Ending the Argument

[davparlr]

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.

 

[pbehn]

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.

I would say a Griffon P51 would maintain that advantage because the Spitfire was limited by its propeller diameter.

 

[pbehn]

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.

Great post S/R shouldn't there be an additional BHP loss through the added output of the supercharger.?

 

[pbehn]

? 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.

.

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.

 

[Shortround6]

Great post S/R shouldn't there be an additional BHP loss through the added output of the supercharger.?

might depend on the cruise settings?
again the supercharger power required is somewhat proportional to the sq of the speed of the impeller (or it's tips).


Griffon 61 used 13.4 and 11.3 in impellers and 5,84 and 7.58 gears.
Merlin V-1650-3 used 12 and 10.1in impellers and 6.39 and 8.095 gears.

Using 2000rpm cruise for the Merlin the impeller tips are moving at 847fps on the big impeller in high gear and using 1800rpm for the Griffon the the tips are moving 797fps on the big impeller in high gear if I have done the math right. The Griffon will be moving more air per revolution of the impeller so it isn't tip speed alone but at cruising speeds the supercharger isn't sucking up anywhere near the power they do at full speed. For example the supercharger will use 2.25 times the power at 2700 engine rpm as it does at 1800 engine rpm.

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

 

[pbehn]

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

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.

 

[Koopernic]

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.

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 Griffon Spitfire did climb like the clappers and above 25000ft.

The Tempest with Griffon probably would have been a faster aircraft.

 

[Shortround6]

A P-51D with wing racks empty could do about 5.5 miles to the US gallon at 25,000ft while doing 335mph which is a bit higher than they used/planned for cruising. I don't have the pilot's manual at hand to show the charts with underwing loads.
I do believe a Griffon engine versions would use a bit more gas but since the Mustang was using under 700hp hp (maybe way under) I don't see why the Griffon engine would use that much more while cruising? Once you go to combat settings where the Griffon is making hundreds of horsepower more than the Merlin it is going to use fuel in proportion the power made. If the Griffon is making 20% more power it is reasonable to assume it will use 20% more fuel.
The B-17s cruised about 180mph and the P-51s "while on station" were doing 305 or above and essing above them. They were going to esse regardless of engine or version of engine.

Max take-off for a P-51D included either a pair of 1000lb bombs or a pair of 165 gallon drop tanks. You can use 110 gallon drop tanks and save 710lbs worth of fuel and tanks (the 110 gallon tanks weigh less than the 165 gallon tanks) .
Granted this may not have been the best idea from ALL air fields but on the other hand, the Griffons would not have been installed by units in the field. Proper bracing and upgraded landing gear would have been part of the package.

Please note I am not advocating such a conversion. It would not have been available in enough numbers to do anything until well into 1944 and only at the cost of shorting other programs of Griffons unless you can magic up a completely new engine factory.

 

[Koopernic]

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.

The P-51B had in essence the Merlin 61.
The P-51D had in essence the more powerful Merlin 66 whose supercharger was set to a lower altitude but because of greater boost and power was almost as fast as the P-51B despite its loss in high altitude power.
A P-51B/C/D with a high altitude Merlin 70 would have been extremely fast. I'm guessing 450mph.

Although the mustangs wing easily lost laminarity due to bugs, dirt and dings the very same gradual positive pressure distribution designed into it also greatly delayed compressibility and shock drag. At Mach 0.66 it made a difference. Eastman Jacobs, who designed the wing mathematically knew of this. Jacobs was designing a transonic aircraft called jakes Jeep.

 

[Koopernic]

Hello
if somebody has enough info on CAC CA-15, that might give a clue on "Griffon P-51" consumption.

 

[Shortround6]

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.

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.

 

[wuzak]

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.

Never seen that before. Where did you get that information.

From what I have read the Spitfire XIV had much the same handling as Merlin versions, and was rated as more manoeuverable because of the extra power.

 

[Stig1207]

Spitfire XIV has 4 tanks. They total 111 gallons. It consumed 22.5 gallons climbing to 20,000 feet, leaving 88.5 gallons.

Including warmup? 22.5 gallons from start to 20.000 ft seems to be low fuel consumption in comparison with other numbers I have seen.

Forgot to specify that I haven't seen other numbers for the Spitfire. I have read, somewhere, figures giving fuel consumption of 28 gallons from start to 5.000 ft for a P-40.

 

[Koopernic]

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.

You are misled about the fuel grade during the BoB, as I was earlier.

http://www.newcomen.com/wp-content/uploads/2012/12/Chapter-11-Marshall.pdf
I also invested in an SAE paper
A Short History of Aviation Gasoline Development, 1903-1980


The USAAC decided to convert to 100 octane fuel in 1935 after Shell and Standard had delivered useful quantities. The US specification steadfastly focused on the lean ON octane number and was indifferent to rich mixture response. The process used was polymerisation of isobutylene to create iso-octane and the feedstock was in short supply. This was a far sighted decision. Without the US decision of 1935 it there would be no plant to produce 100 octane of any type for the RAF for 1939.

