That was a plan, in reality it was little bit chaotic. If you check aircraft status cards for Beauforts it seem like they were instaling whatever engine was available at the moment. You can find for example Beauforts VII numbered A9-205 onwards or even Beauforts with Twin Wasp S1C3-G produced in 1944 in "series" A9-600 to 700. Sometimes they instaled nonstandard engines, like R-1830-43 or -63 you mentioned.
A Radial Engined Fighter for the Australians to build (and maybe the Chinese and Indians)
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That was a plan, in reality it was little bit chaotic. If you check aircraft status cards for Beauforts it seem like they were instaling whatever engine was available at the moment. You can find for example Beauforts VII numbered A9-205 onwards or even Beauforts with Twin Wasp S1C3-G produced in 1944 in "series" A9-600 to 700. Sometimes they instaled nonstandard engines, like R-1830-43 or -63 you mentioned.
Shortround6
Major General
You are falling into the trap about weight again.
Sometimes the exact configuration of the test aircraft is not stated. Sometimes somethings are noted but there were seldom, if ever, a 10-20 point checklist.
There is a difference in weight, but all too often old authors would list off some changes form model Q to model R and then say "model R was 800lbs heavier than Model Q and speed fell by 20mph" and never go into the changes in drag that the extra weight may have (or may not ) have added.
According to some sources the P-40C was 7mph slower than the P-40B, now
was the entire 7mph speed change due to the weight and the brackets/racks for belly fuel tank was totally drag free?
was the entire 7mph speed change due to the brackets/rack and the increase in weight caused no change in speed?
was the 7mph speed change attributable to 3-5MPH being from the drop tank brackets/rack and 2-4mph due the increase in weight?
A couple of P-40 photos.
A non standard rear view mirror should have been noted in a test.
The hard demarcation line on the camouflage may not have been? Sometimes front line units just masked over the bottom color and sprayed over the mask and tape without sanding afterwards, the raised lines could be worth several mph.
There is one test of the older style exhaust stacks vs a flame dampening exhaust on a Kittyhawk which may or may be the type that was revered to a "fishtails". In any case the flame dampening exhaust cost 1-2 mph in the test. What is unanswered was if this was due to increased drag (larger exhaust?) or due to reduced exhaust thrust (exhaust gases were slowed down before exit.)
I have no idea if the short blast tubes were lower drag than the long blast tubes on the .50 cal guns.
A P-40E photo
This does have the fishtail exhausts, it also has a "standard" rear view mirror. At least drawings exist for it. How many were actually fitted I don't know.
Somewhere the is another test on paint and they got a 10mph difference by filling in low places and gaps in addition to sanding and doing the water/pumice thing.
That test broke it down into two steps with how much change from each step.
It was possible to have minor equipment changes that could affect speed more (not saying it didn't effect it all) than a several hundred pound weight change would.
Also be careful when an author says "change in performance" and not change in speed. Change in performance certainly affects climb, turn, take-off and landing.
For tests done by the RAF and the RAAF they may not have been aware off the degradation in performance caused buy dirty anti-backfire screens. Not picking on them, Some US AAF mechanics weren't aware of it either.
These tended to clog up fairly quickly and since they were mounted in-between the Pressure gauge and the actual cylinders you could be getting the right pressure on the manifold gauge but the engine might not be making the power it was supposed to because dirty screens were partially blocking the air flow.
MiTasol
1st Lieutenant
Even on the D and E there were multiple gun port/blast tube configurations. Here is one combination that is often overlooked.
That installation above did not use the more common -904 gun cover which is discussed below by a NASM expert on P-40s in reply to a question on a -702 found at a wreck site. Later it was found the -702 was used on H87A-3 aircraft for the RAF/Commonwealth.
-904 is item 20
Some of those minor equipment changes definitely included drag penalties - for a major example think of the football DF antenna. There were multiple other radio installations, all with different drag issues.
Change of performance due to dirty filters and backfire screens and other issues related to operational conditions are very real but difficult to quantify as they are often not detected until well after the event - for example at the next maintenance event where they can see what happened but can only guess at when, and in some cases, why. On a P-40 was that clogged screen a result of multiple flights in a dusty environment or just one flight where the aircraft was following another at low level or was it from flying through a dust storm etc. As another example of why - at one stage I was maintaining a fleet of Otters and one aircraft had a string of engine failures. The cause was eventually found when I did a test flight on a new engine and the young fella we had to do cleaning, fueling, and to go along as mooring crewman when operating off rivers came for the joyride. He asked me why I only used 36" on take off. It turned out he had only flown right seat on that aircraft with one pilot who always used 40". If he had flown right seat with any other pilot we would have known earlier.
