Manual pre-start prop turning.

[pjpahs]

When I took rides in the B-17 "909" and B-24 "Witchcraft" the "Riders" were given the task of giving the pilot so many prop tips to clear the lower cylinders. I found that the B-24 1830's were easier to turn than the B-17 1820's and we turned them counterclockwise when viewed from the front of the aircraft. I was watching some video of WW2 and the ground crew was turning the props of a B-25 R2600 clockwise ,looking from the front. Is this an issue or does it really matter? Turning them the way they turn when working seems correct, and wouldn't that also get the oil pump to prelube . When I flew in "Panchito" I was given the priviledge of turning on and off the engine pre-lube pumps , so I guess I was part of the" Flight Crew" (yeah right).

[Dan K]

Pipjahs,

You absolutely must read this link to understand the importance of hand turning props (and especially why you never, never, ever rotate the prop backwards!).

Enjoy the read!

http://www.douglasdc3.com/sohn/1.htm

[pjpahs]

I may have been a victim of viewing a film where the negative was reversed. What I thought was the ground crew going backwards on the #1 engine, pushing the prop bottom towards the fusilage was actually the #2 engine being turned correctly only the film being reversed. The video is at "work" and I'll get it tomorrow. If there was" nose art" or numbers I didn't notice, and the article from Douglas was very informative, thanks. But why did it seem easier to turn the 1830 than the 1820. 14 cylinders against 9 cylinders?

[b29driver]

I may have been a victim of viewing a film where the negative was reversed. What I thought was the ground crew going backwards on the #1 engine, pushing the prop bottom towards the fusilage was actually the #2 engine being turned correctly only the film being reversed. The video is at "work" and I'll get it tomorrow. If there was" nose art" or numbers I didn't notice, and the article from Douglas was very informative, thanks. But why did it seem easier to turn the 1830 than the 1820. 14 cylinders against 9 cylinders?

1830/14=130.7 cu/in per cylinder
1820/9= 202.2 cu/in per cylinder
I don't recall for sure, but I seem to recall a higher compression ratio on the Wrights and there is a difference in nose case reduction ratios.

[robkamm]

good article Dank. my ground running r4360 puts a lot of oil into the lower cylinders. Pratt put a lot of drain plugs on the lower intakes to help drain it. if i let it sit for a few weeks ill get 1/2 gallon or so of oil out of it. we hand turn the engine before we start it and it still pushes a lot of oil out of the lower cylinders. i think it would easy hydo lock real easy if not drained.

[The Inspector]

good article Dank. my ground running r4360 puts a lot of oil into the lower cylinders. Pratt put a lot of drain plugs on the lower intakes to help drain it. if i let it sit for a few weeks ill get 1/2 gallon or so of oil out of it. we hand turn the engine before we start it and it still pushes a lot of oil out of the lower cylinders. i think it would easy hydo lock real easy if not drained.

Or tweek a link rod, not a happy thing!

[Glenn Wegman]

I'm pretty sure P&W warns against pulling the prop through by hand on R-2800's and recommends using the starter. The starting system incorporates a clutch that is supposed to be set to slip before internal engine damage can occur. Pulling on a six and a half foot or longer prop blade can exert far more torque. If the engine does not turn from hydraulic lock you need to drain the cyls, not pull harder.

Inertia starters are a whole different thing.

I'll give an example using an engine that doesn't need pulling through since I know the numbers for that. A Merlin has a starter clutch set to slip at 300 ft lbs of torque. A 200 lb person hanging on an 18" bar will exert 300 ft lbs of torque. The propeller is 11'2" so a 200 lb person hanging on the prop tip can exert 1100 ft lbs of torque.

[jcw]

Hi Glenn

I can tell you that the props were NOT pulled thru backwards as Mac would turn you into a grease spot on the ramp if you tried. If you don't know what you are doing then use the starter.

Glenn, just got off 16 days with them and 34 hrs of "C" time.. Learned more about the gear than i ever thought possible..

take care

jcw

[b29flteng]

We use the starter only on FIFI. The starters have a built in clutch designed to release if necessary and it works quite well. With 3 people pushing an eight foot long blade, they will miss a "hydraulic locked" cylinder and push right through it. The R-4360s on the KC-97 and B-36 were turned with the starters too, 8 blades on FIFI and 20 blades on the KC-97 and B-36. Without a pre-oil pump installed you're not pre-oiling by pulling the prop through.

[DC3R4DC47]

most of the Dougs flying today have the clutch type starters that will slip in case of hydraulic lock,that being said at the YAF we still pull the blades thru before start, better safe than sorry.

[CAPFlyer]

I'm pretty sure P&W warns against pulling the prop through by hand on R-2800's and recommends using the starter. The starting system incorporates a clutch that is supposed to be set to slip before internal engine damage can occur. Pulling on a six and a half foot or longer prop blade can exert far more torque. If the engine does not turn from hydraulic lock you need to drain the cyls, not pull harder.

Never saw that warning in the R2800 books for the CV-240. We pulled the props through, but it was one person only and we never forced the blades through. As for the clutch, it's great and all, but you'd better be sure it's working right. I know of a DC-3 which had a clutch that failed and almost blew a cylinder head because of it.

[pjpahs]

Just reviewed the WW2 video "Timeless Video-Wings of Glory- and it did show the B-25's prop being pulled backwards. The nose art was not reversed , the Jeep had the correct left hand drive, the ground crew was pushing the "fat" ,leading edge clockwise looking from the front. Maybe they did this as a prank knowing they were being filmed and being 19-20 year old men they were pulling someones chain. If anyone has this video collection it's in the beginning of chapter 13-"expanding air power June 1943", right after the officers training school segment on the support officers. Has some footage that I haven't seen and is actually pretty good.