SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Jul 24, 2012, 05:21 PM
Facts, Logic, 3D
Tom K.'s Avatar
Florida
Joined Nov 2010
3,585 Posts
Quote:
Originally Posted by Jovanx View Post
In theory, there should be no such thing as a downwind turn. The theory states that wind is of no concern to the pilot unless he is taking off, landing, or navigating.

My question is, why do so many people get into trouble when turning downwind? Whether or not there is any logical explanation, it is apparent that many crashes have been caused by not correctly performing that maneuver.

There has been some heated discussion of this on other forums. Some people passionately believe it exists, and other people passionately believe it does not. Hopefully this discussion will not degenerate into people calling other people idiots. My purpose in starting this thread is to try to understand this phenomenon and how to avoid it.
I'm thinking they're just too slow to begin with. They are traveling downwind, and therefore your ground speed is greater than your airspeed creating the illusion you are travelling faster (when you're not). Then you bank the wings. This means the "lift" is now being directed to a side and not "up". Now you pull back without adding adequate power (from what I've seen, this happens mostly when somebody is trying to land, so they don't have power on like they should), this decreases the airspeed more, as well as increasing the angle of attack. At some point, a wing stalls because the mix of no power, banked wings, and reduced airspeed forms a threesome of and it snaps over into the ground/trees/pond/fence/goal post/etc.

--Tom K.

P.S. I've been flying for a few years (since '08) and for a while I've been able to "judge" my airspeed with how mushy and responsive the controls are and avoid stalls and snaps while turning and flying. I suppose having a 3D background helps.
Tom K. is offline Find More Posts by Tom K.
RCG Plus Member
Last edited by Tom K.; Jul 24, 2012 at 05:27 PM.
Reply With Quote
Sign up now
to remove ads between posts
Old Jul 25, 2012, 05:59 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,160 Posts
Quote:
Originally Posted by Wookster View Post
let me throw my .02 on what my limited hobby time has noticed. In high winds they are usually very gusty. gusts to the nose or tail are expected and uneventful. Now lets look at the downwind leg. halfway through your downwind turn you have the wind and associated gusts coming at 90 degrees. Now how are your wings banked? that wind is essentially hitting a downward angled spoiler. It will cause the plane to drop, the solution is to pull up quickly for a lot of people. If you are cruising slow, you could induce a stall and you will be scrubbing airspeed. alternatly on the upwind turn the wings are angled upwards to the wind. it will cause the plane to lift, you counter by pointing the nose down and gain airspeed. you have to keep in mind in small scale like this a 5-10 mph wind gust is going to affect the plane when its hitting it in the side. especially if the wings are banked.

That's my theory and I'm sticking to it.
You're still thinking in up wind, down wind, across wind mode, i.e. ground based.

The plane is still flying in that block of air at an 'airspeed'. It is still travelling though air fast enough to fly. There is no up wind or down wind, or cross wind to the plane, it just flies at its airspeed, unless the models pilot affect that airspeed.

Flying in any gusty condition, wind sheer etc, will affect the model, visually from the ground. Even flying though a thermal or downdraft on a near flat calm day also affect the model.
Gusts and turbulence, (vertically or angled air flow) affect models, agreed. Straight forward wind speed does not.
eflightray is offline Find More Posts by eflightray
Reply With Quote
Old Jul 25, 2012, 06:57 PM
Tossing planes into the snow
Canada, BC, Smithers
Joined Nov 2011
2,988 Posts
Quote:
Originally Posted by Tom K. View Post
I'm thinking they're just too slow to begin with. They are traveling downwind, and therefore your ground speed is greater than your airspeed creating the illusion you are travelling faster (when you're not). Then you bank the wings. This means the "lift" is now being directed to a side and not "up". Now you pull back without adding adequate power (from what I've seen, this happens mostly when somebody is trying to land, so they don't have power on like they should), this decreases the airspeed more, as well as increasing the angle of attack. At some point, a wing stalls because the mix of no power, banked wings, and reduced airspeed forms a threesome of and it snaps over into the ground/trees/pond/fence/goal post/etc.

--Tom K.

P.S. I've been flying for a few years (since '08) and for a while I've been able to "judge" my airspeed with how mushy and responsive the controls are and avoid stalls and snaps while turning and flying. I suppose having a 3D background helps.
You make some good points here. The phenomenon occurs near the ground, when we are thinking about landing, and we are over-controlling the plane because there is limited room to land. At that point we are less than one mistake high, and the winds are usually more turbulent near the ground.

