Packard P40

GregP said:

Everyone touts the performance of the Mosquito, but the XP-40Q was faster. It would have been a good new mount. Alas it is a "might have been," as were many other potentially good planes. I'mnot crying over it all these years later, but at least give the thing it's due credit. It definitely DID represent a pretty good performance upgrade over the P-40N. That would have been welcome, no matter where it came from.

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Well, the Mosquito was a bomber or PR aircraft, or night fighter.

An equivalent period Mosquito bomber, the B.XVI could do 400mph+ with a 4000lb bomb on board. And very nearly the same speed as the P-40Q without a bomb load.

It is a similar situation for the PR.XVI - very nearly as fast as the P-40Q.

The NF.XXX was faster than the P-40Q. And that carried a radar and much heavier armament.

But of course the Mosquito and P-40Q aren't really directly comparable aircraft.

The Spitfire IX and VIII are. They are slower by about 10-15mph, but at least half of that is due to the drag caused by the 20mm cannon barrels.A trade-off between speed and armament.

But what advantage does the P-40Q give over the Spitfire IX and VIII other than that slightly higher top speed? A better rate of roll? Longer range?

The Spitfire has it beat in terms of climb, turn and firepower. And a clipped wing version would be competitive in roll, if it sacrificed some or all of its other advantages.

You mention that it had the advantage of roll against the P-51. Where else would it have an advantage?

The P40F with the single stage Packard built Merlin seemed to achiev the same speed as the Spitfire V with the single stage Merlin. Exact comparisons not possible as the Merlin 28 in the P40F had two speeds while that in the Spitfire V had more power but only one speed.

In all likelihood the P-40F was the better aircraft overall, possibly climb rate excepted, and note climb rate is very power dependant: it had a much higher roll rate, faster acceleration in the dive and for practical purposes better dive rate. It had a much greater range and likely out turned the spitfire much as the Hurricane could. Given equal engine power at equal altitude it was surely a better overall aircraft. Fitting the inter cooled two stage Merlin might have presented a task in airframe modification but it might have been easy, we don't know. Had a two stage Allison or Merlin using water injection instead of inter cooling for charge cooling been available to the P40 in mid 42, the same time the Spitfire IX received the two stage Merlin 61, it might have been one of the great aircraft of history. The 422 mph speed of the P40Q on less power than the Spitfire IX shows this is likely true. Remember the P51B only flew its first missions in December 1943.

The P40 might be inferior to the Mustang in speed but this is not clear cut with the Spitfire. The range of the P40 might have made it a suitable escort with the right engine.

GregP said:

Well now Shortround, the speed I have is 422 mph at 20,500 feet.

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From my post #12 "The 422mph needed at least 1600hp if not more and 75in manifold pressure and 3200rpm and water injection" so I would say that was WEP.

No two fighters of WWII had the same drag coefficient. Does that make them all inferior to the one with the lowest Cd? I'd have to say no to that one. The guys who flew the immprtals like the Spitfire and the Bf 109 might beg to differ, too.

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Kind of misses the point doesn't it.

The premise of this thread is that the author wondered why a 2-stage Merlin wasn't installed in the P-40. It certainly could have been and might have been, but was never proceeded with. The XP-40Q doesn't fit the thread's premise.

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It sort of does. Author of thread wondered why they didn't stick two stage Merlin in a P-40. Two stage Merlins were not hanging around looking for airframes to go in and the test flights of the XP-40Q show that the XP-40Q needed more power to go slower than a P-51. Using a limited supply engine to build an inferior aircraft doesn't make sense. Main difference between a two stage Merlin Powered P-40 and the XP-40Q would be that the XP-40Q doesn't have the drag of the intercooler used on the Merlin. Granted the Merlin version would have a bit more power at higher altitudes.

And that is the point. The US had it's choice of airframes to use the Packard Merlin in. Using them in P-40 airframes would result in better P-40s but the better P-40 won't do what the P-51 would do.

