Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: HoHun on March 19, 2005, 06:44:49 AM
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Hi everyone,
Trying to analyze aircraft performance, I found that turbo-supercharged aircraft are both poorly documented and enigmatic in their documentation.
The problems are simple:
- (US) power graphs for turbo-supercharged engines give power as constant from sea level up to critical altitude.
(This is unrealistic, considering that most turbo-supercharged engines had a two-speed, mechanically-driven supercharger stage, too. This stage would subtract a certain amount of power in low gear, and a greater amount of power in high gear, thus creating a drop in power at altitude.)
- Speed graphs/data points (which are few) for the P-47 show that the plane is not using the constant shaft power engine curve. The data does indeed suggest that the power is increasing with altitude.
(This is the opposite of what one should expect since a) the engine doesn't provide exhaust thrust, b) the useful power drops due to decreasing propeller efficiency, c) the mechanically driven stage subtracts more power).
- Performance graphs/data points usually show a hard break in the speed curve at critical altitude, but no such hard break in the climb graph at critical altitude. Climb also seems to drop more quickly than the assumption of constant or even increasing power with altitude suggest.
In addition to the effects described above, I also believe that even without them, the turbo-supercharger wouldn't yield the constant power-over-altitude curve we're used to. The overspeed tendency of the WW2 US turbochargers at high altitude is one indication (reduced ambient air pressure makes them more effective), some German power graphs for turbo-supercharged BMW801 versions reinforce it:
http://hometown.aol.de/HoHunKhan/BMW801Turbo.jpg
I'd say that the R-2800 power curves probably should have a very similar look to the BMW801J power curve (disregarding the exact figures).
However, that would result in considerably different performance graphs for the P-47 than those I have seen.
Does anyone have an idea how to solve this puzzle? In my attempt to achieve a break-through, I seem to have hit an impenetrable wall of contradictions :-)
Regards,
Henning (HoHun)
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Couldnt you just extrapolate a P-47s speed at sea level to its speed at 30,000 feet, and then check that against its real life speed?
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Henning, while the aircraft had a mechanical stage as well, they were single speed blowers, not two speed ones! This is at least so for all US installations. Honestly speaking, having two speed mech stage would be very silly.
Another point you must remember is that is some installations it might have been necessary to throttle the engine at very low level (therefore slightly less hp at SL) while at higher up the throttle would be allways wide open and the boost would be determined solely by waste gate control. In can be safely assumed that any high power operation above 10,000 ft of the P-47 would be with the throttle fully open with the MAP being controlled via waste gate.
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Originally posted by pasoleati
Henning, while the aircraft had a mechanical stage as well, they were single speed blowers, not two speed ones! This is at least so for all US installations. Honestly speaking, having two speed mech stage would be very silly.
Another point you must remember is that is some installations it might have been necessary to throttle the engine at very low level (therefore slightly less hp at SL) while at higher up the throttle would be allways wide open and the boost would be determined solely by waste gate control. In can be safely assumed that any high power operation above 10,000 ft of the P-47 would be with the throttle fully open with the MAP being controlled via waste gate.
well said
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Hi Suntracker,
>Couldnt you just extrapolate a P-47s speed at sea level to its speed at 30,000 feet, and then check that against its real life speed?
Have a look at this estimate, showing that constant power would yield too high speeds near sea level:
http://hometown.aol.de/HoHunKhan/P-47Dcalculation.gif
(It's not as bad as I thought it would be :-)
However, if you look at the climb rate, I calculate a much higher climb rate than it is reported for the P-47D in the F4U-4 comparison report which I used as a data source. What's more, I calculate a definite knee at critical altitude while other sources, including Aces High (http://www.hitechcreations.com/ahhelp/models/p47d25.html) and America's Hundred Thousand, show a rounded climb graph without a knee.
Regards,
Henning (HoHun)
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Hi Pasoleati,
>Henning, while the aircraft had a mechanical stage as well, they were single speed blowers, not two speed ones!
Hm, I checked an overview of the R-2800 types, and you seem to be right. Strange, I had read anecdotes from P-47 pilots and they described automatic gear changes - must have been when they flew P-51s later, or I misunderstood them entirely :-)
>Honestly speaking, having two speed mech stage would be very silly.
Well, not really as you get better high-altitude performance while avoiding low-altitude throttling losses.
But I'm glad you pointed out I was in error there as it reduces the magnitude of the problem I'm facing consiberably :-)
>Another point you must remember is that is some installations it might have been necessary to throttle the engine at very low level (therefore slightly less hp at SL) while at higher up the throttle would be allways wide open and the boost would be determined solely by waste gate control. In can be safely assumed that any high power operation above 10,000 ft of the P-47 would be with the throttle fully open with the MAP being controlled via waste gate.
Very good point! I had thought about this, too, but couldn't find any data on it. It would certainly help to explain the 10 km/h gap at sea level which I get from the constant power assumption.
