F7F (P-65) Tigercat

[tomo pauk]

Hi, KJ,
The aircraft critical altitude during high speed flight is not same as engine's critical altitude - in most cases it is significantly higher, depending on the true air speed, how good is the ram air intake projected & executed, and whether there is something that might obstruct o rinterfere with the airflow prior entering the supercharger. With that said, the F7F-1 having the critical altitude at 23400 ft when on military power is suspiciously high, I agree.
The altitude where the cruise is performed depends on current doctrine and level of technology, not where this or that engine has the critical altitude.
None of RoC figures in the doc are for zoom climb.

[KJ_Lesnick]

tomo pauk

With that said, the F7F-1 having the critical altitude at 23400 ft when on military power is suspiciously high, I agree.

How would one figure out the range at the critical altitude?

The altitude where the cruise is performed depends on current doctrine and level of technology, not where this or that engine has the critical altitude.

So it's doctrine based more than engine based?

None of RoC figures in the doc are for zoom climb.

Then why does the graph look so weird?

[tomo pauk]

How would one figure out the range at the critical altitude?

By applying the elementary school maths upon the flight manual.

So it's doctrine based more than engine based?

It also takes into account whether one can realistically fly at this or that altitude, and whether the flight is above water or enemy held territory.

Then why does the graph look so weird?

It does not.

[KJ_Lesnick]

Tomo Pauk

By applying the elementary school maths upon the flight manual.

I don't know the mathematics formula required actually

It also takes into account whether one can realistically fly at this or that altitude, and whether the flight is above water or enemy held territory.

Wouldn't it be easier to fly high -- enemy fighters would often have to struggle to get you

It does not.

It looks like there are two different sets of figures that go in different directions.  If the one on the right is climb-performance with speed -- it behaves more like a jet.

[wuzak]

How would one figure out the range at the critical altitude?

By applying the elementary school maths upon the flight manual.

I don't know the mathematics formula required actually

miles per gallon x gallon = miles

Tomo talks of the charts in flight manuals that show fuel burn at different altitudes and engine settings (cruise speeds).

[tomo pauk]

I don't know the mathematics formula required actually

Covered by wuzak.

Wouldn't it be easier to fly high -- enemy fighters would often have to struggle to get you

Agreed, plus it makes enemy AAA non-factor.
However, the piston-engined aircraft, esp. the ones with non-turbo engines, will give better mileage flying low and slow.

It looks like there are two different sets of figures that go in different directions.  If the one on the right is climb-performance with speed -- it behaves more like a jet.

One set of graphs is for the air speed, another set of graphs is for rate of climb.

[tomo pauk]

Great stuff about the reworked F7Fs.
The (obviously) US-produced bird for the USAF - can use 2-stage Packard Merlins (advantage vs. R-2800 is much more power above 20000 ft, less drag, greater mileage), or two-stage V-1710 (less drag & better mileage vs. R-2800, not using and intercooler means easier installation vs. Packard Merlin). Having only one crew member being both advantage and disadvantage vs. P-82.
Another option might be the turbo in the back of nacelle, coupled with a V-12 in front, like seen at XP-67 'Moonbat'. Or maybe a V-1710 in the turbo compound layout, for 3000 HP per engine like in the V-1710-127? Of course, the turbo-compound R-2800 would've also turn the F7F into a rocket.

[NARSES2]

I've merged these 2 topics

Chris

[KJ_Lesnick]

NARSES2

I've merged these 2 topics

Thanks: The thread was sort of beginning to morph to a point where it was first about boosting a design like the XA-41 into something longer ranged and faster; and from there to the physics behind piston aircraft (which was clearly in furtherance of the original subject at first) which eventually deviated into it's own subject, and then from there into an idea around the F7F.

tomo pauk & wuzak

For the purpose of moving everything to the right spot, I've ended up chronicling things from the previous thread as a sort of repository of where we left off.  I've color coded the poster listing in red, green, and blue: Red will be for me, green will be for wuzak, and blue will be for tomo pauk


BEGIN CHRONICLE


Poster: KJ_Lesnick
Date: 11/20/2015
Time: 00:53:28 AM

Tomo Pauk

Both F7F an F8F used single-stage supercharged engines, without intercoolers.

I beg to differ,
http://www.wwiiaircraftperformance.org/f7f/F7F-1_80262.pdf
Performance charts clearly list low and high blower

All of those four USN fighters mentioned used water-alcohol injection, the Hellcat and Corsair starting from early 1944 on.

That's correct, and that allowed more horsepower to be produced


Poster: wuzak
Date: 11/20/2015
Time: 01:20:07

Tomo Pauk

Both F7F an F8F used single-stage supercharged engines, without intercoolers.

