P-39 Expert
Non-Expert
Go to Mike Williams site and look at the official government/military tests. It didn't matter how much horsepower an engine developed, what mattered was how the airplane performed.
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Go to Mike Williams site and look at the official government/military tests. It didn't matter how much horsepower an engine developed, what mattered was how the airplane performed.Hello P-39 Expert,
Why would you consider this an outlier? The 190A-3 had an engine of approximately the same power as later versions but was one of the lightest versions built. Why is it a wonder that it should climb very well? The only issues with this testing were that the plugs were probably not in the best of shape and the engine was de-rated but the British did not run it in that manner.
I was referring to the FW 190A-5/U4 that was captured and tested by the USN. It was a ground attack version and did not carry the two outboard cannon. Even so, it carried enough armament with 2 x 20 mm and 2 x 7.92 mm guns to be pretty dangerous. It weighed substantially less than the typical fighter versions and climbed better.
....and no, it did NOT climb the same as the Hellcat and Corsair. That is pretty good performance for a captured bird that isn't even running emergency power.
Why are you so convinced that the Airacobra was a miracle aeroplane?
Either one of these FW 190s was running in the neighbourhood of 1700 - 1750 HP at Sea Level and 1450 - 1550 HP at 20,000 feet. The Airacobra had a nice slick airframe but that doesn't make that much difference at best climb speeds and its airfoil had a relatively low coefficient of lift.
The only place where any of the Airacobra could possibly have comparable power is very near the ground and running manifold pressures well beyond War Emergency.
FW 190A-3 loaded weight is 3855 Kg or 8500 pounds.
FW 190A-5/U4 was ballasted to 8690 pounds for testing which was about 400 pounds less than the typical A-5 fighter with full armament. The A-6 fighter would weigh about 175 pounds even more than that.
- Ivan.
BiffF15 is correct about the engine not running at the time of the landing.
Anti-aircraft fire over Dutch Harbor had cut an oil line and Koga had flown his crippled bird to a previously scouted site to put it down.
Good point. On an American aircraft (other than Grumman) it probably would. US landing gear trunnions tend to be hell for stout, but Horikoshi was a master of lightweight construction, and likely created a design that was strong for vertical loads, but less so for sheer. Also, his one-piece integral wing design didn't have the weak points of detach fittings for the wing panels. "Sheet metal forensics" can generally determine if a fabricated structure of complex shape, such as a wing, has been deformed. The trauma usually wrinkles skins and pops rivets. We did a little of that in mech school.I would have expected force that is violent enough to rip off landing gear might also seriously deform the wing structure.
Spot on! People get over fixated on Coefficient of Lift and Total Lift because they're simple single-value functions and sound impressive. What really matters in most all aircraft performance regimes is Lift/Drag. As Shortround points out, best climb occurs at or very near the best Lift/Drag ratio, tempered slightly by powerplant concerns such as prop efficiency or tailpipe deflection angle. This is where thrust available exceeds thrust required by the greatest amount, and thrust required is, of course, tied to L/D. The excess thrust can be converted to linear acceleration in the horizontal plane, or by maintaining airspeed constant, find an upward inclined plane that achieves the maximum defeat of gravity by that excess thrust.lift of the wing actually doesn't have a whole lot to do with climb. This is counter intuitive but I believe it is true.
In the series "Air War" by David Jablonski, it was mentioned the area Koga chose was a predetermined emergency landing site and it was thought the surface would be acceptable for an emergency landing, it turned out to be soft muddy tundra. Lt. Michio Kobayashi who was flying a Kate actually scouted the landing spot and witnessed the crash. It was also mentioned that he was leaking fuel. Photo from wikiWhat I wonder is why didn't Koga make a gear up belly landing? He probably would have walked away, the plane burned, and Naval Intelligence frustrated.
Also Faber's 190 was using Brit fuel which was different from the German C3 fuel.
Couple more things. I'm not convinced that the Airacobra was a miracle airplane. Just that it was a much better plane than we all have been lead to believe for the last 75 years. All the reference books, every single one listed the performance figures for the P-39 well below the figures and graphs in wwiiaircraftperformance.org (Mike Williams site). Those were the official military tests. William Green, America's Hundred Thousand, all the reference books were pretty accurate except for the P-39. The information on Mike Williams site for the P-39 were released in 2012. Makes me wonder if his information had been somehow lost for the past 75 years. My whole contention is that the P-39 in most all its models was a better performing plane than previously published books indicate. This also helps explain why the Soviets were so successful with it.Hello P-39 Expert,
Why would you consider this an outlier? The 190A-3 had an engine of approximately the same power as later versions but was one of the lightest versions built. Why is it a wonder that it should climb very well? The only issues with this testing were that the plugs were probably not in the best of shape and the engine was de-rated but the British did not run it in that manner.
I was referring to the FW 190A-5/U4 that was captured and tested by the USN. It was a ground attack version and did not carry the two outboard cannon. Even so, it carried enough armament with 2 x 20 mm and 2 x 7.92 mm guns to be pretty dangerous. It weighed substantially less than the typical fighter versions and climbed better.
