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R-2800 for fighters: how would've you done it?
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Shortround6
Major General
It may be the same. AHT says the later "D"s went to the 13 foot prop while the "paddle blade" prop was a little bit less in diameter.
GregP
Major
I would like to have seen an R-2800 aircraft with the engine mounted mid-ship, similar to a P-39, but with the turbo right on the engine, as they were subsequently mounted later on in the life of the R-2800. I think the air ducting for cooling could have been designed quite easily and could have exhausted similar to the P-51 on the bottom of the fuselage.
I would put the cockpit at the leading edge of the wing and the aircraft would not need long runs of heavy ducting ala the P-47's exhaust ducting since the turbo is right on the engine. I'm thinking a 7,500 pound empty weight aircraft would be possible, with gross being about 9,500 pounds … and would have altitude capability.
The power to weight would have been better than the P-47, and it could have been fielded about early 1943.
Of course we are talking a "what if," so it is also possible that teething problems would delay things or even prove unsurmountable. But as long as I an "what iffing," I might as well take a sunny view of technical problems. The thing is, we would not be ducting exhaust a long way and there is no radiator, so I think the main issue would be the drivehaft, and the P-39 / P-63 worked … why not a radial driveshaft?
I'd choose a good cannon for it, not the wimpy cannon in the P-39. I'm thinking a Russian 37 mm with two or more 23 mm units along with it.
I would put the cockpit at the leading edge of the wing and the aircraft would not need long runs of heavy ducting ala the P-47's exhaust ducting since the turbo is right on the engine. I'm thinking a 7,500 pound empty weight aircraft would be possible, with gross being about 9,500 pounds … and would have altitude capability.
The power to weight would have been better than the P-47, and it could have been fielded about early 1943.
Of course we are talking a "what if," so it is also possible that teething problems would delay things or even prove unsurmountable. But as long as I an "what iffing," I might as well take a sunny view of technical problems. The thing is, we would not be ducting exhaust a long way and there is no radiator, so I think the main issue would be the drivehaft, and the P-39 / P-63 worked … why not a radial driveshaft?
I'd choose a good cannon for it, not the wimpy cannon in the P-39. I'm thinking a Russian 37 mm with two or more 23 mm units along with it.
wuzak
Captain
I think you may end up with a very portly fuselage still.
http://www.warbirdsresourcegroup.org/URG/images/xp56-5.jpg
http://d951443.u114.weberz.com/images/Northrop_XP-56_Black_Bullet/XP-56_Plan.JPG
I think that the P-47 fuselage could have been more compact if they didn't have the air fot the turbo and intercooler ducted from the front. Maybe using a water to air intercooler would have reduced its size requirements too. A P-51 style scoop under the fuselage, or leading edge intakes could have fed air to the turbo and intercooler.
http://www.warbirdsresourcegroup.org/URG/images/xp56-5.jpg
http://d951443.u114.weberz.com/images/Northrop_XP-56_Black_Bullet/XP-56_Plan.JPG
I think that the P-47 fuselage could have been more compact if they didn't have the air fot the turbo and intercooler ducted from the front. Maybe using a water to air intercooler would have reduced its size requirements too. A P-51 style scoop under the fuselage, or leading edge intakes could have fed air to the turbo and intercooler.
A viable design may have been the YP-60E.
It took a lot of time, energy and dead ends before the YP-60E was arrived at - much too late.
But I wonder how quickly the YP-60E could have been fielded had this path been taken aggressively from the get go.
If Curtiss could get their heads out of their arses, it seems they could have brought this design to bear more quickly than Vought could have fielded a lighter version of the F4U.
It took a lot of time, energy and dead ends before the YP-60E was arrived at - much too late.
But I wonder how quickly the YP-60E could have been fielded had this path been taken aggressively from the get go.
If Curtiss could get their heads out of their arses, it seems they could have brought this design to bear more quickly than Vought could have fielded a lighter version of the F4U.
GregP
Major
Hi Wuzak!
I didn't mean a rear driveshaft, I meant a front one. The engine could have been mounted neatly, as in the Vought XF5U. it was projected to go 500 mph and they COMPLETED it, only to scrap it before flying it! Idiots! They should have at least investigated the configuration with a completed airframe ... assuming the wind tunnel tests didn;t show it to be unflyable. We may never know, huh?
It could have also been mounted horizontally and had a blended wing-fuselage contour, as in the McDonnell XP-67 to handle the engine bay.