I know that feeling where the controls feel mushy and the plane is starting to look like a lead weight. If it is close to the ground, it is already too late by the time I notice it. I can see how 3D experience would be a benefit, because it allows you to push that stall envelope and still have the power to defy gravity.
Jovanx is offline Find More Posts by Jovanx
Reply With Quote
Old Jul 25, 2012, 07:05 PM
Facts, Logic, 3D
Tom K.'s Avatar
Florida
Joined Nov 2010
3,585 Posts
Quote:
Originally Posted by Jovanx View Post
I can see how 3D experience would be a benefit, because it allows you to push that stall envelope and still have the power to defy gravity.
Yeah, the power helps. Being able to throw the right stick back and the left stick forward and be at 200ft in 1.5 seconds is a big plus. But even with non-3D planes, having a little 3D and post-stall flight background helps because you know how to use the left stick effectively regardless of what you're doing. IMO, a lot of bad landings can be avoided with proper throttle and rudder management. At low speeds, the ailerons become almost useless because all it will do is bank the wings, and without speed, there's not enough lift to effectively turn the airplane. Also, when you tip stall, all countering with aileron does is throw in a whole bunch of adverse yaw and can really screw up a pilot's orientation... and low and slow with lost orientation is never good no matter how good you are. Also, if you bank then pull the elevator, all you're doing is asking the airplane to stall.

--Tom K.
Tom K. is offline Find More Posts by Tom K.
RCG Plus Member
Latest blog entry: 12S on the 3DHS 74" Edge 540
Reply With Quote
Old Jul 25, 2012, 07:52 PM
Augernaut
Wookster's Avatar
United States, KS, Overland Park
Joined Jan 2010
1,430 Posts
Quote:
Originally Posted by eflightray View Post
You're still thinking in up wind, down wind, across wind mode, i.e. ground based.

The plane is still flying in that block of air at an 'airspeed'. It is still travelling though air fast enough to fly. There is no up wind or down wind, or cross wind to the plane, it just flies at its airspeed, unless the models pilot affect that airspeed.

Flying in any gusty condition, wind sheer etc, will affect the model, visually from the ground. Even flying though a thermal or downdraft on a near flat calm day also affect the model.
Gusts and turbulence, (vertically or angled air flow) affect models, agreed. Straight forward wind speed does not.
heres what i experience. I have an aircraft that is very overweight and underpowered on takeoff. It doesn't fly well on very windy days. Even on full power the downwind turn will get a bit wild. There is something to the downwind turn. not saying that its the cause for the majority of the crashes, or even a fraction, but its there. Although the hardest part flying that plane isn't the downwind, its the upwind turn climbing out after takeoff. That I know is an airspeed related issue, she's gotta clear the trees, and in order to gain that altitude I lose airspeed. that first turn is just a bit above stall, better be ready to counter with some rudder. Then I'll clear the turn, fly the pattern a couple times to get a feel for the wind and if it's strong the darn thing will try and snap roll on the downwind turns.

my only other thought would be that its not so much an issue with airspeed vs groundspeed on the downwind straight flight, but the fact that on the transition from downwind to crosswind you are turning more than 90 degrees. in order to fly a square pattern you are turning to the crosswind and crabbing the plane. so on the upwind you are turning less to fly the crosswind. then you turn to the downwind and pick up speed. now as you turn to the crosswind again you are moving faster relative to the ground, you are also going to have to turn more than 90 degrees heading to do a 90 degree turn relative to the ground. this means more g force. maybe that is what induces some of the snaps? generally when I have that happen its early in the flight while im heavy, flaps up and flying full speed. after I recover I just kick on some flap and dump my hopper without making a run. lightens the plane up by about 10% once the powder is gone and I bring her in to land. Put too much work into that bird to lose her flying the pattern
Wookster is online now Find More Posts by Wookster
Reply With Quote
Old Jul 25, 2012, 09:36 PM
Facts, Logic, 3D
Tom K.'s Avatar
Florida
Joined Nov 2010
3,585 Posts
Quote:
Originally Posted by Wookster View Post
heres what i experience. I have an aircraft that is very overweight and underpowered on takeoff. It doesn't fly well on very windy days. Even on full power the downwind turn will get a bit wild. There is something to the downwind turn. not saying that its the cause for the majority of the crashes, or even a fraction, but its there. Although the hardest part flying that plane isn't the downwind, its the upwind turn climbing out after takeoff. That I know is an airspeed related issue, she's gotta clear the trees, and in order to gain that altitude I lose airspeed. that first turn is just a bit above stall, better be ready to counter with some rudder. Then I'll clear the turn, fly the pattern a couple times to get a feel for the wind and if it's strong the darn thing will try and snap roll on the downwind turns.

my only other thought would be that its not so much an issue with airspeed vs groundspeed on the downwind straight flight, but the fact that on the transition from downwind to crosswind you are turning more than 90 degrees. in order to fly a square pattern you are turning to the crosswind and crabbing the plane. so on the upwind you are turning less to fly the crosswind. then you turn to the downwind and pick up speed. now as you turn to the crosswind again you are moving faster relative to the ground, you are also going to have to turn more than 90 degrees heading to do a 90 degree turn relative to the ground. this means more g force. maybe that is what induces some of the snaps? generally when I have that happen its early in the flight while im heavy, flaps up and flying full speed. after I recover I just kick on some flap and dump my hopper without making a run. lightens the plane up by about 10% once the powder is gone and I bring her in to land. Put too much work into that bird to lose her flying the pattern
Also, be aware that rolling and rudder in the same direction, coupled with up elevator is airplane talk for "SNAP!" regardless of orientation to the wind.

