Great Planes 25% Yak CG Help

[Pappy]

I have the subject plane with:

• Brillelli 46 (stock mount and muffler), stock spinner, Xoar 21x8
• CH Ignition, Brillelli 1-cell Lipo Ign. pack, JR821 throttle servo, and Fromeco 2600 mAh radio pack mounted to the engine box
• 3 JR 8611a's in the tail
• Fromeco regulator between the langing gear

With all this and the motor mounted at the max forward recommended position, the airplane balances almost an inch aft of the recommended spot. Even moving the rudder servo to the internal rail (pull-pull), I need to add over 9 ounches to get it to balance per the manual. I've read here and there that the CG as published (5 1/8" ) is too far forward.

Those of you that have flown the plane, where do you have it set? I intend to use it primarily as an IMAC training platform but would like to try my hand at 3D.

Though I've built and flown more than 30 airplanes over the last 25+ years, this is my first gasser and first fully 3D capable airplane so I'm not as prone to just go fly it and see what happens.

Thanks.

[mtwister]

I have the same airplane, with a DL up front. It has the cg about 1/2 " back of recommended. I don't think I ever start at the recommended, because I always ended up moving it back anyways. The 8611's are fairly heavy if I remember right ( i use Hitec's) but if you want to easily move your cg, add about another 1/2" to your engine stand offs. That should bring it right about dead on.

[beto m.]

Im interested in this airplane with a bme 50cc, do you recommend it?

[Black Bird]

I had this plane. First with an OS 160Fx. Was not satisfyed with the performance, then went with a 46cc. Any gas engine in the 50cc range will work well. The bme is suitable. You will not have a balance issue if choice locations for equipment are correct.

My balance point was an inch behind aft recommended. Hands off inverted level flight. Weak landing gear platform. Makes sure to reinforce with metal brackets or an aluminum sheet.

[Pappy]

I set the CG 1/2" aft (5 5/8") and it flew great. Needs virtually zero down elevator inverted and I'm pretty happy with that for now. I'm going to try adding 2oz. to the nose to move a lttle more forward, then move it a little more aft just to explore the range.

As for power, the B46 is awesome rich and unbroken-in. I can't wait to see how it evolved as I gradually lean it out and it breaks in. In this state, it turn a Xoar 21-8 at 6750 and idles steady at 1350. Half throttle yields a brisk takeoff and application of full power after lift-off yields a Space-Shuttle climb rate.

Definately correct about the gear mounts - very weak. I added 1/4" birch 5-ply gussets which passed their stength tests: 'Landing' on an imaginary runway...

...that was four feet higher than the real runway. SMASH! Gear flexed almost all the way to the wing panels but didn't affect the gear mounts at all.