P-40 what-if

[Marshall_Stack]

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

It figures that it had to be someone from Canada that had to point this out....

Elvis, the logo is the "blue note" (a musical note). It is based on an old song entitled "The St. Louis Blues".

Sorry for the digression in this thread.


GO BLUES!

 

[Ivan1GFP]

I believe Elvis commented that "the early 51's COULD'VE been a very effective aircraft at a lighter weight than the Merlin versions". I believe that it WAS quite effective, just not at the higher altitudes. Seems to me that the lack of engine power was more of an issue than the lack of a good propeller.

With the Allison engine, you have a plane that was faster than the Merlin engined up to 15,000 feet. This fact is hidden somewhat by the typically quoted 390 mph at 20,000 ft. The critical altitude for the P-51A was only about 12,000 ft, and it was certainly lighter, a bit less draggy and carried the same armament. The Allison engined planes also seemed to last longer than the Merlin engined because some F-6 types were still operational at the end of the war.

Although late model P-40's had the same engine and probably a very similar propeller, their propeller efficiency was probably much reduced because of that awfully big radiator. I am not an aerodynamics person, but from reading a few NACA and other reports, it seems that propeller efficiency is reduced by having a large area in the air stream behind the propeller such as on the radial engined planes or the large-mouthed P-40.

Just a little food for thought.
- Ivan.

 

[Elvis]

I believe Elvis commented that "the early 51's COULD'VE been a very effective aircraft at a lighter weight than the Merlin versions". I believe that it WAS quite effective, just not at the higher altitudes. Seems to me that the lack of engine power was more of an issue than the lack of a good propeller.

YES!
Thus my point about reconfiguring the blower system.
The Allison's biggest problem was an inability to breathe effectively much beyond 15K feet.
if one could introduce a system onto the engine to produce better breathing at higher altitude, it would follow that the plane would perform better at a higher altitude.
However, its a lighter engine, so it won't take the same amount of stress, thus you have to breathe on it a little easier and allow some of that increased power to come from the increased displacement of the Allison (compared to the Merlin).
As I stated earlier, I never meant for my version of the "improved Allison" to be a competitor to the Merlin. but rather, as a companion.
What it would lack in power, over later models of the Merlin, it would make up for in a lighter weight aircraft, yielding better balance and manuverability.
It would basically make the "razorback" 51's a better dogfighter at a more competitive altitude.



Elvis

 

[Elvis]

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)

North American could've also mandated that fuzzy pink slippers were manditory footwear for all production staff.
The mach number stays the same. The Speed of sound is the speed of sound.
A smaller diameter prop only allows the engine/propeller to run at a higher rpm before the tips reach transonic.
The smaller prop also creates less thrust, but my point had nothing to do with any of that.
Rather, only that the descrepencies between the figures were close enough that it could be that all of the props mentioned, where infact, the same one.

That's all I was saying.
Sometimes ya' gotta see through all the figures and use a little reasoning.



Elvis

 

[Elvis]

It figures that it had to be someone from Canada that had to point this out....

Elvis, the logo is the "blue note" (a musical note). It is based on an old song entitled "The St. Louis Blues".

Sorry for the digression in this thread.


GO BLUES!

No apologies needed, although I did get a nice chuckle out of the "Canadian" comment.
I understand the connection between the "blue note" and "St.Louis".
I actually have that 78. Very popular tune for a very long time now.
Thank you for taking the time to explain it, anyway.
Very nice of you to do that.



Elvis

 

[Ivan1GFP]

Sometimes a slight difference in propeller diameter makes a serious difference. The F4U-1 Corsairs had two different diameter Propellers in the 13' something" range. The smaller prop was the more efficient. In fact, with the larger prop, the aircraft was actually slower at higher throttle settings presumably because the prop tips went supersonic and were less efficient.

Regarding differences between the Allison and the Merlin, I don't think they are that directly comparable. Yes, the Allison is lighter, but there are MANY more differences than that. Displacement, Compression, modular design, issues with the intake manifold, etc.

