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simple, they cut the impeller down from 10.25in to 9.5 in and left most (or all) of the rest of the supercharger alone.So what is the deal with the Merlin 45M?
See post 887
Is that still the case adjusting for overclaiming? That 's not always possible, but in the Western Desert at any rate there certainly seems to be a significant amount of overclaiming going by the MAW series.
I don't know what you mean by "overclaiming of 2-3" but if you mean 200-300% then I don't think there is any evidence for that. Specifically with the Aces as I showed it looks like on that particular day of Nov 22 1941 they underclaimed and the Luftwaffe were the ones doing fairly substantial overclaiming.
So what is the deal with the Merlin 45M?
You have to take into consideration that there really wasn't a ''standard'' MkV, they had three different engines, three different boost ratings, two different rev limits, two different exhaust systems, about four different configurations, both float and injector carbs, fared and unfared mirrors, fixed and whip aerials and by 43 they were getting tired, by 44 they were worn out. When you add a few mph with fishtails and a injector carb then subtract a few from poor paint finish and a fixed aerial there's big differences between them.
To add to what Sr6 said:
Does a similar table exist for the Merlin 46?
Looking around for the past little while I have a feeling the Merlin 46 curve in my chart should be knocked back about 15 mph ...
I'd still like to know where the 52mph the Darwin MkV's lost went?.
simple, they cut the impeller down from 10.25in to 9.5 in and left most (or all) of the rest of the supercharger alone.
This meant it took less power to turn the impeller but also meant the supercharger provided less boost at a given altitude and engine rpm.
Centrifugal superchargers are also not positive displacement devices. too much clearance between the impeller tips and the housing means some of the air (or a higher percentage) near the housing walls isn't moving with the air near the impeller tips.
The Merlin 45M (and the other cropped impeller engines) took less power from the crankshaft, heated the intake air less and ran at low altitudes with the Throttle plate open wider, all of which gave more power at low altitudes for the same manifold pressure, but the cropped impeller and large housing could not provide high pressure at altitude.
How do you get that I suggest that there were no aces flying Tomahawks in the Western Desert ????
IIRC, you earlier have stated that a 3-1 overclaim ratio was the norm in general, with which I agree; so why would a 2-3 overclaim ratio in the Western Desert be surprising?
Nov 22 is hardly repesentive of the whole period; the picture is very different if you look at 29 Nov and 5 + 12 Dec, and the norm is generally somewhere in between those outliers.
Btw, if you do want to use aces as a measure of fighter type success, you should try verifying the victories of the top scoring Allied ace over the desert with known Axis losses.
Given that an aircraft is operating at the same RPM, how does the extra power get translated into torque or forward motion? Via the prop pitch?
The extra power would be absorbed by increasing the prop pitch. Less power to run supercharger means more to the prop, essentially it's like a small engine car not running the air conditioningGiven that an aircraft is operating at the same RPM, how does the extra power get translated into torque or forward motion? Via the prop pitch?
To add to what Sr6 said: the engines with suffix M (45M, 50M) were also operating on greater maximum boost: +18 psi vs. +16 psi. All of this meant perhaps 150-200 HP more power under ~5 thousand feet (with ram) for the Spitfires with the 45M or 50M. Take off power was also modestly increased, the take off boost still being limited to +12 psi.
Merlins 45M and 50M were the closest equivalents of the V-1710 of mid-war, engine powers maxing out at almost 1600 HP down low.
I also have a mechanics diary from the 33rd FG who mentioned specifically sanding and polishing the wing leading edges on the fighters. My thought was "why just the leading edges?" But I guess now I know.
That is really interesting since it seems the British were able to get the P-40 F or L ("Kittyhawk II") to 370 mph at 20k ft in testing (though other tests show down around 355 at lower boost). P-40K modified to P-40N standards also famously got to 378 during testing though that too depended a lot on configuration and boost settings. That plus the Australian test makes me wonder if the later model P-40s (F, K and L) were faster than the Spit V generally speaking.
I would expect the Spitfire was better streamlined and has a thinner and slightly shorter wing, a generally more powerful engine (at least at higher altitudes) and is also considerably lighter so that drag is surprising to me. Was that from production issues from rapid ramping up?
The P-40F and L were the versions with Packard Merlin V-1650-1.
Advantages vs. plain vanilla Spitfire V might be: better carb, ram air intake (no ice guard) & exhausts, fit&finish (although the P-40 probably was not as good as P-51 in that regard - that's IMO), retractable tailwheel, possibly the windscreen. Not sure about cooling system, by 1942 neither was in world class.
Disadvantages: thicker wing, main U/C sticking out when retracted a bit.
(I've listed the stuff that should matter with drag, probably some other details can also be found)
P-40N received a new version of V-1710, with improved altitude power (still not up the V-1650-1 standard, though) , so it should be faster than P-40K and earlier. The P-40N that clocked 378 mph was a lighter & less draggy version, with 2 HMGs deleted (less weapon-related drag) and one fuel tank also removed, as well as other bits and pieces - weight can influence the speed a bit.
WRT speed - the Spitfire V and later P-40s (P-40M, N, plus F and L) were probably as evenly matched as one can imagine, typically between 360 to 370 mph. The P-39N/Q was faster than either, BTW, and P-51A was still faster.
Desire to have as many Spitfires as possible certainly meant that some corners were cut. That is not just a thing of fit&finish, but also some other choices that got to be made - BP glass is easier to fit and retrofit to the outside rather than to inside (corrected with Mk-VII and on, but not retroactively on previous examples), draggy undercarriage, no decision to copy exhausts from Bf 109E, no streamlined rearview mirror etc. Not having good carbs on Merlin already before the ww2 was an unfortunate oversight (impacted not just top speed, but also ceiling and negative-G use).
Spitfire VII and later corrected a lot of this (carb, exhausts, BP glass installation), meaning that Mk.IX was measured to have same Cd0 as the Mk.V, despite receiving much bigger radiators.
The value of the constant speed prop and its governor are often not appreciated or understood by those who don't work with them regularly. Essentially, they constantly vary the pitch of the propeller to keep the load on the engine matched to its torque at the selected RPM and manifold pressure, thus keeping RPM constant. In combat or other acrobatic flight this is a godsend, as the pilot doesn't have to monitor the tach and jockey throttle to keep revs within limits. Throttle can be adjusted to desired thrust throughout maneuvers without worrying about revs, and the engine can be kept at its most efficient RPM through all changes of airspeed, attitude, and G load.Given that an aircraft is operating at the same RPM, how does the extra power get translated into torque or forward motion? Via the prop pitch?
One of the reasons Rolls Royce fell in love with the P-51 was its superior fit and finish. Hives complaining to Freeman 8 Nov 1942:
"The manufacturing finish of the Spitfire is bad. This is shown up by the variation from machine to machine in performance, and the controls. We do not think it is sufficient to improve the paintwork, although this is the last thing we should want to stop, but given a continuity of production we should expect the aircraft to be manufactured to a higher quality."