A Radial Engined Fighter for the Australians to build (and maybe the Chinese and Indians)

[Shortround6]

That's a very common issue with the boost ratings during tests, and it certainly cuts both ways - almost all the British tests done at Boscombe Down on a variety of US types, Martlet, Hellcat, Corsair, P-39, P-40 etc. were routuinely done at low boost ratings, for example the Allisons were at military power 40-42" etc (+5 boost)., which severely limited the peak performance. Not that it matters, so long as they are consistently testing all aircraft all the same way, but not all British types were tested with such restrictions. The Hurricane Mk II tests I've seen for example were done at the max allowed boost levels at the time, at 50.5' Hg. (+10 boost), or +12, or +14

This is where some people get the idea that the Hurricane had a higher top speed relative to various US types than it actually did.

The British were using the boost settings in the manuals or in the official notes/memorandums.

The USAAC did not allow combat ratings of the Allison until October 1942.

It doesn't matter how many squadrons or pilots were over boosting the Allisons, if the USAAC and Allison said you shouldn't do it, the the British testers weren't going to do it.
2nd factor is that the US tested different for climb than the British did.

The US would use full throttle, in the case of the Allison 3000rpm, and the max boost listed in the manuals for the first 5 minutes of the climb and then throttle back to 2600rpm and the appropriate boost level for max continuous power level. Planes using radial engines would use the appropriate full throttle rpm and full boost for the first 5 minutes and then throttle back to max continuous power for the rest of the climb.

The British normally did their climb tests at a "climb rating or 30minute rating" which did not exist for American engines. American engines, for much of the war had full power (military) for 5 minutes and then either max continuous (as long as the fuel lasted) or 1 hour, in the early part of the war could see charts with either label, not both. Later it was max continues only the 1 hour time limit disappeared.
The British climb rating changed over time and according to the engine.

Basically when looking at British and American climb charts the British planes (or planes under test) will climb slower than the equivalent American planes for the first 5 minutes and then climb a bit faster after 5 minutes. In no case were the British measuring the "combat climb" unless the test specifically says so.

The British were a bit more practical, if a particular engine seemed to be operating with few, if any problems in service they often, in conjunctions with test results, would allow more boost to be used and then wait a while to see there were any problems, and if their were none they might raise the boost limit again.
For the US the was a test procedure that had to be passed.
To get a WER the engine had to run at the desired power level for at minimum of 5 hours (and usually 7 1/2 hours) worth of 5 minute intervals with cool down periods between every 5 minutes. If the engine suffered a mechanical failure during the test, even at the end, it failed and the engine had to modified and retested or repaired and run at a lower power setting for the required time period.
The fact that officer Schmoe had run his engine for 4 1/2 hours in 10 minute bursts in a number of missions before it threw a rod didn't count to to the USAAC.

This gets a bit weird as the USAAC with the Merin powered P-40s were not OK'ed to use the the same boost settings that the Merlin XX was cleared to use in British planes.
this goes beyond the WER rating. Military power was restricted to 48in/3000rpm (9lbs boost) and max continuous was 44.2in/2650rpm (7lbs) which was the max cruise setting for British engines. the 30 minute climb rating was 48in/2850rpm.

Now the British often tested American planes to British protocols and when climbing they didn't use military power at all and since there was no climb rating to use they dropped down to the max cruise rating for the climb. This basically means that American planes in British tests look they sucked but the British tested all of them the same way. As I have said all the British planes were demonstrating a less than combat climb also. Like the Hurricane II would climb for sea level to 35,000ft using 2850 rpm at whatever boost it could manage that was under under 9lbs (at times the boost control would be out of whack and the boost might be a bit higher but 3000rpm was almost never uses in a climb).

You do have to read the descriptions in the test reports as sometimes they were doing a test for a specific purpose, sometimes they wanted to see how long it took to climb using 3000rpm and full boost but it would be noted that it was a special test.

