P-40 Warhawk/Kittyhawk

[Clay_Allison]

That may be true but how much low altitude performance do you want to give up?
You still have to take-off and climb to combat altitude.
Some of the later P-40s did trade 125hp at take-off for an extra 100 or so hp at 20,000ft. if you want several hundred HP than that several thousand feet higher then you are going to loose several hunderd more HP at sea level. Take- off and low altitude climb using less than 1000hp isn't going to impress too many peaple.

I'd probably be willing to trade 250hp at sea level to get it back up high if it meant having a few squadrons capable of "bouncing" 109s from above in North Africa. Remember I'm also suggesting stripping it of all armor and two guns to get its rate of climb up. It would be well worth it to me just to let the Germans and Japanese know that they were not guaranteed an altitude advantade.

You know it's a damned shame that we didn't have P-47s available in the early phases of the war. The Jug was in its element at 35k feet with that turbocharger. No axis fighter pilot ever wanted to see a P-47 above them. You could beat one when you had energy or you were down on the deck, but fighting them from below meant he had all the cards.

 

[Elvis]

......

 

[Elvis]

No you gain very little on top Or at least over 18-20,000ft.

Later single speed Allisons could give over 1100hp at 15,500ft. using 44in of boost. You are already operating at a pressure ratio of 2.6. even a better supercharger that could give a presure ratio of 3 to 1 at the same or better efficency so that the charge temperature doesn't go up will only give you about 50.7in of boost for about 1300hp at that altitude.

You are going to gain a lot on the low end however. THe above Allison was good for 1200hp at take off so by using a second gear you could go back to the 1325HP take off rating of the lower altitiude Allisons. THe better supercharge would really improve things at 4-7000 ft for WER.

Pulling a stiffer gear dosn't solve the limitations of the compressor itself. Maybe with a stiffer gear you could pull 1100hp at 16,500-18,000ft instead of 15,500ft but that isn't enough to turn the plane into a high altitude fighter.

Try checking out the performance of single speed single stage Merlins and two speed single stage Merlins. Leave out the two stage merlins (the 60 series and 70 series engines) . Try comparing the Merlins from the same year and see what you get.

Just to clairify, you do realize when I mentioned a "second gear" in my prior post, I was suggesting a change from the single-speed setup to a two-speed setup.
I state that because you seem to go on about the limitations of a single speed setup and this has me wondering if you overlooked the fact that my post concerned changing to a two-speed setup.
Also, the advantage of the second gear may not match the performance of, say, a P-47, but it would make the plane a better performer at altitudes above 12K-15K feet, compared to the single speed version that was actually used during the war.
There's no way that it couldn't improve the plane's performance above the listed altitude range.

Concerning your comments on my question about adapting a two-speed/two-stage S.C. system to the Allison, yes, I was thinking about the British setup.

FWIW, I did some rather rudimentary calculations last night and based on the listed take off power of the Merlin and Griffon engines, it seems a similarly set up Allison would have a take-off HP rating in the 1600HP range.



Elvis

 

[Shortround6]

Just to clairify, you do realize when I mention a "second gear", I'm saying change the single speed setup to a two-speed setup.
Also, the advantage of the second gear might not match, say a P-47, but it would make it better than the single speed versioin, wouldn't you agree?



Elvis

I do realize what you mean buy a second gear.
A second gear can make a lot of difference to an airplane.
It just does't change things much at 20,000ft if the original single speed engine was already using a high altitude gear.

As far as not matching the P-47, the P-47 at 27,000 feet was getting a 5.2 to 1 pressure ratio from it's supercharger set up. A far cry from the 2.4 Pressure ratio of the Allison engine using 8.80 gears.

The stiffer the gear the more power it takes to drive the supercharger. For instance the Allison required around 110-120 hp to the supercharger to get 10,000lb of air an hour uisng 6.44 gears. It required around 250 hp to get the same amount of air using 9.60 gears. So assuming you are at an altitude that both gears will allow the supercharger to deliver 10,000lb an hour the high gear ratio costs you 130 hp to the propellor. The advantage of the 2 speed supercharger. keeping performance at 15-20,000ft without sacrificing take -off and sea level power. Yes the stiffer gear does allow the supercharger to deliver the required air higher up but you are getting into diminsioning returns. Too stiff a gear is going to suck up almost all the extra power at a given altitude.
A large part of the power consumed goes into heating the intake charge so that doesn't help things.

