Jim,
Thats not a feckless idea. Thats bananas!
Youve understood the situation exactly and Ill take your recommendation with gratitude. Only potential setback is I had hoped to run all-thread down the center of the payload section. That would clamp the coupler bulkhead to the couplers edge. Wanted to do that because, as you recognized, Ill need access to the e-box. Maybe divide the all thread into two pieces either side of the donut?
All good stuff and much appreciated.
Feckless
If you incorporate this idea, it also solves the av-bay problem. The entire volume of the doughnut is sealed. Use your threaded rod going between the BP/CR's to hold one plate on. Permanently fix one end of rods and plates to coupler & make the other removable.....
Ta...da now you have the perfect place for altimeters, inside the doughnut on sleds ....on threaded rods [4 maybe] add 1-1/4 threaded for the sleds only [simplicity & moving to other rockets]. Now you can have the needed vents spread around the outside of coupler as in a normal situation.
Drogue goes in back around motor...I think you have plenty room. Main out the front of coupler. If there is too much volume in payload or you want to cut it down to minimum for a safer lower BP charge.....install a bulk plate as far forward in payload as possible, leaving you just enough room for chute, cords etc. Small hole in that BP is all that's needed for Matches & charges.
This also keeps your CG as far forward as possible & keeps recovery gear from shifting around inside the "cavern".
Yes I have done this [all the above] on various projects, so it is tested, valid and NOT feckless.........:smile:
PS used 3/8 bolts and well nuts to install coupler/av-bay into payload. The well nuts give you a bit more "wiggle" room when doing field assembly than just bolts and threaded inserts. Much easier to assemble on field [experience taught us this one] & the rubber well nut keeps the paint job intact. Wet the well nut goes in better than dry.
If you wish to discuss details, PM me & I'll give you my ph# .
Added pics of a smaller version of this design I came up with. I used aluminum stepped BP's . Notice the Y-harness for recovery gear.