That's a great start, except...I've got a Mac that's such an antique, the OS WINE supports is too new: they're at 10.8, & I'm still running 10.5...
Yeah, I'll make it as easy as possible and share it in a universal format (not .xls). In fact, I (literally, this is my network test on it) just recently got my personal laptop up and running again for the first time since the kids fried it in May and have gone to Linux so I will be converting most of my files out of Office formats anyway.
As for the equations themselves, I have done all sorts of stuff with ballistics over the years. The nice thing is when it come terminal ballistics it is all based on nice and easy E=(1/2)MV^2 (aka E=MC^2). Now, in-flight ballistics...yeesh
I can point you to some good references and resources online for all that, though if you like. Shoot me a PM if you're interested.
marathag
Banned
If you dig around, you can find WINE version that will run on that, I had one for 10.2
marathag
Banned
When I had done it, I got it in by using FINK, but that was when 10.2 hadn't been out for long, but you really need to like playing with the linux side of things to go that route
A preview of the data (which is almost ready, I just need to wash and repeat to get Rate of Climb for the other propellers):
Hamilton-Standard 3 blade Hydromatic
Take-Off Weight: 18,347 Lbs.
Best Climb (VY) (Sea Level, 3200 RPM @ 64"Hg "Dry" 1760 BHP/Engine): 4141 ft/min @ 169.2 mph
Best Climb (VY) (Sea Level, 3200 RPM @ 76"Hg "Wet" 2314 BHP/Engine): 5769 ft/min @ 174.5 mph
Maximum Speed Achieved (VH)(*20,800 ft, 3200 RPM @ 76"Hg "Wet" 2314 BHP/Engine): 474.5 mph
*Critical Altitude for 76"Hg M.P. with RAM effect.
I already have the VH for each A/C in 5000 ft increments (with 20,800 replacing 20,000). I have finally gotten all the maths done for Rate of Climb calculation and am running those numbers now.
One interesting thing I have discovered is that regardless of which A/C (propeller) I use, I cannot get a level speed above about 480 at any realistic loading...the airplane has too much drag and is too heavy. A better finish, some major weight loss, and maybe new wings (or an anachronistic modern high performance propeller) will be able to get it over the 500 mark but unlike Republic (when they made their one-off 502mph P-47) Lockheed doesn't have the time to bother doing it.
Hamilton-Standard 3 blade Hydromatic
Take-Off Weight: 18,347 Lbs.
Best Climb (VY) (Sea Level, 3200 RPM @ 64"Hg "Dry" 1760 BHP/Engine): 4141 ft/min @ 169.2 mph
Best Climb (VY) (Sea Level, 3200 RPM @ 76"Hg "Wet" 2314 BHP/Engine): 5769 ft/min @ 174.5 mph
Maximum Speed Achieved (VH)(*20,800 ft, 3200 RPM @ 76"Hg "Wet" 2314 BHP/Engine): 474.5 mph
*Critical Altitude for 76"Hg M.P. with RAM effect.
I already have the VH for each A/C in 5000 ft increments (with 20,800 replacing 20,000). I have finally gotten all the maths done for Rate of Climb calculation and am running those numbers now.
One interesting thing I have discovered is that regardless of which A/C (propeller) I use, I cannot get a level speed above about 480 at any realistic loading...the airplane has too much drag and is too heavy. A better finish, some major weight loss, and maybe new wings (or an anachronistic modern high performance propeller) will be able to get it over the 500 mark but unlike Republic (when they made their one-off 502mph P-47) Lockheed doesn't have the time to bother doing it.
Those are impressive numbers. Is that with the H-S high activity paddle bladed propellers?
It is, indeed. All four props are pretty close to equal but each is a little better in different areas. The H-S has the best high-altitude performance and the highest ceiling but it suffers against the AeroProducts propeller in top speed because it was designed to be most efficient in the 2000 +/- bhp range, where the AP was built specifically for the 2300+ bhp of the new engines.