No WW II fighter was the best at everything. But if you are looking for high performance low drag certainly helps. Typhoon vs Tempest? Bf 109E vs Bf 109F? Spitfire vs Hurricane?

And that was the problem with the P-40, it was high drag and nothing short of a total redesign was going to fix it.

Hi Shortround,

You're the one who touted drag as a factor, so it is right on your point. I wouldn't have brought up drag myself, not from any lack of impoprtance, but more from not wanting to reduce the XP-40Q to an aerodynamics discussion. And I just didn't want to argue about it. Had the XP-40Q gone into production, we'd have some real-world combat and test performance numbers to look at. As it is, all we have are test reports on the prototypes. Few prototypes were representative of the production combat planes. Some of the production planes were better and some of the prototypes were better. I daresay a Spifire XIV was a considerably different beast from the Spitfire prototype and was much better.

Hi Wuzak,

I threw in the Mosquito because it is widely believed in here that catching a Mosquito was impossible or nearly so. If that were really true, then no Mustang or Spitrfire should ever have been shot down when on reconaissance, and that was not the case. But if the XP-40Q was faster than a Mosquito, then it could easily have been an effective aircraft ... I was not trying to replace the Mosquito with hordes of XP-40Q's by any means. That might get me lynched in here ...

I'm going to try to talk with Steve Hinton this weekend about his Mosquito flight a couple of weeks ago, but he also might not be there and might be pretty busy. They are doing last-minute work on the Mustangs and the Horsemen have a P-51 aerobatic show in Michigan and one in Anchorage in July at Elmendorf (Arctic Thunder). Hopefully he has some time and can tell me a thing or two. We'll see ... my task tomorrow is to remove the carburetor from our P-47, so it might be a busy day. ALso I think Bent-Metal may show up at the museum to say hello and look around. That almost guarantees a bust day!

Meanwhile, they're pretty much finished with a new baby Tigercat at Fighter Rebuilder and I'll get pics Saturday to post in here. It's not really completely finished, but definitely looks close. Still needs the vertical fin, but that won't fit into Fighter Rebuilder's shop. Actually it does fit but won't clear a support beam to roll out, so it has to be off when the Tigercat is rolled out the shop door. They have to move it into the Planes of Fame restoration hangar to install it. It is ready to be mounted and the Tigercat SHOULD be flying sometime soon. Hopefully I can get pics ...

Shortround6 said:

In fact the XP-40Q sucked, it just didn't suck as bad as earlier P-40s.

It needed more power to go slower than a P-51 while weighing less. The 422mph needed at least 1600hp if not more and 75in manifold pressure and 3200rpm and water injection. A P-51D could do about 416-418mph at the same height using just under 1300hp. Using a bit over 1400hp the Mustang could was good for 428mph? and the Mustang could go faster higher up and weighed 760lbs more. P-5D performance figures include a bomb rack under each wing. P-51D may be carrying 6 guns ( a 50% increase over the P-40Q) and more ammo.

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I might be wrong but the Spitfire never managed 422 mph on 1300 hp. Would you say in this timeframe the spitty sucked too?

rank amateur said:

I might be wrong but the Spitfire never managed 422 mph on 1300 hp.

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Neither did the P-40Q.

Yes it did 422.

Not too sure about the HP but I doubt it was 1,300 at 20,500 feet. The 1,425 HP was a sea level for takeoff. If I am not mistaken it made about 1,100 HP at 20,000 feet or so at Mil setting. The figure is hard to nail down but the 1,425 definitely was sea level takeoff only. It DID have a WER (sea level) and COULD be operated at 75 inches of MP down low, Don't know what WER was at 20,500 feet, but it wasn't the full 1,600 HP. That's for sure.

wuzak said:

Neither did the P-40Q.

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I never claimed it did. That's the whole point. The mustang did but lots of other highly respected fighters did not..

The test report re. XP-40-2 is available at Williams' site.

Looking through my data I can find that the were three XP-40Q prototypes.

