Spitfire Mk.XIV vs P-51D Mustang

[kool kitty89]

OK, heres the thread I was referring to, but it doesn't include the P-51 like I'd thought:
http://www.ww2aircraft.net/forum/technical/man-hours-build-aircraft-10190.html

 

[kool kitty89]

However at about 16k ft, the Fw-190D-9 engine starts losing significant power, while the P-51 engine is into its second wind. This starts to show up around 20k where the P-51 gains significant improvement of airspeed over the Fw.

Airspeed
P-51B 442 mph
Fw-190D-9 426 mph
Significant advantage P-51

Inless you're talking about the P-51 at 75" boost (with 100/150 grade fuel) that's much too fast.

P-51 Mustang Performance (which tends to be a bit biased toward allied a/c anyway)

Gives ~420-426 mph at 20,000 ft at 67" for the P-51B with either the 1650-3 or -7. (as power oupput was similar for both engines at this altitude)

I don't think the Mustang had a significant speed advantage over the Dora until ~23,000 ft.




And Bill,
Don't forget the P-51D's armament was also less prone to jamming than the earlier mustangs. (and wasn't there a structural redesign that allowed higher diving speeds without risking a structural failure)

 

[Soren]

The P-51B didn't climb at 4,700 ft/min Davparlr, not even at 75" MAP where at at the most reached 4,380 ft/min.

At 75" MAP the P-51B-15's performance figures were as follows:

Top Speed: 388 mph at SL, 444 mph at alt.
Climb rate: 4,380 ft/min

These figures are from WWIIaircraftperformance.

 

[davparlr]

We had this a couple of times now and there is no "truth" in neither what you or Soren say, because it's all just seculation.

Well, I admit that "the truth" was in my opinion only. However, I still think my premise is correct.

Besides that, the Tempest II never seeing any action was due to a pretty messed up production planning not because it wasn't needed.

I'll bet that if there was a critical need, the production problem would be solved quickly.

It also makes more sense to evaluate the Dora vs. the P-51 D because the transition had progressed well when the Dora arrived in numbers and I highly doubt the USAAF would've ever switched back because of the B's small performance advantage.

The fact that there were a number of P-51Bs flying at wars end has been established.

But here are some comparisons with the P-51D. There is a strange note here. The climb rates have been modified to 75" Hg, however, I have not determined a factor for updating airspeed to 75" Hg yet, so the airspeed numbers below for the P-51D is at 67" Hg. I expect the 75" Hg numbers to be closer to the P-51B numbers but a bit less. P-51B airspeed at 75" Hg numbers are in parenthesis.

20k
A/S
Fw-190D-9 426 mph
P-51D 421 mph (442 mph)

Climb
Fw-190D-9 2992 ft/min
P-51D 3080 ft/min
Note: I made an error in the previous entry in the P-51B climb at 20k, rate should be 3480 ft/min, not 2940 ft/min.

25k
A/S
Fw-190D-9 417 mph
P-51D 440 mph (440 mph)

Climb
Fw-190D-9 2158 ft/min
P-51D 2350 ft/min

And, with a better dive, I think you can see that even the P-51D would be quite a handful for the Fw-190D-9 at 20k ft. and above.

Inless you're talking about the P-51 at 75" boost (with 100/150 grade fuel) that's much too fast.

By the time the Fw-190D-9 arrived, 75" boost had been approved,

http://www.wwiiaircraftperformance.org/mustang/75inch-clearance-v-1650-7.jpg

and used.

http://www.spitfireperformance.com/mustang/combat-reports/357-yeager-6nov44.jpg

Of course I used 75" boost.

P-51 Mustang Performance (which tends to be a bit biased toward allied a/c anyway)

Are up implying that Spitfire Performance alters government test documents to reflect a bias?

I don't think the Mustang had a significant speed advantage over the Dora until ~23,000 ft.

I think you will find that test results at 75" boost does not support this comment (see my data.)

The P-51B didn't climb at 4,700 ft/min Davparlr, not even at 75" MAP where at at the most reached 4,380 ft/min.

