Corsair and Hellcat in Europe

[DarrenW]

Here, the Hellcat has both the largest wing area and greatest Cd0, which is consistent with it being the slowest of the three.

But that's the thing Swampy, I'm not really sure if the Cat really was slower than the Jug when flown at a similar horsepower rating. I'm thinking that the superior speed of the Thunderbolt at certain altitudes had more to do with higher engine output than superior aerodynamics. What say you?

 

[Greyman]

I know he addressed F4U v 190 but do not recall the verdict.

Corsair II Versus Focke-Wulf 190A-4
This would be a contest between a heavyweight and a lightweight fighter, with virtually all the advantages on the side of the latter. Having flown both aircraft a lot, I have no doubt as to which I would rather fly. The Fw 190A-4 could not be bested by the Corsair.
Verdict: The Fw 190A-4 was arguably the best piston-engine fighter of World War II. It is a clear winner in combat with the Corsair.

 

[swampyankee]

But that's the thing Swampy, I'm not really sure if the Cat really was slower than the Jug when flown at a similar horsepower rating. I'm thinking that the superior speed of the Thunderbolt at certain altitudes had more to do with higher engine output than superior aerodynamics. What say you?

At high altitudes, certainly: the critical altitude of the turbocharged engine of the P-47 was much higher than the mechanically supercharged engines of the Hellcat and Corsair.

 

[eagledad]

Darren W and swampyankee

Thank you for the explanations.and patience.

Eagledad

 

[DarrenW]

Darren W and swampyankee

Thank you for the explanations.and patience.

Eagledad

I appreciate the kind sentiment, your input is always valued as well.

 

[Dawncaster]

SR
However, in looking at William's site, the F4U is rated at approximately 350 at sea level using 2000 hp.
I have seen a navy document that shows production F4U-1s have a sea level speed of 339.

350 mph at sea level with 2000 bhp for F4U-1's prodction inspection trials, and it was first batch(BuNo 021xx) production model birdcage F4U-1.

339 mph was not for production model F4U-1, it's included in F3A-1's report of prodction inspection trials. F3A-1s generally showed many problems with poor production quality.

Interestingly, the F3A-1 didn't have 2000 bhp at sea level in that report. This also applies to FG-1A's prodction inspection trials report. However, Vought's F4U-1s did not suffer from such a problem. Vought Corsairs seem to have better quality than other company Corsairs. or maybe it's the difference between PW's R-2800 and Nash's Licensed R-2800. Nash's R-2800 showed only 1890 horsepower with military power at sea level in FG-1A's prodction inspection trials report.

 

[davparlr]

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..
.

I think I read that the AAF were having a tough time with high altitude Japanese bombers over Port Moresby, New Guinea, early in the war. Their P-40s and P-39s could not intercept them.

 

[P-39 Expert]

I think I read that the AAF were having a tough time with high altitude Japanese bombers over Port Moresby, New Guinea, early in the war. Their P-40s and P-39s could not intercept them.

To intercept a Japanese Betty bomber the interceptors needed early warning radar or the ability to fly standing patrols. No airplane in existence on either side could intercept high altitude high speed bombers without early warning or standing patrols.

No American radar until August '42 at Milne Bay. Few standing patrols since there were only two squadrons of P-39s defending Moresby.

Plenty of Japanese bombers and fighters were shot down in the defense of Moresby, the defending P-39s exacted a little better than a 1 to 1 victory ratio against their more experienced, better trained, and better supplied Japanese opponents. They managed to just barely hang on until radar and reinforcements arrived. And the Navy stopped the Japanese Moresby invasion force in May at the battle of Coral Sea.

With early warning after August '42 the bombing raids on Moresby dwindled from multiple daily raids in May to sporadic raids thereafter.

 

[parsifal]

This article states that 29 RS (RAAF) transported to Moresby 19 February 1942 and began operations 1 month later.

Radar performance was hampered by the mountains adjacent the town, with GCI plots limited in range initially to 40 miles (for targets coming in at 18-22000 feet). If the Japanese attacked at altitudes above 18000 ft, the performance of the p-39s fell away so badly they simply couldn't reach enemy altitudes in time. There are occasional early warnings provided by coast watchers but really the issue could not be rectified until the p-39s were replaced by better defenders for moresby

http://www.radarreturns.net.au/archive/EchoesRRWS.pdf

 

[P-39 Expert]

This article states that 29 RS (RAAF) transported to Moresby 19 February 1942 and began operations 1 month later.

