High Speed Stall

Suddenly ramming in a bunch of elevator will stall one or both wings, depending on the airplane's coordination of flight and any misalignment between the wings. The dropping wing may have a bit more incidence in it, or the leading edge might be a bit sharper, or the top surface may have some roughness. It might also be twisting under load and increasing its angle of attack, stalling it first.

Dan

I have to Extra300 and one is snapping when I use to much elevator. What can be the problem? Is not that Elevator is missaligned, this I check alredy.

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Thank you wery much..

Is this happening when you are doing a loop? Gord Schindler MAAC6694

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Ja vid ca 30-40% elevator eller smalare diameter på lopen.

I gather that is a "Yes". It sounds as though you are trying to force the plane through the loop, rather than flying it through. A loop is a nice round circle with full power and just enough elevator to carry you up over the top. Cut the throttle at the top and control the down side with just enough elevator to keep the speed constant. The speed should be constant all the way through the circle. Applying too much elevator on the up side can stall the wing and it will fall out of the loop at the top. Gord Schindler MAAC6694

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Yes I now every aircraft have a limit with high speed stall, but my first Extra300 dont have this problem before 90% of up elevator, this have problem already with 30%. But I have a indicent meter and going to look tomorrow if the wing is good or not..

Reduce elevator throw.

How do I do that? Do you mean dont pull upp to much? Or use dual rate and 30%?

Most decently set up aerobatic planes will have a snap-attack if you're too quick on the elevator, that's part of the skill of flying the suckers - you only pull back hard when you *want* to snap. Any other time, you've made a mistake.

Brad wrote:

Ain't that kind of flying exciting? I mean, like WOW!

Yes i start to understand, I have a AT6 to and this have same problem. My first trainer was high wing but newer have problem when doing smal loops. Is that becuase it is a high wing?

Best regards Peter

Peter, It is obvious that you need some general guidance of how to set a plane up, so I will give you the guidelines I start with. Some aircraft require different final setups, but in general this works.

First flight is strictly a trim and test flight. Before first flight, make sure your engine will idle for 5 minutes and not fail when the throttle is hammered to full suddenly. That must be fixed before you try some of these tests as it is critical that you have power available when needed. You also need to make sure the plane is correctly balanced with the fuel tank empty. I suggest very slightly nose down for trainers because beginners need stable airframes and level (while upside down) for most low wing birds. Do not first fly a plane that is tail heavy as you may not fly it twice.

The first thing to be done in the first flight is to get the plane trimmed out hands free. The second thing to do is to get 3 mistakes height at full throttle and hammer the elevator. If the plane will not do a smooth loop with no 'stepping' or snapping out of the loop, you have too much elevator throw and need to land at higher speeds than you are used to. Do so immediately and reduce the throw and then repeat the fist flight.

If the loop is smooth the next step is to test the wing and stall recovery so you know what it looks like and how the airframe responds. Get three mistakes high and begin reducing the throttle. For newer pilots the goal is to get the elevator stick hard on the bottom of the quadrant and the airplane stepping through stall. The thing you need to watch for is the reputed 'tip stall' which occurs when the root stalls after the tip of the wing. This is common with heavy wing loaded birds and those with sharp leading edges. There are some substeps here for specialty aircraft and I will mention them at the end of this.

The next step is to try some turns at that low speed while still three mistakes high. What you are looking for is how gentle you have to turn to keep the plane from snapping out on you. Some are incapable of any turn at full elevator and others will allow significant banks. The first turns (left and right) will be done with aileron only in both directions. Once you have completed these first turns, climb back to the initial altitude and continue with the test. The second turns will be done with rudder only, again in both directions. What you will probably find that many low winged birds will gently turn on rudder only when at slow speed. That is an important piece of information you need to have in the event of a servo problem (BTDT!). The last set of turns while at altitude is to restore your confidence in the rules of aerodynamics. Get slow again, and do coordinated (aileron AND rudder) turns in both directions.

Now you know what the plane is capable of and what it looks like when it is executing what you want it to do. Changing it to be more reactive for aerobatics is easy when you have a known start point. Once the elevator is set for a new pilot and you are comfortable with the airframe at lower speed, you can increase the throw and add exponential. This gives you the wild throws many 3D folks want, but leave the center of the control stick movement what many use to make landing approaches. All you have to do is to remember (learn?) not to hammer the elevator.

Good luck,

Jim Branaum

Isn't it obvious from what you've just said?

Answer: Too much elevator deflection.

Contrary to belief of the self-informed, *excessive* deflection (throw) isn't the aerodynamically correct answer to either reducing radius or increasing rate.

Ersatz solution: Reduce your elevator throw to 25 degrees deflection

*maximum*, and ensure your C of G is inside either the manufacturer recommended limits ("C of G for Dummies") or mathematically derived forward and aft limits for the airframe.

If your Extra has a predisposition to dynamically stall and snap with inadvertent ham-fisted application of elevator, a C of G forward of datum mid-point in conjunction with conservative throw and smoother application of elevator (use lots of expo if you can't fly apply control input smoothly) will minimise that characteristic.

However, if the double taper wing has either zero wash-out or even wash-in, there's not a lot you can do to alter the inherent dynamic stall characteristics of the design itself except fly it smoothly with aerodynamically appropriate throws - or buy another model more appropriate to your ability and preferred performance requirements.

Firstly, you need to buy with an eye to function rather than form.

The image you wish to project doesn't appear to coincide with the manoeuvre envelopes you wish to fly or apparent proficiency level.

Then you want a 3D orientated model, for small radius manoeuvres prefer a light wing loading, large control surfaces and slower speed flight. Decreasing speed is the easiest way to reduce the radius or diameter of a manoeuvre without increasing AoB or 'g', both of which are critical in a double tapered wing planform, and especially if the model is over-engined and overweight (high base wing loading) and deadly in conjunction with zero wash-out and too much elevator throw exercised by a 'ham-fisted Harry'.

Something like either a Kyosho Flip 3D design, which is good quality, or a ESM Freestyle Rush (design compromise) will possibly do what you want, even if they don't appeal to you aesthetically as the semi-scale Edges etc do. The Flip 3D isn't a high speed flyer. The Rush is capable of faster flight, but is essentially still a 3D model just capable of a wider compromise envelope. Both will serve you better in close proximity of the great granite 'cloud'.

If you don't want snappy, stop thinking Extra, Edge, Katana, Yak, Giles, CAP or Sukhoi no matter how much you like the way they look. Those designs are intentionally stability neutral to slightly negative orientated for aerobatics, of too high a wing loading and particularly prone to poor inherent model design, errant construction or end user assembly, all of which are severely exacerbated by relevant size due to Reynolds number effect. ¼ scale and larger replicas (IMAC) of Extras etc fly much better than their .40cu² through .60cu² counterparts.