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Old May 06, 2007, 04:04 PM
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what does 'dropping a wing' mean? I think it happened on my Jibe!

I had a 'Jibe' which I test flew off a slope, the rh wing dropped away and the plane barrel rolled into the ground. I can't decide if it was a faulty servo or if it was what happens with a 'tip stall' or 'dropping a wing' (I have heard both these phrases but never experienced either and therefore don't know anything about them) as it was flying slowly at the time.
Thanks
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Old May 06, 2007, 04:14 PM
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davidfee's Avatar
San Diego, CA, USA
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Yep... tip stall. The solution is to fly faster.
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Old May 06, 2007, 05:08 PM
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Christchurch, New Zealand
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Well, it could be a wingdrop stall. It could also be a faulty servo.

A wingdrop stall is what you get if one wing stalls before the other. The unstalled wing typically makes much more lift than the stalled one, so the plane starts to rotate, which increases the angle of attack on the stalled wing making the stall deeper, and decreases the angle of attack on the unstalled wing... you can see what's going to happen, it's going to keep rolling until something changes the AoA. Tipstall is a horrid term, it doesn't really say what is going on.

During a wingdrop, the ailerons will do nothing much... in fact, they might even make it worse. The correct recovery is to center both sticks, wait a moment, and if that doesn't work (it almost certainly will) push some down elevator. Then fly out of whatever situation you're now in.

Basically, a wingdrop stall is an unintentional snap roll. You can do it deliberately (up high!) by inputting full rudder, aileron to stop the roll and smoothly pulling back on the elevator. Eventually it's going to wingdrop in the direction you applied rudder.

If a model wingdrops without putting in any rudder, by definition the rudder trim is off and you can tell which way by the direction of the drop.

Fast slope gliders typically need a very hard throw to launch, sometimes a little bit of flap will help. However, if the model has flaperons, be aware that while they'll reduce the stall speed, they most probably will also increase the intensity of the stall when it happens, so the wingdrop will be bigger and even harder to control.
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Old May 07, 2007, 11:58 AM
Yes..ok..maybe..lol.....
Tucson Avra Valley, Arizona, United States
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Flying slowly is the perfect recipe for a tip stall!
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Old May 07, 2007, 01:44 PM
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PetruSoroaga's Avatar
Bellevue,WA
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Quote:
Originally Posted by Andrew McGregor
Well, it could be a wingdrop stall. It could also be a faulty servo.

A wingdrop stall is what you get if one wing stalls before the other. The unstalled wing typically makes much more lift than the stalled one, so the plane starts to rotate, which increases the angle of attack on the stalled wing making the stall deeper, and decreases the angle of attack on the unstalled wing... you can see what's going to happen, it's going to keep rolling until something changes the AoA. Tipstall is a horrid term, it doesn't really say what is going on.

During a wingdrop, the ailerons will do nothing much... in fact, they might even make it worse. The correct recovery is to center both sticks, wait a moment, and if that doesn't work (it almost certainly will) push some down elevator. Then fly out of whatever situation you're now in.

Basically, a wingdrop stall is an unintentional snap roll. You can do it deliberately (up high!) by inputting full rudder, aileron to stop the roll and smoothly pulling back on the elevator. Eventually it's going to wingdrop in the direction you applied rudder.

If a model wingdrops without putting in any rudder, by definition the rudder trim is off and you can tell which way by the direction of the drop.

Fast slope gliders typically need a very hard throw to launch, sometimes a little bit of flap will help. However, if the model has flaperons, be aware that while they'll reduce the stall speed, they most probably will also increase the intensity of the stall when it happens, so the wingdrop will be bigger and even harder to control.
What "down elevator" means? down stick, or down surface?

You want to pull the plane up or down?

