Corsair and Hellcat in Europe

[swampyankee]

The Hellcat was optimized for lower altitude performance than either the Merlin P-51 or any P-47, simply because high altitude bombers had a hard enough time hitting a stationary target, let alone a moving ship.

That said, the Hellcat did serve in the ETO, but wasn't involved in air combat to any significant degree. It would most certainly be competitive; several aircraft noted as failures in the Pacific did quite well in Europe, and the Hellcat and Corsair were successful there.

The P-51, in all the reports I have seen, has quite the lowest zero-lift drag coefficient of any single piston engine fighter, about 0.017, vs almost all others, between 0.022 and 0.025. In other words, it was probably the most efficient single-engine fighter with pistons banging back and forth.

 

[DarrenW]

Improved performance would be under 18,500ft even in high gear as the supercharger can't supply any more air above that altitude regardless of the fuel used.

Good point SR6. I actually noticed this while examining special WEP flight tests of the Hellcat, where boost pressures were raised to 64" Hg, using 100/130 fuel and ADI. Critical altitude in high blower was reduced to about 15,000 feet and to around 10,000 feet in low blower settings.

The Mustang also fell victim to this. Here's a chart which shows a critical altitude drop of over 2,000 feet in both supercharger settings, when boost pressures were increased by some 8" Hg, using 150 octane fuel:

Source: http://www.wwiiaircraftperformance.org/mustang/eglin-p51b-level.jpg

I also noticed that top speed was 445 mph @ 23,000 feet, independent of manifold pressures.

 

[DarrenW]

The Hellcat was optimized for lower altitude performance than either the Merlin P-51 or any P-47, simply because high altitude bombers had a hard enough time hitting a stationary target, let alone a moving ship.

That's a very unique perspective and one that never dawned on me before....

 

[Dawncaster]

Good example for 60 to 65"hg manifold pressure.

case of F4U-1.

The maximum speed improvement was not great, and the most distant altitude was about 17,000 ft with a speed increase of approx 18 mph. the reduction in critical altitude was about 2,000 ft. One model had low-type cabin(birdcage canopy), so this could have had some effect.

Special overboosting by improved water injector was tested by F6F-3 and F4U-1 until 1945. The reports on both models did not specify a definite manifold pressure(reports used the carburetor impact pressure instead), but likewise the top speed improvements were not large.

I think the P-47 is more advantageous because it uses a turbocharger.

 

[wuzak]

You can see on that graph that the critical altitude for the engine with extra boost and ADI was at or below 0ft when the auxiliary supercharger was in neutral..

 

[Dawncaster]

You can see on that graph that the critical altitude for the engine with extra boost and ADI was at or below 0ft when the auxiliary supercharger was in neutral..

That's right. In that case, the manifold pressure will not reach 65 "hg, although a turbocharged model would be possible.

 

[MIflyer]

Two USN light carriers were equipped with nothing but F6F's and supported Operation Dragoon, the invasion of Southern France. They did the P-47 style mission, bombing and strafing to support the invading forces. There was an article entitled "Hellcats over France" in a 1945 issue of Flying magazine. I have an electronic copy on disk but it refused to print out properly so I could post it here.

 

[DarrenW]

Good example for 60 to 65"hg manifold pressure.

case of F4U-1.

View attachment 501911

The maximum speed improvement was not great, and the most distant altitude was about 17,000 ft with a speed increase of approx 18 mph. the reduction in critical altitude was about 2,000 ft. One model weighs about 40 lbs and has a low-type cabin, so this could have had some effect.

Special overboosting by improved water injector was tested by F6F-3 and F4U-1 until 1945. The reports on both models did not specify a definite manifold pressure(reports used the carburetor impact pressure instead), but likewise the top speed improvements were not large.

I think the P-47 is more advantageous because it uses a turbocharger.

Thanks Dawncaster, you've provided compelling evidence that overall maximum speed seems to just shift to lower altitudes, with no appreciable increase to speak of but a paltry 5 mph. To me this example shows that using the higher octane fuel would not have helped either naval fighter perform better at altitude, and thus would not have improved their ability to provide high-altitude escort for the strategic bombing campaign. Maybe some speed advantage would be gained however if they were used in the fighter-bomber role, and the climb rates of the two aircraft most certainly improved when manifold pressures were increased beyond 60" Hg.