 

[Shortround6]

Re the self sealing tanks. While I agree in general with what you say I am fairly sure that, despite the lessons from Spain, the Mk 1 Hurricanes, like the Mohawk, did not have self sealing tanks until after the war started. This is supported by the excerpt from AP 1746 dated 1939 but amended in 40/41 quoted by Geoffrey Sinclair above where he quotes The 97 gallons on the Hurricane I weighs 725 pounds, the 97 gallons on the mark II weighs 698 pounds. The specific gravity of the fuel did not change that significantly so the more likely reason for the 29 pound difference in fuel weight is the manual was only partially revised to show the reduction in fuel volume when bullet proof tanks were fitted but the fuel weight was left at what applied to any aircraft which was not modified to bullet proof tanks at the stage the manual was revised.

For anyone who does not have this yet I would recommend it.

http://www.wwiiaircraftperformance.org/P-36/Curtiss_Hawk_75-A_Detail_Specifications.pdf

This is a 24 page specification--- advertising brochure for the Hawk 75 airplane, with a number of things offered that never made it into production aircraft, or at least not many.
For keeping the South American natives in line there were a variety of bomb rack options. South American being a fertile marketing area for Curtiss planes in the 1930s.
Max bomb load was 850lbs comprising of a single 500lb bomb under the fuselage, a 100lb bomb under each wing inboard of the normal bomb rack (small fragmentation bombs) with three 25lb bombs under each wing.
I don't doubt that the under fuselage rack, if it was there, wouldn't be hard to fit with a drop tank, assuming you had them. But nowhere in the Brochure is there any mention of of a drop tank. Perhaps they thought with 163 US gallons internal it would be enough? The description of the tank behind the seat is interesting for what it doesn't say. While the two tanks in the wing are described as having baffles the fuselage tank is described as being two pressed ends welded to a central strip forming an oval tank. You have a 58 gallon tank with no baffles?

 

[Wild_Bill_Kelso]

Pretty sure A&AEE Boscombe Down tested aircraft at the manufacturer's recommended boost settings.

The Hurricane was only tested at +12psi boost when the Merlin was cleared for +12psi boost. Before that it was tested at +6psi boost, then +9psi.

American engines did not have WEP early in the war, and Allison tended to lag behind Rolls-Royce on boost, at least officially.

I don't think there was anything malicious about it, but I suspect there was some kind of lag or institutional inertia afoot in terms of whatever the settings were supposed to be, probably due to relative familiarity with the different types. If they had a question about a Spitfire or a Hurricane they could just telephone the manufacturer, but to talk to somebody at Curtiss or Lockheed was probably more of a big deal. The result is the tests are misleading, for example this test of a Kittyhawk done in Sept 1942, was done at 41.5' Hg, and the report states that the maximum boost was 42", when the boost was already up to 60" for WEP in the manual, and was 57" before that. I'm sure the people at the time knew how to interpret these tests accurately, but it affects people's perceptions today such as we have seen in this thread, and is also brought over into things like video games.

 

[Wild_Bill_Kelso]

This gets a bit weird as the USAAC with the Merin powered P-40s were not OK'ed to use the the same boost settings that the Merlin XX was cleared to use in British planes.
this goes beyond the WER rating. Military power was restricted to 48in/3000rpm (9lbs boost) and max continuous was 44.2in/2650rpm (7lbs) which was the max cruise setting for British engines. the 30 minute climb rating was 48in/2850rpm.

Are you sure about that? I have the manual for the P-40F/L from Dec 1942 and it states take off power at 54.3" Hg / + 12 lb, and "War Emergency" at 61" Hg

Screen shot:

 

[Wild_Bill_Kelso]

As you noted though, these things changed quickly. It's possible Boscombe Down had manuals that were a few months old, they would therefore use the older settings. There was no internet back then.

Notable that WEP is listed up to 4,500 feet and 12,00 feet for second gear.