--Tom K.
Tom K. is offline Find More Posts by Tom K.
RCG Plus Member
Latest blog entry: 12S on the 3DHS 74" Edge 540
Reply With Quote
Old Jul 25, 2012, 09:45 PM
Augernaut
Wookster's Avatar
United States, KS, Overland Park
Joined Jan 2010
1,430 Posts
Quote:
Originally Posted by Tom K. View Post
Also, be aware that rolling and rudder in the same direction, coupled with up elevator is airplane talk for "SNAP!" regardless of orientation to the wind.

--Tom K.
absolutely. I use a little rudder for coordinated turns, but when she starts to drop a wing without your input you have to put in opposite rudder and decrease up elevator One thing I love about the cub and the pawnee is its almost like the sticks have feedback. You can just feel what the plane is going through up there. I can feel the heaviness of the controls when she's loaded and the powder load lightening as she dusts. Maybe thats normal to experienced folks, but I'm still tickled about how sensory the R/C experience is.
Wookster is online now Find More Posts by Wookster
Reply With Quote
Old Jul 25, 2012, 09:55 PM
Facts, Logic, 3D
Tom K.'s Avatar
Florida
Joined Nov 2010
3,585 Posts
Quote:
Originally Posted by Wookster View Post
absolutely. I use a little rudder for coordinated turns, but when she starts to drop a wing without your input you have to put in opposite rudder and decrease up elevator One thing I love about the cub and the pawnee is its almost like the sticks have feedback. You can just feel what the plane is going through up there. I can feel the heaviness of the controls when she's loaded and the powder load lightening as she dusts. Maybe thats normal to experienced folks, but I'm still tickled about how sensory the R/C experience is.
Yeah, that comes with experience, so it seems you're pretty good with the sticks. It took me probably a year and a half before I started to "feel" the plane. One of my veteran flying buddies (who also was the secondary instructor at my field to sign me off for my solo when I was learning) told me "My instructor told me eventually you'll get to the point where you can 'feel' the plane, and it took me a while but I'm there now. In time, you too will 'feel' the plane." I kinda felt like I was being told about "the force" for the first time, but eventually I understood what he was talking about.

--Tom K.
Tom K. is offline Find More Posts by Tom K.
RCG Plus Member
Latest blog entry: 12S on the 3DHS 74" Edge 540
Reply With Quote
Old Jul 25, 2012, 10:06 PM
3D? I only got two thumbs!
United States, MA
Joined Jul 2012
1,200 Posts
Quote:
Originally Posted by eflightray View Post
You're still thinking in up wind, down wind, across wind mode, i.e. ground based.

The plane is still flying in that block of air at an 'airspeed'. It is still travelling though air fast enough to fly. There is no up wind or down wind, or cross wind to the plane, it just flies at its airspeed, unless the models pilot affect that airspeed.

Flying in any gusty condition, wind sheer etc, will affect the model, visually from the ground. Even flying though a thermal or downdraft on a near flat calm day also affect the model.
Gusts and turbulence, (vertically or angled air flow) affect models, agreed. Straight forward wind speed does not.
As a practical matter, I've never seen wind that is a smooth block of uniformly moving air around here. Especially at a flying field rimmed with trees. There are always changes, there are times when you set up an approach only to have your downwind leg turn into an upwind leg halfway through, and have to turn around to land the other way. Wind can be going 90 degrees at the edge of the field from what it is where your standing. And of course there are sometimes bursts of wind followed almost instantly by calm. So I respect the theory of the uniform wind, but I fly in the reality of the slightly unpredictable breeze.

- Ken
AeroKen is online now Find More Posts by AeroKen
Reply With Quote
Old Jul 25, 2012, 10:18 PM
Augernaut
Wookster's Avatar
United States, KS, Overland Park
Joined Jan 2010
1,430 Posts
Quote:
Originally Posted by AeroKen View Post
As a practical matter, I've never seen wind that is a smooth block of uniformly moving air around here. Especially at a flying field rimmed with trees. There are always changes, there are times when you set up an approach only to have your downwind leg turn into an upwind leg halfway through, and have to turn around to land the other way. Wind can be going 90 degrees at the edge of the field from what it is where your standing. And of course there are sometimes bursts of wind followed almost instantly by calm. So I respect the theory of the uniform wind, but I fly in the reality of the slightly unpredictable breeze.