....and no, it did NOT climb the same as the Hellcat and Corsair. That is pretty good performance for a captured bird that isn't even running emergency power.
Why are you so convinced that the Airacobra was a miracle aeroplane?
Either one of these FW 190s was running in the neighbourhood of 1700 - 1750 HP at Sea Level and 1450 - 1550 HP at 20,000 feet. The Airacobra had a nice slick airframe but that doesn't make that much difference at best climb speeds and its airfoil had a relatively low coefficient of lift.
The only place where any of the Airacobra could possibly have comparable power is very near the ground and running manifold pressures well beyond War Emergency.
FW 190A-3 loaded weight is 3855 Kg or 8500 pounds.
FW 190A-5/U4 was ballasted to 8690 pounds for testing which was about 400 pounds less than the typical A-5 fighter with full armament. The A-6 fighter would weigh about 175 pounds even more than that.
- Ivan.
That Merlin 46 graph is with ram air. Allison figures a without ram air.Yeah, real simple.
It just took Allison two stages, a hydraulic coupling (with variable speed) to do what R R did with one stage on a Merlin 46. And RR did it well before March of 1942.
Getting airflow to match between two compressors wasn't quite so easy.
That shaft from the starter and the hydraulic coupling (torque converter) had to handle 225 hp at a minimum.
and at part throttle or less than full rated height about 25% of the power used drive the auxiliary compressor went to heating up the oil in the hydraulic coupling. At full boost the loss was only 4%. But the oil cooler for the Auxiliary stage had to get rid of around 45hp worth of heat at lower altitudes.
Working out the increased cooling loads for radiators and oil coolers might not have been that simple. As in the engine needs to make an extra 225hp in the cylinders above what was needed for the same power to the prop in a single stage engine. Now if you are flying in thinner air you need even bigger radiators/oil coolers or improved ducts.
Concepts can be simple, getting them to work under varying conditions sometimes isn't simple.
BTW the -47 engine was originally envisioned with an inter-cooler. As was the -93 engine.
Wasn't Brit fuel (avgas) for the Merlins 100 PN?
The AAF increased the time limit for military power from 5 minutes to 15 minutes for the Allison V-1710 (and P&W R-2800) in mid year 1942. About the same time they finally discarded the unnecessary and performance robbing backfire screens. Prior to that the 5 minute limit required reduction to normal power (2600rpm for the Allison, 2550 for P&W) during climb tests which greatly reduced the tested climb rate. The simple use of combat power for 15 minutes increased the tested climb rates dramatically, especially at the higher altitudes reached after 5 minutes. If you look at the tests, all of them reduced power after 5 minutes before 6/30/1942, and used full power at all altitudes after that date.lift of the wing actually doesn't have a whole lot to do with climb. This is counter intuitive but I believe it is true.
Best climb is achieved at the point where the induced drag curve crosses the profile drag curve.
Like this.
View attachment 596925
with the plane flying at the minimum drag speed the rest of the engines power can be used for climbing. This assumes that the minimum drag speed has a comfortable margin above the minimum control speed.
Lift goes up with square of the speed, which is why the induced drag (or drag from creating lift) goes down so quickly, at least to a certain point. However the profile or parasitic drag also goes up the square of the speed so trying to fly faster to create more lift to increase climb doesn't work very well. You have less power left to actually do the work of lifting the plane.
You can estimate climb to some extent if you have (or can reasonable guess) the power needed to fly at the minimum drag speed and figure the power to weight ratio of the plane using the excess power available.
Any of our members who know more about aeronautics ( a bunch of them) are free to correct me on this.
However we can also make the same mistakes than many designers of the 30s made. Those inaccurate estimates of drag and/or induced drag that often under estameted the power needed to fly at minimum speed (prop efficiency can also screw things up).
When you have planes that outperform similar aircraft by a large margin you really have to start looking for the answer. Not always easy to find and make sure you are comparing the same things.
The US was one of the few countries that used military power for the first 5 minutes of a climb, Both Britain and Germany used a much longer time period rating. The US also, at some point during the war on certain aircraft ran take-off power for 5 minutes and then some WEP rating for the rest of the climb unless the engine overheated.
Sometimes a Non US test did use full power for a climb but it is almost always noted.
British tests for the Spitfire for instance used 2600rpm for the early Spitfire with Merlin III engines, later Spitfires used 2850rpm for the climb. Later on some spits were allowed to use 3000rpm at the higher altitudes where the supercharger could not provide full pressure. But finding a test for a Spitfire where they used 3000rpm and full boost from the ground to 25,000 ft or more is going to be a very rare test.
The P-39N in those tests seems to outperform, and by a large margin, the P-39s that came before it and the P-39 that came after it (the Q).
It was also running over the allowable temperature limits.
Clearly they had never flown gliders.Even into the early 30s there were people who should have known better (like editors of aviation magazines) who thought that biplanes would outclimb monoplanes because they had more LIFT.
