Douger: 5-motor cluster

Douger: 3-Motor and 5-Motor Cluster Rocket

Having acquired an Estes Designer's Special and perused the JimZ site, I got the idea for a cluster. Although the BT-60 airframe can readily handle a triangular cluster arrangement, I opted to arrange the motor tubes in a line with the two outboard tubes protruding through the airframe.

At first, I expected to have the outboard motors eject themselves while the center motor would eject the parachute, but I later changed my mind and drilled through the outboard tubes and installed vents connecting the outboards to the center tube. I also then added external motor hooks to the outboards. That way, there would be more than one motor ejecting the chute, and protection in case the center motor didn't light.

Thinking I had it all figured out, I loaded three C6-7 motors into it and let it rip.

The flight appeared flawless, but when I finally retrieved it, I found that one outboard motor had slipped its hook and ejected itself, while the other had blown out its tube. Arrggghhh! The retrofitted internal vents were entirely inadequate.

Anyway, after a long time taking up shelf space in my rocket cabinet, I began a salvage operation to reclaim the fins and nosecone for use on another rocket, this time a five-motor cluster.

Below is a view from the business end. Brass retention clips fit on the threaded rods to retain the motors.

All five motors are vented into the airframe to eject the chute, and none are constricted - there won't be any more blowouts (I hope).

It still needs filling and sanding work, but it should be ready for NSL in late May (2004).

Update: Well, it wasn't ready for NSL, but I plan to fly it at NTHP in Windom on August 28 (2004). Left: Here it is finished. I mixed the pink myself (using RustOleum) and applied it with my airbrush. The decal is from Tango Papa.

Further update

Here's all five motors loaded and hooked up on the pad.

This is the ensuing liftoff Nov 22, 2008).

An awkward landing resulted in a broken fin

The repair was done by gluing the pieces together and splinting them until the glue dried. The splints are made from craft sticks selected for straightness then wrapped wtih foil to keep any glue from sticking to them. Some spring clamps from the hardware store hold the splints in place while the glue sets.

8-16-2010

Retention for the 5-motor cluster begins with all-thread installed in the aft bulkhead between the motor tubes. Two pieces of 2-56 are used. The nuts shown, and the corresponding ones on the backside of the bulkhead, were epoxied onto the all-thread and to the bulkhead. With the bulkhead glued in place, the backside nuts are inaccessible so the extra precaution was taken to ensure the all-threads don't come loose.

Two brass plates were cut and drilled to retain the motors. In a sense, they are little more than washers. The all-threads were cut to stick out only minimally past the nuts. Because of this, in the event someone tries to catch the rocket coming down under chute, there is little chance of getting poked by these.

This shot shows clearly the tabs bent into the ends of the brass plates. These keep the plates from turning. With that, there's no chance of one of the plates turning to a position such that one of the motors could slip out.

9-19-2010