> the guys from upstate NY flew an upscaled 15" diameter Fat Boy today at the
> RATS launch in south jersey. the name of the rocket was "YO BATF" (fat boy
> scrambled). beautiful rocket, absolutely outstanding job. i delieve it weighed
> about 50-60 pounds and flew on a M1419. the total height was less than 6 feet.
> my main question is........how the heck is this thing stable with a 17 pound
> motor in it's rear. i believe the custom nose cone weighed about 13 pounds and
> no nose weight was added. the boost was perfectly straight and true with no
> wobble or spin. can any one explain to me how this thing was stable when the
> calculated cg should be around the base of the nose cone. thanks guys for a
> great flight and congradulations. Bill
questions, since I built and flew 'YO BATF', with a lot of help from Ray
Halm, Pat Finan, the guys in TRA Western NY, Ed LaCroix from Aerotech,
and Roger Dwyer (who lent the motor casing).
Before flying the upscale, I assembled a stock Estes Fat Boy, inserted a
C6-3, and measured the CG. Then I used this CG location (scaled up, of
course) in the big version (14.4"diameter, approx 5.4 x upscale).
My calculations with VCP show a calculated CP approximately 21" from the
rear of the BT. My liftoff CG was 26" from the rear, for about 1/3
caliber stability. This required the nosecone to weigh about 18 lbs
(ballasted with lead).
I agree with AstronMike; a larger model will certainly be less affected
by wind gusts (mass goes up as the cube, profile area only goes up as