P-40 what-if

[Clay_Allison]

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.
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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

I was thinking of three speed so that you could have Low, Medium and High alt settings. Mostly I was thinking it was a way to get around our lack of a two-stage supercharger. Adding an extra speed is just another little gear on the gearbox. The larger Impeller is a must though.

 

[MikeGazdik]

Clay, one your done fixing up your P-40, I want to put a Packard Rolls Royce Merlin into a P-39 Airacobra! That would be interesting!!!!!

 

[Clay_Allison]

Clay, one your done fixing up your P-40, I want to put a Packard Rolls Royce Merlin into a P-39 Airacobra! That would be interesting!!!!!

The P-39 was a tragedy. They could have had the original turbocharger, I think if they replaced the cannon with one that didn't suck (a little more modern, maybe 25mm), it would be impressive.

 

[Ivan1GFP]

The bottom line is that with the high drag and lack of refinement of the P-36/P-40 airframe, it isn't worth putting the hottest engine you can find just to prove a point. Just about anything you bolt onto a P-40 would get you better results with a P-51. Consider that the P-51A (F-6B) was able to achieve 410 mph at about 12,000 feet with 1350 hp or so from a V-1710-(81?). The Mustang was just an exceptionally clean plane.

I am also not so sure that the P-40 would need a 4 blade prop to use additional HP. Consider that the P-38 had fairly high power Allison engines but used 3 blade props.

You can't really fault the P-36 / P-40 for being what it was considering the time it was originally designed. It was barely out of the biplane era.

- Ivan.

 

[Demetrious]

Just about anything you bolt onto a P-40 would get you better results with a P-51.

That's kind of obvious, isn't it? The real "what-if" concerns if Allison corp. had produced a properly powerful, turbocharged engine to power the P-40, or perhaps if Rolls-Royce Co. had produced enough Merlins to go around.

Remember, the P-51A came about because the British came to North American aviation asking for them to build more P-40s, because the Curtiss-Wright plant was running at capacity. That's why A-36s and P-40s served side by side in the Desert Air Force- there was a tremendous demand for any fighter available, and the P-40 was more then good enough for the role, even if the early Mustangs were better.

It came down to an issue of only having enough "good" engines to go around, and obviously they chose to put them in the newer, faster airframe, which was the right choice. The "what-if" is, what would have happened if the domestic American aero-engine industry had been on the ball? Quite likely the P-51 would have rode to victory with an Allison powerplant in the D-model and onwards, and there certainly would have been enough of the supercharged engines to equip the P-40s that were still being pumped out at capacity for most of the war. The consequences of more good engines of course is more good fighters- in this case, the P-40 (though it could have been another ship as well.) So of course, it's an interesting "what-if" that really concerns the war at large. Better P-40s is just the fine point of the spear.

The P-39 was a tragedy. They could have had the original turbocharger, I think if they replaced the cannon with one that didn't suck (a little more modern, maybe 25mm), it would be impressive.

The decision to ditch the supercharger on the P-39 hurt it much the same way the P-40 was. The P-39 really was a great performer- an excellent turner, though I think she was a bit slow in a roll. A fairly durable aircraft, as well, and generally nimble.

The cannon wasn't bad at all, in my opinion- it was typical of mid-war heavy cannon, comparable to the 30mm "melon-launcher" in later Bf-109s. That is to say, a heavy cannon with a low rate of fire and anemic ballistics. The Germans learned how to employ it properly, and so did the Russians.

Replacing the 37mm doombringer with a single 20mm hispano would have reduced the hitting power but made actually hitting a lot easier, for sure, giving the P-39 a battery roughly akin to the P-38.

 

[Marshall_Stack]

I am also not so sure that the P-40 would need a 4 blade prop to use additional HP. Consider that the P-38 had fairly high power Allison engines but used 3 blade props.

- Ivan.

The XP-40Q had a 4 blade prop.

 

[Elvis]

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

Demetrious,

Glad you finally saw that comment and links from the other thread, and no worries. None of us are "eagle eyed" all of the time.
You're right about the engine petering out at low altitudes.
I wish I had an answer as to why the USAAF never addressed the low ceiling of the P-40.
Later engines made similar power at slightly higher altitudes, but even 15K feet is a bit low, when everyone else is playing at 20K feet +
BTW, if you look again, you'll see all of those engines were indeed supercharged, there just didn't seem to be enough "blow" to get the plane to perform at a proper altitude.
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I was thinking of three speed so that you could have Low, Medium and High alt settings. Mostly I was thinking it was a way to get around our lack of a two-stage supercharger. Adding an extra speed is just another little gear on the gearbox. The larger Impeller is a must though.

