Structural weight of early U.S. fighters compared to Spitfire Mk1 and Bf-109,

[tomo pauk]

Lack of altitude performance for both, insufficient speed and lack of protection for the P-36 / H75. Lack of climb / insufficient power for weight for the P-40

That big flaws had a lot to do with what was in front of the firewall - ie. engines not being as good as what many other fighters had in the same time. Nothing to do with 'severe limitations inherent to design'.

The single biggest issue was performance at altitude above 12-16,000 ft (depending on variants). With the Merlin P-40s extending that up to about 20,000, which was better but still insufficient for NW Europe, especially for heavy bomber escort. Turned out to be useful in most of the other theaters though where the emphasis was more on tactical air war.

As above - the R-1830s being, at best, 3rd best engines for fighters in 1938-39, and no-turbo V-1710 being 3rd-7th best engines for fighters from 1940 on (without counting Soviet and Japanese engines there).

 

[Wild_Bill_Kelso]

Sure, but effectively the engines were part of the design. The P-40 remained mostly with the Allison V-1710 until the end of the war, and this was not made into a two-stage supercharged version until the ill-fated (though somewhat promising) P-40Q which never saw service.

P-36 may have gotten a new lease on life for secondary Theaters with the R-1820-65 of the FM-2, but as Shortround6 noted those arrived a bit too late and the FM-2 was probably good enough or better in that niche anyway, being carrier capable.

I wonder if a British engine like a Taurus or something may have helped? Could you fit a Hercules in a P-36?

The Merlin XX made for a better version of the P-40 for a while, but priorities limited the availability to a relatively short run of planes, and the Merlin 60 series Packard-Merlins as we know went to the better and more modern P-51.

 

[Wild_Bill_Kelso]

Could they have built a P-40Q in say, 1943 if they hadn't wasted all that time with P-46 and P-60?

 

[pbehn]

I think the fundamental problem for early and even later fighters was no one knew what type of war they were preparing for. Most were designated as interceptors, but no plane was developed by anyone in WW2 that could attack the USA from land. US carrier based planes had an easier "brief" since they were obviously carrier planes, that was the environment.

 

[Wild_Bill_Kelso]

And yet, carrier aircraft were still quite tricky to do well, I think. They knew what the environment was (somewhat) but it was a very challenging environment to design for!

 

[pbehn]

And yet, carrier aircraft were still quite tricky to do well, I think. They knew what the environment was (somewhat) but it was a very challenging environment to design for!

Of all the combatants in WW2 only the Japanese could claim to be on par initially with the USA, Germany didnt even get a carrier or any planes for it, same for Italy. The job of the Hurricane and Spitfire was clear to intercept. The job of the Me 109 and Fw 190 was also clear, they were not so well suited to the roles they were later asked to do. Here's a daft line in argument, if the UK surrendered US airplanes are much better suited to a war in Europe, N Africa.

 

[tomo pauk]

Sure, but effectively the engines were part of the design. The P-40 remained mostly with the Allison V-1710 until the end of the war, and this was not made into a two-stage supercharged version until the ill-fated (though somewhat promising) P-40Q which never saw service.

V-1710 was not a part of P-36 design, yet installing that engine on the P-36 airframe transformed it (after a few hiccups) into a far better performing fighter. Likewise, 2-stage Merlin was not a part of P-51 initial design, yet that engine transformed it woderfuly.
It was really too bad that better V-1710s were not available at least 6 months earlier, if not 9-10 months (but that goes for other fighters craving for better engines, too). Fault of Allison, not Curtiss, if we're to point fingers around.

I wonder if a British engine like a Taurus or something may have helped? Could you fit a Hercules in a P-36?

Dear lord, not Taurus. Hercules would've been ... interesting.

Could they have built a P-40Q in say, 1943 if they hadn't wasted all that time with P-46 and P-60?

Hopefully, yes. It is about the availablity of 2-stage V-1710s, though, and that was meager until late 1943.

 

[Wild_Bill_Kelso]

It seems like Curtiss was experimenting with a lot of other engine options for P-46 / 60 right? Maybe if they had asked Allison a bit earlier...

 

[tomo pauk]

It seems like Curtiss was experimenting with a lot of other engine options for P-46 / 60 right? Maybe if they had asked Allison a bit earlier...

