Allison-Merlin Mustang wing differences

[72modeler]

Almost as much discussion (and dissension!) on this subject as the Chicken/Egg debate, but for what it's worth, and hopefully to shed a little more light on this nagging question that has been perplexing Mustang modelers for decades, here is what I was able to find. I am NOT a Mustang authority, and I am not qualified to express an opinion, learned or otherwise, on this subject, so please consider that before launching any flak in my direction...as they used to say, "Don't shoot me, I'm just the piano player!"

 

According to an NAA document I read on the SIG, the basic wing structure, airfoil, etc. was unchanged from the NA73X to the P-51D/K. The P-51F/G/H wings were structurally different. The only other significant changes noted in the numerous discussion topics concerning the wings of Mustangs leading up to the D and the D were the LE extension, main gear fairing doors, gun fit, and stiffeners ahead of the ailerons.

 

The LE extension on all variants prior to the D had a downward camber- this also affected the shape of the wingroot fairing at the LE. On the D, the LE extension began further outboard and had no camber.

 

The inner fairing doors on the D were not the same outline and shape compared to the earlier variants, mainly due to the retraction jacks and uplocks being moved from the front to the rear of the wheel bays. In addition, the stiffeners and shape of the bulkhead at the front of the wheelbay/LE extension was different on the D as compared to the earlier variants.

 

The P-51B/C/D also had two chordwise stiffeners in front of  each aileron on the upper surface and one on the lower surface of each wing.

 

The reasons for the LE extension on the D was a subject of much discussion, from pilots, crew chiefs, and enthusiasts, as well as excerpts from NAA correspondence and documents, and the general concensus seemed to be the change could have been due to various reasons, but there was no unanimous winner. Possible reasons for the LE extension change given were: (1) simplification of the structure/parts count in that section of the wing (2) change due to the  new fairing doors/retraction jacks (3) cg consideration- much discussion of the rearward shift in cg which began when the Merlin was fitted to the P-51B/C, quoting larger radiator/oil/cooler/intercooler/85gallon fuel tank; the LE extension increased fwd wing area and helped to bring the cg forward.

 

It was also discussed that the D wing was not thicker than the wing on the previous variants because of the extra two guns fitted, or that this was done so that the .50cal guns could be mounted upright, versus being canted, as they were in the earlier  variants that had .50cal wing guns. NAA evidently engineered the wing from the beginning to take heavier armament at some point, thus the reason to cant the guns to allow feed chutes for .50cal or 20mm guns to fit within the wing without blisters or fairings, so the guns were canted from the outset. Since it was determined that 20mm armament was not going to be fitted, the guns were mounted upright- this also alleviated to a great extent, the jamming that was taking place on the B/C models.

 

I will try to find at which point on the wing the LE extensions began, probably will be at which wing station this took place, not inches/feet from the wingroot; If I can find this, I will add it to this post.

 

Hope this helps; a lot of people much smarter than I am are still undecided on this topic, but there is no disputing the fact that the LE extensions, main gear fairing doors and retraction jacks, and the forward section of the wheel bays were different between pre-D's and D's; I guess for those of us who model, it's not important knowing why these changes were made, but how the changes affected the appearance. I have four of the old Monogram 1/72 P-51B's, and if nobody can see their way clear to release an accurate wing, I'm gonna start cutting mine up after I figure out which kit/s would be the best recipient... pretty amazing that Monogram got this often overlooked part right so many years ago! Whew- I'm pooped!

Mike 

Edited September 26, 2017 by 72modeler
corrected grammar, spelling, and one fact

[John Thompson]

Thank you for that, Mike! The comment here and in the other thread regarding the goodness of the Monogram P-51B wing has me curious about whether the old Hawkeye resin replacement wing that was intended for the Hasegawa P-51B is correct WRT the droop of the leading edge extension.

 

John

[72modeler]

On ‎9‎/‎25‎/‎2017 at 8:54 PM, John Thompson said:

Thank you for that, Mike! The comment here and in the other thread regarding the goodness of the Monogram P-51B wing has me curious about whether the old Hawkeye resin replacement wing that was intended for the Hasegawa P-51B is correct WRT the droop of the leading edge extension.

 

John

I have one, and I just checked it. They did get the LE extension droop correct, but unfortunately they made the same mistake as almost every other 1/72 kit as they depicted the rear wall of the wheel bay (main spar)  following the outline of the bay instead of being straight for its entire length. This could be hidden by posing the inner bay fairing doors almost closed, as they would be right after engine shut-down before the pressure in the hydraulic system bled off and the doors dropped completely. Other than that, it's a nice piece, as it has provision for dropped flaps, correct case ejection chutes, and correctly aligned gun port openings.

