What if the F-82 was based off the XP-51F/G instead of the P-51H?

[BarnOwlLover]

Pretty informative. This is the sort of info I've been been looking for for a while, and why when I got back interested in World War II aircraft I came here.

It's also the figures I've commonly seen for the P-51B/D climb rates being only 3200-3600 fpm, when it's been disclosed at that combat weight and on combat power it was more like 4400-4500 fpm, and on half fuel (sort of interceptor trim) it got as high as 4900+fpm.

Planes like the Spitfire and the Me-109 it has to be said that the figures quoted for them as far as especially climb are basically what you see is what you get. Because as point interceptors (by World War II definitions), when flying clean they were for their missions almost certainly flying with full fuel or close to it on take off, due to limited fuel capacity and range. For escort fighters, as you pointed out, things are different and hence combat weight vs TO weight factors in.

BTW, basic SAC manuals did say that the P-51H was normally capable of 5000+ fpm, while the larger one does go into deeper detail on climb rates and speeds and under what conditions they could be expected to be achieved. I do sort of doubt that such info from SAC exists for the XP-82 or P-82B since only about 22 Merlin Twin Mustangs got made, the rest were Allison powered, and in terms of climb and top speed, were noticeably inferior to the Merlin versions.

 

[Shortround6]

Planes like the Spitfire and the Me-109 it has to be said that the figures quoted for them as far as especially climb are basically what you see is what you get. Because as point interceptors (by World War II definitions), when flying clean they were for their missions almost certainly flying with full fuel or close to it on take off, due to limited fuel capacity and range.

Yes and No.

You do have to careful that you are comparing the "normal climb" to the "combat climb". The British especially would rate planes using a 30 minute rating for the engine.
For most Merlins this was 2850rpm and 9lbs of boost. Combat climb (the the British did not use the terms WEP or WER) was 3000rpm and whatever boost rating the particular Merlin was rated for.
Same for Griffons except the RPM was 2600 for climb and 2750rpm for combat. Climb using a Griffon and 18lbs of boost could be pretty amazing.
The Americans would often use the 5 minute "military" rating for climb and then drop to "normal (1 hour or more) for the duration of the climb.
Yes you can find the climb speeds at higher boost levels but make sure you are comparing the same thing.
A DH Hornet using 20lbs of boost was still climbing at 4600fpm at 18,000ft, Sea level was over 5500fpm.

 

[BarnOwlLover]

For the P-51H as far as SAC's detailed findings, there's this on page 4 of this document:

http://www.wwiiaircraftperformance.org/mustang/F-51H_Mustang_SAC_-_22_March_1949.pdf

This gives speed and climb ratings for various situations. It should be noted under the interceptor portion that the P-51H was still climbing at over 3200 fpm at 25,000, from an initial climb of almost 5500 ft at sea level. Based on what I've been told, the Merlin Twin Mustangs should've been capable of roughly similar performance. The basic SAC document did say that for normal missions that about 5000 fpm initial for the P-51H should be more commonly expected however.

I don't question the DH Hornet sea level climb of 5500 fpm (I've seen the document at World War II Aircraft Performance), but I do question at what weight that happened. Both books I have on the Hornet do note that clean it weighed just over 14,000 lbs, but for combat missions it seems to weight more than that (it seems between 16,500-17,500 lbs).

And I've seen on here some pretty impressive climb rates for not only the P-51H (including one as an interceptor of over 6000 fpm), but for the XP-51F and G models. Though for the latter, those were experimental lightweights flying often with boosted engines (XP-51F ran a V-1650-3/7 boosted to 90") or war emergency (XP-51G) and were flying light (75 gallon fuel tanks) to try an get them to 500 mph (they ultimately did 493 and 495 per NAA respectively, while RAE reportedly got 498 out of a P-51G they tested).

Which does circle around to the origins of this thread. If there was a lighter version of the F-82 based on the F/G models (and not evolved from the H), what would it's performance been like possibly? I'd bet that speed might be slightly better (not by much, looking at the P-51H vs the F/G), but climb would probably improve due to reduced weight, though range would take a hit (?).

The XP-51F/G only had the wing tanks, which could hold up to 105 or so gallons of fuel (more than the P-51B/D's wing tanks). Part of why they were redesigned to become the P-51H was to house a 50 gallon fuselage tank. That being said, I've seen F-82 cutaways, and I've never seen one with a fuselage tank as standard.