By the way the later 10.4" supercharger using 7.48 gears used almost the same amount of power as the 9.5in supercharger using 8.10 gears. They had about the same tip speed. The 10.4in supercharger could flow a larger volume however.

 

[Elvis]

I do realize what you mean buy a second gear.
A second gear can make a lot of difference to an airplane.
It just does't change things much at 20,000ft if the original single speed engine was already using a high altitude gear.

Who says the single speed s.c. used "high altitude gearing"?
Its apparently a compromise, meant to give good performance at sea level and retain some semblence of that performace for as high up as they could get (and that appears to be in the 12K-15K foot range).
Of course, adding another gear is going to cost HP. This is the downfall of any gear-driven supercharger.
However, that faster gearing has to help in some way, otherwise even the vaunted two-stage systems would be single speed units.

As far as not matching the P-47, the P-47 at 27,000 feet was getting a 5.2 to 1 pressure ratio from it's supercharger set up. A far cry from the 2.4 Pressure ratio of the Allison engine using 8.80 gears.
By the way the later 10.4" supercharger using 7.48 gears used almost the same amount of power as the 9.5in supercharger using 8.10 gears. They had about the same tip speed. The 10.4in supercharger could flow a larger volume however.

I only cited the P-47 for comparison purposes, so lets not drag that one into this conversation any more than is neccesary, please.
Thank you.
Interesting comparison you made with the two superchargers you listed.
Even though power usage is the same, the larger supercharger is still moving a larger volume of air, so it is having an even more positive affect on engine power output, compared to the smaller impeller.

If you really want to get hot and heavy with the calculator, try to figure out the gear ratio of the higher gear so that it creates the most NET power in the 15K-25K foot range.
I don't think I have the mathamatical capability to handle it, but if you feel up to it, please...be my guest.
It would be interesting to see how much different the higher gear ratio would be, compared to the lower one and what the increase in power would be.
If you need a "base line" to compare to, I believe the "-81" and "-99" engines made 1150HP on take-off 800HP @25000ft.

...also, I'd like to explore the idea of adapating the Birtish Two-Speed/Two-Stage S.C. to the Allison.
I'll see if I can find any evidence of that ever being attempted.



Elvis

 

[Elvis]

While searching around for something on the Brit s.c.'d Allison, I ran across this thread from another form...

http://warbirdsforum.com/showthread.php?t=1282

Some very interesting comments in there.



Elvis

 

[Shortround6]

Who says the single speed s.c. used "high altitude gearing"?
Its apparently a compromise, meant to give good performance at sea level and retain some semblence of that performace for as high up as they could get (and that appears to be in the 12K-15K foot range).
Of course, adding another gear is going to cost HP. This is the downfall of any gear-driven supercharger.
However, that faster gearing has to help in some way, otherwise even the vaunted two-stage systems would be single speed units."

The Allison "81" and "99" models were using the 9.60 gear which was as high as Allison went. Yes you could make a different gear ratio but the 9.60 gear had the impellor tips moving at 1200ft per second (supersonic) so that is about as fast as as you could drive that impellor and hope to get resonable efficincy from the supercharger. For good performance at sea level try the 8.10 gears from a P-38 engine. 1425hp without any help from the turbo and at a mere 54" of manifold pressure compared to the 51.5" of the "81-99". 225hp more for 2.5" of manifold pressure? Of coourse the lower charge heating of the lower gear set means that the charge air is denser for the same pressure and the lower temperatrue measn the extra boost can be used without fear of detontaion.
Rolls never went higher than a 9.49 gear on a production 2 speed Merlin with their 10.25" impellor.

"However, that faster gearing has to help in some way,otherwise even the vaunted two-stage systems would be single speed units."

Uh, No and Yes, the extra gear was a low gear that allowed for take off.

"I only cited the P-47 for comparison purposes, so lets not drag that one into this conversation any more than is neccesary, please.
Thank you.
Interesting comparison you made with the two superchargers you listed.
Even though power usage is the same, the larger supercharger is still moving a larger volume of air, so it is having an even more positive affect on engine power output, compared to the smaller impeller."