The test report you refer to has a test weight of 9680 lbs for the P-51B which is about the fighter weight of the P-51D (according to "America's Hundred Thousand"). The fighter weight of the P-51B is about 9070 lbs. I think if you calculate climb performance with 600 lbs less, you will be pretty close to the 4700 ft/min rate at SL.

 

[kool kitty89]

Didn't the P-51 have a problem with the 100/150 grade fuel due to the merlin's tendency for spark plugs to foul rather heavily and rapidly when using it. (compared to the R-2800 and V-1710 which were deemed satifactory in terms of fouling using 100/150 grade)

 

[KrazyKraut]

Hello KrazyKraut
Later Tempest Vs with Sabre IIB were faster than 190D-9 at sea level and up to appr 9500ft and then again from 19500ft upwards, early Tempest Vs with Sabre IIA were faster than 190 D-9 between appr. 1,000 - 10,000 ft and then again from 19500ft upwards.

Juha

I don't know too much about the Tempest V, but according to some accounts I read from German pilots they found the Dora to be about as or slightly slower than the Tempest at low altitude but found its climb and maneouverability to be better. These are subjective assessments of course and also depend on fit and finish of the respective pilot's aircraft. For every aircraft mentioned here there is a wide range of different performance graphs available that's why I won't jump on the figure posting wagon. If I find the time I'll try to research some representative stats and draw my conclusions then. So far I'll go by the wording of the books I have which all pretty much say that these aircraft were about even, with the Dora's performance dropping off rather sharply above critical altitude.

 

[davparlr]

Didn't the P-51 have a problem with the 100/150 grade fuel due to the merlin's tendency for spark plugs to foul rather heavily and rapidly when using it. (compared to the R-2800 and V-1710 which were deemed satifactory in terms of fouling using 100/150 grade)

All I know is what is on the internet. Apparently higher maintenance was required but production was high and there were several reports of 70+boost being used. Maybe someone else has knowledge of its usage.

 

[drgondog]

All I know is what is on the internet. Apparently higher maintenance was required but production was high and there were several reports of 70+boost being used. Maybe someone else has knowledge of its usage.

Plug fouling was a problem with the 150 octane fuel and the crew chiefs basically changed the plugs every two missions. Speculation was that a very high percentage of engine failures resulting in a lost Mustang in late 1944 through the end of the war were in fact due to the fuel/plug issues.

The 1650-9 which came out in the P-51H, and retrofitted in post war P-51D's apparently were more reliable with the 150 octane.

 

[davparlr]

Plug fouling was a problem with the 150 octane fuel and the crew chiefs basically changed the plugs every two missions. Speculation was that a very high percentage of engine failures resulting in a lost Mustang in late 1944 through the end of the war were in fact due to the fuel/plug issues.

The 1650-9 which came out in the P-51H, and retrofitted in post war P-51D's apparently were more reliable with the 150 octane.

On further reading, it appears that the Air Force did a review and determined that plug fouling was the main issue with the fuel and replacement/cleaning was required at about 50% of the time of the previous fuel. This affected the P-38, 47, and 51 equally. Procedures, like reducing idle time and "blowing" out the engine, were generated to ease the fouling problems. Also, it appears that all P-51s, 38s, and 47s, were issued the 100/150 fuel in May, '44.

The report is included in this summary.

150 Grade Fuel

 

[Soren]

9,300 lbs seems to be the fighter weight of the P-51B davparlr, not 9,080 lbs.

 

[DAVIDICUS]

"This affected the P-38, 47, and 51 equally."

c. P-51 (V-1650 Engines).

The same type of lead fouling as described in a and b above happened in the case of the P-51 except that is was probably more serious than in either of the other two types.

 

[DerAdlerIstGelandet]

Wow, been a long time since you posted here! Where have you been?

 

[davparlr]

9,300 lbs seems to be the fighter weight of the P-51B davparlr, not 9,080 lbs.

