My Funtana 90 rocks pretty badly in harriers and elevators.

All servos in stock locations per the manual, Saito 100. Battery mounted out front(you can see it through the right cowl opening).

I first flew it with one ounce of lead right behind the fuel tank. Lead came loose and got stuck behind the right elevator servo(found out after the first 3 flights). I'd assume the CG was WAAAYYYY back. Probably at least 8.5", mabye more. Elevators were solid as a rock, as were harriers with no wing rock. Harriers were tough due to the extreme aft CG, it would pop into a hover.

Removed the lead from the tail, and added 3oz on top of the engine mount beam. CG is right around 7-7/8", mabye a tiny bit more. Wing rock is now prevelant in harriers and elevators, and it's bad, even with spoilers up.

I'm not sure what I might be doing wrong...[&:]

Too much elevator throw?
Move the CG back another 1/4 inch?

Or am I just flying it wrong? I've tried very steep AOA harriers to be sure the wing is deep stalled, but it still wants to rock. Heck, my UCD has less wing rock!!

Any help appreciated.

I would move the c/g back and decrease the elevator throw some so it that it might not be so pitchy when you try to harrier

Make sure that your lateral or wing tip to tip balance is dead on, this can make ALL the difference inthe world. DO NOT use the engine prop shaft as a forward support for checking this as most engines are not perfectly centered due to the offset thrust that is built into many of these planes.

I put a screw eye in the firewall at the exact center as measured from left to right across the fuse. You can support the rear on the tailwheel bracket as they tend to be centered on the fuse.

I have a seen 1/2 oz. placed on one wingtip totally eliminate rock in a couple of planes. Of course it doesn't always work but it's well worth making sure it's correct because it can help with other maneuvers like loops.

I believe that u experience wing rock when the wing loading is way above what it should be. whats ur plane setup? lets discuss that first!

Freek,

I think I have a ligher setup than some. I'm using the Saito 100, which is a very light engine. A YS 91/110/120 is in the neighborhood or 9-11oz more. Servos are HS-625MG, 1.9oz each. The battery pack is an 1100 5-cell. Only additional weight is a SIG tailwheel which probably weighs an ounce or two more than the stock one. I've got 3oz of lead on the front of the engine mount for balance. Currently the CG is about 7-7/8", possibly a tad more or less.

I can tell you for a fact that the wingloading is not way above what it should be. This thing floats forever!

I have found that there are a couple of things that will slow or stop wingrock altogether.
When performing an elevator too much throttle or not enough elevator throw will cause wingrock,,,, see if backing off on the throttle helps. Also a spoileron mix will help too. That means a mix that moves the ailerons up when up elevator is applied, start with about 15 degrees of up ailerons when full 3D up elevator (50-70 degrees) is applied. With the mix the ailerons will move up OR DOWN the same direction as the elevator throw. Doing this kills some of the wings lift which is the goal of an elevator, The wings lose lift but trememndous elevator throw keeps the aoa up enough to keep the nose from dropping. Reducing wing lift stops the wings from rocking in an elevator in my opinion. IMO, Rocking is caused as one wing loses lift and then the other back and forth. Stop them from fighting each other by bringing the ailerons up, but not so much as to cause total lift loss and stall. Its a balancing act. Adjusting CG and the other thing mentioned in this thread help too, but these are some other things I have found.

I have a question..
What is it about my foamie biplane that it drops like a STONE and im talking rapid vertical descent in an elevator but absolutely no instability WHATSOEVER. Go to high rates, chop the throttle apply full up elevator 70degrees and that succer comes straight down, if theres no wind its PERFECTLY flat and a nice smooth but rapid vertical descent. If the breeze picks up just a little, maybe 2-5mph I can land an elevator the descent is so slow and predictable.. What is the difference between my foamy bipe and my glow planes??My U CAN Do does really nice elevators with a spoileron mix, but my foamies are just sick!!!!

Harriers or rolling harriers I use a flaperon mix, really stabilizes the plane,,,, no rock.. and rolling harriers are about twice as easy to control with flaperons. Flaperons are exact oppsite of spoilerons. Elevator goes up Ailerons go down and vice versa.

Mike

Remove some elevator. Too much elevator will cause it to rock. Anything more than 45 degrees is wasted. This has held true in several planes I have had. First the H9 Edge. Then the Phoenix models Funstar. Then the Funtana 40 and now the H9 Sukhoi. All had a elevator and harrier problems until I removed a little elevator. Just put it into a harrier and when the wings start rocking, just remove a little. Of course you could move the CG back and that will probably help since you said it did fine with an extremely rearward CG.

Im convinced that BigNed is right about this one!!

Thanks for the advice ned. I do have spoilerons and I use them on my UCD to reduce wingrock. Also have them setup on the F90 but everyone else tells me I shouldn't need them. I am gong to play with CG and elevator throw, I think it is a combination of the two. I think I may have added TOO MUCH lead to the front, because it went from zero rock to a bunch. I will have to play with it until I get it right.

About your foamies, I wonder if the outrageously light wing loading has anything to do with the extreme stability and angle of descent??