I have a CA Models Extra 330L kit that I built that has some strange flight characteristics. The kit was a builders kit that I purchased from Aeroworks when they used to sell this brand. It is 50cc size with a 82 1/2 inch wing span, total flying weight being 17 lbs. All servos are Hitec digital with the elevator halves and rudder being 7955 hi torque servos. The airplane flys well except when it comes to looping. When I do a medium size loop at medium speed, it tracks well all through the loop except just before it comes out of the loop at the bottom, it will veer off to the right (almost 30 degrees clockwise) and goes up slightly. It does this both with inside loops and outside loops. It even does this when I pull a hard split S. I fully realize that with this type of airplane, if you pull too hard in a slow tight loop they will snap out but usually this is at the top of the loop. All the other airplanes at my field of this size and type can track all the way threw a loop way better than mine. I checked all the wing and tail insidences and everything is almost perfect. One wing has a slight twist starting from zero degrees at the root to 3/4 of a degree at the wing tip. I have checked both elevator halves many many times and they track perfectly and at the same speed. I have even changed the elevator servos thinking that maybe I had one that wasn't holding properly. The elevators are large and sensitive and for the type of IMAC flying that I do I have they set up with only and inch or so up and down movement on medium rates. Another club member has this same airplane and he has similiar problem. His airplane will even jump out of the loop on the way up. One club member said he had read on one of the forums that other people had problems with this airplane and found that the tail was twisting. The back fusealage sides are light ply with large lightening hole cutouts. There are no cross bracing in the fuse. I had someone hold on to the landing gear whilst I attempted to twist the stab and didn't seem to have any twisting. I am stumped as to what is causing this. The airplane itself is very conventual design, nothing out of the ordinary. It fly well but I sure would like to get this problem resolved. Any ideas ?????????

All Extras have a highly tapered wing. On models this can lead to tip stalling in high G turns. And at 17lbs for an 82 inch span it seems like your Extra may be on the high side of acceptable for wing loading of a model of this sort of size. If that is the case it sure isn't helping the issue any.

Pull up a Search for "turbulator tip stall" within this Aerodynamic forum. Threads about Extras with your same sort of trouble and options for trying out outer panel turbulators to try to fix this issue are common and pleantyful.

Thanks for your reply. I will check out some of the other threads on this subject. I wouldn't think it would be a tip stalling issue since I can land it slowly and it doesn't drop a wing.
Would like to hear from others who have this CA Models Extra to see what they think.

Having built a LOT of EXTRAS in this as well as other sizes - The problem you describe is almost always the fact that you can easily stall the wing at ANY speed
NOTE: at slow speeds the wing becomes more docile

The structural capabilities must be addressed too- a crooked setup -or one with gap-osos and offset hinge lines will always cause problems
Typical problem: the model stalls and changes heading as if by magic.
The problem is that the applied elevator force is actually shifting the model sideways
The changing of throws/hingline errors etc., can cause this
This causes a momentary DIFFERENCE in forward speed of EACH wing panel as the model yawas -even so slightly that you don't notice it
The result is the model veers to the side which has the trailing panel
This is the begining of a snap/spin/turn - call it what you may
The lower the wing loading or speed envelope - the less this sensitivity will manifest it's self
So It ain't the wing design which is at fault - it is simply that you are exceeding the symmetrical lift necessary to continue along a straight line .
The fix is to get everything as straight - even and equal as possible -and throw out all un needed weight
There is no such thing as adding weight to a aerobatic powered model -to improve performance
Liighter is always better.

A highly tapered wing CAN be touchy if it is flying at close to it's intended max angle of attack
Actually - I like em-
It makes for a very maneuverable aerobat which is what the EXTRA was intended to be .

OK, you've gotten two opinions from two very experienced modelers. Want a 3rd opinion?

They're right. What you're experiencing with your Extra is classic. The solutions are just what've been suggested.

The only thing worth adding is from what I just experienced an hour or so ago. Flying my Extra300, I noticed a difference in the way it flew. It ran the 45* up line with a half roll halfway up without having to push a bit of elevator after the roll to inverted. It went over the top of loops and didn't need WOT to do it. And it didn't even give a wiggle at all the places where an Extra might highspeed stall a wing and turn out of the path you're trying to fly.

What was the difference? I swapped out the tired old engine for a brand new one and the slight difference in horsepower pulled the wing along a couple mph faster. Over the years I've seen a couple of Extras/Edges/Yaks/Sukhois/CAPs/etc that flew with less tendency to high speed stall with a change of engine to get more power. Often all you need do is test a few props and find a better one.

What was the difference? Slightly higher airspeed. But in this case it came from slightly higher horsepower. It's not usually listed as a cure to what you're seeing.

Dick, could you explain a little more about how "the applied elevator force is actually shifting the model sideways." Also, what happens in a high speed stall?
thanks

1) Is it a pure yaw or some roll is noticed? Do you keep the same radius during the loop?

2) Control-wise, what changes at the bottom of the loop? Where and how much power do you input to finish the loop? Have you tried with no power addition at the bottom?