 

[ThomasP]

Hey Wild_Bill_Kelso,

The SPEC AN-H-8 DEC 18, 1942 notation is not the date the engine ratings went into effect. It is the date of issue of the specification for the format of the SPECIFIC ENGINE FLIGHT CHART FORM ASC-512, ie it is the arrangement of the data blocks on the piece of paper, and what information is required to be included in the data blocks. To know when the engine ratings became effective you would have to look at the manual or handbook the particular SEFC was first published in, and/or the revision information at the top or bottom of the page.

This type of SEFC is normally published in Pilot Flight Operating Instruction manuals and has the revision marked at the top or bottom of the page, such as in the following:

 

[Wild_Bill_Kelso]

Ok, well the date of the manual is March 10, 1943. But my understanding is that those engine settings were mandated in the third quarter of 1942.

The famous memo from Allison (Allison division of General Motors) was dated Dec 12, 1942. In that memo Allison notes that "this company has agreed to the war emergency operation at 60" manifold pressure (15 lbs./ sq.in. boost) and approximately 1570 hp at 3000 R.P.M." Referring to V-1710-39 and -73 (P-40D/E and K). From that wording (notice past tense) I would conclude that this was already in effect and had been approved by the War Dept. The Allison memo also said that "...from the Middle East our Representative who just returned advises that they are resetting boost controls to 66" Hg (18#/sq.in.) maximum boost pressure."

Which sounds to me that squadron or fighter group leadership in the Theater had already signed off on this, since mechanics were resetting the automatic boost controls.

Sure would love to see a speed test for a P-40 or P-39 or P-51A at 66" Hg, or even 60" Hg. Sadly I don't know of one. Same for the Merlin versions at 61" Hg or higher.

 

[MiTasol]

I don't doubt that the under fuselage rack, if it was there, wouldn't be hard to fit with a drop tank, assuming you had them. But nowhere in the Brochure is there any mention of of a drop tank. Perhaps they thought with 163 US gallons internal it would be enough? The description of the tank behind the seat is interesting for what it doesn't say. While the two tanks in the wing are described as having baffles the fuselage tank is described as being two pressed ends welded to a central strip forming an oval tank. You have a 58 gallon tank with no baffles?

But none the less the 52 USG P-36/P-40 drop tank installation drawing is 75-45-408 BELLY TANK INSTALLATION and the tank itself is 75-45-433 TANK ASSEMBLY BELLY - FUEL. Maybe it was a restricted export item for some countries, or maybe no-one had asked for it at the time that undated brochure was created.. Thanks for that link by the way. I had two versions of that brochure but that one is far cleaner than mine. As an aside I have never seen a photo of the P-36/H75 with a belly tank so maybe they had such an adverse affect on performance they were not used. Certainly the P-36 A&C flight manual I have has no mention of them which might support that assumption. Then again the USAAC may have decided they just did not need them.

My microfilm of the first drawing (frame M168) is almost unreadable but this is part of the drawing for the tank itself and the same tank and installation drawings are used on the P-40s. This tank drawing applies to both the P-36 and P-40D thru M and includes the H75A-5 which definitely was an export model. Interestingly it was not used on long nose P-40s.

 

[MiTasol]

A quick look through an on line P-40B/C manual shows that the B had metal tanks and no belly (drop) tank but the C did. Unfortunetly I do not have a copy of the -2 and neither does any of the on line sources I use.

 

[wuzak]

I don't think there was anything malicious about it, but I suspect there was some kind of lag or institutional inertia afoot in terms of whatever the settings were supposed to be, probably due to relative familiarity with the different types. If they had a question about a Spitfire or a Hurricane they could just telephone the manufacturer, but to talk to somebody at Curtiss or Lockheed was probably more of a big deal. The result is the tests are misleading, for example this test of a Kittyhawk done in Sept 1942, was done at 41.5' Hg, and the report states that the maximum boost was 42", when the boost was already up to 60" for WEP in the manual, and was 57" before that. I'm sure the people at the time knew how to interpret these tests accurately, but it affects people's perceptions today such as we have seen in this thread, and is also brought over into things like video games.

