Hello, I hope that someone can help me with my UDC setup.

The airplane has been up about 3-dozen times and is a joy to fly with a Saito .91 up front. I started at the recommended CG, but have steadily moved it back for better 3D. Moving the CG back has helped stabilize the hover.

Here are my observation and questions:

1. The airplane requires a significant amount of "up" elevator trim - darn near 3/16". This is counter intuitive to me since I have been moving the CG back I would expect to have to crank in "down" trim like I do on my foamie.

2. Inverted flight still requires a "push" on the stick.

3. The airplane is not stable in a parachute. I dive and pull full "up" and she will transtion to a parachute. It will gradually start a spiral that degrades into a spin. I have it laterally balanced to perfection. A little aileron "reflex" doesn't seem to help. Again, I would expect some wing "rock" but it starts what looks like a tip-stall spiral.

Can anyone see a pattern here or offer some advice?

Thanks!

JC

If you still have to push down, then that sounds like the CG needs to go back more. Nose heavy tends to like to snap/spiral.

Thanks for the advice. I'll keep moving it back.

Can anyone tell me what their optimal CG is for this bird?

Thanks!

JC

Are they independent elevators or connected. In either case check the slop from one side to the other. Sometimes theres a lot of play still left in the oposite side of the elvator where the sevo isnt. And in an aggresive manuver one side may respond quicker or even with sligthly more control than the other because the point of contact where the horn is is so far away from the oposite side of the elevator. My brother has that issue with his Funtana. He found a fair amount of play in his elevator at full deflection oposite the control horn end. And i have independent elvators in my Giles and had an issue similar. Turns out I had to tune down one side it was throwing a bit more than the other. Just a suggestion. Good luck.

The elevators are independent and have separate channels on seperate servos. No slop in these linkages.

Good point though...I will check to see if the deflections are the same!

JC

I checked and yes there was some asymmetry in the elevator deflection. I'll test fly tonight to see if it helps. I will also move the CG back a little more.

JC

I moved the CG back and aligned the elevators for equal deflection.

Good News: I did some successful parachutes without the wing drop/spiral. Hover was also improved. Landing was a little like dancing on a bowling ball - the nose came up at reduced throttle.

Bad News: Even with the CG way back, I still needed "up" elevator trim. I decided to investigate some more. At higher throttle she wants to go down. Back off the throttle and she goes nose high. It has to be a thrustline problem. I believe that I have downthrust in the model. I'll get out ye olde incidence meter and see what it says. Sheesh, these things are jig-built aren't they? The thrustline should be spot-on.

I'll report back.

JC

JC, in my experience, yes the plane needs upthrust.

I am also using the Saito .91.

I ended up putting in a little bit of upthrust, and a LOT of right thrust, using 4-40 washers behind the engine mount, so I wouldn't have to fight it so much in a hover.

Bill,

Thanks for your advice, I'll be breaking out the jar of washers tomorrow.

JC

Update:

Incidence meter showed approximately -1.0 degree on the thrust-line (down-thrust). I did some mild shimming to get about +1 degrees (up-thrust).

Won't be able to test until Friday night.

JC