For the Moment of Inertia rocket I’m going to be using a Cesaroni Vmax motor. In particular, the 29mm 3-grain H410. 410 Newtons is a lot for this size motor: 42 kgf, or 92 lbf. It makes you wonder, how do they get that much thrust out of such a small motor? It has to have either a high chamber pressure, a large throat, or both.
Chamber pressure came out to 870 psia, and sure enough, the nozzle is properly expanded for one and a third atmospheres.
The place where I launch is at 5000 ft elevation, about 0.83 atmospheres ambient pressure. Proper expansion would be a nozzle area ratio of 8.8 instead of 6.25. That would mean extending the exit diameter from 0.75″ to 0.89″. It should get 1.6% more thrust, or 417 instead of 410 Newtons.
Robert Steinke of SpeedUp has posted a new update, building a Mach breaker rocket
I’m starting on an extra little side project. I’m going to build a Mach-breaker rocket using the Cesaroni 29mm H410 Vmax motor. Here’s a picture of the basic layout.
I imagine the fist question I’m going to get is, “Why did you choose tube fins? Tube fins are high drag. Don’t you need low drag for a Mach-breaker?”
Worth a read for those interested in the physics of it all.