On a minor note, I believe that I've read those same over-boosting reports that you speak of and manifold pressures are indeed discussed along side water impact pressures (the Hellcat was tested at 58", 60", 62", and 64" respectively). But just as you said maximum level speed did not increase by appreciable amounts during these tests.

 

[DarrenW]

Two USN light carriers were equipped with nothing but F6F's and supported Operation Dragoon, the invasion of Southern France. They did the P-47 style mission, bombing and strafing to support the invading forces. There was an article entitled "Hellcats over France" in a 1945 issue of Flying magazine. I have an electronic copy on disk but it refused to print out properly so I could post it here.

I would very much like to read this article, if you find a way to post it.

 

[Dawncaster]

Greg, the alierons on the 190A in that test were incorrectly adjusted, and so the aircraft wasn't rolling nearly as quickly as it should have been. There is correspondence between the RAF and the US on the tests relating to the rate of roll, including a side by side list of relative rolling rates. The USN tests were down by about 30% at some points.

The British also have some documentation on Corsair II (F4U-1D) on FW 190 roll rates

150 mph
'Corsair II' roll (Vought figures): 81 deg/sec FW190 (RAF tests): 108 deg/sec

200 mph:
Corsair II: 97 FW190: 119

250 mph:
Corsair II: 88 FW190: 160

300 mph:
Corsair II: 84 FW190: 128

350 mph:
Corsair II: 75 FW190: 96

400 mph
Corsair II: 64 FW190: 75



USN tests of a F4U-1 vs various USAAF fighters in August 1943 reports that the aircraft had the same rate of roll as a P-47C up to 300 mph (indicated), above which the P-47C is better and "remains better as the diving speed increases".

Same tests report that F4U-1 has a better rate of roll than the P-51 (type not given) "at all level flight speeds", but at 280 mph ASI the P-51 becomes better and remains better as diving speeds increase.

Against a stripped down ("light weight" is the exact wording) P-38G the F4U-1 "may have a slight edge" in rate of roll at slow speeds, but the P-38G has "the better rate of roll because of the high stick forces and ineffective ailerons" on the F4U-1.

Early Corsairs did not have boost tabs on ailerons. A good example is the first batch(BuNo 21xx) of Corsairs as shown in the USAAF report you mentioned. Corsair's aileron boost tab was appeared with birdcage Corsairs in mid or late 1943. with boost tabs, Corsair's steady roll rate rises up to 300 knots. The first boost tab was the balance tab and was installed to eliminate wing heaviness in flight. Later, it became a spring type balance tap, and it got more additonal performance in high speed.


(Feb 1943, Guadalcanal - Henderson Field)


(Sep 1943, Espiritu Santo)

For case of F4U-1 vs Fw 190 report, Perhaps Corsair has benefited from the boost tab at the start of the roll, and USN pilots might have evaluated it. If full ailerons deflection situation, Fw 190 would have been faster. The roll rate could vary considerably depending on the measurement conditions. A good example is FM-2.

Unlike the 90 degree roll rate, 360 degree roll rate was poor, due to included starting and stopping time and extra control to maintain the ball centered position while complete roll.

with boost tabs, Corsair was better in this problem, so 'felt' of the roll was pretty fast.

(F3A-1, 90 degree)

(F4U-1D, 270 degree)

(Corsair IV, 360 degree)

(FG-1, 360 degree)

So there was a 'possibility' that F4U actually got good results for instant roll rate in ACM against Fw 190.

And I am interested in the roll rate of that Corsair II that you wrote. At low speeds, it is superior to the figures in the US inspection report for various Corsairs. Perhaps that seems to be the roll rate of the Corsair without the boost tab.

 

[parsifal]

The two formations that supported the landings were TG 80.2 and TG80.6 built around 6 x RN CVEs and 2 x USN CVEs. There were no light carriers fielded for operation Dragoon. There were a further 3 RN CVEs acting as the floating reserves.

The major aircraft utilised in the invasion was not the hellcat, it was the seafire. Whichever way you want to cut this, the major effort in support of this operation was provided by the RN and its equipment



RN

Emperor: Hellcat
Pursuer – Wildcat
Searcher – Wildcat
Attacker – Seafire
Khedive – Seafire
Hunter – Seafire
Stalker – Seafire

USN

Tulagi – Hellcat
Kasaan Bay - Hellcat

Seafires performed better than they had over salerno, though the insistence they carry 500lb bombs in this operation and the still air condition were not ideal for them.