(Von Gersdorff also mentions boost air bleeding as secondary throttling technology, used in addition to waste-gate controlled exhaust gas bleeding - boost air was bled at lower power settings. I'd imagine it was more responsive and perhaps more effective, while waste gate control was more efficient at high power.)
Thanks for your help! :-)
Regards,
Henning (HoHun)
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Henning, where is the P-47 vs. F4U-4 comparison report to be found?
E.g. the Jumo 211F/J has a system where in conditions of high rpm, low boost, excess boost air is bled out before the throttle valve. The operatorīs manual says it is to prevent induction air overheating.
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Hi Pasoleati,
>I had thought about this, too, but couldn't find any data on it. It would certainly help to explain the 10 km/h gap at sea level which I get from the constant power assumption.
To get my calculations match the P-47D from the F4U-4 comparison report, I've to reduce power at sea level from the rated 2600 HP to 2520 HP.
Of course, this has an impact on the climb rate as well so that I drop below the quoted initial climb rate. Since my calculation shows a much better climb than the F4U-4 report, the rest of the climb rate graph is safely above the reported data of course.
Do you have any data on the throttling losses (or a hint how to get such data)? There are so many variables in turbocharger performance that I'm hesitant to guess anything :-)
The next thing to compare it to is Baugher's data for the P-47D-25RE. The high critical altitude indicates that his data is actually for 2300 HP, while I have a power plant chart for the type indicating a WEP rating of 64" Hg, which should yield the oft-quoted 2535 HP. On the other hand, this power plant chart is dated 11-1-44 (which I take to be November 1944), so it might be that when the D-25RE came out, it was only cleared for 2300 HP. On the other hand, Baugher explicitely quotes 2535 HP. No way his speed curve matches this! Unfortunately, the climb rate he quotes is in the middle between those I'd predict for 2300 HP and 2535 HP, so that's no help either.
The Aces High P-47D-25 seems to have 2535 HP, too, judging from the climb rate. It's considerably slower than one might expect from both Baugher's data and the F4U-4 report, though. Surprisingly, the Aces High D-30 climb better at the same power, weight and only very slightly improved speed. I wonder if this could have something to do with the paddle blade propeller?
The Aces High D-11 seems to be the fastest of the Aces High Thunderbolts, but as it also has the worst climb rate despite being 1000 lbs lighter, it looks like it has only 2300 HP and the speed gain is due to the better aerodynamics of the razorback fuselage. Or does it have the toothpick propeller that harms climb rate?
Unfortunately, I don't have any real-life data on the razorback to compare this to. Which Thunderbolts had which propeller type, anyway?
Regards,
Henning (HoHun)
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Originally posted by pasoleati
Henning, where is the P-47 vs. F4U-4 comparison report to be found?
E.g. the Jumo 211F/J has a system where in conditions of high rpm, low boost, excess boost air is bled out before the throttle valve. The operatorīs manual says it is to prevent induction air overheating.
found it here,
http://mywebpages.comcast.net/markw4/index1.html
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Hi Pasoleati,
>Henning, where is the P-47 vs. F4U-4 comparison report to be found?
I believe F4UDOA posted it once, but I'm afraid I don't have the link. As it has more than 5 MB, I'd offer to send it per email if your inbox can take it :-)
>E.g. the Jumo 211F/J has a system where in conditions of high rpm, low boost, excess boost air is bled out before the throttle valve. The operatorīs manual says it is to prevent induction air overheating.
Highly interesting, that seems to be the exact equivalent of what von Gersdorff mentioned with regard to turbo-superchargers! :-)
Regards,
Henning (HoHun)
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Milo, wrong report! I am looking for the P-47 vs F4U-4 report.
Henning, you may send the report to paso.leati@@reppu.net (remove extra @).
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Turbocharger:
(http://hogsden.dyndns.org/~jsavola/dumppi/TurboCharger.jpg)
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Did a bunch of this a while back. See if these help.
http://mysite.verizon.net/vze479py/index.html
Originally posted by HoHun
Hi Pasoleati,
>I had thought about this, too, but couldn't find any data on it. It would certainly help to explain the 10 km/h gap at sea level which I get from the constant power assumption.
To get my calculations match the P-47D from the F4U-4 comparison report, I've to reduce power at sea level from the rated 2600 HP to 2520 HP.
Of course, this has an impact on the climb rate as well so that I drop below the quoted initial climb rate. Since my calculation shows a much better climb than the F4U-4 report, the rest of the climb rate graph is safely above the reported data of course.
Do you have any data on the throttling losses (or a hint how to get such data)? There are so many variables in turbocharger performance that I'm hesitant to guess anything :-)
The next thing to compare it to is Baugher's data for the P-47D-25RE. The high critical altitude indicates that his data is actually for 2300 HP, while I have a power plant chart for the type indicating a WEP rating of 64" Hg, which should yield the oft-quoted 2535 HP. On the other hand, this power plant chart is dated 11-1-44 (which I take to be November 1944), so it might be that when the D-25RE came out, it was only cleared for 2300 HP. On the other hand, Baugher explicitely quotes 2535 HP. No way his speed curve matches this! Unfortunately, the climb rate he quotes is in the middle between those I'd predict for 2300 HP and 2535 HP, so that's no help either.
