The page was developed to share information on commercially available hybrid rocket motors. Hybrid motors consist of one solid component, and one liquid component. For all hobby hybrids, the oxidizer is the liquid, and the fuel component is made from plastic or cellulose. Nitrous oxide, (N20) is the oxidizer of choice because it is self pressuring, and has a high oxygen density. It is stored as a liquid under pressure. For N20 to release it's oxygen, it must be heated to over 500º C. The easiest way to reach this temperature in a motor, is to ignite a "pre-heater" slug of propellant before adding the N20.
For a person just getting involved in this area of the hobby, there are several choices of hybrid technology, each being produced by different manufacturers.
1. Aerotech Hybrids (except M-845)
2. Hypertek Hybrids (except L and N)
3. R.A.T.T. Works Hybrids (monotube)
AT hybrid motors work by prefilling a flight cylinder with N20. The flight cylinder is then screwed on to a special 54 mm front closure. The front closure contains a "pyrovalve" disk that seals the gas in the cylinder until after motor ignition. When the flight cylinder is screwed into the front closure, a valve similar to a tire valve stem is actuated, and allows the N20 to flow into the closure, where it is restrained by the pyrovalve. The flow of N20 is controlled by 2 to 4 jets, that can be plugged or opened as required for each motor configuration.
The motor itself is AT's 1280 casing, using special reloads. The reloads contain from 1 to 5 grains of AP and cellulose, (paper) grains. The AP grain is lit by e-match, which then ignites the pyrovalve. When the pyrovalve burns through, the N20 is release into the combustion chamber of burning AP, releases it's oxygen, and burns the cellulose aggressively!
To fill the flight tank with N20, you must first chill it. I put mine in the freezer for a coupler hours, and it fills easily. In the field, you must partially fill, then vent some of what you filled to "shock cool" the cylinder to a temperature where you can fill it completely
AT's motors do not need any special launch pad equipment. The entire system is self contained, and can be used off of any standard rod or rail. To use this system, you need a cylinder of N20, a fill hose, a scale accurate to +/- 2 grams, and the AT motor. Approximate costs of the system are:
| 20 lb N20 Cylinder | 100 |
| Scale | 100 |
| Fill tube | 70 |
| Total | $270 |
Approximate costs to fly the system are:
| Motor | $300 ($200 if you have the 1280 casing |
| Reloads | $26-40 |
Per flight costs are $26-40 per reload kit + $3-5 N20. The $26 load is a small J, the more expensive 5 slug reload is almost a K.
Hypertek (HT) hybrids are the only pyrogen free rocket motor currently available. The motor consists of an aluminum flight tank and an ABS plastic fuel grain, both 54 mm. HT also makes a "hammerhead" flight tanks that used the same grain, but has a 3.2 inch diameter tanks that holds 835cc's of N20 for almost twice the total impulse. There is no casing to hold the grain, the ABS is strong enough to hold the pressure on it's own. After a flight, the grain is thrown away, and a new one can be screwed on. Cleanup is minimal. The complexity of this system is in the Ground Support Equipment (GSE). In this system, the empty flight cylinder with grain are loaded into a rocket, and the rocket is put on a special pad. The pad has a "stinger" system of 2 steel tubes that the rocket is slid onto. One of the tubes goes up through the grain and seals by o-ring into the flight cylinder. This allows the N20 to be remotely filled. The second tube goes into the grain, but does not reach all the way to the flight cylinder. This tube supplies gaseous oxygen (GOX). The last part of the system is the high voltage supply. This supplies 7500V to a speaker wire igniter. The motor also has to be tied down to the pad so that when the N20 tank is filling, the pressure won't lift the rocket off the pad.
To ignite the motor, after it is filled with N20, the GOX is turned on, which pours into the combustion chamber and escapes though the nozzle. At the same time, the 7500V is turned on, causing an electrical arc high up in the combustion chamber. In the GOX atmosphere, the arc produces a substantial flame, starting the ABS to burn. When the flame coming out of the nozzle melts through the tie wrap holding the rocket to the pad, the rocket begins to move up off of the N20 fill tube. As soon as the fill tube pulls out of the O-ring seal, the N20 pours out into the burning ABS, instantly producing the required thrust.
Use of HT motors requires GSE. The ROC club has two systems available. The GSE has a suggested price of about $550, and that does not include supply cylinders. Approximate costs to fly the HT system:
| Flight cylinder | $125 for 440cc (+$25 for 835cc) |
| Reloads | $25 |
These motors are made from a single aluminum tube. A floating bulkhead separates the N20 side of the tube from the fuel grain side. Grains are made from polypropylene pipe, with a graphite nozzle. This motors come in 29mm H and I motors, and 2.5 inch L motors. In this system, N20 is loaded remotely, through a U/C valve. This is a piece of high pressure nylon tube than connects from the supply tank to a connection in the floating bulkhead. When assembling these motors, a small slug of AP is inserted into the grain just below the floating bulkhead. The fill tube runs through the hole in the AP slug into the bulkhead. To ignite the motor, an e-match ignites the AP, which in turn melts through the N20 fill tube. As it burns through, the N20 is released and the motor fires. The nylon fill tube is replaced after each flight. The HT GSE can be used to load and fire this system. An adapter to connect the HT fill tube to the RATT nylon tube must be fabricated. In addition, Pratt Hobbies will be introducing a new N2O control system for the RATT style of motor. Approximate costs to fly this system are:
| Motor H, I, L | $60,80,295 |
| Reloads | $8,8,33 |