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38mm Raven Altimeter Bay length - FG Coupler

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EBurg

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Working on my first DD project - using a 38mm Wildman Warrior. I have a Raven Altimeter bay that I'd like to use and wondering about the length of the coupler. The Wildman DD kit comes with a 4" coupler, so I either need to cut it down to 2", or extend the allthread to match the longer coupler. I'm torn between keeping the small form factor of the 2" raven bay and making it easy for my first attempt. Seems to me the longer coupler would be more reliable physically, but worried about the battery bouncing around if I extend the raven bay. Thoughts?

Eric

38mm AV Bay.jpg
 

dhkaiser

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Shortening the coupler could weaken the integrity of the construction. I would think it best to lengthen the av bay.
 

patelldp

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You could also fashion rings to locate 2" of 38mm coupler offset inside the coupler. This would allow you to locate the magnetic switch as close to the wall of the rocket as possible and also add some sort of shock cord attachment on the fat side of the ring.
 

stealth6

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There are a couple of ways to go about it.

One would be keeping the 4" long couple, and using longer threaded rods as you indicated. You could rig up a "stop" of some sort to keep that battery in place without too much difficulty.

Or you could go with the 2" coupler. The trick here is to realize that you permanently glue the coupler to one of the pieces of airframe (typically the payload). This makes it a bit tricky to load the altimeter and bits into the bay, but it's not too hard. You simply mount the alt and battery to the active bulkhead, and attach your shock cord and deployment charge, and then drop the whole thing down the top of the payload tube, wriggle it around a bit until the threaded rod ends stick out the bottom of the bay, and then mount your passive bulkhead/shock attachment/charge there. Also, one the trickiest things is gluing that coupler into the payload airframe so that it is dead straight...this is because you are only gluing it in about 1/2" deep. It's very easy to glue it up cock-eyed which is obviously not a good thing. Pay close attention during this process, and make sure it's straight before the glue sets up.

I can't post any pics right now to illustrate things, but if you search around I'm sure you can find lots of good examples.

My preference is definitely to use the 2" coupler, glued into the payload airframe.

good luck with your build,
s6
 

Adrian A

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There are a couple of ways to go about it.

Or you could go with the 2" coupler. The trick here is to realize that you permanently glue the coupler to one of the pieces of airframe (typically the payload). This makes it a bit tricky to load the altimeter and bits into the bay, but it's not too hard. You simply mount the alt and battery to the active bulkhead, and attach your shock cord and deployment charge, and then drop the whole thing down the top of the payload tube, wriggle it around a bit until the threaded rod ends stick out the bottom of the bay, and then mount your passive bulkhead/shock attachment/charge there. Also, one the trickiest things is gluing that coupler into the payload airframe so that it is dead straight...this is because you are only gluing it in about 1/2" deep. It's very easy to glue it up cock-eyed which is obviously not a good thing. Pay close attention during this process, and make sure it's straight before the glue sets up.

I can't post any pics right now to illustrate things, but if you search around I'm sure you can find lots of good examples.

My preference is definitely to use the 2" coupler, glued into the payload airframe.

good luck with your build,
s6
I second that. The part of the coupler that gets glued in only needs about 1/2" of overlap for a very strong joint, leaving you with a 1/1 L/D ratio on the exposed coupler. That's enough to keep everything straight if your clearances are reasonable. As the coupler glue sets up you can roll your tubes around on a flat surface to make everything axisymmetric.
 
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