For the motors that you plan using, consider heavier wall LOC or Aerotech tubing. Either will be a bit sturdier than Estes BT-80. The nose cone (PNC-80K) will fit into either tube, although the base will need to be built up to smooth the nose cone/body tube joint.
The nose cone location for the altimeter will play havoc with any barometric device until ejection. That is why altimeters and avionic bays are placed in a straight section of the rocket.
Thank you for your suggestions! I really appreciate it and will make sure I give strong consideration to every one. These are two issues that I have given a good bit of thought to already, so I'll explain my thinking and would be
glad to hear responses to my reasoning.
On the altimeter location: This an issue I have gone back and forth on. I actually made an alternative Rocksime file for the AIM 54 with a mid-ship avbay. Advantages of midship design: 1- No/less interference with barometer, although still not seven calibers back from shoulder of nosecone (probably not an issue unless exceeding mach); 2- Can attach ejection charge leads directly to altimeter instead of running extension wires aft into fin canister (through small, sealable hole in bulkhead) and to rear of payload bay; 3- Easier to mount 29mm tube/coupler (for prefab Raven e-bay) in airframe/BT80 coupler than deep in nosecone. Disadvantages: 1- Probably would not have enough room for a parachute-sized bay both above and below avbay; 2- heavier build, because weight of avbay would not be in nose and would need to add some there to get good static margin.
I also looked at some other mid-power and level one rockets flown with nose-mounted altimeterspurchasing the Raven altimeter and discussed the issue with an altimeter manufacturer. I addressed the primary disadvantage by: 1- Purchasing the Raven altimeter, so I can use accelerometer for apogee detection, then baro for main deployment; and 2- Until I have flown enough to be fully confident in acel-based apogee detection, I will use motor ejection with delay 2-3 seconds past predicted apogee so I should minimize chance of early deployment or simultaneous motor and altimeter deployment.
So, after considering all of the above, I plan to epoxy 2.5" 29mm tube and one or two steel 4-40 all-thread into front of nosecone creating a stud assembly inside 29mm tubing; I will assemble Raven bay using 2" 29mm coupler and one or two supplied aluminum all-threads, then slide it onto studs inside 29mm airframe and snug down using steel nuts; primary launch cord attachment will be to nose cone itself (so decleration forces upon extension tend to force assembly and nosecone together and not apart) with a tail attaching to one of the steel studs; that way, even if the epoxy did let go of the nose cone, the avbay will still be attached to the recovery harness.
Again, I welcome your additional thoughts. Do you think I can depend on the accelerometer to detect apogee?
Concerning the airframe material: Part of the reason I made this design is to use up materials I have left over from my last big scratch build. That means about 26 inches of BT80 and an Apogee 2.6" polystyrene nosecone. I'm cheap.
The last build I mentioned has flown on E's and F's and a five-motor cluster that reached 118 Newtons of peak thrust. That rocket also has a much longer airframe with a heavier nosecone, so the tubing sees more stress at the same levels of thrust. I have seen no signs of stress to that airframe. I have also talked to a number of rocketeers much more experienced than me who say BT80 should be fine, and that in the early days of high-power they were using thin-wall airframe (with and without glass) for lower high-power applications. Also, this design has through-the-wall fins and fin supports and a motor mount running more than half its length, and they will substantially reinforce things.
I am more concerned about zippering than I am about acceleration-based frame failure. I plan to protect againt that by 1- using long shock cords, including a length of elastic-type shock cord; 2- making sure the section of cord that runs past the edge of the airframe is a wide type, and not thin kevlar; 3- carefully selecting deployment delays/times; and 4- not flying in breezy weather so I do not get a lot of arch-over and horizontal speed.
Further thoughts? Particular concerns? Anything I can do to further reduce the risk of airframe failure or zippering?