Ok, I had to tweak some numbers and refine my methods a bit but I think I have it now. Speed and Climb tables are done and the framework for the report and the surrounding narrative is also done. I just need to do some rough range estimations and then I will have a complete comparison and the final recommendations.
Ch.28 - P-38J Propeller Comparison (Feb 1944)
ARMY AIR FORCES
MATERIEL COMMAND
MEMORANDUM REPORT ON
YP-38J Airplane, AAF Nos. 43-28250, 43-28251, 43-28252, 43-28253
SUBJECT: Flight Tests
SECTION: Flight
A. Purpose
1. To report comparison of YP-38J airplane propeller installations as received from the manufacturer.
B. Methods
1. Standard Performance Flight Tests were carried out on four different YP-38J airplanes, AAF Nos. 43-28250, 43-28251, 43-28252, and 43-28253. Each airplane was subjected to multiple tests under similar conditions and the performance of each test batch was collected and adjusted for standard variances.
C. Condition of Aircraft during Tests
1. A/C #43-28250:
a. The airplane was equipped with wing racks, otherwise the configuration was normal with all flights at a gross weight at take-off of 18,347 pounds with the c.g at 23.25% m.a.c., gear down; and 26.75% m.a.c. , gear up. Gross weight included 400 gallons of fuel, 26 gallons of oil, 30 gallons of Water, 457 lbs. of ballast for ammunition, and automatic observer, complete radio equipment and antenna, and 200 pounds for the pilot. All items effecting the drag of the airplane may be seen in the photographs which are included at the end of the report.
b. The airplane was equipped with Allison V-1710-117 & 119 engines with water injection, type B-33 turbo superchargers with A-13B turbo regulators and 12 ft. 6 in. diameter Hamilton-Standard three blade propellers (Propeller 1) through a 2.36:1 reduction. All power figures are based on a power curve from Eng. Spec. No. 303, dated 22 November 1943.
c. The armament consisted of four 50 caliber machine guns and one 20 mm. cannon in the nose with 457.5 lb. of ballast corresponding to the weight of 1200 rounds of 50 caliber and 150 rounds of 20 mm. ammunition.
d. All flights were made with flaps neutral, gear up, air filter off, intercooler, coolant and oil shutters automatic, and mixture automatic rich unless otherwise stated.
2. A/C #43-28251:
a. The airplane was equipped with wing racks, otherwise the configuration was normal with all flights at a gross weight at take-off of 18,351 pounds with the c.g at 23.25% m.a.c., gear down; and 26.75% m.a.c. , gear up. Gross weight included 400 gallons of fuel, 26 gallons of oil, 30 gallons of Water, 457 lbs. of ballast for ammunition, and automatic observer, complete radio equipment and antenna, and 200 pounds for the pilot. All items effecting the drag of the airplane may be seen in the photographs which are included at the end of the report.
b. The airplane was equipped with Allison V-1710-117 & 119 engines with water injection, type B-33 turbo superchargers with A-13B turbo regulators and 12 ft. 6 in. diameter Curtiss Electric three blade propellers (Propeller 2) through a 2.36:1 reduction. All power figures are based on a power curve from Eng. Spec. No. 303, dated 22 November 1943.
c. The armament consisted of four 50 caliber machine guns and one 20 mm. cannon in the nose with 457.5 lb. of ballast corresponding to the weight of 1200 rounds of 50 caliber and 150 rounds of 20 mm. ammunition.
d. All flights were made with flaps neutral, gear up, air filter off, intercooler, coolant and oil shutters automatic, and mixture automatic rich unless otherwise stated.
