drgondog
Major
The P-51B at 5% less GW had less induced drag for the same throttle settings, altitude and load out. It was not 'cleaner'. In fact the windscreen canopy enclosure was slightly 'draggier' than the P-51D bubble canopy.
P-38 vs P-51: Full internal fuel dogfighting
- Thread starter gjs238
- Start date
Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
drgondog
Major
Tomo - I just checked 106-00001 P-51D Three View and 117-00001 P-51H Three View. The elevator and aileron data I presented is correct. Gruenhagen did transpose the P-51D and P-51H elevator and aileron deflection data and I just sent him an email just in case somebody else hasn't noted this before.
drgondog
Major
I just pulled 102-00001 P-51B 3 View and found more data different from Bob's page 176 posting. He lumped B/C/D/K in one column and there were several differences such as 50 degree flap for B and 47 for D/K, Vertical Stab area of 20.02 sq ft versus Bob's 20.68 sq ft for B/C/D/K... there are a few more that I pointed out to him in an email.
In Gruenhagen's defense it could have simply been an editor error in transcribing from type written to editor copy and Bob missed it on revue.. It happened to me on my last corrections with (Schiffer) Our Might Always.
In Gruenhagen's defense it could have simply been an editor error in transcribing from type written to editor copy and Bob missed it on revue.. It happened to me on my last corrections with (Schiffer) Our Might Always.
That's fascinating, I didn't know the F-15 used engine bleed air to pressurize the tanks. I know the F-106 used some kind of engine-driven bleed-air system to move fuel around in the tanks though (there was a concern that a single round could incapacitate the whole thing).
Makes enough sense
For the Me-109 and Fw-190's...
I never even knew who he was, but I know about one sports-car he built.
Now that's pretty cool: I guess you flew during the Vietnam War era into the 1980's right?
You mean the P-51D had 5% less gross weight and less induced drag? Because if I read what you said right, the P-51B was 5% lighter and had less induced drag, and was draggier than the P-51D...
I am puzzled regardless how the P-51D was less maneuverable than the P-51B and thus at low-speeds was less maneuverable at lower speeds than the Me-109, and at higher speeds, more so (if I recall altitude provided a disadvantage for the Me-109 due to having less power up there).
drgondog
Major
"
You mean the P-51D had 5% less gross weight and less induced drag? Because if I read what you said right, the P-51B was 5% lighter and had less induced drag, and was draggier than the P-51D...
I am puzzled regardless how the P-51D was less maneuverable than the P-51B and thus at low-speeds was less maneuverable at lower speeds than the Me-109, and at higher speeds, more so (if I recall altitude provided a disadvantage for the Me-109 due to having less power up there).
No. The P51B w/85 gallon tank, at full load out, with the same 1650-7 engine as the P-51D also at full load out is 4-5% lighter than the P-51D. Induced drag is related to Lift and proportional to the square of CL.
Another point which should be made is that all the references to '440mph' points to the P-51B-1 and -5 with no 85 gallon tank and having the 1650-3 for best performance at 29,000 feet. For that condition the weight differences are closer to 10% from the fully loaded P-51D.
The P-51B and D with 1650-7 's both have FTH at 24-25000 feet and top speed at 67" MP roughly the same top speed at 25,000 feet ~ 437 mph at full GW with slight edge to the P-51B-10, -15 and all prior blocks modified to include the 85 gallon tank.
The REAL benefit for the weight differences isn't top speed for same GW conditions. They are turn radius and Climb (notable) and acceleration (very slightly)
You mean the P-51D had 5% less gross weight and less induced drag? Because if I read what you said right, the P-51B was 5% lighter and had less induced drag, and was draggier than the P-51D...
I am puzzled regardless how the P-51D was less maneuverable than the P-51B and thus at low-speeds was less maneuverable at lower speeds than the Me-109, and at higher speeds, more so (if I recall altitude provided a disadvantage for the Me-109 due to having less power up there).
No. The P51B w/85 gallon tank, at full load out, with the same 1650-7 engine as the P-51D also at full load out is 4-5% lighter than the P-51D. Induced drag is related to Lift and proportional to the square of CL.
Another point which should be made is that all the references to '440mph' points to the P-51B-1 and -5 with no 85 gallon tank and having the 1650-3 for best performance at 29,000 feet. For that condition the weight differences are closer to 10% from the fully loaded P-51D.