I beg to differ,
http://www.wwiiaircraftperformance.org/f7f/F7F-1_80262.pdf
Performance charts clearly list low and high blower

Means it is two speed, not two stage.

It allowed more boost to be used and thus more power. But also that would be at a lower altitude.


Poster: KJ_Lesnick
Date: 11/22/2015
Time: 22:44:47

Wuzak & Tomo Pauk
I'm confused about a couple of things
Regarding the F4F

• I've received all sorts of conflicting information on the F4F Wildcat
  
• One website says the F4F was thought to be the first aircraft to use a twin-speed, twin-stage supercharger
  
• "Wings of the Navy" by Captain Eric M. Brown lists the F4F to have a twin-speed, twin-stage supercharger with inter-cooling
  
• Other sources seem to state a twin-stage, single-speed supercharger
  
• The http://wwiiaircraftperformance.org page seems to show performance curves for the F4F that indicate a single-speed supercharger
  

Regarding the F7F

• I'm curious why the F7F would use a single-stage supercharger when the F4F, F6F, and F4U used twin-staged
  
• I'm also curious why they'd do away with inter-cooling
  
• I figure either would jack up the critical altitude well above the amount specified
  

.

Poster: tomo pauk
Date: 11/22/2015
Time: 23:08:30

The engines, whether Cyclones or Twin wasps on the F4F, were always 2-speed supercharged. Most of the people don't separately state that any 2-stage engine have had an intercooler (reasoning it is understood as such), and the 2-stage, 2-speed version of the Twin wasp featured a pair of intercoolers indeed. The F4Fs with single stage Twin wasps were with suffix 'a' - ie. F4F-3a. Sometimes, the gearing on the 2-stage P&W engines is described as 3-speed, since the 1st stage could be de-clutched - only in low altitudes, where it is not needed, hence leaving more engine power to drive the prop.
No ww2 aircraft engine that matter used only 1-speed gearing when was outfitted with a gear-driven 2-stage supercharger; the US engines did use 1-speed for engine-stage impellers, though (and multiple gears for 1st stage) - they did not featured both impellers on same drive shaft as it was common by RR 2-stage engines.

The sigle stage radial engine is very difficult to intercool/aftercool, there is no single intake manifold that leads from compressor to the cylinders. The US 2-stage radials used intercooler to cool down the compressed air that went from 1-st stage to 2-nd stage of the compressor system. RR 2-stage engines cooled down the air/fuel mixture that went through both stages, one after another.
Why no 2-stage engines on the F7F (and F8F)? Probably a matter of 'it's good enough between SL ad 20000 ft'? The 2-stage engine will weight more, will have more drag, and will be bulkier. The USN already have had the F4U to cover high altitudes anyway. The F8F featured, vs. the Hellcat & Corsair, a smaller fuel tankage, smaller weight of armament, smaller fuselage and wings, so the single stage R-2800 was seen as a good fit.


Poster: KJ_Lesnick
Date: 11/24/2015
Time: 05:09:57

tomo pauk

The engines, whether Cyclones or Twin wasps on the F4F, were always 2-speed supercharged. Most of the people don't separately state that any 2-stage engine have had an intercooler (reasoning it is understood as such)

So, it should be implied...

Sometimes, the gearing on the 2-stage P&W engines is described as 3-speed, since the 1st stage could be de-clutched - only in low altitudes, where it is not needed, hence leaving more engine power to drive the prop.

Strange though the power-curves: Usually when there is a two-speed set-up, you usually see the brake horsepower staying about the same until you reach the critical altitude (true airspeed of course keeps going up), then you get a drop off in horse-power (and some speed falls off a little) until the next speed clutches on and then it stays there for awhile (true airspeed keeps on going up) and then above the critical it falls off and so on.

No ww2 aircraft engine that matter used only 1-speed gearing when was outfitted with a gear-driven 2-stage supercharger

Was this because of the fact that you'd over-boost too easily?

the US engines did use 1-speed for engine-stage impellers, though (and multiple gears for 1st stage)

I'm not sure I understand you, I will try and make sure we're on the same page

• The US did use 1 speed for 1-stage superchargers in some cases
  
• The US did use 1 speed superchargers with 2 or more speeds in some cases
  

Am I right or wrong?

they did not featured both impellers on same drive shaft as it was common by RR 2-stage engines.

I was under the impression that the F4U was laid out like this, while I'm not sure here, my impression was as follows

• First stage supercharger is integral to the engine and single-speed and this is what they called "neutral blower".
  
• Second stage supercharger seems to be de-clutched at this point, and then is clutched into low and then high speed
  

I was under the impression that other than that (and possibly the P-63) they were tacked onto the same shaft.

