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The British were using the boost settings in the manuals or in the official notes/memorandums.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.
For anyone who does not have this yet I would recommend it.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.
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.
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.
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?
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.
And that gets us into the realm of RAM and claims of 1700hp Allisons and a host of other things.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.
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.
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?
Mustangs with the same engine were doing this routinely at much higher (70") boost for extended periods
And here we get into what RAM is/was.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
So how far can you push an R-1830?
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).Probably no more pushing than it was historically done, unless water/alcohol injection is used. Ie. under 49 in Hg 'dry'?