F4U vs F6F & Top-Speed: Let's Settle This

[Zipper730]

Please understand that there are many omissions to meet the 20k character limit

Yeah, I've run into that at times.

I think there seems no 'special tail wheel faring' for F4U-1 BuNo.17930

Basically, I was kind of referring to the modification of the rear that sort of blended the taller tailwheel into a tear-drop when retracted.

This image you posted earlier, but I'll use it for an example...

While this may/may not sound ignorant: I'm curious why they went to the whole trouble of redesigning the whole tailwheel? Was this related to visibility?

Removing the folding mechanism and tail hook, after halves of the doors were bolted closed and the cove for the tail hook was skinned over. the aircraft was to average an increased top speed of 4 mph . . . . Land-based configuration gives additional 4 mph actually for Corsair, there was no additional 6(or 8) mph.

What caused there to be such discrepancies between the drag-coefficient chart and the itemized chart that displayed methods to increase speed?

Looking at this image...

Was it possible to fair over any of these plates for an operational aircraft? As for the fairing over the wing-fold line, was this done on land-based aircraft?

In my view, for estimated +8 mph, smooth and faired cowling would have had a substantial impact.

Wait, they could have made improvements to the engine cowling?

I think Zipper 730's calculation is a good indication of why the early F4U-1's old 13'4" prop was losing efficiency at high altitude high speed range

Actually, even with the 13'1" blade -- it's still supersonic at the tips. It's just not quite as extreme 1.0699 vs 1.0791 within 200 feet of each other in altitude. That said, with the F6F's propeller you're going 6 miles an hour faster at the same altitude.

In conclusion, the F4U-1 BuNo.17930's 431 mph seems the best performance actually achievable with standard drag condition for standard production F4U-1 with 13'1" prop as Navy stated, even assuming the worst, can subtract up to 6.4 mph.

That would put you about 0.6 mph of 425 mph.

F6F-5 BuNo.58310 graph, the auto-lean curve showed faster than the auto rich at altitude, the vmax was about 8 mph faster, and the critical altitude increased about 400 ft

Critical altitude goes up because you have a lower fuel/air ratio, and it's closer to the stoichiometric ratio for gasoline combustion.

http://www.wwiiaircraftperformance.org/f4u/f4u-1-02334.pdf

In the F4U-1 BuNo.02334's report, standard F4U-1 expected 404 mph @ 25300' for military power and ACP showed 407 mph @ 24800' actually obtained for military power. this is a fairly close result and seems resonable for Navy's estimate.

If I read this right, the test involved a 13'0" propeller instead of the F4U-1's 13'4", or the F6F-3's 13'1" design. The gear ratio was also 0.4 instead of 0.5. So the ability to estimate performance to within 500 feet was pretty decent at the time?

To be honest, looking at this image: This seems to fit the F4U-1A/C/D's arrangement pretty good. I would have thought the bubble would have slowed the plane down a bit, not sped it up by 2 mph.

 

[Zipper730]

Testing was performed on both engines using different sized water jets and carburetor impact pressure settings with very good results being obtained (up to 65" Hg was deemed safe while using 130 octane fuel). . . . They used larger water jets and made adjustments to the supercharger fuel and water regulators which allowed for a higher flow rate to occur (hence more impact pressure), and this allowed for higher manifold pressures to be developed safely without detonation which in turn produced more power.

So this has to do with pressure carburetor set-up the ratio between impact and venturi pressures, or something of that sort?

Don't you just love talking Corsairs and Hellcats? It's probably one of my favorite past times, and I thank Zipper very much for creating this very interesting thread....

No problem, Darren

 

[DarrenW]

So this has to do with pressure carburetor set-up the ratio between impact and venturi pressures, or something of that sort?

I'm sorry, I really don't know much more about the water injection system than can be gleaned from pilot's manuals and test reports. I'm sure there is someone here that can help you with your questions better than I can. I actually would like to learn more about how the system works as well.....

 

[Dawncaster]

Basically, I was kind of referring to the modification of the rear that sort of blended the taller tailwheel into a tear-drop when retracted.

This image you posted earlier, but I'll use it for an example...

View attachment 576522

Good point.

In fact, I also considered that possibility, but the It should be visible at the ground, was not found in the included photo for F4U-1 BuNo.17930 report and others.

And I actually found a 'block' in the attached F4U-1 BuNo.17930's photo. I guessed with it the block mentioned in the report because the block was not found on the high tail wheel of the F4U-1s in service.

