The three small Fat boys in this picture are downscales. The smallest one is BT-5 sized and is a bit smaller than a mosquito. The next one is BT-50 sized and has a 13mm motor mount. It is small enough that there is no room for a recovery system. It just pops the nose cone and uses drag for recovery. It flys on 1/2A and A motors.
The next one is BT-60 based and has a 12" parachute but only has room because I went with mini motors. It has my 3-mini engine mount. It flies on 1 to 3 13mm motors.
The 4" diamater one is a great flier on F and G motors, it has a 38mm mount long enough for a 38/240 reload (H123 or H242). It is a 1.54x upscale. It is made with the upscale mosquito nose cone from Scotglas.
The large one is not complete yet. It is based on some 6" tubing that
I found and fiberglassed inside and out for strength. It has a 54mm mount
and a 2 stage baffle system so little or no wadding is needed. It was short
enough that I had to make room for the recovery system inside the nose
cone. I made the cone from a wood frame, styrofoam and fiberglass. It should
fly on H-J motors and has a 60" parachute. I didn't build an electronics
bay. I may retrofit it after completion when I have more experience
with altimeters.
Following is a chart of scale information for every size of tubing I know of. It can give you the information you might need if you're trying to build your own upscale or downscale Fat Boy. As with many other upscales, the hard part of building a upscale or downscale Fatboy is fabricating the nose cone. Commercially available nose cones exist for BT-60, BT-80, BT-5, 4" and 7.5" LOC tubing. The 4" and 7.5" cones are made by Scotglas. There is even a Level II Fatboy upscale kit from Smokin' Rockets
| My Fleet | Description | BT Size (OD) | BT Length | NC Length | Scale |
| T-2+ (MicroMaxx) | 0.281 | 0.86 | 0.43 | 0.11 | |
| TT T-3 | 0.375 | 1.15 | 0.57 | 0.14 | |
| TT T-4 | 0.448 | 1.38 | 0.68 | 0.17 | |
| * | BT-5 | 0.544 | 1.67 | 0.83 | 0.21 |
| BT-20 | 0.736 | 2.26 | 1.12 | 0.28 | |
| Rogue T-22 | 0.850 | 2.62 | 1.30 | 0.33 | |
| T-.908 (ST-8) | 0.908 | 2.79 | 1.39 | 0.35 | |
| * | BT-50 | 0.976 | 3.00 | 1.49 | 0.38 |
| 29mm motor tube | 1.210 | 3.72 | 1.85 | 0.47 | |
| BT-55 | 1.325 | 4.08 | 2.02 | 0.51 | |
| BT-56 | 1.300 | 4.00 | 1.98 | 0.50 | |
| * | BT-60 | 1.637 | 5.04 | 2.50 | 0.63 |
| Rogue T-45 | 1.750 | 5.38 | 2.67 | 0.67 | |
| Aerotech 1.9 | 1.880 | 5.78 | 2.87 | 0.72 | |
| T-2.04 (ST-20) | 2.040 | 6.28 | 3.11 | 0.78 | |
| BT-70 | 2.217 | 6.82 | 3.38 | 0.85 | |
| 54mm motor tube | 2.260 | 6.95 | 3.45 | 0.87 | |
| BT-80 | 2.600 | 8.00 | 3.97 | 1.00 | |
| 3" LOC/PML | 3.100 | 9.54 | 4.73 | 1.19 | |
| ^ | 4" LOC/PML | 4.000 | 12.31 | 6.10 | 1.54 |
| T-4.476 | 4.546 | 13.99 | 6.94 | 1.75 | |
| 5.54" LOC | 5.540 | 17.05 | 8.45 | 2.13 | |
| ^ | 6.15" PML | 6.155 | 18.94 | 9.39 | 2.37 |
| 7.67" PML | 7.672 | 23.61 | 11.71 | 2.95 | |
| 11.6" PML | 11.660 | 35.88 | 17.79 | 4.48 |
My Fleet indicates the ones I have built (*) or that are under construction (^)
Description is what the tube is commonly called
Tube OD is the outside diameter of the body tube, all scale data is based on the original Fat Boy being an Estes BT-80 which has a diameter of 2.6"
BT Len. is the length of the cut body tube
NC Len. is the approximate exposed length of the nose cone
Scale is the scale factor, how many times the original size the
model will be