The sigle stage radial engine is very difficult to intercool/aftercool

Well technically the word intercooler/aftercooler are all based on their position: To have an intercooler you have to have at least two stages of compression as I understand it, it would be an after-cooler or pre-cooler otherwise.

there is no single intake manifold that leads from compressor to the cylinders.

You mean several airflow paths which go into each cylinder?

The US 2-stage radials used intercooler to cool down the compressed air that went from 1-st stage to 2-nd stage of the compressor system.

Which makes sense: The key word being "inter" cooler, which means in between.

RR 2-stage engines cooled down the air/fuel mixture that went through both stages, one after another.

As I understand it the engine had an after-cooler that included cooling of the air-passageways between the first and second stage as well: An after-cooler that also doubled as an intercooler too...

Why no 2-stage engines on the F7F (and F8F)? Probably a matter of 'it's good enough between SL ad 20000 ft'?

True, but for a WHIF design the F7F might very well have had the potential for a good escort: Consider the following

• The original intention was for Grumman to develop a twin-engined fighter that would be built for the Navy and the Army
  
• The USN version would use traditional supercharging, and an unpressurized cockpit; the USAAF version would be called the XP-65 and utilize a turbocharger and a pressurized cockpit (possibly differences in armament)
  
• The two designs grew so different that eventually the XP-65 was cancelled
  
• It should be noted that the USN's then design and the USAF's XP-65 were substantially different from the later F7F-1
  
• The USN continued to develop the design into the refined F7F-1
  
• While the P-38 was turbocharger-equipped, it was not often operated at the high-altitudes used for bomber escorts: The intercoolers and/or oil-coolers provided reliability issues and were damage-prone; though the P-38J did away with that, new problems popped up that took some time to be fixed
  
• An F7F-1 had a critical altitude of around 23,400 to 24,000 feet would be a little low for bomber escort (which would typically be around 25,500 to 31,500 feet, with a median of 28,500, being that 3,000 to 5,000 feet was favored over the bomber)
  
• The F7F-1 was more maneuverable than the P-38 (sans maneuvering flaps at least, and prior to the -J in terms of roll-rate at speed) and both had excellent climb-performance
  
• The baseline speed, and climb-rate performance of the F7F could be boosted by removing the tail-hook (which isn't needed for land-based operations), the wing-fold (un-needed for land-based operations)
  
• The baseline range performance could be improved without engine modification by doing the following: Removing the 4 x 20mm cannon and laying tankage in that area, and/or laying additional fuel-tankage outboard of the normal fold-line
  
• Engine improvements would drive up critical altitude however: Twin-stage, twin-speed with intercooler would do the job, alternately using a single-stage hydraulically clutched system (similar to the P-63) behind a single-speed integral supercharger with some form of cooling.
  

.

Poster: tomo pauk
Date: 11/24/2015
Time: 02:39:25

The reason people were using multi-speed supercharger drives is that this is a far more flexible thing then to have just one speed drive - it will suck less power down low (hence more power goes to the prop), while at higher altitudes the supercharger system will receive more power in order to improve the engine's power at the desired altitude range.
Overboosting was imited by throttling, in real world.

I'm not sure I understand you, I will try and make sure we're on the same page

....1# The US did use 1 speed for 1-stage superchargers in some cases
....2# The US did use 1 speed superchargers with 2 or more speeds in some cases

Am I right or wrong?

1# - Yes, vast majority of V-1710s, and all turbocharged and 2-stage engines were employing 1-speed drive for the intergral supercharger/impeller
2# - It is either one speed or two speed (or 3 speed like in Jumo 213E/F, or infinite number of speeds like in DB engines) drive, can't be both. Sometimes the drive for auxiliary supercrager of the 2-stage P&W engine was described as 3-speed: neutral (de-clutched), low gear, high gear.

I was under the impression that the F4U was laid out like this, while I'm not sure here, my impression was as follows

....1# First stage supercharger is integral to the engine and single-speed and this is what they called "neutral blower".
....2# Second stage supercharger seems to be de-clutched at this point, and then is clutched into low and then high speed

I was under the impression that other than that (and possibly the P-63) they were tacked onto the same shaft.

1# - As above, the term 'neutral' applies here on the auxiliary supercharger (1st stage). The integral supercharger (2nd stage) have had 1-speed drive and was always turning when engine was running.
2# - The auxiliary supercharger is the 1st stage here, and indeed was not clutched in in low altitude.

The auxiliary supercharger on the 2-stage V-1710s didn't share the drive, or the shaft with integral supercharger, but was provided with hydraulic coupling.

