the ground as reference may get mislead by the higher ground speed when flying downwind.

But that's not the full story, because if one thinks that as long as he/she just keeps staring at the airspeed meter there would be no danger, sooner or later something like what is shown in that video may happen… suddenly the airspeed disappears while the ground is always waiting below.
I agree. Big advantage birds have over us: they have airspeed and stall sensors and can even do mental vector transformations at lightning speed, yet I am sure even they watch out for downwind turns. I have seen eagles circling in windy conditions and definitely the downwind and into the wind turns were differently executed.

[DT56]

This discussion has reached the point of "Paralysis of Analysis".

A full scale demo flight could show you what happened in the sailplane skid-stall-spin accident. Why not hire a glider with instructor and find out?

Link for soaring sites in USA:

http://www.ssa.org/sport/wheretofly.asp

I could show you in just a few seconds what happened-PM me FunFly if you'd like and we can see if your proximity would permit scheduling the flight.

[kevinhines]

JB, have you found an answer to your original question about the relationship between an aircraft's wing loading and its ability to fly in windy conditions?

Kevin

[Cory]

The original topic of this thread was discussed a bit in the DS forum in a thread about maximizing DS speed. Dr. Drela showed that DS speed was not dependent on weight, even though most fast DSers are ballasted. The conclusion is that the increased mass allows for a smoother flight, with less drag producing control imputs, which allows faster speed. I'd expect that you'd find a similar outcome in a powered plane that isn't already marginal on power. In this thread you will find plenty of mathematically proven concepts as well as real world experience from some of the best pilots in the world at flying in strong winds. Optimum DS Path, Airplane (http://www.rcgroups.com/forums/showthread.php?t=931565)

[admodesi]

Just had a CLOSE look at funfly2's video. Did anyone note that the spoilers were deployed at the very instant of the loss of control? If it is an instructor, it seems to prove even they make mistakes! Besides the large angle of bank anyone else figure out the increase in stall speed in that configuration? Level the wings, put the nose down, retract the spoilers... and live to tell the tale!

Before I started flying full-size I went through about 6 instructors before I found one that actually KNEW about aerodynamics!

To answer my own question I just noticed this previous post (#43)and I agree.

in that situation, since takeoff is in the direction of the wind, what side you choose to turn on doesn't matter. He wouldn't have crashed if he had kept the nose down and left the spoilers closed. Here's how it's done properly:

[mrblucor]

I broke my U can Do 46 fuse in half landing in the wind the other day. I was crabbing into the cross wind and the mains and the tail touched at the same time and broke the fuse clean in a sideways snap. I think the only thing holding it together was the covering. I put it back together and am waiting for time to fly it again. Flying in a strong wind is not for the faint of heart.

JB

[Cory]

Nor is it for the frail of structure. :)