Happy Easter everyone!
- Ivan.

 

[Jeffro]

Gday All,

Those those dreaming of the P51 with a Griffon,

Also posted somewhere here by desert Fox a few years back.

from CAC CA-15 - Wikipedia, the free encyclopedia

General characteristics

* Crew: one
* Length: 36 ft 6 in (11.05 m)
* Wingspan: 36 ft (10.97 m)
* Height: 12 ft 2 in (3.71 m)
* Empty weight: 7,540 lb (3427 kg)
* Loaded weight: 12,340 lb (5,609 kg)
* Powerplant: 1× Rolls-Royce Griffon supercharged V-12, 2,035 hp (1,517 kW)

Performance

* Maximum speed: 448 mph (721 km/h)
* Range: 2,450 mi (3,920 km)
* Service ceiling: 39,000 ft (12,870 m)
* Rate of climb: 4,900 ft/min (1,531 m/min)

Armament

* 6 x 12.7 mm machine guns (250 rounds each)

 

[HoHun]

Hi Elvis,

>A smaller diameter prop only allows the engine/propeller to run at a higher rpm before the tips reach transonic.

You have to consider the total tip speed, which includes forward speed of the aircraft. With less drag, but the same engine, the Allison Mustang will go faster than the Allison P-40 at the same power (and rpm), so a smaller propeller might be better to avoid Mach-induced efficiency loss. At these speeds, the smaller propeller might yield better thrust (though at climb speeds, the larger one will be superior - aviation is a science of compromses

Regards,

Henning (HoHun)

 

[davebender]

Regarding differences between the Allison and the Merlin, I don't think they are that directly comparable. Yes, the Allison is lighter, but there are MANY more differences than that. Displacement, Compression, modular design, issues with the intake manifold, etc.

I agree. If it had been a simple matter then Allison would have installed a license built copy of the RR Merlin supercharger on their own engine, vastly improving performance of the P-39 and P-40 plus the early model Mustangs.

 

[Colin1]

Those dreaming of the P-51 with a Griffon...

Not seen that before
reminiscent of a Wyvern, superficially. I'd like to see another view of the radiator housing though, the curves look less than compound in that picture.
I'm not sure how you'd validate the statement 'clearly superior to existing single-engine, propeller-driven fighters' when

i. it didn't fly until 1946
ii. didn't see any operational service anyway

at the close of the war, the P-47M, Ta152 and Do335 could all top the CA-15; post-war the late-mark P-51s, MB.5, Spiteful and Sea Fury could too.

Impressive though, 450mph is not to be sniffed at; typical that they scrapped the sole example...

 

[Elvis]

HoHun Ivan,

Valid points, I'll give you that.
However, THEY WERE NOT THE ONE I WAS CONVEYING WHEN I POSTED THOSE REMARKS.
-----------------------------------------

Re: Allison vs. Merlin.

As I stated earlier, I never meant for my idea of the "improved Allison" to be a competitor (or replacement) for the Merlin, but only to compliment it.
Why didn't they do that?
Who knows. Probably because it was quicker and easier to simply license-build the Merlin.

JMHO.


Elvis

 

[Ivan1GFP]

This may be a rehash, but the USAAC made some strategic choices pretty early on (way before the war). The high altitude supercharger type they were backing was the turbocharger and not the highly boosted mechanical superchargers.

Seems like the work on turbochargers was fairly successful with installations in the P-38, P-47, B-17 and B-24. Pity there was no solution for "middle altitude" aircraft.

- Ivan.

 

[V-1710]

Take a look at the performance figures for the two starge V-1710-93 installed in the P-63A. I don't know if that particular two-stage design would have been feasable in the P-40 or P-51, as it was quite large. The second stage was actually a separate centrifical blower driven by a hydraulic coupling. It must have worked, the P-63 could reach 20,000' in less than 5 minutes.