 

[PStickney]

For the P-51H as far as SAC's detailed findings, there's this on page 4 of this document:

http://www.wwiiaircraftperformance.org/mustang/F-51H_Mustang_SAC_-_22_March_1949.pdf

This gives speed and climb ratings for various situations. It should be noted under the interceptor portion that the P-51H was still climbing at over 3200 fpm at 25,000, from an initial climb of almost 5500 ft at sea level. Based on what I've been told, the Merlin Twin Mustangs should've been capable of roughly similar performance. The basic SAC document did say that for normal missions that about 5000 fpm initial for the P-51H should be more commonly expected however.

I don't question the DH Hornet sea level climb of 5500 fpm (I've seen the document at World War II Aircraft Performance), but I do question at what weight that happened. Both books I have on the Hornet do note that clean it weighed just over 14,000 lbs, but for combat missions it seems to weight more than that (it seems between 16,500-17,500 lbs).

And I've seen on here some pretty impressive climb rates for not only the P-51H (including one as an interceptor of over 6000 fpm), but for the XP-51F and G models. Though for the latter, those were experimental lightweights flying often with boosted engines (XP-51F ran a V-1650-3/7 boosted to 90") or war emergency (XP-51G) and were flying light (75 gallon fuel tanks) to try an get them to 500 mph (they ultimately did 493 and 495 per NAA respectively, while RAE reportedly got 498 out of a P-51G they tested).

Which does circle around to the origins of this thread. If there was a lighter version of the F-82 based on the F/G models (and not evolved from the H), what would it's performance been like possibly? I'd bet that speed might be slightly better (not by much, looking at the P-51H vs the F/G), but climb would probably improve due to reduced weight, though range would take a hit (?).

The XP-51F/G only had the wing tanks, which could hold up to 105 or so gallons of fuel (more than the P-51B/D's wing tanks). Part of why they were redesigned to become the P-51H was to house a 50 gallon fuselage tank. That being said, I've seen F-82 cutaways, and I've never seen one with a fuselage tank as standard.

Pardon my contradiction, but, other than a superficial visual similarity, the P-51H and the P-82 have nothing in common.

The P-82 (North American Design NA-123) from the start was a high performance all-weather capable Very Long Range Escort Fighter, conceived in 1943, the design presented in January 1944, and the initial contract let in February 1944. And that they did. A P-82B, carrying 4 drop tanks, flew from Hawaii to New York, something over 5,000 miles, nonstop, at an average speed of 347 mph. That's still the record for a piston-engined fighter.

The P-51H (North American Design NA-126) is a restringing of the earlier K models (Identical to the D but with an Aeroproducts rather than a Hamilton Standard propeller) with the application of lessons learned, and more evolved construction techniques, with the hottest engine they could get stuffed in the nose. This was the result of the poor showings of the "Lightweight" Mustangs - (It's worth noting that despite their high performance on paper, their poor stability and control characteristics and limitations as a weapon (Lower limiting G, fewer guns, less fuel, lower bomb loads) None of the lightweight Mustangs got more than 50-60 flight hours, I believe), and the decision was made to make a "Normal" weight Mustang applying the lessons learned. The initial contract was let in June 1944, anticipating the completion of the design.

When it comes to airplane speed performance, particularly a high speeds weight isn't very relevant - the component of the aircraft's drag that's weight related decreases as speed increases. Induced Drag, or Drag Due to Lift - basically drag produced by how hard the wing is working to make the required amount of lift) It's significant at low speeds, but not at the high end.

The real issue is the engine/propeller combination, and how it turns power into thrust.
At a given power setting, a piston engine (Or the gearbox end of a turboprop) produces a fixed amount of power. The propeller turns it into thrust.
Power = Thrust * Velocity * Units conversion * propeller efficiency.
(Units conversion is getting all your units straight.
For example, to get HP from Thrust in lbs and speed in ft/sec, it sould be
1/550 - for speed in mph, it would be 1/375, and so forth.)