Ok, well the date of the manual is March 10, 1943. But my understanding is that those engine settings were mandated in the third quarter of 1942.

The famous memo from Allison (Allison division of General Motors) was dated Dec 12, 1942. In that memo Allison notes that "this company has agreed to the war emergency operation at 60" manifold pressure (15 lbs./ sq.in. boost) and approximately 1570 hp at 3000 R.P.M." Referring to V-1710-39 and -73 (P-40D/E and K). From that wording (notice past tense) I would conclude that this was already in effect and had been approved by the War Dept. The Allison memo also said that "...from the Middle East our Representative who just returned advises that they are resetting boost controls to 66" Hg (18#/sq.in.) maximum boost pressure."

Which sounds to me that squadron or fighter group leadership in the Theater had already signed off on this, since mechanics were resetting the automatic boost controls.

Sure would love to see a speed test for a P-40 or P-39 or P-51A at 66" Hg, or even 60" Hg. Sadly I don't know of one. Same for the Merlin versions at 61" Hg or higher.

Note that the report from the A&AEE was dated 14th September 1942, and the tests were performed between 9th June and 30th July 1942.

That is, the tests were performed ~6 months prior to the memo, 9 months prior to the manual.

Also note that the chart posted by ThomasP indicates that the critical altitude for 60inHg MAP is sea level. Which means that 60inHg was not available at 1,000ft, let alone 10,000ft.

 

[Shortround6]

From what I have read the P-40 and the P-40B were not built with the drop tank capability, what may have been done in the field I don't know.
The P-40C got the drop tanks, in part because the change in the interior fuel tanks to accommodate the new self sealing material is supposed to have reduced the fuel capacity from 160 gallons to 135 gallons (?) according to one source. P-40 fuel tank capacities are all over the place and sometimes old books do not line up with what the manuals say, and sometimes the manuals don't even agree between pages of the same manual (early version of cut and paste for manuals?)

From the Hawk 75/P-36 to the end of the P-40 series there was quite a lot of shuffling around with how the tanks were used despite the capacity not changing that much except for the P-40 stripper models which had the forward tank taken out. When they stuck the Allison in the nose a lot stuff got moved around it seems like the CG got moved aft a few inches, Just Guess but the radial engine planes don't seem to be able to use the rear tank for anything but ferry flights?
The Long nose P-40s go from 105 gallons in the wing tanks to 120 gallons in the wing tanks or 15 gallons allowed in the Rear tank for combat or it changed depending on which long nose?
The P-40D & E could only hold 83 gallons in the self sealing wing tanks which required 37 gallons in the rear tank to get up to 120 gallons. The P-40F & L manual I have does not agree as to the tank capacities on the Fuel system chart/drawing and and the fuel capacities on the weight and balance chart.
On the F & L with the Merlin engine the reserve tank shifts from being the forward wing tank to being the fuselage(rear) tank. The fuselage(rear) tank is to be used after take-off until 35 gallons are left in it and the the forward wing tank used up completely followed by the rear wing tank and then go back to the fuselage (rear) tank for the last tank to be used.
Basically you have gone from not using the rear tank for combat in the radial engine fighters to using the rear tank as 35 gallons (210lbs) of ballast for Merlin engine
And this went for the long fuselage P-40s.

 

[Wild_Bill_Kelso]

Note that the report from the A&AEE was dated 14th September 1942, and the tests were performed between 9th June and 30th July 1942


That is, the tests were performed ~6 months prior to the memo, 9 months prior to the manual.

That is just one example among many. This test was from May 1943, they never put the boost over 42"

Also note that the chart posted by ThomasP indicates that the critical altitude for 60inHg MAP is sea level. Which means that 60inHg was not available at 1,000ft, let alone 10,000ft.

