Hybrid cannon
A hybrid is a type of spudgun that combines principles of the combustion and pneumatic spudgun. It uses a pressurized mixture of fuel and air to get more power out of a given chamber volume. The hybrid is capable of higher velocities than a combustion or pneumatic spudgun, projectiles fired by a hybrid have broken the sound barrier (Source). This is possible because of the higher pressure and temperature gasses.
A hybrid launcher consists of seven basic elements:
- High pressure combustion chamber
- Pressure-triggered main valve (usually a burst disk)
- Barrel
- Fuel system (usually metered propane)
- Air filling valve
- powerful Ignition source
- One or more pressure gauges
opperation therory
A hybrid is first injected with fuel, then with pressurized air. The amount of air depends on how much fuel was added, and is calculated to achieve a stoichiometric fuel/air ratio in the chamber. A hybrid using twice as much fuel and air as a comparable combustion gun is said to be using a 2X mix, higher mixtures can be used and will produce even higher pressures. The fuel and air needs to be measured and matched carefully to ensure reliable operation, pressure gauges and fuel meters are used for this.
The ignition of a hybrid gun is more difficult, as the length of a spark is roughly inversly porpotional to the density of the gas. This neccicitates the use of high-powered ignition source such as a stungun.
The resulting gasses are released to the barrel via a self-operating valve of some sort, most commonly a burst disk because of it's simplicity and reliability, although self-venting piston/diaphram valves have been used. Appon ignition of the fuel-air mix, the pressure rises and the valve opens.
Safety
A hybrid is the most dangerous launcher that can be built. It is advised to build with pipe that can handle the high pressure environment (200+ PSI) such as Sch. 80 PVC or metal. Remote ignition is a must, and the limit of a 4x propane/ 4 atmosphere mix should never be breached. If a higher mix is attempted, DDT (deflagration to detonation transition) can occur, causing an extreme pressure spike. Most pipe cannot handle the spike, and will shatter, launching plastic shards every where. Therefore utmost care must be taken with these launchers.