So - that gives us Power = T*(Vmph/375) * Eff.
Or, to solve it for thrust, T = P * (375/Vmph) * Eff.
This means that as speed goes up, the amount of thrust that the engine-propeller combination produces is decreasing linearly with speed.
Just plugging in some numbers:
for a 1000 Hp engine, Ideal (Eff = 1) Thrust at:
100 mph = 3750 lbs
200 mph = 1875 lbs
300 mph = 1250 lbs
400 mph = 935 lbs
450 mph = 833 lbs
500 mph = 750 lbs
When you figure in Propeller Efficiency, it gets much worse. At speeds below 400 mph, the efficiency, as a rule, will be around 0.85 - but, as speeds increase, and more of the propeller goes transonic, the efficiency drops sharply -
At 450 mph, it may be as low as 0.6,
Now, the drag on the airplane is increasing with the square of the airpspeed. Double the speed (say 100-200 mph) You now have 4 times the drag. Go 4 times as fast (100-400 moh) it's 16 times the drag. Because of this, Propeller powered airplanes, except in some extreme cases, are limited to a maximum speed between 450 and 500 mph. Or, to talk Mach, 'bout Mach 0.59-0.65 at sea level, and M0.68 - 0.75 at high altitudes. (36,000' or higher)

So, really, it doesn't matter much how much weight you take out,

 

[BarnOwlLover]

This sort of doesn't go along with what drgondog (one of the authors of the P-51B Bastard Stepchild book) has said about the LW P-51s in my communications with him on here. He did say that the USAAF considered the XP-51F as an interceptor, and Bob Chilton (one of NAA's chief test pilots) loved the XP-51F. The G did have stability problems, in part due to the Merlin RM 14SM making over 2000 hp vs the 1700 of the V-1650-3/7, and also the 5 bladed Rotol prop was also blamed for causing instability (and why it was ditched after only a couple of flights).

The LWs were passed over mostly because of insufficient range for long range escort, per our conversations (no room for a fuselage fuel tank). The XP-51F/G and the P-51H were designed for the same 7.33g load limit. Difference was that the H had it applied for combat weight and clean gross weight (9450/9550 lbs approx) vs the gross weights of the F/G (increased fuel and armament, as well as re-stressing for the higher weight). The Lightweights were the results of the USAAF and North American wondering why the Allison and Merlin Mustangs were heavier and slower climbing than the Spitfire.

Also, the max loading of the P-51D could be as low as 6.3g at 10,200 lbs. That's take off weight and not combat weight (which could be several hundred pounds lighter), so they weren't fighting that heavy. This basically meant that in the end the P-51H was stronger per pound than the D was at the end of the day, aside from landing gear.

And yes, I'm well aware that weight doesn't have a significant bearing on speed. It does, however, have a huge bearing on climb rate and acceleration--things that the LW program were looking to address.

And I'm also well aware of the distinction that the design of the F-82 was developed from the P-51H, not an exact clone of them mated together. I'm well aware that aside from power units for the Merlin versions that the F-82 ultimately shared few parts with the P-51H, and even fewer than the D model. The XP-82 restoration project team say that only 4-5 parts on their XP-82 were common to the D model, and only a few more with the H.

 

[drgondog]

Best Data that I have for the XP-82 - Vmax 482 mph / 25100' on 3600 HP. That would correspond to a V1650-11 Wet War Emergency (90" MAP/ 3000R) rammed, 2 engines (1800 each)
Climb numbers are 4.5 minutes to 20,000', service ceiling (100 '/min 43,100', single engine ceiling 28,900'

Information from the USAAF Aircraft Characteristics and Performance Quarterly Chart, Experimental Aircraft, October 1945,

That is one I haven't seen before. From USAAF MC Wright Field in Sarah Clark Collection or USAFHRC? or neither?

 

[BarnOwlLover]

That would be the type of info he's looking for, since he'd like to include the XP-82/P-82B in his next Mustang book, but has been having issues finding the info he wants/needs for it.

I'm also wondering why I've seen that the XP-82 was about a foot longer than the P-82B even though they're basically the same airframe powered by the same engines.

 

[drgondog]

Pardon my contradiction, but, other than a superficial visual similarity, the P-51H and the P-82 have nothing in common.

The P-82 (North American Design NA-123) from the start was a high performance all-weather capable Very Long Range Escort Fighter, conceived in 1943, the design presented in January 1944, and the initial contract let in February 1944. And that they did. A P-82B, carrying 4 drop tanks, flew from Hawaii to New York, something over 5,000 miles, nonstop, at an average speed of 347 mph. That's still the record for a piston-engined fighter.