Well technically the word intercooler/aftercooler are all based on their position: To have an intercooler you have to have at least two stages of compression as I understand it, it would be an after-cooler or pre-cooler otherwise.

The term is based on the position of the observer - in the UK, people called the device 'inter-cooler' (as between supercharger and engine), the term 'after-cooler' (as after the supercharger) was mostly used in the USA.

You mean several airflow paths which go into each cylinder?

Each cylinder has it's own intake manifold, going directly from supercharger.

True, but for a WHIF design the F7F might very well have had the potential for a good escort:

Agreed


Poster: KJ_Lesnick
Date: 11/24/2015
Time: 19:34:11

Tomo Pauk

The reason people were using multi-speed supercharger drives is that this is a far more flexible thing then to have just one speed drive - it will suck less power down low (hence more power goes to the prop), while at higher altitudes the supercharger system will receive more power in order to improve the engine's power at the desired altitude range.

Correct, plus it's performance more closely mirrored a turbocharger.

1# - Yes, vast majority of V-1710s, and all turbocharged and 2-stage engines were employing 1-speed drive for the intergral supercharger/impeller

Okay

2# - It is either one speed or two speed (or 3 speed like in Jumo 213E/F, or infinite number of speeds like in DB engines) drive, can't be both.

Well, what I was trying to get at was all 2-speed superchargers were two-speed, but one stage superchargers could be one speed, two speed, etc.

Sometimes the drive for auxiliary supercrager of the 2-stage P&W engine was described as 3-speed: neutral (de-clutched), low gear, high gear.

Okay, that I understand.

2# - The auxiliary supercharger is the 1st stage here, and indeed was not clutched in in low altitude.

Now that is unexpected and I'd probably have to see it to visually grasp the layout though I grasp the basic idea.

The auxiliary supercharger on the 2-stage V-1710s didn't share the drive

Why?

The term is based on the position of the observer - in the UK, people called the device 'inter-cooler' (as between supercharger and engine), the term 'after-cooler' (as after the supercharger) was mostly used in the USA.

I thought it was relative to the impellers...

Each cylinder has it's own intake manifold, going directly from supercharger.

Got it

Agreed

I think the USAAF had too much of a predilection for turbochargers: I could understand with the B-17, B-24, and P-38, and P-47's: However it wasn't largely necessary for everything.


Poster: tomo pauk
Date: 11/24/2015
Time: 20:33:56

Correct, plus it's performance more closely mirrored a turbocharger.

Generaly it did, if the supercharger was of 2-stage variety.

Well, what I was trying to get at was all 2-speed superchargers were two-speed, but one stage superchargers could be one speed, two speed, etc.

Yes, all 2-speed superchargers were two-speed   The 2-stage superchargers have had multi-speed drives.

Now that is unexpected and I'd probably have to see it to visually grasp the layout though I grasp the basic idea.

Schematics of the supercharger system on the Hellcat: http://www.mediafire.com/view/wpz44qeyz01kdbq/stager.jpg#
The stages are numbered as the air (that they are supposed to compress) encounters them. Hence the auxiliary supercharger is the 1st stage, the integral (or main, or engine-stage) is the 2nd stage. Please note that, with auxiliary stage de-clutched (inoperative, 'neutral'), the air flow goes directly to the carburetor and then into the main stage.

(The auxiliary supercharger on the 2-stage V-1710s didn't share the drive)Why?

No need, and it does not offer anything.  

I think the USAAF had too much of a predilection for turbochargers: I could understand with the B-17, B-24, and P-38, and P-47's: However it wasn't largely necessary for everything.

It was not used on everything - many important aircraft flew well without it, and so did the ones that used turbo


Poster: KJ_Lesnick
Date: 11/26/2015
Time: 04:56:38

Tomo Pauk

Generaly it did, if the supercharger was of 2-stage variety.

Wait, if it was a supercharger (single speed) with a variable-speed tacked-on: Wouldn't it behave like a turbocharger with a supercharger too?

Schematics of the supercharger system on the Hellcat: http://www.mediafire.com/view/wpz44qeyz01kdbq/stager.jpg#
The stages are numbered as the air (that they are supposed to compress) encounters them. Hence the auxiliary supercharger is the 1st stage, the integral (or main, or engine-stage) is the 2nd stage.

Okay, I got it

Please note that, with auxiliary stage de-clutched (inoperative, 'neutral'), the air flow goes directly to the carburetor and then into the main stage.

Okay

No need, and it does not offer anything.

Why did the British use them?