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Shortround6
Major General
Some of the Allison screens could get fouled with stuff from dirty fuel. The fuel filters were supposed to get out most of the crud but some of the screens were supposed to be picking up some of the dye used for coloring the fuel. Any oil leaks from the engine into supercharger (how good was the seal on the impeller bearing?) and so on. You would hope the fuel would clean the screen?
even a clean set of screens were worth about 1000ft of altitude to the engine and since the only way to check them was to pull the intake manifolds and visually check them it may not have been being done unless the engine was displaying some sort of out of the ordinary behavior.
It took a while to sort out the backfire problem but after some point in 1942 (?) many of the older manifolds were refitted to eliminate the screens and new engines didn't have them so trying to figure what was going on with 1941-2 test aircraft also gets a bit difficult.
even a clean set of screens were worth about 1000ft of altitude to the engine and since the only way to check them was to pull the intake manifolds and visually check them it may not have been being done unless the engine was displaying some sort of out of the ordinary behavior.
It took a while to sort out the backfire problem but after some point in 1942 (?) many of the older manifolds were refitted to eliminate the screens and new engines didn't have them so trying to figure what was going on with 1941-2 test aircraft also gets a bit difficult.
Shortround6
Major General
The super P-40 gets a little old.
From a chart on the V-1710-33 engine. This is what the engine could make, not what it was rated at.
The chart has horizontal lines every 20hp and vertical lines every 500ft. So some of these could be off by 10-20hp
altitude..........................horsepower.
2000ft.................................1580
4000ft.................................1490
6000ft.................................1400
8000ft.................................1300
10,000ft.............................1220
12,000ft.............................1140
This is with NO RAM.
feel free to extend the altitude at a given power level by 2000-3000ft. However that ONLY works for max speed.
When Climbing or exiting a a tight turn the RAM effect, while present, is going to be much reduced.
Also note that while the Service squadrons used higher boost, the P-40D and E were never approved for higher boost. Neither were the long nose P-40s.
Here is the chart I worked from.
Please note that the "Specific Engine Flight Chart" has several errors as it apparently was an early one.
the 1040hp rating at 14,300ft was changed to 1090hp at 13,200ft. The 1090hp rating was at 38.9in.
In 1940 Allison was having a lot of trouble with -33 engine and there were a lot a changes made. The early engines had magnesium intake manifolds and several aircraft were lost when backfiring engines set fire to the manifolds and/or blew parts of the manifold off the engine. Of course having an engine blow a pressurized stream of fuel/air over a hot engine is going to lead to problems real quick.
It took quite a while but the major fix for the back firing problem was to change the valve clearance on the intake valves. The extra fraction of a second and/or the better sealing of the valves (clearance was set cold and as the engine got hot much or all of the clearance went away) but a lot of efforts was expended on sturdier intake manifolds that wouldn't blow off and the previously mentioned changes to back fire screens (polite name for flame arrestors in the manifolds) that required tweaking of manifold pressures to get the desired power output.
These Allisons would make very large amounts of power at low altitude but it didn't extend upward as much as some people believe.
Not errors, just different ratings. It is chart from late manual, issued July 20, 1943. At this point P-40B/C were used only for training, even the front page of manual is saying RP-40B and RP-40C. I believe that is also reason for lower "Emergency Maximum", there is no need for full 1090 hp in training.
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Wild_Bill_Kelso
Senior Master Sergeant
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I'm definitely not making any kind of "super p40s" argument, and I think the obfuscation and sidestepping is getting pretty old.
I just would like in general for all aircraft to have more accurate information supersede the myths and tropes which is also I think what you claim to want to do. But I guess we all have our favorite tropes.
