>I've had this plan in my head forever.. Its been buggin me. I took the
>already two staged Fat Boy (who came up with this?)
That would be me. :-)
and put a 3 18mm cluster
>in the booster with the normal 24mm in the sustainer. I haven't built it
>*yet*. I am a little uneasy about the weight, and the CG. Any other
>GYRO # 13 (Lucky me...)
John Stein wrote in response:
>John O'Donnell is the one, at least that's >where I received the information
>for mine. I use a D12-0 and three C6-3's >in the booster, and a D12-7 in the
>sustainer. Really rocks! Of all the flights, >I have only had one failure,
>and the was at NSL. The three C6-3's lit, >but not the D12-0. Landed nose
>first with no damage, thanks to the >plowed field. Add 1.5 ounces of lead to
>the nose. Plenty stable.
I'm glad nothing serious happened to the model.
John Y., there is really nothing to worry about as long as you add the nose
weight and increase the size of the booster fins slightly. I have flown 2
different versions of mine a total of eight times now with no problems. Out of
40 motors used in those 8 flights, only one has not lit. Fortunately, it was
one of the outboard 18mm motors, so the rocket was still able to stage. There
was also no noticeable angle to the flight due to the off-center thrust.
As Peter Clay said, you should have one of those three booster motors under the
sustainer motor, and the only way I can think of to do that would be to have
the motor in a straight line across the body tube. This setup *will* cause
problems if either one of the outer motors doesn't light. You will be much
better off using a four motor setup like mine and John's: one core motor
(either 18mm or 24mm) and three "outboards" (18mm) spaced equally around it.
Check out my website below for a couple of pictures of my original SFB (4 x
18mm booster, 24mm sustainer). I have plans drawn up for it if you'd like a
copy and didn't get the SpRocketry that had them in it. Just email me you
snail mail address and I'll send them to you.
John O'Donnell NAR 60742 Sr. L2
Visit my web page at http://members.aol.com/jon3854/science3/index.htm
"The last man to leave here was never heard from again, he won't be back this
way 'til 2010" - Planet P