For P-46, V-1710 was the engine. For the P-60 - indeed, they went bonkers there
Unfortunately, it took Allison about a year to debug the 9.60:1 step-up gearing for the S/C on the V-1710 (from late 1941 to late 1942) - that change alone if present on engines from early 1942 on would've meant a lot for people flying P-40s and P-39s during the dark days of 1942.
They also tried to cheap out on the development of the 2-stage V-1710, with ordinary, small supercharger (9.50 in impeller) for the 1st stage, before settling out with a 'proper', big impeller for the 1st stage. That took a few months. Preference of the USAAF for the 2-stage V-1710 to be installed on P-63 was also a problem, the 1st P-40 with 2-stage V-1710 was flying IIRC a full year after the XP-63.

 

[drgondog]

Could they have built a P-40Q in say, 1943 if they hadn't wasted all that time with P-46 and P-60?

I don't know enough about the P-40Q dialogue with MC. The two speed/auxilliay 2nd stage engine was not near ready in 1942- long after the P-46 was dead. NAA rejected the engine(s) out of hand because a major redesign to get the CG envelope meant moving the wing.

The P-40Q was the first installation (IIRC) of the V-1710-121. The earlier version -47 and -93 had significant gestation problems even after the first flight in May 1943 of the XP-63.

So the following issues had to be dealt with to shorten the release cycle of the P-40Q
1. Design for much larger aftercooler requirements - note that first prootype was inadequate with imbedded cooling intakes in the wing.
2. Select wing to change from NACA 2415?
3. Change wing location to accomodate cg change., basically changing both Powerplant section fwd of aft frame andfirewall, as well as longeron/wing attach mods to use P-40K basic airframe. Turned out no major change was required but I have yet to find out how they accomodated bigger engine (longer) with engine cg forward compared to V-1710-73 without having to move wing forward? Ballast?
4. Make changes to aft deck to accommodate sliding canopy - significant redesign of upper aft fuselage frame
If Ok, proceed.

By contrast the NA-91 (P-51-1NA) required upscaling Cooling system, installing the Packard 1650-3, and redesigning cowl to accomodate updraft carb for the XP-78/51B. Additionally NAA had fallback capability (somewhat impractical) of installing the R-R Merlin 61.

Back to question 1. When did Curtiss begin Preliminary design to accommodate the Allison they chose? and 2.) when was the new engine forseeable as a reliable alternative to the conventional single speed/stage V-1710? It took Packard close to a year from beginning bench tests at Wright Field to deliver production 1650-3 #1 to P-51B-1-NA #1 for tests beginning May 1943.

Note that neither ROC or top speed were validated by AAF, nor was armament installed, nor was fuel load fraction to production max internal fuel discussed for the test. The P-51B-1 in half fuel condtion had top speed of 450mph without wing racks and 4200 fpm ROC at 61" - and a ceiling of 42000 feet. May 1943. That is what Curtiss had to shoot for - then ask 'for what mission'? About all that come to mind is short to medium range air supremacy role and perhaps same as fighter bomber as P-40N.

Compare vs XP-51F which flew Feb 1944.


Finally. both the XP-46 and the XP-60 gossly underachieved stated Curtiss claims when loaded up with self sealing tanks, armament, etc. AAF wasn't buying what Curtiss was selling in new designs.

 

[Shortround6]

Some of this gets back the structural weight/original design/s.
It also took a lot of time.
The Army wanted a 300mph, all metal cantilever (no struts or braces) monoplane with enclosed cockpit, retractable landing gear and near 1000hp engine.
This was in 1934.

Lack of altitude performance for both, insufficient speed and lack of protection for the P-36 / H75. Lack of climb / insufficient power for weight for the P-40

This was the original Hawk 75 prototype that flew in April 1935. There were some "limitations"
Empty weight.........3760lbs
useful load...............1083lbs
gross weight............4843lbs
guns............................two .30 cal in the cowl.
Wright R-1670-5 engine of 900hp max (??) accounts don't line up well, Wright may have intended 900hp, not sure if it got there. This engine only showed up in a few experimental aircraft and was so bad that Curtiss (a division of Curtiss-Wright) replaced it with a P & W R-1535 engine.
This started the engine saga of the Curtiss 75-81-87 and indirectly the P-46/P-60 series.
It was supposed to do 280mph at 10,000ft but did it?
Curtiss had changed to the Wright R-1820 Cyclone by 1936 when both the Curtiss and Seversky prototypes failed to meet performance guarantees but Seversky did well enough to get a contract for 77 P-35s (Hawker was getting a contract for 600 Hurricanes?)