It was not used on everything - many important aircraft flew well without it, and so did the ones that used turbo

Well... the following fighter-planes didn't

• P-36: They did toy with the idea of fitting a turbo in it, but it was unreliable
  
• P-40: It was mostly intended to operate around 15,000 feet and didn't require it
  
• P-39: It was intended to use a turbocharger, but it was removed for a number of reasons to the dismay of many who flew it
  
• P-51: It was developed by NAA internally, but was launched by the British Purchasing Commission and built around RAF specifications; it originally used a V-1710, and later a V-1650-3 or -7
  
• P-61: Though a night-fighter was seen as useful in the US, the aircraft was largely developed to RAF specifications for a turret night-fighter with an endurance of 8-hours; turbochargers were omitted to save weight and volume (it was realized it would add 50 mph and 10,000 feet altitude))
  
• P-63: It was basically built to correct the deficiencies of the P-39, and for obvious reasons they weren't going to use a turbocharger...
  
• P-75: It was basically a prototype and while the V-3420 was designed to carry a turbocharger, it didn't for some reason even when escort requirements were added: No idea of what kind of superchargers were used.
  

Regardless, the P-37 was fitted with one (even though it looked absurd and part of me speculates they built it largely to get a sufficient demand of V-1710's); the P-38's and P-47's had it, and the intention was for the P-39 to use it.

Pretty much all the attack planes didn't use it because they weren't designed for high altitude operation.

The bombers that didn't used them included

• The B-18
  
• The B-25
  
• The B-26
  

The B-18 was built in relatively small numbers and often used for missions at low altitudes such as MPA duty; the B-25 and B-26 were medium altitude planes; regardless, the B-17, B-24, B-29, the proposed XB-28, and B-36 all did; the XB-42 however didn't appear to


END CHRONICLE

[wuzak]

I don't think an R-2800 turbo compound was ever available. It may have run on the test bench at or after the end of the war, but I'm not sure on that either.

The V-1710-127 did run in testing but did not fly. The issue with the -127 was that the turbine (an uprated turbine from a C-series turbocharger) coudl not cope with the exhaust gas temperatures at WEP, or possibly even Military power. Thus, if the turbo-compound V-1710 had continued in development it would have got a new, custom designed turbine with air cooled blades. As the Wright turbo-compound had when it appeared several years later.

[KJ_Lesnick]

wuzak

Similar, but not the same.

Of course

The variable speed drive had less of a range of rpm than the turbo, and the drive losses increased with altitude (as the compressor was spun faster to give a higher pressure ratio).

The graph would show a more gradual drop off in power than an engine with distinct supercharger gear ratios.

The lower range of RPM is of course a disadvantage, and while horsepower is taken off the shaft to drive the device at higher speeds, a variable not mentioned is exhaust thrust.  Though I wouldn't be surprised that turbochargers would still have some useful thrust that would be left over after it goes through the bucket-wheel (I don't know why they didn't just call it a turbine), though I'm not sure how much.  

It does seem to be noteworthy on a supercharger with good exhaust pipes as the exhaust does not go through any turbine and straight out: Provided the critical altitude can be kept high (dependent on the supercharger and ram-compression), you'd have potentially a hotter, faster, and higher pressure exhaust.  Above 350 mph or so, a pound of thrust is about the same as a pound of jet-thrust and at higher altitudes; the air-pressure is quite low so the exhaust would expand more forcefully against it.

The way the V-1710 supercharger was set up was such that it was a bolt on.

Was this based on the idea of modularity, to make production simpler?

I take it what Tomo meant was that the two impellers were not mounted on the same shaft Rolls-Royce style. The reason being that you would end up with both impellers spinning at the same speed, and the variable speed function of the auxiliary supercharger would be lost.

Not if both superchargers were variable speed (I'm not sure how practical that would be admittedly)

The reason why Rolls-Royce did it that way was because it was compact, and limited the extra length added to the engine.

How much extra length would a second stage add on the V-1710 out of curiosity?

Really? Or was this the XP-37, which was adapted from the P-36 to experiment with a V-1710/turbo combination?

There was the XP-37/YP-37, but there was also the Model 75R which was a P-36 with a turbocharger: It had a top-speed of 330 mph at some altitude allegedly, but it was overly complicated.

Not actually the case.

The turbo in the X/YP-37 was woefully unreliable, and created compromises that limited the practicality of the aircraft.

I'm surprised the XP-37/YP-37 got as far as it did: It's basic shape was almost comical.  I'm surprised somebody didn't realize that the design would be a disaster, who knows, maybe they did

Don Berlin, therefore, requested that a non-turbo V-1710 be provided, teh P-40 becoming a more practical and usable aircraft.

So the P-40 was built because the turbocharged YP-37 was impractical?

Really, source for that?

