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Originally Posted by chalinaty
I have a group of high school students building model rockets from 9" BT-20 body tubes. They are using friction-fit 18mm motors (mostly B6's)
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Here's an idea of what you can achieve with that 9" tube and the right shape in the fins. I used the very common 2.75" Ogive nose cone known as the BNC-20N, and 1/16" thick balsa sheet stock for the fins, together with your 9" BT-20.
Study the 2D drawing to see what else you need to put in the model, like a thrust block and a recovery system. I used a 10" 6-line parachute, which you can make from garbage bags to save money. Grab that demo version of RockSim and study the RKT file for additional information.
Notice the breathtaking performance numbers, all generated by RockSim:
Length: 12.27"
Fin Span: 2.87"
Diameter: 0.736" (BT-20)
Weight: 0.35 oz
There is no additional weight added to this rocket to achieve stability!
A8-5.......647'......Dv 5 FPS......Margin 1.47
B6-6......1190'......Dv 12 FPS.....Margin 1.32
C6-7......2076'......Dv 4 FPS......Margin 1.01
Note these altitude values again. These are true simulation values, and RockSim is very accurate in its predictions! You've got a missile with almost 2100 feet altitude capability in your students' hands! For reference, those Dv numbers represent how fast the rocket is moving at the moment the parachute is deployed. Dv means Velocity at Deployment.
If I can be of additional assistance, just holler out loud! (Preferably through this forum, of course. I monitor it all day long...)
Enjoy!