However, this is a "what if," and you know how I dislike participting in them. So, I won't argue the point any further except to say I thinkw as feasible. Didn't happen, but could have been feasible.
I didn't mean a rear driveshaft, I meant a front one. The engine could have been mounted neatly, as in the Vought XF5U. it was projected to go 500 mph and they COMPLETED it, only to scrap it before flying it! Idiots! They should have at least investigated the configuration with a completed airframe ... assuming the wind tunnel tests didn;t show it to be unflyable. We may never know, huh?
It could have also been mounted horizontally and had a blended wing-fuselage contour, as in the McDonnell XP-67 to handle the engine bay.
However, this is a "what if," and you know how I dislike participting in them. So, I won't argue the point any further except to say I thinkw as feasible. Didn't happen, but could have been feasible.
GregP
Major
Hi Wuzak!
I didn't mean a rear driveshaft, I meant a front one. The engine could have been mounted neatly, as in the Vought XF5U. it was projected to go 500 mph and they COMPLETED it, only to scrap it before flying it! Idiots! They should have at least investigated the configuration with a completed airframe ... assuming the wind tunnel tests didn't show it to be unflyable. We may never know, huh?
It could have also been mounted horizontally and had a blended wing-fuselage contour, as in the McDonnell XP-67 to handle the engine bay.
However, this is a "what if," and you know how I dislike participting in them. So, I won't argue the point any further except to say I think it was feasible. Didn't happen, but could have been feasible.
I didn't mean a rear driveshaft, I meant a front one. The engine could have been mounted neatly, as in the Vought XF5U. it was projected to go 500 mph and they COMPLETED it, only to scrap it before flying it! Idiots! They should have at least investigated the configuration with a completed airframe ... assuming the wind tunnel tests didn't show it to be unflyable. We may never know, huh?
It could have also been mounted horizontally and had a blended wing-fuselage contour, as in the McDonnell XP-67 to handle the engine bay.
However, this is a "what if," and you know how I dislike participting in them. So, I won't argue the point any further except to say I think it was feasible. Didn't happen, but could have been feasible.
GregP
Major
The above was a completely unintended double post. Mr. Moderator, please delte the first one! I checked spelling a bit late ...
wuzak
Captain
Horizontal? As in with the crankshaft axis vertical?
Not sure if that is feasible, as the R-2800 is longer than it is wide.
I know you meant that the engine drives the prop at the front via an extension shaft. One problem with that, though, is the drive shaft would be in an inconvenient location, unless the pilot sits quite high in the fuselage.
I understand that the layout of the XF5U was extensively tested in the V-173.
Vought V-173 - Wikipedia, the free encyclopedia
Not sure if that is feasible, as the R-2800 is longer than it is wide.
I know you meant that the engine drives the prop at the front via an extension shaft. One problem with that, though, is the drive shaft would be in an inconvenient location, unless the pilot sits quite high in the fuselage.
I understand that the layout of the XF5U was extensively tested in the V-173.
Vought V-173 - Wikipedia, the free encyclopedia
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swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
The US carburetors would cope with transient negative accelerations. There are many other things which are required for an aircraft engine to cope with sustained negative accelerations, mostly involving the design of the lubrication system.
By the way, the XP-55 stalled its main wing, which is generally considered to be unrecoverable, with or without power, in a canard or tandem wing aircraft, regardless of whether engine power is available or not. Similarly, flat spins are very difficult to recover from.
Some random points:
1) As long as the Americans stuck to the 0.5" machine gun (too heavy in relation to its firepower, e.g. the Berezin was a much superior weapon) which meant 6-8 guns with copious amounts of ammunition their airframes had to be unnecessarily large.
2) Most US radial installations were quite crude in terms of drag reduction. What should have been done is to add a cooling fan and replace the village blacksmith design circumferential outward opening cowl flaps with sliding cooling flaps. In addition, e.g. oil coolers hung beneath the engine should have been relocated to wing roots. Improved cooling would have allowed leaner mixtures to be employed even at higher settings, thus fuel tanks could be smaller which in turn would allow a smaller airframe.
1) As long as the Americans stuck to the 0.5" machine gun (too heavy in relation to its firepower, e.g. the Berezin was a much superior weapon) which meant 6-8 guns with copious amounts of ammunition their airframes had to be unnecessarily large.