They always say that, because there is more power available the lower you go, but that WEP boost setting is not actually limited to Sea Level, not even close. As you can see here (boosting at 57" Hg) the WEP power for a Kittyhawk Ia was available in the V-1710-39 up to just below 10,000 ft, and only slowly tapered off after that, still making 50" at 13,000 ft., and it doesn't get down to 42" until you hit 19,000 ft. In this January 1943 test with a P-40N, also at 57" they noted that "Critical Altitude for war emergency power in level flight" was 10,550' ,where they made 378 mph, and they are still getting 1125 hp (and making 371 mph) at 17,300'. That is with a V-1710-81.

Obviously with the P-40F/L (which Boscombe Down also tested) the higher boost ratings are available in two altitude bands, asI've previously noted.

 

[Shortround6]

Also note that the chart posted by ThomasP indicates that the critical altitude for 60inHg MAP is sea level. Which means that 60inHg was not available at 1,000ft, let alone 10,000ft.

And that gets us into the realm of RAM and claims of 1700hp Allisons and a host of other things.
The engine in the chart will make over 60in of MAP at sea level even with no RAM, wither it should or not is another story.
I would note that there are some mistakes in a number of these charts so use them with caution.
The P-40 F & L manual shows the same power for take-off at 54 in as the engine was supposed to make at 61in using ram at 4500ft.
Of course some of the test results for the P-40F as having some rather strange results.
Like having almost 2000ft less FTH than a Hawker Hurricane Using a Merlin XX engine in high speed flight.
Hawker Hurricane could pull 9lbs of boost (48in) at around 20,000ft using RAM. The US army figured 18,500ft which is close to what the British figured it would do when climbing at 2850rpm instead of 3000rpm?

It could be true but then that means the P-40F air intake was costing over 1500ft of altitude over the Hurricane intake (not tropical), maybe the US did build a filter into the intake?

 

[tomo pauk]

Note that the report from the A&AEE was dated 14th September 1942, and the tests were performed between 9th June and 30th July 1942.

That is, the tests were performed ~6 months prior to the memo, 9 months prior to the manual.

Also note that the chart posted by ThomasP indicates that the critical altitude for 60inHg MAP is sea level. Which means that 60inHg was not available at 1,000ft, let alone 10,000ft.

Without any throttling, a V-1710 of ww2 vintage running at 3000 rpm, no ram, S/C geared at 8.80:1, will be making about 1750 HP at S/L. Power figure of 1550 HP at S/L means that some throttling is applied, ergo it is not a critical altitude, ergo the data sheet is a wee bit wrong.

 

[Wild_Bill_Kelso]

And that gets us into the realm of RAM and claims of 1700hp Allisons and a host of other things.
The engine in the chart will make over 60in of MAP at sea level even with no RAM, wither it should or not is another story.

Seeing as it was a matter of life and death, and also that Mustangs with the same engine were doing this routinely at much higher (70") boost for extended periods, and that Allison had specifically signed off on 60" as a compromise, it's probably fine. I suspect the reason they didn't (at least officially) push them to 70" in North Africa, China or the Pacific is that the airfields they were flying out of were rougher / dirtier / less well equipped than the ones those British recon Mustangs were based in.

I would note that there are some mistakes in a number of these charts so use them with caution.
The P-40 F & L manual shows the same power for take-off at 54 in as the engine was supposed to make at 61in using ram at 4500ft.

And again at 12,000 ft, don't forget second gear Up to about 16,000

Of course some of the test results for the P-40F as having some rather strange results.
Like having almost 2000ft less FTH than a Hawker Hurricane Using a Merlin XX engine in high speed flight.
Hawker Hurricane could pull 9lbs of boost (48in) at around 20,000ft using RAM. The US army figured 18,500ft which is close to what the British figured it would do when climbing at 2850rpm instead of 3000rpm?

It could be true but then that means the P-40F air intake was costing over 1500ft of altitude over the Hurricane intake (not tropical), maybe the US did build a filter into the intake?