- Ken
heck I live in Kansas. Every now and then the wind gets crazy enough it starts dropping houses on in-laws.
Wookster is online now Find More Posts by Wookster
Reply With Quote
Old Jul 25, 2012, 10:22 PM
Facts, Logic, 3D
Tom K.'s Avatar
Florida
Joined Nov 2010
3,585 Posts
Quote:
Originally Posted by AeroKen View Post
As a practical matter, I've never seen wind that is a smooth block of uniformly moving air around here. Especially at a flying field rimmed with trees. There are always changes, there are times when you set up an approach only to have your downwind leg turn into an upwind leg halfway through, and have to turn around to land the other way. Wind can be going 90 degrees at the edge of the field from what it is where your standing. And of course there are sometimes bursts of wind followed almost instantly by calm. So I respect the theory of the uniform wind, but I fly in the reality of the slightly unpredictable breeze.

- Ken
Right, but really, unless you're 18 inches off the ground flaring, you really shouldn't be so close to a stall that a "slightly unpredictable breeze" can put you in the trees..

Quote:
Originally Posted by Wookster View Post
heck I live in Kansas. Every now and then the wind gets crazy enough it starts dropping houses on in-laws.
LMAO!!!

--Tom K.
Tom K. is offline Find More Posts by Tom K.
RCG Plus Member
Latest blog entry: 12S on the 3DHS 74" Edge 540
Reply With Quote
Old Jul 25, 2012, 10:25 PM
Tossing planes into the snow
Canada, BC, Smithers
Joined Nov 2011
2,988 Posts
Quote:
Originally Posted by AeroKen View Post
I've never seen wind that is a smooth block of uniformly moving air around here. Especially at a flying field rimmed with trees.
It's the same for me, living here in the mountains. There are gusts on a macro scale (valley-wide) that basically amount to changes in wind direction. Then once you are below the tree tops, the local gusts can come from any direction at any time. Sometimes the main component of the wind has a constant direction, but even then the gusts close to the ground are unpredictable.
Jovanx is offline Find More Posts by Jovanx
Reply With Quote
Old Jul 25, 2012, 10:28 PM
Facts, Logic, 3D
Tom K.'s Avatar
Florida
Joined Nov 2010
3,585 Posts
Solution!



--Tom K.
Tom K. is offline Find More Posts by Tom K.
RCG Plus Member
Latest blog entry: 12S on the 3DHS 74" Edge 540
Reply With Quote
Old Jul 25, 2012, 10:29 PM
3D? I only got two thumbs!
United States, MA
Joined Jul 2012
1,200 Posts
Quote:
Originally Posted by Tom K. View Post
Right, but really, unless you're 18 inches off the ground flaring, you really shouldn't be so close to a stall that a "slightly unpredictable breeze" can put you in the trees..
--Tom K.
Well a 5-8 mph breeze that switches direction makes for a 10-16 mph difference in the air the plane is flying through. And that's what you might call a light breeze. As you say, it can be startling if you are 18" over the ground flaring, even if you expect it.

- Ken
AeroKen is online now Find More Posts by AeroKen
Reply With Quote
Old Jul 25, 2012, 10:31 PM
Facts, Logic, 3D
Tom K.'s Avatar
Florida
Joined Nov 2010
3,585 Posts
Quote:
Originally Posted by AeroKen View Post
Well a 5-8 mph breeze that switches direction makes for a 10-16 mph difference in the air the plane is flying through. And that's what you might call a light breeze. As you say, it can be startling if you are 18" over the ground flaring, even if you expect it.

- Ken
It was, if I remember the weather report for that day, 25-30, gusting to 45. Of course, it's unfair because I have over a 2:1 power to weight and 75 degrees of elevator travel...

Tom Kitt - Extreme Flight Edge 540T EXP__Wind Therapy (9 min 6 sec)


--Tom K.
Tom K. is offline Find More Posts by Tom K.
RCG Plus Member
Latest blog entry: 12S on the 3DHS 74" Edge 540
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Astro Flight 109 Facts or Fiction. everydayflyer Batteries and Chargers 12 Jan 22, 2005 11:27 AM
Stock: Fact or Fiction..... Geoffrey109 Micro Helis 0 Nov 26, 2004 09:26 PM
Razor Fact Or Fiction? mike3976 Power Systems 9 Oct 26, 2003 05:12 PM
LI-PO Fact or Fiction? gbruce Electric Ducted Fan Jet Talk 4 Oct 24, 2002 01:48 PM
Kyosho F16, Fact or Fiction? stuart warne Electric Ducted Fan Jet Talk 20 May 31, 2002 12:49 AM