Can you guess what he is doing?

Spinning a flywheel so it can be engaged by a clutch to turn over the engine and start.

This man is starting a Proctor-Gamble PBJ-7 Porky biplane using the manual crank. The Porky was affectionately referred to as the "Hog," so his man is demonstrating what ground crews called "cranking his hog."

Spinning the Tasmanian Devil inside so that he can start the plane

Winding up that rubber band thingie.

That’s where the rubber band is wound

grinding coffee

winding up the big rubber band that engages the magneto flux capacitor starting mechanism to align the di-lithium crystals for warp drive? contact!!!

When safety was an afterthought. “Hey don’t worry you’ll be 2 feet away from the prop when it starts spinning. “

cranking up the inertial starter. And if the pilot screws up and doesn't get it started the first time, he'll have to do it again, and not be happy about it.

It's a hand cranked inertia starter. When it's spinning fast enough, a clutch mechanism is engaged to transfer the flywheel's flywheel's kinetic energy to spin over the engine and fire it up so long as the pilot hasn't forgotten the ignition and fuel switches...

The starting sound is also the sound for the millennium falcon stalling

When he turns that handle it releases food for the hamster that then run around the hamster wheel. The wheel is connected to an inertia starter that will start the engine once the hamsters have built up enough energy.

inertia starter, wait till he gets in the cab and does the wobble pump

Winding up a spring that turns the engine over when released.

I like the the engines that are started by an exploding shotgun shell.

He's turning the inertial/centrifugal starter. "Winding" is not really accurate here. Get the flywheel spinning fast then the pilot hits the mesh switch to engage with the engine.

Using a crank operated inertial starter to start the engine of a bi-plane

Getting knackered

Inertial starter

Cranking up the big rubber band

Winding it up

Jorkin it

Inercial starter

Spinning up the flywheel

Trying to roll down the window.

Winding that plane’s watch so it can tell when to stop flying.

Our DHC2 Beavers had an inertial starter a darn sight safer than swinging the prop on an Auster, Just put the handle in and wind it up, 4/5 pumps of the wobble pump, Switch the mags on and "Start", Still preferred having a servicable battery though.

Either trying to die, or doing the new Airplane dance

Winding up the inertia starter?

Winding up the rubber band that turns the propeller?

Winding the rubber band

Whiffing up the rubber band

Spinning the flywheel for an engine start.

Setting the clock. They were strange like that.

All planes are powered by big watch springs.