The single biggest issue was performance at altitude above 12-16,000 ft (depending on variants). With the Merlin P-40s extending that up to about 20,000, which was better but still insufficient for NW Europe, especially for heavy bomber escort. Turned out to be useful in most of the other theaters though where the emphasis was more on tactical air war.

This is years later, RR was head an shoulders above the rest of the world. We also need to use power at altitude, The Merlin III was good for 1030hp at 16,250ft in 1938, nobody else came close until 1940 using production engines. Other people got to the 12,000ft mark in 1940, with the exception of the Two stage engine in the Wildcat but they only made 98 of the engines during 1940 (and only 6 before Aug) so actual planes flying with them?
This also is where everything with the Curtiss 75-81-87 and cousins goes totally wonky. By the middle of 1940 they are trying to get the P-40B and protected Tomahawks (Hawk 81s) into production. They have already the P-40D/E (Hawk 87) ordered, they have ordered the P-46 and the P-53 prototypes, The P-60 order shows up in the Spring of 1941 and is a P-53 with a Packard Merlin engine. Sept of 1940 also sees the order for the P-47s, and 1940 sees the ordering of P-39s and P-38s. Everything that would arm the USAAC except the P-51 is already on order/development in 1940.

Sure, but effectively the engines were part of the design. The P-40 remained mostly with the Allison V-1710 until the end of the war, and this was not made into a two-stage supercharged version until the ill-fated (though somewhat promising) P-40Q which never saw service.

P-36 may have gotten a new lease on life for secondary Theaters with the R-1820-65 of the FM-2, but as Shortround6 noted those arrived a bit too late and the FM-2 was probably good enough or better in that niche anyway, being carrier capable.

The problem was that the P-40 was showing it's age, at 400mph it was hitting a drag wall. It needed hundreds of horsepower more than a P-51 to go the same speed.
It was about the same speed as a Spitfire IX and needed water injection to beat the Spitfire, and it wasn't carrying the gun armament of the Spitfire.

I wonder if a British engine like a Taurus or something may have helped? Could you fit a Hercules in a P-36?

Taurus was the kiss of death ( or more accurately being attacked with a blunt spoon)
Hercules? You could but WHY? Stop looking at just the max power. Look at the actual power at altitude and the weight and the drag and the lack of exhaust thrust.

Could they have built a P-40Q in say, 1943 if they hadn't wasted all that time with P-46 and P-60?

The Problem was the engine. If you don't have a better engine then building P-46 airframes gets you nothing.

It seems like Curtiss was experimenting with a lot of other engine options for P-46 / 60 right? Maybe if they had asked Allison a bit earlier...

The P-46 got the same engine as the P-40D/E. Trouble there is that the P-46 was actually a smaller plane 208 sq ft of wing.
If you don't have the room for a better supercharger set up in the P-40 you do not have it in the P-46.

And gotten Allison to stop making/developing what?
The engines for the P-55?
The engines for the P-75?
The 24 cylinder engines for back up to the wright R-3350s used in the B-29s?
Part of the problem was that the Army was asking Allison to spread themselves rather thinly to begin with.
2nd part of the problem was supercharger design in the US was behind that of RR, it got better but not by much in 1940-43 years.

Part of the Allison genius was in the design of the engine. They could swap back and forth from P-38 engines to P-40 engines to P-39 engines almost on a week by week basis to keep the engines flowing to the airframe makers by just changing the front gear boxes and some stuff on the rear accessories sections. If you want them to make even more specialty engines you either need a new factory or you start getting Rube Goldberg contraptions like the two stage supercharger, which could be added to a standard engine assembly at the cost of weight and length (harder installation).

Allison made over twice as many aircraft engines in 1942 than Packard. And almost 50% more engines in 1943.

 

[BarnOwlLover]

From what I read at Old Machine Press, the XP-40Q did 4300 fpm climb and 422mph, but both were on WEP and it's not known at what weight or load condition. The P-51B with half fuel was over 25 mph faster and not far behind in terms of climb rate on 61" supercharger boost. The P-51D probably would've had roughly similar performance under identical conditions (slightly lower rate of climb due to slightly heavier weight).

Basically, the XP-40Q was made obsolescent by the Merlin Mustangs before it even flew.