The P-51H (North American Design NA-126) is a restringing of the earlier K models (Identical to the D but with an Aeroproducts rather than a Hamilton Standard propeller) with the application of lessons learned, and more evolved construction techniques, with the hottest engine they could get stuffed in the nose. This was the result of the poor showings of the "Lightweight" Mustangs - (It's worth noting that despite their high performance on paper, their poor stability and control characteristics and limitations as a weapon (Lower limiting G, fewer guns, less fuel, lower bomb loads) None of the lightweight Mustangs got more than 50-60 flight hours, I believe), and the decision was made to make a "Normal" weight Mustang applying the lessons learned. The initial contract was let in June 1944, anticipating the completion of the design.

When it comes to airplane speed performance, particularly a high speeds weight isn't very relevant - the component of the aircraft's drag that's weight related decreases as speed increases. Induced Drag, or Drag Due to Lift - basically drag produced by how hard the wing is working to make the required amount of lift) It's significant at low speeds, but not at the high end.

The real issue is the engine/propeller combination, and how it turns power into thrust.
At a given power setting, a piston engine (Or the gearbox end of a turboprop) produces a fixed amount of power. The propeller turns it into thrust.
Power = Thrust * Velocity * Units conversion * propeller efficiency.
(Units conversion is getting all your units straight.
For example, to get HP from Thrust in lbs and speed in ft/sec, it sould be
1/550 - for speed in mph, it would be 1/375, and so forth.)

So - that gives us Power = T*(Vmph/375) * Eff.
Or, to solve it for thrust, T = P * (375/Vmph) * Eff.
This means that as speed goes up, the amount of thrust that the engine-propeller combination produces is decreasing linearly with speed.
Just plugging in some numbers:
for a 1000 Hp engine, Ideal (Eff = 1) Thrust at:
100 mph = 3750 lbs
200 mph = 1875 lbs
300 mph = 1250 lbs
400 mph = 935 lbs
450 mph = 833 lbs
500 mph = 750 lbs
When you figure in Propeller Efficiency, it gets much worse. At speeds below 400 mph, the efficiency, as a rule, will be around 0.85 - but, as speeds increase, and more of the propeller goes transonic, the efficiency drops sharply -
At 450 mph, it may be as low as 0.6,
Now, the drag on the airplane is increasing with the square of the airpspeed. Double the speed (say 100-200 mph) You now have 4 times the drag. Go 4 times as fast (100-400 moh) it's 16 times the drag. Because of this, Propeller powered airplanes, except in some extreme cases, are limited to a maximum speed between 450 and 500 mph. Or, to talk Mach, 'bout Mach 0.59-0.65 at sea level, and M0.68 - 0.75 at high altitudes. (36,000' or higher)

So, really, it doesn't matter much how much weight you take out,A

Foremost, don'ttake the following as a contradiction - more a combined approach to add to your comments to further illustrate BarnOwls questions.

While I agree the analytical approach for thumnail performance analysis, I would suggest a couple of points.

What I cover below is straight out of NAA Performance analysis methodology applied to P-51 and P-82. Best example is NA-5534 for P-51B as discussed below. I refer to it most often, all the way back to my undergrad senior performance project.

First, drag is on the other side of the equation from Thrust and even in high V range. Induced drag is a factor (small) and AoA, as Cdp as related to CL, is a factor particularly at high altitudes/low density. Reducing Weight always 'helps'. Further it is a major determinant in another xpression for THPrequired, namely THPreq = (W/375)*(CD/CL)*V. For this equation the full set of parameters affecting CD (i.e CDp +Del CD) Mc/Minc + CDi must be set in table form to sum up to Total Drag at the desired RN and altitude.

Second, The freebody balance at top speed is that THP avail matches THP required. Various components for P-51/82 for THPavail include not only the prop/engine THP calculated from engine bench HP, ram, prop efficiences (varies through a significant range of altitude and RPM) but also the THP conversion from Thrust in pounds as f(HP, Boost, mass flow rate, exhaust gas temp and velocity, ambient temp - presented in charts constructed in collaboration by Packard, NACA and NAA). Conversely the THPreq must also consider momentum recovery of carb air as well as the drag of the Prop vortex over the inner wing and fuselage.
Next, while 400 mph is a good framework for discussion, the three prime issues for THPreq at 400mph are are a.) CDt Total Parasite Drag; b.) THPavail due to prop efficiency reduced by local mach drag rise at the tips (Much higher at 30K than SL), and c.) Mach correction to CDt vs M at varying altitudes for the entire airframe. FWIW, the Ham Std tables have around .784 for prop efficiency at 444mph @30K and .789 at 412mph @30K.