The Aces High P-47D-25 seems to have 2535 HP, too, judging from the climb rate. It's considerably slower than one might expect from both Baugher's data and the F4U-4 report, though. Surprisingly, the Aces High D-30 climb better at the same power, weight and only very slightly improved speed. I wonder if this could have something to do with the paddle blade propeller?
The Aces High D-11 seems to be the fastest of the Aces High Thunderbolts, but as it also has the worst climb rate despite being 1000 lbs lighter, it looks like it has only 2300 HP and the speed gain is due to the better aerodynamics of the razorback fuselage. Or does it have the toothpick propeller that harms climb rate?
Unfortunately, I don't have any real-life data on the razorback to compare this to. Which Thunderbolts had which propeller type, anyway?
Regards,
Henning (HoHun)
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Hi Joe,
>See if these help.
Hm, not immediately. I had thought I might be able to see from the specific consumption whether 2300 HP required water injection (which I'm not certain of), but the turbo-supercharged engine are only graphed up to 2000 HP. Do you happen to have R-2800 power plant charts similar to this one?
http://hometown.aol.de/HoHunKhan/p47-d-30-power_small.jpg
The key is that we have boosts and rpms given along with a date - but unfortunately, it's November 1944 so it doesn't tell us much about the timeline of P-47 performance.
If we had more of these, with earlier dates, we could probably figure out the exact history of the P-47 pretty well :-)
Regards,
Henning (HoHun)
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I've got some engine calibration curves for P&W A&B series engines. Let me see what these say. The dates on the curves are earlier (1942 if memory serves me). But those are not for the turbocharged engine.
-Blogs
Originally posted by HoHun
Hi Joe,
>See if these help.
Hm, not immediately. I had thought I might be able to see from the specific consumption whether 2300 HP required water injection (which I'm not certain of), but the turbo-supercharged engine are only graphed up to 2000 HP. Do you happen to have R-2800 power plant charts similar to this one?
http://hometown.aol.de/HoHunKhan/p47-d-30-power_small.jpg
The key is that we have boosts and rpms given along with a date - but unfortunately, it's November 1944 so it doesn't tell us much about the timeline of P-47 performance.
If we had more of these, with earlier dates, we could probably figure out the exact history of the P-47 pretty well :-)
Regards,
Henning (HoHun)
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Hohun
I have posted two Charts for the R2800-21.
http://mysite.verizon.net/vze479py/sitebuildercontent/sitebuilderpictures/p47_sefc.gif
http://mysite.verizon.net/vze479py/sitebuildercontent/sitebuilderpictures/p47_foic.gif
This is the engine that powered all the early P47C/D models. One chart is dated May of 1942. Both have been posted on the bulletin board frequently in the past.
I have two engine calibration curves for the A & B series Double Wasp. Unfortunately these are for engines with a single stage, two speed supercharger. I am pretty sure neither engine had water injection.
The A series engine (S1A4-G) generates 1850 HP at 2600 RPM on war emergency. This power can be maintained for altitutdes from 0-5,000 feet in low blower. This power curve dates from dec 1940.
The B series engine (2SBG) generates 2000 HP at 2700 RPM at sea level in low blower. This power curve dates from Oct 1942.
I have a calibration curve for a postwar engine, but unfortunately it's only for auto-lean.
From another source (1945), I have data on a Double Wasp R-2800 2SB-G (B series) that gives the same military rating as reported above. The associated MAP is 52 inches. The same source specifically refers to a turbosupercahrged engine (Double Wasp R-2800 TSB1-G), a B series engine producing 2000 HP at 2700 RPM at takeoff & military settings. This is the -21 (military designation) initially put into the The P-47C/D.
From that same source (1946), I have a military rating for a C series engine (Double Wasp R-2800 CA15) of 2100 HP at 2800 RPM at essentially sea level. But I have take-off power with ADI of 2400 HP at 2800 RPM. The MAP is 56.5 in + 13lbs. I Imagine the later number refers to the water.
Note the F6f flew a B series engine (-10 or 10/w with ADI in the Navy nomenclature) and the F4u flew the C series (-18 or 18/W).
The P-47C/D was outfitted with the -21 model, a B series engine rated at 2000 HP at 2700 at 25k ft with a GE turbosupercharger and single stage mechanical supercharger. Later versions got better engines (-59 without ADI and -63 with ADI) but these were still B series engines. ADI provided 300 additional HP - But ADI did little above critical altitude. The P47N got a C series engine (-57) producing 2500 HP at 2800 RPM.
Model
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Joe, I checked out your La-7 figures and the fuel consumption figures appear to be very high. As it can be estimated that the Ash-82 and the R-2600 produce about the same power at the same rpm and boost it appears that the Ash-82 has some 20% higher cruising fuel consumption if those figures are compared to the R-2600 data I have. Weird.
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You'll have to give me some comparable numbers on the R-2600 as I don't have them.
The table I posted there is derived from a translation of Russian data posted by tilt. When I have a chance I'll go back and check my conversions to American units.
-blogs
Originally posted by pasoleati
Joe, I checked out your La-7 figures and the fuel consumption figures appear to be very high. As it can be estimated that the Ash-82 and the R-2600 produce about the same power at the same rpm and boost it appears that the Ash-82 has some 20% higher cruising fuel consumption if those figures are compared to the R-2600 data I have. Weird.
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Here it comes from the SEFC on the R-2600-13 (taken from B-25 PM):
2100 rpm/31.5 in/1125 hp/115 gph
2100 rpm/29.5 in/1005 hp/90 gph
2000 rpm/27 in/900 hp/75 gph
1600 rpm/19.5 in/420 hp/33 gph
These are applicable at about 5000-7000 ft. I think you can draw a graph based on this!
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Pasoleati:
I've made the following comparison chart:
http://mysite.verizon.net/vze479py/sitebuildercontent/sitebuilderfiles/r2600_v_ash82.pdf
The data for the ASH-82FN is from a translation of a Russian flight test report (VVS) translated by Tilt some time ago. The data for the R2600 is from a May 1942 Specific Engine Flight Chart for the B25C/D with a Wright R2600-13 engines.
On the chart, for all but one setting, the fuel consumption of the Russian engine is less than for its American counterpart. But the difference is not that great and is largely explained by differences in manifold pressure for the power settings I have for the two engines.
The one oddity, as you point out,is at the lowest power setting reported where the R2600-13 seems to have the advantage. For a number of reasons, I would discount that setting though.
First, on the SEFC chart itself, this setting is included under "conditions to avoid." Second,typical crusing HP is 50-60 percent of rated horsepower and yet this lowest setting for the R2600 is less that 1/3 of rated power. Third, other data sources suggest the two engines have comparable fuel economy.
I went back to my data from Wilkinson (Aircraft Engines of the World) and found a number of entries for the ASH-82. These are from the 1949 edition so they are likley to reflect very late models, but that is all I have. In any case, the Specific Fuel Consumption reported for the ASH-82FNW is 0.46, using American measurements. This is a fairly typical value of the fuel economy of a wartime radial engine operated at its most fuel efficient settings.
Wilkinson also reports Specific Fuel Consumption for a number of versions of the Wright R2600 and the number is also 0.46. This is the best value that can be derived from the SEFC chart too.
-blogs
Originally posted by pasoleati
Joe, I checked out your La-7 figures and the fuel consumption figures appear to be very high. As it can be estimated that the Ash-82 and the R-2600 produce about the same power at the same rpm and boost it appears that the Ash-82 has some 20% higher cruising fuel consumption if those figures are compared to the R-2600 data I have. Weird.
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Hi Joe,
>I have posted two Charts for the R2800-21.
Thanks, I didn't have these previously! :-)
VERY interesting to see that 18250 rpm are the limit for the turbine. Later versions were limited to 20000 rpm/22000 rpm Norm/WEP.
This seems to be reflected by the lower full throttle height given for 52" Hg boost - 27000 ft in your chart compared to 34000 ft in the later chart.
I hadn't been aware that there were different turbosupercharger versions before the advent of the "C" engine.
>This is the engine that powered all the early P47C/D models.
Do you know which blocks?
>Unfortunately these are for engines with a single stage, two speed supercharger.
I guess that won't help with the supercharged engine, judging by the BMW801 example :-(
>From that same source (1946), I have a military rating for a C series engine (Double Wasp R-2800 CA15) of 2100 HP at 2800 RPM at essentially sea level. But I have take-off power with ADI of 2400 HP at 2800 RPM. The MAP is 56.5 in + 13lbs. I Imagine the later number refers to the water.
56.5" Hg = +13.06 lbs/sqin in British terminology :-)
That value seems to confirm the "C" power from the F4U-4 report and also that the 64" Hg of the later "B" chart must yield more than 2300 HP.
>Note the F6f flew a B series engine (-10 or 10/w with ADI in the Navy nomenclature) and the F4u flew the C series (-18 or 18/W).
Hm, didn't the F4U start out with the R-2800-8(W)? Interesting to see the "C" in broad use in WW2, I thought there were just the few P-47M engines before VE day.
>ADI provided 300 additional HP
That's something where I'm not sure. Some indications point to 2300 HP WEP, but others, including the 64" Hg/2700 rpm chart - which is for a "B" series engine - point to about 2500 HP. I am a bit confused here!
Regards,
Henning (HoHun)
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Joe, I wouldnīt count on Wilkinson as it is a most unreliable source.
I think the Conditions to avoid remark in the SEFC is an error. After all, most higher powered WW Two aircraft neede to only 25-30% power to reach the best range IAS. See e.g. the P-38L Pilot Manual and the range charts: only 1600rpm/23 InHg is needed for max range cruising. That setting produces about 400 hp per engine, i.e. only 25% power needed for cruising, not 50-60% as you suggested.