Mike

 

I just found an excellent photo from Warbird News that shows the droop of the leading edge extension of the early Mustangs on a beautifully restored P-51C that just completed its first post-restoration flight. You can clearly see the droop in the photo of this link!

 

http://www.warbirdsnews.com/aviation-museum-news/texas-flying-legends-museums-p-51c-mustang-lopes-hope-3rd-flies.html

 

 

Edited October 26, 2017 by 72modeler
added link

[John Thompson]

1 hour ago, 72modeler said:

I have one, and I just checked it. They did get the LE extension droop correct, but unfortunately they made the same mistake as almost every other 1/72 kit as they depicted the rear wall of the wheel bay (main spar)  following the outline of the bay instead of being straight for its entire length. This could be hidden by posing the inner bay fairing doors almost closed, as they would be right after engine shut-down before the pressure in the hydraulic system bled off and the doors dropped completely.

 

Oops - that raises another point of controversy - I seem to recall that the Allison Mustangs had inner main gear bay doors which did not drop down while the aircraft was parked because the doors were either electrically operated (instead of hydraulic) and/or they had latching devices which held them closed. If I was building an Allison P-51, I think I'd close the doors anyway - it looks neater and helps emphasize the really sleek appearance of these aircraft!

 

John

Edited September 26, 2017 by John Thompson

[72modeler]

1 minute ago, John Thompson said:

 

Oops - that raises another point of controversy - I seem to recall that the Allison Mustangs had inner main gear bay doors which did not drop down while the aircraft was parked because they were either electrically operated (instead of hydraulic) and/or they had latching devices which held them closed. If I was building an Allison P-51, I think I'd close the doors anyway - it looks neater and helps emphasize the really sleek appearance of these aircraft!

 

John

You are correct, John. From what I have read, those doors did latch when in the up position, and would not drop down on their own, but could be unlatched by the ground crew for inspection/maintenance. When I built the Frog Mustang, I glued them up to save having to correct/detail that part of the wheel bay.

[72modeler]

I managed to find some photos that reveal the differences in the LE extension, inner fairing doors, case ejection chutes, stiffeners, and wheel bays between the early and late Mustangs. You can see the different contours, shapes, and retraction jacks of the inner fairing doors, the different chord and camber of the LE extensions, as well as the presence of the stiffener ahead of the aileron on the wing undersurface. Photos include P-51D, P-51B/C, and Allison-engine variants. The two XP-51 photos are of the 4th Mustang I built, AG348, which was taken over by the AAF as an XP-51, and is all-original- note the lack of the stiffeners on the upper wing ahead of the ailerons, unlike the photos of an XP-51 restoration posted earlier. See what you think.

Mike

 

http://www.airliners.net/photo/Untitled/North-American-P-51D-Mustang/4231015/L?qsp=eJwtjDEOwkAMBP/iGgpAUKQD0ZOCD1j2CiICd7ItwSnK37kLdLOz0kwk6RX4xLVkUEcONrnTijIbP526iR4o72Ramfr1fnOupyeLU6lCOXAUQQ7o319MYe2Cy9K5te62Iaz/rd2hTh08j7xUEDyMNM9fKr4uBw%3D%3D

 

http://www.airliners.net/photo/Untitled/North-American-P-51D-Mustang/4598339/L?qsp=eJwtjMEKwkAMBf8lZz0U0UNvind78AdC8qjF6i7ZgC6l/266eBtmYBaS9HZ8/V4zqKcCNnnQjjIbvwr1Cz1RP8k0mIb9sbtGLMn8UkMoO84iyA79%2B5spbEso0j5jfLsA2NCYDqfwOpU8c3vAeZppXX/b9i3C

 

http://www.airliners.net/photo/Untitled/North-American-P-51D-Mustang/4499625/L?qsp=eJwtjMEKwkAMBf8lZz0U0UNvind78AdC8qjF6i7ZgC6l/266eBtmYBaS9HZ8/V4zqKcCNnnQjjIbvwr1Cz1RP8k0mIb9sbtGLMn8UkMoO84iyA79%2B5spbEso0j5jfLsA2NCYDqfwOpU8c3vAeZppXX/b9i3C

