Warbird Information Exchange

Hi All. Hear is a question that has puzzeled me for a while about the V-1710 instalation on the P-38. The aircraft has counter rotating props so the engines are "Handed" My question is... When is this done? Is it done in the engine shop as the unit is built up from a pile of bits, or is it some thing you can do "on the day" when you have just hung the engine onto the aircraft? I can imagine some poor crew chief in a rain soaked East Anglian field, surounded by "Lefties" needing a "Rightie" !!!
Hope that this is an easy one, if not perhaps it will be an excuse to look at some more P-38 photo's

Thank you in advance

Cking

The crankshafts are different as are the camshafts in the -111 and the -113 models used on the P-38L's.

_________________
If God had wanted man to fly behind a flat motor, Pratt Whitney would've built one.

WOW!!! That is an imense difference! I always imagined that it was a just a gear swap/addition in the reduction gearbox housing.
Thanks for the prompt reply, I thought you would all be tucked up in bed in the States!

Rgds Cking

I don't believe all model p-38's had counter rotating props.

regards,

t~

Only the British and French Lightnings did not, which became the P-322 when the British cancelled their orders.

I am not saying you are incorrect but that information is highly contradictory to my experience with the Allison and all the information I’ve ever read or have been told about it. That however does not make my info 100% gospel.

The real beauty and simplicity of the 1710 shines through on this point…as well as the designers ingenious thought process (This I will attest to since I’ve been through one top to bottom). The only major change you have to do to the engines power section when assembling it is to turn the crankshaft end for end and remove an idler gear on each cam drive. I’m not sure what is involved in the blower section but obviously you can’t turn the oil pump and accessories backwards and expect them to work…not to mention asking the blower impellor to compress air while it’s turning backwards! Am I missing something?

John

John you are correct. There are no real parts differences between the -111 or -113 Allison. Just make the mods as you described.

so the engine would actually have a reverse rotation from left to right? I always assumed that it was some magic in the reduction gearing area that made the prop on that engine rotate in reverse, and that both cranks turned the same way.

pretty impressive engineering and foreplanning, especially considering no computers, only slide rules...

cheers

greg v.

You are correct. I think it would have been a lot easier to accomplish the task in the reduction gearing but considering the size of idler gears that would have been required, it would have really disrupted the sleek lines the typical hot water twelve is prized for.

I need to do a little more research into what happens with the accessories. I'm guessing there is a provision for an idler gear on the accessory case input shaft that re-establishes forward rotation in a "reverse" rotation engine. In essence, for the cost of a few gears you can make any engine either a lefty or a righty. Yankee ingenuity! I wonder where along the line GM lost that kind of capable thinking?

John

To change the rotation of RH/LH Allison to opposite you turn crank end for end, change the crank couplers to opposite ends as required. There are idler gears in the accesory case that the locations are changed to a differant position as well as 1 (?) gear that is changed out entirely. The scavenge gears in the nosecase scavenge pump are flip flopped to the other position otherwsie they fill up the pan rather than the oil tank. In either rotation engine the cams, mag and blower turn the same direction.

Sparrow

Thanks for taking the time to ansewer my question Gents! I to would have thought that they would have reversed the direction at the reduction gear end for simplicitys sake.

Thanks a lot Cking

Thanks for the confirmation Mike. I thought I was on the right track. Never gave the front scavange pump a second thought.

John

In the -23 & -25 Merlins, P-82 engine's, they changed the direction of prop rotation in the -25 by the use of an idler in the nosecase of the engine. Merlin cranks turn LH, so by the installation on an idler in the reduction gearing, the prop shaft then turned LH as well.

Sparrow

Thanks SparrowV12. That was going to be another question! Hears another. Why didn't they put two Merlins int a P-38?

Rgds Cking

because the USAAF had too much invested in the Allison, I guess. Apparently Lockheed had the Merlin installation designed, but never implimented it. Allison apparently never used the design info from RR to eliminate/reduce backfiring either. These last two bits of info are from "The Lockheed P-38" by Warren M. Bodie, for what it's worth.

cheers

greg v.