F6F Vs. F4U

[F4UDOA]

FYI,





Two things about this report.

1. Why is the F6F-5 so fast at sea level? It did not use rammed air in neutral blower as did the F4U so why is it just 7MPH slower. Even Corkey Meyer admits to a 25knots disadvantage at this alt. Is this another F6F CAS problem?

2. If the F6F-5 climb 600FPM slower than the F4U-1D then why does it climb almost 500FPM better at the same altitude in AH?

[Shuckins]

I've seen data published by Francis Dean and a couple of other sources which indicate that when Hellcat and Corsair have the same engine, propeller, and operational weights their rates of climb are nearly equal.

The Corsair possessed a speed and climb advantage at lower levels because the main stage blower and carburetor got ram air directly from the forward wing duct.  The Hellcat got its carburetor air directly from the accessory compartment of the fuselage, just behind the engine, with no ram effect, yielding the same effect as it would if the aircraft were motionless on the ground.  The Corsair's was getting carburetor air supercharged by the speed of the airplane.  In both aircraft the design was similar in that they provided ram air to the low and high blower stages.

In the Hellcat, the warmer air coming from the accessory compartment prevented inadvertent carburetor icing engine failure.  Grumman Wildcats had ram air in the main stage just like the Corsair, and many were lost because pilots failed to take precautions to prevent it.

At medium and higher altitudes both Hellcat and Corsair benefitted from ram-air, so the performance gap narrowed significantly.

Comparing top speeds posted by different sources or manufacturers is problematic.  No two test at exactly the same fuel capacity, operational loads, etc. Dean's climb data showed the F4U-1D holding a distinct advantage in climb...but at 400 lbs. less test weight than did the F6F-5.  Weight effects rate of climb more so than it does top speed.

By way of example, let's say a theoretical fighter has a top speed of 400mph.  Add 500 pounds to it's operational weight and top speed drops to 394 mph....but climb rate, which had been 3500 fpm at sea level, drops by 500 fpm.  Top speed is affected by about 2%, while climb rate drops by more than 14%.

[Widewing]

Originally posted by F4UDOA

Two things about this report.

1. Why is the F6F-5 so fast at sea level? It did not use rammed air in neutral blower as did the F4U so why is it just 7MPH slower. Even Corkey Meyer admits to a 25knots disadvantage at this alt. Is this another F6F CAS problem?

2. If the F6F-5 climb 600FPM slower than the F4U-1D then why does it climb almost 500FPM better at the same altitude in AH?

Well, assuming the F6F-5 was faster than it is supposed to be is probably not the likely answer. Perhaps this particular F4U-1D was a dog. I've seen the test data for the Zero used and it was exceptionally slow at sea level. Even the bog-slow FM-2 was 6 mph faster than the Zero....

Indeed, if you look at the Zero's speed chart in the document, it could manage only 291 mph at sea level. 291+41 is 332 mph...right where it's supposed to be for the F6F-5.

If we look at Grumman's speed data for the F6F-5, we see that the TAIC test produced speeds 17 mph slower than Grumman claimed (348 mph). Navy data for the F6F-5 shows 319 mph at 12,740 lb. The TAIC F6F weighed 12,285 at take off, and was surely lighter during the speed runs.

So, the TAIC sea level speed falls to the slow side of the middle, exactly what one would expect for this plane at this weight (12 mph faster than the Navy data for a much heavier F6F and 17 mph slower than factory data for a slightly heavier Hellcat than that used by TAIC).

On the other hand, the F4U-1D is markedly slower than we would expect @ 339 mph. However, that isn't inconsistent with a plane burdened by the drag associated with rocket tabs and bomb mounts.

Maybe the F6F was fitted for the centerline tank only. Also, the F6F was carrying 120 lb more fuel than the F4U, but 30 lb less oil.

We also do not know the state of tune for each aircraft, nor do we know the overall condition of each. Poor cowling and panel fit can eat up considerable speed.

Whatever the cause, the test doesn't show that the F6F is unually fast, but it does show that the particular F4U was slower than one would expect. Since we don't have specifics on configurations, all we can do is view the data at face value.

My regards,

Widewing

[Widewing]

Oh yeah, I forgot to mention one thing...

In AH2, the A6M5 does 289 mph at sea level, with the F6F-5 able to attain 330 mph... The difference is 41 mph, exactly the same as in the TAIC test.

My regards,

Widewing

[F4UDOA]

Widewing,

The A6M5 listed in the TAIC chart is from the Army test and may not even be the same airplane. The AAF test says their airplane was damaged (the landing gears doors would not close)and indeed the max speed reached on the Army test was 325MPH where as in the Navy test the max speed reached was 335MPH.