The P-51B and D with 1650-7 's both have FTH at 24-25000 feet and top speed at 67" MP roughly the same top speed at 25,000 feet ~ 437 mph at full GW with slight edge to the P-51B-10, -15 and all prior blocks modified to include the 85 gallon tank.
The REAL benefit for the weight differences isn't top speed for same GW conditions. They are turn radius and Climb (notable) and acceleration (very slightly)
drgondog
Major
P-51 Mustang Performance
Great site. That said, you have to look VERY carefully at each summary narrative to glean critical GW and external configuration. Most of the top speeds and climb rates contained in the various Flight Test reports are a.) do not have both full internal fuel load out (269 gallons) and full ammunition load, and b.) have the external bomb racks attached.
The other factor when looking at the three different P-51s (B/C without 85 gallon tank having the 1650-3, B/C with 85 gallon tank modified at Depot also having 1650-3, and B/C with factory 85 gallon tank but using the 1650-7) to compare with P-51D/K (all P-51D/K in combat units in ETO/MTO/PTO/CBI had 1650-7) for Performance - is that you have to look at 'apple to orange' comparisons for power plant.
Great site. That said, you have to look VERY carefully at each summary narrative to glean critical GW and external configuration. Most of the top speeds and climb rates contained in the various Flight Test reports are a.) do not have both full internal fuel load out (269 gallons) and full ammunition load, and b.) have the external bomb racks attached.
The other factor when looking at the three different P-51s (B/C without 85 gallon tank having the 1650-3, B/C with 85 gallon tank modified at Depot also having 1650-3, and B/C with factory 85 gallon tank but using the 1650-7) to compare with P-51D/K (all P-51D/K in combat units in ETO/MTO/PTO/CBI had 1650-7) for Performance - is that you have to look at 'apple to orange' comparisons for power plant.
So with the same engine and 85-gallon tank, the P-51D was 4-5% lighter?
So without the 85-gallon tank, the P-51B's were 10% lighter?
Why would the P-51B have a slight advantage if it had the same fuel-load, FTH, and weighed 4-5% more?
So the P-51D would turn tighter at the same fuel status for a given engine?
drgondog
Major
Zipper - please re-read #107 carefully.
Also, to help you do the math
Empty Tank weight = 55 pounds
85 gallons of fuel =~ 510 pounds
6x50 caliber guns =~414 pounds
1880 rounds of 50 Cal =~ 620 pounds
4x50 caliber guns =~276 pounds
1260 rounds of 50 Cal =~ 422 pounds
The Delta in ammo/guns between the P-51A/B/C and P-51D/K is (620+414) - (422+276) = 336 pounds
The Delta in 85 gallon tank plus full fuel = 565 pounds.
Summary - The P-51B-1-NA 43-12093 with 1650-3 Merlin, as tested at Eglin, did not have a Fuselage Tank or extra 85 gallons of fuel. All P-51D had the 85 gallon tank installed at factories and when tested with full fuel and ammo, not only weighed 900 pounds more than the P-51B-1 but also had the 1650-7 Merlin.
The empty weight difference (No Guns, No Ammo, no 85 gallon fuel tank, no fuel (wings and fuselage), no bomb racks) between the P-51B and P-51D is 7205-6988 = 217 pounds
Note: Dean's data for ammo weight on pg 329 of America's 100K for 1880 rounds of 50 caliber is nearly 50 pounds too low. His data of 576 pounds would be good for 1710 rounds. That said page 328 and 329 are best single source for NAA published data across several sources.
Also, to help you do the math
Empty Tank weight = 55 pounds
85 gallons of fuel =~ 510 pounds
6x50 caliber guns =~414 pounds
1880 rounds of 50 Cal =~ 620 pounds
4x50 caliber guns =~276 pounds
1260 rounds of 50 Cal =~ 422 pounds
The Delta in ammo/guns between the P-51A/B/C and P-51D/K is (620+414) - (422+276) = 336 pounds
The Delta in 85 gallon tank plus full fuel = 565 pounds.
Summary - The P-51B-1-NA 43-12093 with 1650-3 Merlin, as tested at Eglin, did not have a Fuselage Tank or extra 85 gallons of fuel. All P-51D had the 85 gallon tank installed at factories and when tested with full fuel and ammo, not only weighed 900 pounds more than the P-51B-1 but also had the 1650-7 Merlin.
