The Coldfire airframe is flexible phenolic with two layers of fiberglass applied. The nosecone is plastic and the fins are G10 fiberglass.

Coldfire was specifically designed to fly on the HyperTEK hybrid motor system.  This system uses ABS plastic for fuel and liquid nitrous oxide (N₂O) as the oxidizer.

Coldfire is designed to deploy the main parachute at apogee. A dual deployment system was deemed unnecessary based on the expected altitudes and was also eliminated to save weight.  Coldfire should reach 4000 feet with the K240 hybrid motor. It can also fly on many different solid propellant motors to higher altitudes.

Coldfire has a large payload bay inside the nosecone that will be used to carry a GPS downlink transmitter system.

View Coldfire design drawings

The photo above shows the 835cc flight tank mated with a HyperTEK "J" series grain to complete the K240 motor system.

The drawing at the left shows how the K240 hybrid motor is installed inside the Coldfire booster section.   Click on the image for a closer look.  The K240 motor is accessed by unscrewing the tail cone and then removing eight screws that hold the motor thrust plate onto the aft end of the booster. 

The overflow vent tube is a nylon set screw that has been drilled out lengthwise.  The screw threads hold it securely in place while allowing it to be easily installed and removed.

The HyperTEK product manual is a very good overview of the entire system. It describes the motors and the ground support equipment.

This photo shows all of the airframe parts for Coldfire ready to start assembly!  Click on it to see a page with details about individual parts. 

Airframe construction starts with four inch diameter phenolic tubing that is 48 inches long.  Two layers of 6 oz fiberglass were added along with an anti-zipper reinforcing steel band.  Click on the photo at the left to find out how this was done.

The body tube for the booster section needed to have three lengthwise fin slots cut in it. Click on the photo at the left to see how that was done.

Coldfire required a custom sized motor tube to hold the 81mm diameter Nitrous tank.   This photo shows the carbon fiber tube that was created.  Click on the photo or the link below to see how that was done.

Click on the photo at the left to see the whole process of aligning and attaching the fins to the motor tube.  It includes adding reinforcing strips of Kevlar at the fin root.

The HyperTEK nitrous flight system requires a special vent port in the side of the rocket.  Liquid nitrous will vent from this port to indicate the on-board flight tank is full.  Click on the photo or the link below to see how that was designed and built.

The bulkhead at the top of the booster serves is a recovery system attachment point. A special reinforcement method was used to connect it to the top of the motor tube. See how that was done by clicking on the photo at the left or on the link below.

View booster bulkhead construction

The fin fillets were formed by using a small section of PVC pipe and some West System epoxy.   Click on the photo or the link below to see how that was done.  After that the booster section was sprayed with a filling primer and wet sanded to achieve a "perfect" surface finish.

The Coldfire nosecone started out as a 5:1 Ogive "Pinnacle" nosecone from Giant Leap Rocketry.  However, a payload compartment was added inside the nosecone and a anchor point was added at the aft end that allows the nosecone to screw onto the body tube to secure it in place.  Click on the photo or the link below to see how all that works.

The Coldfire altimeter bay construction is a little bit different than is commonly used.  A special foam seal was created that isolates the ejection charge gasses from the electronics. Click on the photo or the link below to see how it was done.

The parachute flame protector is cut from a large piece of Kevlar cloth.  The recovery harness is made from tubular Kevlar and tubular nylon. Learn all about it by clicking on the photo or the link below.

A special motor adapter tube and tail cone are used to secure the HyperTEK motor system inside Coldfire.  Click on the photo or the link below to see how that was designed and built.

Coldfire decals add a nice finishing touch.  Click on the photo or the link below to find out how they were made and applied.

Coldfire uses two linear rail guides available from Public Missiles.  A custom metal backer plate was used to hold them in place.  Click on the photo or the link below to see how that works.

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