I'm not sure what your point is above but I guess you're saying that the V-1710-33 also theoretically had the same engine capacity as the - 39, -73 etc. Technically this is correct but contrary to your mystifying statement that they were not approved for higher boost, the Hawk 87 (D, E and all later models) WERE in fact approved for higher boost. In fact the specific engine charts and flight operation manuals for the 87, depending on the specific date, do indicate the 57-in Hg boost setting "officially", which provides in the neighborhood of 1450 horsepower all the way up to 8 to 10,000 ft depending on atmospheric conditions. Which is exactly what I said i.e. "350 horsepower or more" over what is indicated in the manual for the hawk 81. I actually downplayed it a bit since it's more than 400 hp over. The Allison memo on overboosting also specifically mentions the -39 and - 73 for which they note they agree to a 60-in setting which is over 1500 horsepower.
The hawk 81 models, although rumored to be used with over boosting so far as I know were never officially approved for higher boost settings. As you yourself have mentioned several times there are quite a few minor improvements done to the - 39 and - 73 engines which amounted to strengthening them for higher boost.
The -33 lacked these changes to crankshaft crank case bearings & so on, not to mention that higher octane fuel was not necessarily available when they were being used most, so 1400 horsepower etcetera is not as likely with a Hawk 81/ Tomahawk..
As you like to frequently point out, the Hawk 87 was heavier than the 81 and considerably so than the original p-40. As a result, this affected performance particularly climb and altitude, possibly turning as well though this is never mentioned by pilots. This is why boost ratings were increased typically, has higher boost brought the aircraft into a more 'normal' performance envelope... just as was done for many other fighter types like hurricanes spitfires etc. Flying at the higher rated boost (not referring to overboosting here as that is less precisely documented) gave these aircraft much higher performance up to around 8-10,000 ft (or more like 12-14 in later types with higher tuned supercharger gears). Which is probably why they remained on the front line as fighters in so many theaters for so long.
It's just not accurate to pretend they're limited to 1,000 horsepower. Or to pretend that high boost was only available at Sea Level. As for ram, combat doctrine emphasized maintaining high speed using zoom to climb, performing nose down turns etc. All of which helped to maintain higher performance.
As with any successful fighter design emphasis of the optimal performance envelope was key to survival.
As for the 'weight doesn't matter for speed' argument, I agree that drag tends to matter more, and engine power matters a lot too, and some 20th century aviation authors over emphasized the importance of weight on speed specifically, but it's also overstating the case to suggest that 500 or 1,000 or 2,000 pounds weight difference with the same HP and RPM wouldn't affect top speed because it certainly did.
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Wild_Bill_Kelso
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And Hawk 87 had lower drag than Hawk 81 (or 75). Later Hawk 87 had lower drag than earlier Hawk 87.
Hawk 87 with 2 speed supercharger (Merlin XX) had considerably higher speed than the 1 speed Hawk 87, because it had more power up high (in the thinner air). Same would hold true for a Hawk 75 with 2 speed (or especially 2 stage) supercharger compared to the 1 speed.
A 2 speed Hawk would confer greater capability to Allied forces, arguably, potentially, and could have been better than most available fighters for certain roles (defense of Darwin comes to mind)
Hawk 87 with 2 speed supercharger (Merlin XX) had considerably higher speed than the 1 speed Hawk 87, because it had more power up high (in the thinner air). Same would hold true for a Hawk 75 with 2 speed (or especially 2 stage) supercharger compared to the 1 speed.
A 2 speed Hawk would confer greater capability to Allied forces, arguably, potentially, and could have been better than most available fighters for certain roles (defense of Darwin comes to mind)
FLYBOYJ
"THE GREAT GAZOO"
I don't have a dog in the fight, but where is this coming from? What are the actual numbers?
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Wild_Bill_Kelso
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Well I posted sources showing Hawk 87 had a thinner, smaller fuselage, and listed a few of the other small changes.
Shortround6
Major General
Yes the obfuscation and sidestepping is getting old.
The V-1710-33 and the 39 and the 73 had just about the same capability in regards to the air flow through the supercharger.
There were 2 variables that are well known, one is the backfire screens and there was minor adjustment to the inlet vanes of the superchargers.
The D & E were approved for higher boost, my mistake, but it was not officially done until Dec 1942 for the -39 engine.
Now where the argument comes from is from
" the 57-in Hg boost setting "officially", which provides in the neighborhood of 1450 horsepower all the way up to 8 to 10,000 ft depending on atmospheric conditions."
Now there may be a some sources that say 56' and some some sources that say 57" but now we are talking about less than 2%.
56" is supposed to give a rating of 1490hp at 4300ft. on the -39 engine.