The empty weight difference (No Guns, No Ammo, no 85 gallon fuel tank, no fuel (wings and fuselage), no bomb racks) between the P-51B and P-51D is 7205-6988 = 217 pounds
Note: Dean's data for ammo weight on pg 329 of America's 100K for 1880 rounds of 50 caliber is nearly 50 pounds too low. His data of 576 pounds would be good for 1710 rounds. That said page 328 and 329 are best single source for NAA published data across several sources.
Peter Gunn
Master Sergeant
Trying to get a handle on all this, you guys make me feel like a real dummy...
Question on the Merlins used, or really the differences between them, specifically the 1650-3 and the 1650-7, I'm assuming one was optimized for higher altitude performance? And then how does the 1650-9 of the H model fit in?
Thanks.
Question on the Merlins used, or really the differences between them, specifically the 1650-3 and the 1650-7, I'm assuming one was optimized for higher altitude performance? And then how does the 1650-9 of the H model fit in?
Thanks.
The -3 was the hi-alt model, the -7 was mid-altitude among the 2-stage supercharged Merlins. Main difference between the two was the supercharger multiplication gearing. The -9 was a new version, having many common fetures with the Merlin 100 series from Rolls Royce. One of features added was provision for water injection, meaning a considerable jump in short-term power.
Peter Gunn
Master Sergeant
Many thanks Tomo, much appreciated.
drgondog
Major
Tomo is correct. Much of the data for the -9 was the same as the -3 with two significant differences. The -9 FTH in High Blower (at 67") was around 26000 vs 29000 at (47") for the -3, and the engine itself was more robust to withstand 90" Boost with WI.
The crankshaft design with end to end oil feed is a very desirable feature over the -3 and -7.
The crankshaft design with end to end oil feed is a very desirable feature over the -3 and -7.
Peter Gunn
Master Sergeant
In perusing Tomo's chart I see the use of 100/130 grade fuel, so would it be correct to assume then that they'd be running at 67" boost and not 75"?
And to further be a pain with dumb questions, what would the -9 be capable of with 44-1 and running 90" MP?
And to further be a pain with dumb questions, what would the -9 be capable of with 44-1 and running 90" MP?
There won't be 90 in Hg of boost unless water/alcohol injection is used on the Packard Merlin. With w/a injection, 115/145 fuel (post war) and 90 in Hg of boost, the power was 2220 HP in low gear (9000 ft), or 1790 HP in high gear (22700 ft); both altitudes with ram, ie. actual flying aircraft. From here
These charts show a bit greater power: link.
These charts show a bit greater power: link.
I did the math and got a different delta and numbers than you diddrgondog said:
P-51B-1NA
Empty: 6988 pounds
Guns & Ammo: 7686 pounds (delta: 698 lbs)
Fuel in Wings: 8790 pounds (delta: 1104 lbs)
P-51D
Empty: 7205 pounds
Guns & Ammo: 8239 pounds (delta: 1034 lbs)
Fuel in Wings: 9343 pounds (delta: 1104 lbs)
Center Tank: 9853 pounds (delta: 510 lbs)
P-51D had 1043 pounds vs 900 pounds on the P-51B (I've found a multitude of different weight figures for the P-51B also, I'm not sure what to make of them), though in truth it would be more like 533-713 because in combat you would have already either drained the center tank or had 30 gallons at max present.
As for turning performance, the P-51D had a slightly different wing and less drag. With the turning circle can I just vary the weight difference, or is this going to require more complicated calculations due to the wing and drag?
I'm not sure if I missed something, but why would you want to reduce FTH on the P-51D's over the P-51B/C if they're being used as bomber escorts?
Better lubrication it sounds
I wouldn't say that -- it's a complicated subject and drgondog might be an aerospace engineer, and I have a combination of asperger syndrome, and obsessive compulsive disorder.
wuzak
Captain
Still more than enough performance at escort altitudes while giving improved rate of climb and level performance at altitudes where most of the fights occur.
ie better all-round performance
wuzak
Captain
Somewhere around that.
But you are overlooking the fact that when the bombers were attacked the escorts chased after the fighters which, in most cases, saw the lose altitude.