 

[Elvis]

Ivan,

Just found something, thanks to V-1710's remarks about the "-93" varient.
I'd forgotten about this, but the Allison's were actually supposed to be turbosupercharged units.
However, heavy bomber production mandated that as many turbo's as possible be prioritzed to them, with other Allison powered aricraft coming second.
In the end, only the P-38 retained its turbo and (pretty much) everything else was left with the single-stage mechanical supercharger.
My apologies for not noting that fact before. I'd completely forgotten about it.

...still, the "-93" sounds like it would've been a nice addition to both the P-40 and the early 51's, from a power output aspect, but pretty much loses the weight advantage the other Allison models discussed have over the Merlin.
Seems to have similar performance numbers to the "-99" (final P-40 varient), except more take-off HP and same rating at "altitude", only 5k feet higher with the "-93".
Maybe the "-97" would be even better, considering it features a counterweighted crankshaft and (it seems, anyway), the "-93" does not.
"-93" is listed at 1520 lbs.
"-97" is listed at 1500 lbs.
(info from enginehistory.org)

Comparitivly, the "-99" (the final Allison varient for the P-40) is listed at 1350 lbs. and I've seen the Merlin commonly listed at around 1600 lbs.




Elvis

 

[V-1710]

Ivan,..........I'd forgotten about this, but the Allison's were actually supposed to be turbosupercharged units......Elvis

Absolutely true! The Curtiss P-37 and of course the P-38 used the V-1710 as intended- turbocharged with a small centrifical blower for low r.p.m.'s. I may have brought this up before, but anyone with an interest in the V-1710 and its derivitives should read 'Vee's For Victory' by Daniel D. Whitney (Schiffer). It is the most comprehensive study on the V-1710.

 

[Elvis]

In addition, doing a quick check of the V-1710 pages from enginehistory.org, it seems the "best-of-both-worlds" would be the "-89A" varient.

1425 HP on take-off, and rated @ 1100HP @ 2600 RPM, but still retaining the full 1425HP when the engine's sped up to 3000 RPM, and all at an altitude of 30,000 feet ( ), yet listed weight is only 1350 lbs.

If I were going to install the "ultimate" Allison V-12 for the P-40, of those that actually existed during the war, this is the one I'd give some very serious thought to.

...now the down side. It appears it was used on the P-38, thus the extra power was coming from the turbocharger it was supposed to have in the first place and we all know how that went down.

Too bad really. Could've made the P-40 shine like the sun and the early 51's probably would've never needed the Merlin, using this powerplant, as well.




Elvis

 

[Elvis]

P-37

P-40

Man, now THAT'S a pair of beautiful planes.




Elvis

 

[MikeGazdik]

Love those photographs! If the XP-37 had a turbo installation like the P-38,at the top of the cowling, that would have made a very good windshield defroster!!!

 

[red admiral]

1425 HP on take-off, and rated @ 1100HP @ 2600 RPM, but still retaining the full 1425HP when the engine's sped up to 3000 RPM, and all at an altitude of 30,000 feet , yet listed weight is only 1350 lbs.

Unless Allison found a way to massively lighten their engine whilst adding a turbocharger and creating more power, I find it unlikely that the turbocharger and intercooler are included in the engine weight. Those systems should add about another 0.22lb/hp so 320lb or so, bringing the weight up to 1670lb which is still fairly reasonable. Now, the turbocharger also adds a lot of volume - unless you increase the size of the aircraft towards the P-47 scale it doesn't fit satisfactorily.

 

[Elvis]

Hey, Clay Allison wants to shove a Griffon into a P-40....and it may just work (although you'd probably end up with a completely different airplane).
If one can make a Griff fit into a P-51 (seen it) or a P-40 (hypothetical) then the extra piping of the turbo-supercharged engine should fit, too....and with much less modification.
Also, if you look at those weight figures at enginehistory.org, over all the models, you'll see where the two stage engines gained a LOT of weight, so the supercharging system, whatever form it took, must be included in the listed weight.


Elvis