I purchased a Seagull Extra arf (.75 to .95 size / 63" ws) as an aerobatic "trainer" if you will. After getting it home I read mant reviews that said it tip stalled easily. Since I am not a skilled pilot, I'd like to build in feature(s) that will minimize the tip stalling trait before I maiden it. What do you think of putting a strip or two of a flexible, plastic "L" material across the top of the wing as a sort of short fence? Also at the tip? Lastly, what do you guys think of building and adding a spacer 1" wide that matches the wing at the root? What would happen if you added one to each side of the fuse and used a wing tube that was 2" longer? I just want the plane to behave till I have a chance to get used to it.

RPool- I don't profess to be an aerodynamics expert and I'm sure you'll get some in-depth suggestions on this from the crew on here. However, keep in mind that a tip stall results from the wingtip stalling before the wing root. Therefore the LAST thing you want to do is disrupt the airflow over the wingtip as that would make the tipstalling worse.

On some of the older designs, installation of a flow disruptor near the root was tried in order to make the wing stall more evenly. This technique works but takes some experimentation. I used the tecnique on my Livewire Champ and it works perfectly. But that plane is not a true aerobat.

Get some more opinions before you proceed.

Augie

Washout usually helps to prevent tip stalls but adversely effects some maneuvers.

On those planes, keeping the speed up, and the c.g. in the proper location, with just enough elevator travel is about the only cure for the built-in tendency to tip-stall at low speeds... the top of loops or landing.
Any deviations in the surfaces from straight will have some effects on the performance.
And, once you have a handle on it, knowing how to induce the tip-stall can be fun!

You wanted a trainer for aerobatics. That will be a good one. Aerobatic airplanes need to stall the wing. It's part of what they do.

The advice about tuning your elevator throws is excellent advice. It's how a lot of aerobatics pilots setup their airplanes.

You will notice that all the aerobatic planes have tapered wings. OK, except for the biplanes but they have such stubby wings. Tapered wings naturally stall from the tips. Mess around all you want to, and unless you really go crazy, your tapered wings are still going to stall from the tips. Can you mess around and reduce the probablilty? yes, but you can also tune your elevator throw and learn to watch airspeed and AOA more closely... and become an aerobatic pilot. Or become a better "bore holes in the sky" pilot no matter how your aerobatics goes.

Check out an IMAC meet someday. Watch the guys flying BASIC. Those are the maneuvers to learn first. And notice all their planes have tapered planforms. And they can actually be boring to watch, so few of them snap out of maneuvers.

Yeah, you got a good aerobatic plane and it really isn't a kamikaze at all.

There is a trend to fit "optional" wing droops on some trainers to prevent tip-stall

BTW, want a couple of tips on flying that tip stalling sucker safely?

Landings...........
Always have a couple of clicks of throttle on until you're over the threshold.
Keep the AOA safe on final.

A tip on flying a safe AOA:
1. have a couple of clicks of throttle and
2. if you see the underside of the airplane, you're about to see the insides of the airplane soon. (ok, 2 tips)

Is this the Extra 260 90 ARF?

If so, I don't believe it could be a trainer with 8.4~9.9 lb supported by 728 sqin of wing (27~31 oz/sqft) in 63" wing span.

Use as small throws as you can and keep AOA small at all times.

were can i get lhe leading edge exstentions??[X(]

I think you probably can't find them made for just any airplane. There are a couple of models made that come with them so you might find those models and see if the cuffs are in the replacement parts. And then guess if they'd fit your model or not.

Also, if any fit symmetrical airfoils I'd be surprised. I think most so far were for "trainers".

But look at Horizon and Tower and start in the trainer lists.

Small throws...check. So I'm guessing 3D experimentation with a tip stall prone plane is foolishness.

One of the best ways to prevent tip stalling is to have a light airplane. The type of aircraft ou have chosen is designed to tip stall/snap. The key thing to remeber here is what it takes to "pull the trigger" so to speak. Just because an aircraft has the ability to snap, does not mean it is hard to fly or is not capable of flying slow.
If you fly your new plane gently, and without excessive control travel and an aft CG, you will be just fine. Test out how slow you can get it before it stalls, up high, before attempting your first landing.

Oh, and where to find the droops? I have seen many of those in the trash can at the flying field! A waste of time in my opinion.

