Fokker D VIII C.G.

[Don Cooper]

I am building a Fokker D VIII. I started with Stahl's plans for a 54" free flight but made several modifications including scaling it to a 36" span, removing the dihedral and adding ailerons. Because of the short nose, I am worried about balancing it (adding lead is an absolute last resort). I want it to fly slowly, so am using an undercambered airfoil with a high CL max and benign stall characteristics (according to Profili). I noticed that the airfoil also has a sizeable negative pitching moment coeff. Will that negative moment provide any leeway on where the C.G. can go and still have adequate stability. I was shooting for a C.G. at the 25% point for initial flights, but am not sure I will be able to make it without adding lead.

Don

[Dave Robelen]

Hi Don,
Even with the negative pitching moment, I would not let the CG go aft of 30% for the first flights. Those early birds were not exactly the most stable machines in the sky, and the Stahl plan would not account for the small vertical tail along with the blunt nose.
Regards, Dave

[Don Cooper]

Dave,

Thanks for the help. I have gotten far enough along to do some preliminary balancing, and it looks like things might not be as bad as I had feared. I tried to keep everyhing aft of the wing light (hopefully not too light) and by mounting the ESC and most of its associated wiring on the front of the firewall and putting the battery and rest of the electronics right behind the firewall, it looks like I can get pretty close to the 25% point - definitely in front of the 30% point.