P-40 what-if

[drgondog]

Re: Allison vs. Merlin.

Also, concerning your comments about a Merlin-powered P-51A...that is exactly what happened, except we called it the P-51B/C.
Not too much difference between the A and the B/C. Main one was the powerplant!


Elvis

Elvis - the wing was dropped 7 inches to accomodate an entirely new Cowl from the bulkhead in front of the cockpit all the way to the spinner. New Prop. New radiator and radiator cowl design. It was close to being given an entirely new aircraft designation.

The changes from the B/C to D/K were fewer in substance.

The change to the H was nearly 100%

 

[Vincenzo]

Pilots claim that contemporary Spitfires were matched in turn performance of the P-40B, but that the P-40 fell behind in performance when the SpitV came out.

Spit V it's the contemporary of P-40B, there is some wrong in the claim

and afaik there was little difference in turn within Spit I and V

 

[gjs238]

a problem with the Merlin/P-51 dream is timing.

In 1938-39 the Merlin was a single speed-single stage engine that showed little difference in potential from the Allison. A two-speed single stage version was on offer but in it's original form it showed very little difference in altitude performance over the single speed (the most common single speed version being optimized for high altitude work). It is not until Hooker does his bit that things improve for the Merlin and that is about the middle of 1940. The improved single speed engines (40 series) and two speed engines (XX or 20 series) engines are what is first contracted for with Packard. The American versions power the P-40F. Please note introduction dates for the P-40F and then figure performance for a P-51 with that engine and not the later 2 stage engines.

Work starts on the 2 stage Merlin engine but Allison has started work on a 2 stage engine at the end of 1938!

It takes Rolls-Royce several years to get the two stage engines into production and sharing info with Packard and Packard doesn't deliver any real quantity of 2 stage engines until 1943. These are the -3 and later Packard Merlins.

Allison has development problems with their 2 stage supercharger and development is slower. A good engine once developed it reaches production just a little too late to have any real impact on the war (same could be said of the P&W R4360 on which work started in 1940)

How were the Daimler-Benz DB series of engines performing during these times?
If the DB's were performing as well or better, how was that being achieved?

 

[Shortround6]

In April 1942 2,000 two stage Allison engines were ordered. The V-1710-47´s critical altitude was 22,400ft. Early 43 seems doable IF someone make an effort to get the engine ASAP.

The V-1710-47 turned out not be a production engine. By the time they got it straightened out other improvements had been worked in and a later model number was the first production engine.

 

[billswagger]

Spit V it's the contemporary of P-40B, there is some wrong in the claim

and afaik there was little difference in turn within Spit I and V

Hmm, not sure of that either. From what i read the P-40 could turn with spits and dive with 109s, it just suffered in climb.
This changed as fighters got bigger engines and increased in performance, where the P-40 fell behind,
although other comparisons put the P-40 as having better range and offering more protection to the pilot and engine with armor plating.


Bill

 

[Shortround6]

How were the Daimler-Benz DB series of engines performing during these times?
If the DB's were performing as well or better, how was that being achieved?

The Early DB engine's superchargers didn't perform any better or worse than the superchargers on the early Merlins and Allisons. The larger displacement, slower turning DB engines didn't need as much boost to make their rated power however. A Merlin using 6lb of boost is running at 1.4 Ato as is an Allison at just 42in. The more boost used to make rated power the lower the ceiling a given pressure ratio supercharger is going to work. Once the British and Americans start going to 12lbs of boost or 50in plus of manifold pressure to make rated power either the altitude performance suffers (or more accurately low altitude performance improves but high high altitude does not) or improved superchargers are needed.
The Germans with their lower manifold pressure needs can keep up the pressure to higher altitudes using the same basic supercharger. The Germans did improve their superchargers too as the war went on. A better impeller or a different diffuser design or even just a better inlet geometry could give small but useful improvements without any out change in appearance or weight.

 

[Vincenzo]

Hmm, not sure of that either. From what i read the P-40 could turn with spits and dive with 109s, it just suffered in climb.
l

not sure of P-40B it's contemporary of V? or that turning performance of V and I are similar?
afaik P-40B can't turn with spit I or also V or best can turn but it's beat to spit, this generally talking, it's every possible that a pilot with a P-40B can turn and win a pilot with spit for many reasons.

 

[gjs238]

The Early DB engine's superchargers didn't perform any better or worse than the superchargers on the early Merlins and Allisons. The larger displacement, slower turning DB engines didn't need as much boost to make their rated power however. A Merlin using 6lb of boost is running at 1.4 Ato as is an Allison at just 42in. The more boost used to make rated power the lower the ceiling a given pressure ratio supercharger is going to work. Once the British and Americans start going to 12lbs of boost or 50in plus of manifold pressure to make rated power either the altitude performance suffers (or more accurately low altitude performance improves but high high altitude does not) or improved superchargers are needed.
The Germans with their lower manifold pressure needs can keep up the pressure to higher altitudes using the same basic supercharger. The Germans did improve their superchargers too as the war went on. A better impeller or a different diffuser design or even just a better inlet geometry could give small but useful improvements without any out change in appearance or weight.

