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I would say a Griffon P51 would maintain that advantage because the Spitfire was limited by its propeller diameter.My data, mostly from Spitfireperformance, shows a max speed of the P-51B (-3) at sea level (which I think is the best measurements for aerodynamic performance) is 370 mph at 67" (max speed of the -7 engine at 67" was 360 mph). Fastest speed I found for the Spitfire IX, the Merlin 66, was 336 mph (18 lbs boost, equivalent to 67" US). This supports the claim that the Mustang was 20 - 30+ mph faster than the equivalently powered Spitfire, at SL.
Great post S/R shouldn't there be an additional BHP loss through the added output of the supercharger.?It shouldn't consume a lot more while cruising. Power required it pretty much dependent on drag. Yes the extra weight will cause a bit of extra drag ( higher angle of attack for wing at same speed) but that is going to be rather small. Larger radiator scoop? but airflow through the radiator will be in proportion to the power being made.
That leaves the actual fuel economy of the engine. The Griffon is 36% bigger in swept volume to be sure but it runs approximately 10% slower. It also has about 22% more scrubbed area of cylinder wall and pistons scrubbing cylinder walls are roughly 75-80% of the friction in an engine. Fiction goes up with the square of the speed soooo.......
Running an engine even 200rpm slower can make a difference in friction losses (one big reason for dropping the revs and using high boost (relatively) for cruising.
A clean Mustang (tanks gone) can cruise at over 300mph true at 1850, boost not given, at 25,000ft using 59 gallons an hour. I don't know what the power is but is seems to be well under 700hp. (2400rpm and 36in/3lb is 775hp at 22,500ft)
I have no idea what settings are needed to get 5-600hp out of a Griffon at 22-25,000ft.
That was exactly my point posted before. As an escort the P51 did not have to out perform the enemy, even with the Me262 it could still have an affect simply by making sure it kept at close to maximum speed to avoid combat not the best speed to hit the bombers. In absolute performance it was behind the Tempest at low level and many LW aircraft at high level, about on par in speed but not allround performance with Griffon Spitfires. The jet age had already arrived but in terms of propeller driven aircraft the P51 was not the best, it was quite obviously good enough though to do the job that was asked of it, over Berlin and Poland.? From mid 44, to the end of the war the P-51D with high octane fuel, was a class A fighter easily contesting the skies over Germany and Japan. Not until late 1944 did Germany generate any aircraft that could challenge the Mustang but never had the quantity to do it.
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Great post S/R shouldn't there be an additional BHP loss through the added output of the supercharger.?
My argument in this case is that there isn't a free lunch. In my opinion the Griffon would have used at least as much fuel if not more when cruising and would certainly have used more while on station and in combat. Against this the Griffon is heavier while the P51 was pushing the boundaries of safe take off weights with a Merlin.If the Griffon is making 25-33% more power at a given rpm (using the same manifold pressure) then it doesn't need to turn as many rpm to make "cruising power" in a low drag airframe.
I am not saying the Griffon is better than the Merlin in fuel consumption but the automatic assumption that it is a fuel hog when cruising may need a lot closer look.
Obviously once you go to power settings over 2400rpm and 7lbs boost (max lean) fuel consumption can skyrocket
Since the Spitfire 'swallowed' the 2-stage Griffon without breaking a sweat, looks like the supposed early 1930s airframe have had more stretch than it's designer team ever reckoned. Modifications nothwitsanding.
Spitfire's aerodynamic technology was unmatched by many design tems in years to come. By 1944, the only thing that was aerodynamically probelmatic was layout of it's big radiators. Other people also went with brute power when available (including NAA, Republic, Hawker, Focke Wulf), so that point is moot.
It's a bit of a myth that the Mustang was significantly faster than a Spitfire with the same engine. The oft-quoted statement that the Mustang was '20-30 mph faster' applied to an early Spitfire IX with the Merlin 61 (nominally capable of 403 mph). By contrast the Spitfire HFIX with normal wing-tips and the Merlin 70 could do 419 mph, which suggests that a P51B would be ~10 mph faster if both aircraft were in pristine condition. Of course, the Mustang's wing was much more sensitive to dirt and dents and after a few missions the speeds would probably be more-or-less identical. The top speed of about 430 mph for the P51 is also quoted in Bowyer and Sharp's Mosquito.
