View Full Version : STS CG questions

09-27-2005, 08:28 PM
I'm in the process of trimming out my new STS which I maidened last week. I have a BP21 with a 13503S lipo and an 8040DD prop. Well, it flies like it's very tail heavy. I added an ounce of lead to the front, but still flies poorly. I still need to add the landing gear which will help with nose weight, but I don't think that will be enough.

Unpowered, it glides like you wouldn't beleive! Another sign of it's tail heavy condition. I just hate to add dead weight.

I checked the CG marks on the print and it seems to be closer to the leading edge of the wing than that standard "1/3 of the chord". Anyone know how far back the CG needs to be on this plane to fly well?

Another question is about the BP-21 outrunner. I'd like to put a 1047 on it, but I'm concerned with frying the motor. Anyone have experiences with this motor using props larger than the 8040's in the power charts?

09-27-2005, 11:59 PM
thrust angle?

09-28-2005, 12:05 AM

09-28-2005, 12:47 AM
Just built some LG and it's brought the CG to where it shows on the plans. It does fly better. Seems to be best at 1/3 throttle and flies real slow and still glides into a landing well.

The thrust angle is about 3deg down and maybe 4 or 5deg right. It does pull to the right on takeoff, but straightens out after a few seconds.

All I need to do now is finish the windows and build a tail wheel and try different prop combinations.

Another change might be to put in ailerons but with the dihedral on planes like this, I really don't think they would make much difference.

I tried a loop and it went into a really crazy cork screwing snap roll! :eek: