XP-40Q-2: test data emerged!

wuzak · Apr 10, 2018

tomo pauk said:
Engines in production, but without a 2-stage supercharged version:
R-2600, R-1820. Sabre, Griffon, Hercules or any other non-Merlin British engine. All Japanese engines. All German engines. All Soviet engines, V12 or radial, apart from problematic M-105PD delivered in token quantities.

The Griffon can't have been far of 2 stage production in Spring 1943, since the Spitfire VIIIG was testing with one in January, and production Spitfire XIVs were rolling off the line in the Autumn of 1943.

GregP · Apr 10, 2018

Allison proposed a 2-stage engine much earlier to the USAAC and they declined to fund it. End of development except for MUCH slower privately-funded development work. They weren't much behind the curve except for acceptance of the concept from the money holders.

P-39 Expert · Apr 18, 2018

tomo pauk said:
One series of series does not represent The Curve.
A 2-stage V-1710 is on production by Sping of 1943, so is the 2-stage R-1830 and R-2800, and obviously the Merlin.
Engines in production, but without a 2-stage supercharged version:
R-2600, R-1820. Sabre, Griffon, Hercules or any other non-Merlin British engine. All Japanese engines. All German engines. All Soviet engines, V12 or radial, apart from problematic M-105PD delivered in token quantities.

If we're going to count stages of supercharging and use that metrics on who is at, behind or ahead curve, the 2-stage supercharged V-1710 certainly does not look like it is behind the curve.

The R1820 was turbocharged in the B-17, wasn't it?

tomo pauk · Apr 18, 2018

P-39 Expert said:
The R1820 was turbocharged in the B-17, wasn't it?

It was, though I don't know what bearing that has on the engines with gear-driven 2-stage superchargers.

wlewisiii · Apr 18, 2018

I read in that report (thank you, BTW) about how the maneuverability is supposed to be greatly improved. And I remember Jeff Ethel describing flying in a P-40E as being like a "Pitts with an Allison engine" (see here: (REVISED) Most Formidable Low-Med Altitude Fighter Aircraft ) which seems to mean that it had to have been pretty amazing.

The first bubble canopy, I believe was in 1940 (the Miles M.20) but lacking a 2 speed supercharger on the -39 engine even the aerodynamic clean up of the Q probably wouldn't have helped a lot. Perhaps getting the E to 380? Considering the Zero's issues over 250, that alone would have helped!

Still it would have been interesting had the Q been the E model in the line even if still saddled with the -39 until Allison could catch up to the airframe. I also wonder if the F Merlin might have done better in a Q style airframe? Excuse me, Doctor? Could I use your phone booth for a moment, I need to visit a friend in Buffalo, New York ... say, January 1940...

What if what if what it... it's the game we play for all our favorite planes, isn't it?

tomo pauk · Apr 18, 2018

wlewisiii said:
...
The first bubble canopy, I believe was in 1940 (the Miles M.20) but lacking a 2 speed supercharger on the -39 engine even the aerodynamic clean up of the Q probably wouldn't have helped a lot. Perhaps getting the E to 380? Considering the Zero's issues over 250, that alone would have helped!

Still it would have been interesting had the Q been the E model in the line even if still saddled with the -39 until Allison could catch up to the airframe. I also wonder if the F Merlin might have done better in a Q style airframe? Excuse me, Doctor? Could I use your phone booth for a moment, I need to visit a friend in Buffalo, New York ... say, January 1940...

What if what if what it... it's the game we play for all our favorite planes, isn't it?

The engine on XP-40Q was outfitted with a 2-stage supercharger, not a 2-speed one. 2 stage supercharging means the air is compressed two times before entering the cylinders. That will provide a bigger boost (manifold pressure), especially at high altitudes, and more boost = more power. Thus, the XP-40Q was defined by it's engine, not by it's shiny 'new' canopy or clipped wings.