Two were fitted with V-1710-101 engines (F27R models) and the third was fitted with a V-1710-121 (F28R). XP-40Q # 1 had a V-1710-101 rated at 1,100 HP at 28,500 feet and 3,000 rpm at 50" MAP and 1,220 HP at 25,000 feet, 56" MAP at 3,000 rpm. XP-40Q # 2 had a V-1710-101 rated at 1,250 HP at 25,000 feet, 50.0" MAP and 1,500 HP at 6,000 feet, 60.0" MAP. There is no record of WEP power at 20,000 feet.

XP-40Q #3 was fitted with a V-1710-121 rated at 1,100 HP at 28,000 feet but no specified MAP. The WER was 1,700 HP at 26,000 feet with no specified rpm or MAP. Separate reports, one from Mike Williams' site, indicate 75.0 inches and 3,200 rpm for the 422 mph run, but no power level was indicated at 20,500 feet. It wasn't the same as at 26,000 feet and could be higher or lower. I'd assume lower since max power was usually quoted by all manufacturers whenever possible. I have 1,050 HP at 2,600 rpm at sea level without a specified MAP … assume it to be 57" and you won't be far off. That would be normal takeoff unless it was a short field.

The -121 had a 50 spline shaft and was likely fitted with a Curtiss-Electric propeller, though an Aeroproducts or Hamilton-Standard might have done better. Wider chord helped.

The Mike Williams site specified XP-40Q-2 with less HP than was available for XP-40Q-3 with the -121 engine, less HP by about 450 HP or so … but we don't HAVE a flight test report for XP-40Q-3, so … it is an exercise in frustration. We know they didn't adopt the P-4Q, but little definitive other data is known except for ONE flight report we have access to. The bets one has no data I have seen. It could well be faster, but by how much?

With no drag change, going from 1,250 HP to 1,700 HP would yield about 468 mph … but we have no record of that. If the HP at best height was less, I don't know how much less.

Frustrating to say the least …. and in no way definitive. I make no claims here for the XP-4Q-3 and only wonder if the data may someday surface.

Mike Williams site: http://www.wwiiaircraftperformance.org/P-40/XP-40Q2_Eng-47-1728-A.pdf

Included in the 18 page report are speed graphs (page 8 ), climb graphs (pages 10 11) and power graphs (pages 9 12). Power graphs show power for 3000 rpm/ 59.5in map, 3000rpm/75in map ( or whatever the supercharger maintain at altitude) and 3200rpm/75in map.
Perhaps a different prop and/or working speed control may have improved things a bit but the P-40 airframe/wing was never going to equal the P-51 ( just look at the Allison powered versions).

The charts say that the 422mph was done at 3200rpm and 75in Map and the power chart says 1700hp or more at that height.

rank amateur said:

I might be wrong but the Spitfire never managed 422 mph on 1300 hp. Would you say in this timeframe the spitty sucked too?

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depends doesn't it ?

The Spitty was about 2000lbs lighter than a P-51 using the same engine and about 1500lbs lighter than a P-40 using the same engine. This means it could do something the American planes had a harder time with (like climb and turn).

However the Spitfire was not going to be the long range fighter the P-51 was even if you could find room in the plane for fuel. It might have come close but it's higher drag means less less range for the same fuel.

BTW a MK IX Spitty could do 404mph at 21000ft on about 1500hp. (18lbs boost./66in ? ) with a Merlin 66.

When trying to use speed as a comparison for drag you need to know not only the power ( and exhaust thrust gets hard to figure, use of water injection may increase exhaust mass, it might not depending on fuel settings.) but the altitude as the different air density changes the drag. Roughly 2% per 1000ft so a 1000ft difference isn't too bad. Trying to compare speeds at 4-5000ft difference gets a lot harder. (difference in altitude also changes exhaust thrust).

Shortround6 said:

The Actual P-40Fs and P-40Ls with single stage Merlins went to North Africa as it was known that the Allison powered P-40s were at a disadvantage against the German fighters, unfortunately by the time they show up in numbers the Germans are converting to the 109G.