So we know that at least at 20K the Navy A6M5 was a full 10MPH faster than the Army test bird. So if you add 10MPH to the speed of the A6M5 at sea level the F4U sea level speed is 348MPH which is roughly the listed speed with rocket rails and pylons.

However the peice that is the most curious is the 5,000FT speed of the F6F-5. It goes from being 41MPH faster at sea level to only 25MPH faster at 5K, why?? The F6F does not use rammed air at low alt in Neutral blower stage so why the large drop in performance? The F4U has a 42MPH adavatage at 5K but the slight drop is to be expected because of a linear increase in performance in the A6M5 and the dip in speed caused by the F4U blower shift and then increasing into low blower.

What could cause the F6F-5 to have a performance spike at sea level but not at 5K?

The weights of the two aircraft are actually more equal than they normally would be. The F6F-5 at a full load would weight at least 300LBS more than the F4U-1D. It was 200lbs heavier empty and carried 13 gallons more fuel internally.

Shuckins,

The only problem with the same engine, same prop, Ram air theory is that it didn't hold up in post war flight test of both A/C or range calcualtions for both a/c. Check the Flight manuals for both aircraft and their speeds at the same cruise settings. The speed differences are vast and these were Navy range test.


For instance both A/C with 150 gallon DT's at 25,000FT 350 gallons of fuel.

F6F-5 Flight operation instruction chart Column II
2300RPM 36"MAP 106GPH 283MPH TAS 935 Statute miles

F4U-1D Flight operating chart Column III
2200RPM 37"MAP 126GPH 341MPH TAS 970 Statute miles

So the F6F has a better fuel consumption but the F4U cruises at 58MPH faster at a comparable fuel setting at 25,000FT and it fly's farther!! I guess Corky Meyer theory about the F6F being as fast as the F4U a the same power settings needs a little work unless his maps and airspeed indicator are out of calibration.

FYI Just to equilize the fuel consumption here is column IV for the F4U

2100RPM 34"MAP 96GPH 316MPH TAS gives a range of 1170 Statute miles.

[F4UDOA]

One more thing,

I was looking at the FM-2 comparison with the Navy A6M5. The FM-2 is listed as being 12MPH slower than the Zero at 10K and 8MPH slower at 15K. This is important because the top speed reached by the FM-2 in the test is 321MPH at 13K. So we know that the Zero was between 12MPH and 8MPH faster than the FM-2 at 13,000FT. So 10MPH faster sounds about right?

That is 331MPH at 13K which is already 5MPH faster than the AAF test A/C. But from that you can also tell that the F4U (70MPH faster at 15K)was crossing 400MPH at 15K in low blower and the F6F would have been at approx 390MPH at 15K (62MPH faster).

The F4U speed is accurate as can be expected but the F6F doing 390MPH at 15K? That is higher than the listed top speed of the A/C. Is this another IAS/CAS error?

[Shuckins]

Widewing and F4UDOA,

The TAIC test aircraft undoubtedly reflects a fairly accurate picture of top speed, free to a great extent of the type of bias or cooking-of-the-books often found in the manufacturer's performance data.

Most of the pictures I've seen of F6F-5s show them equipped with the same rocket-rails that equipped the Corsair.  The eights sets of these rails reduced the top speed of the F4U-1D by 13 mph, according to data that F4UDOA posted in his Nav-Air thread on the Corsair.  It would be fair to say that the rails on the Hellcat, although two fewer in number, had a commensurate affect on that aircraft's top speed.

It would be helpful to know what the TAIC test Hellcat was equipped with.  If that aircraft was armed with those rails, then the Hellcat's top speed would have been somewhere between five and ten mph faster than the 409 mph quoted in the test data.  On the other hand, if that aircraft was NOT equipped with the rocket rails, then their installation would have reduced the -5s top speed to near 400 mph.

These are the problems that make it so hard for enthusiasts to come to any kind of consensus of opinion on the actual speeds of these aircraft relative to each other.

[bkbandit]

THe one thing that takes me out of the f4u is its accel, its a freakin bus, if i get out and push the thing ill accel better. F6F isnt a super fast accel plane either but it out does the f4u and u arent dead in the water with low in in a F6F. In every single documentary(every pacific war doc and also docs that talked to the actually men that flew f4u) all say that f4u got well above 400mph, i have only got the f4u1 and the f4u4 to that speed(of course i went took a shower and came back well i was waiting), shouldnt the d model do it too. It has rocket rails and pylons but so does mustang. F4U with 2000 horsepower and that big prop cant really accel that dam slow, its not a small plane but the 51 isnt small either and she accels way better, im not excepting a drag machine but it sure aint a dump truck.

