F7F (P-65) Tigercat

[tomo pauk]

I am interested in the V-12 powered F7F, even if just as a mental excesise - a what-if Hence finding the more or less a convinient way to install the intercooled Packard Merlin on it. Good deal of the lack of power down low will be cancelled by the lower drag, and the F7F powered by V-1650-9 will probably be faster than the historic F7F at any altitude.

Then why would the horsepower keep going up?

It will go a bit up with altitude due to the lower back-pressure the exhaust must overcome, up until the the critical altitude for the observed gear the compressor is currentl using, for a current engine power setting. Also the ever cooler air helps. The power with ram is not always listed in engine charts, though some power charts and tables have it (like for the Jumo 210/211 or some US engines). Nobody was calculating the exhaust thrust into the power with intent to add it to the engine power, though some charts do show either thrust as force or as power (like it was the case for the docs about DB 601A/Aa or BMW 801D).

[wuzak]

Tomo, I believe the intake below the spinner on teh 2 stage Mosquitoes was for teh intercooler.

http://www.ausairpower.net/APAA/DH-Mosquito-PR-XVI-071017-F-1234S-017-1S.jpg

The exit is on the side of the nacelle, above where the carb intake is.

[tomo pauk]

Yes, in case of Mosquito with 2-stage engine the intercoolers were just under the spinner.

[KJ_Lesnick]

tomo pauk

I am interested in the V-12 powered F7F, even if just as a mental excesise - a what-if

Okay

It will go a bit up with altitude due to the lower back-pressure the exhaust must overcome, up until the the critical altitude for the observed gear the compressor is currentl using, for a current engine power setting.

So back-pressure affects superchargers too?

Also the ever cooler air helps.

Makes enough sense

The power with ram is not always listed in engine charts

Weird...

Nobody was calculating the exhaust thrust into the power with intent to add it to the engine power, though some charts do show either thrust as force or as power (like it was the case for the docs about DB 601A/Aa or BMW 801D).

Frankly, I think it should be counted as thrust, not as HP to be honest.


wuzak

Tomo, I believe the intake below the spinner on teh 2 stage Mosquitoes was for teh intercooler.

http://www.ausairpower.net/APAA/DH-Mosquito-PR-XVI-071017-F-1234S-017-1S.jpg

The exit is on the side of the nacelle, above where the carb intake is.

Understood

[tomo pauk]

The back pressure does not effect effect the superchargers.

Listing the power vs. altitude without ram effect accounted for makes lots of sense, since that altitude depends on plenty of factors. Like the layout of ram air intake ( eg. the well executed in the P-40, Mosquito, P-51 and Bf 109 vs. badly executed in P-39 and Whirlwind; squished air intake on the Fw 190A that sucks the turbulent air vs. the 'full profile' external air intakes in a handful of such outfitted Fw 190As) and real air speed an aircraft powered with such an engine can make (faster P-51 vs. slower P-40). Having a better carb also helps (see tests of Spitfire with injection carb vs. float carb); the ice or stone guard presence or absence also makes difference in altitude power of an engine.

[tahsin]

Entirely off topic and unrelated to F7F but the guys to impress are of the kind that trolled Bill Gunston for daily fun. It starts when some guy sort of proved that it was Gunston who coined the phrase the Harrier could carry a box of matches across a football field. Gunston swore vengeance and played as if he took the bait. For 26 years they promised to sell a flying saucer to him and he played it in the stoical British way of doing stuff, expecting to expose them as frauds. Good hunting!

[KJ_Lesnick]

tomo pauk

The back pressure does not effect effect the superchargers.

So you're talking about the exhaust having less resistance as it shoots out the stacks?

Listing the power vs. altitude without ram effect accounted for makes lots of sense, since that altitude depends on plenty of factors. Like the layout of ram air intake ( eg. the well executed in the P-40, Mosquito, P-51 and Bf 109 vs. badly executed in P-39 and Whirlwind; squished air intake on the Fw 190A that sucks the turbulent air vs. the 'full profile' external air intakes in a handful of such outfitted Fw 190As) and real air speed an aircraft powered with such an engine can make (faster P-51 vs. slower P-40). Having a better carb also helps (see tests of Spitfire with injection carb vs. float carb); the ice or stone guard presence or absence also makes difference in altitude power of an engine.

So it gives a baseline figure for the engine and also helps gauge what performance you'll get based on speed?

[KJ_Lesnick]

tomo pauk & wuzak

I found something I think everybody here will like: A cutaway!



As for the purposes of a land-based escort-fighter/fighter-bomber design: Would the following traits provide sufficient range

• Drop tanks
  
• A twin-stage supercharger with one stage being twin-staged, and the other being variable-speed (i.e. F4U-4)
  
• Doing one of the following: Enlarging the oil-cooler intake to work as an intercooler; adding an F4U-4 style intake under the engine to serve as a carburetor intake, with the previous carburetor intake to provide the intercooling; other
  
• Removing the wing-fold mechanism
  
• Laying fuel-bladders/tanks across parts of the leading-edge where permissable and/or the outboard wing area
  

.

As another interesting note: This is a quote from joncarrfarrelly and suggests another interesting possibility...

The Army XP-65 wasn't actually a variation of the USN F7F, both were iterations of Design 51.

The story starts with the Grumman Design 46 of October 1939, a large twin 1,600hp R-2600 powered aircraft (two-stage mechanical superchargers or turbo-superchargers) for the Army. A derivative was offered for export in February 1940 as the Design 49.
The preliminary design work for these two projects worked to Grumman's advantage when they decided to submit a proposal to a 21 December, 1940 RFP for specification SD-112-18. Seeking to satisfy both Army and Navy requirements, Grumman incorporated most features of Designs 46 and 49 into the Design 51 proposal, which was submitted to BuAer 24 March, 1941, and emerged as the winner of the Navy competition on 14 May. By then the Army and Navy and had agreed to seek the development of twin-engined fighters differing only in details, the Army opted for turbo-superchargers, the Navy for mechanical superchargers. The Army version was to be pressurized and armed with two 37mm cannon and four .50 MG, whereas the Navy version was to be unpressurized and armed with four 20mm cannon in place of the two 37mm weapons.

