UStik

Guten Morgen Sal,

I ignored the polyhedral so far, sorry. It makes for some spiral stability both in the calculation and the simulator model so there's less top aileron required. But the wingspan is just too big and the amount of top aileron required is still bigger than usual. A roll gyro would be nice.

Again an interesting picture of IM, quite nose-down. Since the simulator model does likewise I suspect that was a fast fly-by (for demonstration, maybe without load). At least nobody stands on top of the fuselage like in the other picture.

Anyway, the simulator seems to be set up (wing incidence) and trimmed realistically. With the rearward C/G, I just increased stab incidence until I got comfortable behavior in powered flight. That turned out to be also the correct trim for power-off glide (22 mph). It was just hard to fly the model "tail heavy", that is with too little stab incidence. Easier to begin with is too much stab incidence ("nose heavy", as always), which could be achieved by down elevator on the real model (hence pitch gyro).

I had started with a wild guess of drive power. Now I did an educated guess, assuming an 8 cell LiPo for your AXI 4130/20 and 16x8 prop. That turned out to be a good choice, but my assumption was rather bad. 8 cells make for about 12.5 lbf thrust per motor, meaning more than 1:1 thrust:weight ratio. Other than usual I wouldn't say "better more than less power" in this case. Of course you can always throttle back, but one of Dick's hints applies: You'll see the result of too much power quite late, only when tucking begins. The more speed the earlier (dive angle) tucking begins. Still it is stopped easily with up elevator, but here 25° throw is advisable and you don't have time to flip the dual-rate switch. Of course it's nice to see the model leap off the ground but that's not realistic anyway and not needed. The motor is rated for 6 to 8 cells LiPo, and 6 cells will do nicely. Well, I should stop rambling and just ask what kind of cells and how many you intend to use.

I flew the simulator model a bit this last weekend. The more I fly it the more I love it. It really was a matter of getting used to it, like learning where to fly and what to avoid on a new airfield. The airplane does nothing unusual, it's just satisfying to fly it around, knowing and avoiding the limits without having to think about them. It's a warm feeling to know you're on top of it, all is under control. It's like a tamed wild animal in the circus, the tamer can treat the tiger like a kitten as long as he doesn't the slightest mistake, and he knows he is far from that. (I know I'm exaggerating/rambling, but I like to play with the English language for practice.)

My funny assessment in my first post couldn't be wronger: The model is not sensitive to wind. In a 3 Beaufort wind with appropriate gusts, the simulator model is remarkably steady. Actually you notice the wind only by a bit yaw wobbling, which could be eliminated by a yaw damper gyro.

Looking forward to your further information.

Burkhard


P.S.: Nose-down in fast flight means you have to avoid any nose-up attitude in any flight regime, even in touch-down. Just do a wheel landing and let the tail settle. Touch-down speed is less than 20 mph and is quickly dissipated (short roll). If the model is trimmed as decribed above, you may leave the elevator alone and control approach path with power, if there's no pitch hold gyro. More and more I think such a gyro would be needed for the first flights but no longer when the model is trimmed. It doesn't help in avoiding too much pitch, anyway. You can (and maybe should) fly this model like an old rudder-and-throttle (class 1) model. It needs more speed (hence power) in turns and even flare is done with power. Other than the old class-1 models, this one needs that because it's on the verge of stalling if trimmed for glide, what is recommendable because it's then trimmed for powered flight as well.There'll be just enough speed reserve for a nudge to flare and to cope with gusts. I believe this behavior was meant when they wrote IM was hard to fly.