talon58

My Feedback: (125)

Been flying my Katana for a while now. Made a few minor changes to the elevator. Only have about 10 degrees of up and down elevator. If I'm at almost any throttle setting, and speed and give any where near full up elevator the plane will snap to the right. Never did this before. I checed both elevator halves, the both have the same amount of travel.

I checked to see if the elevator and wings were aligned, and noticed that the right side of the elevator was just a little higher then the left side. This was viewed looking from the front of the wings back (using the wings as reference).

Anybody got any ideas?

Thanks!

Tired Old Man

My Feedback: (1)

Is it possible that if you are using two elevator servos one of them is getting slower or weaker? Or, could your linkage be bending under loads?

Not knowing what you are using for servo arms and linkage leaves the question of a plastic or nylon servo arm twisting also.

There are other possibilties, but that's a couple to consider.

talon58

My Feedback: (125)

Using Hitech 5645's. Rocket City horns, Hangar 9 prolinks to connect the two. Plane flys great, except when I give moderate up elevator, always wants to snap to the right.

mglavin

My Feedback: (31)

What change were made to the elevators? Sounds like we can rule out mismatched surface travel and or end-points? Are the surfaces level at neutral? What are you using to verify equal throw?

Have you checked lateral balance?

Tired Old Man

My Feedback: (1)

Talon,

All else being correct and equal, this has been seen before. The owner of the problem went to great lengths to blame the aircraft for having a poor design and to have been defective. Later it proved to be the servo. That's why I brought up the subject of a weak servo. Is it possible for you to perform an electrical current check on the servos when they are warm? This could reveal some surprising differences, especially under a load.

Lateral balance, as Michael noted, is another possibility, but unless the imbalance is pretty large, is not too likely. Also, being out of alignment as you stated in the first post will cause this problem, but if it wasn't happening before, or was it, why suddenly now?

Geistware

My Feedback: (16)

What deflection did you have before and what do you have now?
If you put it back to where you had it before, does it not snap?
Does it snap inverted?

RonHill

My Feedback: (1)

Try this....Put a prop with less pitch on and see what happens. Many times a high pitch prop will torque a plane when it has massive elevator input.

It gets worse with rear CG.

I had an Extra that snapped like hell, and Caps are famous for it. A lower pitch prop reduced it for me.

Wings-RCU

My Feedback: (2)

Torque, P factor, Slipstream & Gyroscopic Precession will all cause a LEFT yaw or snap with excessive elevator. 10 degrees is not excessive!
If your elevators are equal & servos OK & wing incidence equal left to right, root to tip, it’s too much right engine thrust or you have right rudder trim. I'll bet it will completely go away by getting rid of most of your right engine thrust! Changing props can slightly alter the slipstream & P factor but probably not enough to stop a plane that is snapping right with 10 degrees of elevator.

CDignition

My Feedback: (9)

Just for chuckles, check lateral balance

Ryans Rebel

My Feedback: (12)

I know you said Katana and not a Funtana but the H9 Funtana I had was famous for the tip stall with only elevator input. Crashed it before I cured it! And I had it for a while.

Ryan

JB Rekit

My Feedback: (3)

sounds pretty tail heavy

also, what size plane is this b.c I fly 3D and pattern and had a servo arm come off elevator on my 33% edge twice last year and even with just one elevator, it wouldn't snap without rudder and ail. input. I flew the whole pattern and some 3D before noticing it dangling there.

I am pretty sure it is a balancing issue. If not tail heavy, it would have to be WAY off on its lateral balance

JB Rekit

My Feedback: (3)

If it is a .40 - .90 sized plane, what I just said may not pertain b.c I remember my .60 Extra was very squirrly and it was more of a weight issue, so if it is a smaller plane, you may want to check the wing loading if it balances properly and see if it can be put on a diet.

3DFanatic

My Feedback: (5)

Sounds UBER tailheavy...

Wings-RCU

My Feedback: (2)

Ahh... Tail heavy is GOOD if you want to get rid of high-speed stall tendencies. It helps to unload the wings with elevator control and will require less elevator input to get the same elevator response. Lateral balance makes only a slight difference in a "Power Off" stall. We fly full scale planes with tanks in the wings where one wing will get significantly heaver then the other and the planes will still stall left due to the 4 factors mentioned earlier. I'm still betting on too much right engine thrust.

talon58

My Feedback: (125)

Ok, here is what I found. As mentioned earlier, the only things that had changed were a fine adjustment on the elevator, and the cg was moved back just a hair. The plane had flown a day or so before, with no problems. Then on the last flight, any time I would pull up elevator, it would snap to the right.

Are you guys ready for this................................

The ultracote (or what ever the covering is) has a seam that is just below the center of the leading edge, running the full length of the leading edge. I was runing my hands over the right wing seam and notced that i could lift the top seam up, about 1/8 to 1/4 of an inch. Ahhhh, this would account for the snap to the right, as the AOA would increase, wind would get under the seam and lift it up. I'm sure it created a lot of drag on that right wing. In any case the coveing has been ironed down, and we should get to test the "fix" tomorrow.