Myself and another beginner at the club both kit built the Great Planes PT40. While the other guy was building it, he brought the wing into a club meeting and the more experienced flyers thought the wing had way too much dihedral so they convinced him to take a bandsaw to it and flatten it out. I insisted on keeping mine per print and giving it a shot.

He put his plane up first. I haven't seen it fly but they say it is barely contollable and he hasn't yet been able to solo as a result (this is with less dihedral mind you). My instructor put mine up today and had a hard time with it at first. It would fly straight but the aileron had little effect and he had to fly with rudder all the way around. He had a hard time landing it (whew!) and we changed the servo arm on the aileron to give it more throw. We also realized that it was a bit breezy and he was really struggling with it downwind. One of the other pilots thought he needed a little more power/velocity to keep the control surfaces more lively.

So he put the plane back up again and found the aileron performance to be significantly better and did find that flying downwind was probably part of the problem and knew what to expect the time. THe plane landed like a cream puff. It got dark and I didn't get a chance to buddy up

The other guy, with less dihedral, is apparently still having problems, I'd like to get both our planes out to the field at the same time and compare. DOes anyone know anything about this situation? i.e. is this plane naturally sluggish for some reason? I know the kit offers 2 dihedral options, one for trainer, one for sporty but I would expect the trainer to perform OK as a 4-channel.

Thanks for any comments...

Mike

What engines are in use?

I'm using an OS .46LA, not sure about the other guy.

Have nothing but good things to say about the pt40,on grass,our field,with the 40la the plane uses a bit of runway to build flying speed,with the fx engines they are a lot more brisk,the pt40 has more recovery built in than some trainers which as a trainer I really like.As lite as the plane is,high wind buffs it,check the center of gravity,if to nose heavy it will be sluggist in flight.

Have a goodun,John

I flew a PT 40 for years. I opted for the aileron version, which had less dihedral that the rudder-only version. If they are rudder, only, you must have the extra dihedral to turn.
If aileron version, the stated dihedral is needed for stability. The things you are saying are exactly what I experienced when I re-built the wing for very little dihedral. By that time, I was not flying the model and was a more experienced flier with several other higher performance airplanes.
One thing to check. The ailerons cause significant adverse yaw. IF you add some aileron differential, it will improve the situation. To sol;ve the situation, add the diff and learn to coordinate rudder and aileron.
Biggest lesson, any expert who tells you to modify a proven design is mostly not an expert, except in his own mind. There are mods to make on all kits to improve performance, depending on your def of performance. For a trainer, it is controllability and stability. You expert can show you how to add the differential. It is unequal movement of the ailerons, with less down than up. It is the down aileron that causes yaw in the direction of the down elevator, which is in the opposite direction of the turn. You cause it by moving the linkages above the centerline of the servo(s) such that an up elevator moves towards and across the servo axis at right angles to the linkage, and the down aileron moves away from that axis. IIRC, that was explained in the instructions.
Good luck,
Mike

I helped a few newbies build and fly the PT-40, and in every case we opted for the lesser of the two dihedrals. The planes flew so well, that I would never dream of telling someone to build the more dihedral version. Make sure that your hinge gaps are sealed and recheck the balance. That should be one terrific airplane.

I learned on a PT-40 ARF with an OS FP .40 powering it. It flew great.....I think that Mike S. hit the nail on the head. Make sure you set up the ailerons with differential as per his instructions.....it should make a big difference.