XP-51 Lightweight/F-82/P-51H design evolution, parallels and divergence

[BarnOwlLover]

This was touched upon in a different thread, but it seems that these programs had their genesis at much the same time (at least for the XP-82 and the XP-51 Lightweight program). But there seemed to be some cross pollination of ideas and concepts as time went on, though the programs were still ultimately separate. Even the P-51H, which owes quite a bit to the LW program, did diverge from it.

So I'm wondering if anyone can point out similarities that I don't know, divergences that I don't know, and maybe other details as far as commonalities and differences between the designs of the programs.

 

[BarnOwlLover]

I'm primarily wondering about what may've transferred between projects and evolutionary details of them basically from late 1942 until 1945/46. I know that a lot has been discussed in various threads, but I've started to wonder how these programs might have converged and diverged over time.

 

[pinehilljoe]

Wings/Airpower did a multipart article on the P-82 development. We're in the middle of a move, when we're settled I'll try and copy and post. If I remember the XP-82 was based on existing production airframes. The production P-82 were new designs with few parts from the single engine P-51/

 

[BarnOwlLover]

Thanks for the items you might post. I always heard that even the XP-82 was it's own design vs the P-51 series. The XP-82 restoration team said that the plane the restored had only 5 or so parts in common with the P-51D and only a few more in common with the H/lightweights.

 

[BarnOwlLover]

After looking at some photos of the XP-51F/G and the P-51H and F-82B/XP-82 (in particular, the P-51s/XP-51s), I'm trying to determine where the added foot or so of length that the P-51H gained over the XP-51 lightweights came from. I know that the fuselage was extended to try and offset directional stability issues that the lightweights had (especially when run at higher power settings--which was only completely fixed with the taller tail unit).

The radiator scoop length front to rear seems to be about the same and terminates just ahead of the horizontal stabilizer. I do def. know that the P-51H did have the engine moved forward a few inches (judged by the distance between windshield base/engine cowling line and TE of the engine mount outer skin vs wing LE). Thus, I'm wondering what contributed to the increased length of the H, and by how much.

 

[drgondog]

The NA-120 contract 1-44 preceeded the NA-123 contract by months. The NA-120 contract was for two prototype XP-82 airframes, which when designed - did incorporate the same wing as P-51H for the outer wing panel. April 45 flight testing pointed to unsuitable stall behavior and the outer wing panel was redsigned. AAIK, that is a.) the only thing in cmmon between the H and the XP-82, The XP-82 had nothing in common with P-51D. The NA-123 P-82B was the same as XP-82 save the wing, for 500 unit production.

 

[BarnOwlLover]

I thought that the only thing for sure that the P-51H and P-82 (Merlin variants) had in common was power unit components (basic engine, cooling system, maybe engine mounts and cowling were at least similar). I do doubt that most of the airframe had much in common with the P-51H--based on and exact copy are two different things IMO.

One minor difference is that the XP-82/F-82B did have the radiator inlet indented downward above the boundary layer splitter, the P-51H didn't. Interestingly, the Allison powered F-82s adopted the P-51H intake shape.

Again, citing what was said by the XP-82 restoration team, only about 5 parts or so on their XP-82 was common to a P-51D (and those were fairly minor parts), and only a few were common to the P-51H.

By the same token, I'm guessing that the P-51H had a similar evolution compared to the XP-51F/G. Again, based on the basic design, but did diverge/evolve from it.

 

[BarnOwlLover]

Was looking through my copy of Building the P-51 Mustang tonight and in the P-51H section, there seems to be something maybe/maybe not strange. It featured a P-51H mock up (then provisionally known as the NAA-117) with a four gun wing. Like the P-51D/K, the production P-51H could have 4 or 6 (usually 6) .50 Browning MGs. However, the guns in the mock up didn't like like Ma Deuces. Namely, they had what looked like a gas cylinder on them. The only US produced aircraft MG or cannon that was gas operated was the AN/M2, AN/M3 and M24 cannons--all based on the Hispano-Suiza HS404.

The guns in the mock up also looked like they used a feed system consistent with a Hispano cannon (drum type feeder and all).

I guess this maybe gives creedence to something I read on Secret Projects that the USAAF did favor the P-51H initially having 4 20mm Hispano cannons until the 6 .50s were standardized instead.

 

[drgondog]

Was looking through my copy of Building the P-51 Mustang tonight and in the P-51H section, there seems to be something maybe/maybe not strange. It featured a P-51H mock up (then provisionally known as the NAA-117) with a four gun wing. Like the P-51D/K, the production P-51H could have 4 or 6 (usually 6) .50 Browning MGs. However, the guns in the mock up didn't like like Ma Deuces. Namely, they had what looked like a gas cylinder on them. The only US produced aircraft MG or cannon that was gas operated was the AN/M2, AN/M3 and M24 cannons--all based on the Hispano-Suiza HS404.

The guns in the mock up also looked like they used a feed system consistent with a Hispano cannon (drum type feeder and all).