But it is possible that you are correct, as I wrote above, I also have made the same guess as you.

Because I have a photograph of it installed on F4U-1 BuNo.17930

In this case, I miscalculated what was called 'block' and the specificity of F4U-1 BuNo.17930 is further reduced.

When I saw the old guess again from you, I began to get confused again and began to feel as if my old guess was right. I mean, I think your guess is right.

I realized again that I knew too little about this beautiful aircraft.

While this may/may not sound ignorant: I'm curious why they went to the whole trouble of redesigning the whole tailwheel? Was this related to visibility?

If the performance was most considered, the smooth surface of the first batch F4U-1's tiny tailwheel unit and the slotless tailwheel door, would have been the best. It seems to me that continued improvements to the tailwheel section are related to improved landing capabilities. As noted in the old post, it affected performance but was slight, on the other hand, landing capabilities would have come as a greater issue for the F4U-1, which targets carrier operations.

What caused there to be such discrepancies between the drag-coefficient chart and the itemized chart that displayed methods to increase speed?

Charts from the Navy and NACA reports appear to be based on lift cofficient for level flight(about 0.2). But the other appears to have been zero lift drag coefficient chart. so instead of applying it as it is when I use it, I only made a relative comparison based on the data actually obtained from flight and calculation. In addition, NACA's drag coefficients were averaged figures, and even with similar commented drag reduction, there may be slight differences in actual work for drag reduction to F4U-1.

Looking at this image...

Was it possible to fair over any of these plates for an operational aircraft? As for the fairing over the wing-fold line, was this done on land-based aircraft?

According to Dana Bell, the wing fold seams were taped, puttied, and smoothed. As the attached photo shows, Some Corsairs even carried a "Wings Won't Fold" warning.

Wait, they could have made improvements to the engine cowling?

They did, with F4U-4 and other post war variants. but that's not what you're trying to say.

Air leakage creates drag, so if faired it and make smooth surface, the drag coefficient will decrease.

The above picture is F6F-3's cowling with a total of 6 cowling flaps, 3 on each side. for drag reduction, faired cowling-flaps and hinge line-gap-leakage gives 3 mph.

Assuming that the F4U-1 BuNo.02390 had 18 cowl flaps because there was no mention in the report that the fixed upper plate was installed, because there was more air leakage, it can be expected that making a smooth surface by fairing it is more likely to achieve more performance.

Actually, even with the 13'1" blade -- it's still supersonic at the tips. It's just not quite as extreme 1.0699 vs 1.0791 within 200 feet of each other in altitude. That said, with the F6F's propeller you're going 6 miles an hour faster at the same altitude.
View attachment 576539
View attachment 576540

Then perhaps a major change in design has affected it than tip speed. The old 13"4' propeller was called the narrow chord prop and the new 13"1' was called the paddle blade prop.

And I have a few points to make. The performance of the first batch birdcage F4U-1 with 395 mph Vmax and 348 mph at S.L, which you labeled 1944/7/28, was actually measured in 1943/1/28 and F4U-1D's detail specification was company estimated figures. too many differences and variables exist between the two samples - between actual first batch birdcage F4U-1 and company estimated F4U-1D. In order to know the performance achieved by the new propeller, except for the propeller, the same power, same airframe and same drag condition will be required.

I think I've already introduced samples that are 'standard' to compare the 13'4" propeller with the 13'1" propeller. F4U-1 ACP and F4U-1 BuNo.17930 with 'standard' drag conditions by the Navy and measured performance in similar period(1944/3/1 for ACP and 1944/3/4~1944/3/8 for F4U-1 BuNo.17930).

Cross-validation with ACP and F4U-1 BuNo.17930 well shows both the matching and difference of performance that should be between the 13'1" propeller and the 13'4" propeller under the same drag condition. It showed the characteristic of a 13'4" propeller losing efficiency in a high-altitude high-speed range above 16.5k ft, while at the same time the two F4U-1s show well matching performance(or showed a convincing similarity) at same drag conditions below 16.5k ft. according to this, If make a comparison at same altitude for military power as you did, the 13'1" propeller was abuot 8 mph faster at 25,000 feet.

In conclusion, the Navy succeeded in correct the F4U-1 BuNo.17930 to 'standard' drag condition for production F4U-1(F4U-1 ACP), and as a result of installing a new propeller, it seemed able to clearly identify the performance that could be achieved compared to the old propeller. I recommend using these for calculation because it's Navy corrected samples to military standard that well showed the performance difference caused by the replacement of the propeller for F4U-1 at same and standard condition.

If I read this right, the test involved a 13'0" propeller instead of the F4U-1's 13'4", or the F6F-3's 13'1" design. The gear ratio was also 0.4 instead of 0.5. So the ability to estimate performance to within 500 feet was pretty decent at the time?

F4U-1 BuNo.02334's four-bladed propeller would be closer to F4U-4's because it was also four-bladed propeller with 0.45 gear ratio. and the propeller's diameter seems affected not only by the propeller blade design, but also by other units. for example F4U-4's propeller diameter was 13'2" with 6501A-0 blades but F4U-1's propeller diameter was 13'1" with same 6501A-0 blades. And the report described F4U-1 BuNo.02334 that the new propeller(6501A-0) was installed 'instead' of the old propeller(6443A-21), the 'standard' F4U-1 mentioned in the report would have had an old propeller(6443A-21).

 

[DarrenW]

In conclusion, the Navy succeeded in correct the F4U-1 BuNo.17930 to 'standard' drag condition for production F4U-1(F4U-1 ACP), and as a result of installing a new propeller, it seemed able to clearly identify the performance that could be achieved compared to the old propeller. I recommend using these for calculation because it's Navy corrected samples to military standard that well showed the performance difference caused by the replacement of the propeller for F4U-1 at same and standard condition.

Hi Dawncaster,

I took one last look at what you had to say concerning rich vs. lean mixtures and the subsequent horsepower/speed produced and noticed that there was a 25 hp/9 mph difference between BuNo. 17930 & 50030 at 20,000 feet. They both had the more efficient F6F-3 propeller, taped shell ejector openings, and weighed exactly the same at 12,162 lbs. The only drag component that was different between the two was that BuNo. 50030 had tail and (quite possibly) catapult hooks installed:

F4U-1 BuNo. 17930

http://www.wwiiaircraftperformance.org/f4u/f4u-1-17930.pdf

F4U-1 BuNo. 50030

http://www.wwiiaircraftperformance.org/f4u/f4u-1-50030-final.pdf

After realizing that F6F-5 BuNo. 58310 was 8 mph faster while using a lean mixture rather than rich, I was curious what the horsepower difference was between the two settings as well, which turned out to be roughly 70 hp (1660 hp vs. 1590 hp). Being that the horsepower difference between the two F4U-1s was only 25 hp, I'm puzzled as to why a seemingly large 9 mph speed difference exists between them? Of course a portion of it can be attributed to the extra drag of the tail and catapult hooks, but according to your calculations this is at most only 3 mph. Do you believe 25 hp is enough to produce the extra 6 mph?

I'm not really sure myself, I'm just intrigued by the topic and want to exhaust all avenues before moving on to things less mentally exhausting.....

P.S. If we subtract the 2.4 mph for open shell ejector openings in the wings of BuNo. 50030 we get a maximum speed of 418.6 or about 419 mph. This seems very close to what is quoted in both the ACP and the Chance-Vought document concerning the F4U-1D.

 

[Dawncaster]

Hi Dawncaster,

I took one last look at what you had to say concerning rich vs. lean mixtures and the subsequent horsepower/speed produced and noticed that there was a 25 hp/9 mph difference between BuNo. 17930 & 50030 at 20,000 feet. They both had the more efficient F6F-3 propeller, taped shell ejector openings, and weighed exactly the same at 12,162 lbs. The only drag component that was different between the two was that BuNo. 50030 had tail and (quite possibly) catapult hooks installed:

F4U-1 BuNo. 17930
View attachment 576652
http://www.wwiiaircraftperformance.org/f4u/f4u-1-17930.pdf

F4U-1 BuNo. 50030
View attachment 576659View attachment 576660
http://www.wwiiaircraftperformance.org/f4u/f4u-1-50030-final.pdf

After realizing that F6F-5 BuNo. 58310 was 8 mph faster while using a lean mixture rather than rich, I was curious what the horsepower difference was between the two settings as well, which turned out to be roughly 70 hp (1660 hp vs. 1590 hp). Being that the horsepower difference between the two F4U-1s was only 25 hp, I'm puzzled as to why a seemingly large 9 mph speed difference exists between them? Of course a portion of it can be attributed to the extra drag of the tail and catapult hooks, but according to your calculations this is at most only 3 mph. Do you believe 25 hp is enough to produce the extra 6 mph?

I'm not really sure myself, I'm just intrigued by the topic and want to exhaust all avenues before moving on to things less mentally exhausting.....

P.S. If we subtract the 2.4 mph for open shell ejector openings in the wings of BuNo. 50030 we get a maximum speed of 418.6 or about 419 mph. This seems very close to what is quoted in both the ACP and the Chance-Vought document concerning the F4U-1D.

First of all, the paragraphs you quoted are for F4U-1 ACP and F4U-1 BuNo.17930, remember what I wrote in the paragraphs above it.

'I think I've already introduced samples that are 'standard' to compare the 13'4" propeller with the 13'1" propeller. F4U-1 ACP and F4U-1 BuNo.17930 with 'standard' drag conditions by the Navy and measured performance in similar period(1944/3/1 for ACP and 1944/3/4~1944/3/8 for F4U-1 BuNo.17930).'

'Cross-validation with ACP and F4U-1 BuNo.17930 well shows both the matching and difference of performance that should be between the 13'1" propeller and the 13'4" propeller under the same drag condition. It showed the characteristic of a 13'4" propeller losing efficiency in a high-altitude high-speed range above 16.5k ft, while at the same time the two F4U-1s show well matching performance(or showed a convincing similarity) at same drag conditions below 16.5k ft. according to this, If make a comparison at same altitude for military power as you did, the 13'1" propeller was abuot 8 mph faster at 25,000 feet.'

'In conclusion, the Navy succeeded in correct the F4U-1 BuNo.17930 to 'standard' drag condition for production F4U-1(F4U-1 ACP), and as a result of installing a new propeller, it seemed able to clearly identify the performance that could be achieved compared to the old propeller. I recommend using these for calculation because it's Navy corrected samples to military standard that well showed the performance difference caused by the replacement of the propeller for F4U-1 at same and standard condition.'

There seems to have been a lack of explanation for mentioning the 'similar period' and 'standard'.

F4U-1 ACP : 1944/3/1
F4U-1 BuNo.17930 : 1944/3/4 and 1944/3/8

Look at the date attached to their performances. the 'period' in which their performance was measured is virtually the same, In other words, the 'standard' for this period seems also virtually same for both F4U-1s. however, there was a gap with F4U-1 BuNo.50030 and I had already mentioned it in the my old post.

'Firstly, I really don't seem to be good at explaining, as you said, Mixture was a hypothesis to explain the actual power losses, but the important thing about it is that there has actually been a loss in power. I think it's because of the difference in operation restrictions.'

'This is part of the report for F4U-1 BuNo.50030, the report states that performance has been reduced to standard conditions in accordance with standard flight test methods. In the report of F4U-1 BuNo.17930, no similar content can be found and I speculated that 'standard' Flight Test Methods was the main factor that made a difference in performance. I think it is the same as operation restriction.'

'Perhaps the operation restrictions in early 1944, when the F4U-1 ACP and F4U-1 BuNo.17930 were tested, was lax compared to 1945 when F4U-1 BuNo.50030 or F4U-1D were tested. and seems that It's more accurate and practical operation restrictions were founded over time as operating hours increased and more data obtained.'

Of course, the 'reduced' performance would not have been as good as the first obtained. the mixture setting was just one of the hypotheses for explaining the actual power loss. because of the different period, there seems to be too many variables under different standard. In fact, F4U-1 BuNo.50030's report was referred the F4U-1 BuNo.17930's report PTR 2105. so under the Standard Flight Test Method at that time, the 'reduced' performance of the F4U-1 BuNo.17930 was may have been similar to F4U-1 BuNo.50030's and may not have been so special as to stated it.

 

[DarrenW]

First of all, the paragraphs you quoted are for F4U-1 ACP and F4U-1 BuNo.17930, remember what I wrote in the paragraphs above it.

'I think I've already introduced samples that are 'standard' to compare the 13'4" propeller with the 13'1" propeller. F4U-1 ACP and F4U-1 BuNo.17930 with 'standard' drag conditions by the Navy and measured performance in similar period(1944/3/1 for ACP and 1944/3/4~1944/3/8 for F4U-1 BuNo.17930).'

'Cross-validation with ACP and F4U-1 BuNo.17930 well shows both the matching and difference of performance that should be between the 13'1" propeller and the 13'4" propeller under the same drag condition. It showed the characteristic of a 13'4" propeller losing efficiency in a high-altitude high-speed range above 16.5k ft, while at the same time the two F4U-1s show well matching performance(or showed a convincing similarity) at same drag conditions below 16.5k ft. according to this, If make a comparison at same altitude for military power as you did, the 13'1" propeller was abuot 8 mph faster at 25,000 feet.'

'In conclusion, the Navy succeeded in correct the F4U-1 BuNo.17930 to 'standard' drag condition for production F4U-1(F4U-1 ACP), and as a result of installing a new propeller, it seemed able to clearly identify the performance that could be achieved compared to the old propeller. I recommend using these for calculation because it's Navy corrected samples to military standard that well showed the performance difference caused by the replacement of the propeller for F4U-1 at same and standard condition.'

There seems to have been a lack of explanation for mentioning the 'similar period' and 'standard'.

F4U-1 ACP : 1944/3/1
F4U-1 BuNo.17930 : 1944/3/4 and 1944/3/8

Look at the date attached to their performances. the 'period' in which their performance was measured is virtually the same, In other words, the 'standard' for this period seems also virtually same for both F4U-1s. however, there was a gap with F4U-1 BuNo.50030 and I had already mentioned it in the my old post.

'Firstly, I really don't seem to be good at explaining, as you said, Mixture was a hypothesis to explain the actual power losses, but the important thing about it is that there has actually been a loss in power. I think it's because of the difference in operation restrictions.'

'This is part of the report for F4U-1 BuNo.50030, the report states that performance has been reduced to standard conditions in accordance with standard flight test methods. In the report of F4U-1 BuNo.17930, no similar content can be found and I speculated that 'standard' Flight Test Methods was the main factor that made a difference in performance. I think it is the same as operation restriction.'

'Perhaps the operation restrictions in early 1944, when the F4U-1 ACP and F4U-1 BuNo.17930 were tested, was lax compared to 1945 when F4U-1 BuNo.50030 or F4U-1D were tested. and seems that It's more accurate and practical operation restrictions were founded over time as operating hours increased and more data obtained.'

Of course, the 'reduced' performance would not have been as good as the first obtained. the mixture setting was just one of the hypotheses for explaining the actual power loss. because of the different period, there seems to be too many variables under different standard. In fact, F4U-1 BuNo.50030's report was referred the F4U-1 BuNo.17930's report PTR 2105. so under the Standard Flight Test Method at that time, the 'reduced' performance of the F4U-1 BuNo.17930 was may have been similar to F4U-1 BuNo.50030's and may not have been so special as to stated it.

I remember reading all of this before but I believe that I finally understand what you were getting at. If F4U-1 BuNo. 17930 were tested in 1945 it wouldn't have reached a maximum speed of 431 mph, due to different operational guidelines which changed the testing methods employed. It most likely would have had a performance very similar to BuNo. 50030 (maybe a few miles per hour faster because it was configured for land use only). Things such as safety were probably the driving force behind the operational restrictions that were implemented after knowledge was gained over time about the aircraft's performance limitations.

Of course this is the case as well for the performance data found in the ACP dated 1 March 1944. It would also be reduced by roughly the same amount as F4U-1 BuNo. 17930.

 

[Dawncaster]

I remember reading all of this before but I believe that I finally understand what you were getting at. If F4U-1 BuNo. 17930 were tested in 1945 it wouldn't have reached a maximum speed of 431 mph, due to different operational guidelines which changed the testing methods employed. It most likely would have had a performance very similar to BuNo. 50030 (maybe a few miles per hour faster because it was configured for land use only). Things such as safety were probably the driving force behind the operational restrictions that were implemented after knowledge was gained over time about the aircraft's performance limitations.

Of course this is the case as well for the performance data found in the ACP dated 1 March 1944. It would also be reduced by roughly the same amount as F4U-1 BuNo. 17930.

I'm glad you understood my posts correctly, my hypotheses were to guess how it was done. my lack of explanation seems to have troubled you.

and That's why I've always considered Hellcat's actually achievable maximum speed to be over 400 mph(about 410 mph). for example, according to AHT,

' Jan. 44, A modified F6F-3, including some of the features to be included in the later F6F-5 version, is flown at a speed of 410 mph at 21000 feet altitude. '

In my view, this is similar to the case in F4U-1 BuNo.17930, It was conducted in early 1944, and improvements for late production model were applied to test plane. what's regrettable is that I don't have a detailed report on it.

 

[Zipper730]

In fact, I also considered that possibility, but the It should be visible at the ground, was not found in the included photo for F4U-1 BuNo.17930 report and others.

Just look at the image again... move your finger about an inch to the right the front part of the tear-drop blending is right there, it looks like it's under the wing, but it isn't -- it's under the tail, in front of the wheel...

If the performance was most considered, the smooth surface of the first batch F4U-1's tiny tailwheel unit and the slotless tailwheel door, would have been the best. It seems to me that continued improvements to the tailwheel section are related to improved landing capabilities. As noted in the old post, it affected performance but was slight, on the other hand, landing capabilities would have come as a greater issue for the F4U-1, which targets carrier operations.

Would it affect bounce or approach angle, based on attitude or visibility?

Charts from the Navy and NACA reports appear to be based on lift cofficient for level flight(about 0.2). But the other appears to have been zero lift drag coefficient chart. so instead of applying it as it is when I use it, I only made a relative comparison based on the data actually obtained from flight and calculation. In addition, NACA's drag coefficients were averaged figures, and even with similar commented drag reduction, there may be slight differences in actual work for drag reduction to F4U-1.

So the reason has to do with the fact that the coefficients are under different conditions? You calculated by the effect on the actual plane in flight.

According to Dana Bell, the wing fold seams were taped, puttied, and smoothed.

This would have only been on land-based aircraft, correct? Having wings that won't fold seem useless for carrier ops...

They did, with F4U-4 and other post war variants. but that's not what you're trying to say.

From what I remember, I was under the impression that a redesign to the cowling would have got more performance than the various other proposals for the F4U-1

Then perhaps a major change in design has affected it than tip speed. The old 13"4' propeller was called the narrow chord prop and the new 13"1' was called the paddle blade prop.

It would have a greater surface area per blade, which would move more air; additionally, you may/may not see a thickness/chord ratio that might be lower, which would favor high speed performance. The cross section of the blades might also differ in the two designs.

As for the dates made for performance, I'm not sure where I got the July 28 date from. Looking at the data I derived everything from, it seemed to be from October 31, 1944. The aircraft number matches up too. As for the performance of the F4U-1D figures being based on company estimates, that could be dubious.

I think I've already introduced samples that are 'standard' to compare the 13'4" propeller with the 13'1" propeller. F4U-1 ACP and F4U-1 BuNo.17930 with 'standard' drag conditions by the Navy and measured performance in similar period(1944/3/1 for ACP and 1944/3/4~1944/3/8 for F4U-1 BuNo.17930).

Much of the performance is the same at lower altitudes, with more at higher altitudes using the same manifold pressure settings, so it seems the propeller did the bulk of the work. I'm not sure if fairing over the top cowl-flap had any effect on speed.

F4U-1 BuNo.02334's four-bladed propeller would be closer to F4U-4's because it was also four-bladed propeller with 0.45 gear ratio. and the propeller's diameter seems affected not only by the propeller blade design, but also by other units. for example F4U-4's propeller diameter was 13'2" with 6501A-0 blades but F4U-1's propeller diameter was 13'1" with same 6501A-0 blades. And the report described F4U-1 BuNo.02334 that the new propeller(6501A-0) was installed 'instead' of the old propeller(6443A-21), the 'standard' F4U-1 mentioned in the report would have had an old propeller(6443A-21).

From what I recall, the F4U-1 had a gear-ratio of 0.5 not 0.45. That would improve the tip-speeds of the blades. That said, I was under the impression that the F4U-4 used a different blade design.

 

[DarrenW]

and That's why I've always considered Hellcat's actually achievable maximum speed to be over 400 mph(about 410 mph). for example, according to AHT,

' Jan. 44, A modified F6F-3, including some of the features to be included in the later F6F-5 version, is flown at a speed of 410 mph at 21000 feet altitude. '

In my view, this is similar to the case in F4U-1 BuNo.17930, It was conducted in early 1944, and improvements for late production model were applied to test plane. what's regrettable is that I don't have a detailed report on it.

I have read that about the F6F-3 too and that's a very good comparison. It would fall in line with the average speed advantage the Corsair held over the Hellcat throughout much of the war. I will have to be more careful in the future concerning test report dates and possible changes to the methods employed during testing. Thanks for bringing all of this to light.....

 

[DarrenW]

As for the performance of the F4U-1D figures being based on company estimates, that could be dubious.

Yes that can be an issue sometimes, but thankfully Vought acknowledges a maximum speed that is pretty much identical to what we see in the ACP for the F4U-1D.

 

[DarrenW]

Although the 13' 1" propeller became the preferred option, the original 13' 4" variety was still an acceptable substitute. This tells me that it's performance was considered reasonable and enough for the job at hand. This was probably because a large portion of the fighting in the PTO took place at low and medium altitudes, so there wouldn't be a lot to choose from between the two types anyway in a practical sense.

AN 01-45HA-1 (1 June 1944)

AN 01-45HA-1 (15 March 1945)

 

[DarrenW]

I'm not sure if fairing over the top cowl-flap had any effect on speed.

Not challenging you on this, but how did you draw this conclusion?

 

[Dawncaster]

Just look at the image again... move your finger about an inch to the right the front part of the tear-drop blending is right there, it looks like it's under the wing, but it isn't -- it's under the tail, in front of the wheel...
design.

I'm sorry, but could you explain it with photo?

Would it affect bounce or approach angle, based on attitude or visibility?

It would have affected at ground runs, not only AOA and visibility but also take-off distance and take-off speed.

And the bounce problems have been solved by improvements in oleo.

So the reason has to do with the fact that the coefficients are under different conditions? You calculated by the effect on the actual plane in flight.

It remains unchanged because it's figure actually obtained from flight tests. I was talking about the zero lift drag coeiffcient chart used to make relative comparisons in the process because I had to divide it up for explanation. It had different lift condition compared to the drag coefficients of NACA charts based on level-flight.

This would have only been on land-based aircraft, correct? Having wings that won't fold seem useless for carrier ops...

I'm pretty sure. because it can take off from carriers barly, but cannot land.

From what I remember, I was under the impression that a redesign to the cowling would have got more performance than the various other proposals for the F4U-1

However, the cowling of the F4U-1 was not redesigned during the service....

As for the dates made for performance, I'm not sure where I got the July 28 date from. Looking at the data I derived everything from, it seemed to be from October 31, 1944. The aircraft number matches up too.

Performance curve what I mentioned was this.

I'm not sure if fairing over the top cowl-flap had any effect on speed.

Even if it's only few of the total cowl flaps, I guess it would slight affect to performance because it provides more air leakage. although it's expected to almost flushed at Vmax due to the overload relief system.

But for comparison, I think you don't have to so consider the speed difference caused by it. as the actual obtained results showed, the Navy had correct the drag condition to standard.

In fact, It was a improvement to get rid of oil leakage, not air leakage. after installed it, pilots won't have to learn to look for rain clouds to give their windscreens a quick wash.

From what I recall, the F4U-1 had a gear-ratio of 0.5 not 0.45. That would improve the tip-speeds of the blades. That said, I was under the impression that the F4U-4 used a different blade design.

F4U-1 BuNo.02334 had 0.4 gear ratio four blade 13'0" dia propeller with blade design 6501A-0, compared to standard 0.5 gear ratio three blade 13'4" dia propller with blade design 6443A-21, I felt it was more similar to F4U-4.

 

[Dawncaster]

I have read that about the F6F-3 too and that's a very good comparison. It would fall in line with the average speed advantage the Corsair held over the Hellcat throughout much of the war. I will have to be more careful in the future concerning test report dates and possible changes to the methods employed during testing. Thanks for bringing all of this to light.....

You're welcome. I also want to thank you. despite the lack of explanation following the flow of my esoteric consciousness, pointed out what I was trying to say.

We share the experiences of two great fighters suffering from biases.

Although the 13' 1" propeller became the preferred option, the original 13' 4" variety was still an acceptable substitute. This tells me that it's performance was considered reasonable and enough for the job at hand. This was probably because a large portion of the fighting in the PTO took place at low and medium altitudes, so there wouldn't be a lot to choose from between the two types anyway in a practical sense.

AN 01-45HA-1 (1 June 1944)
View attachment 576747


AN 01-45HA-1 (15 March 1945)
View attachment 576749

Good point, Agreed. It is convincing considering the situation that from the end of the Rabaul campaign to the arrival of the F4U-1D, the F4U-1 was mostly used for ground attacks.

 

[DarrenW]

We share the experiences of two great fighters suffering from biases.

Yes, but luckily we're both here to help set the record straight....

 

[Dawncaster]

Yes, but luckily we're both here to help set the record straight....

OH No, I forgot to put 'can' between 'We' and 'share'.

 

[DarrenW]

OH No, I forgot to put 'can' between 'We' and 'share'.

I understood exactly what you meant....

 

[Zipper730]

I'm sorry, I really don't know much more about the water injection system than can be gleaned from pilot's manuals and test reports. I'm sure there is someone here that can help you with your questions better than I can. I actually would like to learn more about how the system works as well.....

Off the bat, I figure S Shortround6 and W wuzak might be able to better explain the matter -- wuzak might be the forum's authority on engines.

Not challenging you on this, but how did you draw this conclusion?

It had to do with the basics of cowl design (and there might be errors here, so bear with me -- I'm used to being the village idiot when it comes to propeller driven aircraft).

1. Propeller: Since almost all aircraft were tractor props, the propeller would be in front of the cowling. The propeller accelerates the airflow and increases the pressure of the flow.
2. Cowl-Lip: The cowl is divergent in shape, which slows down the airflow going through the cowling: This effectively provides more pressure and more air in a given area to absorb the heat from the engine. Provided the velocity is slowed down and builds up pressure, yet remains fast enough to carry away the heat, you have a design that seems workable. While increasing pressure does produce heat, it's not particularly massive (this becomes more significant when supersonic), and the air outside is very cold, and the air temperature isn't that high.
3. Air-Cooled Engine: Air flows from the cowl-lip to the engine, and is heated up substantially by the engine. This causes the air to absorb the heat, and bringing down the engine temperature. It also causes the air to heat up, and expand. Provided the expansion goes more rearwards than forwards, you have a degree of "thrust" that is produced (unfortunately, it almost never equals the amount of drag, but it will negate some of the drag produced by the assembly).
4. Aft Cowl / Cowl-Flaps: I'm not sure the exact term but it's basically the shape of the cowl/fuselage behind the engine, which form a convergent shape. Theoretically you want to make the shape quite convergent as it accelerates the airflow the most, but pressure plays a role in imposing limits on this. The pressure gets too low, and you'll see the air dam up, so you'll have cowl-flaps to allow extra area for the air to escape. This arrangement reminds me a bit of the nozzles on jet-fighters, which are fully open at idle to allow the airflow plenty of area to escape; as the engine spools up, the exhaust pressure goes up, and the nozzle can be narrowed down, and produce a faster exhaust velocity. When 100% power is produced, the nozzles are narrowed in as much as possible. This set-up seems the same on cowling flaps.

Some aircraft have tighter cowlings than other aircraft, being barely big enough to encompass the engine they're built around; a more prominent bell-mouthed shape, a fatter spinner, and a narrower aft-cowling, and so on. These are generally aimed at reducing cooling drag, though they have a tendency to reduce cooling. I figure, if the top-cowling flap was faired over by a metal-plate, then the airflow would have to escape out the other flaps, or the cowling would simply be "tighter" in the back.

I'm sorry, but could you explain it with photo?

Sure...

I encircled the area in a brighter shade of red than the area you encircled, and connected them together. The front area is the front of the tear-drop.

It would have affected at ground runs, not only AOA and visibility but also take-off distance and take-off speed.

The higher tail-wheel seems to increase takeoff run in either carrier deck operations, and also raises takeoff speed. The only benefit I can see is visibility.

And the bounce problems have been solved by improvements in oleo.

So, the tail wheel had no effect on this matter?

I'm pretty sure. because it can take off from carriers barly, but cannot land.

Makes sense

However, the cowling of the F4U-1 was not redesigned during the service....

The cowling configuration question was a hypothetical...

Performance curve what I mentioned was this.

I didn't even notice that... that's normally something I would immediately spot.

Even if it's only few of the total cowl flaps, I guess it would slight affect to performance because it provides more air leakage. although it's expected to almost flushed at Vmax due to the overload relief system.

I would figure the top cowl-flap being covered over would reduce air-leakage, since the flap is closed? Also, what's the overload relief system?

In fact, It was a improvement to get rid of oil leakage

That, I already know. And I'd agree with it on that.

As for your graph on the F4U-4, I was under the impression that, up to this point, that the propeller was 13'4" instead of 13'2". You learn something new everyday. As for the gear ratio being reduced from 0.5 to 0.45, is definitely smart.

While the tip-speed is still quite high, it only goes supersonic at critical altitude in WEP and Military power settings, despite being considerably faster...

 

[Graeme]

Sure...
I encircled the area in a brighter shade of red than the area you encircled, and connected them together. The front area is the front of the tear-drop.

I'm pretty sure your "front of the tear-drop" circle is part of the wing. Imagine the wheel retracted - it's nowhere near the front of the wheel....