HM5 Hybrid Rocket Project

Project Team Members

  • Joshua Herrmann
  • Logan Maltbie
  • Samuel Radinsky
  • Joe Vanherweg

Under construction

HM4 Hybrid Rocket Project

Under construction

HM3 Hybrid Rocket Project

Project status unknown

HM2 Hybrid Motor Project

Last updated: May 16, 2006

HM2 Full Size Test Fire We have done two test firings of a full-scale version of the HM2 using two kinds of fuel: polypropylene and HTPB. The polypropylene test went well, although the exhaust speed didn't get high enough and the motor only produced 15 pounds of thrust. The HTPB test started well, and the motor "choked", but a problem with our injector angle cause the casing to burn through near the top and the motor stopped sooner than expected.


HM2 Scale Test Fire On April 10, 2006 we successfully fired a scaled-down version of the HM2 hybrid motor for the first time. We used N2O as the oxidizer, and HTPB for fuel; we poured and cured the HTPB here at CPSS. This is not as easy as it sounds—it took us a few tries to get just the right ratio of diisocyanate and HTPB and the right curing temperature before we got a nice, clear fuel grain. If there are any bubbles or voids in the grain, the motor could easily explode.

This test fire was primarily to see if the HTPB fuel would burn safely and also served to practice new motor firing safety procedures.

Our biggest problem was getting the APCP igniter to light, but once we figured that out the motor started up and ran great, burning clean and smooth. We used an oversized nozzle which gave us negligible thrust, but this was expected. We did not gather any performance data from this firing, because we wanted to make sure our procedures were correct, and that the HTPB compound would burn without incident.

With the safe firing of this motor the club is now moving as quickly as possible to make the large scale HM2 and begin test firing.

Test Stand


The Test Stand

This test fire marks the first time we used our new CPSS test stand. This stand was entirely designed and built in-house by CPSS members. For this test fire, we had a load cell as the only measuring device on the motor, but we can easily add more.

The HM2 Combustion Chamber The HM2 Combustion Chamber

We machined the HM2 combustion chamber ourselves here at Cal Poly. It is 18" long and 3-5/8" in diameter, made from T6061 aluminum.

The HM2 Motor Casing The HM2 Motor Casing

This is a view of the HM2 motor casing all assembled. The top is a special plug we made so we can use the combustion chamber as a mold for the HTPB; this plug gets replaced with a nozzle cap during normal operation. Missing from this picture is the N2O tank and all the fittings.

HM1 Hybrid Rocket Motor

The task of the Cal Poly Space Systems Propulsion Team was to provide a hybrid motor for use in the Rocketoon project. Previously CPSS had used a Rattworks K240 hybrid motor for Rocketoon testing, but these tests were limited to ground tests only because the K240 lacked the ability to store the oxidizer liquid over long periods of time. Because a balloon launch required a safe storage mechanism for the liquid oxidizer it was decided that the Propulsion Team would design and create a hybrid motor capable of storing the oxidizer for a period of time before igniting and firing.

CPSS Hybrid Motor Version 1 (HM1) was designed with the Rattworks K240 as a reference. HM1 used the same polypropylene fuel grains as the K240. This meant that the HM1 and K240 combustion chambers had the same diameter and length, about 2.5 x 12 inches. Also, the amount of nitrous oxide needed would be the same. An aluminum Catalina Cylinders 9007 tank with storage capacity of 103 in3 was given as a sample to CPSS at no cost. The Catalina 9007 tank is rated to 1800 psi, and provides a safe means of storing nitrous oxide. On the K240, the combustion chamber and nitrous oxide container are in the same aluminum tube. Using a separate tank for nitrous oxide in the HM1 allowed for the weight of the oxidizer fuel to be moved forward in the rocket and thus move the rocket CG forward and increase stability. During early testing of HM1, standard industry tank valves were used for sealing the nitrous oxide tank. However, through testing it was found that standard tank valves were either too large for the Rocketoon body or did not allow for enough mass flow. Also, the lack of a good vent system on standard valves made filling the oxidizer tank a difficult task. CPSS with the help of the Cal Poly Mechanical Engineering hangar machine shop machined a tank fitting to both seal the oxidizer tank and enable gas venting during filling.

Oxidizer flow was controlled with a Holley Performance Super Pro Shot solenoid specifically designed for automotive nitrous systems. Even though the Super Pro Shot is rated at requiring 12 volts and 8.6 amps the CPSS Electronics team found a way to cut the power usage of the solenoid to the point where it could be used onboard the Rocketoon.

The combustion chamber and oxidizer injector provided a machining task that was far beyond the capabilities of CPSS. Duke Energy of Morro Bay generously offered to machine the HM1 combustion chamber and injector at completely no cost. Many hours went into the machining and the result was a pristine aluminum chamber and injector. It is no exaggeration to say that without the help of Duke Energy, Cal Poly Space Systems would not have been able to build a hybrid motor.

Successful static firing of the CPSS Hybrid Motor Version 1 was first made on January 27 at the Cal Poly Test Cell. The first two test firings both used a direct oxidizer line from the large nitrous oxide storage tank. The third test firing used the flight capable Catalina Cylinder 9007 tank. After three successful static tests it was decided to move onto tests for measuring thrust. A swinging horizontal test stand was build to be used in thrust measurement tests. The decision to use a horizontal test stand was prompted by the large hole in the asphalt cause by the successful vertical firings of the hybrid motor. After several failed firing attempts a successful thrust measurement test was made on May 5. The peak thrust was 70 lbs and the average thrust was 41 lbs.



Please note this site is under construction, as of Jan 22 2013.