Radar performance was hampered by the mountains adjacent the town, with GCI plots limited in range initially to 40 miles (for targets coming in at 18-22000 feet). If the Japanese attacked at altitudes above 18000 ft, the performance of the p-39s fell away so badly they simply couldn't reach enemy altitudes in time. There are occasional early warnings provided by coast watchers but really the issue could not be rectified until the p-39s were replaced by better defenders for moresby

http://www.radarreturns.net.au/archive/EchoesRRWS.pdf

The performance of the Moresby radar was poor as judged by the operators. The sets were "experimental" models and were still on the south side of the Owen Stanley mountains which limited their range. They still could not adequately warn of incoming raids.

Milne Bay is on the eastern tip of NG and was not obstructed by mountains. It also provided a panoramic view of the Japanese held areas.

The P-39s obviously could intercept Japanese bombers at over 22000' as they did on numerous occasions.

 

[MIflyer]

But that's the thing Swampy, I'm not really sure if the Cat really was slower than the Jug when flown at a similar horsepower rating. I'm thinking that the superior speed of the Thunderbolt at certain altitudes had more to do with higher engine output than superior aerodynamics. What say you?

Note that the Hellcat was not flush riveted. It is true that turbocharged engines generally perform better at altitude than mechanically supercharged engines - hence the superiority of the AP-4 over the XP-41, which led to the T-Bolt. But aerodynamic drag was a secondary consideration for the Hellcat.

Grumman claimed that the difference in top speeds of the Hellcat and Corsair was almost entirely due to ASI errors in the F4U and that the low altitude difference was due to a decision to reduce the direct ram air to the carb in their airplane to reduce the chance of carb icing.

It is true that the F4U had a rather more direct path to the carb than the Hellcat's chin intake, and Grumman incorporated that approach in the F8F.

Note that the picture shows the RIGHT root intake for the F4U, which has the oil cooler and intercooler cooling air intake. The carb intake is on the other side but you can still see that it is a short trip to the carb on the back of the R-2800.

 

[DarrenW]

I took another look at sea level speeds at military power (without WEP) and found a few examples worthy of comparison:

Type / Configuration / Speed / Engine Output

F6F-5 BuNo. 58310 / 1 wing pylon / 319 mph / 1850 hp

F65-5 BuNo. 72731 / 2 wing pylons & rocket launchers / 312 / 1900 hp

P-47D S/N 42-26167 / 2 wing pylons / 303 mph / 1950 hp

P-47N S/N 44-88406 / 2 wing pylons / 327 mph / 2060 hp

Sources:

http://www.wwiiaircraftperformance.org/p-47/p47d-44-1-level.jpg
http://www.wwiiaircraftperformance.org/f6f/72731-level.jpg
http://www.wwiiaircraftperformance.org/f6f/58310-level.jpg
http://www.wwiiaircraftperformance.org/p-47/p-47n-88406-speed.jpg
http://www.wwiiaircraftperformance.org/p-47/p-47-tactical-chart.jpg


I think that the difference we are seeing with level speeds of various P-47s at similar power settings is mostly due to whether or not the aircraft is configured with wing pylons or not. For example, when comparing S/N 42-26167 to the P-47 tactical planning chart (which shows speeds at 5K feet without pylons), I see a decrease in top speed anywhere from 22-30 mph (42-26167 with pylons was clocked at 325 mph at this same height in military power).

To me these pylons look far "draggier" than either type carried by the Hellcat or Mustang so I think the speed difference is plausible (on the low end anyway). Mustang wing pylons caused 12 mph loss, Hellcat lost about 10 mph for faired wing pylons and an additional 4 mph for rocket launchers.

Anyone have statistics that show exactly what the speed loss would be for the Thunderbolt with these pylons installed? The only way to know for sure is to have the same aircraft tested with and without the pylons under the same set of circumstances (weather conditions, engine output, ect.).

After considering this, I'm currently under the impression that at similar rated power and without wing pylons the P-47 had a slight speed advantage over the F6F at sea level, but this advantage quickly faded once pylons were installed on each perspective aircraft.

I also noticed that with the examples I gave the P-47N is 11 mph faster than the F6F-5 similarly configured (Hellcat speed would be 316mph carrying two pylons and no rocket launchers), but the Republic fighter also has 160 more horsepower available as well. Not sure however if this is enough of a difference in power to give the P-47 that much of an edge in speed without it being slightly "cleaner" aerodynamically.

 

[DarrenW]

Note that the Hellcat was not flush riveted....

Yes I was aware of that but in the end it's not an absolute given that an aircraft with flush riveting will have lower overall drag then one which is not. From my understanding flush riveting isn't as structurally strong, and because Grumman wanted to make it's fighter inordinately rugged it chose strength over surface refinement. Most if not all would agree that they made the right choice.