They did have a dust filter ('air cleaner' to the British) but it was supposed to cut out after takeoff. This report says critical altitude for a P-40F was 19,270'

 

[Shortround6]

Mustangs with the same engine were doing this routinely at much higher (70") boost for extended periods

I suspect the reason they didn't (at least officially) push them to 70" in North Africa, China or the Pacific is that the airfields they were flying out of were rougher / dirtier / less well equipped than the ones those British recon Mustangs were based in

And here we get into what RAM is/was.
It is the increase in pressure in the intake duct before the air enters the carburetor. This increase in air pressure over static air pressure is due to the forward motion of the aircraft through the air.
In theory it is proportional to the square of the speed of the entry air. Double the speed of the air entering the same and you should see a rise in pressure of 4 times. A 10% increase in air veleocity should give you a 21% increase in air pressure (over static air pressure, not a 21% rise in total air pressure)
However due to drag in the intake duct, both friction and turbulence and losses through any bends you are never going to get the full pressure rise.
But Spitfires always got more Pressure rise than Hurricanes using the same engines. Allison P-51s are going to get a higher pressure rise than a P-40 due higher veleocity in the intake duct. It was easier for the Mustangs to reach the magic 70-72in pressure mark.

The other thing is that that 70-72 manifold pressure is based, in test charts from engine house test stands, on 29.92 air pressure so it goes 29.92 X RAM effect x the pressure ratio in the supercharger =?
72with no ram was impossible. Engine chart for the V-1710-33 shows 1700hp at 61in MAP. But that is in the test house. you need RAM to reach the 70-72 MAP levels.

We have ignored temperature.
The hotter the intake charge is, for the same pressure, the less dense (pounds per cubic ft) the air is. The Supercharger is heating the air up by hundreds of degrees and this is something else that changes with the intake conditions. IF you raise the intake temperature from 59 degrees F to 89 degrees F you have two things (or more) against you.
One is that the air is less dense to begin with so you aren't taking in as much air.
Two, the supercharger is going to raise the temperature of the intake charge the same amount so your air exiting the supercharger is hotter (less dense)
The hotter air/fuel mixture is closer to the detonation limit when it goes into the cylinders, you can't run at at the same manifold pressures.

Now you do have somethings working against each other. If you are looking for an honest 1700hp from the Allison engine at 3000rpm and 70in of MAP you are not likely to get it in tropical conditions. Your gauge, which is a pressure gauge only, doesn't tell you how much air you are actually flowing.
I was a firefighter, we had pressure gauges on the pumps, water is incompressible (at least by practical standards) but we were guessing as to how much water we were actually flowing. A kink in the line can show good pressure on the pump end and a dribble on the nozzle end. Some departments have shifted to flow meters.
And again, in tropical conditions you were more likely to blow the engine up due to high intake temperatures than over Europe. Not saying you can't hit a hot day in Europe or a cold day in NA. but the odds are????

You have to push harder to reach that 70-72 in pressure in the P-40 vs the Mustang (less free boost due to RAM) you have the lower density air and the higher temperatures.

Saying you could do it Europe may not work, It may be justification to using than the 60-61in limit they are using but pushing for the 70in limit may have been very dangerous indeed.

And again, things inside the engine are not equal, You want to flow more air through the supercharger you are going to need more power to drive the supercharger. An Allison supercharger flowing 10,000lbs per hour need about 210hp to drive the supercharger, if you are trying to flow 11,000lbs per hour you need around 235-240and for 12,000lbs you need just over 250hp. The more power you use the drive the supercharger the more heat is used heating the charge up. Most superchargers were doing good if they were over 70% efficient. the other 30% or so went into heating the intake charge over and above the heating you get when you compress a gas.

 

[Wild_Bill_Kelso]

I agree with you, I suspect 70" or more is quite dangerous in a P-40, and probably risky in a P-51 too unless you know exactly what you are doing, and the only place i know of their doing it for extended periods is basically in the North Sea, in Mustangs down very low over the very cold water. You also have a good point about the no doubt far more efficient air intakes on the Mustang vs. the P-40.