3. A/C #43-28252:
a. The airplane was equipped with wing racks, otherwise the configuration was normal with all flights at a gross weight at take-off of 18,264 pounds with the c.g at 23.5% m.a.c., gear down; and 27.0 % m.a.c. , gear up. Gross weight included 400 gallons of fuel, 26 gallons of oil, 30 gallons of Water, 457 lbs. of ballast for ammunition, and automatic observer, complete radio equipment and antenna, and 200 pounds for the pilot. All items effecting the drag of the airplane may be seen in the photographs which are included at the end of the report.
b. The airplane was equipped with Allison V-1710-123 & 126 engines with water injection, type B-33 turbo superchargers with A-13B turbo regulators and 11 ft. 10 in. diameter AeroProducts four blade propellers (Propeller 3). The V-1710-123 & 126 engines are identical to the V-1710-117 & 119 engines with the exception of using a 2.24:1 reduction. All power figures are based on a power curve from Eng. Spec. No. 303, dated 22 November 1943.
c. The armament consisted of four 50 caliber machine guns and one 20 mm. cannon in the nose with 457.5 lb. of ballast corresponding to the weight of 1200 rounds of 50 caliber and 150 rounds of 20 mm. ammunition.
d. All flights were made with flaps neutral, gear up, air filter off, intercooler, coolant and oil shutters automatic, and mixture automatic rich unless otherwise stated.
4. A/C #43-28253:
a. The airplane was equipped with wing racks, otherwise the configuration was normal with all flights at a gross weight at take-off of 18,292 pounds with the c.g at 23.5% m.a.c., gear down; and 27.0% m.a.c. , gear up. Gross weight included 400 gallons of fuel, 26 gallons of oil, 30 gallons of Water, 457 lbs. of ballast for ammunition, and automatic observer, complete radio equipment and antenna, and 200 pounds for the pilot. All items effecting the drag of the airplane may be seen in the photographs which are included at the end of the report.
b. The airplane was equipped with Allison V-1710-123 & 126 engines with water injection, type B-33 turbo superchargers with A-13B turbo regulators and 11 ft. 10 in. diameter Curtiss Electric four blade propellers (Propeller 4). The V-1710-123 & 126 engines are identical to the V-1710-117 & 119 engines with the exception of using a 2.24:1 reduction. All power figures are based on a power curve from Eng. Spec. No. 303, dated 22 November 1943.
c. The armament consisted of four 50 caliber machine guns and one 20 mm. cannon in the nose with 457.5 lb. of ballast corresponding to the weight of 1200 rounds of 50 caliber and 150 rounds of 20 mm. ammunition.
d. All flights were made with flaps neutral, gear up, air filter off, intercooler, coolant and oil shutters automatic, and mixture automatic rich unless otherwise stated.
D. Flight Characteristics
1. It is understood that each tested A/C behaves similarly under most flight and ground conditions so detailed evaluation of specific handling characteristics were not performed as part of the comparison evaluation. Individual Flight Acceptance Performance Tests for each airplane are available and include the general Flight data.
E. Factual Data
1. High Speed
a. High Speeds in flight at 3200 rpm and 64”Hg M.P., oil flaps automatic, coolant flaps automatic, and intercooler shutters automatic. These speeds for A/C #3 and #4 were obtained with the Unit Engine Control disengaged to achieve the indicated engine Speed and M.P.
b. High Speeds in flight at 3200 rpm and 76”Hg M.P. using Water Injection, oil flaps automatic, coolant flaps automatic, and intercooler shutters automatic.
2. Cruise Data
Cruising speed at 12,100 feet with mixture as specified, oil shutters flush, coolant shutters automatic, and intercooler closed. This cruise data was obtained on A/C #1 and #2 by setting engine speed and M.P. to match the Unit Engine Controls of A/C #3 and #4.
3. Climb Data
Climb performance at 3200 rpm with oil and coolant shutters automatic, and intercooler shutters wide open. These speeds for A/C #3 and #4 were obtained with the Unit Engine Control disengaged to achieve the indicated engine Speed and M.P.
Climb performance at 3200 rpm using Water Injection with oil and coolant shutters automatic, and intercooler shutters wide open. Tests were performed in series and total Time to Climb was calculated based on the achieved average maximum rate of climb for at each altitude.
