How to build a fiberglass rocket, part 5: nose cone

Like many fiberglass rocket kits, the Darkstar Extreme has an aluminum-tipped nose cone. The aluminum tip is for more than just show: it has a couple of structural purposes.

One is the manufacturing method of the nose cone itself. The process uses “filament wound fiberglass,” which involves placing resin-impregnated fibers around a mandrel (a gently tapered cylinder). It is difficult to make this come to a point, and instead the manufacturer just shortens the nose cone and puts an aluminum tip on.

Another purpose is that during flight, the tip of the nose cone absorbs the most heat, and aluminum is a better material to use for this specific part of the rocket.

grey nosecone
aim with the pointy end

So, the question for me now is: how to connect the nose cone to the rest of the airframe?

You might be asking: how hard can that be? And you’d be right; it isn’t particularly difficult. But some nose cones have a portion that can fit inside the rocket body, as though there’s a built-in coupler. This nose cone, though, is the same diameter as the rocket body and will not fit inside it.

The good news is, the rocket comes with a 6 inch long coupler. Half goes inside the nose cone, half inside the airframe (payload section). On the nose cone side, I just epoxied them together to create a permanent bond. On the other side, I drilled three small holes through the airframe (and coupler) and inserted nylon screws (shear pins). This allows everything to stay together until a large force is applied mid-flight and the airframe separates from the nose cone, deploying a parachute.

The bad news, however, is that I need to attach a kevlar cord to the nose cone somehow, and the best way to do this is to put a bulk plate with a forged eye bolt on one side of the coupler. Either side will do, but it makes sense to put it on the side that goes a few inches into the nose cone, rather than the side that comes a few inches out, since that increases the available storage space inside the rocket for things like the parachute and 25 feet of kevlar cord.

The kit came with a fiberglass bulk plate with no edge or lip (see above picture). It will fit inside the coupler, but I don’t feel too confident that epoxy alone will hold it in place. Instead, I ordered another aluminum bulk plate with an edge or lip – the inner part fits inside the coupler, but there is an outer lip that sits above the coupler so it cannot be pulled through, no matter how hard the cord is yanked.

green aluminum bulk plate attached to red fiberglass coupler
a christmas coupler

I epoxied the aluminum bulk plate to the coupler, and then used more epoxy to attach the forged eye bolt (with a long screw attached) and two nuts to the bulk plate itself. There’s no way this setup is coming loose during flight regardless of the forced applied.

view inside coupler, from above
masking tape dam keeping epoxy near walls

Above is a view of the inside of the coupler. I added some masking tape in an attempt to create a very crude barrier or dam, keeping the additional epoxy a bit closer to the edges to seal them.

red fiberglass coupler secured inside grey nosecone
a perfect fit

That’s it! The coupler and nose cone are in good shape, and I’m ready to move on to the next section: my old friend, the e-bay.

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