Confused by flying problem - can you help?

[alibopo]

Hi folks, I've been working on a little high-wing foam board plane using the remains of my Pilatus Porter - roughly 800mm wingspan. I've a flight problem that has me baffled. The plane is reasonably stable with either rudder turns or banked turns, but as soon as I apply more than a little up elevator (think bank and yank) the plane immediately and aggressively self-rights. At first I didn't understand it was caused by the elevator, but I can replicate the problem at will now. All I can manage is slow turns, anything more aggressive, and the plane levels and straightens up. Any clues? Thanks.

 

[jayz 84]

Thats a new one to me the only thing i can think of is sence you do have a high wing aircraft which a good for calm flying. It sounds like you dont have enough power to pull off a high rate of climb. Not having enough power can cause the wing to stall in a high rate of climb or in a roll. Cause the wing then acts like a brake. And inturn the noise want to drop or stall completely into a noise dive. Plus you have to check your cg are you to on the noise heavy side

 

[IFlyRCstuff]

That wouldn't be adverse yaw would it?? Maybe I am misunderstanding. If you motor up, does it "skyrocket"??

 

[earthsciteach]

Just for clarification...

You are in a turn, banking to one side. If you apply too much elevator, instead of turning in a tighter radius, the wings level?

 

[Techno]

This may take some tinkering... My first guess is try weighting the wings, this will let the wingtips tip more easily and could counteract the effect. Also, are you using a computer radio? you may have a mix dialed in incorrectly. In addition, what attitude is the plane at when it self-rights? climbing, level or descending?

 

[alibopo]

Just for clarification...

You are in a turn, banking to one side. If you apply too much elevator, instead of turning in a tighter radius, the wings level?

Yep, that's exactly what happens! Has me completely baffled.

 

[alibopo]

This may take some tinkering... My first guess is try weighting the wings, this will let the wingtips tip more easily and could counteract the effect. Also, are you using a computer radio? you may have a mix dialed in incorrectly. In addition, what attitude is the plane at when it self-rights? climbing, level or descending?

Weighting the wings? I've never heard of that, though I'm a relative newbie. Time for some research I'll also have a look at the radio - DX6i - I'll run through all the settings again. Good idea, I might have got some switch allocations mixed up creating duplication.
This behaviour happens when the plane is flying level. I did have some quite long control rods on the elevator and rudder, so I wondered if they were flexing under load - I've shortened them off and stuck the servos at the back. Haven't had a chance to try it in the air since that change. Also it is a quite fast spinning motor (for me) 1700KV on a 3S Lipo - would that require more motor (right/down) angulation to counteract thrust-line effects?

 

[alibopo]

Thats a new one to me the only thing i can think of is sence you do have a high wing aircraft which a good for calm flying. It sounds like you dont have enough power to pull off a high rate of climb. Not having enough power can cause the wing to stall in a high rate of climb or in a roll. Cause the wing then acts like a brake. And inturn the noise want to drop or stall completely into a noise dive. Plus you have to check your cg are you to on the noise heavy side

Hi, in theory my CG is OK. I'm moving towards the 30% point and the plane's still stable (straight and level). I did plug the basic numbers/stats for the plane into an online 'CG finder' and it came up with a surprising 35% of chord, which I was a little sceptical about. If that is the correct CG then yes, I'm flying nose heavy. I was reluctant to shift the CG back too much until I got the plane a bit more controllable. It gets pretty scary when it flips itself out of the turn and decides to head off across the field. I've never really experienced such a badly behaved plane, maybe I've just been lucky before?

 

[ViperTech]

It looks like you have flaps on it? and in the picture they appear to be down some what and the elevator is huge I wonder if the diehedrial combined with some down flap combined with a large elevator movement pitches the nose up and it goes into a "air brake" mode and slows down fast enough to self right, by pulling the air away from the ailerons?

 

[BigGary]

I had the same issue with my plane. I have the new DX6 radio with AR636 receiver. I made adjustments with the radio and I think that is what was causing my problems. This receiver has AS3X and needs all adjustments made to the receiver instead of the radio.