4. Estimated Ceilings
Military Ceiling for maximum Rate of Climb of 500 ft. per minute and absolute ceiling for maximum rate of climb of 0 ft. per minute are estimated from Climb and Speed curves.
F. Conclusions
1. A/C #1 (#43-28250) displays the best low speed efficiency, best Rate of Climb, and highest ceiling under all conditions.
2. A/C #3 (#43-28252) displays the best high speed efficiency and top speed.
3. A/C #3 (#43-28252) shows the best cruise speed at the tested altitude and engine settings, equating to the best range.
4. A/C #2 (#43-28251) closely replicates the performance of A/C #1 (#43-28250) and A/C #4 (#43-28253) closely replicated the performance of A/C #3 (#43-28252).
5. A/Cs #1 and #2 are heavier and produce more drag due to the larger diameter propellers and engine nacelles.
G. Recommendations
1. That production P-38J airplanes be ordered with Allison V-1710-123 & 126 engines (F-33R and L) using either the AeroProducts Four blade or Curtiss Electric Four blade propellers.
2. That the airplanes be constructed in such a way that the entire propeller assemblies may be changed by aircraft mechanics at operational fighter groups.
3. That all production P-38J airplanes be equipped with the boosted ailerons
4. That the airplanes use the cockpit as found in A/C #4 (#43-28253) using a single control stick
5. That the arming switch on the control stick be replaced with a rotary type selector switch on the top of the stick with positions for SAFE (OFF) – Machine Guns Only – BOTH Machine Guns and Cannon – Cannon Only.
6. That the airplanes all be fitted with the Unit Engine Control system.
7. That the Unit Engine Control be redesigned to allow automatic access to 3200 rpm at and above Normal Military Power of 54”Hg. M.P.
MATERIEL COMMAND
MEMORANDUM REPORT ON
YP-38J Airplane, AAF Nos. 43-28250, 43-28251, 43-28252, 43-28253
SUBJECT: Flight Tests
SECTION: Flight
A. Purpose
1. To report comparison of YP-38J airplane propeller installations as received from the manufacturer.
B. Methods
1. Standard Performance Flight Tests were carried out on four different YP-38J airplanes, AAF Nos. 43-28250, 43-28251, 43-28252, and 43-28253. Each airplane was subjected to multiple tests under similar conditions and the performance of each test batch was collected and adjusted for standard variances.
C. Condition of Aircraft during Tests
1. A/C #43-28250:
a. The airplane was equipped with wing racks, otherwise the configuration was normal with all flights at a gross weight at take-off of 18,347 pounds with the c.g at 23.25% m.a.c., gear down; and 26.75% m.a.c. , gear up. Gross weight included 400 gallons of fuel, 26 gallons of oil, 30 gallons of Water, 457 lbs. of ballast for ammunition, and automatic observer, complete radio equipment and antenna, and 200 pounds for the pilot. All items effecting the drag of the airplane may be seen in the photographs which are included at the end of the report.
b. The airplane was equipped with Allison V-1710-117 & 119 engines with water injection, type B-33 turbo superchargers with A-13B turbo regulators and 12 ft. 6 in. diameter Hamilton-Standard three blade propellers (Propeller 1) through a 2.36:1 reduction. All power figures are based on a power curve from Eng. Spec. No. 303, dated 22 November 1943.
c. The armament consisted of four 50 caliber machine guns and one 20 mm. cannon in the nose with 457.5 lb. of ballast corresponding to the weight of 1200 rounds of 50 caliber and 150 rounds of 20 mm. ammunition.
d. All flights were made with flaps neutral, gear up, air filter off, intercooler, coolant and oil shutters automatic, and mixture automatic rich unless otherwise stated.