Pretty damn good atmospheric conditions to raise the "neighborhood" of the WEP to 8 to 10,000ft.
Or does neighborhood mean 1350hp?
Or does neighborhood mean 1250hp?
Now from tests is sure looks like the P-40D & E had trouble maintaining it's 1150hp rating much above 12,000ft despite what the engine chart in the manual says.
That claims it was good for 1150hp at 15,000ft but doesn't say if it was with RAM or without it.
Trouble is we have another chart that says something rather different.
Hmmmmm.
only 54 in at sea level and 1470hp at sea level?
and we only have 1150hp at 11,800ft?
we lost over 3,000ft of altitude between charts?
and is does say with RAM.
Strangely enough the chart for the -73 engine also says with RAM
However the results of tests show that the engine in the P-40E could hold 43.X to 44.X at higher altitudes than 11,300-11,800 in high speed level flight.
Go back to the chart for the -33 engine, it is showing 54 in (1480-1490hp) at 4,000ft in the test house with no RAM at all, It is not hard for me to believe that the engine could make 1490hp at 4300ft at 56in as installed in the airplane. I can even believe with no trouble at all that the plane could get that power at 2-3,000ft higher.
The problem I have is that the engine is going to make neighborhood of 1450 horsepower up to 8 to 10,000 ft and then it is going to fall over a cliff power wise as the plane gets to 12,000ft were the power drops to 1150hp.
Just for a Reference a Merlin 50M with a cropped impeller In A Spitfire V was supposed to be rated at the factory at 18lbs of boost (66in?) at 2750ft but in test it managed 18.2lbs to 3800ft while flying at 170ASI when climbing at and it held 18.2lb to 5900ft when doing 335ASI (350.5mph true) in level flight.
There is your atmospheric conditions.
The Spitfire V had dropped to 11.4lbs at 10,000ft while climbing and 13.4lbs in high speed flight.
Shortround6
Major General
The P-40F had better speed because its top speed was at an altitude quite a bit higher than than the Hawk 81(or an Allison Hawk 87)
Altitude.................................speed................................power
12,800ft ...........................350.5mph...........................1280hp (low gear)
19,270................................364.5mph..........................1105hp (High gear)
P-40F was using almost 200hp more to go about the same speed at the P-40B/C at little bit lower.
It was using about the same power to go about 13-17mph faster at over 4,000ft higher in the thinner air. (no adjustment for higher exhaust thrust)
Sure doesn't prove to me that the P-40F had lower drag than the P-40B/C.
FLYBOYJ
"THE GREAT GAZOO"
Well that really doesn't prove much unless you can really substantiate the actual drag the aircraft is producing. Off the cuff, the only way I think you're going to do that is in a wind tunnel
Shortround6
Major General
If we compare two aircraft at the same altitude and using the same power (or very close to the same) and they go the same speed we can pretty much figure they have the same drag.
What we don't know is what details were contributing what percentage of the total drag. And that is for either plane. A wind tunnel can figure that out a lot quicker by allowing faster modifications with much more stable conditions.
Once we start using data that is 2, 3, 4, 5 thousand feet different in altitude or speeds that are more than just 1-2% different or different powers then things go to pieces in a hurry.
For the "size equals drag school of thought" one chart has the following
Aircraft.........................................equivalent flat plate area.
F2A-3..................................................6.27 sq ft
P-47B..................................................6.39 sq ft
F4F-3...................................................6.53 sq ft
P-38J....................................................8.84 sq ft
F6F-3...................................................9.08 sq ft
So yes, a wind tunnel is a very, very good thing to have to try to figure out anything more complicated than a side by side speed test.
The side by side by speed test only really tells you that Plane A was faster than Plane B (or slower) sort of like a greater than > or lesser than < result. trying to figure out how much greater or lesser gets to be very hard.
What we don't know is what details were contributing what percentage of the total drag. And that is for either plane. A wind tunnel can figure that out a lot quicker by allowing faster modifications with much more stable conditions.
Once we start using data that is 2, 3, 4, 5 thousand feet different in altitude or speeds that are more than just 1-2% different or different powers then things go to pieces in a hurry.
For the "size equals drag school of thought" one chart has the following
Aircraft.........................................equivalent flat plate area.
F2A-3..................................................6.27 sq ft
P-47B..................................................6.39 sq ft
F4F-3...................................................6.53 sq ft
P-38J....................................................8.84 sq ft
F6F-3...................................................9.08 sq ft
So yes, a wind tunnel is a very, very good thing to have to try to figure out anything more complicated than a side by side speed test.