Ok, I think I see what you're getting at now.
The problem I see here is that you're making a part of the airplane more complex than it really needs to be.
If you had a two-speed supercharger, and say the higher speed section used a 50% overdrive, that would effectively spin the impeller twice as fast.
So if your "first gear" is 8.8:1, then the impeller speed @ 3000 RPM is going to be 26,400 RPM.
Once the engine starts "weezing" at around 12-15K feet, the second gear kicks in, changing the effective gear ration to 17.6:1, and that spins the impeller at 52,800 RPM, and that's a whole lotta extra air going into the engine.
I think it would work fine for the remaining 10-15,000 feet you'd still need to climb.
Remember, the plane did fine to about 12-15,000 feet, it was past that altitude that things went "horribly" wrong.
By keeping the gearbox simpler, you make it more reliable. If you can set the gearing and build the box so that it would stand up to that gearing, you've now got a reliable piece of equipment that will do the job you need it to do.
...and who's to say the gear even needed to be that high.
Testing would be needed to see how the engine actually performed at the requred altitude.
Not sure if such a facility existed at that time.
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The bottom line is that with the high drag and lack of refinement of the P-36/P-40 airframe, it isn't worth putting the hottest engine you can find just to prove a point. Just about anything you bolt onto a P-40 would get you better results with a P-51. Consider that the P-51A (F-6B) was able to achieve 410 mph at about 12,000 feet with 1350 hp or so from a V-1710-(81?). The Mustang was just an exceptionally clean plane.

I am also not so sure that the P-40 would need a 4 blade prop to use additional HP. Consider that the P-38 had fairly high power Allison engines but used 3 blade props.

You can't really fault the P-36 / P-40 for being what it was considering the time it was originally designed. It was barely out of the biplane era.

Excellent points, Ivan.
Thus my suggestion for the supercharging upgrade to the Allison.
I wouldn't want to make it a competitor to the 60/61 series Merlin, since we already had the Merlin.
However, making the Allison a "better" engine at more useful altitudes, using a supercharging system we already had access to (thart used on the Merlin series 20 engine), would be worth the effort at a minimum of cost and testing.
BTW, the 51A used the same engine as the P-40, although this page lists the HP a little higher, @ 1200.

The P-51A was powered by the Allison V-1710-81 which had automatic boost control and rated at 1,200 horsepower. This Allison had increased performance at altitude over the V-1710-39 used in the P-51. The propeller was a 3-blade, 10 feet 6 inch Curtiss electric. Top speed was 390 mph at 20,000 feet and the service ceiling was 31,500 feet.

I believe that prop is approximately the same size as that used on the P-40, as well (I'll have to verify that, though. Not sure).
What I like about the early 51's is that it could've been a very effective aircraft, at a lighter weight than the Merlin powered version, thus giving it better balance and agility.
As for the prop, you're going to need to "more" as the altitude gets higher, since what is highly effective at sea level to, say, 5,000 feet, is not nearly as effective at 25K or even 15K feet.
You're right, though, it doesn't neccessarily have to be an extra blade.
The difference might just be a longer blade or a wider blade.
Any way you slice it though, to effectively work at higher altitudes, you're going to need more blade, how ever you attain it, and the fact is, you now have a lot more power to twist those blades with, so why not take advantage of that.
It would seem almost stupid not to.



Elvis

 

[Marshall_Stack]

Demetrious,

However, making the Allison a "better" engine at more useful altitudes, using a supercharging system we already had access to (thart used on the Merlin series 20 engine), would be worth the effort at a minimum of cost and testing.

Elvis

Didn't the Merlin equipped P-40s have the RR Merlin 20 series? If it did, it really didn't make that much of a difference in performance at altitude. Its critical altitude was only a couple of thousand feet higher.

 

[Elvis]

Yes, but it still made more power than the Allison, as it was normally equipped in the P-40 (the Allison, that is).
With the Allison's increased displacment over the Merlin, a similar system should yield a better performing engine...at least compared to the one's that were actually fitted to the P-40.

...and I like your new avatar. Did you design that?




Elvis

 

[HoHun]

Hi Marshall,

>Didn't the Merlin equipped P-40s have the RR Merlin 20 series? If it did, it really didn't make that much of a difference in performance at altitude.

You're right. Here is a diagram showing the various versions of the P-40, supplemented by a hypothetical P-40 with Merlin 61. For the latter, I have looked at the Spitfire V/IX comparison and added 300 kg of weight and 15 % in terms of Cd0 for the Merlin 61 model over the standard Merlin model.

Performance is not all that impressive.

Regards,

Henning (HoHun)

 

[Elvis]

HoHun,

Just wondering where you got the figure for climb rate of the P-40N from?
It appears you're giving that version an initial climb rate of 19 m/s, which converts to about 3740 ft/min.

Am I reading that correctly?




Elvis

 

[claidemore]

...and I like your new avatar. Did you design that?

Elvis

Marshalls avatar is the logo of the St. Louis Blues hockey team.

 

[Elvis]

Ah. Very nice.
Thanks for the info.



Elvis

 

[HoHun]

Hi Elvis,

>Just wondering where you got the figure for climb rate of the P-40N from?
It appears you're giving that version an initial climb rate of 19 m/s, which converts to about 3740 ft/min.

>Am I reading that correctly?

Yes, that's correct. There is no direct source for this climb rate as the analysis is a match of several different, often partially incomplete and sometimes contradictory data sets. However, a good source for P-40 data can be found here: Perils P40 Archive Data (and Peril actually provided tons of data for my analysis).