2. A/C #43-28251:
a. The airplane was equipped with wing racks, otherwise the configuration was normal with all flights at a gross weight at take-off of 18,351 pounds with the c.g at 23.25% m.a.c., gear down; and 26.75% m.a.c. , gear up. Gross weight included 400 gallons of fuel, 26 gallons of oil, 30 gallons of Water, 457 lbs. of ballast for ammunition, and automatic observer, complete radio equipment and antenna, and 200 pounds for the pilot. All items effecting the drag of the airplane may be seen in the photographs which are included at the end of the report.
b. The airplane was equipped with Allison V-1710-117 & 119 engines with water injection, type B-33 turbo superchargers with A-13B turbo regulators and 12 ft. 6 in. diameter Curtiss Electric three blade propellers (Propeller 2) through a 2.36:1 reduction. All power figures are based on a power curve from Eng. Spec. No. 303, dated 22 November 1943.
c. The armament consisted of four 50 caliber machine guns and one 20 mm. cannon in the nose with 457.5 lb. of ballast corresponding to the weight of 1200 rounds of 50 caliber and 150 rounds of 20 mm. ammunition.
d. All flights were made with flaps neutral, gear up, air filter off, intercooler, coolant and oil shutters automatic, and mixture automatic rich unless otherwise stated.
3. A/C #43-28252:
a. The airplane was equipped with wing racks, otherwise the configuration was normal with all flights at a gross weight at take-off of 18,264 pounds with the c.g at 23.5% m.a.c., gear down; and 27.0 % m.a.c. , gear up. Gross weight included 400 gallons of fuel, 26 gallons of oil, 30 gallons of Water, 457 lbs. of ballast for ammunition, and automatic observer, complete radio equipment and antenna, and 200 pounds for the pilot. All items effecting the drag of the airplane may be seen in the photographs which are included at the end of the report.
b. The airplane was equipped with Allison V-1710-123 & 126 engines with water injection, type B-33 turbo superchargers with A-13B turbo regulators and 11 ft. 10 in. diameter AeroProducts four blade propellers (Propeller 3). The V-1710-123 & 126 engines are identical to the V-1710-117 & 119 engines with the exception of using a 2.24:1 reduction. All power figures are based on a power curve from Eng. Spec. No. 303, dated 22 November 1943.
c. The armament consisted of four 50 caliber machine guns and one 20 mm. cannon in the nose with 457.5 lb. of ballast corresponding to the weight of 1200 rounds of 50 caliber and 150 rounds of 20 mm. ammunition.
d. All flights were made with flaps neutral, gear up, air filter off, intercooler, coolant and oil shutters automatic, and mixture automatic rich unless otherwise stated.
4. A/C #43-28253:
a. The airplane was equipped with wing racks, otherwise the configuration was normal with all flights at a gross weight at take-off of 18,292 pounds with the c.g at 23.5% m.a.c., gear down; and 27.0% m.a.c. , gear up. Gross weight included 400 gallons of fuel, 26 gallons of oil, 30 gallons of Water, 457 lbs. of ballast for ammunition, and automatic observer, complete radio equipment and antenna, and 200 pounds for the pilot. All items effecting the drag of the airplane may be seen in the photographs which are included at the end of the report.
b. The airplane was equipped with Allison V-1710-123 & 126 engines with water injection, type B-33 turbo superchargers with A-13B turbo regulators and 11 ft. 10 in. diameter Curtiss Electric four blade propellers (Propeller 4). The V-1710-123 & 126 engines are identical to the V-1710-117 & 119 engines with the exception of using a 2.24:1 reduction. All power figures are based on a power curve from Eng. Spec. No. 303, dated 22 November 1943.
c. The armament consisted of four 50 caliber machine guns and one 20 mm. cannon in the nose with 457.5 lb. of ballast corresponding to the weight of 1200 rounds of 50 caliber and 150 rounds of 20 mm. ammunition.
d. All flights were made with flaps neutral, gear up, air filter off, intercooler, coolant and oil shutters automatic, and mixture automatic rich unless otherwise stated.
D. Flight Characteristics
1. It is understood that each tested A/C behaves similarly under most flight and ground conditions so detailed evaluation of specific handling characteristics were not performed as part of the comparison evaluation. Individual Flight Acceptance Performance Tests for each airplane are available and include the general Flight data.