It does actually get cold in North Africa in the Winter, but you also have things like more dust to contend with, fewer clean hangars, a more tenuous supply chain etc. In the South Pacific I think it pretty much stays hot and humid year round, plus you get crazy storms all the time, and the supply chain is much more tenuous. The effects of climate on aircraft, not just engines but also the comparative lift and drag, are probably under- utilized in terms of analysis of these aircraft. The kind of conditions ground crew were enduring in places like the Solomons, Papua New Guinea, and Burma are also very likely contributing factors to maintenance. Hard to stay on top of a temperamental race engine when you have Malaria.

I think what happened is that P-51As (et al), P-40s and P-39s went into combat with pilots using the original official boost limits, and they found them dreadfully underpowered. They were also disappointed to learn how well Axis aircraft performed, how well-trained their pilots were, and how good their tactics were. This led to several Allied pilots pushing the throttle well past the boost limit, more or less in a panic. I have read personal accounts of some pilots doing exactly this. Some got away with it, some didn't. I have also read many accounts of blown engines from those early days.

Later some pilots realized they had gotten away with much higher boost settings than what the manual said they could do, and shared this info in the debrief. Given the extreme attritional pressure on these units in the early weeks and months of the war, local commanders either officially or otherwise okayed some kind of change upward in boost levels. This went up the chain of command. It got back to Allison. Allison responded by strengthening components of the engines and agreeing to compromise boost levels. Better fuel also became available which made higher boost more tenable.

Given the extreme pressures of the war, changes were made pretty quickly, and it seems by mid 1942 official boost ratings had already gone up, and by the fall of that year they had arrived at 56", 57" or 60" as an official boost level. And up to 70" for the Mustang Is (etc.). This helped enormously and contributed to stabilization of the more or less catastrophe experienced by Allied fighter units in late 1941 and the early days of 1942. I think the Soviets also did something like this with both their P-40s and their P-39s, though it is not entirely clear. Some Soviet pilots have mentioned increasing the RPM.

This in turn contributed to the sustained, surprise success of the P-40 in Anglo-American use in the Med, Pacific, and CBI, (and the P-40 and P-39 in Soviet use) later in 1942 and into 1943, to the point where several units flying these aircraft became elite units by early 1943, even though in early 1942 it looked like these same machines and units were totally outclassed.

At 56" or 57" Hg a P-39D or P-40E basically becomes a 1,500 hp fighter below 10,000 ft. In a real emergency it can probably be pushed a bit higher. The K model P-40 was making almost 1600 hp down low. This to me really helps explain why these aircraft kind of had a split Jeckyll / Hide reputation, IMO.

So how far can you push an R-1830?

 

[GTX]

https://airpower.airforce.gov.au/sites/default/files/2021-03/WP12-The-Australian-Aviation-Industry.pdf

 

[tomo pauk]

So how far can you push an R-1830?

Probably no more pushing than it was historically done, unless water/alcohol injection is used. Ie. under 49 in Hg 'dry'?

 

[GTX]

Probably no more pushing than it was historically done, unless water/alcohol injection is used. Ie. under 49 in Hg 'dry'?

Or you could go the R-2000 route which was a developed R-1830 and produced 1,300 hp @ 2,700 rpm with 87 octane, 1,350 hp with 100 octane and 1,450 hp @ 2,800 rpm with 100/130-grade fuel. Tying this back into this thread, The CA-14A development of the Bommerang was to install a 1,450 hp R-2000 engine and GE B-9 turbosupercharger. The estimated speed of an R-2000-powered Boomerang was 286 mph (460 km/h) at sea level and 372 mph (599 km/h) at 27,000 ft (8,230 m). The aircraft's rate of climb at sea level was 2,100 fpm (10.7 m/s) and 1,770 fpm (9.0 m/s) at 30,000 ft (9,144 m).