At SL, 400mph Mach no. =~ 0.53 - low on CD vs M curve as f (CDm/CDinc). At 30K the M=1 @679mph so 400mph = 0.59 M. The higher altitude has CD/CDinc = 1.11 vs 1.065 at SL. That is 5% increase of parasite drag solely due to Mach no. difference.

As CL/CD is dominant factor in range achievement, CD/CL is also key to THPreq. Obviusly both ratios are influenced by GW. That said, Induced drag due to CL is very low in higher speed bandwith compared to CDp.

As Barnowl mentioned Climb was an even more important reason to focus on stripping weight

On the other subject, the first XP-82 actually did have a P-51H outer wing panel that was totally redsigned and replaced for XP-82 #2, due to some stall real issues at low speed similar to XP-63. That said, P-51H totally different from P-51D and mostly different to XP-51F/G (trying to research the meaning of 'mostly').

I have yet to receive XP-51F/G Flight test reports from NARA, nor hav I seen the XP-82 reports. What I do know about XP-51F flights by Chilton is that he favored that particular Mustang most of all and the characterisic stability issue were much similar to Mustang X and XP-51B when power applied or reduced - namely yaw damping.

As I have noted in the past, as late as November 1943 the P-51F was being considered for long range point interceptor - with more range than the P-47D on internal fuel alone through Block D-22/23. The XP-51G would have been more suitable with a reliable engine.

The internal plumbing was provided for external racks and tankage had either the F or G proceeded to production. As I have yet t see the Materiel Command flight tests I can't comment on other issues that may have been discovered, but the P-82 was contracted before the first flight of the XP51F and several months before P-51H

 

[drgondog]

Pretty informative. This is the sort of info I've been been looking for for a while, and why when I got back interested in World War II aircraft I came here.

It's also the figures I've commonly seen for the P-51B/D climb rates being only 3200-3600 fpm, when it's been disclosed at that combat weight and on combat power it was more like 4400-4500 fpm, and on half fuel (sort of interceptor trim) it got as high as 4900+fpm.

Planes like the Spitfire and the Me-109 it has to be said that the figures quoted for them as far as especially climb are basically what you see is what you get. Because as point interceptors (by World War II definitions), when flying clean they were for their missions almost certainly flying with full fuel or close to it on take off, due to limited fuel capacity and range. For escort fighters, as you pointed out, things are different and hence combat weight vs TO weight factors in.

BTW, basic SAC manuals did say that the P-51H was normally capable of 5000+ fpm, while the larger one does go into deeper detail on climb rates and speeds and under what conditions they could be expected to be achieved. I do sort of doubt that such info from SAC exists for the XP-82 or P-82B since only about 22 Merlin Twin Mustangs got made, the rest were Allison powered, and in terms of climb and top speed, were noticeably inferior to the Merlin versions.

Careful - Specifically the P-51D flight tests presented are only at 67", using 130 octane, whereas the 1650-7 and -3 and -9 and -9A were all approved for 75" (-9 with W/I at 80" and at 90"). The P-51B-15 with 75" was tested over 4400fpm at combat GW Low Blower and 3700 fpm in high blower at 15K w/racks. The P-51D is a cleaner airframe which should match or exceed P-51B-15 perfomance in comparable condition for GW and racks/no racks and RPM/Boost.

To answer an earlier question - the XP-51F flight tests I have seen are all at 67"MP but possible that tests after April-May may have used 75". I also do not have evidence that the RM 14 engine in the XP-51G ran with WI. The XP-51F explicitly did not have W/I,

 

[BarnOwlLover]

Kind of makes me wonder how the XP-51 LW/P-51H/XP-82/Merlin Twin Mustang saga all intertwines.

As far as the Merlin RM 14SM/Merlin 100 series, they're rated for 25 lbs of boost, which is roughly 80 inches of Hg. I don't think that normal Merlin 100s used ADI (the RM 17SM did), but the V-1650-9 engines used it for anything above 80", certainly for 90". It does have to be remembered that the -9A didn't use ADI as standard due to being used in the P-51M (P-51D airframe using uprated engine).

 

[drgondog]

Kind of makes me wonder how the XP-51 LW/P-51H/XP-82/Merlin Twin Mustang saga all intertwines.

