The design guidelines for Arnor are set by the Hedonic Treadmill project


This rocket has three fins. The core of the fins will be laminated balsa stock. This balsa-ply core will be shaped into a Prandtl-D tip NACA airfoil profile before being reinforced with 1/64” plywood, 3oz fiberglass, and 6oz carbon fiber. The fin stock will be tapered radially to maintain a proportional airfoil across the entire span of the fin to keep the Reynolds number low (see Apogee Technical Publication #16 et. al.).

Shaping a complex airfoil by hand is difficult so a few steps will be taken to make the results more consistent. Each fin will be assembled from two halves. Each half will be tapered radially using a custom extra-long sanding block and beveling jig made from Makerbeam based on the work of Bart Hennin published in Peak of Flight #271. The fin shape was chosen so that the thickest part of the airfoil will be perpendicular to the root edge which makes it easier to form the aft bevel of the airfoil with the tapering jig. The fore bevel of the airframe will still have to be shaped by hand.

Once the fin cores are shaped, a strip of 1/64” plywood will be bonded to the outer surface of the trailing edge of the airfoil to increase toughness. The two halves of each fin core will then be bonded together. The through-the-wall fin tab will be made slightly oversized so that it can be sanded to conform to the surface of the motor mount tube.

The fins will be bonded directly to the motor mount. Once they have been filleted epoxy thickened with colloidal silica a 4-layer tip-to-tip composite layup will be applied: 3 layers of 3 oz fiberglass with a top layer of 6 oz plain weave carbon fiber.

Avionics Bay

Ejection Charges

The ejection charge design is based on an article by Jim Jarvis that was originally published in Rockets Magazine in June 2011 and further refined in subsequent years both by Jim and by the Princeton Space Shot team. The charge canister dimensions used in the first revision of the Princeton Space Shot launch vehicle was 1/4” by 6” (page 21). I’ll be shortening that slightly to 5.75” to match a standard size of paper straw that will act as a disposable liner.

Help Me Choose

The cocktail-size straws have an OD .248” and are 5.75” long. They should nest nicely into this high-temperature FR4 tubing:


Additional notes:


From the EggTimer Quark User’s Manual: