Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: F4UDOA on September 24, 2002, 09:13:39 PM
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Heya's,
After years(no toejam, years) of trying to figure out why the F4U-1 series doesn't seem to climb as well in the charts as one would expect when hearing of such bold statements like outclimbing Zero's, F6F, P-51B and FW190(below 160MPH)I finally put reason to this riddle with a little help from our friends at the British Air Ministry.
I'll start with this chart showing F4U-1 climb focusing on Military power which equals 52.5" of MAP . Keeping in mind that the F4U and the F6F used the same engine P&W R2800-8/10(W designates the use of water injection after the 8/10). And that these engines use Mechanical 2 stage superchargers. Which incorperate three Blower stages
1. Main or Neutral.
2. Low Aux Blower.
3. High Aux Blower.
Here is the climb chart for our F4U-1 (non paddle prop) focusing on the Mil power climb. I'm a novice at labeling so stay with me.
(http://mywebpages.comcast.net/markw4/chrt1.jpg)
I labled the Blower shift points as Manifold pressure dropped they shifted gears(blower stages) to increase MAP and HP.
1. Neutral blower to 5K
2. Low Blower to 18.5K
3. High Blower 18.5K and higher
Now I shift to the British Evaluation of the F6F-5 again focusing on MIL power.
PDF format
http://mywebpages.comcast.net/markw4/Hellcat14.pdf
Looking at the Mil power climb rate at 2K 2460FPM is nothing spectacular but notice there is no drop off climb rate or MAP up to 15K in Mil power. Seem strange?
Well the reason is this
1. The whole test was in low blower stage which kept MAP at 52.5" the whole way up to 15K.
2. Notice the * indicating full throttle speed. The throttle was retarded the whole way up until 11,200FT. Only then was it full throttle to prevent over boost at lower alts.
Now look at the same test on the F4U MKII(No water) in Mil power. The climb matches our lowly F4U-1 in Mil power.
PDF format
http://mywebpages.comcast.net/markw4/MKIICRT.pdf
Also this note about the Low blower during the test
PDF format
http://mywebpages.comcast.net/markw4/peice.pdf
In this test they did not use the Low blower until they reached 8,000FT even though they reached full throttle at 800FT.
1. At the same Manifold pressure an early F4U-1 out climbs the F6F-5 at Mil power even without a paddle prop.
2. The F4U as well as the F6F have manual engine controls for super charging and could be used to increase MAP and even overboost for short periods at the pilots doing.
3. As shown by the F6F chart the current climb charts we use are not the MAX climb of the F4U as they do not use max possible MAP of 52.5 inches for most of the climb. This is where the AH model has a flaw. While the manifold pressure may read 52 inches most likely the performance reflects a much lower setting. Some indication of Supercharger stage should be displayed in the cockpit or manually available for the pilot in certain A/C.
In any case it is aparent that it is possible to control max performance by shifting into a higher gear and applying throttle. And that all A/C with these types of engine controls are capable of various levels of performance that may not be documented
very clearly.
In any case unless HTC changes its current engine model we will probably never see full power out of many A/C.
I hope I did a halfway decent job of expaning that.
Any thoughts??
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Sssooo.. if I read this correctly, the P-38 is slower than it should be? ;) :D :D :D :D :D :D
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Originally posted by Tac
Sssooo.. if I read this correctly, the P-38 is slower than it should be? ;) :D :D :D :D :D :D
yes, but it also shows the p-38's tail being weaker than indicated.
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Waiting for Glasses to deny this:)
Dog out..........
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EXCELLENT work DOA, I am eagerly awaiting Pyro or Hitech to read this thread.
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I could be wrong - but won't all the planes in AH with multi-stage superchargers suffer from this?
The power curves we see tend to show the supercharger stages kicking in at full throttle height because those were the automatic change points (for the obvious reason that, if they changed any lower and you were at full throttle already, the engine would be overboosted and could blow up).
Any of the planes which had manually selected blower stages could change gear lower down and moderate the MAP using the throttle instead. Why the testing authorities generally didn't use this methodology... I don't know.
(edit) re-read the original post and my point was already made by F4UDOA. Sorry mate, I'll leave this up just to reinforce it.
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I think it simply means that the various options for "plane management", which in real life could be utilized to enhance the performance of a plane, is not available in AH.
It'd be certainly interesting to see what would happen if management issues such as mixture control or supercharger gears were depicted in AH. I think we'd appreciate the Kommandogerat a lot more then. :)
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I'm not sure if this is even a topic for Pyro. In the current FM there is no consideration for engine management. In my mind after seeing this I thing it should be like auto trim. You can manage your engine manually or have AH do it. Fuel mixture is another animal.
However I think the F4U, F6F and others (I have heard the FW190A8 may have had manual control) are at a large disadavantage because they reach the best performance at many altitudes.
Also I would appreciate a binary response of 1 or 0 from HT just to let me know if he read the post or not.
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You are a dedicated man. Good work digging up that answer.
Charon
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Originally posted by Bombjack
Any of the planes which had manually selected blower stages could change gear lower down and moderate the MAP using the throttle instead. Why the testing authorities generally didn't use this methodology... I don't know.
They didn't do this because higher supercharger gear robs the engine of some of it's power, so you need a higher manifold pressure for a given power and fuel consumption is worse.
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Wells,
Glad you range in.
It seems that maintaining the 52" of MAP was the most important factor in these test.
If staying in low blower at lower alt is not an advantage then why did the F6F maintain an Identical Climb rate/MAP the whole way up in low blower?
F6F climb (http://mywebpages.comcast.net/markw4/Hellcat14.pdf)
This is the same engine as the F4U(I know you know that).
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Hi F4UDOA,
>1. The whole test was in low blower stage which kept MAP at 52.5" the whole way up to 15K.
I'm afraid you're victim of a slight misunderstanding here. Constant manifold pressure does not mean constant power output. Even partially closing the throttle to keep the manifold pressure decreases the volumetric efficiency of the engine and results in a reduced power output.
According to the USN data sheet from:
http://www.history.navy.mil/branches/hist-ac/fighter.htm
the F6F-5 has a drop in climb rate in military power in aux. low gear - unlike what is indicated in the British document (which I think has to be viewed with some caution).
Here's the power drop with altitude for the F6F-5's R-2800-10W in MIL power (from the USN standard aircraft characteristic sheet):
2000 HP @ 1000 ft
1800 HP @ 15500 ft
1650 HP @ 22500 ft.
This is close to, but not quite exactly identical to the F4U-1's R-2800-8W data from the respective data sheet:
2000 HP @ 0 - 1700 ft
1755 HP @ 5400 ft
1800 HP @ 15700 ft
1640 HP @ 18100 ft
1650 HP @ 21000 ft
With regard to the supercharger gear change altitudes, the British F4U climb data you provided indicates quite clearly:
"For optimum climb performance the supercharger gear should be changed as follows: -
Main to Aux.low when the manifold pressure has fallen to 45 ins.Hg.
Aus. low to Aux.high when the manifold pressure has fallen to 45 1/2 ins.Hg."
If you reference these points with the climb table, you see that the critical manifold pressures are reached at 5000 ft and at 18500 ft. These gear change altitudes are nicely repeated in the American chart (the graph you highlighted in red).
>In this test they did not use the Low blower until they reached 8,000FT even though they reached full throttle at 800FT.
As pointed out above, they changed gears at 5000 ft, not at 8000 ft.
>1. At the same Manifold pressure an early F4U-1 out climbs the F6F-5 at Mil power even without a paddle prop.
Actually, it does only appear so in comparison to the British table for low altitude where the F4U-1 is flying on main supercharger ("neutral") while the F6F-5 is using the aux. low supercharger for the test. As you can see from the USN sheet, if the F6F-5 is allowed to choose the supercharger gear optimally, too, it beats the F4U-1 with 2850 fpm versus 2550 fpm.
>In any case it is aparent that it is possible to control max performance by shifting into a higher gear and applying throttle.
Actually, maximum performance is achieved by shifting into the correct gear. Applying throttle means that you adopt a different power setting beyond military power, which would have to be considered running at emergency power. Both the F4U-1 and the F6F-5 have this possiblity, so I'm not sure what your point might be?
>In any case unless HTC changes its current engine model we will probably never see full power out of many A/C.
I'm not quite convinced that I understand what you're aiming at, but analysing the data you posted, it's not my impression that the F4U-1 climb performance should be any different from that indicated in the USN sheet, or that it should be able to outclimb the F6F-5. The official AH F4U-1 climb performance picture seems to match the USN data sheet with a certain degree of precision as well.
Regards,
Henning (HoHun)
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"Full throttle height" does not mean that you run with less boost, or less throttle, below this height. It is the same as "critical altitude" i think, where the supercharger or turbo isnīt capable anymore to keep up desired boost.
The origin of this expression is in WWI, where they designed engines with "Überverdichtung" and "Überbemessung" (over-compressed, over-dimensioned). They had no supercharger back then, so they designed compression and dimensions in a way that the pilot wasnīt allowed to use full boost at lower altitudes. Only from a certain altitude on, the "full throttle height", the pilot was allowed to push the throttle full forward. Atmosphere density drops very quickly, and so does engine power drops without charger.
Typical full throttle height in WW1 was 2-3km. This was a huge improvment of altitude performance in WW1, but i donīt think that itīs the correct term for a WW2 engine with supercharger and boost limiter. Because you control the boost with the throttle, you canīt say the throttle was retarded.
