XP-82 vs P-82B Twin Mustang length.

[BarnOwlLover]

I've read from a couple of sources (including a book I got yesterday) that there was a foot difference in length between the XP-82 and the P-82B, even though they used the same power units and basically the same airframe. Anyone know how this is explained?

 

[SaparotRob]

Overinflation.

 

[Skyediamonds]

That's something new to me. My best guess, if it were true, would be to increase longitudinal stability in lieu of adding larger dorsal fins to the vertical stab.

 

[BarnOwlLover]

Actually, the XP-82 was recorded as being longer than the P-82B by a foot depending on sources. Although there was also a claimed difference in armament (ammo capacity) between the XP-82 and the P-82B and subsequent versions (300 rpg for the XP-82 and 400 rpg for the P-82B and later). This was debunked by the XP-82 Restoration Team who put 413 rounds per a gun in the XP-82's ammo boxes.

 

[GrauGeist]

Actually, the XP-82 was recorded as being longer than the P-82B by a foot depending on sources. Although there was also a claimed difference in armament (ammo capacity) between the XP-82 and the P-82B and subsequent versions (300 rpg for the XP-82 and 400 rpg for the P-82B and later). This was debunked by the XP-82 Restoration Team who put 413 rounds per a gun in the XP-82's ammo boxes.

So in essence, you just answered your original question...

 

[Snautzer01]

So in essence, you just answered your original question...

Dont think so.

 

[ThomasP]

Hey BarnOwlLover,

re "the XP-82 was recorded as being longer than the P-82B by a foot depending on sources."

It might help if you post the lengths you are asking about (if you have them). Sometimes errors were made in recording various dimensions, just as there were errors in performance numbers.

I realize that none of the following is for the XP-82 or P-82B, but maybe it will help sort something out. These are the different lengths I have found for the P-82E/F/G and the F-82x (unknown letter). All of them are from official sources of one type or another.

39' 9.115"_P-82E (this is probably correct as I believe it is from the Erection & Maintenance Manual) Note that the STA 0 (station 0) is 8.965" behind the tip of the propeller spinner and 39' 0.15" from the aft end of the fuselage. See the 3-view with dims below.

39' 1.32"__F-82E (from "Encyclopedia of US Air Force Aircraft and Missile Systems Vol 1, Post World War II fighters 1945-1973" published by the Office of Air Force History)

39' 0"____ F-82E (PHOI manual - numbers are sometimes kind of approximate in the PHOI manuals)

38' 3"____ F-82x (NACA tests in 1953)

39' 5"____ P-82F and G ("including nacelle" according to the PHOI manual) This is almost certainly incorrect as the tip of the radar pod stuck out in front of the propeller spinners by a noticeable distance - unless it is not the 'standard' radar nacelle?

The F and G models were based on the E model so the overall lengths should be greater than 39' 9.115"???

42' 3"____ F-82F and G (from "Encyclopedia of US Air Force Aircraft and Missile Systems Vol 1, Post World War II fighters 1945-1973" published by the Office of Air Force History) From tip of the 'standard' radar nacelle to the aft end of fuselage.

P-82E 3-view&dims

 

[BarnOwlLover]

Well, from the Twin Mustang Images of War book I have, it says that the XP-82 was 39' 1", while the P-82B was 38' 1". I know that the Allison powered F-82s were longer in part due to the Allison engine being longer than the Merlin (because of supercharger arrangement, based on the XP-51J being similarly longer than the XP-51F/G). But I've never found a reason for that discrepancy, especially given that the XP-82 and P-82B were using the same Merlin engines.

 

[ThomasP]

Thank you for posting the lengths you have found.

Unfortunately, as the sources I posted above indicate, even in 'official' documents the authors often use incorrect (or perhaps less precise?) values.

When you have an additional evaluation by book authors you get the added chance of previous mistakes/inaccuracies being perpetuated and/or new inaccuracies being created, which can then become commonly accepted as correct. Some authors will misread the values or make typos, and some will round off to one degree or another.

Since many (nearly all) authors do not list their sources for dimensions in their bibliography/citation sections or in footnotes, it is almost impossible to know if the dimensions they use are correct - it will depend on how careful they are and which 'official' source they use. If you want to know for sure you will have to find some original source document to prove/disprove them.

As I indicate in my signature section I am an engineer and a draftsman. As I indicate by my participation in this forum I am also interested in the history and technical aspects of the aircraft we talk about. Inaccuracies like the ones we are talking about offend all three of my 'occupation' senses of professionalism (ie engineer, draftsman, amateur historian/aviation enthusiast - or whatever the correct name for my interest/hobby is).

If you (or anyone else reading this with an interest in such) ever find any original source documents with values like these, please supply then to the forum. I know there are many here who are interested in such details.

Hmmm . . . maybe there is a need for a thread where we post origianal source 3-view with dims pages, or the detailed dimension list pages from the descriptive sections in the manuals???

 

[BarnOwlLover]

Maybe to muddy the waters more, the XP-82 Twin Mustang Restoration Project does list 38' 1" as the length of their XP-82. They also do, however, list 300 rounds per gun for ammo capacity (when they themselves confirmed the 400 rpg number when they were able to put 413 rounds in each box when the fitted the guns to it).

 

[ThomasP]

Looking at photos it does appear to me that there were different spinners used between the variants, but this may just be optical illusion and/or may not contribute to differing lengths.

 

[ThomasP]

re the 300 rpg

It may be that the 300 rpg was intended to be the 'normal load' with the 400 rpg being the 'overload' value. This was a common way of listing the aircraft ammo loads for 'normal' TOGW vs 'overload' TOGW.

 

[BarnOwlLover]

Coming back to this and also from a book update I got this morning from drgondog at secretprojects. Right now, the sequel to P-51B: NAA's Bastard Stepchild for sure will have the P-51D, XP-51F/G/J, the NA-117 and the P-51H and P-51M (and will also discuss the stillborn P-51L). However, at least as of now, he and co-author Lowell Ford are reluctant to do much with the P-82 due to difficulties in nailing down certain specs for sure and such. I'd hope that either Boeing or AirCorps Aviation would have something (the latter from documents that were liberated from Rockwell and later donated to AirCorps), and/or the XP-82 Restoration Team would have some documents (I know that it seems that they have a copy of the XP-82/P-82B pilot's manual made by NAA).

Anyone know anything about this subject that we don't?

 

[GrauGeist]

I doubt Bill and Lowell will cover much (if any) on the P-82, as it wasn't a Mustang.

It bore some resemblance, but was a clean-sheet project and was about as much a Mustang as the NA-143/145 Navion was.

 

[BarnOwlLover]

Bill did say a couple of times here and at secretprojects that he wanted to cover at least the XP-82/P-82B if he could, but they're having a hard time nailing down 100% accurate dimensional data (due to various minor variations between sources). Though I'm pretty glad that they're working on the lightweights/P-51H, since there's certainly not a ton written about them.

Wouldn't mind seeing a detailed book about the F-82 on the level of Bill and Lowell's book(s). Or maybe a book about it geared towards modelers like the Wingleader books (have to get both Mustang volumes when they come out). Maybe one day, considering that for instance AirCorps has tons of NAA documents from the NA-16 though to the F-100 that they're working on archiving and digitizing (which includes F-82, P-51H and maybe LW P-51 documents), and I do believe that Lowell was an assistant/contributor to the XP-82 Restoration Project.