Dual deployment question

I\'ve never used it but I took a look at some pictures and drawings. It\'s nice but to me it seems like overkill and it\'s expensive. From what I can see it seems like you wouldn\'t be able to use the motor ejection charge as a backup for the altimeter at apogee. If the electronics fail or you fail to turn them on (it happens) your rocket is going to come streamlining in. Even with no chute, a rocket coming down with the top and bottom sections separated is a lot safer.

I have used the CPR 3000 and it has it\'s advantages and disadvantages. As a matter of fact I just used it in the Black Brant X I flew at the last launch on a J-355. I have only had one failure in the past with it and that was when the upper coupler of the CPR system pulled out of the upper body tube and so the nose cone, main chute and upper body tube came down separately from the booster, main body and altimeter bay.

A couple of things about the system:

- You can still use motor ejection as a backup if you understand that the main body tube (usually holding the drogue and shock cord, or just the shock cord for drogue-less apogee deployment) is connected to the altimeter bay in the center of the rocket, and not to the booster section holding the motor as is typically done. You need to take the appropriate steps to protect the contents (chute etc) of the main body of the rocket from the motor charge. In PML kits they usually have a bulkhead to seal off the top of the booster section. You can either drill holes in the bulkhead to let the motor ejection gasses out, or as I did, add an additional bulkhead in the coupler also with holes drilled in it offset from the other bulkhead to make a nice baffle, or you can just leave that bulkhead off completely but you will lose strength in that section (not recommended).

- I do like the way the rocket screws together in the center using the aluminum fittings but just make sure the outer couplers are glued in well.

- Some people have said the inner tubes that hold the altimeter is a stress point and are not strong enough. They recommend replacing the cardboard tubes with a fiberglass version but I haven\'t had that fail in about a dozen flights of that rocket. It can be a little tricky fitting and sliding the altimeter into that tube but it gets easy with practice (once you line things up correctly).

- PML worked with Missile Works to re-design a version of their altimeter to work with that system but it\'s easy enough to use another you may like better. FWIW though, that Missile Works altimeter has not failed me yet.

All in all, I like the system and I have not had any major problems with it and nothing negative to say about it. It may be a bit of overkill and it does cost a bit more than a simple altimeter bay, but I did learn a lot from using it on the Black Brant X (the 4\" dia. version) and it got me my level 2. I also have another rocket I am building (a Hawk Mountain Talon 3) which will use that system.

All that said, you can get a nice basic altimeter bay from Giant Leap for under $30.00.

I also HIGHLY second Boris\'s recommendation for getting Mark Canepa\'s book MHPR-2. There is a TON of useful info in that book.

Please let me know if you have any other questions about the PML system.