For my Level 3 project, I bought a 5.38″ Karman nose cone. It is a filament-wound fiberglass (with a black pigment–it’s not carbon fiber) nosecone with a machined aluminum tip. Originally, I wanted to make the entire nose cone myself by doing a fiberglass overlay of a hot wire-cut foam block, but this would have been more trouble than it was worth for this project. The nose cone is an impressive 30 inches in length (not including the shoulder for seating it into the airframe), so there is a lot of empty volume to put stuff. Additionally, I would have to find some way to retain the nose cone to the rest of the airframe. (Simple glue or riveting would have been unacceptable due to parachute bay placement.)
Thus was born the nose cone payload fairing. The payload carrier bay is a 4″ cardboard tube (not a standard 3.9″ cardboard airframe tube) approximately 14.5 inches long. There are two centering rings that constrain the tube in the nose cone. The forward ring is made of 1/4″ plywood and the aft of 1/2″ plywood. The aft centering ring has eight holes backed with stainless steel tee nuts that accept #6-32 stainless steel screws. This hole pattern matches a similar hole pattern on the payload fairing cap, a 1/2″ plywood disk which also supports a 2″ steel U-bolt (with 1/4-20 threads). There is no forward closure to the payload carrier bay as the cardboard tube matches the inner diameter of the nose cone spline at the termination of the cardboard tube. This also allows easy access to the nose cone tip attachment point. Both centering rings are JB Welded to the cardboard tube, though these joints carry essentially zero load. The spacing between the two centering rings matches the length of the nose cone shoulder piece (10 inches). The inner surface of the fiberglass nose cone shoulder was roughened with sandpaper and the payload carrier bay was JB Welded in place. The same was done to the nose cone body to attach the shoulder to the nose cone spline. The nose cone (except the tip) was painted in metallic gold.
The vehicle side of the nose cone shoulder was sanded down with a rotary tool to allow an easier detachment of the nose cone from the airframe. It was previously discovered in a dry fit test that the nose cone and parachute bay had a very tight fit (possibly an interference fit, depending on the weather). To maximize the probability of successful parachute deployment without structural damage to the airframe, material had to be removed from either surface for a smoother fit with greater tolerance. With the removed material, the joint is still not a loose fit, but the nose cone may be removed with a nominal application of force.
A payload carrier rack was also made from 1/4″ plywood. This payload carrier rack features segmented flat surfaces to mount various thin payloads. It integrates directly into the payload bay cap U-bolt attachment point. Nominally, it will carry a GPS tracking device to locate the rocket after flight (and possibly collect data throughout flight).