P-40 what-if

One would have to wonder about the 1930s aerodynamics (radiators, airfoils) of the P-40 as opposed to aircraft like the P-51. At what speed would the P-40 reach compressibility problems? What is the VNE of a P-40 - how fast could it go before the wings just folded back? : )

The Griffon was actually quite inferior to the Merlin at the beginning. Consider that the Spitfire Mk. XII was a Griffon engined Spitfire Mk. V and was not able to beat 400 mph while the Merlin engined Spitfire Mk. IX from the same time period was easily able to exceed 400 mph.

The series production of the Packard Merlin was not quite as easy as it appears. The engines were conceptually the same, but were not parts interchangeable. I believe the RR engine was mostly Metric while the Packard was SAE. There was a great demand for Merlin engines while there wasn't such a demand for Griffons which were not very well developed at the time. Packard Merlins were used in Lancasters as well as other multi-engine aircraft as well as some marks of Spitfire. The difference between the Spitfire Mk. IX and Spitfire Mk. XVI is just the producer of the engine.

Regarding the development potential of the P-40, even Curtiss recognized fairly early that the airframe had very little future, which is why there was development on the P-46. Pity that the P-46 never made it to series production.

I actually happen to like the P-40. I believe the aircraft has a character about it that few others have. I wanted one of my own so built one for Combat Flight Simulator a few years back.

http://www.ww2aircraft.net/forum/schematics/p-40d-drawing-12109.html

Also, it was a favourite aircraft of Snoopy!

- Ivan.

Clay_Allison said:

I was thinking about the P-40 and the reasons it wa considered a stopgap at best. What if, though, the P-40 had been reengined, not with the Merlin (as in the P-40F) but with the RR Griffon (if it had been turned over to an American comany for development when it was de-prioritized). Would that have worked?

Click to expand...

i don't see why it wouldn't have worked.
I'm also not sure how much modification would need to be done to fit the new engine into the relatively small P-40 airframe, but to get the type of performance the engineers were looking into would've also required a super charger. (not sure if the P-40 ever had one)

Aside from performance, the war efforts were concentrating on increased range to escort bombing runs. I'm not sure the P-40 had the fuel capacity to fly such missions even if it could hypothetically achieve the altitudes with the Griffon and a super charger.

Ivan1GFP said:

The Griffon was actually quite inferior to the Merlin at the beginning. Consider that the Spitfire Mk. XII was a Griffon engined Spitfire Mk. V and was not able to beat 400 mph while the Merlin engined Spitfire Mk. IX from the same time period was easily able to exceed 400 mph.

Click to expand...

That's the difference between a single speed two stage engine (Griffon III/IV) and a two stage, two speed engine (Merlin 60/66), rather than the difference between the airframes.

Its all about the horsepower available at altitude, not about the total horsepower.

The Spitfire XII was about 10-12 mph faster than the Spitfire XI at sea-level on essentially the same power, but it was about 900 ft/ minute slower in the inital climb, and about 45 seconds slower to 10,000 feet.

Later, when the Spitfire XII got the more powerful Griffon IV, it was about 350 ft/ minute better than the Mk IX in the climb and about 25 seconds faster to 10,000, but still slower to 20,000. It was also about 15-18 mph faster than the Mk IX at sea level.

The Spitfire XII actually had a cleaner airframe than the Spitfire IX, with more extensive use of welding, flush riveting and fewer panels.

In the comic strips I have seen Snoopy normally flew a doghouse. Compared to that a P-40 would undoubtedly be an improvement.

Jabberwocky,
Why do you say the Spitfire XII had a better airframe than a Spitfire IX? Both were re-engined Spitfire V's. Are you perhaps thinking of the Spitfire XIV which used a Spitfire VII/VIII airframe? One notable difference is the retractable tail wheel.

The Spitfire XII can be distinguised among the Griffon Spitfires in that it retained the asymmetrical oil cooler / radiator setup of the Spitfire V.

I am sure that a later model Griffon with improved supercharging would provide better performance, but I am just comparing installations of contemporary engines in the SAME airframe.

Hello davebender,
Don't forget that Snoopy flew the Kittyhawk as well as his Camel!

- Ivan.

Why didn't any of the major American auto producers attempt to create an in-line engine? The only one that I know of is Chrysler's prototype hemi engine that was put in the XP-47H. Although it had a lot of horsepower, it was too big and the thunderbolt couldn't do much over 400 mph.

Marshall_Stack said:

Why didn't any of the major American auto producers attempt to create an in-line engine? The only one that I know of is Chrysler's prototype hemi engine that was put in the XP-47H. Although it had a lot of horsepower, it was too big and the thunderbolt couldn't do much over 400 mph.

Click to expand...