The side by side by speed test only really tells you that Plane A was faster than Plane B (or slower) sort of like a greater than > or lesser than < result. trying to figure out how much greater or lesser gets to be very hard.
Allisons V-1710-33, -39 and -73 were basically capable to produce same power. They have same supercharger impeller diameter, same compression ratio, same rpm. This is confirmed by graphs in Airplane engine performance data charts, they are (within variation) same for all Allisons V-1710 in this configuration (9.5 in impeller, 6.65:1 compression ratio, 3000 rpm) including series E engines (found in P-39s).
You are right that V-1710-39 was cleared for 56 inHg and V-1710-73 even for 60 inHg. Let's not talk right now about fact that those ratings were officialy only allowed with instalation of Automatic manifold pressure regulators which P-40E get very rarely (if ever) with combat squadrons, but that is not important. By the way I agree with Shortround6 that "1450 horsepower all the way up to 8 to 10,000 ft" is a little bit stretch, maybe in Allison powered Mustang you can get close to 8000 ft, maybe.
You are also right that V-1710-33 was never cleared for War emergency rating. However, if we take a look when was War emergency rating as a thing even established than it make sense. Story goes like this - during 1942 there were reports about using engines in combat well beyond established ( by manufacturer ) ratings without catastrophic failures. USAAF Material Command (in cooperation with manufacturers) therefore introduced near the end of 1942 War Emergency Rating, aka "How much maximum safe power can we squeeze from engines in our service now that we don't care about time between overhauls that much". And here is the thing, at this point (end of 1942) airplanes with V-1710-33 were out of frontline service, so why even bother with testing and other things required for engine to be cleared for WER. Make sense? Now, I am not saying that V-1710-33 was capable to withstand same "abuse" as V-1710-39/-73. It probably wasn't (and some sources sugest that), but I do not believe that it was impossible to have much higher power as WER in V-1710-33. However we will never know.
Why do you think that Hawk 75 would be faster than Allison powered P-40 in any altitude? Why Wildcat even with 2 stage supercharger was slower(or as fast) in high altitude in comparison with P-40E than? I am sure that someone will wrote that Wildcat was much better (faster) fighter than P-40E, especialy in altitude, but is it really true? Anyway, this is way off topic here.
Are we talking about Hawk with two speed supercharger R-1830? If so than no, it could not have been better than most available fighers for certain roles. It will be worse than P-40E or Airacobras. It can be useful for really short period of time when there was no fighter in Australia, we are talking about few weeks here. I mean sure, they will be wiped out in Darwin in February 42 raid instead of P-40Es (which were there kinda incidentally and not for defence of Darwin) and/or decimated in Rabaul month earlier, but that's about it. To be fair, they can defend Port Moresby for some time until 75. sqn with Kittyhawks arrives, better have something there than empty hands for sure.
Critical altitude (aka Full Throttle Height) of R-1830 with two speed supercharger is pretty low, some 13 500 ft for high blower (2nd speed) and you have there around 1050 bhp, depend on engine rating. My point - two speed Twin Wasp is not really altitude engine and Hawk with this engine is not at all high altitude fighter.
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Wild_Bill_Kelso
Senior Master Sergeant
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You're forgetting that most of the hawk 81s used in combat we're not used by the us but rather by Commonwealth and Soviet units. Some of which were still flying them as late as 1943 (one SAAF unit at least)
None, I was comparing with 1 speed Hawk 75. I know that was a bit jumbled together & therefore probably not quit clear.
I agree that the wildcat was not faster, but it was probably more useful against certain kinds of bombing raids. And I think the hypothetical two-speed hawk 75 probably would be as well definitely a two stage
No it wouldn't be true
I think it would be better for intercepting high flying bombers, or for escorting say b17s or B24s. In that Theater I think it would be at least as good probably better than an Aircobra and probably easier to maintain
Depending on exactly what the performance at altitude would be I think it could have been better than Kittyhawk I or Ia
I was really thinking more for medium altitude. That is admittedly a little lower Critical altitude than I thought, but like the wildcat hawk would be a little bit lighter than a p40. And the wildcat had a better altitude performance.