 

[alibopo]

It looks like you have flaps on it? and in the picture they appear to be down some what and the elevator is huge I wonder if the diehedrial combined with some down flap combined with a large elevator movement pitches the nose up and it goes into a "air brake" mode and slows down fast enough to self right, by pulling the air away from the ailerons?

Hi, thanks for the input. I did go 'around the houses' on the flaps/ailerons combinations; flat wing, under-camber wing, washout with the ailerons... without any progress, but very importantly what I did get from the replies was that (as I suspected) this was quite an unusual problem.

One of the responses on transmitter mixes (which I checked, and they were all fine) got me thinking about the receiver and servos. A quick visit to YouTube threw up a pile of videos where either a dodgy or even 'different' servo caused motion and fluttering in other servos. I may be wrong (I haven't had a chance to test fly it yet) but it could be a dodgy servo firing back interference to the other servos, or, I strongly suspect, the receiver is faulty - cross/firing input from one servo to other servos under certain load conditions. So as not to waste time, and risk 'unnecessary' crashing ,I've replaced both the receiver and the servo.

Fingers crossed, and I'll post my results.

 

[alibopo]

I had the same issue with my plane. I have the new DX6 radio with AR636 receiver. I made adjustments with the radio and I think that is what was causing my problems. This receiver has AS3X and needs all adjustments made to the receiver instead of the radio.

Thanks for the input. I think I just came to the same conclusion - I'm using orange DSM2 receivers, and I suspect it is faulty. It could also be a defective servo, so I've replaced both. I'll let everyone know how it goes. Cheers, Alibopo.

 

[quorneng]

alibopo
What you are describing sounds to me like the effects of adverse aileron yaw on what is basically a very stable plane.
I have a home built light weight 40" (1016mm) Super Cub that was almost impossible to turn as a 'bank and yank'. As it has proportionally bigger ailerons it did not self level as such but just continued to fly straight on even though it was banked, particularly when trying to bank against the motor torque.
I suspect in your case the adverse yaw is creating a self righting force sufficient to overcome the ailerons. This effect will be more noticeable as the plane gets closer to its stall speed.
The simplest solution is to coordinate both rudder and aileron to turn.

 

[alibopo]

alibopo
What you are describing sounds to me like the effects of adverse aileron yaw on what is basically a very stable plane.
I have a home built light weight 40" (1016mm) Super Cub that was almost impossible to turn as a 'bank and yank'. As it has proportionally bigger ailerons it did not self level as such but just continued to fly straight on even though it was banked, particularly when trying to bank against the motor torque.
I suspect in your case the adverse yaw is creating a self righting force sufficient to overcome the ailerons. This effect will be more noticeable as the plane gets closer to its stall speed.
The simplest solution is to coordinate both rudder and aileron to turn.

Hi, thanks for the careful description. I've another plane, which I now fly as my "Morphocoupe", that behaves exactly as you describe in terms of adverse yaw. I've been flying co-ordinated turns with that for some time, so much so that I now find that when I go back to 3 channel planes (bank-and-yank - rudder servo connected to the ailerons), I unconsciously 'work' the rudder control as I'm turning even though it's not connected to anything. I'm now pretty 'tuned' to flying coordinated turns.
The plane has had several 'evolutions' and most recently I added more dihedral. The plane will fly bank-and-yank on ailerons and 'very gentle elevator' or rudder and 'gentle elevator' only. On gentle manoeuvres requiring very light elevator (I tuned the throws down to a low range of movement) I can keep the plane in the air and fly around my field. It will climb happily in a straight line with stronger elevator input - but it all goes wrong during a banked turn requiring continuous up elevator input to maintain altitude.
I'm moving towards the faulty servo/faulty receiver thinking, and have swapped out both on the plane. The next flight will tell me whether that was the cause.
Again, thanks for taking the time to input on this, it all helps.

 

[alibopo]

Hi folks, thanks for the help advice and discussion on this problem. The plane is now flying - video in the 'Pilatus Hi top' article in the articles section. I didn't solve the problem, but overcame it by limiting the elevator throws to stay within the 'safe' predictable flying envelope. Now it's just like any other plane; with its limitations, quirks and individual flying style. I might not manage super-tight turns, but not all aircraft do. Cheers.

 

[ClearSkiesCalmWinds]

Love your designs. Have you considered sharing the plans to your planes. they are interesting.