Binder Design 3.9" Avionics Bay

Binder Design - Dual Deploy Kit for 3.9" Diameter Rockets {Component}

Contributed by Jon Hatch

Manufacturer: Binder Design
(by Jon Hatch - 06/01/03)

The Parts list is as follows:

  • 4" long section of 3.9" body tube
  • 6" couplers
  • Outer bulkheads to cap the ends of the couplers and slide inside the BT of your rocket
  • Inner bulkheads that just fit inside the tube couplers to help provide a seal
  • 12" lengths of "all-thread"
  • Key switch
  • Eye bolts
  • Plenty of nuts and wing-nuts to complete the job (extras were included in mine).

Packaging - As with the Binder Design kits, the packaging is among the best in the industry. Every category of part has its own individually sealed section of the bag. Quality of the parts appears to be top-notch, with the plywood bulkheads already sanded smooth and all of the hardware included and burr-free. Fit is snug with minimal sanding required. This being my first altimeter bay, the inclusion of the mini-key switch is an excellent bonus, as it's one less decision I need to worry about.

Construction of the bay is not difficult and all steps are clearly described in the instruction sheet. There is only one diagram and a cut-out template for illustration, but this is more than sufficient. The only improvement I could imagine would be the inclusion of suggested deployment techniques, as a prekitted alt-bay of this type would probably be most frequently built by a beginner. Telephone conversations with Mike Fisher at Binder Design made me believe that such suggestions 'may' be included in the future.

One thing to note: When soldering your wires to the key switch, solder them towards the ends of the leads and provide a heat sink between the soldering and the switch itself. That's one I found out the hard way as I shorted the first switch. I personally modified the design slightly by placing terminal blocks on the outside of the bay that I wired through the bulkheads so that I could get a permanent seal around the wiring using epoxy and not have to worry about sealing the bulkhead on each flight.


  • Easy construction
  • Everything needed is included
  • Spacious for larger electronics


  • Could use a bit more along the lines of technical tips and suggestions for use (such as adding external terminal blocks) for beginners.

Overall -- From what I've seen of other entry-level avionics bays, I'd have to say that Binder Design has a good thing going by including enough coupler to allow a full 4" extension from each end of the body tube. This allowed me to separate both the drogue and the main directly from the altimeter bay instead of ejecting a nose cone, effectively creating a "zipperless" design. Having a full 4" section of body tube as well provides plenty of room for epoxy to adhere between the couplers and the BT. In addition, the 12" length of the assembled bay allows for even the longest of altimeters to fit comfortably (such as the MissleWorks RRC).

Overall Rating: 4 out of 5

Other Reviews
  • Binder Design 3.9" Avionics Bay By Wayne Miller

    Altimeter bay kit for 3.9inch rockets. 2 coupler tubes 4 bulkheads 2 all-threads 4 wing-nuts 4 washers 4 nuts 1 key switch Construction PRO's: Instructions were complete and easy to follow, backed up with great illustrations. Construction was easy. Only gotcha is the cutting out of airframe hole for switch to go in. No special tools are needed. Summary: PRO's: ...


W.A. (July 12, 2004)
Be careful with the switch. I didn't find them to be very durable. The first one broke, the second melted. The rest of the bay was very good though.

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