As a result of the guaranteed orders the US oil industry developed and invested in the following production capacity.
1 addition of tetraethyl lead
2 synthesis of iso octane
3 catalytic cracking with regenerative catalyst (Houdry process)
4 Acid alkylation of butane and propane (a British patent, it improved both lean and rich mixture response, it hadn't been developed but was serendipitous). US invested purely to increase lean response.

This ensured that when the UK required 100/130 it was merely a matter of blending from the above options which were all coming on line in 1938.

(So jimmie Doolittle did win the BoB)

The Germans started construction of alkylation plants in 1940 but only one was ever completed and that was in 1943. It takes that long to build plant. Britain's 1937 work on 100 octane would be too late for the BoB were it not for the 1935 US decision. The Germans were suck with synthesis of iso octane because cracking didn't work well with synthetic fuel and alkylation plant s took too long to build.


Although there were initial British experiments with US 100 ON octane they had for years had an appreciation of rich mixture responses.

The Schneider Trophy races with the Rolls Royce R-type (early Griffon) used fuels consisting of acetone, benzol(benzene & toluene), methanol which had a massive charge cooling and rich mixture anti knock effect)

The initial 1937 air ministry specification still lacked a performance number but it did have a work instruction for blending cuts of fuel that would produces fuel that would have a ON/PN of around 100/130. The actual 130PN requirement came later when the test engines had been developed and manufactured to prove this from samples taken from production. There was no such PN test engines in the USA till 1942.

The British specification for blending however produced a fuel of 100/130 from the very beginning. Initially it relied on exotic Caribbean fuels or of Borneo from its overseas possessions and colonies.

US 100 octane was 100 ON but the specification was indifferent to the rich mixture. In reality it was probably around 100/120, same as pure octane The US was interested in sustained economical sustained power.

The BoB 100 octane was 100/130 from the beginning. It was controlled but not as tightly as it was from 1942 and it's possible they used 100/125.
===========

The fuel Britain and France used in WW1 was approx 75ON. It was distilled from crudes taken from the Caribbean and Asia. American crude is inferior and aviation fuel X supplied in WW1 was only 45 to 55 ON ran well in the well designed Liberty engine but not in Nieupoerts or Sopwiths.
============


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.

 

[Milosh]

The R-R R engine is not directly related to the 1939 Griffon. There was a derated R known as the Griffon tested in 1933.

 

[tomo pauk]

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 1st sentence is your opinion. 2nd sentence is hard to comprehend for a non-original speaker.

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.

??
Spitfire became a legend already in 1940, when there was no 100/130 grade fuel, DB 605, and V-1710s were produced in penny packets.
It is not a fault of the Spitfire that RR came out with ever better engines, it is to it's credit that it was able to accept those engines in timely manner and without problems.
Shove the DB 601A on the Spitfire I or DB 601E on the Spit V and difference will be barely felt.

It required the Me 109G1 and the DB605A of 1942 to match the 1310hp the Spitfire had in 1940.

Wrong on year stated, engine stated and Bf 109 version stated.
It also seems like the altitude where power is attained ceased to be relevant for ww2 aircraft.

 

[tomo pauk]

<snip>
(So jimmie Doolittle did win the BoB)

Hugh Dowding won it, if we really want to pick a person.

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

For such a Luftwaffe fanboy, I don't know why posting wrong data?
DB-601E: 1450 PS
DB 601A restricted: 1400
DB 605A full: 1540

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.

Bf 109 was far smaller aircraft, with limitations involved due to the size. Spitfire was rarely out-climbed, from 1941 on usually carried twice the cannons, and was capable for carrying much greater fuel tankage and bigger & much more powerful engines. Also better visibility.

Power = improved manouverbillity and speed.

A 1320 hp Me 109 would beat a 1100 hp Spitfire but it was infact the other way around.

It was not.
Curiously enough, there was no recon Bf 109s flying 600+ miles and back, free from interception. Unlike the Spitfires.

 

[Barrett]

Intriguing subject--thank you for bringing the article to our attention. Enjoying the skookum comments from so many knowledgable folks. I was in the antique-warbird community at the time (1990) but missed it. FWIW, the wartime joint fighter conferences held at Patuxent River and Eglin Field showed the F4U as the best fighter-bomber and in fact the best fighter in some regimes. I knew two participants. Rex Barber (of Yamamoto fame) said that if the US were to build one fighter, it should be the F4U. Grumman test pilot Corky Meyer tended to agree, though with some Hellcat reservations!

 

[GregP]

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.

 

[Shortround6]

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.

Modern racers at operating at 5-7,000ft? with Reno temperatures that is equivalent to what at sea level on a "standard" day? even higher? but a far cry from the prop needed at 25,000ft.

and prop optimized for speed is different than a prop optimized for climb.

Fighter props are almost always going to be a compromise between different requirements.