E. Factual Data
1. High Speed
a. High Speeds in flight at 3200 rpm and 64”Hg M.P., oil flaps automatic, coolant flaps automatic, and intercooler shutters automatic. These speeds for A/C #3 and #4 were obtained with the Unit Engine Control disengaged to achieve the indicated engine Speed and M.P.
b. High Speeds in flight at 3200 rpm and 76”Hg M.P. using Water Injection, oil flaps automatic, coolant flaps automatic, and intercooler shutters automatic.
2. Cruise Data
Cruising speed at 12,100 feet with mixture as specified, oil shutters flush, coolant shutters automatic, and intercooler closed. This cruise data was obtained on A/C #1 and #2 by setting engine speed and M.P. to match the Unit Engine Controls of A/C #3 and #4.
3. Climb Data
Climb performance at 3200 rpm with oil and coolant shutters automatic, and intercooler shutters wide open. These speeds for A/C #3 and #4 were obtained with the Unit Engine Control disengaged to achieve the indicated engine Speed and M.P.
Climb performance at 3200 rpm using Water Injection with oil and coolant shutters automatic, and intercooler shutters wide open. Tests were performed in series and total Time to Climb was calculated based on the achieved average maximum rate of climb for at each altitude.
4. Estimated Ceilings
Military Ceiling for maximum Rate of Climb of 500 ft. per minute and absolute ceiling for maximum rate of climb of 0 ft. per minute are estimated from Climb and Speed curves.
F. Conclusions
1. A/C #1 (#43-28250) displays the best low speed efficiency, best Rate of Climb, and highest ceiling under all conditions.
2. A/C #3 (#43-28252) displays the best high speed efficiency and top speed.
3. A/C #3 (#43-28252) shows the best cruise speed at the tested altitude and engine settings, equating to the best range.
4. A/C #2 (#43-28251) closely replicates the performance of A/C #1 (#43-28250) and A/C #4 (#43-28253) closely replicated the performance of A/C #3 (#43-28252).
5. A/Cs #1 and #2 are heavier and produce more drag due to the larger diameter propellers and engine nacelles.
G. Recommendations
1. That production P-38J airplanes be ordered with Allison V-1710-123 & 126 engines (F-33R and L) using either the AeroProducts Four blade or Curtiss Electric Four blade propellers.
2. That the airplanes be constructed in such a way that the entire propeller assemblies may be changed by aircraft mechanics at operational fighter groups.
3. That all production P-38J airplanes be equipped with the boosted ailerons
4. That the airplanes use the cockpit as found in A/C #4 (#43-28253) using a single control stick
5. That the arming switch on the control stick be replaced with a rotary type selector switch on the top of the stick with positions for SAFE (OFF) – Machine Guns Only – BOTH Machine Guns and Cannon – Cannon Only.
6. That the airplanes all be fitted with the Unit Engine Control system.
7. That the Unit Engine Control be redesigned to allow automatic access to 3200 rpm at and above Normal Military Power of 54”Hg. M.P.
Ch.28b - The Future of the Lightning (15 Feb 1944)
15 February 1944
Wright Field, Ohio, USA
The stack of memorandum reports on the performance testing of the various P-38J models dominated Lt. Col. Kelsey’s desk. In addition to the comparison summary report of the four different propeller installations there was the full performance report for each aircraft and a fifth for #43-28254 which was similar to #43-28250 with its 117/119 engines and Hamilton-Standard Hydromatic but which had an additional 600 pounds of pressurization equipment and bulkheads.
The cost of pressurization, when taken in direct comparison to #250, was about a 3,000 foot reduction in critical altitude, a loss of about 200 peak bhp, a reduction of 10 mph top speed at critical altitude. In addition the best rate of climb without water injection was reduced by nearly 400 feet per minute, or about 10%, at sea level. In light of the potential performance losses, especially in the rate of climb, Kelsey was inclined to halt additional attempts to pressurize the P-38 which would have the additional benefit of keeping Lockheed’s resources available for continued development on the XP-80.