Shelby Cobra and 427 Corvette Lose to Austin Cooper S ! (Old school Mini-Cooper bored out to 1.5L)According to at least one pilot, whatever they gained on the straightaway they lost in the turns
Clearly they had never flown gliders.
Shelby Cobra and 427 Corvette Lose to Austin Cooper S ! (Old school Mini-Cooper bored out to 1.5L)
I saw it happen at le Circuit Mont Tremblant in 1968 at an SCCA regional. Admittedly, a rather tight course: the winning average speed at the Canadian GP later that year was barely 100 MPH. Saw that too. Monaco without the buildings and waterfront.
I have Reardon's book on the Akutan Zero, but it's packed away in storage. Good excuse to dig it out and read it again. Fascinating read.In the series "Air War" by David Jablonski, it was mentioned the area Koga chose was a predetermined emergency landing site and it was thought the surface would be acceptable for an emergency landing, it turned out to be soft muddy tundra. Lt. Michio Kobayashi who was flying a Kate actually scouted the landing spot and witnessed the crash. It was also mentioned that he was leaking fuel. Photo from wiki
View attachment 596929
Some more on this...
The Akutan Zero – the first intact to be captured by the US in 1942 and the last flight of Tadayoshi Koga – WW2Wrecks.com
Pretty amazing what they were able to do with the old 1.5L F1 with no turbos allowed. But apparently the fans didn't find it "interesting enough" and there was agitation for more performance. Quantum leap when it went to 3L in the mid 60s.Have a read about Stirling Moss winning at Monaco 1961 in a Lotus Climax which only had 145hp against the two Ferrari cars which had over 200hp.
Couple more things. I'm not convinced that the Airacobra was a miracle airplane. Just that it was a much better plane than we all have been lead to believe for the last 75 years. All the reference books, every single one listed the performance figures for the P-39 well below the figures and graphs in wwiiaircraftperformance.org (Mike Williams site). Those were the official military tests. William Green, America's Hundred Thousand, all the reference books were pretty accurate except for the P-39. The information on Mike Williams site for the P-39 were released in 2012. Makes me wonder if his information had been somehow lost for the past 75 years. My whole contention is that the P-39 in most all its models was a better performing plane than previously published books indicate. This also helps explain why the Soviets were so successful with it.
And the FW190 did climb about the same as the Hellcat and Corsair. Look at the climb graphs in my post #118. At 20000' the 190 climbed at about 2000feet per minute, about the same as the 1943 Hellcat, Corsair, Thunderbolt, Lightning F/G, Typhoon and Zero. All in the 1800-2200fpm range.
I have Reardon's book on the Akutan Zero, but it's packed away in storage. Good excuse to dig it out and read it again. Fascinating read.
The P-39D-1 was the heaviest of the early P-39s at 7850lbs. My whole point is that the weight could be easily reduced AT FORWARD BASES by removing some equipment that wasn't needed. The weight reduction was primarily to increase climb rate and ceiling AT ALL ALTITUDES. The P-39 was already 40mph faster at all altitudes than the 1942 Zero. Just using combat power in climb would make the early P-39s equal to the Zero, and the weight reduction would increase climb rate to well above the Zero. With climb AND speed greater than the Zero the air battles would have been very different.Hello P-39 Expert,
For the most part, I agree with your statements above. The problem though is that I am finding that very often you have a tendency to cherry pick tests under one test and load condition and use them as a general conclusion under all conditions. The early P-39 with the -35 and -63 engines are a good example. They were cool little screamers at low altitude, but those engines didn't have enough performance at altitude. The climb test at each altitude against the Aleutian A6M2 proved that despite attempts by the pilot to play with boost settings, he couldn't make up the difference past about 12,500 feet even though the testing was arranged to make US fighters look as good as possible against a beat up A6M2.
The point is that the Airacobra isn't the horrible fighter that some people think. It had its strong points, but it also had some serious limitations inherent in its design that were impossible to correct without a serious re-design.
FWIW, the data from AHT isn't necessarily inaccurate. There are just plenty of typos and the data may not always be complete. The roll rates quoted for P-39 actually are in pretty good agreement with those in NACA testing.
Your ideas for armament reduction may have its merits but it obviously wasn't acceptable to US Army. I don't know that my idea of reverting back to P-39C armament would have been acceptable either.
Your charts are showing a different model FW 190. Take the same aeroplane and delete about 550 pounds of equipment from it and see how it behaves. This equipment deletion isn't a "custom" modification or speculation; it was simply not found on the ground attack FW 190A-5/U4. They were serious load lifters but also pretty respectable hotrods when the ordnance was gone. The problems though were a difference in engine tuning and also non-pressurized ignitions which is probably why they could not get the test aeroplane to fly above 34,500 feet.
- Ivan.
It's that mid-engine design with optimum weight distribution. Works a lot better for a Porsche 914 than a Bell P39.When the competitions were run, I was a bit surprised when the 914s were winning everything. Some of the faster drivers simply laid on the gas and drifted through every turn. None of the other cars could do the same.