The aircraft originally started out as a USAAC design, which was then developed into a USN & USAAC design, which the USAAC/USAAF dropped out of and the USN then modified further into the F7F-1.

Since SD-112-18 was a USN specification: I assume the USAAC hadn't fully signed off on the program by this point?  From a WHIF-standpoint: What if they did?

[kerick]

I wonder how far back the idea of building one aircraft to satisfy both the Army and the Navy goes back to? Appears to fail even back in 1941.

[rickshaw]

I wonder how far back the idea of building one aircraft to satisfy both the Army and the Navy goes back to? Appears to fail even back in 1941.

It appears to have worked for the RN FAA and the RAF.  The problem is, neither the USN or USAF want it to work...

[tomo pauk]

...
As for the purposes of a land-based escort-fighter/fighter-bomber design: Would the following traits provide sufficient range

• Drop tanks
  
• A twin-stage supercharger with one stage being twin-staged, and the other being variable-speed (i.e. F4U-4)
  
• Doing one of the following: Enlarging the oil-cooler intake to work as an intercooler; adding an F4U-4 style intake under the engine to serve as a carburetor intake, with the previous carburetor intake to provide the intercooling; other
  
• Removing the wing-fold mechanism
  
• Laying fuel-bladders/tanks across parts of the leading-edge where permissable and/or the outboard wing area
  

...

Drop tanks are no-brainer, they are already supported.
In supercharger, one stage can't be twin-staged. In F4U-4, main, or engine stage was 1-speed (= fixed gearing), the auxiliary stage was 2-speed, that can be declutched, 'behaving' like it is 3-speed. No need to reinvent the wheel, use the 2-stage R-2800 that is currently available. The change from 1-stage R-2800 to 2-stage will make next to no change on range/radius.
Oil cooler won't help with intercooling, those are two separate systems. Perhaps use straight tunnel for the oil cooler instead the 'S' shaped one, so the intercooler can be located nearby the engine in the wing.
Leading edge won't be a good place for extra fuel tanks, it already is occuied with different intakes and cannon ports. Use the space between the spars instead.
Fixed wings are good idea.

[KJ_Lesnick]

Drop tanks are no-brainer, they are already supported.

Yup

In supercharger, one stage can't be twin-staged.

Yes, but you could replace the single staged arrangement with a twin-staged layout...

In F4U-4, main, or engine stage was 1-speed (= fixed gearing), the auxiliary stage was 2-speed, that can be declutched, 'behaving' like it is 3-speed. No need to reinvent the wheel, use the 2-stage R-2800 that is currently available.

I thought the F4U-4 had a hydraulic clutch system on one stage?

The change from 1-stage R-2800 to 2-stage will make next to no change on range/radius.

Why?

Oil cooler won't help with intercooling

No!  I was trying to figure out where to supply the air for an intercooler.  I don't care where it comes from so long as it's there.

Leading edge won't be a good place for extra fuel tanks, it already is occuied with different intakes and cannon ports. Use the space between the spars instead.

Okay

[tomo pauk]

Replacing an existing supercharger system on an engine already installed in an aircraft, if that's your intention, is reinventing the wheel, or a recipe for problems, or both. The R-2800 was available in 1942 in 2-stage supercharged form, so let's use what is available.
The R-2800-18 indeed have had hydrauilcal clutch for auxiliary stage, thing being that speed ratios were pre-set, there was no variation of speed like it was the case with Allison take on the same problem.
R-2800 was still a powerful engine, and a fuel hog. Want more range? Increase fuel tankage. Let's remeber that P-47 was good for 450 miles of combat radius (not range, that was greater of course) with 300 gals internaly plus 300 gals externally; 600 miles with 370 + 300 gals, 1000 miles with 556 + 600 gals. F6F was under 300 miles, it carried 250 gals internally
So unless we have the F7F with at least 700 gals internally (two engines to feed...), plus 600 gals externally, it wont be much of a long range fighter, at least not under USAF conditions, that were demanding much greater cruise speed and altitude than USN conditions. Perhaps it would be a good idea to get rid of .50s and their ammo, cram more fuel there.

[KJ_Lesnick]

tomo pauk

Replacing an existing supercharger system on an engine already installed in an aircraft, if that's your intention, is reinventing the wheel, or a recipe for problems, or both.

Uh, no -- the idea would have been to have designed the aircraft from the start around the difference.

The R-2800 was available in 1942 in 2-stage supercharged form, so let's use what is available.

Actually the F7F-1 used a single-stage, twin-speed supercharger -- which is why I proposed twin-stages.

The R-2800-18 indeed have had hydrauilcal clutch for auxiliary stage, thing being that speed ratios were pre-set, there was no variation of speed like it was the case with Allison take on the same problem.

Oh... okay

So unless we have the F7F with at least 700 gals internally (two engines to feed...), plus 600 gals externally, it wont be much of a long range fighter, at least not under USAF conditions, that were demanding much greater cruise speed and altitude than USN conditions. Perhaps it would be a good idea to get rid of .50s and their ammo, cram more fuel there.

I had considered the possibility of removing some guns...

[tomo pauk]

Not sure what is the issue - I know that Tigercat used 1-stage supercharged engines, and I agree with proposal to have 2-stage engines if we want the new variant to be great performer also at 25000-30000 ft. Just pointing out that sticking another stage and intercooler on any engine installed is non-starter