Modification - Fat Boy

Modification Fat Boy - 24mm

Modification - Fat Boy - 24mm

Contributed by Morgan Hendry

Manufacturer:

This project begun when I read several posts from rec.model.rockets on placing a 24mm motor mount in a Fat Boy, normally a 18mm kit. I first looked at the instructions and made a list of what I needed to do.

Replace the 18mm motor tube with a 24mm one
Make bigger motor mount with modified centering rings (higher strength) and an engine block
Remove some of the "through the wall tab" on the fins
Add nose weight
Possibly insert a baffle system to eliminate wadding

I bored out the centering rings with a drill to accommodate the 24mm tube (Estes Bt-50). I constructed the motor tube by the instructions but instead of a 18mm tube I used a 5 1/2 inch 24mm tube. Also, I used a larger engine hook and an engine block made of a heavy duty BT-50/BT-20 centering ring. I changed the engine hook to accommodate the larger engine. After I glued the first centering ring in the normal position (per instructions) with epoxy, I used small strips of thin plywood to reinforce the rings. These were on the side of the centering ring facing the front of the rocket. I repeated this step with a second ring whose reinforcements were facing the front of the rocket and the distance of the "through the wall tab" of a fin from the first centering ring. Looking back, it would have been easier and probably stronger to make a new ring out of aircraft plywood. Oh well. Note the 18mm conversion tube to use smaller engines and the reinforcements on the centering rings:

Rocket Pic

The balsa strips on the side of the conversion tube were added because the centering ring was not on the inside of the tube. Another mistake that could be corrected. The shock cord was tied to the to the upper centering ring for strength. The ring was then glued on. The fin was used to show the appropriate distance between the rings. Steel wool and another green centering ring were added to the motor tube. A small disk of balsa with holes drilled into it was glued onto the top of the motor tube to make a baffle.

I shaved off some of the TTW fin mounts to accommodate for the larger motor mount tube. Using epoxy, I glued in the fins. They were reinforced with hot glue. I made a 12 inch nylon parachute to attach to the nose. I will add 1.5 ounces of nose weight for stability.

Rocket Pic

All done!

Rocket Pic

Other Reviews

Modification Fat Boy - 24mm By Colin Westgarth-Taylor
An Estes Fat Boy modified with a 24mm MMT for D and E motors. External dimensions are stock. These modifications change one of Estes best packaged kits into a true performer. Modifications: Construction sequence was pretty normal for a MPR capable rocket: forward CR epoxied to the MMT, shock cord mount epoxied to the MMT (two 1/32" holes were drilled in the front CR to tie the Kevlar cord ...

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