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While it's better to have the actual manufacturers data, I've not found any significant problem with the data reported in Wilkinson. And it has the advantage of using the same metric for measurement across engines, which makes comparisons easier.
In any case, for the Ash-82, there is nothing in Wilkinson that is at variance with the actual Russian data Tilt found.
Perhaps I was not clear in the earlier post. I did not mean to say you could not cruise at 25 percent power, but rather, for American engines at least, this was not typically the most efficient in terms of specific fuel consumption.
Something I have noticed in a number of the American engines I have looked at is that fuel consumption (measured as lbs/hp/hr) at very low power settings is very sensitive to the carburetor being used. Often it is higher than if a bit more power is employed.
-blogs
Originally posted by pasoleati
Joe, I wouldnīt count on Wilkinson as it is a most unreliable source.
I think the Conditions to avoid remark in the SEFC is an error. After all, most higher powered WW Two aircraft neede to only 25-30% power to reach the best range IAS. See e.g. the P-38L Pilot Manual and the range charts: only 1600rpm/23 InHg is needed for max range cruising. That setting produces about 400 hp per engine, i.e. only 25% power needed for cruising, not 50-60% as you suggested.
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There were several improvements in the GE turbo during the war. I have to find an archived file somewhere with details on that. One was limiting speed but I can't remember the details.
Yes it is rather difficult to compare engines with one vs two stages, or vs turbo. Still looking for more calibration curves for two stage models of this engine (other than for F4u). If anybody's got one, please let me know.
And yes, I made a typo, the initial engine for the F4u was the R2800-8.
I'll see if I can sort engine model's by blocks of the P47 but I seem to recall trying that before and it was problematic with the information I have.
As for a B series engine generating 2500 HP, that has got to be wth ADI, and even then I am not sure we are really talking a B series. You probably have to have 2800 RPM to do it. But I've seen anomalies like that in documents before.
Thanks for the heads up on the English measurement of MAP. That was my alternative conjecture.
Originally posted by HoHun
Hi Joe,
>I have posted two Charts for the R2800-21.
Thanks, I didn't have these previously! :-)
VERY interesting to see that 18250 rpm are the limit for the turbine. Later versions were limited to 20000 rpm/22000 rpm Norm/WEP.
This seems to be reflected by the lower full throttle height given for 52" Hg boost - 27000 ft in your chart compared to 34000 ft in the later chart.
I hadn't been aware that there were different turbosupercharger versions before the advent of the "C" engine.
>This is the engine that powered all the early P47C/D models.
Do you know which blocks?
>Unfortunately these are for engines with a single stage, two speed supercharger.
I guess that won't help with the supercharged engine, judging by the BMW801 example :-(
>From that same source (1946), I have a military rating for a C series engine (Double Wasp R-2800 CA15) of 2100 HP at 2800 RPM at essentially sea level. But I have take-off power with ADI of 2400 HP at 2800 RPM. The MAP is 56.5 in + 13lbs. I Imagine the later number refers to the water.
56.5" Hg = +13.06 lbs/sqin in British terminology :-)
That value seems to confirm the "C" power from the F4U-4 report and also that the 64" Hg of the later "B" chart must yield more than 2300 HP.
>Note the F6f flew a B series engine (-10 or 10/w with ADI in the Navy nomenclature) and the F4u flew the C series (-18 or 18/W).
Hm, didn't the F4U start out with the R-2800-8(W)? Interesting to see the "C" in broad use in WW2, I thought there were just the few P-47M engines before VE day.
>ADI provided 300 additional HP
That's something where I'm not sure. Some indications point to 2300 HP WEP, but others, including the 64" Hg/2700 rpm chart - which is for a "B" series engine - point to about 2500 HP. I am a bit confused here!
Regards,
Henning (HoHun)
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Hohun:
Here are some excerpts from an interesting article on Wikipedia
http://en.wikipedia.org/wiki/Republic_P-47
The P47B used the R2800-21.
The initial batch of 602 P47C ordered in Sept 1942 - includes an improved turbo regulator. After 1st 57 of these, they went to the C-1 block with 8" longer fuselage (55 built) followed by 128 C-2s with belly attachment point for a 200 gallon drop tank or 500 lb bomb.
The most Cs built were the C-5 block with R2800-59 and ADI, delivering 2300 HP.
The first 110 D models were identical to C-2s. 12,602 D models were built in a sequence of blocks. The D-1 through D-11 included improved cowl flaps to solve a cooling problem and uprated engines. The D-15 adds plumbing for drop tanks in the wings and internal gas is increased to 375 gallons.
The D-16 to D-23 blocks had many small improvements but also a change to a larger propeller (from 12'2" Curtis Electric to a 13'2" Hamilton Standard or a 13' Curtis Electric).
Curtis built the G series of planes that map to certain blocks of the D series.
