I am flying a Sig LT-25 Kadet that really likes to climb when I add throttle. I have lots of down trim too. Is this a thrust issue? Thanks

Sounds like the wing has too much incidence, and as a result, you'll need more engine down thrust.

I agree about the incidence but it is much easier to change the wing incidence than mess with the engine thrust once the plane is built. Just get you some thin cardboard(matchbook size or slightly thicker) and shim the trailing edge of the wing until she flies level with centered elevator trim. I had to do this with one of my SPADs for about 4 flights before I got it right.

You can also shim the top of the engine mount to angle the engine downward one or two degrees. It's probably easier just to shim the trailing edge of the wing.

As others have indicated either shim the wing trailing edge or add downthrust. The decision as to which to do however should not be predicated on which is easiest.

All airplanes with a thrustline much lower than the wing such as a high wing cabin type will have a tendency to pitchup with increases in power. Thats why virtually all well designed cabin types will have at least some downthrust designed in to the firewall and I am sure the LT-25 will have some.

The decision as to which to do, shim the wing trailing edge or add more down thrust should be decided by how the airplane glides with power off. If you shim the wing trailing edge, yes that will reduce the pitch up tendency with added power but at the same time when in a power off glide it will require more up elevator. This can reduce the avaliable elevator authority when trying to flare for landings.

Many reduce downthrust in cabin type airplanes thinking it helps handling or some such which usually just makes the airplane less pleasent to fly. It is my opinion that from your description that down thrust is inadaquate for the power installed and I would add a few degrees more. It not a huge issue either way but it does boil down to how nicely you want the airplane to fly

John

Easy to diagnose--fly your plane at full throttle. When you let off throttle, does the nose drop? If it does, you need to add down thrust to your engine. If it doesn't, then it is probably an incidence problem. Remember, though, trainers tend to climb with power anyway, and sigs are really known for having a lot of positive incidence in their trainers--especially in the kadet series (speaking from experience of my Dad's senior arf). Anyway, either fix will probably solve your problem.