Hand crank

[GN]

I was watching the mil. channel the other day. It was about WW2 fighters. Why did they hand crank the motors for startup? Was it to charge the magnetos?

[Magnumcharger]

Priming the fuel pumps, and circulating the oil....from what I've heard.

[Nacho-RT74]

maybe because they didn't have starter motor ?

[Arthu®]

Combine the last two answers and you have the answer I believe. It has been a long long time but I asked myself the same question and I remember reading somewhere that they actually did it twice, the first time to oil and prime the fuel pumps with the contact switched off, than they would switch the contact on and crank it again to start it.

Arthur

[Troy]

I say oil circulation. I think they all had starter motors in WWII.

Troy

[Nacho-RT74]

Bombers maybe yes, but I thing not every fighter, specially earliers

[Troy]

I think the last hand-started plane in WWII was the Stuka. Of course, I'm usually only thinking of US planes too. Many other planes had a hand crank on the side to wind up an inertia stater or magneto.

After further review, rotating the propeller by hand was used to "clear" the cylinders of oil which may have seeped in while it was sitting (especially radials). Depending on the engine and plane it may also have been to "prime" the cylinders with fuel.

The larger engines (bombers and big fighters) would have been nearly impossible to start by yanking on the propeller by hand.

Troy

[b5blue]

Near as I can figure the radial engine will pool oil in the bottom cylinders and they spin it clearing the cylinders to prevent hydrostatic lock on start-up.

[PocketThunder]

I was just thinking how do the piston rods connect to the crankshaft on a radial engine.  This picture answers my question.  I suppose the firing order has to be 123456789...

[PocketThunder]

You can find all kinds of stuff on the internet..  Who would have thought to put an aircraft engine in a motorcycle.. 

[b5blue]

If you look into the "Wasp" line of engines you will find the Germans and Fiat used a licensed copy against us in the early stages of WWII! Also note the difference between a Rotary and Radial aircraft engine.

[LeadfootBob]

An interesting fact: during WWI, certain fighters (like the Sopwith Camel and Fokker Dreidecker) had the crank mounted to the airframe with the whole engine spinning around it
This made for some interesting flight characteristics, the Camel being notorious for killing rookie pilots banking/turning the wrong way during takeoff and low altitude flight. They were supposedly the fastest turning fighters in the whole war... In one direction at least 
As to why they did this... Beats the hell out of me. Oiling? Cooling?

[mopar73]

The Hucks Starter

An early advance in the development of aircraft engine starting was the invention of the Hucks starter, which was named after its inventor. This unit was an external mechanical starter, employing a Ford motorcar chassis. A special chain from the gearbox was made to drive a layshaft mounted high up and adjustable. At the forward end of this shaft was a coupling which could be made to engage with a special "dogged" fitting attached to the propeller hub in the same manner as a motor-car crank handle was used to engage the engine crank shaft. Starting was effected by engaging the coupling and rotating the layshaft. Disengagement of the driving dog from the engine was automatic upon starting of the engine. The Hucks starter, although an improvement over the method of hand swinging was in turn, very impractical. Delays in starting occurred when there were a large number of airplanes to be started. Also, it was sometimes out of action or did not exist at places where a start was required. At the same time, it must be remembered that engines were increasing in size and compression ratio to the point where swinging of the propeller by hand as well as turning the propeller mechanically by means of the Hucks starter were impracticable. This brought about the development of the hand turning gear, which is used in a modified form at the present time for certain aircraft installations.

Hand Turning Gears



The development of the band turning gear type of aircraft engine starter was primarily due to the need for an aircraft engine starter capable of cranking engines rated up to 600 horsepower not equipped with batteries or generators. The hand turning gear consists, in general, of a gear reduction unit, which operates an automatic engaging and disengaging mechanism through an adjustable torque overload release. Mechanical features are incorporated in the unit to safeguard both the operator and starter from injury in case of engine backfire. In case of the engine backfiring, the torque overload release automatically disconnects the starter drive, thus preventing damage to the starter mechanism. As a further protection to the operator, a ratchet is provided in the hand crankshaft to preclude the possible transmission of any reverse motion to the crank-handle. Unusual care is exercised in the design and manufacture of a hand turning gear to eliminate friction, thereby assuring maximum even cranking. In addition, the ratios of the gear reductions used have been carefully determined in order to permit the highest engine cranking speed consistent with the average manual effort which can be expended in cranking. Thus, the operator is assured of a prompt start with minimum effort, provided the other factors which influence engine starting are normal.

[John_Kunkel]

It depends on what you mean by "hand crank"; radial engines and inverted inline/V12 tend to puddle oil in the bottom cylinders when they sit, so the props are turned by hand at least two full revolutions with the ignition off to prevent hydraulic locking when the starter is engaged.

If you mean turning a crank handle on the side of the fuselage just behind the engine, this is called an "inertia starter". Turning the crank handle gets a heavy flywheel spinning up to speed and the inertia in the spinning wheel is coupled to the gearbox by a clutch to turn the engine over for starting.

Here's a video of an inertia starter in use:

http://www.youtube.com/watch?v=WkPFRpbSU9o

[mopar73]

Gotta love the Radial Engine!!

[PocketThunder]

Here's a video of an inertia starter in use:

http://www.youtube.com/watch?v=WkPFRpbSU9o

Thanks for that.  that was really cool.