 

[MIflyer]

I would very much like to read this article, if you find a way to post it.

DarrenW, I am unable to get the article to print properly either to paper for scanning or direct to PDF. But you can go over to ebay and buy a disc as I did for $7.99. It has all of the Flying Magazines from 1945 to 1963. It is called "Popular Aviation Magazines Volume 2"

 

[MIflyer]

The Hellcat, like the F4F and the F4U were not optimized for lower altitudes due to the inability of bombers to hit ships from high altitude. When they designed those airplanes, especially the F4F they had no practical knowledge of that experience. The F4F and the F6F and F4U that came after it used the less efficient two stage mechanical supercharging approach because it was available and easier to implement than the USAAC favored approach of using a turbosupercharger for the 1st stage. The F4F's high altitude engine was inspired by the USN's fear of the Y1B-17 and its ability to defeat them in the budget battles in DC. When Gen Billy Mitchell sank those German ships off the VA coast the Washington Times headlines screamed that battleships were worthless and airplanes were a cheaper and more effective defense. The USN's response was the aircraft carrier, which would defend the fleet from the heavy bomber in war games.and thus protect the Navy budget in DC.

The YIB-17 combined with the YB-17 interception of the Italian Liner Roma far out at sea showed the USN the jig was up! The Y1B-17 had virtually the same top speed as the USN's new highly advanced F2A monoplane fighter - but 10,000 ft higher! Given the lack or radar the probability of intercepting turbosupercharged B-17's was zero with an F2A as defense. As a first step they rushed to get the US Army to prohibit flying its bombers far offshore. Meanwhile, the USAAC had tried out the XP-41 with two stage mechanical supercharging but found they much preferred the turbo equipped version, Seversky's privately financed AP-4, which led to the P-43 and P-47. But the mechanically supercharged R-1830 was already available and was easier to implement in the revised F4F. The result was that the USN put high altitude fighters in service before the USAAF, which was the real promoter of the idea, because the USN's approach was easier to implement than the higher performance turbo approach. Turbos blowing up in flight were all too common in the late 30's and early 40's, among other things.

In reality in WWII the USN found that the only high altitude bombers were the USAAF's - and the Navy even bought some for their own use. The F7F and F8F had single stage superchargers, since there was no real threat either on the high seas or in DC..

Forgive my soapbox approach, but I had planned to write an article on this for Wings/Airpower had they not gone out of business, and did research at the Air and Space Museum as part of that effort. . .

 

[DarrenW]

DarrenW, I am unable to get the article to print properly either to paper for scanning or direct to PDF. But you can go over to ebay and buy a disc as I did for $7.99. It has all of the Flying Magazines from 1945 to 1963. It is called "Popular Aviation Magazines Volume 2"

Sounds like a pretty good deal!

 

[DarrenW]

So let me see if I have this straight. The Hellcat and Corsair, by virtue of their supercharged R-2800, could not benefit as much as the Thunderbolt from the increased octane ratings because their engines didn't "breathe" as effectively as a turbo system in order to improve the fuel/air mixture necessary for similar increases in horsepower. That's why we only see minor increases in overall maximum speed from what was realized at the critical altitudes while using 100/130 fuel (maybe 5 mph or less). On the other hand, the Thunderbolt experienced double digit gains in maximum speed while using 100/150 because it's turbocharger was more efficient.

Please let me know if I'm way wrong here....

 

[Shortround6]

What you have is that most of the increase in the power in the cylinders in the P-47 was used to power the propeller.
Since the turbo was powered by the exhaust gases the only "loss" or minus to the "theoretical" power (going from 54in to 65in in theory is a 20% increase in power in the cylinders)going to the prop is the loss caused by increased back pressure at the exhaust ports. Not quite as much burnt gases leaving so a bit less fresh mixture gets in. But more mixture going in means a high mass leaving which means more power for the turbo.

For the Navy engines the power to run the compressor comes from the crankshaft. You want to move 20% more in? you need to put more power (around 20%????) into the supercharger drive even at the same rpm. (Throttle is part closed at anything other than the critical height so the volume/weight of the air can change even at the same RPM.)
This very simple theory takes no account of the higher intake mixture temperatures (less actual charge density) or the effectiveness or capacity (one way or the other) of the inter-coolers involved.

