Flip Over...

[WishIWasAPunkRocker]

Not sure if this query belongs here, please feel free to move it to somewhere else if more appropriate.

I have recently purchased a Model Engines (at least that’s who markets them in Australia) ExtraFun 300 as a step up from my Hobby Zone Super Cub (with ailerons).

It is a terrific little flyer, not to fast (although its cruising speed is faster than the Super Cub ever managed at WOT!) and very direct control wise - with the throws turned down (as I presently have it set up) its a very manageable aircraft that has enough power to pull it's self out of trouble without disappearing off into the sunset or having to compensate for massive amounts of torque.

One problem I am experiencing however is that it has a tendency to flip over if full up elevator is applied. If you attempt to put it into a sharp climb - even at full speed or from a dive - it will flip upside down and (very rapidly) start heading for the ground. As I mentioned above, it is very direct and if you let go of the elevator, apply full aileron in either direction (until it's the right way up again) then feed in a slight amount of up elevator it will correct and level out in a split second, however it is very nerve racking.

It doesn’t appear to matter which orientation the plane is in either - i.e: if it is in a sharp turn, with the wings vertical (or near enough) to the ground and too much elevator is fed in an attempt to snap it around, it will again 'flip over' and start turning the other way.

When I first purchased this model, I knew there would be certain differences from my Super Cub: have to keep the speed up, land under power, no tendency to self correct at all and that it would be a lot less forgiving (stalls for instance are a lot more vicious), but I did not expect this. The SC would simply loop if you pulled the elevator up (provided you had enough speed up).

One thing - I have the COG set a little forward of the generally accepted position (no mention of where it's supposed to be in the manual) From reading around it appears most people have had the best success with the COG directly above the thickest part of the wing. I have it set about half way between there and the leading edge and am gradually moving it back.

Not sure if this is a problem I'm experiencing due to the set up, or is a well known characteristic of these type of planes that I will simply have to compensate for. Any comments would be greatly appreciated...

[Biplane Murphy]

Sounds like an elevator induced snap..... try using less elevator at high speed.... or more elevator only at lower speeds....

This is a fairly common occurence with 3D and aerobatic planes.....

I have a couple planes that do this every single time....one elevator snaps so predictably that I can use it to aggressively change directions degrees in a split second on command..... Kind of a crazy looking split "s" thing happens everytime.

pretty fun if you are expecting it..... Not fun at all if it is a "surprise".

[WishIWasAPunkRocker]

Thanks Biplane - what your describing sounds exactly like what I'm experiencing.

I was experimenting with it this afternoon at my local park and it is very predictable - I can even use it (elevator snap) to get it to quickly flick to inverted flight - not game enough to use it to flick back yet though! Also, as you stated, bleed off some speed before applying up elevator (and feed in some throttle as it climbs) and it loops beautifully.

Its a bit of an odd thing to try and work out from the ground - full up elevator is applied, the plane nose begins to lift, then all of a sudden it sort of collapses onto it's side and continues over until it's upside down. At this point the nose is still actually pointing towards the sky, however with full up elevator applied and the plane now inverted it quickly heads towards the ground.

Any idea as to what causes it? As I mentioned earlier, my SC showed no tendency to do this and as such it came as a complete surprise with the Extra.

[Biplane Murphy]

I don't really undertand why it happens......only that too much elevator can cause this to happen.

Perhaps because the midwing and low wing designs are not as stable as a high wing plane...... this has occurred in my planes that were low and midwing....(I have seen it in bipes as well)

I suspect it has something to do with a combination of airspeed, control throw, angle of attack and a stall condition....all happening at a high speed....which when combined forces the plane into another angle of attack very quickly.
But this is only a guess!!!!

[oimmuk]

Is it as quick of controll manuvers as this plane???http://youtube.com/watch?v=Gulv_bvZS94

[jasmine2501]

What you describe is a classic tip stall. It is a characteristic of your plane, and you can't do much about it, but there's some things you can do to prevent it. The main thing you need to do is fly faster and use less elevator. What happens to you is that the outside tip of the wing stalls first, before the inside, causing a sudden violent roll. Usually it happens on one side a split second before the other, and it's enough of a difference to cause one wing to drop.

However, if it's happening in the knife-edge, you've probably got something else going on, like the elevator is warping or something.

[Charley]

Jasmine is dead right. To expand on it a bit, if you apply enough elevator to at too low a speed, you will stall the wing. In your case the tips stall first. What you have is a 1/2 snap roll without the rudder input. It stops inverted because most of the weight is then below the wing.

CR

P.S. Have you checked the lateral balance?