Bubble tops appear in the D-26 to D-30 blocks, which also included some improvements to the engine.
The D-40 has the cut down rear fuselage and a new computer gun sight (the K-14)
The XP47J has a lightened airframe and a closely cowled R2800-59(C) engine w up to 2800 HP. The M includes this engine and a GE CH-5 Turbo. 130 were built and saw action in Europe at the end of the war.
The N series has an R2800-77(C). 1816 were built.
Originally posted by HoHun
Hi Joe,
>I have posted two Charts for the R2800-21.
Thanks, I didn't have these previously! :-)
VERY interesting to see that 18250 rpm are the limit for the turbine. Later versions were limited to 20000 rpm/22000 rpm Norm/WEP.
This seems to be reflected by the lower full throttle height given for 52" Hg boost - 27000 ft in your chart compared to 34000 ft in the later chart.
I hadn't been aware that there were different turbosupercharger versions before the advent of the "C" engine.
>This is the engine that powered all the early P47C/D models.
Do you know which blocks?
...
Henning (HoHun)
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This is the fuel consumption pattern for the Wright R2600-13:
http://mysite.verizon.net/vze479py/sitebuildercontent/sitebuilderfiles/sfc_r2600.pdf
-blogs
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Hi Joe,
Thanks for the excerpts from the Wikipedia article! Escpecially the break-down of the P-47C variants was interesting - that the subvariants used different engines can be verified from the Pratt & Whitney index.
(I think there are some inccuracies in the article as well - usually the D-25 and not the D-26 is given as first bubbletop. The paddle-blade propeller is typically quoted for the D-22, etc.)
I've come to the conclusion that the type of the supercharger employed can not be deducted from the engine number as they were not part of the engine package.
That could mean that we have both 2000 HP, high full throttle height P-47s and 2300 HP (water-injected), low full throttle height ones.
It seems that the R-2800-59/-63 were virtually the same as the R-2800-21 except that is was prepared for water injection. Apparently, use of the R-2800-59 doesn't mean that water injection was factory-provided for the P-47 initially, making the situation a bit confusing. (Accordingly, the designation -21W seems bogus, and -59W/-63W apparently weren't used by Pratt & Whitney either. In fact it, it seems that the USAAF didn't use any W designations until fairly late, I suspect until after WW2.)
http://www.enginehistory.org/reference.htm
Regards,
Henning (HoHun)
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For the Pratt & Whitney's the mechanical supercharger is their own. The problem is that for the turbo's that is GE and there were a number of models. I have almost no documentation on them either. I do know that during the war the turbo controls were gradually improved and the limiting speed of the turbine impellers were increased.
I think you are right about the -59/63 models.
-blogs
Originally posted by HoHun
Hi Joe,
...I've come to the conclusion that the type of the supercharger employed can not be deducted from the engine number as they were not part of the engine package.
That could mean that we have both 2000 HP, high full throttle height P-47s and 2300 HP (water-injected), low full throttle height ones.
It seems that the R-2800-59/-63 were virtually the same as the R-2800-21 except that is was prepared for water injection. Apparently, use of the R-2800-59 doesn't mean that water injection was factory-provided for the P-47 initially, making the situation a bit confusing. (Accordingly, the designation -21W seems bogus, and -59W/-63W apparently weren't used by Pratt & Whitney either. In fact it, it seems that the USAAF didn't use any W designations until fairly late, I suspect until after WW2.)
http://www.enginehistory.org/reference.htm
Regards,
Henning (HoHun)
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Originally posted by HoHun
It seems that the R-2800-59/-63 were virtually the same as the R-2800-21 except that is was prepared for water injection. Apparently, use of the R-2800-59 doesn't mean that water injection was factory-provided for the P-47 initially, making the situation a bit confusing. (Accordingly, the designation -21W seems bogus, and -59W/-63W apparently weren't used by Pratt & Whitney either. In fact it, it seems that the USAAF didn't use any W designations until fairly late, I suspect until after WW2.)
http://www.enginehistory.org/reference.htm
Regards,
Henning (HoHun) [/B]
Working on a more detailed reply for later. IIRC the -63 was a -21 with factory H2O injection rather than a refit kit. The -59 was the same as the -21/63, but with different magnetos. But the core engine is the same on all of the them, so performance should be identical.
Greg Shaw
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Some time ago I was asked about which models of the DoubleWasp went into the P47, when, what were the differences. We tossed around what we could find from the web, but thanks to Graham White's new book R2800, things become a little more clear.
The Principal engine used in the P47 models through the F model was the R2800-21. This was a "B" series engine rated at 2000 HP at 2700 RPM for takeoff & military. 5,720 of these engines were built, most by Ford.
But there are two related engines put on later versions of the P47C&D - these are the -59 and -63. The B series engines are practically the same as the -21, except they have ADI offering an additional 300 HP. The only other differences are in things like Fuel grade (125 PN rather than 100 Octane) the exact model of carburetor or the magnetos. The power curves & operating instructions are the same as with the -21. 11,391 of the -59 model were built, nearly all by Ford. 2,029 of the -63 model were built.