As far as the Merlin RM 14SM/Merlin 100 series, they're rated for 25 lbs of boost, which is roughly 80 inches of Hg. I don't think that normal Merlin 100s used ADI (the RM 17SM did), but the V-1650-9 engines used it for anything above 80", certainly for 90". It does have to be remembered that the -9A didn't use ADI as standard due to being used in the P-51M (P-51D airframe using uprated engine).

For certain all three projects began with a blank sheet of paper.

The XP-82 began with confidence from AAF that NAA could deliver a high performace VLR fighter to escort B-29s from locations 2000 miles from the target. The P-51H began as the necessary evolution of the P-51D/XP-51F attributes - namely better performance, same long range as P-51D via rigid weight control standards.

 

[BarnOwlLover]

It does seem clear that the F-82's concept came first, then the XP-51 lightweights and then the P-51H production version. You are suggesting that they did essentially start out as clean sheet projects independent of each other, but it's obvious that some cross pollination of ideas happened. The P-51H grew out of the XP-51F/G models as a longer ranged version/more general purpose version of them incorporating lessons learned from their development. And the F-82s ended up (it seems) incorporating a lot of the lightweight structure stuff learned from the lightweights and the H's development (how much I'm far from certain, though the XP-51F/G, P-51H and Merlin F-82s all shared the same power unit concept--engine mounts, radiator ducting, cooling arrangement, supercharger intake, etc).

I do wonder when the ideas started to be exchanged and why that occurred. Obviously, the F-82 couldn't be built on all the exact same tooling as the P-51H, and same would've probably applied for the P-51H vs the F/G. But useful lessons that are learned can be applied to other aircraft even if it's not a simple copy/paste job.

I'd bet that in detail the NA-133 (navalized P-51H for the USN/USMC that was proposed) is different in quite a few details from the P-51H it was based on as well.

 

[PStickney]

Foremost, don'ttake the following as a contradiction - more a combined approach to add to your comments to further illustrate BarnOwls questions.

While I agree the analytical approach for thumnail performance analysis, I would suggest a couple of points.

What I cover below is straight out of NAA Performance analysis methodology applied to P-51 and P-82. Best example is NA-5534 for P-51B as discussed below. I refer to it most often, all the way back to my undergrad senior performance project.

First, drag is on the other side of the equation from Thrust and even in high V range. Induced drag is a factor (small) and AoA, as Cdp as related to CL, is a factor particularly at high altitudes/low density. Reducing Weight always 'helps'. Further it is a major determinant in another xpression for THPrequired, namely THPreq = (W/375)*(CD/CL)*V. For this equation the full set of parameters affecting CD (i.e CDp +Del CD) Mc/Minc + CDi must be set in table form to sum up to Total Drag at the desired RN and altitude.

Second, The freebody balance at top speed is that THP avail matches THP required. Various components for P-51/82 for THPavail include not only the prop/engine THP calculated from engine bench HP, ram, prop efficiences (varies through a significant range of altitude and RPM) but also the THP conversion from Thrust in pounds as f(HP, Boost, mass flow rate, exhaust gas temp and velocity, ambient temp - presented in charts constructed in collaboration by Packard, NACA and NAA). Conversely the THPreq must also consider momentum recovery of carb air as well as the drag of the Prop vortex over the inner wing and fuselage.
Next, while 400 mph is a good framework for discussion, the three prime issues for THPreq at 400mph are are a.) CDt Total Parasite Drag; b.) THPavail due to prop efficiency reduced by local mach drag rise at the tips (Much higher at 30K than SL), and c.) Mach correction to CDt vs M at varying altitudes for the entire airframe. FWIW, the Ham Std tables have around .784 for prop efficiency at 444mph @30K and .789 at 412mph @30K.

At SL, 400mph Mach no. =~ 0.53 - low on CD vs M curve as f (CDm/CDinc). At 30K the M=1 @679mph so 400mph = 0.59 M. The higher altitude has CD/CDinc = 1.11 vs 1.065 at SL. That is 5% increase of parasite drag solely due to Mach no. difference.

As CL/CD is dominant factor in range achievement, CD/CL is also key to THPreq. Obviusly both ratios are influenced by GW. That said, Induced drag due to CL is very low in higher speed bandwith compared to CDp.

As Barnowl mentioned Climb was an even more important reason to focus on stripping weight

On the other subject, the first XP-82 actually did have a P-51H outer wing panel that was totally redsigned and replaced for XP-82 #2, due to some stall real issues at low speed similar to XP-63. That said, P-51H totally different from P-51D and mostly different to XP-51F/G (trying to research the meaning of 'mostly').