So I guess it comes down to the old adage, "there's no replacement for displacement?"
I assume the DB engines were heavier as well?
If so, it sounds like they performed very well despite the weight - while not suffering the supercharger/turbocharger issues.

 

[Clay_Allison]

Why do you want to pay RR 6,000 $ per engine if the V-1710 just needs an aux. stage supercharger and an intercooler to be as good? The Allison was stuck with the lesser supercharger not because of technical reasons but because the USAAF did not want a better one. They had 100% faith in the turbocharger and even objected to Allison developing altitude rated engines.

Pay? Owe. Big difference. Take it out of the lend lease they still haven't paid off. (They haven't screwed us out of it, they make payments very slowly because our rate of inflation is higher than the interest)

The Aux-Stage supercharger only worked so soon on the Merlin because the Vulture Supercharger happened to be the perfect size for the Merlin. Ask Shortround about it. In order to develop the same for the V-1710, it would take much more development time/cost.

 

[Shortround6]

So I guess it comes down to the old adage, "there's no replacement for displacement?"
I assume the DB engines were heavier as well?
If so, it sounds like they performed very well despite the weight - while not suffering the supercharger/turbocharger issues.

The early DB engines were quite similar in weight. While engine designers might argue about power per cu. in or liter, the aircraft designer was much more interested in power per pound of engine weight.

DB and Junkers used a different approach. AS did Hispano.

The smaller, high revving engines were actually in the minority.

The DB engines (and Junkers) had critical altitudes several thousand feet higher than the Merlin/Allison but without NO2 systems could not really compete with two-stage-engines in the altitude race.

 

[Clay_Allison]

Could the Allison have been bored out to ~2000 CID (similar to the R-1830 becoming the R-2000)? An Allison V-2000 could have had a pretty high critical altitude if it was possible. I know the engine types are different, and I am asking for even more, but could it be done?

Alternately, what if we had bought the patent for the RR Griffon with its huge 36L displacement?

 

[Colin1]

Could the Allison have been bored out to ~2000 CID

Re my post #275
regarding low mechanical strength I'd hazard a guess unlikely

 

[tomo pauk]

...

Alternately, what if we had bought the patent for the RR Griffon with its huge 36L displacement?

36L was medium/small displacement for a better part of ww2 - only when compared with Merlin's 27L it looks huge. Griffon was to late for US planes, since R-2800 Merlin already filled the needs perfectly.

 

[Colin1]

Griffon was to late for US planes, since R-2800 Merlin already filled the needs perfectly

I still think it's a shame NAA didn't consider building a P-51 around it

 

[Shortround6]

Could the Allison have been bored out to ~2000 CID (similar to the R-1830 becoming the R-2000)? An Allison V-2000 could have had a pretty high critical altitude if it was possible. I know the engine types are different, and I am asking for even more, but could it be done?

Alternately, what if we had bought the patent for the RR Griffon with its huge 36L displacement?

If the bore spacing was big enough to allow it, it might have been possible, if the bore spacing wasn't big enough then you are dealing with essentially a new engine.

As a for instance, many sources say that the R-R Vulture used Kestrel/Peregrine cylinder blocks which used 5in dia. pistons. It didn't, While the Vulture did use 5in dia. pistons it's cylinder blocks were sized to allow the use of 5.4in dia. pistons in a later (never built) version. Using the larger pistons would mean a cylinder block 2in longer between the 1st and last cylinder centers even if the spaces between the cylinders was kept the same compared to the Kestrel/Peregrine.

The Griffon used the same bore and stroke as the late 20s Buzzard and the racing "R", as well as the overhead cams and 4 valves per cylinder, not sure how much else carried over.

Packard had built aircraft engines of up to 2500 cu in during the 20s and 30s but got little or no sales.

 

[Colin1]

Could the Allison have been bored out to ~2000 CID?

If the bore spacing was big enough to allow it, it might have been possible, if the bore spacing wasn't big enough then you are dealing with essentially a new engine

Umm, well, OK...
assuming that there was some spare diameter, how would this affect the mechanical strength issue?

