Figure 12 Test stand for small liquid-fuel rocket engines.
Figure 12 shows schematically the proper arrangement of components for a safe rocket engine test stand. The rocket engine is separated from the propellant flow control valves by a 1/8-inch thick steel barricade. The engine is firmly attached to a section of steel channel in the nozzle down position. This is the safest orientation for a liquid-fuel rocket engine since excess fuel, in the event of an ignition failure, simply drains out of the engine nozzle. The engine is mounted high enough from the ground so that no flame chute or other complicated exhaust deflector or fixture is required. The compressed gas cylinders (one nitrogen and two oxygen) are mounted at the rear of the test stand and are separated from the control valves compartment by another barricade made from one-inch thick plywood. The nitrogen and oxygen regulators are mounted on this plywood barricade above the cylinders. In this manner, expended cylinders may he replaced with charged cylinders without disturbing the regulators or plumbing. A formed piece of stainless steel tubing between the oxygen manifold and the oxygen regulator and a similar piece of tubing between the nitrogen cylinder and its regulator are removed during cylinder exchange, and then reconnected. Lines should always be capped when not in use to prevent entry of dirt and other foreign objects.
The fuel tank is mounted beteeen the forward steel barricade and the rear plywood barricade on a metal cross-piece attached to both barricades. The tank is mounted in the vertical position with the liquid outlet at the bottom.
The propellant flow control valves are mounted one atop the other in a metal bracket which is attached to the forward steel barricade. Panel mounted needle valves are recommended since they facilitate mounting in the manner described, and do not place mounting or operating stresses on the propellant flow tubing. Valve stem extensions, made from 1/4-inch pipe permit operation of the control valves from the operator's remote control station, which is located at least twenty feet from the test stand proper. Pressure gauges for fuel tank pressure, oxygen line pressure, cooling water exit pressure and combustion chamber pressure are mounted in a panel which is attached to the forward and rear barricades and which faces the operator's remote station.
Cooling water for the rocket engine is brought into a hose coupling attached to the stand, with semi-permanent plumbing between the coupling and the rocket engine. Water flowing from the cooling jacket should be directed away from the engine or can be directed downward onto a 3-inch deep layer of coarse stones laid beneath the roeket engine exhaust. These stones will prevent the engine exhaust from picking up dirt and dust; the water will cool the stones and extend their useful life. The jet of cooling water can be observed by the operator as an indication that cooling water is actually flowing through the engine.
The test stand proper should have a framework made from welded or bolted steel angle. The forward steel and rear plywood barricade are bolted to this angle framework providing rigidity and strength. Thee test stand should be firmly attached to the surface Of the test area either by bolting to a concrete pad or by weighing down with sand bags or concrete weights.