I have yet to receive XP-51F/G Flight test reports from NARA, nor hav I seen the XP-82 reports. What I do know about XP-51F flights by Chilton is that he favored that particular Mustang most of all and the characterisic stability issue were much similar to Mustang X and XP-51B when power applied or reduced - namely yaw damping.

As I have noted in the past, as late as November 1943 the P-51F was being considered for long range point interceptor - with more range than the P-47D on internal fuel alone through Block D-22/23. The XP-51G would have been more suitable with a reliable engine.

The internal plumbing was provided for external racks and tankage had either the F or G proceeded to production. As I have yet t see the Materiel Command flight tests I can't comment on other issues that may have been discovered, but the P-82 was contracted before the first flight of the XP51F and several months before P-51H

Thanks, Very informative. I didn't know that about the first XP-82, but it makes sense. Is the XP currently flying in Florida (The rebuilt Soplata airframe) the #1 or #2 airplane?
I'll keep an eye out for the Materiel Command data.

 

[PStickney]

That is one I haven't seen before. From USAAF MC Wright Field in Sarah Clark Collection or USAFHRC? or neither?

USAFHRC in Montgomery, AL. On a quick check, I think Ryan Crierie's new replacement for Alternate Wars has this, and others, as well.

 

[drgondog]

Thanks, Very informative. I didn't know that about the first XP-82, but it makes sense. Is the XP currently flying in Florida (The rebuilt Soplata airframe) the #1 or #2 airplane?
I'll keep an eye out for the Materiel Command data.

I think #2. I know they were shocked that nothing in P-82 fabrication or drawings was related to P-51H.

 

[drgondog]

It does seem clear that the F-82's concept came first, then the XP-51 lightweights and then the P-51H production version. You are suggesting that they did essentially start out as clean sheet projects independent of each other, but it's obvious that some cross pollination of ideas happened. The P-51H grew out of the XP-51F/G models as a longer ranged version/more general purpose version of them incorporating lessons learned from their development. And the F-82s ended up (it seems) incorporating a lot of the lightweight structure stuff learned from the lightweights and the H's development (how much I'm far from certain, though the XP-51F/G, P-51H and Merlin F-82s all shared the same power unit concept--engine mounts, radiator ducting, cooling arrangement, supercharger intake, etc).

I do wonder when the ideas started to be exchanged and why that occurred. Obviously, the F-82 couldn't be built on all the exact same tooling as the P-51H, and same would've probably applied for the P-51H vs the F/G. But useful lessons that are learned can be applied to other aircraft even if it's not a simple copy/paste job.

I'd bet that in detail the NA-133 (navalized P-51H for the USN/USMC that was proposed) is different in quite a few details from the P-51H it was based on as well.

Actually, the NA-133 Proposal (not accepted) had only the tail hook and some wing changes - strengthened spar/main gear and slight crank to the inboard leading edge to accomadate wheel well changes for larger wheel. I have no idea why NAA even wasted time on the proposal - the USN would not (Could Not) buy a in-line engine for carrier ops - every gallon of coolant was a gallon less of AvGas.

 

[Shortround6]

every gallon of coolant was a gallon less of AvGas ICE CREAM!

Fixed it.

Coolant was not really a consumable. The plane was expected to return with the same amount of coolant it left with (or nearly) unlike oil and fuel.

How much coolant did the Mustangs you flew use per flight?

The Navy was certainly using some fuel hog aircraft with those R-2800 engines.

 

[drgondog]

Fixed it.

Coolant was not really a consumable. The plane was expected to return with the same amount of coolant it left with (or nearly) unlike oil and fuel.

How much coolant did the Mustangs you flew use per flight?

The Navy was certainly using some fuel hog aircraft with those R-2800 engines.

You're right of course, but storing coolant meant retrofitting to provide separate storage in a vessel 'all booked up'.

 

[tomo pauk]

You're right of course, but storing coolant meant retrofitting to provide separate storage in a vessel 'all booked up'.

USN started storing the ADI fluid from winter of 1943/44, that was a consumable, unlike the coolant.

FWIW, one gallon of fuel for a P-51 was worth much more than it was worth in an F8F, let alone in a F4U or F6F.

 

[BarnOwlLover]

Wonder of the Royal Navy would've been interested to have a longer ranged plane than a Seafire?

I'm really looking forward to the new book once it's completed, even if it doesn't have much on the F-82.