Chesley's Certification Rocket
My certification rocket is a combined level 1 / level 2 certification rocket. The mission is simply to fly on any class 1 and class 2 motor with as little modification as possible needed to switch between motors. Ideally, I should be able to certify up to level 2 in something like an hour, starting from being uncertified.
The main feature of a combined certification rocket is that the motor casing is compatible with at least one level 1 motor and at least one level 2 motor.
I choose an Aerotech casing because that is what I am familiar with. It turns out that not only can an RMS 38/720 casing fit an Aerotech J-350W motor, it can also fit an I-211W if you use an adapter with 2 spacers. If you ignore the instructions, you can use 4 spacers and use an H-123W engine. The reason you'd try to use the H-123W is you can get it about $25 cheaper if you're using the motor to certify . (They have specials to encourage people to certify.)
For this design, I will use the J-350W and the I-211W with 2 spacers; the I motor will cover level 1 requirement and the J motor will cover the level 2 requirement. As these both use the same casing, there only needs to be one rocket capable of holding one particular casing.
Some years ago, when I was beginning this design, I thought I would make it a minimum diameter rocket for "simplicity". However, after getting some advice from a more experienced designer, I dropped this idea in favor of a wider body. Evidently, a minimum diameter rocket is not actually simpler; if I remember correctly, the main issue is one of packing everything in such a tight space.
The complicating factors in a two-motor-choice design are that the rocket needs to be stable for both configurations and survivable in both configurations. Stability can be achieved through proper fin sizing and the use of nose weight, if needed. Survivability depends on either avoiding very high speeds or building it for supersonic flight. Some initial designs in OpenRocket flew somewhat "slow" on the I motor and very supersonic (like Mach 2) on the J motor. The rocket can either be built to survive these speeds or slowed down with added weight or drag. Slowing it down is simpler and conforms to what I know better, so I will be shooting for a slower rocket.
I will be using parachute recovery for simplicity. Electronics will be used, since I'm familiar with the Featherweight Raven from my UTA AeroMavericks days; it's not simpler than a delay grain + ejection charge, it's just what I know better. The nose cone will be von Karman since it's not going slow enough to use a parabolic cone and I don't like any of the other shapes.
After the initial building began, and I had completed the nose cone, fins, and motor tube + centering ring assembly, I discovered the estimate of the nose cone weight in software was far heavier than the real nose cone weight. This meant that the original CG estimate was too far forward, and the real rocket would have been far less stable (and somewhat faster) due to the lighter nose cone. This meant the fins were undersized, and the already-cut fins needed to be scrapped. I'm happy I discovered this before I glued the fin can together!
- Cut fins
- Re-cut body tube
- Re-cut fin tube
- Cut, glue adapter
- Create altimeter bay
- Create charge holder
- Get LEUP
- May need to make or get magazine
- Glue together fin can
- Consider re-bondo-ing the nose cone
- Outer tube
- Motor tube sub-assembly
- Glue body tube, coupler, and altimeter bay as required
- Shock cords as required
- Black powder
- Wadding / chute bag
- Paint, as required
- Altimeter switch
- Glue mount point into / onto nose cone
- Paint the rocket as desired
(steps done as soon as feasible)
- Fully assemble rocket
- Test for fit
- Test for difficulty of assembly
- Ejection testing (ground)
- Run Raven's test function
- Become Tripoli / NAR member
- Study for L2 written test