Remember cooling is as much to do with the radiators as it is engine power. Just because MW 50 use was permitted for 10 minutes doesn't mean the radiators could cope for that long.
AFAIK, the Germans did speed tests used closed radiators. With closed radiators, cooling is minimal, and the engine will overheat quickly.
So MW 50 might have been useable for 10 minutes, but after a short period you'd have to open the radiators, which would slow down the plane.
Spitfires could not fully close their radiators, they were always at least half open, so cooling (on the VIII/IX at least) was always sufficient.
I believe most Mustang speed figures are also done with partially open radiators, a British test of a Mustang IV (P-51D) at 25 lbs boost notes cooling at the "normal" setting of 7.25" was inadequate, and 8.5" was used instead.
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Finally, you have any more info regarding the use of WEP for more than 5 minutes in the Mustang and late Spitfire?
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There's this from US instructions to P-51 pilots:
"It is often asked what the consequences will be if the 5-minute limit at Take-off Power is exceeded. Another frequent inquiry is how long a period must be allowed after the specified time limit has elapsed until Take-off Power can be used. These questions are difficult to answer, since
the time limit specified does not mean that engine damage will occur if the limit is exceeded. Instead, the limit means that the total operating time at high power should be kept to a reasonable minimum in the interest of prolonging engine life.
It is generally accepted that high-power operation of an engine results in increased wear and necessitates more frequent overhaul than low-power operation. However, it is apparent that a certain percentage of operating time must be at full power. The engine manufacturer allows for this in qualification tests in which much of the running is done at Take-off Power to prove ability to withstand the resulting loads. It is established in these runs that the engine will handle sustained high power without damage. Nevertheless, it is still the aim of the manufacturer and to the best interest of the pilot to keep within reasonable values the amount of high-power time accumulated in the field. The most satisfactory method for accomplishing this is to establish time limits that will keep pilots constantly aware of the desire to hold high-power periods to the shortest period that the flight plan will allow, so that the total accumulated time and resulting wear can be kept to a minimum.
How the time at high power is accumulated is of secondary importance; i.e., it is no worse from the standpoint of engine wear to operate at Take-off Power for one hour straight than it is to operate in twelve 5-minute stretches, provided engine temperatures and pressures are within limits. In fact, the former procedure may even be preferable, as it eliminates temperature cycles which also promote engine wear.
Thus if flight conditions occasionally require exceeding time limits, this should not cause concern so long as constant effort is made to keep the over-all time at Take-off Power to the minimum practicable. "
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However, when I came accross the Bf-109 dara things didn't make that much sense. If the spitfire cooling is better, how comes it has a lower maximum cruising speed?
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It didn't.
The problem is the definition of "cruise" can be very different to different people. The Spitfire LF VIII (basically the same as the IX, slightly heavier, but retracting tail wheel) had a speed of 386 mph at it's 1 hour rating, ie it could maintain 386 mph for an hour. (and the amount of fuel used at that speed means it wouldn't have had sufficient fuel to maintain that speed for an hour)
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On the other hand I think that data should be taken with caution. The cruise velocities for a G-2 were much lower (I checked on the manual).
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Cruise is normally a setting designed to balance speed with range, these high cruise figures are the fastest it's possible to maintain for a considerable period, and not by any stretch of the term "normal".
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Depends on the Aircraft. The Spitfire and the Bf-109 and Fw-190A stayed pretty close to each other on performance, the Fw-190D and Ta-152 overtook the Spitfire pretty much on performance.
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The Spitfire was both faster and had a better climb rate than the 190D. Only at extreme altitudes, above 30,000ft, did the handfull of Ta 152s built outperform the Spitfire XIV. Below that the Spitfire was faster with a higher climb rate. The Ta 152 was really a specialist aircraft designed to operate at extreme altitude, it's performance at the actual altitudes combat was taking place at was no more than average by 1944 standards.
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