2) Most US radial installations were quite crude in terms of drag reduction. What should have been done is to add a cooling fan and replace the village blacksmith design circumferential outward opening cowl flaps with sliding cooling flaps. In addition, e.g. oil coolers hung beneath the engine should have been relocated to wing roots. Improved cooling would have allowed leaner mixtures to be employed even at higher settings, thus fuel tanks could be smaller which in turn would allow a smaller airframe.
- Thread starter
- #93
There were plenty of factors that were driving historical R-2800 fighters towards being large.
The P-40 and P-51 did have 6 HMG batteries and plenty of ammo aboard, despite the moderate dimensions - meaning that some other factors were to be considered first. Main factor is the engine itself, a big powerful brute. If 'our' fighter is to be equipped with auxiliary stage compressor, along with intercoolers and place for ADI kit, there was no way that fighter's fuselage is to remain of moderate size. The powerful engine means a lot of fuel need to be carried around, especially if the USAF or USN is the costumer. That again drives size weight up. Big power also dictates big prop and plenty of engine oil to be carried.
Now we come to wing size. P-47 was featuring a big heavy fuselage, there was no way that wing will be small for such a big brute, especially if we account in the high altitude the Jug was supposed to operate. The F4U and F6F were to have good CV behavior, meaning their wing is to be a big and heavy one.
So wit all that accounted for, there was slim chance that a R-2800 fighter will be a smallish one. Unless we go for a single stage engine, 4 HMGs, under 200 gals of fuel - in other words, the Bearcat-sized one, but with less power, lower performance and less range than demanded/needed. It might be earlier available than two-stager fighter, though - the 1st single stage engines were available a year before 2-stagers.
The P-40 and P-51 did have 6 HMG batteries and plenty of ammo aboard, despite the moderate dimensions - meaning that some other factors were to be considered first. Main factor is the engine itself, a big powerful brute. If 'our' fighter is to be equipped with auxiliary stage compressor, along with intercoolers and place for ADI kit, there was no way that fighter's fuselage is to remain of moderate size. The powerful engine means a lot of fuel need to be carried around, especially if the USAF or USN is the costumer. That again drives size weight up. Big power also dictates big prop and plenty of engine oil to be carried.
Now we come to wing size. P-47 was featuring a big heavy fuselage, there was no way that wing will be small for such a big brute, especially if we account in the high altitude the Jug was supposed to operate. The F4U and F6F were to have good CV behavior, meaning their wing is to be a big and heavy one.
So wit all that accounted for, there was slim chance that a R-2800 fighter will be a smallish one. Unless we go for a single stage engine, 4 HMGs, under 200 gals of fuel - in other words, the Bearcat-sized one, but with less power, lower performance and less range than demanded/needed. It might be earlier available than two-stager fighter, though - the 1st single stage engines were available a year before 2-stagers.
swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
To put the "crude US radial installations" in perspective: the F4U had a zero-lift drag coefficient of about 0.02, which is about the same as that of the Bf109 or Spitfire, which, as super-low-drag inline aircraft should have much lower drag coefficients. The people who designed US radial engine installations had a couple of things going on: first, commercial aircraft need to make money, so the installations in the DC-3, Boeing 247, Curtiss C-46, etc had to be quite good.
There's are reasons they call it a "NACA Cowling": because it was invented here, and it was heavily researched to minimize drag and maximize the effectiveness of cooling air. No US radial installation used a cooling fan. Maybe it's because the US (and British) designers actually knew what they were doing, heh, and the German's didnt?
There's are reasons they call it a "NACA Cowling": because it was invented here, and it was heavily researched to minimize drag and maximize the effectiveness of cooling air. No US radial installation used a cooling fan. Maybe it's because the US (and British) designers actually knew what they were doing, heh, and the German's didnt?
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Well, quite a few late British and US projects did have a cooling fan. And e.g. the performance achieved by e.g. the F8F does not indicate a paeticularly succesful drag reduction for a late-war fighter.* As for those airliner installations, fuel wasn't particularly expensive at that time, so optimizing engine installation from a lowest possible drag point was not necessarily the prime factor. As you said, the bottom line was more important than technical finesse.
Good comparison is the F8F vs. the Tempest II.
Good comparison is the F8F vs. the Tempest II.
swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
No US radial-engined airplane with a fan-cooled radial installation ever went into production. If they wanted to move air through a cowling when the aircraft wasn't moving, they'd use ejector exhaust, which can easily provide negative cooling drag. Fan-cooled installations are common in piston-engined helicopters, which routinely need to operate at high powers at low or zero airspeed.