Actually, they work but you never know when, because you don't have the tip stall that would tell you should have had them.

I just did a quick search, and didn't find any for symmetrical wings.

Most have already been said, aerobatic airplanes are designed to stall in a certain maner.

If you realy want to change the aeroplane behaviour there is at least two possibilities with a symmetrical wing section,

-Add a "trip" device at the wing root to stall this part of the wing prematurely.
(A flow distruptor as mentioned in first answer.)

-Add a wing "cuff"/ leading edge extensionto the outer part of the wing. No "wing droop" as the wing have a symmetrical section.
This is easy made out of foamwith a hot wire cutter. The wing section is unaltered but the wing area increased and the taper ratio decreased.

Buy a piece of TE stock at the LHS. Cut 1' sections. Tack glue the piece at each wing tip to the underside of the wing, make it so it has the thick section in the front and even with the LE of the wing. Round the bottom LE part of the TR stock, not a lot, just enough to take the sharp corner off it. Now take a roll of Ultracoat trim and cover the bare wood starting 1/2" behind the wood rapping the trim up an over the top of the tip.

You have just made a high-lift device called an air-dam, not quit a LE cuff, but it works the same way. My friend had a slope ship that he just could not slow to a landing without it tip-stalling, after doing this to it it was a *****cat. The nice thing is it's easy to remove, and if you want you can take it off a little at a time.

The suggestion that you land without seeing the bottom of the wing is a good tip. Close to the ground if you can see the bottom of the wing you better be flaring, because the plane is going to be on the ground shortly.

Simple things to do to help prevent nasty tip stalls:

1. Radio setup: use independant servos for each aileron and adjust for much less down than up.
2. Seal the control surface gaps to improve effiency.
3. Keep air speed up and G's pulled low to prevent unintentional tip stalls.
4. During landings, use the rudder to point the aircraft, not the ailerons.

This is just a short primer.

Tip stalls are usefull in aerobatics. Learning what they are is only the first step in mastering an aircraft. The stalling characterists of the aircraft are used to supplement the simpler aerobatic routines of pilots. The stall maneuvers make routines awe inspiring. Flying close to the edge is fun, flying over the edge is exciting!

Bliksem

From the full-scale world..
A replica DH Comet tip-stalling just before touchdown at Fox Field... very narrow wing and aileron deflection at a high angle of attack will do this..
A push-pull Kadet tip-stalling and kept in it due to the aileron..

BVM used to make droops for their jets (symetrical wing)> if you can find a pair

Here's a good thread:

http://www.rcuniverse.com/forum/m_10037915/tm.htm

As already noted, to reduce stall/snap tendency:
1. Reduce weight.
2. Reduce elevator throw.
3. Move CG forward.
4. Limit aileron use on final.
5. Keep speed up on final.

The term 'tip stall' is a misnomer. What's usually experienced is a stall, followed by a roll due to (1) excessive aileron input for recovery, or (2) engine torque. Think about it - why would an aircraft designer make the tip stall first? Wouldn't you want the aileron working right to the last? Right! That's how aircraft are designed - straight wing, single taper, double taper, delta, etc., if properly designed, they are made so the tip (aileron) is working even when the majority of lift is gone. That's why most aircraft have 'washout', an easy way to make the tip keep flying when the rest of the wing is close to a stall.
Airspeed is your friend! Flying the approach with a 'known' throttle setting and keeping the pitch low will keep you out of trouble. Start the landing approach a little fast, and keep reducing power on subsequent landings. You'll start feeling the plane get sluggish, that's when you add a few clicks of power to stay out of trouble.
You shouldn't need to add devices to the wing, you're defeating the purpose. If the airplane's that touchy, you should try another.
The spanwise devices seen on full-scale (a type of vortex generator) aren't meant to 'trip' the airflow over the wing to 'make it stall', but are usually creating turbulence over the horizontal stab or elevator tip to give the pilot a warning 'burble' through the control yoke during slow flight, prior to a stall.

Ed

Speed is your friend.

For any straight flight in balance, the lift of the wing must equal the weight of the model.
In the same way, for any turning flight in balance, the lift of the wing must equal the virtual weight of the model (actual weight plus centrifugal force).
In other words, the wings of a model turning level while banking at 60 degrees must lift twice as much as they would lift when flying straight and level.