The decision was made easier to sell to the Air Force brass due to the recent submissions for Very Long Range escort fighters. North American Aviation submitted a novel adaptation of their experimental lightweight P-51F which joined two of them together into a “Twin-Mustang” distantly resembling a P-38 without the central gondola—instead each “boom” was a complete P-51 fuselage. Vultee—or Convair as it was now known—submitted two proposals: one was an advanced twin-propulsion design which would use a turbo-prop for normal cruise flight and supplement it with a turbojet for high-speed requirements. The other Convair submission was a direct result of their increased involvement with the P-38 and was essentially the Lockheed plane with a lightened and improved gondola and newly designed laminar flow wings.
This latter design was the one the AAF ended up ordering for prototyping as the XP-81 due to the expected shorter development timeline and it would compete directly against NAA XP-82 Twin-Mustang.
The Convair XP-81 would feature a two-seat tandem cockpit which was derived directly from the two-seat gondola of the TP-38. Drawing on Lockheed’s patents to use turbo-supercharger bleed air for pressurization and Vultee’s previous work on the XP-54 the XP-81 cockpit would be pressurized and so long as they could meet the delivery deadlines should obviate the need for a pressurized P-38 and allow earlier availability of the P-38J.
One part of the pressurized P-38J that Kelsey was recommending be kept was the canopy. It was superior to the current P-38 canopy in almost every way. Based on the canopy Lockheed developed for the XP-80, tt consisted of a revised forward windscreen, optimized for pressurization but with the additional advantage of being lighter than the current windscreen due to a smaller bullet-proof panel. The frame where the new one-piece sliding bubble canopy meets the new windscreen was angled forward at the top, creating a slight impediment to the pilot’s vision at a narrow angle but increasing head space over the dash which would allow fitting a gunsight with a larger aperture and finally allow aimed deflection down over the nose the airplane.
All that remained was to submit his final recommendations regarding the P-38J. His final recommendation was largely the same as the recommendations included with the summary report with a few additional points appended to the original.
Lockheed estimated that it would up to four weeks per production line to make the switch to the new design with the potential of additional delays due to Curtiss Electric’s production schedule. Since AeroProducts was currently well under capacity and were ready to begin full production of the new propeller immediately he concluded with one final recommendation:
With that, Kelsey could only hope that the Bell airplanes could be to Europe in time for invasion of France in the coming spring.
Wright Field, Ohio, USA
The stack of memorandum reports on the performance testing of the various P-38J models dominated Lt. Col. Kelsey’s desk. In addition to the comparison summary report of the four different propeller installations there was the full performance report for each aircraft and a fifth for #43-28254 which was similar to #43-28250 with its 117/119 engines and Hamilton-Standard Hydromatic but which had an additional 600 pounds of pressurization equipment and bulkheads.
The cost of pressurization, when taken in direct comparison to #250, was about a 3,000 foot reduction in critical altitude, a loss of about 200 peak bhp, a reduction of 10 mph top speed at critical altitude. In addition the best rate of climb without water injection was reduced by nearly 400 feet per minute, or about 10%, at sea level. In light of the potential performance losses, especially in the rate of climb, Kelsey was inclined to halt additional attempts to pressurize the P-38 which would have the additional benefit of keeping Lockheed’s resources available for continued development on the XP-80.
The decision was made easier to sell to the Air Force brass due to the recent submissions for Very Long Range escort fighters. North American Aviation submitted a novel adaptation of their experimental lightweight P-51F which joined two of them together into a “Twin-Mustang” distantly resembling a P-38 without the central gondola—instead each “boom” was a complete P-51 fuselage. Vultee—or Convair as it was now known—submitted two proposals: one was an advanced twin-propulsion design which would use a turbo-prop for normal cruise flight and supplement it with a turbojet for high-speed requirements. The other Convair submission was a direct result of their increased involvement with the P-38 and was essentially the Lockheed plane with a lightened and improved gondola and newly designed laminar flow wings.