With that said - yes, better layout of radiators, while having just 4 HMGs would've probably improved overall performace on the plain-vanilla P-40s.

wlewisiii · Apr 18, 2018

Two stage. Sigh. I even know that. Thank you for the reminder, I do appreciate it.

GregP · Apr 23, 2018

Isn't it true that all high-altitude aircraft of WWII were pretty much defined by their engines and cockpit environments?

Not disagreeing, Tomo, just applying it to more airplanes than the XP-40Q-2.

*SkyChimp* · Apr 28, 2018

I notice the report comments on improve manueverability due to squared wing tips, yet the photos of the plane include the rounded tips of the earlier P-40s. 42-9987 was initially a modified P-40K without squared tips and without a bubble canopy and was designated XP-40Q-1. "Curtiss Aircraft '07-'47: Peter Bowers" makes no mention of 42-9987 having its wings clipped or a bubble canopy added later, but apparently those modification were gradually added to that particular plane. The photos of the plane in the report may be 42-9987 but it is not in the configuration that was reported in that test, though by the time the pictures were taken it had received the canopy modification.

CORSNING · Apr 28, 2018

GregP said:
Thanks for posting that, Tomo. I've often wondered how it performed and now can read about it. I wonder if we could find a flight report on the XP-72 and the Boeing XF8B ... I always thought those two would have been a great 1 - 2 punch, but really don't have much definitive information to go on except reported top speed. Would be nice to see a V-n diagram and some flight performance data.

HI Greg, what I was able to find on the XF8B-1:
http://www.alternatewars.com/SAC/SAC.htm

P-39 Expert · May 5, 2018

GregP said:
Allison proposed a 2-stage engine much earlier to the USAAC and they declined to fund it. End of development except for MUCH slower privately-funded development work. They weren't much behind the curve except for acceptance of the concept from the money holders.

The 2 stage Allison would have turned P-40s, P-51s and P-39s into high altitude planes. Just a separate impeller in a diffuser yet it took so long to develop.

Shortround6 · May 5, 2018

P-39 Expert said:
The 2 stage Allison would have turned P-40s, P-51s and P-39s into high altitude planes. Just a separate impeller in a diffuser yet it took so long to develop.

Leaves out the intercooler.

Having air enter the 2nd stage or carb at 200-300 degrees instead of 100 degrees or under limits power because A.) the air is less dense (fewer pounds per 1000 cubic ft) B.) you can use less total boost because you are closer to the detonation limit. There are engine details that affect things but the detonation limits are usually most affected by the inlet pressure, the inlet temperature and the engine compression. Now please note the the higher the inlet temperature the higher the peak temperature in the cylinders and the higher the exhaust temperature. In fact it pretty much follows right though. 100 more degrees at inlet to the supercharger means 100 degrees higher in the intake manifold and 100 degrees higher peak in the cylinder (requiring extra engine cooling) and 100 degree higher exhaust (hotter exhaust valve and exhaust port).

Water injection only goes so far and while more compact than a good intercooler setup it starts to get heavy real quick. P-63A with water injection was carrying about 236 lbs of equipment and and fluid.

Water injection can't be used to increase high speed cruise or climb. Both get a bit of boost from an intercooler.

wuzak · May 5, 2018

The nomenclature surrounding intercoolers can be confusing.

Some are actually after-coolers. That is, they cool the air after the compressor rather than between compressor stages.

The cooler on the Merlin was an after-cooler. I believe it was called that in the US, but "intercooler" in Britain.

Cooling between the 1st and 2nd stages of the compressor improves the overall efficiency - so that more boost can be made for the same, or less, power.

This is the way intercoolers worked for engines with turbos (turbo compressor is 1st stage, engine compressor is 2nd stage) and Pratt & Whitney 2 stage engines, where the engine stage was a fixed ratio to the engine and the auxiliary stage was fitted with a 2 speed plus neutral drive.

The Allison 2 stage engine did not have an intercooler, but some were fitted with an aftercooler. Most were not fitted with either, and made do with just ADI.