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Though there were bad moments, the DAF fought at modest altitudes and, on the whole, would seem to support my position. Initially, the bad particularly the US pilots in the DAF can be attributed to the Kasserine Pass syndrome. Against LW aces like Hans-Joachim Marseille and using WWI tactics like the Lufberry circle, the poor performance wasn't the fault of the equipment. Still, gaining knowledge they became effective enough to cause the LW to retire the Bf-109E. The P-40 actually did rather well in an air superiority role. Some of the loss/kill records are at;

Curtiss P-40 Warhawk - Wikipedia, the free encyclopedia

However, the P-40 took on the role of ground support since the battle was about tanks on the ground rather than the LW. Loaded with racks and bombs the P-40 gave up both performance and tactical advantag3 as they operated low and slow. Still, as reported day by day at,

Serving Uncle Sam: The Military Life of Gerald Schwartz

the p-40 crews seem to feel that the job was being done from an advantaged position.

Hi Shortround,

The XP-40Q-2 wasn't cleared for 3200 (though it DID have the 12-countereight crank), it was a -101 engine. And it wasn't cleared for 75" MAP either. It was a 1,425 HP engine for takeoff.

So either the graph is mislabeled as "XP-40Q-2" when it really was the XP-40Q-3 or they exceeded the engine specs by a wide margin in test (not a usual procedure).

Something is very wrong here since the V-1710-101 was not a 1,700 HP engine.

According to "Vees for Victory" the XP-40Q-2 is believed to have flown with both the -101 and -121 engines, page 186.

Flights for the test were done in March of 1944. The -101 engine was ready for 'testing" in July 1943 (ground?). It was flying in a XP-40Q in Nov 1943. 3 were built (?).

The -121 was first built in "early" 1944 (month not given) and is pretty much a -101 with a different gear ratio to the Auxiliary supercharger. 4 built (?).

It is noted that one of the -101s was damaged when the reduction gear broke off and (these engines used a 2.36 prop reduction gear to allow for the 3200rpm limit) and a -89 engine was converted to -101 specs by fitting a new reduction gear setup and the accessories section, carburetor and auxiliary supercharger from the damaged engine. This same engine was later converted to a -121 by changing the gear ratio to the auxiliary supercharger. I have no idea if this engine was counted in the build numbers or not.

The -101 engine was rated at 1500hp at 6,000ft at 3200rpm at 60in (no water injection?) WEP and 1325hp for take-off according to one listing in the book.

Information seems to be a bit confusing. Why install 2.36 prop reduction gears instead of the normal 2.0 gears if the RPM was held to 3000rpm? One source says (or infers) that the -101 didn't have the 12 counter weight crank as the new crank is listed as a change between the -101 model and the -121.

Any report,chart or listing can have possible mis-prints. Is it possible that the report is correct and that the XP-40Q-2 flew in March 1944 with a -121 engine? It seems so to me, depends on what "early 1944" means.

As a further reality check the P-40F was good for about 365-375 mph at 18,100 to 19,300ft using 1100hp depending on which test you read and the P-40N with the -81 engine (9.60 supercharger gears) was good for 371mph at 17,300ft using 1100hp.

If I am reading the charts right (big IF) the XP-40Q-2 needed just under 1350hp to go 390mph at 18,000ft. using military power. Perhaps I am not using the cube rule right but it is not corresponding as well as I would like. And when I try to use it on the XP-40Q-2 to go from 397mph and 422mph the answer comes out almost 200hp lower than what was actually used. I could be using the formula wrong or the P-40 was running into a step rise in drag at around 400mph (much like the Typhoon ?) or the prop used was loosing efficiency at that altitude and power or a combination?

Going back to the original question, Packard could only supply so many engines (about 1300 a month in 1944 of the two stage engines) with a fair number of them going to the British. DO you restrict P-51 production so you can have better P-40s?

The engines (V-1710s here) with both 'Keystone' piston rings and 12-counterweighted crankshafts were allowed for 3200 rpm not only for WER operation, but also for military power and take off. Engines with just 6 counterweights and Kesytone rings were allowed for 3200 rpm just for WER.