Youīre correct that the whole F6F test was done in low blower. But that means that the F6F could have climbed a bit better in neutral blower stage at sealevel. Actually the 2450ft/min for the F6F goes along with the 9-page PDF you can find in the net, where a navy chart lists the climbrate of the F6F-5 at sealevel with 2850ft/min in neutral, and 2500ft/min in low blower position (5k)
The same pdf lists the wep-climb performance of the F6F-5 with 2950ft/min. The RAF lists 3150ft/min. Ah lists 3500ft/min
So maybe the AH-F4U doesnīt climb too bad, but the AH-F6F too good?
niklas
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Typical full throttle height in WW1 was 2-3km. This was a huge improvment of altitude performance in WW1, but i donīt think that itīs the correct term for a WW2 engine with supercharger and boost limiter. Because you control the boost with the throttle, you canīt say the throttle was retarded.
Most British supercharged engines had automatic boost control, so the pilot put the throttle to full, but the ABC kept it below full throttle to avoid overboosting the engine. FTH meant the altitude at which the throttle would really be fully open, not retarded by the ABC.
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HoHun,
You said
>I'm afraid you're victim of a slight misunderstanding here. Constant manifold pressure does not mean constant power output. Even partially closing the throttle to keep the manifold pressure decreases the volumetric efficiency of the engine and results in a reduced power output.
I am just reading the chart the way it is written. The F6F MAP remains at 51.75 inches from 2K up to 15K. And the climb doesn't change 1 foot all the up.
Also I have seen the NAVAIR charts. They used Neutral, low and high blower the same as is reccomended in the manual.
My Question would be this. The F6F chart shows an obvious improvement in SUSTAINED performance. I say sustained because the F4U-1 had a better initial climb in Mil power in the British test but quickly dropped off as MAP fell off. If it was possible to maintain MAP all the way up and not loose climb rate why wouldn't you. It does no harm to the engine and improves sustained performance.
Niklas,
I'm pretty sure full throttle height means what it says. In the F6F test it didn't reach full throttle until 11K. To me that simply means increasing throttle would overboost the engine.
BTW I have no idea where the Climb rate for the F6F comes from. I have never read of any annecdotal evidence that shows the F6F climbing that well or outclimbing a F4U. On the contrary the early F4U-1 was reputed to outclimb the early F6F-3 by 750FPM. And that is from Butch O'Hare an F6F pilot as well as other sources.
Nashwan,
The F6F and F4U had not Automatic Overboost control as far as I know.
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Hi FAUDOA,
>I am just reading the chart the way it is written. The F6F MAP remains at 51.75 inches from 2K up to 15K. And the climb doesn't change 1 foot all the up.
As you can see from the standard aircraft characteristics, the F6F-5 with R-2800-10W is mostly steady for the interesting altitude range, but it's not entirely constant in its climb at MIL power.
In fact, it's very strange to see a perfectly constant climb rate from 2000 to 15000 ft as in the British chart as not only the engine's power output varies with altitude, but also the aerodynamics of a steady-state climb.
The USN values are derived from flight tests. I don't know if the same is claimed for the British numbers, but they look more like the results of a simplified calculation to me. Extrapolated from flight tests, maybe - but simplified.
>My Question would be this. The F6F chart shows an obvious improvement in SUSTAINED performance.
I don't see any improvment. The British chart shows a 2460 fpm climb rate for the F6F-5 up to 15000 ft. At 7500 ft - right in the middle of the altitude range - the American chart shows about 2450 fpm.
>I say sustained because the F4U-1 had a better initial climb in Mil power in the British test but quickly dropped off as MAP fell off.
The better initial climb resulted solely from the F4U-1 benefitting from the use of "neutral" supercharger at low altitude, which the British test denied the F6F-5. Look at the USN figures for the climb rate for a Hellcat on neutral blower - it beats the Corsair easily with 2980 versus 2550 fpm.
>If it was possible to maintain MAP all the way up and not loose climb rate why wouldn't you. It does no harm to the engine and improves sustained performance.
Maximum power at the propeller shaft is not always reached at maximum MAP as the superchargers necessary to sustain the MAP eat some power as well.
Regards,
Henning (HoHun)
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Im with HoHun and Wells on this one F4UDOA.
HiTech
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HT,
I have been trying to find something other than annecdotal evindence to prove what I have read in so many places IE. FW190 vrs F4U/F6F, A6M5 vrs F4U/F6F as well as F6F vrs F4U test and Butch O'Hares Memoirs. All of which point to a 750FPM climb advatage for the F4U-1 and -1D.
BTW where do your F6F charts come from? I have never seen them anywhere from NAVAIR to AHT??
Also I may not be able to prove this point with you but I can prove that your F4U-1D is not on par with reality. Read my next post on carrier takeoffs;)