You are probably right in that minimum drag wasn't the dominant criterion in the Bearcat -- or any other combat aircraft -- design. For the Bearcat, I believe that priority was given to maneuverability, safe departure characteristics, and good low-speed handling. To get an idea of what a minimum drag design would look like, take a peak at the Republic Rainbow.
The Rainbow is indeed a most interesting aircraft, but I think the Tempest II is a good example of proper attention to engine installation drag. It was faster than the F8F with minimal increase in power with 24 % larger wing plus heavier airframe. Another good example is the La-7.
Another good comparison: Tempest II vs. any model of the P-47 at sea level. Closely similar wing areas, yet with settings giving similar power, the former is very much faster.
Another good comparison: Tempest II vs. any model of the P-47 at sea level. Closely similar wing areas, yet with settings giving similar power, the former is very much faster.
Shortround6
Major General
Something to consider when contemplating early use of the R-2800 is that it was really a family of engines, and there was a lot of difference between the early ones and late ones.
A big change came with the "C" series engines which had forged heads instead of cast and more fining on the cylinder barrels. In tests of just the heads alone they found that a constant cylinder baffle pressure drop (air flow and drag) the cylinder temperatures were lower. At a constant head temperature less mass air flow was needed (less drag). At the same detonation resistance the cast heads needed a richer mixture or higher fuel consumption at the same power levels. On Average the forged heads needed about 10% leaner mixture at high power settings OR could allow higher boost settings and more power than the cast heads. On the "A" and "B" engines the limits were 350 degrees at the cylinder base and 500 degrees at the head. With forged heads it was found that the heads reached only 425 degrees when the base hit 350 degrees. The cylinder barrel was given more fins to even things out.
The F8F-1 used a "C" series engine that was good for 1700hp at 16,000ft. The "B" sereis two speed engines were good for 1600hp at 13,500ft and need more cooling air (drag) at the same power levels as the "C" engine and suck down more fuel at the same power levels (high power).
You can make (or propose) an "early" Bearcat but it is going to have several things cutting into it's performance compared to the F8F-1.
A big change came with the "C" series engines which had forged heads instead of cast and more fining on the cylinder barrels. In tests of just the heads alone they found that a constant cylinder baffle pressure drop (air flow and drag) the cylinder temperatures were lower. At a constant head temperature less mass air flow was needed (less drag). At the same detonation resistance the cast heads needed a richer mixture or higher fuel consumption at the same power levels. On Average the forged heads needed about 10% leaner mixture at high power settings OR could allow higher boost settings and more power than the cast heads. On the "A" and "B" engines the limits were 350 degrees at the cylinder base and 500 degrees at the head. With forged heads it was found that the heads reached only 425 degrees when the base hit 350 degrees. The cylinder barrel was given more fins to even things out.
The F8F-1 used a "C" series engine that was good for 1700hp at 16,000ft. The "B" sereis two speed engines were good for 1600hp at 13,500ft and need more cooling air (drag) at the same power levels as the "C" engine and suck down more fuel at the same power levels (high power).
You can make (or propose) an "early" Bearcat but it is going to have several things cutting into it's performance compared to the F8F-1.
SR6: I have White's R-2800 book so the basic series differences are familiar to me, but I don't recall that White mentioned that 10 % difference regarding mixture. A most interesting piece of information! Though if the F4U-5 manual is anything to go by, seems that dry combat power still required substantially richer mixture than e.g. the Centaurus. But then the latter allowed momentary 310 deg C CHT...
Shortround6
Major General
Page 148, It may be the results in bench tests during development. Pushing the "C" series engines to their higher limits may have required the higher mixtures,
The engine used in the F4U-5 is the "E" series "sidewinder" engine and if the power settings you are comparing use the auxiliary supercharger then the specific fuel consumption has to take that into account.
In any case an early R-2800 engine using the same supercharger set up as the F8F-1 will have less power, higher fuel consumption and more drag.
The engine used in the F4U-5 is the "E" series "sidewinder" engine and if the power settings you are comparing use the auxiliary supercharger then the specific fuel consumption has to take that into account.
In any case an early R-2800 engine using the same supercharger set up as the F8F-1 will have less power, higher fuel consumption and more drag.
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