Hope that helps.
Hope I am right

 

[DarrenW]

What you have is that most of the increase in the power in the cylinders in the P-47 was used to power the propeller.
Since the turbo was powered by the exhaust gases the only "loss" or minus to the "theoretical" power (going from 54in to 65in in theory is a 20% increase in power in the cylinders)going to the prop is the loss caused by increased back pressure at the exhaust ports. Not quite as much burnt gases leaving so a bit less fresh mixture gets in. But more mixture going in means a high mass leaving which means more power for the turbo.

For the Navy engines the power to run the compressor comes from the crankshaft. You want to move 20% more in? you need to put more power (around 20%????) into the supercharger drive even at the same rpm. (Throttle is part closed at anything other than the critical height so the volume/weight of the air can change even at the same RPM.)
This very simple theory takes no account of the higher intake mixture temperatures (less actual charge density) or the effectiveness or capacity (one way or the other) of the inter-coolers involved.

Hope that helps.
Hope I am right

It definitely helps. I can now clearly see why the turbocharger gets the most benefit from the higher octane fuel. My next question is why critical altitude decreases with increased boost pressures, when using higher octane fuels and water injection on supercharged aircraft? Is there some correlation between the denseness of the surrounding air and how it relates to the higher pressures developed within the cylinders?

Lastly, with what you know about these Navy engines and their ancillary equipment, would they have been able to operate at 70" Hg (using 104/150 and ADI), and if so would there be any appreciable performance benefit as a result (other than further lowering the critical altitude)?

 

[wuzak]

It definitely helps. I can now clearly see why the turbocharger gets the most benefit from the higher octane fuel. My next question is why critical altitude decreases with increased boost pressures, when using higher octane fuels and water injection on supercharged aircraft? Is there some correlation between the denseness of the surrounding air and how it relates to the higher pressures developed within the cylinders?

Lastly, with what you know about these Navy engines and their ancillary equipment, would they have been able to operate at 70" Hg (using 104/150 and ADI), and if so would there be any appreciable performance benefit as a result (other than further lowering the critical altitude)?

Boost my dear boy.

In an altitude rated supercharged engine, such as Merlins, V-1710s and the R-2800-8/10, boost is controlled by the throttle.

At low altitudes, below critical altitude, the supercharger can deliver more boost. But since this is usually more boost than the engine can handle, the throttle is closed to limit the mass air flow, and thus control the boost to the engine.

Critical altitude is the altitude at which the throttle is completely open. Critical altitude is not just one number, though - there is one for each level of boost.

That is the maximum boost the supercharger can deliver at that altitude, engine speed and supercharger gear. From that point on the boost, and power, reduces. If that is low gear or neutral (as P&W auxiliary superchargers had), the pilot or control system can change up to the next gear at some point after that critical altitude.

Higher octane/PN fuel and ADI allows the engine to use more boost. The only way to get more boost is to open the throttle earlier, at lower altitude, given the same rpm and supercharger gear.

The new boost level will have a lower critical altitude. Once that is achieved, boost falls, until it reaches the previous boost level at the critical altitude for that boost.

* critical altitude is called Full Throttle Height in British engines
** Boost is pressure above standard sea level pressure

 

[BiffF15]

Wuzak,

If I understand you correctly going up in octane lowers FTH, however the engine will still make more power at all altitudes than with the lower octane fuel?...

Cheers,
Biff

 

[DarrenW]

Boost my dear boy.

In an altitude rated supercharged engine, such as Merlins, V-1710s and the R-2800-8/10, boost is controlled by the throttle.

At low altitudes, below critical altitude, the supercharger can deliver more boost. But since this is usually more boost than the engine can handle, the throttle is closed to limit the mass air flow, and thus control the boost to the engine.

Critical altitude is the altitude at which the throttle is completely open. Critical altitude is not just one number, though - there is one for each level of boost.

That is the maximum boost the supercharger can deliver at that altitude, engine speed and supercharger gear. From that point on the boost, and power, reduces. If that is low gear or neutral (as P&W auxiliary superchargers had), the pilot or control system can change up to the next gear at some point after that critical altitude.

Higher octane/PN fuel and ADI allows the engine to use more boost. The only way to get more boost is to open the throttle earlier, at lower altitude, given the same rpm and supercharger gear.

The new boost level will have a lower critical altitude. Once that is achieved, boost falls, until it reaches the previous boost level at the critical altitude for that boost.

* critical altitude is called Full Throttle Height in British engines
** Boost is pressure above standard sea level pressure

Excellent stuff Wuzak. What you say to Biff's question?