F4UDOA asked why the V-1650 could reach higher MAP than B-series R-2800. And the main reason is head cooling. At similar configuration (without ADI) B-series R-2800 was limited to about 52-54" so there is roughly 15" MAP difference. The V-1710 could reach 60" at similar configuration so we know that head cooling accounts about 6-8" of the difference. The rest can be explained with differences in compression ratio and charge cooling.
He specifically asked about the R-2800 in the F4U and F6F. And the reason is induction air cooling. You pointed out correctly that the R-2800 B in the P-47 could develop, and was rated for, 64” hga on 100/130 PN fuel. The Material Air Command directive that allowed that rating stated that same engine could withstand 75” hga for “several hours.” Therefore, the R-2800 B was capable of 64”, 67” and up to 75” hga on 100/130 fuel – with the right induction system.
The base engines for the P-47 and the F4U/F6F are virtually the same, as they are both B series engines. The main differences lie in the induction systems. If the P-47 could achieve high MAPs, and the F4U could not, both with the same base engine, then the reason was due to differences in the induction systems.
BTW, when I say induction system, I am referring to the induction/intercooler(or aftercooler) arrangement, as well as ADI if applicable.
Actually the rating of the two stage V-1710 with ADI and no intercooling ie 75" is a very good and supported evidence. And also comparing these engines without ADI is another. The use of the aftercooler would have resulted only minor advantage if compared to the better head cooling.
My point was you said the R-2800 would not have benefited much from an aftercooler. There is no evidence to support that. But there is evidence that P&W felt otherwise, as they attempted to develop an aftercooler for their R-2800, but abandoned attempts. If they didn’t think it was better, why try?
And as far as the Allison goes: the reason Allison went with ADI instead of an aftercooler was because the plane would have to fly with the added weight of an aftercooler all the time, but the ADI weight would get used up. That was their logic. It’s documented in Whitney’s book. To achieve the high MAPs with ADI alone, they had to use huge quantities of ADI fluid. The P-63C carried 25 gallons of ADI which was enough for just 15 minutes. That’s an astonishing amount of ADI.
One of the main differences between the F-serie and G-serie (used in the V-1710 powered F-82s) was lower compression ratio, which was same as in the Merlin.
That’s correct. Nevertheless, all Fs were rated on 100/130 fuel, and all Gs were rated on 115/145 fuel. 115/145 can withstand more heat than 100/130 without detonation.
Well, F4UDOA asked the reason and charge cooling simply can't explain the difference.
It certainly does, and you helped explain it. Go back to the P-47 and F4U engine comparison. You brought it up. The P-47 could achieve high MAPs and the F4U couldn’t. The main difference was in the induction systems and how well they cooled the charges.
Again, both planes had the same base R-2800 B series engine. But their induction systems were different, both in design and efficiency. If one could do it, and the other couldn’t, then the answer lies in the induction system which was responsible for creating, compressing, cooling and delivering the charge.
You should also mention that the P-47D utilized ADI while the P-38L did not. With ADI the P-38 should have reached 75" as tested by Allison.
As I stated, the 64” hga rating for the P-47 was very conservative. It was already known the engine could withstand 75” for several hours.
Some how you forget here that P-47D, F4U and F6F also carried ADI for the WEP and they should have reached similar MAP as the P-63 or even a bit more because the intercooler.
Yes, the P-47, F4U and F6F carried water. But none of them used it in the quantities the P-63 did.
To achieve 2,200 hp, the base R-2800 required a little less than 8.5 pounds of ADI per minute, which is about 1 gallon per minute. The P-63 used about 14 pound of ADI per minute, which is about 1.67 gallons per minute.
ADI flow rates between the P-47 and F4U/F6F varied. And they all carried different quantities of ADI. The plane that carried the least was the F4U, something like 10 gallons. If the flow rate had been increased to the point where it cooled the charge sufficiently to reach 67” hga, it would have used up its ADI in minutes. The P-47 carried the most, something like 30 gallons for about 25-30 minutes use. The P-63 carried 25 gallons for 15 minutes use.
The P-47, F4U and F6F appears to have sipped ADI compared to the P-63, which guzzled it.
BTW, P&W tested the R-2800 B series engine to 3,800 HP (during ADI system development). 3,800 hp was equivalent to 150” hga. In order to achieve that phenomenal power, Frank Walker (P&W’s ADI development chief) simply continued to increase ADI. No doubt that at 150” hga the air/fuel charge was dwarfed by the ADI charge.
So, there is no doubt the engine in the F4U could have reached the same MAP levels as the P-51, and could have surely exceeded them. But it’s induction system held it back. It needed more ADI, or a better intercooler, or both.
Comparison between the P-47 and P-38 show clearly that at similar configuration V-1710 reached higher MAP as noted several times above.
They weren’t rated all that different, although the P-47 with ADI was rated higher.
You stated earlier that Allison tests showed if water was used on the P-38, 75” hga could be obtained. That’s what could be obtained on the P-47 with water. The 64” limit was a conservative rating.
No one try to deny that here. But I'm answering to F4UDOA's question and you should too.
No, you want me to agree with you. I have answered it. And you’ve unwittingly supported me by bringing up the F4U/P-47 comparison.
The P-47 could obtain MAPs equal to, or in excess of, 67” hga on 100/130 grade fuel. The F4U apparently could not. Since they have the same base engine (R-2800 B), but different induction systems, then the answer lies in the induction systems. (But I do believe there is a little conservatism built into the 60" hga limit for the F4U.)
There is no reason to believe the F4U could not have been boosted to 67” hga + if it could be done in the P-47. What the F4U needed was a cooler charge, which apparently could not be provided by its induction system.
Since the P-47 and the F4U has the same heads, the answer is not the heads, but rather induction system capability.
The difference between V-1710 and V-1650 can be explained with compression ratio and charge cooling. But these can't explain the difference between V-1710 and B-series R-2800 or V-1650 and B-series R-2800.
I compared the V-1710 with 6.0:1 compression ratio pistons to a Merlin with 6.0:1 compression ratio pistons. I did it intentionally for as close a comparison as possible. You left that part out of your quote. Therefore, the difference is mainly the induction air temp.
As I noted above initial rating with ADI was 56-58" later raised to 60-64".
Reread what I wrote. The maximum rating
allowed was 64” hga, even though the person who gave that directive knew the engine was capable of “75” hga for several hours." 64" hga was a VERY conservative rating.
64” hga is very close to the 67” hga of the Merlin, and 75” hga is well above it, all on 100/130 grade fuel
Any engine could handle high MAP for short periods.
gripen
“75” hga for several hours” isn’t a short time. It’s a helluva long time.