As SR said, ADI is limited usefulness. Not enough fluid was carried to use on all engine modes, and could only be used sparingly for war emergency power. I am not sure how much time the ADI gave n the P-63, but the advantage of the inter/aftercooler was that it was available again and again, so WEP could be used again and again (in short bursts, according to the rating).

Note that the Merlin 2-stage intercooler system circulated coolant in around the casing of the supercharger.

Two stage Superchargers

P-39 Expert · May 7, 2018

But you can have the high altitude benefits without an intercooler, just not WEP.

tomo pauk · May 7, 2018

P-39 Expert said:
But you can have the high altitude benefits without an intercooler, just not WEP.

You can have both high altitude benefits and WEP without intercooler, at least for the 2-stage V-1710s.

Shortround6 said:
...
Water injection can't be used to increase high speed cruise or climb. Both get a bit of boost from an intercooler.

Water injection can certainly be used during the climb. Having an intercooler many times meant increased drag, so not having intercooler also helps with high speed cruise.

P-39 Expert · May 7, 2018

Right, I should have said without an intercooler or water injection.

tomo pauk · May 7, 2018

P-39 Expert said:
Right, I should have said without an intercooler or water injection.

2-stage V-1710s were making WER ('WER dry') without intercooler and water injection, though implementation of water injection meant greater boost = greater power in 'WER wet' regime.

BiffF15 · May 7, 2018

P-39 Expert said:
But you can have the high altitude benefits without an intercooler, just not WEP.

P39 Expert,

The way i think about it is there is no free ride with power. More power takes more cooling and more fuel. ADI, intercooler, aftercooler are all about cooling. ADI has a finite limit, and in the case of the P63 weights in at about 240lbs as previously stated. It's weight goes down during use but its use time is limited. An intercooler also carries a weight penalty but is there for the duration of every flight / fight. Of the two set ups, one is okay and the other is much better in my opine.

Cheers,
Biff

Shortround6 · May 7, 2018

Some of the differences are subtle. But look at a Spitfire IX, it was allowed to climb at 2850rpm and using 12lbs of boost (54in map), this was a 30 minute rating which no Spitfire was ever going to need (or actually use) when climbing. This is as much or more boost than the Military rating of the engine in the P-63A was using (no WER, no water injection) but only by a few inches.

The Merlin was allowed to use 2650rpm and 7lb (44in) boost in cruise, granted it used a lot of fuel and may not have been ideal but the capacity was there.

The Allison was rated at 2600rpm and 43in in normal (max cruise) now consider you are "cruising" at over 20,000ft in each plane, with the extra stage of the supercharger providing a fair amount of boost, The Merlin is getting cooler air into the engine than the Allison powered plane with no intercooler. The heat has to be gotten rid of somehow. Larger opening of radiator flaps?

On the Allison in the P-63A 54 in was max military (and only obtainable near the ground) 60 in was WEP without water. And that dropped like a rock at high altitudes.
Water injection allowed 75in down low but actual benefit much over 20,000ft was a bit dubious. At least on the -93 engine.

Merlin could make 15lbs (60in) from about 20,000ft to 25-27,000ft depending on climb or level flight and exact model.

I would note that the R-2800 powered planes used both intercoolers and water injection.

The higher you go the the hotter the intake air gets as the superchargers are compressing it more to get the same manifold pressure and the decrease in temperature at the higher altitudes does NOT compensate for the increase heat of compression.

CORSNING · May 7, 2018

The first bubble canopy, I believe was in 1940 (the Miles M.20) but lacking a 2 speed supercharger on the -39 engine even the aerodynamic clean up of the Q probably wouldn't have helped a lot. Perhaps getting the E to 380? Considering the Zero's issues over 250, that alone would have helped!

Nakajima Ki.27b (Otsu): Production began in December 1938. Not a true
bubble canopy but it did allow the first enclosed all round vision.

XP-40Q-2: test data emerged!

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