For that matter I think Australia would have been well served by some F4F3 style wildcats without Naval equipment
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Wild_Bill_Kelso
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Also worth mentioning that p40d and e and equivalent were in service a lot longer with Commonwealth and Soviet Union than US. Some were heavily used by Commonwealth & then sent to Soviets.. Some more re-engined with V 1710-73, including (I think) some RAAF
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Shortround6
Major General
Actually the talk about the Allison engines is probably off topic
Since we are supposed to talking about radial engine fighters, alternatives to the Boomerang
Part of our problem with this discussion is the fact that the speed at altitude is often being left out. The F4F-4s could do about 320mph at just over 20,000ft. British Data card for the Wildcat V says 332mph at 21,000ft. With 1000-1050hp on tap at 20,000ft or so it didn't do too badly over 20,000ft. The problem was they were bog slow at lower altitudes. 292mph at 3,250 ft and 313mph at 13,000ft.
So against a P-40K or earlier the Wildcat could be superior at some where around 20,000ft and up. It was not superior at lower altitudes.
It might have been possible to set up a single stage supercharger R-1830 for decent performance at 13-14,000ft or so.
The US built one P-36B with a different gear on the supercharger. They got better performance at altitude than the normal P-36s. 317mph at 17,000ft?
But the change in supercharger gears cost 100hp at take-off and for low altitude flying.
Without 1943 knowledge of radial engine cowlings there is no hope of a P-36 coming close to a P-40 in performance.
If you have not seen it please look at
http://www.wwiiaircraftperformance.org/P-36/P-36A_38-180_PHQ-M-19-1152-A.pdf
These are all cruising speed powers and not max speed. BUT there are power numbers in some of the early P-40 tests and the P-36 needs several hundred HP more to go the same speed at the higher cruising speeds.
How much is drag and/or lack of exhaust thrust from the radial engine I don't know but difference was real, it could be measured and it was a big reason that the P-40 was built instead of more P-36s.
And once you move away from the one speed or two speed single stage R-1830 engine the more difficult it becomes, the two stage engine is heavier, and it needs extra volume in cowl.
The intercooler air intakes were in the 4-5 o clock and 7-8 o clock positions inside the cowl. the part with the orange arrow is ONE of the intercoolers. there was another one on the other side. F4F-4s just dumped the intercooler air into the Wildcats wheel wells and didn't have any duct work behind the intercoolers. Not sure how that would have worked on a P-36 or Boomerang.
Here is a picture from the front.
Carb intake is at 12 o clock. Cowl was much bigger than the engine. Oil cooler is the duct just inboard of the wing fold.
I am not saying it cannot be done, just that it was harder than just saying "oh, just stick the two stage engine in the plane."
P & W did build a P-40 Prototype with a two stage R-1830 engine and got over 380mph out of it the low 20,000ft altitude range. But they they didn't do it until well into 1943 which is too late for Australia to start arranging to make the plane (shows up in 1944?)
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Wild_Bill_Kelso
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Well, I think these are all numbers we're familiar with already but we're just parsing them differently. I'm sure you've seen this test many times, it shows full war emergency power 57 inches maintained to 9500 ft and at 10,000 ft aircraft is still making 55 in (which is still going to be over 1400 horsepower I think) and still 46.75" at 15000 ft
Flight chart for this plane says 57" Hg /1480 hp to 7,500' (no RAM) and 10'000 ft with RAM
...but the Australian field test showed it available at 2000 ft higher. I don't know if 'atmospheric conditions' in Australia we're just super ideal here, but I would actually assume the opposite. A US test with the same engine (on a modified P-40k) made about 30 mph better speed.
Now that is the -81 with the higher (9.6) supercharger gear. The K won't make that much power that high up. But I really don't think 8-10'000 ft is such a stretch.
Flight chart for this plane says 57" Hg /1480 hp to 7,500' (no RAM) and 10'000 ft with RAM
...but the Australian field test showed it available at 2000 ft higher. I don't know if 'atmospheric conditions' in Australia we're just super ideal here, but I would actually assume the opposite. A US test with the same engine (on a modified P-40k) made about 30 mph better speed.
Now that is the -81 with the higher (9.6) supercharger gear. The K won't make that much power that high up. But I really don't think 8-10'000 ft is such a stretch.
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Wild_Bill_Kelso
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Unfortunately I don't know of any thorough performance tests like that on a P-40k, though there must be some.... Somewhere.