I too was using the P-47 for comparison purposes. Given the limitations of the the single stage set up there is now way to even come close to the performance of a 2 stage set up. I was trying to show that by comparing the pressure ratio difference of the two systems.

"f you really want to get hot and heavy with the calculator, try to figure out the gear ratio of the higher gear so that it creates the most NET power in the 15K-25K foot range.
I don't think I have the mathamatical capability to handle it, but if you feel up to it, please...be my guest.
It would be interesting to see how much different the higher gear ratio would be, compared to the lower one and what the increase in power would be.
If you need a "base line" to compare to, I believe the "-81" and "-99" engines made 1150HP on take-off 800HP @25000ft."

1. No real need. a higher ratio wasn't going to work. Spinning the impellor any faster just sends it into supersonic tip speeds and ruins it's effectiveness.
2. The "81-99" engines were already using the high altitude gear.

"...also, I'd like to explore the idea of adapating the Birtish Two-Speed/Two-Stage S.C. to the Allison.
I'll see if I can find any evidence of that ever being attempted."

It probably would have worked about the same but when figureing improvements to aircraft performance you have to figure in the extra weight and drag of the 2 stage equipment. Note the enlarged duct under the 2 stage spifires left wing compared to the single stage versions. That is were the aftercooler radiator is.
Yes performance will go up but not by quite as much as a plug in the higher HP alone estimate would have you believe.

 

[Elvis]

So Shortround6, let's say you're a bright and enterprising young engineer who is sequestered by Allison to help them squeeze better performance out of the V-1710 engine.

What would you do, to improve the high altitude performance of the Alllison,without sacrficiing its low altitude performance?

...and lets call the dividing line between "high" and "low" altitude that 12K-15K foot range I've been mentioning (in fact, if you like, you can call that range, "mid" altittude).


Elvis

 

[Shortround6]

Here is an interesting site:

motorgeek.com :: Turbo/Engine Flow Calculations and Maps

Just be sure to plug in some realalistic numbers.

To get manifold pressure as we know it you have to add the environmental air pressure to the boost pressure. And 0.5 pressure loss through an inter-cooler is a bit optomistic.

THe program is for airflow requirements and does not take into acount riction with rpm orthe power needed to drive the supercharger. While it doesn't have anything for detonation limits the heat rise in the supercharger is interesting as are the intercooler and water injection sections.

OF course nothing there considers size, cost, engineering time and other factors which decide wither something is done or not.

And remember in WW II no computers. You had anywhere from a couple of men to a couple of hundred working at desks with sliderules, adding machines, and pencil and paper to do complex calculations.

To get back to you question you have three basic choices.

1. A. Use a 2 speed gear box on the existing engine supercharger.
Advantages=quick, cheap (both in engineering effort and manufacture) , minimal impact on engine size or weight so minimal (or no) problems installing in existing airframes. better take-off, low altitude (6-7000ft?) performance and climb.
Disadvantages= does nothing to improve perfomance at any hight above what the 81-99 engiens can already do. Some slight increase in intial cost and maitainence.
B. design larger capacity, higher effecincy 2 speed supercharger.
Advantages= only a bit more expensive in engineering erfort and manufacture. Only a bit heavier and larger in volume so that installing in exisrting airframes should still be easy.
Disadvantages= may only raise critical height (full throttle) by about 2,000ft, may do nothing for engine at lower altitudes compared to option A.

2. use a 2 speed, 2 stage supercharger.
A. Use a set-up like the Merlin. both impellors on a common shaft, always turning at the same speed. aftercooler not required but strongly recommended.
Advantages= compact for a two stage supercharger. will boost performance into the low 20,000ft area, higher with aftercooler. cheapest 2 stage in terms of intial layout and set up.
Disadvantages=size and weight compared to option 1. may require a fair amount of deveopment time in impellor and diffuser design to "match" the superchargers. it will impact engine installationin existing airframes but probably not to an extent that prevents use.
B. Use set up Like U.S. Navy. 1st stage (auxilary stage) supercharger has it's own 2 speed gearbox with clutch whihle engine has a single speed drive. Auxilery supercharger is dis-engaged for take off/low altitude to save power. Lowgear is engaged for medium altitude and high gear used for high altitude. Intercooler used when 1st stage is engaged.
Advantages= good high altitude performance with no real engine penelities at low altitudes, being able to vary the speeds of the 1st impellor may make supercharger m"matching" easier?
Disadvantages=weight and bulk are starting to get even bigger. engineering time could be getting rather large and the intercooler if aircooled is no longer universal but specific to each air frame.
C. As in B but using a hydralic drive to the first stage. This is what Allsion was working on. Allison also skipped the intercooler and substituted water injection instead. Trade voume of intercooler for smaller but denser ADI tank.

