Hand cranking an engine

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What exactly are they doing here? Cranking something but the prop isn't turning. I assume no electric starter so isn't it a problem if the engine stalls while flying?

 
It's an "inertial starter." Turning the crank spins a small flywheel up to high rpm. When it is going fast enough, the other crew member engages a clutch that transfers the energy to the engine crankshaft.

The flywheel can also be spun up by a relatively small electric motor. This would allow attempting to restart while flying, though if an engine stops while flying it usually has a serious problem and isn't going to restart.
 
It's called an inertia starter. Think of a flywheel or other inertia device (spring release) that is first "charged" using the crank. Some aircraft engines literally used shotgun blank shells as an inertia pressure charge to start the engine.
 
... The flywheel can also be spun up by a relatively small electric motor. This would allow attempting to restart while flying, though if an engine stops while flying it usually has a serious problem and isn't going to restart.
Also, if the engine fails while flying, the airflow from forward movement will keep the prop (and thus the engine) spinning. So there's no need for a starter. As soon as you restore whatever was missing (spark or fuel) the engine will be running again. If the prop stops spinning while in flight, a starter won't help you because it means the engine is physically obstructed with serious damage, like a broken piston rod.
 
Doesn't a flywheel add a lot of weight? Why not turn it over by hand at the prop like I see in old movies?
As a pilot who has flown vintage airplanes, I wouldn't mind hand-propping a 100 HP engine. So long as the pilot and the hand-propper both know the procedure, it's safe. But I would not want to hand-prop a 1000 HP engine. 😲
 
Why not turn it over by hand at the prop like I see in old movies?
That only works on small engines like on WWI planes. These have too much friction and compression to turn by hand. In the video there were two people turning the crank to store energy for more than 20 seconds (they started turning before the video starts). A direct hand start only has available the energy of one person for much less than a second.
 
Don't forget air. An iced up intake system will stall an engine.
Indeed. Or a bird stuffs itself into your intake, blocking airflow. So the prop will still be spinning, and you engage the carb heat (alternate air intake) and it roars back into life.
 
Some aircraft engines literally used shotgun blank shells as an inertia pressure charge to start the engine.
I don't think they were actually shotgun cartridges but they were similar looking. They clearly show the flight crew using them in both versions of the movie 'Flight of the Phoenix'. The later version also shows a close up of the starter cartridges themselves near the beginning of the movie. My father was crew chief in the USAF and told me about using them and still had a couple of them around before he died but I don't know what ever happened to them.
 
I don't think they were actually shotgun cartridges but they were similar looking. They clearly show the flight crew using them in both versions of the movie 'Flight of the Phoenix'. The later version also shows a close up of the starter cartridges themselves near the beginning of the movie. My father was crew chief in the USAF and told me about using them and still had a couple of them around before he died but I don't know what ever happened to them.
Yes, Flight of the Phoeninx......I love that old film, I had forgotten about it. THANKS for mentioning that.

They are called Coffman starters.


 
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The hand inertia starter has a gearbox that may have a ratio as high as 1000 to 1. In some models, the small flywheel spins 1000 times for every rotation of the crankshaft.

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Cuejet, thanks for posting that bit of nostalgia information. Like the Coffman starter, I am sure there are many current pilots and A and Ps that have never heard of neither.
 
Doesn't a flywheel add a lot of weight? Why not turn it over by hand at the prop like I see in old movies?
A starter motor (especially one from back in the day), battery, and charging system probably weigh more.
A power cart to power a starter motor without needing a battery is expensive.
The cartridge style starter is probably the lightest, least labour intensive solution but I don't know how much cleaning they needed compared to the flywheel type that probably needed re-greasing every blue moon and not much else.
 
Man, those videos. I clicked on it… and had to watch the whole thing. Doesn’t matter if it’s an O.S. glow plug engine, the radial 7, or a riding mower. Captivates.
 
I worked at an outfit that had an inertia start DC-3. They can be made (inertia starters) to be energized by a motor electrically from the cockpit and also electrically engaged with a solenoid. But if for some reason you need to start the engines and the battery's are almost dead, you can insert the hand crank do the wind up, and then pull a handle that engages the starter. A good system for flying into the back country in places like Alaska.
 
I flew a P&W R985 for years with an electric inertia starter, later converted to an electric direct drive. The inertia starter was lots more fun!
 
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