 

[DarrenW]

It is true that turbocharged engines generally perform better at altitude than mechanically supercharged engines - hence the superiority of the AP-4 over the XP-41,

...and the P-47's engine was more fuel efficient at high altitude cruise due to the turbo.

I see. So if two engines are developing the roughly same horsepower, RPM, and burning close to the same amounts of fuel per hour, how does cruise speed vary by 12 mph as in this example? There is 4" Hg difference in MP between the two so maybe that's the reason.

Examples from selected P-47D and F6F-5 pilot's manuals (both aircraft with 350 gallons of fuel after reaching altitude, center-line drop tank mounted and no wing pylons):

AC / altitude / engine output / RPM / MP / fuel setting / fuel use rate / airspeed / max. range

P-47D / 25,000ft / 1200hp / 2250rpm / 32" Hg / auto lean / 105gph / 295 mph / 960 miles / 2.81 mpg

F6F-5 / 25,000ft / 1225hp (Low Blower) / 2300rpm / 36" Hg / auto lean / 106gph / 283 mph / 935 miles / 2.67 mpg

At 30,000ft:

AC / altitude / engine output / RPM / MP / fuel setting / fuel use rate / airspeed / max. range

P-47D / 30,000ft / 1200hp (est.) / 2250rpm / 32" Hg / auto lean / 110gph / 303 mph / 960 miles / 2.75 mpg

F6F-5 / 30,000ft / 1125hp (High Blower) / 2300rpm / 34" Hg / auto lean / 111gph / 299 mph / 935 miles / 2.67 mpg

The P-47's ferry tank was far more 'draggy' than the cigar-shaped tank used by the F6F so I believe that actual air frame drag was less with the P-47 and this probably had more to do with airfoil design than anything else (i.e. induced drag).

 

[Shortround6]

Some of those charts are bit on the rough side.

But lets go back to your example. P-47 engine is turning 50rpm less which is no big deal. Barely a blip on the fuel consumption scale. However it is running at 32in of manifold pressure which is 89% of the manifold pressure the F6F is using.

Hmmm, just a tick fewer RPM, 10% less boost (which means 10% less air through the engine), 50 hp more power (better efficiency? )

Something doesn't seem quite right???

F6F has to use more of the power in the cylinders to drive the auxiliary supercharger to get the desired manifold pressure which is were some of the power it should have been making using 36in of pressure goes.

 

[DarrenW]

Something doesn't seem quite right???

Thanks, I forgot to figure in the added power consumed by the supercharger. To get engine output within 50 hp the Hellcat's boost was set 10 percent higher....

 

[DarrenW]

Some of those charts are bit on the rough side.

In what way?

 

[wuzak]

I don't know, is a 4" Hg for 50 less horsepower a lot of difference when running at such low boost? Your explanation is well taken and I can definitely see some added efficiency for the turbocharged engine, but even with this the range of the two aircraft with similar gas load is pretty darn close (within 3%).

And I do realize that once the turbo enters higher boost settings it will start to out-strip the performance of the supercharged R-2800. I was just trying to promote my theory that all three Pratt and Whitney powered aircraft would have almost identical fuel burn rates while using similar cruise (lower power) settings, and knowing the P-47's ETO escort range with a given fuel load we can use simple algebra to determine what would be the theoretical range of the two naval fighters under similar circumstances.

Have I convinced anyone yet?

Even with low MAP the auxiliary supercharger is going to require more power to drive than the turbo, at altitude.

 

[Shortround6]

We have at least 2 variables that contribute to the difference in cruise speed vs the power used.
1. may be the efficiency of the respective propellers at cruise speed/altitude.
2. maybe a difference in exhaust thrust. However this may not be great. The P-47 gets darn little (I think?)
But the amount the F6F gets at cruise speeds may not be a lot either. At 36in and 2300rpm the engine is moving about 57% the amount of air it is at 54in and 2700rpm and since exhaust thrust is mass times velocity the fact that you are running lean means less fuel per pound of air.

F6F exhaust is better than than an early F4U but not as a good as a V-12

That middle pipe in the upper 3 may do pretty good but the top pipe doesn't look so good. The longer the pipe and the more/sharper bends the lower the exhaust gas velocity.
An engine running 54in of boost in the cylinders will have higher pressure/velocity gas leaving the exhaust ports than one running 36 in of boost.
Trying to compare a 1200hp V-12 running at 48in boost to a large radial loafing at 1200hp with 32-36in of boost may not be accurate.

 

[DarrenW]

Even with low MAP the auxiliary supercharger is going to require more power to drive than the turbo, at altitude.

Fair enough. What about throttle response, is "turbo lag" prevelant with aircraft engines as it is in cars? From what I've learned a supercharger has power on demand, does this ever give the supercharger an edge over a turbo in aircraft operations?