A mechanic manually turning the engine on a B6N2 torpedo bomber to prevent hydraulic lock, date unknown

Caption   A mechanic manually turning the engine on a B6N2 torpedo bomber to prevent hydraulic lock, date unknown ww2dbase
More on...   
B6N Tenzan   Main article  Photos  
Added By C. Peter Chen
Added Date 21 Mar 2007

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Visitor Submitted Comments

1. Commenter identity confirmed Bill says:
22 May 2011 11:24:22 AM


What is hydraulic lock? In large radial engines oil would collect in the lower cylinders. The propeller had to be swung to clear the oil, otherwise the engine could be damaged or even destroyed, the oil in the bottom cylinders would compress on firing. This also explains the smoke when the engine is fired up.
Ground crews swing the prop by hand before start up and the smoke after starting is caused by oil leaks past the valve guides of the lower cylinders.


One, Two, Three, Four it ensures that the bottom cylinders are free of oil, and oil can collect in the upside down pistons of a radial engine. Hydrolock, if the start hits a
cylinder full of oil, it just stops, if the engine fires it could blow the cylinderhead off turning the props also opens the exhaust valve and drains the oil.
So counting the blades ensures the engine has turned through one full cycle of each cylinder.
When the ground crew is finished the pilot
switches on starts and Bang, Smoke and Flames
the engine is running there is no other sound in the world like a big radial engine it just says power!
These big radials were designed without any computer adds, just solid engineering, slide rule and calculations.
This is what I remembered about swing the props. it was dangerous but everyone did things by the book.
Photograph of Nakajima B6N2 Tenzan (Heavenly Mountain) Torpedo Bomber the "Jill" could belong to the 752nd or Yokosuka Kokutais.
2. Commenter identity confirmed Bill says:
29 May 2011 08:42:27 PM

KO-B6-11 Nakajima B6N2, Model 12 Tenzen (Jill) was a three-seat torpedo naval bomber.
Operated w/First Naval Air Technical Arsenal
or(Dai-Ichi Kaigun Koku Gijutsusho)aircraft
was used for tests.

1268 "Jills" were built during WWII like most
Japanese aircraft, they were used in Kamikaze
attacks against the US Navy.

One "Jill" survives today this aircraft was on outside display for years, at Willow Grove
NAS, Pa. aircraft has been transferred to the
National Air & Space Museum, Washington D.C.

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