Is this a real engine?

Pratt & Whitney 5600XBSAP

It was apparently on display at the Reno Air Races, and I’ve found pictures from different angles; so I’m guessing it’s not 'shopped.

I found a website where there is speculation that it is a non-running ‘one-off’ design. I haven’t been able to find anything about it; whether it ever ran, or if it was a mock-up. AFAIK, the biggest radial P&W built was the R4360, which had 28 cylinders. This one has 56, so I assume it was made of two R4360s stacked together. But was it ever intended to run?

bentley sell a 56 cylinder radial engine… today !

There’s a claim that the P&W 56 cylinder doesn’t have the crank shaft inside. Its just the crank case bolted together. Any mock up for P&W would have been broken up to sell as spare parts for the 28 or 14 cylinder wasps…

The crank for a 56 cylinder Wasp Major could be made using todays materials.

BUT the external parts would have to look different to run 56 cylinders…
The inlet manifold has to be twice as big, but that may not be a workable solution (loss of pressure by the end .)… You’d sooner have more manifold pipes… eg one at each end, so it would be divided down the middle.

Thank you.

From the second link:

At Spartan school in Tulsa in 1969 or so we had a picture of a R 7000 that was 4 rows air cooled & 3 rows of water cooled.

We also had a picture of a formation of B-36’s, about 12 or 14 with all engines running. Our Carburetor instructor was an ex B-36 mechanic. He said that was a picture of a bonafide miracle as never before or since has that happened in a formation that large. Bawahahaha

I was at the 2013 Reno races also. I saw that thing and wondered too. The engine in question was at the east end by the display aircraft when I saw it. Made my way back to the far west end of the pits and got to Anderson’s Airomotive display. I asked Ray what he knew about it and he said for sure it was just some cases bolted together to look cool.
Great race this year.

OK, the numeric part of the model designation for a radial engine is its CID (Cubic Inch Displacement). Then a R-4360 had a CID of 4360. Since this engine has 56 cylinders, and is purported to be two R-4360 engines bolted together, it should be a R-8720 not a R-5600. As 2 X 4360 = 8720.

Now lets see if Prat & Whitney ever made a R-2800. Note: 5600/2 = 2800. Yes they did! It is an eighteen cylinder made out of two nine cylinder R-1400 “Wasp” engines. Not surprisingly it is called the Double Wasp. If we bolt two Double Wasps together to get a Quad Wasp, a R-5600, it will have
18 X 2 = 36 cylinders. Not the 56 cylinders of the pictured engine.

We have two options, either they said they had a R-5600 when they actually had a R-8720, OR it is all BS. I vote for BS.

The main reasons P&W stopped making bigger and bigger radial engines, was that the jet engines could make more power on less fuel and less maintenance. The frontal area of the jet engines was much smaller then the radials. Frontal area means drag. So less drag, more power, less fuel, and less maintenance from the jet (turbine) engine doomed the large radial engines.

When I worked for Hamilton Sundstrand (a UTC company), I had a chance to talk to some P&W (also a UTC company) engineers. We made parts for them. These old guys were just starting at P&W when the last of the large radial “corncobb” engines were being developed. They were the ones who gave me the low-down on the reasons for the end of development for these engines. So I got it from the “horses mouth” thirteen years ago. They said that the R-4360 was the last large radial engine that P&W did any development on. I got the impression that it was touch & go as to whether they would finish developing the R-4360 as the jets were coming on strong at that time.

IHTH, 48.

Makes sense. The one in the photo looks impossible to cool.

From looking at pictures, it looks like two stripped 4360s stuck together with a made-up name. The two-row engines had a different offset between banks of cylinders.

As has been hinted at but not fully explained by other posters, the 4360 was the practical limit for radials. Not so much because it coincided with the development of jets (which were kind of crap in the early years, hence the 4360 being mass-produced*), but because they were air-cooled, and if you had more than four rows the forward cylinders blocked the cooling airflow to the aft ones (and it was a bit dicey even with four rows). There may have been the odd half-water-cooled engine, but the picture in the OP is obviously all air-cooled.

*early jets had terrible fuel economy, but were much cheaper on the maintenence end than piston engines, having one moving part instead of … a lot. On the other hand, when the time for an overhaul came, a 4360 could be rebuilt by an auto mechanic with a manual, but jets had to be sent off to a specialty shop because of tolerances. Plus the infrastructure for fixing piston engines was in place at every major airport and most minor ones – he may have to order parts, but the guy who worked on five-cylinder cropduster motors could fix a 4360; it’s the same thing, just more so. Jets are so completely different that a piston mechanic is at a disadvantage learning to fix jets compared to a person who’s never gotten their hands greasy.

There Are a couple of point that I respectfully disagree with, and some I agree with.
First the agree, Yes it is two of the “corncob” radials stuck together. These large radials were definitely pushing the limits of the cooling technology that existed at the time. The maintenance for the jet engines was much less.

Now the middle stuff, The TBO for the radials were about 2,000 hours. The TBO for the jet engines were about 10,000 hours. A big difference.

Now for the disagreement, “The guy who worked on five-cylinder cropduster motors could fix a 4360; it’s the same thing”. No it is not!! The 4360 is a geared, supercharged radial engine. According to the FAAs FARs part 43, IIRC, any supercharged or geared engine must be overhauled, not supervised, by an A&P mechanic with an IA. While almost any piston engine mechanic could figure out 90% of the needed technology with little supervision, the gearing and the supercharging is/was different enough that the Feds felt the need for more education and experience. Yes, the CAA was in place at the time the transition from large radials to jets took place. I am not sure what the CAA rules were, but I do know the FAAs FARs as they relate to my vocation.

Also, as an A&P who has worked on both turbine and piston engines, I completely disagree with the statement that these two engines are “so completely different that a piston mechanic is at a disadvantage learning to fix jets compared to a person who’s never gotten their hands greasy”.

One of the many things I and my fellow Lead mechanics look for in a apprentice mechanic, is some experience working on machines. Any machine, farm and ranch kids are usually fairly mechanically minded and thus a good choice. Someone who has never gotten their hands greasy, would be my absolutely last choice! I have to teach them ALL of the basics. Righty tighty lefy loosey, comes to mind. I would prefer someone who has broken a few bolts on their old rigs. At $45.00 to $255.00 a bolt on a turbine engine, I do not want to teach her/him those lessons on a turbine engine.

Another issue is the fuel cost. Remember that two jet engines replaced four large radials. Yes, one jet burned more fuel then one radial, but not more then two radials.

IHTH, 48.