 

[Shortround6]

From what I read at Old Machine Press, the XP-40Q did 4300 fpm climb and 422mph, but both were on WEP and it's not known at what weight or load condition. The P-51B with half fuel was over 25 mph faster and not far behind in terms of climb rate on 61" supercharger boost. The P-51D probably would've had roughly similar performance under identical conditions (slightly lower rate of climb due to slightly heavier weight).

Basically, the XP-40Q was made obsolescent by the Merlin Mustangs before it even flew.

The P-40Q needed 75in of MAP and 3200rpm to get the Performance numbers listed. While the guns were not fitted (they did have dummy barrels) they were carrying ballast,
Gross weight was 9000lbs with the ballast weight for four guns and 235 rpg. Also 11 gallons of water injection fluid.
There were 'proposals' for six 50 cal guns (and more ammo?) or four 20mm cannon but performance would have suffered.

Please compare to the 9000lbs gross weight to the 4843lbs of the 1935 prototype. It was time to stop the flogging the soon to be expired horse.

 

[BarnOwlLover]

And I know that some will make the defense of "the Spitfire and Me-109 were designed at the same time". But how much did their designs change over time? Spitfire was significantly redesigned with the changes to the two-stage Merlin and the Griffon. Only the fuselage from the firewall to just ahead of the tail unit stayed basically the same. And the 109 ultimately showed what could happen with taking a design and stretching it. The 109 was obsolescent from 1942 onwards due to power, weight and armament growth outpacing what the airframe could handle. It just coped a bit better than the P-40.

Yes, if the P-40 got faster as it went on, that might have been a different story. But the P-51 was designed in 1940, used bleeding edge aero tech, and was still at the top of it's game in 1945, let alone the LW evolution that resulted in the P-51H and the F-82 that took things even further. That 5 years did make a big difference, as well as North American's ability to learn and evolve, something that Curtiss basically failed to do.

 

[Shortround6]

Well, the Spitfire started out at 5332lbs (10% heavier) and ended (MK 22) at 9200lbs and that included four 20mm guns and an auxiliary fuel tank or under wing bombs.
The 109 started at about 4700lbs for the B model (prototype was ????) and finished at 6834lbs clean for the K-4 and 7,475lb with external load.

Now to be fair the Hawk 75 did go to 5605lbs for the P-36A or about 800lbs more than the prototype.

But to almost double the weight (clean) of a single engine, single seat piston engine fighter was rather remarkable.

 

[Wild_Bill_Kelso]

I don't know enough about the P-40Q dialogue with MC. The two speed/auxilliay 2nd stage engine was not near ready in 1942- long after the P-46 was dead. NAA rejected the engine(s) out of hand because a major redesign to get the CG envelope meant moving the wing.

The P-40Q was the first installation (IIRC) of the V-1710-121. The earlier version -47 and -93 had significant gestation problems even after the first flight in May 1943 of the XP-63.

So the following issues had to be dealt with to shorten the release cycle of the P-40Q
1. Design for much larger aftercooler requirements - note that first prootype was inadequate with imbedded cooling intakes in the wing.
2. Select wing to change from NACA 2415?
3. Change wing location to accomodate cg change., basically changing both Powerplant section fwd of aft frame andfirewall, as well as longeron/wing attach mods to use P-40K basic airframe. Turned out no major change was required but I have yet to find out how they accomodated bigger engine (longer) with engine cg forward compared to V-1710-73 without having to move wing forward? Ballast?
4. Make changes to aft deck to accommodate sliding canopy - significant redesign of upper aft fuselage frame
If Ok, proceed.

By contrast the NA-91 (P-51-1NA) required upscaling Cooling system, installing the Packard 1650-3, and redesigning cowl to accomodate updraft carb for the XP-78/51B. Additionally NAA had fallback capability (somewhat impractical) of installing the R-R Merlin 61.

Back to question 1. When did Curtiss begin Preliminary design to accommodate the Allison they chose? and 2.) when was the new engine forseeable as a reliable alternative to the conventional single speed/stage V-1710? It took Packard close to a year from beginning bench tests at Wright Field to deliver production 1650-3 #1 to P-51B-1-NA #1 for tests beginning May 1943.

Note that neither ROC or top speed were validated by AAF, nor was armament installed, nor was fuel load fraction to production max internal fuel discussed for the test. The P-51B-1 in half fuel condtion had top speed of 450mph without wing racks and 4200 fpm ROC at 61" - and a ceiling of 42000 feet. May 1943. That is what Curtiss had to shoot for - then ask 'for what mission'? About all that come to mind is short to medium range air supremacy role and perhaps same as fighter bomber as P-40N.