The P47N got a "C" series engine - the -73 - offering 2100 HP at 2800 RPM. It was rated on 100/130 PN fuel. I can't tell if this engine had ADI. Chevrolet built these, 2665 in all. A few other cats & dogs also went into the P47N. With ADI, the extra 100 RPM, and very high PN fuel I'll bet this would get to a maximum HP in the range of 2,500.
One thing you notice from White's detail is that a higher model number on an engine does not necessarily mean it was a later, or better engine...
-Blogs
Originally posted by HoHun
Hi Joe,
>See if these help.
Hm, not immediately. I had thought I might be able to see from the specific consumption whether 2300 HP required water injection (which I'm not certain of), but the turbo-supercharged engine are only graphed up to 2000 HP. Do you happen to have R-2800 power plant charts similar to this one?
http://hometown.aol.de/HoHunKhan/p47-d-30-power_small.jpg
The key is that we have boosts and rpms given along with a date - but unfortunately, it's November 1944 so it doesn't tell us much about the timeline of P-47 performance.
If we had more of these, with earlier dates, we could probably figure out the exact history of the P-47 pretty well :-)
Regards,
Henning (HoHun)
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Hohun pointed out there was no way to map from just an engine model number to the actual performance of a particular vintage of the P47C or P47D, which had many variations within these designations.
White's new book resolves this. He has tables with every variation of the plane. He has about 25 separete versions of the P47D for example, complete with performance specs.
As Hohun guessed, improvements in the GE turbo were introduced along the way, even though the Pratt & Whitney engine designation did not change. The first significant improvement to the turbo, plus ADI, emerges on the P47D-5-RE (Evansville). The P47D-10-RE goes to the R2800-63, which was specifically designed to incorporate ADI and there is another new model of the turbo.
The first significant performance change occurs with the P47D-22-RE, I suspect because the propeller length was increased nearly a foot. The P47D-25-RE gets a bigger fuel tank, more ADI capacity, a bubble canopy and I believe loses the turtleback. The P47D-28 gets P-38 type dive flaps plus new ailerons. This is continued in the D30 model, which was the most numerous of the D varients.
And so it goes... Curtiss built some P47Gs, and these were regarded as dogs. The P47N gets an improved turbo, a lighter airframe, and a lot more gas. Several more improvements to the turbos are introduced throughout the N series.
-blogs
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The P-38 had only a single stage single speed crank
driven centrifugal supercharger, there were no multi
speed superchargers on Allison engines, hence the
lack of power at high altitudes for anything but the
P-38 turbocharged engines.
The GE turbochargers were:
B-2 120#of air per minute 21,300 RPM
B-13 130# of air per minute 21,300 RPM
B-33 165# of air per minute 24,000 RPM
These same turbochargers were used on several different planes, including the P-38 and the P-47, and on the the B-17
and the B-24 as well.
Each model was a detail improvement on the previous model, with improvements in efficiency and maximum turbine RPM. They
were all very similar, and in fact, to my knowledge, were interchangeable as far as the physical installation goes.
However, due to power differences, they had to be installed in matched pairs on the plane.
Unlike modern installations, the GE turbochargers in use then
were not specifically designed for a particular engine with a particular power level. They were designed around a general power level alone. The GE turbocharger was at best about 65% efficient, as opposed to the current efficiency of correctly sized turbochargers that reach or at least aproach 90%.
The limiting factor with the Allison was octane. The turbocharger provided air at a rate regulated to equal sea level. Allison actually slowed down the mechanical supercharger because it could make enough boost with the turbocharger to exceed the limitations of the available fuel. When they slowed the mechanical supercharger down, the RPM required of the turbine in the turbocharger to maintain sea level pressure increased, and exceeded the limit. The wastegate could not dump enough boost from the turbocharger to keep the pressure down at low altitudes, so the mechanical supercharger had to be slowed down.
-
At least for some of the production models, the P47 was getting a "C" series turbo. Improvements were often manifested in the control mechanism rather than the turbo itself.
-blogs
Originally posted by Captain Virgil Hilts
The P-38 had only a single stage single speed crank
driven centrifugal supercharger, there were no multi
speed superchargers on Allison engines, hence the
lack of power at high altitudes for anything but the
P-38 turbocharged engines.
The GE turbochargers were:
B-2 120#of air per minute 21,300 RPM
B-13 130# of air per minute 21,300 RPM
B-33 165# of air per minute 24,000 RPM
These same turbochargers were used on several different planes, including the P-38 and the P-47, and on the the B-17
and the B-24 as well.
Each model was a detail improvement on the previous model, with improvements in efficiency and maximum turbine RPM. They
were all very similar, and in fact, to my knowledge, were interchangeable as far as the physical installation goes.
However, due to power differences, they had to be installed in matched pairs on the plane.