3) What wing shows the warp of 3/4 degrees and in what direction?

The right wing will drop then it will just yawl. I try to keep the loop round but it is a little short in the last 90 degrees. When I do the loop I'm holding a small amount of up elevator then relaxing it slightly as the plane is about to be horizontal again. The power level is about half power threw out the loop reducing slightly on the way down. I can't remember which way the wing twist was, positive or negative, but it is a very small amount. One person suggested that I try to install some electric tape turbulators and I think I might try this since it is a simple thing to do. The weather is getting in Indiana so I'll have to wait for a nicer day.

Is it possible that the vertical stab is losing some grip on the down line as the engine is braking? At the moment of adding power at the bottom, the lower grip yields to an engine yaw force or some other yaw force before prop wash reinforces yaw stability.

It would be easy to test. Get high... very high and do the loop and at the bottom just before you normally see the yaw issue... add rudder either way to see how much rudder grip exist, or keep a bit more power on in the down line.

One of the pattern fliers at our field has a large Yak, which axial rolls wonderfully except in the down line when the engine is braking hard, and then the roll resembles a barrel roll. When asking him about it, he offered that what I see is probably cross mix of some elevator stick with aileron and that he was probably a little careless. I see it so often on his down lines however that I don't think that is the case... I think it is reduced yaw stability when down line braking. He runs a three bladed prop and gets a lot of braking action.

Thanks!

This is a very interesting case; we would like to learn the results of your test with the tape turbulators.
If the problem continues during the next flights, pay attention to the following:

Does it ever happens at the beginning of the inside loop, where the centrifugal force adds to the weight and the elevator is up?

Is there a big difference in speed entering and leaving the loop?

I assume that it happens at the bottom of the outside loops, while the plane is inverted. Is that correct? Does the yaw happen in the same direction then?

Are the tail and aileron hinges taped?

I have asked all these questions because it seems to me that the tip stall should not ocurr when the elevator is being released while ending the loop (AOA decreases).

May be someting else is inducing the right roll-right yaw-pitch up just before the plane comes out of the loop at the bottom (speed, tail, propeller, wing warp).

May it be a bad coupling associated to down pitch? [sm=confused.gif] Does it also happen leaving a 45 down line?

Best luck!

I did try something a month ago. I thought that maybe the fin/rudder was "in the shadow" of the fuse at the bottom of the loop and was not getting in the airstream enough to hold the course. I made a 2 1/2 inch high temporary extension that I attached to the top of the fin. Didn't make any difference. I'll try a few of your suggestions the next time I can get out. Thanks for your interest.

just guessing but is it possible the wing is flexing? can the problem be consistently attributed to one panel flexing up or down depending on if it's upright or inverted? if the wingtip flexes up that will increase lift on that side and cause the nose to pitch up a little when the roll starts.
just a thought
bc

The wing on this airplane is balsa sheeted foam and is very ridged. The stab, elevator, fin and rudder are also sheeted foam.

is it a two piece wing? when you push back on the wing tips do the leading edges at the root pull away from the fuselage? the wings may be rigid but if the fuselage isn't there will still be flexing. i'm having this problem right now with an old lanier extra 300. you could also try sticking the wing tube into the wing socket and see if the socket has any play in it inside the wing.
if the plane weighs 17 pounds, pulling 4 or 5 g's at the bottom of a loop will put 85 pounds or more across the wing. if you're looking for the problem and you're not applying that kind of force you may not see where it's coming from. it's entirely possible it's some aerodynamic anomaly but it doesn't hurt to consider other possibilities.
just be careful you don't break anything!!! []
good luck,
bart

Elevator forces are very often, NOT even and can vary a lot from side to side.
These uneven forces simply shift the tail to one side and presto the wingtips are travelling at different positions RELATIVE to direction of actual flight
This is the prime reason that a rotation or "drop" occurs on a wing panel.
Restated: If the wing panels see exactly same airflow, they will stall at the same time
If ANY variance occurs, the relative lift changes
No magic, just a difference in airflow causes the difference in lift
If you remember nothing else about airydynamics , remember this:
Air wants to remain/return to equalized pressure .
period


If we increase pressure at one point - the pressure is reduced at some opposing point
Sothe portion of the aircraft where the difference is occuring, will try to move in whichever direction will allow equal pressure .
tail- wing -fuselage - prop - ANY point.
Lift is simply pressure difference at work
ditto for a prop.
ditto for cooling in the cowling
etc., etc..
The "high speed stall" is a catch all term
..
A stall occurs anytime the angle of attack of a lifting or control surface reaches a point which causes airflow to to loose the pressure equalibrium which causes lift.
So- the "high speed stall" can be at the wing or the movable /stationary horizontal control planes . (wherever they may be located)
If either looses the equalibrium necessary to provide pressure differential needed, the craft will become uncontrollable .
Controlled flight is simply controlled pressure differences.
Someone will likely prefer textbook terms for the explanations but I prefer this approach.