Warbird Information Exchange

Can anyone with the knowledge, tell me the difference between the R-2800-31, and the R-2800-71? The -31 is what powers the PV-2 Harpoon, and I was told that the -71 is what was installed in the B-26 (Douglas) I am hoping that there will be no installation problems of the -71 in the PV-2, for static display purposes....Gary

The -71 is slightly more powerful than the -31, so there may be some accessory changes which is usually what causes a change in desigantion rather than any major changes in output and front-end items. The only book I have that covers the R-2800 variants is on the Corsair and neither version was used on the Corsair, so I can't help much more than that.

For the most part on the P&W 2800 series of engines the dash number will denote a certain change or specific installation purpose. I know dash model number changes that were for different nose case gearing, or different accessory case mounting etc.. For the purpose of bolting an engine up for a static display you should not have any issues.
Now that if my memory serves me correct, it has been a long, long time since I got to tinker with a radial engine.
Scott……

I'm pretty sure the main difference was the gear ratio. The props on the A-26 are the same as on the B-25. I believe they have a larger diameter than the Harpoon props.

The -71, -31,-31M1 and the -31M2 all have the same gear ratio, but have different blower sections and accessory drives. There are also two different ignition systems too, and different cylinders. Best bet is to put which ever
-31's you have next to the -71's and make some measurements. If you go to www.faa.gov and download the type certificate and you can find all of the differences.

If it has different cylinders, the nose cowl may not fit correctly.

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

You would have to talk to someone that was extremely familiar with the cylinders for the 2800, or find some kind of documentation in the various P&W manuals to be sure. I suspect that the biggest difference between the two types is that one is a heavier design.

Should be OK as long as the cylinders aren't for a CB engine. They are different from the earlier R2800.

According to the R-2800 book by Graham White, the -31 weighs, dry, 2280 lbs & has a prop reduction of 16:9 & uses DF-18RN mags. They both use the same carb, a Bendix/Stromberg PT-13G1-9, but the -31 can also use a -13F1 or -13F5-8. The -71 uses S-18LG-P1 mags & has a 2:1 prop reduction & weighs 2325 lbs dry. It also says the -71 is similar to the -27 with GE tubular harness. Otherwise, the specs are the same. How much these diffs would make, I dunno. HTH

Hey famvburg;
What is name of that book you have? I would like to find a copy if I could still get one.
Scott.......

I misread the type certificate last night. The -71 uses a 2:1 reduction and not the 16:9. It also has a two speed blower.

The -31 is also a two speed blower, but the 16:9 reduction.

The -31M1 is a -31 with C series cylinders.

The -31M2 is a -31 power section with a C series blower and cylinders.

Accompaning that, there are differences in the accessory drives.

The -31, 31M1 and 31M2 have two gun synchronisers while the -71 doesn't have any. There are other notable differences in what accessory drives are available too.

The -31M2 also uses a different carb than the others.

I haven't seen a copy of White's book, so I don't know if he addresses the other versions of the -31, but there are enough differences between the 4 versions of the engines according to the type certificate, that it would take having one of each side by side to be sure that they would interchange without having to strip the back half of the engine. With so much commonality between so many of the versions, I think that you would have to really look closely at all the installed pieces to be sure exactly what dash number you had on hand, rather than take it on blind faith that it was configured as the dash number on the dataplate.

The m1 designation stands for modification 1. These modifications were often done by some one else rather than Pratt such as an airline or freight hauling company .C series cylinders were some times fitted to a B power section because they cooled so much better. Mr. Whites book is an excellant source of information on The R-2800 engine . He also has written a book on thr R-4360.

It's titled "R-2800 Pratt & Whitney's Dependable Masterpiece". I got mine off eBay, but it shouldn't be too hard to find. As mentioned, he wrote one on the '4360, I think it's called "R-4360 Pratt & Whitney's Major Miracle". Both books go in to a lot of detail & IMHO, are good refs. I'm also a fan of the Wright R-3350 & wish he'd do one it as well.

TG: normally that should be the case, but this appears to be an exception. the type certificate TC5E-8 is owned solely by P&W and is for the military contract engines only. I suspect that the various M versions were due to production parts availability and specific engine installation requirements coupled with improvements from field experience.
As far as the FAA STC/TC online records, there are no STC's for any kind of alternate build-up of R-2800's other than some carb and oil pump mods plus the one for cylinder treating that was issued in 1996. TC-5E-8 is so old that it doesn't even have any of the issue data with it, although someone has added a note that references the FAA in a method that was only used around the time the CAA became the FAA as far as I can tell.
Part of the problem is the R-2800 series was built under two different type certificates at the same time, under two different designations, with considerable parts interchangability with the -97 being the bridge between. TC E-231 directly states that the DW CA-18 can be directly interchanged with the -97 military engine by changing the dataplate to the CA designation and adding the correct TC number. It's a convoluted trail of certifications and I would think that should you have to go to the FSDO about liscensing questions, you would be in for a wild ride.

Cw, Maybe some of that paper work for the modification of R-2800 got lost when The CAA became the FAA. I read an antidote in the Journal of the Aircraft Historical Society of how a company called National Aircraft Sales took r-2800-32w's and r-2800-30w's from Corsairs and Bearcats and removed the two stage blowers and replaced them with single stage CB16 single stage blower along with some other modifications and they were then used for civilan use. The r-2800-32w was then called a r-2800-32 am5