This latter design was the one the AAF ended up ordering for prototyping as the XP-81 due to the expected shorter development timeline and it would compete directly against NAA XP-82 Twin-Mustang.
The Convair XP-81 would feature a two-seat tandem cockpit which was derived directly from the two-seat gondola of the TP-38. Drawing on Lockheed’s patents to use turbo-supercharger bleed air for pressurization and Vultee’s previous work on the XP-54 the XP-81 cockpit would be pressurized and so long as they could meet the delivery deadlines should obviate the need for a pressurized P-38 and allow earlier availability of the P-38J.
One part of the pressurized P-38J that Kelsey was recommending be kept was the canopy. It was superior to the current P-38 canopy in almost every way. Based on the canopy Lockheed developed for the XP-80, tt consisted of a revised forward windscreen, optimized for pressurization but with the additional advantage of being lighter than the current windscreen due to a smaller bullet-proof panel. The frame where the new one-piece sliding bubble canopy meets the new windscreen was angled forward at the top, creating a slight impediment to the pilot’s vision at a narrow angle but increasing head space over the dash which would allow fitting a gunsight with a larger aperture and finally allow aimed deflection down over the nose the airplane.
All that remained was to submit his final recommendations regarding the P-38J. His final recommendation was largely the same as the recommendations included with the summary report with a few additional points appended to the original.
Lockheed estimated that it would up to four weeks per production line to make the switch to the new design with the potential of additional delays due to Curtiss Electric’s production schedule. Since AeroProducts was currently well under capacity and were ready to begin full production of the new propeller immediately he concluded with one final recommendation:
With that, Kelsey could only hope that the Bell airplanes could be to Europe in time for invasion of France in the coming spring.
@phx1138 it's posted
I shortened the followup narrative. Instead of a full discussion I just had it summarized by Kelsey to get the main points across.
A note regarding the performance figures...I settled for "good enough" like I said I would and to get the numbers to looks right (and feasible) I had to add more drag than I had originally expected but considering it is still using pretty high-drag wings that may be expected. The Zero-Lift Coefficient of Drag for the OTL P-38L was about 0.0268 and I had originally though the NACA redesign could get that down to about 0.0215-0.0230 but when I used those figures for the A/C I ended up getting Speeds in excess of 510 mph. My options then were either mess with the propeller efficiency curves to bring them down a touch, add drag, or do a bit of both. For simplicity I just added added drag to bring the numbers down but realistically the Cd0 is probably around 0.024-0.025 and the propeller efficiencies are probably a bit less that I used in the equations. To give you an idea of the props, here is a graph showing the combined curves of efficiency (eta) over Advance Ratio (J = V[fpm]/Prop.RPM/Prop.Diameter)--this is the total curve rather than breaking it down to each prop. pitch as in normally done for these (again, I was looking for good-enough, not exact):
I shortened the followup narrative. Instead of a full discussion I just had it summarized by Kelsey to get the main points across.
A note regarding the performance figures...I settled for "good enough" like I said I would and to get the numbers to looks right (and feasible) I had to add more drag than I had originally expected but considering it is still using pretty high-drag wings that may be expected. The Zero-Lift Coefficient of Drag for the OTL P-38L was about 0.0268 and I had originally though the NACA redesign could get that down to about 0.0215-0.0230 but when I used those figures for the A/C I ended up getting Speeds in excess of 510 mph. My options then were either mess with the propeller efficiency curves to bring them down a touch, add drag, or do a bit of both. For simplicity I just added added drag to bring the numbers down but realistically the Cd0 is probably around 0.024-0.025 and the propeller efficiencies are probably a bit less that I used in the equations. To give you an idea of the props, here is a graph showing the combined curves of efficiency (eta) over Advance Ratio (J = V[fpm]/Prop.RPM/Prop.Diameter)--this is the total curve rather than breaking it down to each prop. pitch as in normally done for these (again, I was looking for good-enough, not exact):