I suspect the reasons to be twofold. Firstly, I would suspect (although I am no engineer), that the tolerance expected in auto engineering of the day were nowhere near those sought in aero engine manufacture, requiring a big step up in quality control and engineering finesse from auto makers. And as you have already hinted, an aero engine needs to be as light as possible - not an easy design criteria to adapt to for guys used to making truck engines!

Secondly, I am sure that the auto manufacturers found themselves swamped with demand for engines for tanks and trucks, leaving little production capacity available for the manufacture of large and complicated aero engines. I suspect the numbers that could have been produced would have been quite small compare to the Wright's and P-W's of this world.

Why didn't any of the major American auto producers attempt to create an in-line engine?

Click to expand...

Because the USN and U.S. Army Air Corps didn't provide funding for research and development. Designing an aircraft engine is too expensive to pursue the project without Government funding and guaranteed sales.

davebender said:

Because the USN and U.S. Army Air Corps didn't provide funding for research and development. Designing an aircraft engine is too expensive to pursue the project without Government funding and guaranteed sales.

Click to expand...

The US spent ridiculous sums on money on the various inline designs for the hyper engine program during the late 1930s and early 1940s and all turned up duds. The greatest problem was the lack of experience with inlines as they'd been largely ignored in the US for the past 15 years. All the engines from the program (IV-1430, IV-2220, H-2600, H-3730) were huge failures despite years of development and millions of investment.

Britain and Germany produced great water cooled V12s during the late 1930s. Why not swap American radial engine technology for European V12 technology?

Ivan1GFP said:

Jabberwocky,
Why do you say the Spitfire XII had a better airframe than a Spitfire IX? Both were re-engined Spitfire V's. Are you perhaps thinking of the Spitfire XIV which used a Spitfire VII/VIII airframe? One notable difference is the retractable tail wheel.

Click to expand...

Not a better airframe, just a slightly cleaner one aerodynamically.

They both had airframes which were BASED on the Mk V, but their airframes were not exactly identical.

As I said earlier, the Mk XII used different panneling (in the nose) and was the first Spitfire type to use flush riveting. It also had a revised spinner, new (and improved) removable wing panels and better wing leading edge skinning.

As a result, for the same given power level, the Mk XII was approximately 10-12 mph faster than the Mk IX, despite having slightly more frontal drag.

Clay_Allison said:

I was thinking about the P-40 and the reasons it wa considered a stopgap at best. What if, though, the P-40 had been reengined, not with the Merlin (as in the P-40F) but with the RR Griffon (if it had been turned over to an American comany for development when it was de-prioritized). Would that have worked?

Click to expand...

Clay,

It almost sounds as if you're trying to design an "Allied Me-109".

Interesting concept.

I would think testing would prove that the P-40 would require so much modification from the installation of such a large engine, that it might hasten a totally new design.
Possibly "P-40 based", but after all was said and done, a new aircraft.
That was one nice thing about the Allison. It was a light enough alternative powerplant that only a partial redesign of the P-36 was needed to yield the P-40.

Interesting pics of the Griffon-powered 51's, too.
I've never seen those before.




Elvis

Jabberwocky said:

Its all about the horsepower available at altitude, not about the total horsepower.

Click to expand...

YES, YES! FINALLY, someone put it down succinctly!

Cudo's Jabberwocky!
Well written!






Elvis

Elvis said:

Clay,

It almost sounds as if you're trying to design an "Allied Me-109".

Click to expand...

Interesting comment...

The P-40E was significantly lighter then the P-51 empty- 6,350lbs for the P-40E to the 7,635 lb of the P-51D- making the P-40 a thousand pounds lighter. A Merlin- or a Griffin- would have given the P-40 a power/weight ratio of 0.23 hp/lbs if equipped with a 1500 hp engine, which is comparable to Bf-109 models of it's era. Maneuverability was also similar.

As for engines- the P-39-D2, produced in 1942, mounted an Allison V-1710-63 that put out 1590 horsepower, quite an impressive number. Now, since this Allison engine was clearly available in 1941, was there anything stopping it from being installed in the P-40 besides logistics? Was the P-40's nose too small to accommodate that engine?

EDIT: Random googling turns up values ranging from 1300 HP to 1500 HP for the V-1710-63, but even the low-range estimates give it a good edge over the Allisons installed in the P-40, which never really topped 1100 HP, from everything I've seen.

Hi Demetrious,
The P-40N series had 1300+ HP. The 1150 HP range really goes with the P-40E.

When comparing weights of aircraft, you really need to look at "Basic Weight" and add in the weight of the pilot. Empty weight leaves out essentials such as radios, guns, bomb racks and just about everything else than can be unbolted from the airframe.