Unlike modern installations, the GE turbochargers in use then
were not specifically designed for a particular engine with a particular power level. They were designed around a general power level alone. The GE turbocharger was at best about 65% efficient, as opposed to the current efficiency of correctly sized turbochargers that reach or at least aproach 90%.
The limiting factor with the Allison was octane. The turbocharger provided air at a rate regulated to equal sea level. Allison actually slowed down the mechanical supercharger because it could make enough boost with the turbocharger to exceed the limitations of the available fuel. When they slowed the mechanical supercharger down, the RPM required of the turbine in the turbocharger to maintain sea level pressure increased, and exceeded the limit. The wastegate could not dump enough boost from the turbocharger to keep the pressure down at low altitudes, so the mechanical supercharger had to be slowed down.
-
Originally posted by Captain Virgil Hilts
The P-38 had only a single stage single speed crank
driven centrifugal supercharger, there were no multi
speed superchargers on Allison engines, hence the
lack of power at high altitudes for anything but the
P-38 turbocharged engines.
The GE turbochargers were:
B-2 120#of air per minute 21,300 RPM
B-13 130# of air per minute 21,300 RPM
B-33 165# of air per minute 24,000 RPM
These same turbochargers were used on several different planes, including the P-38 and the P-47, and on the the B-17
and the B-24 as well.
Each model was a detail improvement on the previous model, with improvements in efficiency and maximum turbine RPM. They
were all very similar, and in fact, to my knowledge, were interchangeable as far as the physical installation goes.
However, due to power differences, they had to be installed in matched pairs on the plane.
Unlike modern installations, the GE turbochargers in use then
were not specifically designed for a particular engine with a particular power level. They were designed around a general power level alone. The GE turbocharger was at best about 65% efficient, as opposed to the current efficiency of correctly sized turbochargers that reach or at least aproach 90%.
The limiting factor with the Allison was octane. The turbocharger provided air at a rate regulated to equal sea level. Allison actually slowed down the mechanical supercharger because it could make enough boost with the turbocharger to exceed the limitations of the available fuel. When they slowed the mechanical supercharger down, the RPM required of the turbine in the turbocharger to maintain sea level pressure increased, and exceeded the limit. The wastegate could not dump enough boost from the turbocharger to keep the pressure down at low altitudes, so the mechanical supercharger had to be slowed down.
It might be worth checking where was the wastegate as the wastegate controlled the amount of exhaust gas to turbine, not the amount of induction air to carburettor.
And exactly how did Allison slow down (=reduce the rpm of the impeller) the mech stage? After all, the mech stage has fixed gear ratio...
-
Originally posted by pasoleati
It might be worth checking where was the wastegate as the wastegate controlled the amount of exhaust gas to turbine, not the amount of induction air to carburettor.
And exactly how did Allison slow down (=reduce the rpm of the impeller) the mech stage? After all, the mech stage has fixed gear ratio...
Yes, the wastegate controls the amount of exhaust to the turbine. But that in turn controls the amount of boost to the intake. At least it does on my turbocharged Buick TType Regal, and every other turbocharged setup I've ever worked on (a lot). By the wategate "dumping boost" I mean the wastegate slowed the turbine down. "Dumping boost' is a common term among those of us who race turbo cars. If the wastegate is too small, it cannot allow enough exhaust to bypass the turbine, and therefore cannot "dump enough boost". It is a real problem on compound supercharged engines, as well as multistage turbocharged engines (pulling tractors and such).
Allison changed the fixed supercharger drive ratio. There were at least two or three ratios used in the 6:1-8:1 range. They used the 6:1 (approximate) to reduce boost at sea level because the turbocharger made too much boost when combined with the supercharger. Since the wastegate could not open enough to dump enough boost, they were forced to slow down the supercharger.
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Do check the gear ratio of the V-1710-111/113. It is not 6:1, not even near.
And be specific what you write about. Lots of common misunderstandings in common aviation literature would have been avoided if the author had written clearly and CORRECTLY.
And in how many WW Two docs you have read about dumping the boost? Better keep the language proper and not degenerate it to automobile level.
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Originally posted by pasoleati
Do check the gear ratio of the V-1710-111/113. It is not 6:1, not even near.
And be specific what you write about. Lots of common misunderstandings in common aviation literature would have been avoided if the author had written clearly and CORRECTLY.
And in how many WW Two docs you have read about dumping the boost? Better keep the language proper and not degenerate it to automobile level.
The V-1710-F5/10 in the P-38F/G used a gear ratio of 7.48:1 IIRC, good to increase map from about 30 in Hg @ the carb intake to approx 50 in Hg in the manifold. The F17/30 increased the ratio to 8.1:1, good for a little over 60 in Hg when fed 30 in from the turbo.
Non turbo-supercharged Allisons went from somewhere around 6.0:1 for the early airship engines IIRC, to 8.77:1 for the C-series, 8.8:1 for the F3/4 to 9.6:1 for the F20. The F21 in the A-36 used the same 7.48:1 as the P-38 engines.
Greg Shaw