Mycroft's Rocket Plans
MH-05 "Cherub" - 5/8 scale version of
the Estes Fat Boy
(This plan first appeared in Volume 5, Issue 3 of
the MASA
Planet newsletter.)
 An
original design (MH-05) by Alan Estenson, NAR 69539 SR
RockSim File
PDF file with
instructions and fin template
Length: 197 mm (7.75 in.)
Diameter: 41 mm (1.63 in.)
Weight: 34 grams (1.2 oz.)
Recommended engines:
Best A10-3t: 91 m (300 ft.)
OK A3-4t: 91 m (301 ft.)
Marginal 1/2A3-2t: 39 m (128 ft.)
Parts list:
- One
(1) bt-60 body tube, 127 mm (5 in.) long
- One
(1) “Big Bertha type” plastic nose cone (from Estes NC-60A
pack)
- One
(1) bt-5 motor mount tube, 44 mm (1.75 in.) long
- One
(1) eb-5 engine block
- Two
(2) cr-5/60 flat centering rings
- One
(1) 1/8 in. launch lug, 38 mm (1.5 in.) long
- One
(1) shock cord – 406 mm (16 in.) of 1/8 in. elastic or Kevlar
- 3/32
inch balsa sheet for fins
- One
(1) parachute – 12 inch diameter
- One
(1) snap swivel for parachute (optional)
Notes:
Kitbashing the Estes Baby Bertha kit will
provide you with the nose cone, body tube, launch lug and
parachute. You may have to cut your own 5 to 60 centering
rings as they are not easy to find.
Place bottom of launch lug 2.25 inches up from
bottom end of body tube.
Cut three fins from 3/32 inch balsa
sheet. Make sure wood grain is parallel to leading edge.
Check the dimensions of your fin pattern to make sure it printed
correctly: root 2 in., tip 1.2 in., height 1.5 in.
Center of Pressure is approximately 2.25 inches
forward from the bottom end of the body tube. Simulations show
a small stability margin, but all test flights have been
stable. However, you should be very careful to avoid adding
unnecessary weight.
Friction fit the motor and secure it with
masking tape. Pack the parachute loosely; due to the low
altitudes, it doesn’t have much time to open.
Right photo shows Cherub next to a regular size Fat
Boy.
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