Compare vs XP-51F which flew Feb 1944.


Finally. both the XP-46 and the XP-60 gossly underachieved stated Curtiss claims when loaded up with self sealing tanks, armament, etc. AAF wasn't buying what Curtiss was selling in new designs.

I think I did already stipulate - P-51 was better! Not just for speed but also range.

Was there a niche for P-40Q? Well maybe, considering the US were still using P-40s well into 1944 in the Med and I think to 1945 in China / Burma, a 40 mph faster version with a much higher effective ceiling might be worth having, instead of another 3,000 P-40Ns. If, and big if, they could get something working in time. My fantasy element here is if you took away P-46 and P-60 and just focused on something like a Q, could it have been done a bit earlier. If it arrives by say, mid 1944 I think it's too late, just use the Mustangs and other new designs.

It sounds like the P-40Q they patched together for testing was performing fairly well, though it's hard to say if the prototype crashes were due to aircraft design problems or not. maybe they were.

 

[Wild_Bill_Kelso]

I think P-40Q had different wings than the 75 / 81 / 87 right? Lower drag and shorter span.

But I 100% concede that P-51 was a better investment, once it was available.

V-1710 with a two stage supercharger is very tempting but perhaps not plausible for reasons of the manufacturing emphasis which SR6 described.

 

[Shortround6]

Part of the Problem with the Allison saga is the hiding in the shadows Continental IV-1410 which was pretty much designed by the USAAC and using Continental as the assembly shop of record. How much was designed by the USAAC and how much was designed by Continental may never be know at this point.
However it went through at least 12 variations with different superchargers, different reduction gears (including two speed and contra rotating) and it flipped-flopped with the Allison as to where the future priorities should be. Much of the time the Allison was viewed as the interim or temporary engine while the IV-1410 was perfected at which point the USAAC engineers could step forward and receive their medals/accolades/promotions. Meanwhile the factory that was supposed to build IV-1410 was used to build 9 cylinder radials for trainers until about 1944 when somebody figured that the IV-1410 was never going to be cleared for production and they switched the factory over to Merlins.
And this engine depended heavily on turbo-charging for high altitude performance. So there wasn't a lot of help coming from the government labs for two stage supercharger design.
Indeed the USAAC was acting as their own research/development team for turbochargers.
The USAAC ordered the turbos from GE and delivered them to either the engine companies for some experimental work or to the airframe makers for actual installation. This was further complicated by the USAAC designing and ordering the turbo boost limiting devices from 3rd party companies (not GE or the engine makers) to USAAC designs/concepts and to took a while to sort out some of those problems, when you have 3-4 parties being able to point fingers it takes longer to find the actual problem/s.

How many millions of dollars and 10s of thousands of engineering hours were flushed down the toilet on IV-1410 is unknown.

P & W was sort of out there on their own.

 

[Shortround6]

P-36 may have gotten a new lease on life for secondary Theaters..............

The problem with this is factory space.
Every P-36/super Hawk you make with a radial engine is a P-40 you don't make. They were made in the same factory by the same workers using much of the same tooling.
Unless you have a real shortage of P-40s sitting around waiting for Allisons to show up there is no point to it.

The P & W powered Hawk 81 showed potential but it too was late. It was flying around with very good performance in late 1942 but Merlin powered P-40s were planed to end at that time. The best speed records of the P & W Hawk were made in the summer or early fall of 1943 which is really way to late to alter production.
Nobody is saying what P & W learned about cowling, cooling, exhaust or other aspects of the installation and perhaps P & W got a lot of good information out of the project but it was too late to make a competitive fighter out of the Curtiss airframe.

 

[Shortround6]

I think P-40Q had different wings than the 75 / 81 / 87 right? Lower drag and shorter span.

A lot of bad information.
Basically they clipped the wing tips.
So yes, a bit shorter span and a tiny bit less drag, think clipped wing Spitfire.
Nobody can find any proof of a changed airfoil for the Qs despite many book. article, internet claims.

The P-60 series aircraft had a different airfoil.

I don't know who should take blame for the P-60, Part of it's fate was sealed with the requirement for eight .50 cal machine guns.
What I don't know is if this was a UASSC requirement or if it was a Curtiss sales ploy to counter the P-47. Or if they were both USAAC requirements
The USAAC seemed to be requiring huge quantities of guns and ammo totally unconnected to the power of the airplane.