Shortround6 said:

Perhaps I am not using the cube rule right but it is not corresponding as well as I would like. And when I try to use it on the XP-40Q-2 to go from 397mph and 422mph the answer comes out almost 200hp lower than what was actually used. I could be using the formula wrong or the P-40 was running into a step rise in drag at around 400mph (much like the Typhoon ?) or the prop used was loosing efficiency at that altitude and power or a combination?

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I think you need to use the Prandle Glauert Correction. Supposedly works to Mach 0.7.
http://en.wikipedia.org/wiki/Prandtl–Glauert_singularity


If I plug in Mach 0.57 (about 400mph at 20000ft where Mach might be around 700) the drag rise is already 1.227 times what non compressible flow should be. It's equivalent to the Cd going up by that factor. It would do my head in to try and work its effect on the drag equation using say a spreadsheet, I will have a go at it, as its definitely possible. Laminar winged aircraft tended to have a lower drag at high speed due to their higher mach number. The real advantage of the Mustangs laminar flow wing was this mach effect not the supposed laminar flow.

The thing I'm curious about is how much better an aircraft, in this example a P-40Q, would have to be over a P-51 to rate production? The P-38K (IIRC) was quite a bit better performer than the prevous model but wasn't approved for fear of production line interruption (slightly different arguement due to mission the aircraft were performing). It's tough sometimes in here to see things through the eyes of those making these decisions during WW2 (they were theorectically looking at things on a broader perspective without the benifit of up to date data that we now call "history").

Anyone what to fathom a guess as to how much better a P-40Q would have had to be to warrant production?

Cheers,
Biff

Hi Shortround,

I believe you may have the answer there. It certainly appears as if the XP-40Q-2 had both the V-1710-101 and the V-1710-121 engines installed at some point.That would acount for the apparent discrepancy between the chart and the -101 specs.


Hi Biff,

I think the XP-40Q woiuld have had to outperform the P-51D and would have had to have been shown to be capable of out-delivering the P-51D, too, even in the short-term. The real priotity of the War Meteriel Board seems to have been deliveries, with accent on short-term. Otherwise they would have permitted the improvement of the F6F Hellcat, which was shot down due to short-term delivery impact. They wanted to eliminate the dihedral to improve the roll rate and were denied, and also wanted to make a few other changes that were also denied due to delivery impact that would last for a couple of months.

The decision seems to me as if it came from people interested in statistics rather than the effect of improvements, but maybe that is due to the documents I have read and it might have been otherwise in reality.

To me, the top fighters all had different top speeds and different handling characteristics. So saying the XP-40Q was not proceeded with because it was 15 mph slower than the P-51D's best speed doesn't make sense. Every other fighter that WAS proceeded with was either a bit slower or a bit faster. The real reasons have to lie elsewhere, and finding them may prove somewhat elusive at this point.

You have the problem that the XP-40Q as built with the Allison engine was a bit under armed. While four .50 cal guns might have been OK the 235rpg was probably frowned upon. Production versions were supposed to go to either six .50s (ammo unspecified) or four 20mm guns. The extra .50s and more ammo might not have hurt speed much but climb and ceiling? the drag of 20mm gun barrels might have knocked off a bit more speed.

In early 1944 they were trying to figure out how to wind down P-40 production as production planning had already shuffled it to advanced trainer for the US Forces and for lend lease use only. No new US combat units were to formed using P-40s and existing P-40 units were to be converted to other aircraft types. The P-40 is going to need a miracle to stay in production, especially in a modified form, at this stage. Material allocations were made months before the aircraft were actually built so quick changes of production numbers was hard to do.
The P-40 did a lot of good work in 1942 and 1943 but it's day was done as a fighter by 1944. Perhaps it's reputation would have been even better if more of the Merlin powered versions had been used in the Pacific or if Allison had been able to fit the 9.60 gears sooner to help eliminate the Japanese altitude advantage.