 

[Cromwell]

The Early DB engine's superchargers didn't perform any better or worse than the superchargers on the early Merlins and Allisons. The larger displacement, slower turning DB engines didn't need as much boost to make their rated power however. A Merlin using 6lb of boost is running at 1.4 Ato as is an Allison at just 42in. The more boost used to make rated power the lower the ceiling a given pressure ratio supercharger is going to work. Once the British and Americans start going to 12lbs of boost or 50in plus of manifold pressure to make rated power either the altitude performance suffers (or more accurately low altitude performance improves but high high altitude does not) or improved superchargers are needed.
The Germans with their lower manifold pressure needs can keep up the pressure to higher altitudes using the same basic supercharger. The Germans did improve their superchargers too as the war went on. A better impeller or a different diffuser design or even just a better inlet geometry could give small but useful improvements without any out change in appearance or weight.

If you can get a back-copy of 'Aeroplane' from May 2005 (VE Day Special) there is an article called 'Developing Power' all about DB and the 109

From 1934 to 44 power of the DB went from 850 hp to 2,000 hp

A lot of this was due to Water and Methanol - MW50 - and N2O or Nitrous Oxide.

MW50 - This is another way of getting round the Detonation problem - especially without High Octane fuels to hand. It also increases the Fuel/Air Mass that you can cram into a cylinder

N2O - 25% increase in power at Altitude due to releae of Oxygen from the Nitrous Oxide

This is *still* something of a secret held by DB - even to this day

 

[Shortround6]

Umm, well, OK...
assuming that there was some spare diameter, how would this affect the mechanical strength issue?

It sure wouldn't help

Various parts of the Allison were beefed up as production continued and new models came out. Sort of a question of when the bore job was done. With a late model engine it might have been OK.

Larger diameter cylinders are harder to cool however. A higher ratio of volume to surface area. The larger, heavier pistons aren't going to help bearing loads either. Not that these can't be solved but it might not be quite as easy a a new set of pistons and running a boring bar through the cylinder liners.

 

[Shortround6]

If you can get a back-copy of 'Aeroplane' from May 2005 (VE Day Special) there is an article called 'Developing Power' all about DB and the 109

From 1934 to 44 power of the DB went from 850 hp to 2,000 hp

A lot of this was due to Water and Methanol - MW50 - and N2O or Nitrous Oxide.

MW50 - This is another way of getting round the Detonation problem - especially without High Octane fuels to hand. It also increases the Fuel/Air Mass that you can cram into a cylinder

N2O - 25% increase in power at Altitude due to releae of Oxygen from the Nitrous Oxide

This is *still* something of a secret held by DB - even to this day

Thank you for the suggestion.

Some other engines went through a similar increase.

The Water/ Methanol method was used by a number of American planes and offered some real improvement when combined with an inter-cooler. Inter-coolers also allowed for some high speed-high altitude cruise settings without worry over exhausting supply.

For high altitude work the N2O does show a good increase but unless the boost needed is of short duration the installation may compete with turbos and inter-coolers for weight. The longer the endurance needed the better the turbo/intercooler set-up looks.

I am not sure how much of a secret N2O still is given the amount of use it gets in street performance cars.

 

[Elvis]

a problem with the Merlin/P-51 dream is timing.

In 1938-39 the Merlin was a single speed-single stage engine that showed little difference in potential from the Allison. A two-speed single stage version was on offer but in it's original form it showed very little difference in altitude performance over the single speed (the most common single speed version being optimized for high altitude work). It is not until Hooker does his bit that things improve for the Merlin and that is about the middle of 1940. The improved single speed engines (40 series) and two speed engines (XX or 20 series) engines are what is first contracted for with Packard. The American versions power the P-40F. Please note introduction dates for the P-40F and then figure performance for a P-51 with that engine and not the later 2 stage engines.

Work starts on the 2 stage Merlin engine but Allison has started work on a 2 stage engine at the end of 1938!

It takes Rolls-Royce several years to get the two stage engines into production and sharing info with Packard and Packard doesn't deliver any real quantity of 2 stage engines until 1943. These are the -3 and later Packard Merlins.

Allison has development problems with their 2 stage supercharger and development is slower. A good engine once developed it reaches production just a little too late to have any real impact on the war (same could be said of the P&W R4360 on which work started in 1940)

Exactly.
Very Succinctly stated, Shortround.
What's too bad is that an inter/after-cooled "-45" and later varients of the Allison weren't available by, say, late '42. If it had, maybe dependency on the Merlin series 60 wouldn't have been such a large factor.

One last note - In some earlier discussion, it seemed some here were trying to "re-design" the P-40 into, essentialy, a "P-51 type" aircraft.
Why?
If you want the performance factors of a P-51, get a P-51!
This does not say that the P-40 was a "bad" aircraft.
In fact, there are numerous reports (some of which were quoted in some of those earlier posts) of P-40's being able to dogfight with 109's with no problem, as long as the 109 kept within the P-40's altitude range.
One thing a 109 pilot always had in his back-pocket was the ability to jet up to 25-30K feet faster than you!
Going with a two-speed/two-stage engine takes that away from the 109.


Elvis