 

http://www.airliners.net/photo/Untitled/North-American-P-51C-Mustang/4279511/L?qsp=eJwtjEEKwkAMRe%2BStS6K6KI79QB24QVC8qnF6gyZgA6ldzcd3D3eg7eQpLfj6/eaQT0VsMmDdpTZ%2BFWoX%2BiJ%2BkmmwTTsj901YknmlxpC2XEWQXbo399MYVtCkfYZ49sFwIbGdDiF16nkmdsDztNM6/oD25wtwQ%3D%3D

 

http://www.airliners.net/photo/Untitled/North-American-P-51C-Mustang/2317490/L?qsp=eJwtjDEOwkAMBP/iGgpAUKQDHkAKPmDZK4gI3Mm2BKcof%2Bcu0M3OSjORpFfgE9eSQR052OROK8ps/HTqJnqgvJNpZerX%2B825np4sTqUK5cBRBDmgf38xhbULLkvn1rrbhrD%2Bt3aHOnXwPPJSQfAw0jx/ASpiLgY%3D

 

http://www.airliners.net/photo/Untitled/North-American-P-51C-Mustang/2302906/L?qsp=eJwtjDEOwkAMBP/iGgpAUKQDHkAKPmDZK4gI3Mm2BKcof%2Bcu0M3OSjORpFfgE9eSQR052OROK8ps/HTqJnqgvJNpZerX%2B825np4sTqUK5cBRBDmgf38xhbULLkvn1rrbhrD%2Bt3aHOnXwPPJSQfAw0jx/ASpiLgY%3D

 

http://www.airliners.net/photo/Untitled/North-American-P-51A-Mustang/2061482/L?qsp=eJwtjEEKwkAMRe%2BStS6K6KK79gJ24QVC5qOl1RmSgA6ldzcO7h7vwdtI8svx8VstoJ4MrPKgAxVWfhr1Gy2o76wpmKbjuRsiWlYfa4jEjkEExZH%2B/qoJ%2BkswaZ97fLsA6NSYTpfwabaycnvAeV5p37/a6C2/

 

http://www.airliners.net/photo/Untitled/North-American-XP-51-Mustang/1312236/L?qsp=eJwtjLEKwkAQBf9lay2CaJFOf8AUFrbL7iMGo3fsLegR8u9uDrthBmYhSW/H1281g3oqYJMH7Siz8atQv9AT9ZNMg%2Bk%2B7I9dxJLMLzWEsuMsguzQv7%2BawraEIu0zxrcLgA2N6XAKr1PJM7cHnKeZ1vUH43st1g%3D%3D

 

http://www.airliners.net/photo/Untitled/North-American-XP-51-Mustang/847191/L?qsp=eJwtjLEKwkAQBf9lay2CaJFOf8AUFrbL7iMGo3fsLegR8u9uDrthBmYhSW/H1281g3oqYJMH7Siz8atQv9AT9ZNMg%2Bk%2B7I9dxJLMLzWEsuMsguzQv7%2BawraEIu0zxrcLgA2N6XAKr1PJM7cHnKeZ1vUH43st1g%3D%3D

 

[72modeler]

Wasn't sure of the best location for this,  but I found an excellent collection of Mustang detail photos of several versions, from the XP-51 to the P-51B/C and I posted them in the aviation photography forum- didn't want to clutter this forum with any more of my trivia and junk! I think they will be useful for Mustang modeling projects, so you might want to  go there and look at them. Enjoy!

Mike

[Denford]

On ‎26‎/‎09‎/‎2017 at 4:07 AM, 72modeler said:

I have one, and I just checked it. They did get the LE extension droop correct, but unfortunately they made the same mistake as almost every other 1/72 kit as they depicted the rear wall of the wheel bay (main spar)  following the outline of the bay instead of being straight for its entire length. This could be hidden by posing the inner bay fairing doors almost closed, as they would be right after engine shut-down before the pressure in the hydraulic system bled off and the doors dropped completely. Other than that, it's a nice piece, as it has provision for dropped flaps, correct case ejection chutes, and correctly aligned gun port openings.

Mike

I have some sympathy with Hawkeye and the rear wall of the wheel bay.

Not sure how it was moulded, but as a single piece it would have been difficult - no impossible - to make sufficient undercut to reach the main spar.

Remember too that it came out in the 90's? when modellers were a little less discerning than now.  Even now, the only way to correct the error would be to make the wing in perhaps 3 parts (1 x lower, 2 x upper) both then becoming thinner and therefore harder to mould (?) and with a new difficulty of correctly alignment.  Those familiar with resin casting may know better.