Joe Westrich

My Feedback: (95)

I am working on a Skymaster MB339 project and there is something I just don't get. The CG on the airframe is on the main spar, or very close, and 2 of the 3 fuel cells are behind the spar! The way I see it, is that if you balance the airframe empty, it will come out tail heavy when you fill the tanks. I have never built an airplane with the majority of the fuel sitting behind the CG.

So..... Are you guy balancing empty, or full, or what?

dubd

Have you checked the build thread?

http://www.rcuniverse.com/forum/m_68...tm.htm#9196042

Joe Westrich

My Feedback: (95)

I have. I scanned through it and found some good info like that most are putting the CG 3cm aft of the center of the tube. That still leave the two rear tanks aft the CG, minus the first 1 cm. The front tank is forward of the CG but its volume is less than the sum of the two rear tanks. No one in that thread mentioned specifically what the CG does from empty to full. I stole a picture from that thread to reference the tanks. You can't see the tube but it is just in front of the saddle tanks.

DominicM

I didn't build mine but after 10 flights I've got used to it being slightly tail heavy on take off and having to trim out the changing fuel load during the flight. Only 2 or 3 clicks though.

Joe Westrich

My Feedback: (95)

That's exactly what I was guessing would happen. So you don't think it is unstable on take off with it being slightly tail heavy?

ECalderon

Hi

A friend has one and its very stable all through a flight. Go to Youtube and search for
"MB-339 JetsRC" and watch the video to look for yourself.
Regards
Eduardo

DominicM

Definitley not. If anything it helps.