Photos courtesy Oscar Valent and Vince Huegele
Implementing an 835cc Hypertek hybrid motor during the construction phase of a rocket presents several interesting issues that need to be addressed.

"Hyper Active" is a scratch built modular design I engineered to resolve those issues, and to allow ultimate flexibility of motor selection. Even if "Hyper Activity" isn't a problem for you, read on anyway. There are many design elements presented here that might change the way you scratch-build rockets from now on!

Hypertek J-300 powered Hyper Active, maiden flight at the Rocket City Blastoff, Oct. 1998 in Ardmore, AL

For the purposes of this article, I've skipped the hybrid tutorial, and made some assumptions about general rocketry knowledge, like what epoxy to use, and where to use it, etc, since that information is available elsewhere on the Internet.

I've also let the photo's speak for themselves as much as possible... a picture is worth a thousand words, right?

Figure 1: Finished rocket awaiting flight in Ardmore, Alabama

The airframe is 3.9" filament wound fiberglass tubing, with a hand laminated fiberglass and carbon fiber fin canister, topped by a PML nosecone.

A short electronics bay in the middle of the airframe houses a Cambridge IA-X96 for a dual-deployment duty.

ACME launch lugs do the dirty work of keeping it's 14 lb. fully fueled Hypertek J-300 mass, moving in a straight line until it gets clear of the launch rod.

Figure 2 is a close up of the fin canister. The canister is a short section of fiberglass tube, with an ID matching the OD of the airframe.

Figure 2: Close-up of fin canister

G-10 fins were bonded to the OD of the canister, then re-enforced with two laminates of 5.7 oz. carbon fiber.

Figure 3: Detail shot of aft airframe

With the weave of the laminates offset by 45 degrees for maximum rigidity, the assembly was covered with a finish laminate of 2 oz. fiberglass to fill the coarse weave of the carbon fiber.

Figure 3 is a detail shot of the aft of the airframe, with the motor mount slid out about an inch. 2 inch slices of coupler tubing and centering rings are used to align and support the motor mount in the bore of the airframe, as seen in figures 5 and 6.

Figure 4: Fuel grain installed

This frame shows the mount with a Hypertek fuel grain installed.

Finally, the meat and potato's of the design:

As you can see in Figure 5, the mount, fuel grain, and tank slide inside the airframe like a slug, with the short sections of coupler tubing providing a positive bearing surface.

Figure 5: Detail shot of motor mount assembly

It's assembled outside the airframe, then slid in and secured with counter sunk hex key screws, which thread into blind nuts on the inside of the coupler slices.

Since there is never any thrust on the motor mount and centering rings (it is all directed to the aft edge of the airframe by the aft ring), the only purpose the screws serve is to keep the motor mount from falling out and the fin canister from sliding around after burn out. 

Figure 6 shows the relationship between the motor mount/coupler tube "slices", the hybrid fuel grain, and the nitrous tank.

When the fuel grain is slid through the mount, and screwed on the tank, they cinch down to compress the mount between the aft lip of the fuel grain, and the expanding OD of the tank, as can be seen in Figure 7.

Figure 6: Motor assembly/motor mount relationship

This design takes "Positive motor retention" to a new level!

With exception of the vent tube being piped to the aft of the mount, dual deployment and zipperless design, the rest of the rocket is fairly typical. Of course, this modular approach opens a lot of doors.

The Hammerhead motor module can be used with any 54mm motor, or it can be replaced with a module comprised of most any combination of clusters, as long as the selected configuration fits inside the airframe and coupler tube.

Figure 7: Adapter detail

Motor retention is pretty standard, when using most of the commercial reloadable motors. With a little imagination, even a 98mm motor could make this bad boy take to the skies!

Much credit for the safety of this project goes to Korrey Kline of Hypertek, who has engineered a simple, cost effective, and above all safe hybrid motor system.

Significant thanks also goes to Oscar Valent, owner of STAR ROCKETRY (http://www.starrocketry.com/). Oscar introduced me to a motor system that might have otherwise been discounted as too complex or troublesome.

Credit for the vinyl graphics go to Tom Gelinas. He's done HARA club T-shirts, newsletter graphics, etc, and really has a knack for making things look great the first time. Thanks guys!

Lastly, the biggest pat on the back has to go to my dad, Robert, since his genetic influence on my problem solving and engineering abilities impacts most everything I do, one way or another. "It's in the genes!"

For more details, look for a full blown construction article in a future issue of NAR's Sport Rocketry magazine.