3. Use a turbo-charger. Already being done.
Advantages= Great high altitude performance
Disadvantages= weight and bulk of installation make a tremendous impact on airframe. Maintainence issues for part of the war and perhaps an allocation of resources problem.

So as a bright young spark which way do you go? quick and cheap with limited performance or long and expensive with high performance.

 

[Elvis]

So as a bright young spark which way do you go? quick and cheap with limited performance or long and expensive with high performance.

Hey now, don't be smart young man, or I'll have you doing coffee runs for the whole shop in that leaky old
P-12 we've got parked out back.

Please refrain from throwing the question I posed to you, back at me, without answering it first.
That's very poor form to do otherwise.



Elvis

 

[Shortround6]

Hey now, don't be smart young man, or I'll have you doing coffee runs for the whole shop in that leaky old
P-12 we've got parked out back.

Please refrain from throwing the question I posed to you, back at me, without answering it first.
That's very poor form to do otherwise.



Elvis

Well, I gave you 6 options in total. I just didn't pick one. To narrow the choice you have to be more specific with the question.

How much improvement are you looking for?
When is the start of the project (1940 or 1944)?
How soon do you want the engine in production( 3 months from start of project or 2years)?
what airframes do you want to use it in?

we will leave finicial costs out of it for now. I sure don't have enough information on that area to do moe than take a wild guess.

The best choice from a pure perfomance standpoint of the engine was the turbo charger option but they were already working on that one and it might not fit (in fact it didn't fit ) in all airframes.

 

[Elvis]

Why are you giiving me options?

I asked YOU.

What would YOU do, based on the knowledge you've gained over the years as professoinal mechanic.
Forget the BS parameters you mentioned in your last post, just tell me what you would do.
That's all I'm asking.

...and Charlie wasnts 2 cearms, non-fat, and one sugar, non-saccarin, in his coffee. There's a good lad. Thanks sport.


Elvis

 

[Clay_Allison]

Well, I gave you 6 options in total. I just didn't pick one. To narrow the choice you have to be more specific with the question.

How much improvement are you looking for?
When is the start of the project (1940 or 1944)?
How soon do you want the engine in production( 3 months from start of project or 2years)?
what airframes do you want to use it in?

we will leave finicial costs out of it for now. I sure don't have enough information on that area to do moe than take a wild guess.

The best choice from a pure perfomance standpoint of the engine was the turbo charger option but they were already working on that one and it might not fit (in fact it didn't fit ) in all airframes.

I think 1940 is the time frame to focus on and the question is, "How do you get a high-altitude interceptor available to the US by Jan 1942.

Assuming you want to use the P-40 airframe, how do you fix the power plant to get high altitude performance and decent rate of climb?

 

[Elvis]

You help the British develop the Griffon V-12 and park that little puppy under the "hood".





Elvis

 

[Shortround6]

I think 1940 is the time frame to focus on and the question is, "How do you get a high-altitude interceptor available to the US by Jan 1942.

Assuming you want to use the P-40 airframe, how do you fix the power plant to get high altitude performance and decent rate of climb?

Stick a rocket in the thing and pray

Attemps by Curtiss to build newer fighters than the P-40

Fact Sheets : Curtiss XP-46 : Curtiss XP-46

A contract for two aircraft was signed on Sept. 29, 1939.

Fact Sheets : Curtiss XP-53 : Curtiss XP-53

Two prototypes, designed for the Continental XIV-1430-3 inverted Vee engine, were ordered in October 1940.