Note that (as I have occasionally pointed out before) my calculations do not (yet) account for additional drag in the climb case caused by wide-open radiator flaps, which I suspect can give about 1 m/s high results for aircraft with "draggy" flaps.

However, you can find even quicker-climbing P-40N data sets on Peril's site - though I'm not sure they can actually be accurate. My figure is probably the maximum possible for the lightest P-40 model in perfectly clean configuration at the highest historical power setting.

Regards,

Henning (HoHun)

 

[Elvis]

Interesting.
So if I'm understanding you correctly, I should regard your graphs as "optimistic".
Ok, will do. Thanks for the heads up.
FWIW, I'm at Peril's site now and found some climb info for the P-40N-1, but they are "time-to-altitude" figures and the best I can come up with is a little over 2600 ft./min., up to 15K feet.
The highest "outright" climb rate I could determine, using that chart, was 3000 ft./min., which I determined by noticing that it only took 1:40 to climb from 5K to 10K.

http://www.raafwarbirds.org.au/targetvraaf/p40_archive/pdfs/P40N-1 RAF Test.pdf



Elvis

 

[HoHun]

Hi Elvis,

>Exactly what section of Peril's gave you the 3740 ft./min. figure?

As pointed out above, none

>I'm at Peril's site now and found some climb info for the P-40N-1, but they are "time-to-altitude" figures and the best I can come up with is a little over 2600 ft./min., up to 15K feet.

The average from a time to altitude is inevitably lower than the peak climbrate near sea level.

It's this comparison that gives even better time to altitude figures than I have calculated:

http://www.raafwarbirds.org.au/targetvraaf/p40_archive/pdfs/P40s compared.pdf

Note that this report provides a weight for the P-40N, while the one you quoted provides theoretically more useful small intervals of time-to-altitude, but lacks the important weight information. It also is at a slightly lower power setting than the one I used for calculation.

Assuming 7400 lbs weight, I get 84 s to 5000 ft, compared to 130 s from the British chart. Doesn't look good! But they also provide a total time of 540 s to 20000 ft, while I calculate 578 s - so suddenly their climb rate is better than mine. But we don't know their flying weight, whether they have corrected the data for standard day conditions so that it is comparable at all, and whether they have normalized the data for a constant weight (while in the climb, the real aircraft gets lighter as it climbs because it consumes fuel, ejecting the gases through the exhausts).

Sorry that I can't give a simple answer - the climb data is calculated from the evaluation of multiple data sets of different P-40 aircraft, none of which was actually tested yielding the exact climb curve I originally posted.

Regards,

Henning (HoHun)

 

[HoHun]

Hi Elvis,

>So if I'm understanding you correctly, I should regard your graphs as "optimistic".

Roger that! For the cases in which I had well-documented data to compare to, my calculation often tended to be about 1 m/s on the high side. My best guess is that the additional drag of adjustable cowl flaps in the open position which I have not included in my calculations is causing this difference.

Regards,

Henning (HoHun)

 

[Elvis]

BTW, the 51A used the same engine as the P-40, although this page lists the HP a little higher, @ 1200.
I believe that prop is approximately the same size as that used on the P-40, as well (I'll have to verify that, though. Not sure).

Ok, checked this out earlier this morning and from what I can see, its highly likely both planes used the same prop.
USAAF document found at Peril's P40 site lists the P-40 prop as a Curtiss Electric 3-blade of 11'0" diameter.
The prop listed for the P-51A, at the MustangsMustangs site shows its also a 3-bladed Curtiss Electric, although the text lists the diameter at 10'6", yet the specs shown at the bottom of the page lists the same prop but with a 10' 9" diameter.
Small differences in size, so I'm speculating that all props mentioned are most likely the same one.
This is a great indication of just how much cleaner the 51A was, compared to the P-40, when you start looking at differences in climb rate and speed @ altitude, since both planes used, essentially, the same engine/prop.



Elvis

 

[Elvis]

Hi Elvis,

>So if I'm understanding you correctly, I should regard your graphs as "optimistic".

Roger that! For the cases in which I had well-documented data to compare to, my calculation often tended to be about 1 m/s on the high side. My best guess is that the additional drag of adjustable cowl flaps in the open position which I have not included in my calculations is causing this difference.

Regards,

Henning (HoHun)

Right-0.
Thanks for the clarification.


Elvis

 

[HoHun]

Hi Elvis,

>The prop listed for the P-51A, at the MustangsMustangs site shows its also a 3-bladed Curtiss Electric, although the text lists the diameter at 10'6", yet the specs shown at the bottom of the page lists the same prop but with a 10' 9" diameter.
>Small differences in size, so I'm speculating that all props mentioned are most likely the same one.

Might be ... but on the other hand, North American might have deliberately chosen a slightly smaller diameter propeller for the same engine because they built a faster plane, so the propeller tip Mach numbers they'd experience would be higher, decreasing efficiency more seriously than it would happen with the slower P-40.

You're researching an important parameter here!

Regards,

Henning (HoHun)