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After hard work, time for some what-if:
As the XR-2800 proved it's potential, the decision is made to build a fighter plane around it. What supercharger set-up would've you choose? Perhaps we could divide it in 3 groups:
-turbo-charger for the 2800 (a P-47-like design, with great all-altitude speed, but dictating a hefty airplane with poor mileage climb rate)
-two-stage supercharger (something along F4U, good performance, even better for a true land-based version)
-single stage supecharger (basically the engine from B-26, less power than the versions from above, high blower FTH at ca. 14kft (unless modified), but needing a smaller airframe - better mileage climb rate? - a pre-F8F?)
The time frame is 1940-42, from basic design 'till start of production.
Any takers?
Skip the turbo.
RR Merlin and DB601 engines performed adequately at high altitude using compact supercharger systems. Copy the best features of British and German supercharger systems for the new American fighter aircraft engine. If you want to get really clever copy the German fuel injection and hydraulic supercharger coupling also.
During 1940 to 1942 nobody flew that high except recon aircraft. Nor is there a requirement for a heavy bomber escort as the U.S. Army Air Corps are confident the B-17 can defend itself. Initial models of the new fighter aircraft should be designed for good performance up to 20,000 feet.
During the second half of 1942 the need for a B-17 escort will become apparent. That's when a high altitude variant of the engine will be designed, to enter service during 1943.
I like the F4U-4/5 applications . I also find in turbo engines more negatives than positives.Not really nessecary. I also like the concept of F8F (low weight) but it appears that led to unsatisfactory airframe strength for useful combat weights.
Neither engine performed at 30,000ft or above like a turbo engine. The Merlin set up was as compact as it was going to get and it needed that big intercooler radiator under the wing of the Spitfire. The Merlin two stage supercharger also doesn't show up until late 1941 (in the shops) or 1942 (in service) also making in hard to copy in 1940-41.
Coping the oh so clever German fuel injection system means lots of manufacturing expense. American carburetors did not suffer from the negative "G" problem that the British carburetors did so no advantage there. Using the the German fuel injection also means no cooling of the intake charge from fuel evaporation so you have to use less boost which means less power.
I like the F4U-4/5 applications . I also find in turbo engines more negatives than positives.Not really nessecary. I also like the concept of F8F (low weight) but it appears that led to unsatisfactory airframe strength for useful combat weights.
The intercooler radiator on the P-51 was in the ventral duct with the radiator.
Part of the size of the P-47 was due to the 305 gal fuel tank. Part of it was due to the eight gun armament requirement. And part was due to the ducting.
While it might be possible to place the turbos where the sidewinder superchargers are placed in a physical sense, it might not be a good idea to put them there from a mechanical sense. Putting a few more feet between the engine and the turbo allowed for a bit of cooling of the exhaust gases before they hit the turbo. The turbos were running very close to their temperature limits in many installations as it was. As the war went on later model turbos may have allowed both higher rpm and higher inlet temperatures.
You still have a number of cubic feet to devote to intercoolers and their ducting.
The F4U-5 may have been 10in longer than an F4U-4 and with the new cheek airscoops at 4 and 8 oclock the engine cowl was 8in wider at the maximum dimension.
...
An "A" series engine was good for 1850hp take-off and 1500hp at 2600rpm at 14,000ft with a two speed single stage supercharger.
A "B" series engine was good for 2000hp take-off and 1600hp at 2700rpm at 13,500ft with a two speed single stage supercharger.
A "B" series engine was good for 2000hp take off, 1800hp at 2700rpm at 15,500ft and 1650hp at 2700rpm at 22,500ft with the two stage supercharger.
A "B" series engine was good for 2000hp take-off and 2000hp at 25,000ft with the turbo.
Mileage depends on speed and altitude flown.
P-47s got bad "mileage" because they were hauling twice the guns of an early Bearcat and were carrying almost twice the fuel depending on model. Prototype Bearcat had 150 gals of internal fuel, production models had 185gals. Exactly 1/2 the internal fuel of late P-47D's. While later P-47s may have gotten dirtier (more drag) a P-47B had less profile drag than a F4F-3 Wildcat. I kind of doubt the Bearcat was that much more streamlined than the F4F-3 that it was going to show any significant improvement over the P-47 in "mileage" if flown at the same speeds and near the same altitudes.
Thanks for the data
Could we have some data about the weight penalty of single stage, two stage turbo R-2800s?
The weight plays the part too - heavier plane would consume more fuel to climb at cruise altitude.
It appears maybe the turbo would out due the supercharged version then.
It would be great to see the actual power chart of the engine using the different turbos and superchargers.
What i found was a bit more revealing about "on the bench" data used to find the limits of the engine but i doubt the turbo or supercharger could reproduce similar manifold pressure.
It would have been unwise to modify this program.
In 1940, 41, and 42, the US did not have the fighter maturity as it did the bombers and transports, and did not field competitive aircraft against the Axis when we entered the war, especially in the low to mid altitudes.
I think I agree with all the Shortround6 has said. The P-47 was a tour-de-force of high altitude performance. Its flat rated power up to 33k was unmatched from any WW2 fighter I know, except maybe the P-38. It would have been unwise to modify this program.
In 1940, 41, and 42, the US did not have the fighter maturity as it did the bombers and transports, and did not field competitive aircraft against the Axis when we entered the war, especially in the low to mid altitudes. I think I would have left the P-47 program alone and would have encouraged the development of a smaller and lighter R-2800 vehicle. This could have been a plane based on the F4U, but not the F4U. It would have smaller, straight, wings, and less fuel, 180-220 gal. Empty weight would be around 7000 lbs, wing area 200-220 sqft. Initially, this plane would have the B-26, xF4U-1 type engine.
Another alternative would be to have Vultee redesign the P-66 to include the R-2800, which would include adjusting to the increased weight (the first Vanguard already had a heavier and longer aero front end) and size. Wing area, fuel quantity, and weight would increase. The plane was reported to be favored by pilots for its flying characteristics.
This aircraft would be available in late 1941 and should be faster than the XF4U (lighter and smaller wing) so it would be in 400-415 mph speed area. It should have outperformed the Fw-190A-1/2 and with the upgrade of the R-2800 would have soon over powered the Axis fighter. If this type of performance was available to the Brits in 1941, they would have bought lots. A drawback would be that if the Brits had this aircraft, would they have continued to pursue the P-51?
By the way, the stats look very close to the Fw-190, not all by accident. Think of the Fw-190 with the more powerful R2800 engine.