Why did people turn aircraft propelers by hand?

Answer 1

To start the engine. Early propeller planes had no electric start system as we are accostomed to in automobiles. Turning the propeller to start the plane engine (a very dangerous task, by the way) was akin to roll-starting a car with a bad starter or solenoid. (That was a pretty common practice when cars were less reliable that way and mostly had manual transmissions). Also, then and now, the engine had to be turned to clear each cylinder and prime it with fuel. In the old aircraft, they would turn the engine with the "Swith Off" and then give a command "Swith On" to start it. Later aircraft, had a hand-crank to start the engine. Even aircraft as last as the WW2 Ju-87 Stuka used a hand-crank starter. Many of the early WW1 aircraft had Rotary Engines that were 7 or 9 cyclinders. These are NOT the same as Radial Engines. Rotary Engines were designed so that they rotated on a fixed shaft. The propellor was bolted to the engine and spun when the engine rotated. This meant that when a Cylinder was in one position, fuel was injected, it rotated to another position and it fired and another position it expelled the gasses. So, clearing the cylinders were important part of starting a Rotary Engine. If you can find a real movie clip of a REAL WW1 airplane, you can see the engine rotating. Even photos may show it blurred. Some aircraft with Rotary Engines were Fokker Eindecker, Fokker Dr.1 Triplane, Nieuport 11 & 17, and many of the Sopwith airplanes. See Link for a cool animation of a Rotary Engine. Notice that the Cylinders are attached at one point that is off-set from the center of the rotating engine block. These are notes from the film crew of the movie "Blue Max" for the in-line engine SE-5. Starting

Chocks in place and fire extinguishers at hand. Fuel cockON (Push on), throttle CLOSED, switches OFF. Pull ring at top, right hand side of instrument panel until ground crew confirm that fuel drips out of the carburetor overflow pipe below the cowling. Prime with one to two full strokes of the Kigas primer while the propeller is turned over. Do not over primeor you may start an intake fire.

Throttle set at half an inch OPEN, both switches ON and press the starter button.

After starting, check for normal oil pressure and warm up at 1000- 1200 r.p.m. for 5 minutes when cold. (Oil temperature may not register in this time) Stick hard back during run up. Check for a dead cut, normal static revs 2100. Select hot air (Turn T handle and pull) and check that the engine note changes or the r.p.m. drops indicating that the control is serviceable. Return the cold air. The acceptable magneto drop is 100 r.p.m. Check the oil pressure is normal and the slow running 6 - 700 r.p.m. Same source--but not very detailed. The cockpit layouts in the two aircraft have important differences. Both have fuel and oil cocks. The fuel and oil cocks should be switched OFFbetween flights to prevent flooding of the lower cylinders. Both switches can be used for starting. Hand swinging of these engines can be tricky and the ground over will probably call for the switches OFF between each movement of the propeller.

The engine should be thoroughly warmed up before run up or it may run rough at full throttle. The carburetor heat is permanently but relies on the engine being well warmed. The correct static r.p.m. for each machine is noted on the instrument panel. If this is not obtained the cause is usually both plugs in one cylinder are not firing. The engine will then appear to run normally with little or no mag. drop but the faulty cylinder will be cold to the touch.