Data from "America's Hundred Thousand"

P-51B

Basic weight 7325
Pilot 200 (from P-51D data)
Useable Oil 94 (from P-51D data)
Cal. 50AMMO 378 (from P-51A data, four machine guns)
Internal Fuel 1080 (from P-51D data)
Gross weight 9077

P-51D

Basic weight 7673
Pilot 200
Useable Oil 94
Cal. 50AMMO 564 (six machine guns)
Internal Fuel 1080
Gross weight 9611

Basic weight is empty weight plus trapped fuel, machine guns, and pyrotechnics.

A detailed breakdown of Empty Weight and Basic Weight of the P-51B is in the book, too.

 

[drgondog]

Data from "America's Hundred Thousand"

P-51B

Basic weight 7325
Pilot 200 (from P-51D data)
Useable Oil 94 (from P-51D data)
Cal. 50AMMO 378 (from P-51A data, four machine guns)
Internal Fuel 1080 (from P-51D data)
Gross weight 9077

P-51D

Basic weight 7673
Pilot 200
Useable Oil 94
Cal. 50AMMO 564 (six machine guns)
Internal Fuel 1080
Gross weight 9611

Basic weight is empty weight plus trapped fuel, machine guns, and pyrotechnics.

A detailed breakdown of Empty Weight and Basic Weight of the P-51B is in the book, too.

Dave - I believe that would be for full (184 gallons) wing tanks and empty fuse tank. Having said that most of the 51 jocks burned a minimum of 50 gallons out of the fuse tank while forming up and climbing out. I know my father burned all before switching to external tanks - except on max range mission like the last Shuttle Mission - so the weight as you describe is pretty good combat weight for a 51 at Berlin or Leipzig or Brunswick - after dropping external tanks.

 

[Soren]

According to wright field it is 9,300 lbs for the P-51B and 9,700 lbs for he P-51D.

 

[drgondog]

According to wright field it is 9,300 lbs for the P-51B and 9,700 lbs for he P-51D.

P-51B-5 43-6883 April 24 1944 @ Wright Pat
9205 with full fuel and ammo and pilot and oil - no fuse tank fuel

P-51B-15 43-24777 May 15, 1944 @ Wright Pat
P-51B-15 43-24777 May 20, 1944 @ Wright Pat
9680 w/265 Gallons Fuel (wing and 71 gal fuse) and ammo
9335 w/265 Gallons Fuel (wing and 71 gal fuse) - No Ammo

Subtract ~460 pound for the 71 gallons in the 85 gallon tank expended before crossing German border and the approximate fighting weight for a fully loaded ammo and wing tank fuel configuration and subtract another 50 pounds for oil consumption

P-51B in combat config over Brunswick to Augsburg = ~9150-9170 pounds after dropping external tanks

 

[Vincenzo]

so need to think that luftwaffe interceptors can fly with only half fuel

 

[ratdog]

you couldnt get very far with only half a tank of fuel.....

 

[drgondog]

you couldnt get very far with only half a tank of fuel.....

so need to think that luftwaffe interceptors can fly with only half fuel

'half fuel" for the P-51B and D was enough to fight and fly home to East Anglia from Berlin - and represented the most typical combat condition when engaging the Luftwaffe on Target escort.

So to your points - the 51 cruises at about 235 -250 for best specific fuel consumption at 45 gph and ~ 46" Hg at 2500.. if unmolested, the P-51 "full wing tanks" of 184 gallons is LESS than 1/2 fuel for take off condition - so do the math? The 51 could drop tanks, engage for 10-15 minutes at 240gph over Berlin and still have enough to fly 600 miles back to England

The Luftwaffe interceptors were probably at 2/3 fuel remaining and only had about 40minutes high speed cruise plus 10 minutes of combat left by the time their day started with a fight... and lucky to stay in the air another 100 miles.

So, what point are you trying to make? That the Mustang weight for performance calculations in a dogfight should be Max TO weight for long range escort mission to a target 600 miles away? Or look at the weight as it was most likeley to engage? That is what Dave was saying (and I agree for what it is worth).

 

[Vincenzo]

the point is that if in real engage the p-51 haven't full fuel also the luftwaffe fighter haven't full fuel, and AFAIK commonly interceptors take off already with no full fuel