I like the P-40, but I believe there are too many little "Gotchas" that need to be addressed to make it into a really good airframe:
1. The plane needs a new radiator location such as under the aft fuselage. The Radiator up front makes for less plumbing that can get shot up, but causes turbulent airflow for the rest of the fuselage.
2. The main landing gear has too many bumps and too much exposed. It should be inward retracting with doors covering everything.
3. The wing should be rebuilt with a laminar flow airfoil.
4. The rivetting and panels should be cleaned up. There are control rods and little fairings or holes poking out from various places that should not be there.

The end result of doing all these changes is that you basically have something looking like a P-46. I wonder if you can still call it a P-40 at that point?

- Ivan.

Elvis said:

Clay,

It almost sounds as if you're trying to design an "Allied Me-109".

Interesting concept.

I would think testing would prove that the P-40 would require so much modification from the installation of such a large engine, that it might hasten a totally new design.
Possibly "P-40 based", but after all was said and done, a new aircraft.
That was one nice thing about the Allison. It was a light enough alternative powerplant that only a partial redesign of the P-36 was needed to yield the P-40.

Interesting pics of the Griffon-powered 51's, too.
I've never seen those before.




Elvis

Click to expand...

Well, yeah. The Me-109 was a mass production capable fighter that was a JAck of All Trades with no clear strengths or weaknesses. Its speciality was that it was competitive under all conditions even though it rarely had pure dominance, it always gave its pilots an even shake.

The more I learn about aircraft and aerodynamics, the more unfortunate the P-40 looks to me. The rebalancing it took to make a pretty sleek and light P-36 into what we got makes it look poorly proportioned.

I think that in place of the P-40, Curtis should have made a ground-up light interceptor with a 3-speed supercharged Allison, even if said supercharger was a heavy aftermarket add-on rather than truly integral.

If not that, they should have just put more and more powerful engines in the P-36 with more weapons, pilot armor, and self-sealing tanks.

Ivan1GFP said:

When comparing weights of aircraft, you really need to look at "Basic Weight" and add in the weight of the pilot. Empty weight leaves out essentials such as radios, guns, bomb racks and just about everything else than can be unbolted from the airframe.

Click to expand...

I personally go by "empty weight" simply because that's the only hard and fast measure to go on. For example, comparing the "loaded weights" of the P-40 vs. the P-51 would be unfair to the P-51, because it has 8 hours worth of fuel onboard- at least half of which will be burned up when it enters combat. If you want to compare, say, a Spitfire to a P-51, then you should only weight the P-51 in with 25% fuel, because that would be it's "combat weight" if given the same mission as a Spitfire- intercept.

That's why I go by "empty" weight. It's a rough measure, for sure, but it gives a relative idea of the weights of the aircraft that is somewhat unmarred by variables like those. In my opinion, anyway.

I like the P-40, but I believe there are too many little "Gotchas" that need to be addressed to make it into a really good airframe:
1. The plane needs a new radiator location such as under the aft fuselage. The Radiator up front makes for less plumbing that can get shot up, but causes turbulent airflow for the rest of the fuselage.
2. The main landing gear has too many bumps and too much exposed. It should be inward retracting with doors covering everything.
3. The wing should be rebuilt with a laminar flow airfoil.
4. The rivetting and panels should be cleaned up. There are control rods and little fairings or holes poking out from various places that should not be there.

Click to expand...

Good points, all. The P-40's airframe had a number of vices, and there's only so many that could have been corrected expediently.

Demetrious said:

As for engines- the P-39-D2, produced in 1942, mounted an Allison V-1710-63 that put out 1590 horsepower, quite an impressive number....EDIT: Random googling turns up values ranging from 1300 HP to 1500 HP for the V-1710-63, but even the low-range estimates give it a good edge over the Allisons installed in the P-40, which never really topped 1100 HP, from everything I've seen.

Click to expand...

Demetrious,

That figure is wrong.
I strongly suggest you read (or re-read) my response to you (post #140, 5th down from the top), from this thread - http://www.ww2aircraft.net/forum/aviation/p-40-warhawk-kittyhawk-17083-10.html - and note the link for those performance figures.
They're official USAF documents from 1949.
I can't see verification getting any more definitive than that.
...also, why stop at 1500HP?
The Rolls Griffon eventually made upwards of 2300-2500 HP.
--------------------------------------------------------------------------

Ivan1GFP said:

I like the P-40, but I believe there are too many little "Gotchas" that need to be addressed to make it into a really good airframe:
1. The plane needs a new radiator location such as under the aft fuselage. The Radiator up front makes for less plumbing that can get shot up, but causes turbulent airflow for the rest of the fuselage.
2. The main landing gear has too many bumps and too much exposed. It should be inward retracting with doors covering everything.
3. The wing should be rebuilt with a laminar flow airfoil.
4. The rivetting and panels should be cleaned up. There are control rods and little fairings or holes poking out from various places that should not be there.

Click to expand...

Clay_Allison said:

Well, yeah. The Me-109 was a mass production capable fighter that was a JAck of All Trades with no clear strengths or weaknesses. Its speciality was that it was competitive under all conditions even though it rarely had pure dominance, it always gave its pilots an even shake.

