Largest general production American car engine

[LSLGuy]

No gearing between the prop and crankshaft.

Here’s a mid WWI rotary (not radial) engine Le Rhône 9J - Wikipedia . 9 cylinders, 900 cubic inches and 5:1 compression. The prop blade lever arm would be 2-1/2ish feet where you grip it out of a ~6 foot total diameter.

Here’s a typical late WWI V-type engine. Around 700 cubic inches and around 5:1 compression. Hispano-Suiza 8 - Wikipedia. The prop lever arm would be similar or a few inches bigger at most.
As engines got bigger at and immediately after WWI but before the advent of electrical systems they invented an inertia starter. In this system a crewman used a hand crank to spin up a heavy flywheel over, say, 30 seconds of cranking. Then he’d step aside and the pilot would engage a clutch that connected the flywheel to the crankshaft to spin the engine for at most a few revs before the flywheel ran down. Lather, rinse, repeat as necessary. But it was far safer and more reliable than hand-propping.
These engines Pratt & Whitney R-985 Wasp Junior - Wikipedia and Lycoming R-680 - Wikipedia dates from the interwar years.

They were equipped with an inertia or electric starter and generally swung a 4ish foot blade giving an 8-9 foot prop diameter and a 3 to 3-1/2 foot lever arm for hand-propping when necessary.

I have hand propped one of these Pratts on an airplane with a dead battery. That was not one of the smartest risk/reward decisions in my life. The effort required isn’t all that high even for a smallish guy like me. It takes a good hard pull, but it’s not a gut-busting one time effort.

The hard part is the prop hub and hence horizontal blade you’re grasping is about 7-1/2 to 8 feet above the ground, so you’re working on almost tiptoes to get enough hand onto the blade to get a good grip. Because the airplane is a taildragger, the prop arc tilts back which means it sticks out towards your knees. So you have to lean *into *it to swing it, but then immediately back away from it to avoid being killed when it pops, farts, or starts. Hope you don’t fall forwards into it.

Hook your fingertips over an interior doorway’s top moulding and try to yank it down off the wall while standing with your feet back about 18-24". That’ll give you a feel for the ergonomics. Now imagine the door was about 8" taller.

[Robot_Arm]

@LSLGuy

As engines got bigger at and immediately after WWI but before the advent of electrical systems they invented an inertia starter. In this system a crewman used a hand crank to spin up a heavy flywheel over, say, 30 seconds of cranking. Then he’d step aside and the pilot would engage a clutch that connected the flywheel to the crankshaft to spin the engine for at most a few revs before the flywheel ran down. Lather, rinse, repeat as necessary. But it was far safer and more reliable than hand-propping.

Interesting. There’s a scene in The Great Escape where James Garner and Donald Pleasence are stealing a plane to fly out of Germany. It’s a trainer, I think; Garner has Pleasence turn a crank on the left side engine cowling. Sounds like an inertia starter (if the scene was accurate at all).

Speaking of movie scenes of starting airplane engines, there’s also Flight of the Phoenix. Their starter uses shotgun shells to get the engine turning, somehow. Seems possible (although they get a lot of rotations out of just one shell), but I don’t know if any real engine ever worked that way.

[running_coach]

@Robot_Arm

Interesting. There’s a scene in The Great Escape where James Garner and Donald Pleasence are stealing a plane to fly out of Germany. It’s a trainer, I think; Garner has Pleasence turn a crank on the left side engine cowling. Sounds like an inertia starter (if the scene was accurate at all).

Speaking of movie scenes of starting airplane engines, there’s also Flight of the Phoenix. Their starter uses shotgun shells to get the engine turning, somehow. Seems possible (although they get a lot of rotations out of just one shell), but I don’t know if any real engine ever worked that way.

Coffman engine starter.

The Coffman engine starter (also known as a “shotgun starter”) was a starting system used on many piston engines in aircraft and armored vehicles of the 1930s and 1940s. The Coffman system was one of the most common brands; another was the Breeze cartridge system, which was produced under Coffman patents. Most American military aircraft and tanks which used radial engines were equipped with this system. Some versions of the Rolls-Royce Merlin engine used in the British Supermarine Spitfire used the Coffman system as a starter. The Hawker Typhoon also used the Coffman system to start its Napier Sabre engine.

A derivation of the Coffman starter was used on a number of jet engines, including such engines as the Rolls-Royce Avon, which were used in the English Electric Canberra and Hawker Hunter.

[LSLGuy]

ETA: ninja’d by running coach quoting the wiki I linked to below.
Here’s a real nice vid of an inertia starter in use: N3N inertia start - YouTube

The “shotgun shell” starter was real: Coffman engine starter - Wikipedia. That later morphed into something used on early jets. See http://boards.straightdope.com/sdmb/showthread.php?p=19941920#post19941920 and several subsequent posts for more on both.

[jz78817]

another little tidbit- the sound of an inertia starter cranking an engine was used by Lucas as the sound effect for the Millennium Falcon’s hyperdrive conking out.

Hand-Cranking the Inertia Starter on Restored 1934 Boeing P-26 "Peashooter" Fighter Plane !

Hyperdrive Failure: The Empire Strikes Back (1980)