I guess this maybe gives creedence to something I read on Secret Projects that the USAAF did favor the P-51H initially having 4 20mm Hispano cannons until the 6 .50s were standardized instead.

I had a different take. The A-36 project proposed and installed many different combinations on mock-ups including 37mm and 20mm/37mm combinations but the Army specified only 50 cal in the contract - which wasstructrued as a modification to NA-83.

When the P-51H was being built the RAF intended to buy them and as always wished 4x20mm as armament. I suspect without dcumentation, this was provided in a mock up to explore issues with installaion between the spars. Pure speculation on my part.

 

[BarnOwlLover]

Post #74 hints that the USAAF couldn't make up it's mind at first on the P-51H's armament (as well as the F-82). That (maybe) goes along with the P-51H maybe being cannon armed. The guy who posted this also in the post above got some into on the P-51s that were tested with rocket motors to boost speed for jet aircraft interceptions.

P-51 Mustang & F-82 Twin Mustang Proposals and Variants

All the better ! I think, we'll see it in the mentioned future APR issue ?

www.secretprojects.co.uk

 

[Shortround6]

There was also a lot "flex" in the .50 cal gun program at around this time.
The whole 1200rpm M3 gun situation. Something like 8-10,000 guns had been ordered in late 1944 under a T number for troop trials so 4 guns would equal the firepower of 6 M2 guns for 2/3rds the weight.
They were also troop trialing what would become the M24 incendiary round, Drgondog's father may have participated in this. It took years to sort this one out including changing manufacturer twice so actual introduction was years later than what was "planned".

It was still being sorted out in the early 1950s so the Sabre jets in Korea were NOT using the WW II .50 cal guns or the WW II ammo. It may not have been good enough or what was wanted once in combat but it was significantly better than the WW II Armament. However the 20mm gun/s turned out to have few problems and better effect.
The M3 guns seemed to work pretty well but the ammo gave a lot of trouble with pre-matures either in the barrel or just in front (15-25 yds?)

 

[BarnOwlLover]

Biggest problem I have with the M3 isn't it's rate of fire, but ammo capacity. You have to remember that for 6 guns, the P-51D had 400/270/270, the P-51H had 390/260/260. Even the F-86 had 6 with 270 or 300 (depending on source) rounds per gun. At 1100-1200 rpm, that doesn't last long, though that goes along with have 6 guns in the first place (putting a lot of metal and incendiary/explosive material on target ASAP).

Of course, it's been mentioned that the P-51H had M2s instead of M3s (M3s ended up in most F-82s and may've been fitted/refitted to late P-51Ds).

 

[Shortround6]

ammo for the F-86 was good for about 13.5-14 seconds.
Navy F-9 Panther had about 15 second of ammo. That is using the faster firing AN/M-3 20mm cannon.
Now the M3 .50 fired around 40-50% faster than the M2.
The 20mm M3 gun fired about 20-25% faster than the 20mm M2 gun.

Corsairs with four 20mm guns got about 231 round per gun (924 total) instead 400rpg ( 2400 total).

The M23 .50 cal round had a higher velocity than the M8 API by about 500fps. (17% increase)
It also contained just under 6 grams of incendiary material or just about 6 times the incendiary payload of the M8 API of WW II.
It had no armor piercing ability.

the problem with 1945 and on planned armament, was the difference between what was promised and what was delivered 3-8 years down the road.
The M3 gun pretty much delivered as promised. The M23 .50 cal round struggled, struggled some more, and struggled even more and was finally surpassed (given up on)
But combat trials in Europe were undertaken starting in Nov of 1944. So planned armament for late 1945 and 1946 has to take that into account.

 

[drgondog]

I thought that the only thing for sure that the P-51H and P-82 (Merlin variants) had in common was power unit components (basic engine, cooling system, maybe engine mounts and cowling were at least similar). I do doubt that most of the airframe had much in common with the P-51H--based on and exact copy are two different things IMO.

One minor difference is that the XP-82/F-82B did have the radiator inlet indented downward above the boundary layer splitter, the P-51H didn't. Interestingly, the Allison powered F-82s adopted the P-51H intake shape.

Again, citing what was said by the XP-82 restoration team, only about 5 parts or so on their XP-82 was common to a P-51D (and those were fairly minor parts), and only a few were common to the P-51H.

By the same token, I'm guessing that the P-51H had a similar evolution compared to the XP-51F/G. Again, based on the basic design, but did diverge/evolve from it.

Well, not quite the same. The XP-82 and P-82B had the equivalent 1650-11 (R.M. 16 S.M.) (same as 1650-9A) but with speed density carb variable speed supercharger control - and right/left rotation so 1650-19/-21. Implied are engine mounts common, maybe coolant tanks but I'm not sure at this time.

The inlet geometry changed during XP-51F development with the improved flow properties of the aft plenum/scoop exit geometry.

I suspect that any D parts in XP-82 may have been used only because they were 'close enough' in raw form

 

[BarnOwlLover]

Did the XP-82/P-82B use ADI injection, or was it not fitted (the Allison versions did use ADI)?