The more I learn about aircraft and aerodynamics, the more unfortunate the P-40 looks to me. The rebalancing it took to make a pretty sleek and light P-36 into what we got makes it look poorly proportioned.

I think that in place of the P-40, Curtis should have made a ground-up light interceptor with a 3-speed supercharged Allison, even if said supercharger was a heavy aftermarket add-on rather than truly integral.

If not that, they should have just put more and more powerful engines in the P-36 with more weapons, pilot armor, and self-sealing tanks.

Click to expand...

Ivan Clay,

Yes, you guys get it.
Modifications would have to be so drastic that you're going to end up with a new plane.
A P-46? Maybe.
Ivan's suggestions seem to almost suggest a "Curtiss P-51".

...also, I see no mention of modifying the prop.
I would think it would at least be some waste of all that added power, if it were to simply turn the same prop that was used before the modification.
Wider, longer or more blades, but something should definately change with that aspect, as well.
This would give you the most satisfactory results from the installation of the upgraded powerplant.

Also, Clay, the reason I made the connection to the 109 is that both the Griffon and the DB-605 are of similar displacement and configuration (V-12 of approximately 2230 cu.in.).
Add to that, that the 109 is basically a modified 108 with a great big engine hanging off the front, and you can see that your idea of the Griffon powered P-40 is very similar.
However, remember that the Allison, being a lighter weight engine, isn't as stout (or doesn't appear to be, anyway) as the Rolls engines, thus the problems with added stress when dealing with power enhancing "add-ons".
Triple-speed supercharging might be an almost "Rube Goldberg" approach to the idea.
I still think a two-speed, single stage, intercooled supercharger with a larger impeller is the way to go with the Allison.
As Jabberwocky stated earlier, its not so much about total HP, its how much you can retain upstairs.
So, if the Allison made, lets say, 1350-1400HP at take off, but could still be making 1100-1150 HP at 20-30K feet, both the early 51's and the P-40's would've been better performers, overall.
The two-speed single stage, intercooled Allison with the prop used on the 51-D, would've given the P-40 an infinately better climb rate ("lack of bounce" being a detraction I've heard before about that plane) and better performance at the higher altitudes that the 109 liked to fight at.



Elvis

Elvis said:

Demetrious,

I strongly suggest you read (or re-read) my response to you (post #140, 5th down from the top), from this thread - http://www.ww2aircraft.net/forum/aviation/p-40-warhawk-kittyhawk-17083-10.html - and note the link for those performance figures.
--------------------------------------------------------------------------

Click to expand...

Thank you so much for the links, and I'm sorry I didn't see that post in the old thread before. The links are excellent, especially the P-40 data archive. The issue of the Allison -63 has been bugging me for days. Forgive me for being tremendously thick and missing your original post.

Here's the curious thing:

Actually, it made 1325HP @ 3000 RPM on take-off 1150HP @ the same RPM @ 11800 ft.
It seems that Curtiss skipped this particular version of that engine and went straight to the "-73", going on to mount the "-81" and finally, the "-99" versions of this engine in successive models of the P-40.
The "-73" differs from the "-39" in that there is no gun synchonizer installed and it has improved take-off ratings.
Performance for "-73" is as follows:
1150HP @ 3000RPM - take-off
1150HP @ 3000RPM @ 11800 ft.

Click to expand...

This would explain why it seems the P-40 never received an engine upgrade worth a hoot- apparently all the data I've seen (which puts it consistently at 1100HP) was giving full power at middle altitude, not at it's optimum altitude.

Of course, this also reinforces what Jabberwocky said- the power at altitude consideration. A 200HP advantage over older models (on full War Emergency Power) isn't enough to be a game-changer (400HP and you're talking,) but it would still make a marked difference in a fighter who's primary failing was low power. But if it disappears at the rather low altitude of 12,000 feet, it may as well not exist.

I don't think of 12,000 feet as being very high at all, perhaps middle altitude. I would have expected most engines to suffer significant performance drops somewhere around 16 or 17 thousand feet. A fighter that flounders at 20,000 feet but dances at 10,000 is not a bad ride for lots of missions. A fighter that chokes out by 10,000 feet, however, is in serious trouble. And at any altitude in between- say, five or six- the small boost in power is already being nibbled away at until it goes from useful to ineffectual.

In short, the Allisons in the later model P-40s were game, but it was all useless without a supercharger.

Yes, you guys get it.
Modifications would have to be so drastic that you're going to end up with a new plane.

A P-46? Maybe.
Ivan's suggestions seem to almost suggest a "Curtiss P-51".

Click to expand...

Exactly, especially with the "laminar flow airfoil." When you replace the airfoil you've essentially moved on to building a new aircraft.