Well, I'm not sure how far along they got in the design, though they started whipping up the design in the summer of 1939 according to Joe Baugher's entry on the NA-73, and if I recall Paul A. Ludwig's book (P-51 Mustang: Development of the Long-Range Escort Fighter) made a reference of some of the basic fuselage and wing-design concepts already starting to be fleshed out (not sure if it's true admittedly).

It may have also been thought that the extra speed was not required.

Unsure, to be honest: The only source of information that remotely mentioned the rationale for using a twin-stage supercharger over a turbocharger was Wikipedia.  A speed of around 365 mph would put it above most bombers of the era and if flying standing patrols it wouldn't have to accelerate as much or climb as much (if at all) to reach it's targets.

The P-63 was built around the two stage V-1710.

As far as I know, the reason was because the turbocharger didn't work out: If it did, the P-63 would not have probably existed.  Still, while I'm at it, I'm curious when the twin-stage V-1710's were first underway in development and first available for operational use?

The V-3420 was designed to have 1 stage supercharge, 1 stage supercharger with turbo or two stage supercharger.

The V-3420 would require two B-series turbochargers, the C-series not being large enough.

Like the B-29's?  How much space would two B-series turbos take up?

I believe the P-75 had two stage V-3420s.

Makes sense enough

As I said above, the USAAC wanted to have a liquid cooled fighter (after seeing the Spitfire and Bf 109 performance)

Oh, that I understand.  Paul A. Ludwig's book on the P-51 seems to suggest that they procured it because it would create a demand for V-1710's, though it's possible they genuinely wanted a turbocharger driven fighter: However, it would not surprise me if they realized the design was impractical but continued to procure it because they figured it would create a demand for V-1710's.

miles per gallon x gallon = miles

Thanks

Tomo talks of the charts in flight manuals that show fuel burn at different altitudes and engine settings (cruise speeds).

Just to be clear: When you say manual, do you meant the WWII aircraft performance page?  Otherwise, I don't have an F7F manual...

I don't think an R-2800 turbo compound was ever available. It may have run on the test bench at or after the end of the war, but I'm not sure on that either.

Oh


tomo pauk

See what I've told you

Firstly: I should have clarified that they had a predilection for turbochargers when high altitude was sought out compared to the RAF, Luftwaffe, and US/Royal Navy.

Great stuff about the reworked F7Fs.

Thanks

The (obviously) US-produced bird for the USAF - can use 2-stage Packard Merlins (advantage vs. R-2800 is much more power above 20000 ft, less drag, greater mileage)

I'm looking at the power-curve chart for the P-51D-15NA, which was powered by a V-1650-7, and from what I'm seeing

• Altitude: 0';mn\. Setting: WEP;mmmnnn MAP: 67"; Supercharger: Low-Gear; Horsepower: 1630; Max TAS: 375 mph; K-Constant: 0.00003090962963
  
• Altitude: 0';mn\. Setting: Military;mmnn MAP: 61"; Supercharger: Low-Gear; Horsepower: 1500; Max TAS: 363 mph; K-Constant: 0.000031359662781
  
• Altitude: 0';mn\. Setting: Normal-Rated; MAP: 46"; Supercharger: Low-Gear; Horsepower: 1075; Max TAS: 323 mph K-Constant: 0.000031900750267
  
• Altitude: 5000';n Setting: WEP;mmmnnn MAP: 67"; Supercharger: Low-Gear; Horsepower: 1667; Max TAS: 396 mph; K-Constant: 0.000026844173806
  
• Altitude: 5000';n Setting: Military;mmnn MAP: 61"; Supercharger: Low-Gear; Horsepower: 1520; Max TAS: 382 mph; K-Constant: 0.000027268013429
  
• Altitude: 5000';n Setting: Normal-Rated; MAP: 46"; Supercharger: Low-Gear; Horsepower: 1105; Max TAS 342 mph; K-Constant: 0.000027623834274
  
• Altitude: 10000'; Setting: WEP;mmmnnn MAP: 67"; Supercharger: Low-Gear; Horsepower: 1700; Max TAS: 417 mph; K-Constant: 0.000023444488203; Notes: Critical Altitude (low-blower) on Wartime-Emergency Power
  
• Altitude: 10000'; Setting: Military;mmnn MAP: 61"; Supercharger: Low-Gear; Horsepower: 1545; Max TAS: 401 mph; K-Constant: 0.000023960471828
  
• Altitude: 10000'; Setting: Normal-Rated; MAP: 46"; Supercharger: Low-Gear; Horsepower: 1140; Max TAS: 362 mph; K-Constant: 0.000024031403732
  