Petru
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Old May 07, 2007, 04:51 PM
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USA, CA, Vista
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Quote:
Originally Posted by PetruSoroaga
What "down elevator" means? down stick, or down surface? You want to pull the plane up or down? Petru

Down elevator is down stick .. the Trick is to get it stabilized and flying again not stalling.. So you must get off the stick for a instant,,, but will seem like an eternity.. Eaaaase on the stick to pull out sloooowly ...
This phenomenon can happen at low speed and also at high speeds.
Bottom line is , its “Wing Stall”.. CG too far aft can cause this as well as too much up elevator sometimes especially at a high “G” turns . You change the wings angle of attract to the point it stops lifting and stalls. results are that now it bites ya..
Hind-site is always 20/20/.. you can recover from this (if you have altitude) ,if it happens stay off the controllers for one or two spins .Gently straighten out and pull some up ..If you have the altitude you'll be okay.. If not your screwed anyway..
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Old May 07, 2007, 07:44 PM
tic
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New Cumberland, PA. US
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high speed or accelerated stalls bite the big one... Slow speed stalls usually happen close to the ground (landing) so you're screwed there as Dyno Don points out. Most High Performance gliders do tend to drop a wing during a stall. It's the price you pay for a HP wing..
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Old May 08, 2007, 02:24 AM
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Hong Kong
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Lighten the wingloading could also help to minimize the stall speed.
It is really hard to tell (confirm) the actual reason behind a death spiral. With rough data of my crashed planes, ~60% were caused by such death spiral, at an alt of about 100 ft.
Other than crashed induced by stalls, RF jams/ PCM lockout would also make a plane went in like stalling---time seems to stopped when it is out of control.
I bought an Eagletree telemetry set which could help to prevent stalls by giving alerts when the airspeed is too low, but they are too big for hotrods..

David
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Old May 08, 2007, 11:41 AM
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Troy's Avatar
United States, CA, Lake Forest
Joined Feb 1999
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To help prevent accidental stalls, make sure you are not flying with too much elevator in the first place. Exponential can soften the pitch around center, but it can still allow you to have too much elevator on the highest control input. If you don't use that much elevator for turns or even on flare on landing, it's best not to have it there when you panic and pull full 'up' elevator (back-stick). There is no easy way to prevent tip stalls (wing dropping) other than knowing what slow speed is safe for your airframe and wing loading and watching for the signs you are starting to stall. If you are low and slow, avoid holding too much elevator and adding too much aileron at the same time. If you see you are losing airspeed and/or dropping altitude, relax the back pressure on the elevator and let the airplane's nose drop and gain some speed.
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Old May 08, 2007, 12:31 PM
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Belgium
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Hello franky31 and all,

well, sure the Jibe can and will glide pretty well but don't expect a 1m30 plane with a 1.6% camber low thickness airfoil and a wing loading of 65g/dm˛ to glide at very slow speed like a Gentle Lady would.

This plane was designed as a pylon racer and therefore everything has been optimised for a speed of approx 175mph.

This means ,for instance, that the wing is set at -1° ( yes negative angle) in respect to the the fuselage datum line and that the stabilizer has a positive angle of 0.5° in reference to the wing (-0.5° to the fuselage datum).

These values are very different to those used on slopers or even hotliners.
The consequence is that when you glide, this plane will give you a pretty decent performance as long as you keep the speed up and fly closer to it's design speed. When you slow it down the fuselage will become very draggy because it will have a very nose high attitude, the elevator will be working in a very bad configuration as well and the performance will degrade very quick.

The airfoil also will not work well because a high wing loading and a low camber just don't perform well at slow speed.
As a matter of fact, this airfoil could work quite well on a slippery slope glider but the wing loading unballasted should be kept in the 35g/dm˛ range rather then the 65g/dm˛ that the Jibe has in racing configuration.

So my guess is that you just stalled the plane by flying it too slow in a slight side slip which gave you assymetric stall without enough altitude to recover from the stall.

I hope the damage is not that bad that you cannot repair it.

Basically, the wing should be repairable as long as the spar is not hurt.

