Type

PHRED is a NAR payloader meant to be easily made by the students in my physics class. It is a kit bash of the 20mm diameter Quest Sprint kit and features folded paper fins with integral fillets. The fins are much larger than necessary to allow stable flight without the payload (which accounts for almost half the total flight mass).

Disassembled view. The payload (A 70mm long BT-20 tube filled with 1oz of sand and lead fishing weights) fits into the forward airframe/NC section. The Sprint NC shoulder was cut off leaving a 3/16" glue surface and four small holes were drilled through the remaining shoulder. It was epoxied into the payload tube using the "epoxy rivet" method. A tight friction fit coupler (yellow piece) mates the booster to the payload section and contains the recovery mount. The Kevlar ™ recovery cord is epoxied to the thrust ring in the booster section. Note the dual launch lugs. The forward lug is at the CG with a 1oz payload. With no payload, the lug is way forward of the CG and the model binds on the launch rod under thrust. The aft lug keeps things honest during no payload flights. Click on image for full size picture. Use "BACK" button to return.

Close-up of paper fins and aft "motor mount". The fins are made from two layers of tagboard (manilla folders) soaked with CA. 1/4" tabs at the root edge are spread and glued to the BT forming their own "fillets". Elmer's Fill & Finish was used to smooth the leading edge to the airframe. The 20mm Quest body tube requires a motor mount to fit 18mm motors securely. I just cut a couple rings of BT-20 and glued them in to make forward and aft mounts. The motor is friction fit for flight. Note: You can see exhaust damage in the picture; keep rocket away from blast deflector! Click on image for full size picture. Use "BACK" button to return.

The design is a series of compromises which allow straight-forward construction in a classroom. The standard Sprint nosecone, launch lug, large fins, and "heavy duty" recovery parts really remove this design from serious competition use, but it turns in respectable flights on B6-6 and C6-7 motors. It is not sturdy by design, but has survived a nearly horizontal, high speed deployment and rough landing without a scratch.