• Altitude: 13200'; Setting: Military;mmnn MAP: 61"; Supercharger: Low-Gear; Horsepower: 1560; Max TAS: 413 mph; K-Constant: 0.000022144936709; Notes: Critical Altitude (low-blower) on Military-Power
  
• Altitude: 15000'; Setting: WEP;mmmnnn MAP: 57.7"; Supercharger: Low-Gear; Horsepower: 1480; Max TAS: 411 mph; K-Constant: 0.000021317498926
  
• Altitude: 15000'; Setting: Military;mmnn MAP: 57.8"; Supercharger: Low-Gear; Horsepower: 1475; Max TAS: 411 mph; K-Constant: 0.000021245480348; Notes: Interesting that there's more MAP in Military-Power than Wartime Emergency...
  
• Altitude: 15000'; Setting: Normal-Rated; MAP: 46"; Supercharger: Low-Gear; Horsepower: 1170; Max TAS: 382 mph; K-Constant: 0.000020989194547
  
• Altitude: 16200'; Setting: Normal-Rated: MAP: 46"; Supercharger: Low-Gear; Horsepower: 1175; Max TAS: 387 mph; K-Constant: 0.000020272390886; Notes: Critical Altitude (low-blower) on Normal-Rated Power
  
• Altitude: 20000'; Setting: WEP;mmmnnn MAP: 67"; Supercharger: High-Gear; Horsepower: 1410; Max TAS: 421 mph; K-Constant: 0.000018896128131
  
• Altitude: 20000'; Setting: Military;mmnn MAP: 61"; Supercharger: High-Gear; Horsepower: 1280; Max TAS: 410 mph; K-Constant: 0.000018571988218
  
• Altitude: 20000'; Setting: Normal-Rated; MAP: 40.5; Supercharger: Low-Gear; Horsepower: 1025; Max TAS: 384 mph; K-Constant: 0.000017748938666
  
• Altitude: 25000'; Setting: WEP;mmmnnn MAP: 67"; Supercharger: High-gear; Horsepower: 1410; Max TAS: 438 mph; K-Constant: 0.000016780186413
  
• Altitude: 25000'; Setting: Military;mmnn MAP: 61"; Supercharger: High-gear; Horsepower: 1285; Max TAS: 428 mph; K-Constant: 0.000016389730809
  
• Altitude: 25000'; Setting: Normal-Rated; MAP: 46"; Supercharger: High-Gear; Horsepower: 1025; Max TAS: 404 mph; K-Constant: 0.000015544607838
  
• Altitude: 26000'; Setting: WEP;mmmnnn MAP: 67"; Supercharger: High-Gear; Horsepower: 1410; Max TAS: 442 mph; K-Constant: 0.000016328726116; Notes: Critical Altitude (high-blower) on Wartime-Emergency Power; Maximum TAS
  
• Altitude: 28000'; Setting: Military;mmnn MAP: 61"; Supercharger: High-Gear; Horsepower: 1288; Max TAS: 438 mph; K-Constant: 0.000015328283759; Notes: Critical Altitude (high-blower) on Military Power
  
• Altitude: 29400'; Setting: Normal-Rated; MAP: 46"; Supercharger: High-Gear; Horsepower: 1040; Max TAS: 420 mph; K-Constant: 0.000014037360976; Notes: Critical Altitude (high-blower) on Normal-Rated Power
  
• Altitude: 30000'; Setting: Military;mmnn MAP: 54.5"; Supercharger: High-Gear; Horsepower: 1180; Max TAS: 429 mph: K-Constant: 0.000014945489052; Notes: WEP and Military-Power appear to be the same in terms of speed, horsepower, and MAP from this altitude on...
  
• Altitude: 30000'; Setting: Normal-Rated; MAP: 44.7"; Supercharger: High-Gear; Horsepower: 1010; Max TAS: 416 mph; K-Constant: 0.000014029473785
  
• Altitude: 35000'; Setting: Military;mmnn MAP: 43"; Supercharger: High-Gear; Horsepower: 900; Max TAS: 407 mph; K-Constant: 0.000013349324242
  
• Altitude: 35000'; Setting: Normal-Rated: MAP: 35"; Supercharger: High-Gear; Horsepower: 765; Max TAS: 388 mph; K-Constant: 0.000013096832053
  

The tests that confirmed these figures were based upon a weight of 9760 lbs.

