Type

SCARAB is the rocket that I will use for my NARTREK cluster qualification. It will also be used in a shameless attempt on the NAR "B Cluster Altitude" record (shameless, as there is no current record).

SCARAB is a five motor, in-line cluster design around an "almost" minimum diameter (20mm) airframe. The in-line cluster layout is meant to maintain thrust symmetry for 1, 3, or 5 motor flights and to minimize drag while also providing additional side force stability.

The side motor assemblies have a sloped and rounded leading edge profile and the entire motor section is covered with a thin balsa shroud to lower tube joint interference drag.

This is a sport model and not a real competition bird. Lightweight fiberglass is used to stregthen the model and sport model construction methods are used throughout; the primary goal is NARTREK Cluster qualification and altitude performance is secondary.

Construction

The main airframe is two sections of 20mm Quest tubing joined with a standard coupler which also serves as a Kevlar cord recovery mount. Cluster motor pods are 90mm lengths of BT-20, wood glued in an in-line configuration. The motor pods are streamlined with a leading edge of wet shaped 1/16" balsa and the entire motor section is covered with 1/16" balsa sheet to minimize interference drag. The design allows for venting of cluster motor ejection gasses by ducting them through the hollow leading edge to a tape covered side port. To cope with ejection gas pressure and heat, the leading edge is fiberglassed to both the airframe and the motor pods. The internal areas exposed to ejection gasses were also painted with thin epoxy to help with heat resistance.

This tail-heavy rocket (with 5 motors) is almost certain to pop/break a fin on landing, so the fins are glass reinforced with a single layer of 1.5 ounce cloth and Z-poxy.

Liberal amounts of finishing filler were used to smooth and shape the various joints and transitions.