Question about Electroncs Bay location

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Tripoli 2747
Jan 18, 2009
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Central Viginia - USA
I have a build thread going on over in "scratchbuilt" but given this is a question about the ideal Av Bay location for a large scale model, I'd like to get ideas/opinions from the guys that hang out here.
The question is based on the locations A thru D in the picture:


I had several possible locations when I began, now I 'm thinking of considering more and would like some advice from you all.

Each location has some advantages, and some have distinct disadvantages, but we're still early in the design - so I think some accommodations can be made.

A. Service Module BT - This might be a good location for an Av. Bay - but I had planned on reserving this area for as much lead ballast/weight for CG adjustment as possible. This would also require very long wiring leads to reach the fin can for airstarts, and they would have to detach upon separation. Maybe..there could be a seperate electronic unit in the fin can just for outboard airstart motors. On the positive side, access to an Av Bay in the SM could be just like a traditional mid frame Av. Bay. - using a coupler and bulkheads.

B. Transition - For access I could have a shroud panel open just like on the real thing - but I've never heard anything good about vent holes on a surface area that was slanted.

C. Main Airframe - After spending so much time getting a nice CF tube, the last thing I want to do is start cutting a panel into it. Might affect the structural integrity. However, it is mid point in the overall airframe which is traditionally a reasonable place to put an Av Bay.

D. Tube Tank/Fin Can - This appears to offer the least viable opportunity for sticking an Av. Bay for DD function, given this component is pretty much nothing but a cluster of 3" dia. tubes around a central core tube (for a 54mm MMT). At least four of the outer eight tubes were planned for 29mm and 38 mm outboards. That leaves four empty tubes, but again, working from the back to the front for wiring for DD is problematic, particularly for a main deployment after seperation and droque deployment.
Likewise for anything in the fin can ring itself. Unless I put a dedicated electronic unit in the fin can ring just for airstarts on first motion.



Well-Known Member
Mar 14, 2015
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I would lean toward location "C" ( the main body tube ) given that you want to do DD as well as potential airstarts. It gives you the shortest run to each and gives you the optimal position for vent holes. I would also consider a recovery system like I used on my recent L2 flight. I used a drogue/pilot chute with a main chute in a deployment bag ( which was then released by a tender descender ). The primary advantage is that it allows you to pack the whole recovery system into single compartment, and, of course, not be constrained to run the wires all the way across to the other side ( or have a secondary e-bay ). Then again, it's quite possible that you want separate chutes to bring down the command module and escape tower, to protect your work there, which would complicate the system quite a bit.

Another good option would be to use a MARSA54L with MarsaNet bridge. The main flight controller could be mounted at the top of the craft to trigger the DD, while an MRFPyro unit could be used at the rear to trigger airstarts. This really gives you the best of both worlds as it means that wiring is minimized and the position of electronics can be optimized. It would even be possible to mount the remote pyro unit ( with battery ) in the back end of one of the "empty" 3" tubes for easy access, and the flight computer itself central to the main body tube, for standard dual deployment and a basically ideal position for the vent holes.

I may have to mosey over to "scratch building" to watch this come together. I love the Saturn 1B. It's a beautiful ship.

Martin Jay McKee