Hello
if somebody has enough info on CAC CA-15, that might give a clue on "Griffon P-51" consumption.
The Spitfire did break a sweat with the Griffon. It essentially became impractical and unsafe to loop in realistic circumstances and its handling deteriorated. The spitfires 1930s NACA 4 digit airfoils came at a cost fitness could not overcome.
The Spitfire was made possible by the maturity of the PV12 Merlin, it's superchargers and 100/130 fuel. If it had of been forced to operate with Allison V-1710 or DB601/605 it would have given away so much speed, climb and sustained turn its legend would probably not have been made.
It required the Me 109G1 and the DB605A of 1942 to match the 1310hp the Spitfire had in 1940.
The Spitfire did break a sweat with the Griffon. It essentially became impractical and unsafe to loop in realistic circumstances and its handling deteriorated. The spitfires 1930s NACA 4 digit airfoils came at a cost fitness could not overcome.
Spitfire XIV has 4 tanks. They total 111 gallons. It consumed 22.5 gallons climbing to 20,000 feet, leaving 88.5 gallons.
Not quite right, the DB601E could pretty well match the 1940 Merlin III. if not exceed it handily at high altitudes. The 1310hp the Spitfire had in 1940 was at 9000ft and power faded to the normal 1030hp at 16250ft, ram not included. the MerlinX XIIin the Spitfire II was only coming into service in small numbers at the end of the BoB.
There was NO 100/130 in the Bob. more like 100/115. A Spitfire I with a -33 Allison would have performed almost the same. A Spitfire MK I with a DB601A-1 wouldn't have been much different either. 1020ps at 4500meters (14850ft just 1,400ft below the Merlin) isn't going to show a huge difference.
and strangely enough, the Spitfire, with it's 1930s airframe and old airfoil was faster than the 109E that was smaller and lighter but had almost the same power.
The Spitfire did break a sweat with the Griffon. It essentially became impractical and unsafe to loop in realistic circumstances and its handling deteriorated. The spitfires 1930s NACA 4 digit airfoils came at a cost fitness could not overcome.
The Spitfire was made possible by the maturity of the PV12 Merlin, it's superchargers and 100/130 fuel. If it had of been forced to operate with Allison V-1710 or DB601/605 it would have given away so much speed, climb and sustained turn its legend would probably not have been made.
It required the Me 109G1 and the DB605A of 1942 to match the 1310hp the Spitfire had in 1940.
<snip>
(So jimmie Doolittle did win the BoB)
The Spitfire always had 200-300 more horse power
Me 109E v Spitfire I-III. 1050 to 1310
Me 109F v Spitfire V. 1200 to 1460
Me 109G1 1.3 ata v Spitfire IX. 1300 v 1560 two stage Merlin 61
Me 108G6 1.42 ata V Spitfire IX. 1420 v 1700 two stage Merlin 66
Even with the 1800hp to 2000hp 1.8 to 1.98 ata DB605DB/DC the Merlin on 100/150 seemed 200 hp more powerful.
However when the Me 109 had close to the same power it seemed much faster than the Spitfire.
Power = improved manouverbillity and speed.
A 1320 hp Me 109 would beat a 1100 hp Spitfire but it was infact the other way around.
Regarding post 42, how does propeller diameter limit a Spitfire?
The Reno racers are all running propeller smaller than stock because they don't want the prop tip to exceed something near Mach 0.85 (actual number a team secret). And the two or three fastest ones are all over 530 mph top speed at 5,000 feet. All you have to do is move to coarse pitch and you go faster, assuming you have the power to keep spinning the prop at whatever rpm you are turning.
It isn't quite that simple, but the speed record planes of today all use smaller props than wartime stock.