Maidened my dogfighter today. Went pretty well I think. Plane required a bit of down elevator once in the air as it wanted to climb. Felt like the elevator was really sensitive as well. First time flying this kind of setup. After landing I noted that the elevator was really down a bit in the trimmed position.

Plane was balanced on the front edge of the spar with an empty fuel tank. 6oz fuel tank is directly behind the firewall so it was nose heavy when filled. Pic shows a close up from the side so you can see how much down elevator I had dialed in.

Since CG was in the right place, even a bit forward with a full tank, do I need to change the wing incidence so I can level out my elevator?

Appreciate any input!

somegeek

Well crap... I thought I had this plane trimmed out but looking at it closer it seems like I might have dialed a little reflex in unintentionally. Gonna tweak that a bit and give it another whirl tomorrow.

somegeek

The photo looks like you have "0" downthrust and maybe even a little up thrust? If so, that would account for your symptoms. You might check that.

Jim, are you referring to the wing or engine?

When I removed the reflex, I added 1.5 turns of the clevis on one side and 1 turn on the other side to get the ailerons level.

somegeek

G'day Mate,
You need down thrust on your engine, that flat bottom wing will produce lots of lift, & down thrust will help, start at about 2 degrees, & see how it flys.

Thanks, Alan. The plans don't call for any downthrust so I didn't build any in. Will try shim the top of the engine mount on the firewall with some slim washers and go from there.

If the red arrow is your balance point, you're at about 30%; are you sure it is not tail heavy? Try 25%.

You're not tail heavy. I've flown a lot of those Coroplast planes. The flat bottom, high lift airfoil climbs like mad under full power. I finally put some quarter inch under the trailing edge to prop it up and run the incidence down. That helped a lot. Put a piece of 1/4x1/2 under the TE before you rubber band the wing on and give it a try. I finally glued mine on.

Looking at the photo's it looks like there's no down trust to me too. Now whether that's the problem or not I couldn't say but it's one or the other. Easy fix!

Ed - have you tweaked the engine thrust before incidence on these flat bottom spads?

somegeek

The first set of washers I added to the top mounting bolts between the firewall and the mount to adjust the thrust yielded a noticable difference with the climbing. Added a second set of washers which further remedied my climbing problem, but still required a little down elevator. I've added a third washer set now to the top bolts and hope this will put it near dead on and put my elevator flat when trimmed out.

somegeek