Hey folks,

I've been trimming my 50cc Extra 260 for IMAC and I'm trying to get things setup as described in Peter Goldsmith's article. While the plane is currently setup so that it flies straight and level hands off both inverted and upright, on uplines, it tends to pitch to the belly (power on) and on downlines it pulls out on its own (power off). Chopping the power from cruise does not result in a noticable dive or climb...the plane just keeps going. Other quirks include a strong pitch to the belly during knife-edge flight.

I assume that downthrust is built-in? Has anyone pulled out some of that downthrust? This could be a CG issue, but the inverted 45* upline test shows no climb or descent and the plane stays on track during the 45* power-off downline test. It's tough to get the aircraft to stall...if you creep up on the stall, you can hold about 15* up elevator and it will just float slowly down.


Other details: 16.5 lbs, DA50, 23x8 Xoar prop

Ideas?

Maybe you need more up elevator throw.
I have heard some say they go to high rates to do a stall.

I'm no expert but I did stay at a Holiday Inn Express last night.

Sounds like your tail heavy. Most set their planes up so there is just a slight dive from an inverted 45* upline. Try moving the CG forward about 1/8-1/4" and you will be set.

i think its tail heavy....

OK...added several ozs on the nose and it does seem to fly a bit better. I also have a CF tailwheel and CF horizontal stab tubes on order. So-so weather kept me from really working it over this weekend. Thanks! I'll keep you posted.

UPDATE

Did a lot of flying today. I think moving forward the CG has really helped. It does track better on the uplines, though it will still pitch over to horizontal on its own as it looses speed on the upline.

One thing I have noticed is that there is a good deal of rudder to pitch coupling. Specifically when rudder is applied, the plane will pitch to the belly. This is really most notable on a 45* inverted upline or downline where I am trying to correct for thrust or cross-wind. I assume it's happening all the time, it's just that I notice it most here. It will pitch to the belly during knife-edge flight, too. Is this common? Is a mix-setting a reasonable solution?

Thanks!

Its very common with the 260... just a touch, maybe 4 degrees or so of up elevator mixing will cure that and make knife edges look very crisp. I still had to manage a little rolling with the ailerons, but it was simple to hold a completely verticla knife edge or slip it into a 45.

Very cool...do you leave that mix on all the time? Seems like the rudder to pitch problem is always there...level flight, inverted flight, uplines, downlines...

UPDATE:

Mixed in about 10 units of up with my rudder and it seems to have done the trick. I leave the mix on all the time. Now, when I make yaw corrections on an upline (so long as the corrections aren't major), the plane won't pitch to the belly. There is some rudder to roll coupling that requires opposite aileron when I do a knife-edge.

All in all, plane is flying well and my sequences are getting better.

You can also do a rudder/aileron mix. This is also a standard requirement with most scale aerobatic planes. And you do leave both mixes on at all times.
As for pulling out on its own on the downline, this is again very common, correctable with a 1-2% throttle/elevator mix when the throttle is set at idle.