Looking at the figures for the F7F-1 show at 20,000 feet, a horsepower of 1600 per engine at military power (compared to 1280 hp figure for the V-1650-7 at the same power setting and altitude; furthermore even at WEP at critical altitude of 26000 in high-gear, yields a horsepower of 1410).  An inline would, admittedly be nice from the standpoint of drag, however the only inlines I can readily think of that produced similar power would be the following

• Napier Sabre (2180 to 2260 hp): I'm not sure if they were produced in the United States and I'm not sure the supercharging details
  
• Rolls-Royce Griffon (1490 hp to 2420 hp): The upper power-levels may or may not have been produced prior to November 3, 1943
  
• Allison V-3420 (2600 to 2800 hp): It was available on time, and wouldn't be bad for an up-rated version, though (could be a good alternate for the P-75 though).
  

The Allison V-3420 does seem like a pretty cool idea, but the R-2800 may very well have delivered acceptable performance if critical altitude could be kept up higher

not using and intercooler means easier installation

I'm confused here: Last I checked, the F7F had a pair of intakes in each wing.  I'm not sure the exact function of each intake, though an engine air-intake and oil-cooler would be good candidates: The F4U's interestingly used a set of intakes for both the oil-cooler and air-intake (I think...)

One set of graphs is for the air speed, another set of graphs is for rate of climb.

You mean this one?

[tomo pauk]

Yep - the graph states the velocity in mph and rate of climb in fpm.
The intakes on the F7F indeed served as you stated - one is feeding the sir to the engine itself, another one serves the oil cooler. Going with a liquid cooled engine obviously necessitates the cooler for gylcol/water mixture, if the engine is intercooled then another cooler is needed, at least for Anglo-American engines.

Looking at the figures for the F7F-1 show at 20,000 feet, a horsepower of 1600 per engine at military power (compared to 1280 hp figure for the V-1650-7 at the same power setting and altitude; furthermore even at WEP at critical altitude of 26000 in high-gear, yields a horsepower of 1410).

The engine powers need to be compared without the ram effect. The R-2800-22W have had 1850 HP at 14000 ft, 1600 HP at 16000 ft, that would make maybe 1400 Hp at 20000 ft, and 1100-1200 HP at 25000 ft. Ram effect (most pronounced at high speed) will add some 5000 ft to the listed altitudes in these cases (both P&W and P. Merlin).
The 2-stage Packard Merlin will match that power from 20000 ft and above, that coupled with lower powerplant drag will make such an engined F7F outpacing and outclimbing the historic F7F above 20000 ft, let alone above 25000 ft. The V-1650-7 was available maybe 10 months earlier than the R-2800-22W, that is also a major point of difference historically, another bonus being maybe 20% increase in range/radius. In early 1945, the V-1650-9 will further improve the power figures of the Packard Merlin line of engines, basically beating the -22W (and -34W) already above 15000 ft; same will happen with V-1650-7 when operating on 150 or 145 grade fuel.
The 2-stage V-1710 will also match the power of the -22W by the time the -22W is available (mid-late 1944) above 20000 ft.

As for the alternatives you mentioned - all will work fine in an what-if. Realistically, either Sabre or Griffon (but they are only Made in UK); the V-3420 is too heavy.

Firstly: I should have clarified that they had a predilection for turbochargers when high altitude was sought out compared to the RAF, Luftwaffe, and US/Royal Navy.

The predilection for turbochargers was shared between the US Army and VVS, the LW and RN were firmly in single stage engines camp (and VVS once the experiments with turbo were sidetracked, hence the AM 34 to 37 series of engines, plus the experiments with turboed Mikulin engines), RAF and USN indeed jumped at the chance to have 2-stage engines once available. All said is for the time between mid-1930s to mid war.

wuzak said:

I don't think an R-2800 turbo compound was ever available. It may have run on the test bench at or after the end of the war, but I'm not sure on that either.

The V-1710-127 did run in testing but did not fly. The issue with the -127 was that the turbine (an uprated turbine from a C-series turbocharger) coudl not cope with the exhaust gas temperatures at WEP, or possibly even Military power. Thus, if the turbo-compound V-1710 had continued in development it would have got a new, custom designed turbine with air cooled blades. As the Wright turbo-compound had when it appeared several years later.

The turbo-compound R-2800 will work as an what if
Turbine on the TC V-1710 was probably too close to the cylinders - several feet? With the turbine in one end of nacelle and engine on another, the temperature peaks should be kept under control, we can recall that same turbine have had no problems on the P-47. Indeed for the close coupled turbine the air cooled blades are necessity.

[kitnut617]

[jcf]

The Curtiss Hawk 75R had an auxiliary mechanical supercharger, not a turbo-supercharger.

[tomo pauk]

Apart from obvious, for a what-if, engine change to a V-12, the jet engined F7F will be one sleek machine. The U/C might be retracted next to the jet engine, or alternatively the main legs will retract in the fuselage, in a layout of F-104, or XB-42 or Yak-38. Other option might include the turbo prop.