(Contributed - by Larry Brand - 08/01/03) 
Brief:
The problem with overpowering a "stubby" design like the C-powered
Estes Fat Boy with heavier engines is the CG dilemma -- the more power, the
more nose weight is needed to keep the CG in limits, negating the Oomph you
thought you were adding. I have modified Fat Boy for F-power with a nose cone
extension to counter-ballast this with minimal added weight.
Modifications:
The only other modifications I made to create my Schnoz Boy was some modest
reinforcing to accommodate the 8-fold increase in thrust (C to F).
The stock fins were trimmed to fit a 24mm motor tube (or a 29 mm works,
too) and doubled on one side with 1/64" sheet plywood (a snap, this stuff
cuts with a scissors) epoxied on. A 1/8" Lite-Ply-tm doubler was
constructed for each of the cardstock motor centering rings supplied with the
kit. And that's it. To complete the make-over, I added a
"professional" recovery system consisting of an 18" LOC nylon
chute and 10 feet of nylon Marine Corps shoe lace (see landing photo), anchored
through the body tube with a knot covered with a plastic fairing. Copying a
final touch I saw in a magazine, I couldn't resist rearranging the stock Fat
Boy decal to spell "YO BATF".
Construction:
A 5" 24mm Estes nose cone was ballasted with 35g of lead fishing sinkers
epoxied into the tip. The "supplemental" nose cone is then affixed to
the stock Fat Boy cone, using a self-tapping sheet metal screw set into the
stock cone and protruding 1/2" to allow a gob of epoxy to anchor the
pointy ballast box in place. This puts the CG with a 62g F21 at 6.5" from
the tail, well ahead of the Cp (3.9" from the tail). I call the finished
product "Schnoz Boy", for the obvious reason. See photo.
This was an easy conversion. All the stock pieces were used, and its a great
kit. The through the wall fin design makes this easy to convert to higher
power. You do need to add a proper recovery system for E-F-G power, however,
and reinforcing the balsa fins for the much higher speeds is essential. I know
over the years many folks have had fun overpowering Fat Boys with G80's and
H180's and even more thrust -- but seriously, how many of these plywood-finned,
fiberglass-reinforced cardboard mortar shells do you ever get back in one
piece? Schnoz Boy is a spectacular flier on F-power, and you get it back to fly
again and again. It makes for an interesting drag race when you sneak it
alongside some kid's C6-7 Fat Boy on the club launch rack.
Flight:
How does Schnoz Boy fly? On E30-7's, it roars up to about 800-900' in the blink
of an eye. On an F21-8, it rides a foot long sheet of flame to at least 1700',
with ejection about at apogee (not that you can really see this). I have
several F24 reloads I plan to try in it. A good first flight was had on a
D12-5, but Schnoz Boy is too heavy to fly well on an Estes E9-6 (meaning that I
tried, and I don't want to talk about it). After 11 flights to date, not a bit
of damage (except to the stock 18" Estes plastic chute, which shredded on
the first E30 flight, dropping Schnoz Boy onto a sand dune). The only
shortcoming with Schnoz Boy lies in the future of Aerotech as sole supplier of
single-use 24mm/29mm E-F-G motors, without which it wouldn't be much fun.
Summary:
PRO: This is the way to fly an Estes Fat Boy for "Big Kids"!
CON: Well, of course, you lose the ability to fly on C6-7's, and unless the
flow of AP motors in 24mm size restarts, this conversion is too much trouble
for just a D12-5 upgrade.
Other:
This approach to changing the rules for ballasting -- moving the nose weight
ahead of the stock nose cone instead of inside it -- has a lot of possibilities
for balancing rockets of all sizes with minimal added weight.
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