For either straight or turning flight in balance, when air speed decreases, the AOA must increase.
But the limit to this rule is the stall or critical AOA.
The only way to sustain flight just before reaching the AOA is by increasing the air speed.

For a light model, that necessary air speed is not much (remember how lift depends on AOA and square of air speed).
However, for a heavy model, that air speed needs to be high, or simply, the model will descend because the weight will be higher that the lift produced by that air speed.

Read more about stall prevention here:

http://www.rcuniverse.com/forum/m_89...tm.htm#8947745

The "tip stall" is not from engine torque. It is due to an uncoordinated stall. This means that when you reach the stall your slipping or skidding (depending on if you are in a turn or flying straight.) The tip stall can happen with any throttle setting, but most often happens in a high "G" turn or low speed high throttle setting. The stall in a turn snaps due to improper rudder control and is aggravated when opposite aileron is applied, this can be seen in the photo of the push pull Kadet. You will see the rudders are neutral and the aileron is down, increasing the AOA, and making it more stalled then the up side. The low speed stall with high power is due to the improper amount of rudder being applied to counter "P-Factor," or the left turning tendency of the prop at high AOA's. A "tip stall" is caused by stalling with one wing trailing slightly during the onset of the stall (in full scale this is why it is important to keep the ball centered.) The trailing wing has a slightly higher AOA causing it to stall more. The best recovery is to drop the nose to decrease the AOA, opposite rudder and throttle up to gain airspeed. Keep the ailerons neutral until flying speed is achieved, then roll level and pull out of the dive smoothly. The best way to avoid all of this is as others have stated, 1: keep your speed up. 2: keep just enough elevator to give a smooth full stall on landing. 3: use low rates if nessessary on the elevator when at high speeds. 4: Practice stalls and recovery, at altitude, as this will help you recognize the onset and train you to recover. 5: Above all learn to use the rudder properly.

Wow this is the replyI would have wrote,, what he said ^

no need to add ,, cheers Tim

repeat,, moving the CG forward will keep you from this. It will force you to keep the speed up,
Just have enough upness to flare on landing,, Cheers Tim

What he said...


the basic remedie to cure tip stall is to remember that with an aerobatic plane, speed is your friend; speed of reaction speed of the airframe, speed of the prop...

a more suitable aerobatic trainer will be a straight wing constant chord sport plane with an Assymetrical wing such a GPEscapade or Sig 4 Star or H-9 Pulse. Neutering anExtra with leading edge extensions is asking for trouble since you may actually increase the stall tendency and reduce the self recovery ability of the airfoil. Planes with leading edge extensions have an airfoil shape that is chosen to wok in conjunction with those extensions.
the best wya to keep the Extra managable is too ensure the CG is at least 1/3rd inch ahead of the recommended CG location. that will tame it somewhat.
also important is lateral balance to prevent a wing from dropping too much during low speed flight.
balance of these birds is highly important.

Well, On the basis that you want to continue with this plane, the advice to keep the CoG a bit forward, limit the throws or put exponential on, and keep the speed up until just above teh ground on landing are just about it. Playing with the wing shape could lead to all sorts of trouble.

Wings can tip stall even when in apparently balanced flight. Taper and/or reduction in aspect ratio towards the tip will cause the tip to stall before the centre of the wing as the angle of attack increases. Usually the tip of the wing next to the upgoing prop blade stalls first because there is a small bias in loading due to engine torque meaning that aileron is very slightly lower than the other. Other reasons for one wing stalling first are as stated above, unbalance flight, trailing wing in a turn etc, but may not be true tip stall.

Tip stall in tapered wings can be reduced/prevented by either a significant washout, significantly increasing the aspect ratio towards the tip, or leading edge slats/nosings. The only way you could do any of those easily would be to warp the ailerons so the tips are slightly higher than the centre. This would provide a crude washout, but it would need to be the same amount on both sides and frankly you're better just using the advice above and accepting the plane may not survive.

Noone had hit the nail on the head until Lplus's post. Washout is the key! If the wing does not have sufficient washout built into it, artificial washout can be induced with the ailerons.

While all of the responses have been helpful to prevent stalling (there are many types of stalls), the tipstall is related to the washout in the wing.

http://en.wikipedia.org/wiki/Washout_(aviation)