I got out my T-28 Trojan for the first time in months yesterday. I went to do a loop. After the plane went over the top it did some weird turn I wasn't expecting. What was that? so I flew some more and everytime I did a maneuver with any kind of loop it kind of went out of control.

I looked over the plane and found one of the aileron servos and the rudder servo were a little loose. I pulled them out and put new double sided tape on. I put her back up thinking that was the problem. I trimmed it out real smooth because there was no wind.

Still doing it. I kept doing straight loops trying to see what was going on. It happens so fast you have to react so it took me a few to figure it out.

It seems to bank right, hard. I don't see anything else loose. Any ideas? Is there something out of wack that could cause this?

My guess is you are running out of airspeed and stalling resulting in a snap roll.

I have been flying for years and never had this happen. I've had this plane since they came out and never had a problem till now. I think something is out of line or out of balance.

It may be that your elevator halves are not traveling the same distance ....when you go into the loop and over the top one side may be deflecting more then the other giving you a weird turn/loop. IMO

If you dive down to pick up more speed and then do the loop, do you still have the same problem?

Bad servo connection to the RX, damage to RX or airframe that only shows up inverted although I would suspect vibration would also be an issue. Also check for structural damage or a mounting that shifts when you are inverted altough you did say you checked out the servos. Sounds like something strange I'll give you that...

Are you using a different Battery or battery location/mounting???
Is the battery shifting on you??

It could be blowback. On the ground, give up elevator and push on the control surface. Does the elevator collapse back down despite the servo trying to hold it? Try this with your surfaces.

What about too much elevator movement? Have you changed the travel of the elevator? I once lost a GP Venus due to this snap roll. I learned that my elevator was moving too far. Something about the wing losing lift or something like that.

Maybe reduce the end point on the elevator channel.

Maybe not.......just one other thing to rule out.

Pretty much. Too much travel will snap a model out of loop every time.

Please take video of this when you try.

I go with the too much elevator travel. Has happened to me before . MAX H.

Bottom line is: A lot of things can cause this, and it will be interesting to sort it out.

Yeah, if we could be there to see it we'd have the solution in a minute. Why not ask a respected member in your club to watch it and comment on a likely cause?

One other thing I just thought of is the joiner for the elevator half may be loose, but that probably would cause a problem during any flight mode.


Questions:

Other than what sounds like a snap out of the top of the loop, have you had any other weird things happen?

Have you tried any rolls or inverted flight that has been a problem, even minor?

Where you have had time on the plane is there anything that you have changed prior to now?

Nathan is right, sometimes just being able to see it makes a big difference...

That was it!

I put the duel rate on low and ran through a whole battery doing loops. Not one problem. Then I put it back on high and did some loops trying not to pull all the way back. Worked fine untill I pulled all the way back then at the top of the loop it would turn off 90 degrees.

I'll have to adjust the throws tomorrow. Thanks!

Glad you found the cause and are able to fix it.

I thought that was probably the cause, but didn't harp on it since it was already suggested and you were very familiar with that model. Glad you figured it out.

Glad to hear that's all it was. I have always been curious WHY this happens since I noticed it, and lost my venus because of it.......

Can anyone explain why too much elevator causes a snap?

A rapid elevator input can stall the plane and thats why it enters into a snap.

I had a Vector Flight extra that flew great but with just a touch too much elevator it would snap in a heartbeat.

I'll tell you it scared the crap out of me when I was close to the ground going to do an Immelmann.

I flew all day yesterday. No go today, rain.

Elevator drives the wing's angle of attack. A snap is the result of the wing stalling. A stall happens when the wing's AOA is too great.

Move the elevator far enough that it moves the wing beyond it's safe max AOA and the wing stalls, and the plane snaps.

I'd say one or two things too much travel on the high rates / or the elvs are not throwing the same! just speaking from experiance