Fact Sheets : Curtiss XP-60 : Curtiss XP-60

XP-60 ordered 6 weeks after the XP-53.THE XP-60 prototype first flew 18 September 1941 with Merlin engine.Curtiss was given a contract for 1,950 P-60A'swith turbo-charged Allisons on October 31st, 1941.
Contract Changed after Peral Harbor to 1400 P-40s and 2,400 P-47s.
Jan 1942 Curtiss is given contracts for 1 each: XP-60A. XP-60B, XP-60C and XP-60D

Curtiss was well aware of the fact that the P-40 was not in the forefront of world fighters and was trying to come up with a new airframe.

 

[Elvis]

Fact Sheets : Curtiss XP-60 : Curtiss XP-60

XP-60 ordered 6 weeks after the XP-53.THE XP-60 prototype first flew 18 September 1941 with Merlin engine.Curtiss was given a contract for 1,950 P-60A'swith turbo-charged Allisons on October 31st, 1941.
Contract Changed after Peral Harbor to 1400 P-40s and 2,400 P-47s.
Jan 1942 Curtiss is given contracts for 1 each: XP-60A. XP-60B, XP-60C and XP-60D

Curtiss was well aware of the fact that the P-40 was not in the forefront of world fighters and was trying to come up with a new airframe.

I think this excerpt from the XP-60 page says a lot, as to why the Allison was never developed as "fully" during the war, as was the Merlin...

The Army Air Corps wanted a "Merlin"-powered aircraft...

...and isn't it funny how, after the war, when R-R wanted us to start paying royalties on further production of the Packard-Merlin engine, that the Allison "suddenly" became a 2000+HP engine and P-M production was halted.





Elvis

 

[Clay_Allison]

It might have been possible to create a successor to the P-40 with the easily available Wright R-2600. There is a significant dry weight difference in the engines, but perhaps not as much in installed weight. 1600 Horses would be a huge jump in power from 1100. Also I think our supercharger technology for radials was much better developed.

 

[Elvis]

...another way to go about this is to go back to the P-37 design, but modify it by utilizing a tricycle landing gear arrangement.
This would essentially eliminate the pilots lack of "view" when taxiing and allow the P-36/P-40 airframe to (more) successfully utitilize the Turbo-Supercharged version of the Allison.


Elvis

 

[Colin1]

...another way to go about this is to go back to the P-37 design, but modify it by utilizing a tricycle landing gear arrangement.
This would essentially eliminate the pilots lack of "view" when taxiing and allow the P-36/P-40 airframe to (more) successfully utitilize the Turbo-Supercharged version of the Allison

Elvis
I'm not sure how you'd get that to work, there is an awful lot of aeroplane behind the main landing gear on the P-37 and even if you did somehow persuade it to keep its nose gear on the ground, where would the nose gear fold into?

Have a look at the P-37 in profile in Aviation Pictures/Curtiss P-40 Pictorial History, it really is a non-starter.

The pilot's lack of view while taxying was something that prop job drivers just learned to live with, sure, there were tails chewed off the guy in front and worse but by and large, they coped with it.

 

[Shortround6]

It might have been possible to create a successor to the P-40 with the easily available Wright R-2600. There is a significant dry weight difference in the engines, but perhaps not as much in installed weight. 1600 Horses would be a huge jump in power from 1100. Also I think our supercharger technology for radials was much better developed.

Depends on which company is making the Radial.
Wright either used a two speed single stage or used turbos.
P&W actually built two stage engines for Wildcats 2 years before the Merlin 60 series showed up.
I have no details on the installation or much on it's performance except it allowed the R-1830 to give 1200HP at sea level and 1000HP at 19,000ft. Theree are some accounts of 'surging" troubles with this engine.
P&W used both rather complicated 2 stage systems on the R-2800 and turbos.

The Early Wright R-2600s were rated at about 1400hp at 12,000ft for military power and that is high gear. The 1700hp engines in the B-25Ds were rated at 1700hp at 12,000ft for 5 minutes. While the engine is 550-600lbs heavier than the Allison you do get the ditch the radiators and coolant to save some weight.
what you can't ditch is the strange fact that the R-2600 is actually about 1.5" larger in diameter than an R-2800 and has about 1 square foot more frontal area
or 16sq.ft. compared to the Allisons 6.1-6.2sq.ft.
of course after factoring in the radiators and oil coolers and the fact that even a liquid cooled engine needs a little air flowing over the outside of it things aren't quite that bad.

Granted good cowling can make up for a lot but in 1941-42 really low drag cowlings for aircooled engines were few and far between.