Good luck,
Francois
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Old May 08, 2007, 02:37 PM
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Hi Francois,
So it might not have been a dodgy servo, whats the score with your mates repaired jibe? Mail me.


Quote:
Originally Posted by Florrain
Hello franky31 and all,

well, sure the Jibe can and will glide pretty well but don't expect a 1m30 plane with a 1.6% camber low thickness airfoil and a wing loading of 65g/dm˛ to glide at very slow speed like a Gentle Lady would.

This plane was designed as a pylon racer and therefore everything has been optimised for a speed of approx 175mph.

This means ,for instance, that the wing is set at -1° ( yes negative angle) in respect to the the fuselage datum line and that the stabilizer has a positive angle of 0.5° in reference to the wing (-0.5° to the fuselage datum).

These values are very different to those used on slopers or even hotliners.
The consequence is that when you glide, this plane will give you a pretty decent performance as long as you keep the speed up and fly closer to it's design speed. When you slow it down the fuselage will become very draggy because it will have a very nose high attitude, the elevator will be working in a very bad configuration as well and the performance will degrade very quick.

The airfoil also will not work well because a high wing loading and a low camber just don't perform well at slow speed.
As a matter of fact, this airfoil could work quite well on a slippery slope glider but the wing loading unballasted should be kept in the 35g/dm˛ range rather then the 65g/dm˛ that the Jibe has in racing configuration.

So my guess is that you just stalled the plane by flying it too slow in a slight side slip which gave you assymetric stall without enough altitude to recover from the stall.

I hope the damage is not that bad that you cannot repair it.

Basically, the wing should be repairable as long as the spar is not hurt.

Good luck,
Francois
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Old May 15, 2007, 03:28 AM
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Lier, Belgium
Joined Oct 2004
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This weekend we are gonna fly on the slope at 'cap blanc nez' with our club.
Nick and I are gonna take 2 jibes 1 for trying to slope with them. Nick is gonna fly with the 'heavy' Bleu fuselage and the Yellow full aileron carbon wing. I will fly with the repaired dark bleu wing that Florrain chrashed at the WC. The planes will weight about 500-550 gr. So the wing load will be about 35 gr/dm˛. The results (and perhaps pictures) I'll post next monday.

Grtz
Ivo
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Old May 21, 2007, 02:46 AM
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Lier, Belgium
Joined Oct 2004
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The Jibe of Nick (bleu fuse ,yellow carbon full ailerons) flew verry well on the slope of 'cap blanc nez' in france. Wind was about 4-6 beaufort. Elevator was trimmed a little up, ailerons (for starting) both a little down. Cg was at the max rearwards. The jibe was fast en flew straight. No problems with wing dropping. Next week (if there is enough wind) I'll try the other jibe1 with normal ailerons.
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Old May 21, 2007, 05:01 AM
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Singapore
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Francois,

Im a little confused about the angles you mentioned regarding wing and elevator...when you say -1 deg, does that mean the leading edge is higher than the trailing edge of the wing??

Is there a universally agreed direction that we refence the angles to??

Thanks

Dennis
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Old May 21, 2007, 05:57 AM
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Belgium
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Hello Dennis,

The wing is set at -1° to the fuselage.
-1° means leading edge down.

The stabilizer is set to +0.5° in respect to the wing which means that if the wing is set at 0°, the leading edge of your stabilizer should be very slightly up.

But this also means that the stabilizer is set to -0.5° in respect to the fuselage.
Since the top of the fin is set to 0°, it means you need to shim the rear of your stabilizer with +-0.3mm to get the stab to sit at the correct angle.

The Jibe1 airfoil has quite a lot of camber (1.7%)for a racer which is why it turns so hard whyle keeping it's energy well in the turns.
This relatively high camber value also means it flies at a negative angle in the straights hence the fact that the wing is set at a negative angle on the fuselage.

Does it help getting it clearer or did I get you more confused?
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