M Powered FAT BOY

M Powered FAT BOY

Post by Andy Schecte » Wed, 29 Oct 1997 04:00:00



Quote:

> 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

Thanks, glad you enjoyed the flight. I can answer some of your
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
the square).

 
 
 

M Powered FAT BOY

Post by Andy Schecte » Wed, 29 Oct 1997 04:00:00


Oh yes, I forgot to mention that Jim Sekol provided his great launch
pad, a 10' long unistrut rail, and some nifty delrin rail guides that
bolted on to the rocket. This meant we didn't have to wait in line for
the RATS tower launcher (it tends to get real busy with M projects).
Thanks, Jim!

-Andy

 
 
 

M Powered FAT BOY

Post by AstronMi » Wed, 29 Oct 1997 04:00:00


Quote:
> 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).

Great job, Fred, as well as your 'partners in crime'.

Quote:
>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

Great idea!  Anyone making a L3 nonkit rocket oughta do a smaller scale model
 of thier impending project, and fly it to confirm at least a minimum CG
 location.  Sometimes you can get off with less than one caliber of stability..

Quote:
> 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).

Id say this is probably about as minimum of a Cg as you can get, especially
 with a slower flying rocket.  

Quote:
>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
>the square).

What?! You cant agree with ME!!  If Im NOT talking about gliders, Im totally
 ignorant 8^).

Anyone else ever notice the huge rockets flying straighter than the 'normal
 sized' ones?  Scaling effects...