Coldfire Booster Bulkhead

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One of the main attachment points for the Coldfire recovery harness is at the bulkhead at the forward end of the booster section. The photos below will illustrate how that bulkhead was designed and built. It provides a solid connection to the rest of the booster and a U-bolt connection point for the recovery harness.

View booster section design drawing

These are all the parts needed to build bulkhead B1 at the top of the booster. The large yellow item is a piece of Kevlar cloth 5.35" OD x 0.026" thick. The green tinted plate is G10 fiberglass 3.23" OD x 0.092" thick. The wood plate is 3.75" OD x 3/8" thick aircraft plywood. And of course, the metal items are the U-bolt and mounting plates.

Top view of the bulkhead as assembled.

There is a 13/32" diameter hole in the center to allow an optional threaded rod to pass through if needed to help secure a motor in the booster. The HyperTEK motors do not need it, but other large motor cases typically have a threaded forward closure that accepts an 3/8" threaded rod.

Side view.

The U-bolt is 1.25" ID stainless steel with 1/4-20 threads. It is available from McMaster-Carr as part number 8896T92.

Bottom view.

The G10 plate on the bottom is there to distribute the load forces around the whole circumference of the Kevlar cloth. The Kevlar cloth was purchased from Thermostatic Industries, Inc. It is an 8oz weight fabric with part number 8K-60.

To attach this bulkhead to the booster motor tube, the first step was to saturate the Kevlar cloth with West System epoxy.

The perimeter of the Kevlar cloth that extends out from the bulkhead was cut into eight equal width segments. These allow the cloth to be easily folded down against the motor tube without bunching up and having ridges and air gaps.

Bottom view of the bulkhead. The cuts in the Kevlar don't extend all the way to the G10 plate. They stop short by a distance equal to the wall thickness of the motor tube. About 1/16" or so.

The bulkhead is now placed on top of the booster motor tube. The G10 plate on the bottom of the bulkhead exactly fits into the motor tube and therefore centers the bulkhead on the motor tube.

Some of the Kevlar segments have been folded down against the motor tube. A few still remain to be done.

All of the Kevlar cloth segments have now been folded down, pulled tight and pressed against the motor tube.

Tape was applied to hold everything in place while the epoxy cured.

The tape was removed once the epoxy had cured. The bulkhead is now solidly attached to the motor tube.

The next step will be to slide the coupler tube over the front end of the booster. The bulkhead is sized to fit the inside diameter of the coupler tube so the coupler will slide right over it.

One end of the coupler tube has a large slot in it to accommodate the rail guide backer plate mounted near the top of the booster body tube. Once the coupler tube is in place, an epoxy fillet was added at the top of the bulkhead to secure it to the coupler tube. However, the Kevlar cloth system is what will support the bulk of the load forces during parachute deployment and recovery.