[Bronk]

http://gonzoville.com/ahcharts/index.php

F4U-x vs P51-d in AH


Bronk

[F4UDOA]

bkbandit,

I am really surprised the F4U-1D accerates so bad in AH2 these days. I have been out of the game for a while so I am not flying regularly. I do have the latest version so I will do some accereration test. The last time I check the two aircraft were at a virtual deadheat in acceleration.

As far as the actual top speeds I have test done from as late as mid-1945 and later on the F4U and F6F done by the Navy I will try to get scanned and posted.

[bozon]

Originally posted by bkbandit
THe one thing that takes me out of the f4u is its accel, its a freakin bus, if i get out and push the thing ill accel better. F6F isnt a super fast accel plane either but it out does the f4u and u arent dead in the water with low in in a F6F.

I would not make such statements without checking first. I doubt the F6F out-accelerate the F4uD, especially on the deck. Also since F6F top speed is slower, the advantage will go to the F4U the higher the speed.

The similarity in preformance is not suprising. The F6F, F4U and P47 were 3 different implementations of the same technology designed in the same era under the same philosophy. It not like the engineers of one company were far more brilliant that those of the other. Each had its own fine tuning and tradeoffs but none had a definit overall advantage over the other. The F6F and F4U were also built to answer the same navy requirements which explains the very similar performance. The major difference were narrowed down to production methods and technical stuff unrelated to aircraft preformance.

Bozon

[bkbandit]

bozon i fly nothing but us navy fighters(with maybe 1/3 of my time going to the p51b D and p47d for the attack runs).  Alot of time has been spent in f6f and f4u. F4U is faster but takes too long to get there. By the time u start feelin that speed ur likely to be forced into an evasive move bleeding e and leting the con catch up, i have seen it too many times, and in the t/a the other day i figured what the hell like me see how good this f6f could turn, i went up against a f4u1(the better turner out fof the bunch) and evenutaully came around on him, this isnt supposed to happen f4u should have been able to pull around and get me. If this was the case i doubt the f4u would have been such a lengedary fighter, i have seen alot and read alot about corsair and it is supposed to do everything the hellcat can do better. That in mind hellcat was no push over and it earns its right as being called a killer and a dependable machine but theres a reason that f4u stood in service till korea and f6f didnt. Some real life data on f4u accel would be cool.

0 f4u
1 f6f

[Saxman]

Were flaps involved in the fight?

[Shuckins]

bk,

It's a mistake to think the Corsair did everything better than the Hellcat.  Each was a superbly designed aircraft in its own right.  The Japanese called them the "Terrible Twins."

Indeed, being designed to meet the same Navy specifications and requirements, the similarities between the two are startling. Range, firepower, strike load, durability, and climb rate were well nigh identical.  The Corsair possessed a greater top speed and roll rate, but the Hellcat had its own set of superior assets as well.

The Hellcat's carrier operation capabilities were, according to Hamilton McWhorter and many other Navy pilots, far superior to those of the Corsair.  Visibility over the nose was superior to almost any U.S. fighter extant, with the possible exception of the P-38.  The Hellcat also possessed better all round visibility.  The cowling of the nose dropped away from the cockpit with an 8 degree downward angle, enhancing tracking of targets and offering superior visibility during carrier landings.

In comparisons with other U.S. fighters of the time, service pilots rated the Hellcat's ailerons the best at speeds around 100 knots.  Attitude and longitudinal control in the landing circuit were superb, just what the Navy desired in a carrier-based fighter.

The Hellcat also possessed some of the bast stall characteristics, and one of lowest stall speeds of any fighter of the war.  In addition, handling characteristics were extremely honest and predictable.  As one pilot stated, a pilot could make abrupt and positive maneuvers, even at high speed.

Francis Dean compared the turning rates of U.S. fighters in his book "America's Hundred Thousand."  Using the turning circle of the Wildcat as his baseline figure, and without the use of flaps, the Hellcat's turning circle was rated at 138% of the Wildcat's, while the F4U-1D was rated at 212% .  While use of the Corsair's flaps may have closed the gap somewhat, it had a lot of ground to make up, and once locked into a turning fight with speeds equal and both fighters having their flaps deployed, it is doubtful that the Corsair would have outturned the Hellcat.

Lastly, the Hellcat possessed a slight speed advantage over the Corsair in a dive:  449mph IAS for the Hellcat versus 443mph IAS for the Corsair.

Regards, Shuckins

[Mathman]

In a 1v1 situation in AH, I haven't had any real problems killing the F4U while flying the F6F.

I should add that this is/was typically the case in all four of the distinct versions of the Hellcat in AH (the pre 1.08 FM, the post 1.08 FM, AHII FM, and the current one).