The R-2800 and MAP Ratings

[DarrenW]

Hi all,

I have a question that probably has an easy answer and if I knew more about how an induction system works on the different variants of the R-2800 engine I could probably answer it myself.

Why was the maximum boost pressure with ADI for the -8W and -10W engines set at 60" Hg MAP, while the -59 found in the P-47 was limited to 56" Hg MAP? These pressures of course were with 100/130 fuel which had a much lower detonation point then the 100/150 fuels used in ETO from mid-1944 onwards. What I'm seeing is that the engine used by the P-47 delivered roughly the same power at 56" Hg as the engines found in the F4U and F6F when they are operating at 60" Hg. I'm figuring it had something to do with the turbocharger system but that's just an educated guess on my part. Can someone more educated in this subject set me straight?

 

[swampyankee]

Hi all,

I have a question that probably has an easy answer and if I knew more about how an induction system works on the different variants of the R-2800 engine I could probably answer it myself.

Why was the maximum boost pressure with ADI for the -8W and -10W engines set at 60" Hg MAP, while the -59 found in the P-47 was limited to 56" Hg MAP? These pressures of course were with 100/130 fuel which had a much lower detonation point then the 100/150 fuels used in ETO from mid-1944 onwards. What I'm seeing is that the engine used by the P-47 delivered roughly the same power at 56" Hg as the engines found in the F4U and F6F when they are operating at 60" Hg. I'm figuring it had something to do with the turbocharger system but that's just an educated guess on my part. Can someone more educated in this subject set me straight?

I think your suspicion that it's the turbocharger is correct: a mechanically-driven supercharger may take several hundred horsepower; a turbocharger is not cost-free, as it increases exhaust back pressure, but it's not a massive parasitic direct loss of shaft horsepower.

 

[DarrenW]

the

I think your suspicion that it's the turbocharger is correct: a mechanically-driven supercharger may take several hundred horsepower; a turbocharger is not cost-free, as it increases exhaust back pressure, but it's not a massive parasitic direct loss of shaft horsepower.

Thanks swampyankee for the quick and informative reply. I find it interesting that higher boost pressures weren't authorized for the F6F and F4U because they clearly could handle it. For instance, I have seen testing that took them up to 64" Hg for periods of time with no adverse affects. I presume that they Navy felt it better to keep things within manageable levels though, as the extra performance which would likely come from this increase was un-necessary as their performance already exceeded the majority of Japanese aircraft that they encountered. This decision undoubtedly increased TBO and kept more planes in the air where they belonged. In the ETO however the extra speed afforded by boosting the R-2800 to over 70" Hg was more of a necessity than anything else as German aircraft were becoming steadily faster, especially with the advent of the Me-262.

Do you happen have any boost values for the C series of the R-2800 engine? I'm curious if it was cleared for higher than 60" Hg. I know it had a higher compression ratio than the B series and this was at least partially made possible by having forged internals rather than cast.

 

[tomo pauk]

...
In the ETO however the extra speed afforded by boosting the R-2800 to over 70" Hg was more of a necessity than anything else as German aircraft were becoming steadily faster, especially with the advent of the Me-262.

Boosts of 70 in Hg were attained when 150 grade fuel was used along with water injection = 2800 HP; on 64 in Hg (uses water injection) = 2600 HP. All on 2700 rpm.

Do you happen have any boost values for the C series of the R-2800 engine? I'm curious if it was cleared for higher than 60" Hg. I know it had a higher compression ratio than the B series and this was at least partially made possible by having forged internals rather than cast.

The -57 was cleared for 72 in Hg, on 130 grade + WI + 2800 rpm = 2800 HP. Take off and military power used 54 in Hg.

 

[tomo pauk]

Boosts of 70 in Hg were attained when 150 grade fuel was used along with water injection = 2800 HP; on 64 in Hg (uses water injection) = 2600 HP. All on 2700 rpm.

64 in Hg was also allowed with 130 grade fuel when the turbo regulator A-13 was installed on eg. R-2800-63 engines (on P-47D), instead of the A-17 turbo regulator.

Might be of interest: link

 

[DarrenW]

64 in Hg was also allowed with 130 grade fuel when the turbo regulator A-13 was installed on eg. R-2800-63 engines (on P-47D), instead of the A-17 turbo regulator.

Might be of interest: link

Thanks Tomo for the link to the P-47D pilot's handbook. That's a pretty good find!