Allison-Merlin Mustang wing position changes

[Jamie @ Sovereign Hobbies]

3 hours ago, gingerbob said:

Thanks, Colin. 

 

Finn, yes, that is interesting, but notice that the bottom point that they're measuring to is different, and (if I see it properly) is aft of that joggle on the second (Merlin) drawing.  I'm frankly a little surprised that they updated the drawing that well- there are certainly examples of recycled drawings that do NOT update some features.  So, either a coincidence, a shrewd plan to have that component still have the same overall depth (to fit the existing crates?), or perhaps even an overlooked dimension that is not, in fact, correct.  Probably not the last, but one can't assume!

 

Now, off to see if I can find a thrustline reference- I wouldn't have thought that it would be obscure...

 

OK, from A-36A and P-51D/K Erection & Maintenance Manuals (sorry, no pictures this time):

 

A-36A distance between Fuselage Reference Line and Wing Reference Line: 23.5 inches

     Thrust line 1.5 inches below (I think!) FRL, parallel to it.

     And also noticed... FRL to top of fin: 67 9/16"

     FRL to nominal ground plane (level): 73.5"

 

P-51D distance between: 26.5 inches

     Thrust line: no standoff from FRL shown (to center of mass of engine?) BUT 1 degree 45 minutes downthrust

     FRL to top of fin: 69 9/16"

     FRL to nominal ground plane: 76.5"

 

So, the FRL doesn't change position (I'm sure it is defined somewhere, but I didn't happen to see that), there are 3 inches difference both to the wing Reference and to the ground (tire), and the fin is (apparently) 2 inches taller*.  I wonder where those two inches come from?  [Yes, I know that's been discussed before, also...]

 

*EDIT: However, the fin and rudder part numbers are the same in A-36A and P-51D Illustrated Parts Books, which makes me think that the fin and rudder are actually identical, and only the measurements (numbers) have changed.  Curiouser and curiouser.

So there we have it. The centre of the spinner is not a safe place to measure the wing position against. The Merlin gained downthrust as a minimum and is possibly sitting 1.5 inches higher.

[Bedders]

5 hours ago, 72modeler said:

 

Why couldn't the kitmakers have saved us all of this time and trouble and just given us an accurate model to work from?

My feelings could not have been expressed more succinctly.

 

Justin

[Dana Bell]

Why I LOVE the archives - interdesk Materiel Command memo dated 28 August 1942 [sic]:

 

Left by Alec Burton together with the dope on the Griffin 61, this date.  "Dutch" Kindleberger says the Merlin 28 is out for installation in the P-51, but they are going full blast on the Merlin 61.  About all the re-design necessary is to move the wing forward 3 inches and down 1 inch; also, the nose will be dropped a little to give better visibility than in the P-51.

 

If the aerodynamics isn't ruined, looks like they might have a pretty good airplane.

 

The last line may be one of the greatest understatements of the war, even if the repositioning of the wing was slightly different in the production.

 

A later memo on new models of the P-51 notes that the P-51B will be the standard airframe with the Merlin added, while the P-51C will have the Merlin added AND the wing repositioned.  In the end, of course, the wing was moved on both variants....

 

Cheers,

 

 

Dana

[ColFord]

To add to the data taken directly from the original NAA Technical documentation, diagrams showing key dimensions and fuselage reference line for:

 

P-51 / Mustang Mk.IA

P51 Dimensions by Colin Ford, on Flickr

 

A-36

A36 Dimensions by Colin Ford, on Flickr

 

P-51A  /  Mustang Mk.II

P51A Dimensions by Colin Ford, on Flickr

 

P-51B/C - Mustang Mk.III

P51B:C Dimensions by Colin Ford, on Flickr

 

A bit more to add to the discussion is that when you look at the part or component or design numbers for the components of the main fuselage group, that is the fuselage section shown in the earlier diagrams from firewall back to tail, the majority still reflect the original Mustang Mk.I design on thru the P-51, P-51A and A-36.  The P-51B/C still has a large number of components and design elements, a very high percentage, that still reflect the original Mustang Mk.I design in the main fuselage group.  A lot of the changes in part/component/design numbers is reflected in smaller components or implementation of design changes to accommodate later ancilliary equipment or improvements arising from in service use.  A number of the changes in the P-51B/C in the main fuselage group is in the modifications to accommodate the change in wing position, the different radiator/cooling arrangements - which includes the 'joggle' and relocation of ancillary equipment brought about by the change in engine and in service use. 

 

 

[Work In Progress]

I know Colin knows this as I'm sure do most people but to prevent someone else leaping to wrong conclusions, the point of those diagrams is you can rely on the numbered measurements, but they are not attempting in any way to be scale drawings which capture the shapes of things.  You can take the numbers to the bank, but the drawings are no more than rough sketches and not to be taken as anything other than a guide to what each number refers to.

[Bedders]

V useful. Data for H model perchance...?

[Bedders]

On 06/10/2017 at 5:06 PM, John Thompson said:

<sigh!> Where's Charles Neely when you need him? It's been a while since I've seen or heard anything of him - I hope he's not the late Charles Neely by now...

 

John

I got a reply from him on the P-51 SIG a few months ago; though that was on H model business.

Edited October 7, 2017 by Bedders

[John Thompson]

29 minutes ago, Bedders said:

I got a reply from him on the P-51 SIG a few months ago; though that was on H model business.

 

Good to know - thank you, Bedders!

 

John

[Jamie @ Sovereign Hobbies]

I'm trying to chew this over.

 

Either the entire empenage is moved higher on the B model (which may or may not imply that the rudder is taller) or there's a rabbit off somewhere.

[gingerbob]

Always happy to be corrected, but my current take is that the tail was exactly the same (at least dimensionally).  Interesting, though, that the number changed with consistency when going from Allison to Merlin.  I guess I need to have another poke in the parts books.  Also, think I can come up with a comparable H drawing, though I haven't attempted to post "my own" image since the PB fiasco.  [Edit: yes, I have one, but it is a picture of a page, rather than a direct scan.]

 

Edit again: Here's a quote from Charlie:  (These comments are coming from a long thread HERE.)

Quote

Back up in Post # 92 , I missed pointing out the 2" error in Dimension for Ht of Fin in NAA's P-51D 3-view. If you look back at the A-36 NAA 3-view you will note the ht given is 67-9/16" above FRL (which is correct) while 69-9/16" is given for same ht on D fin. Be assured that the basic Fin/rudder of a D is unchanged from that of the Mustang I.

 

I notice that the spinner is only 3/4" longer (on Merlin), but 4" greater in diameter (per the drawings on page 1)- though that latter is rounded to whole inches, so may not be precisely accurate. [Edit: just found a comment from Charles Neely that the Merlin spinner base diameter is 28.125.  On the drawing rounded up to 29 because that drawing is for "fitting inside the box" dimensions.]

 

p.s. I finally spotted a dimension that confirms that the FRL did not shift- I knew it in my heart, but glad to see "proof".

Edited October 8, 2017 by gingerbob

[Dave Fleming]

2 hours ago, Jamie @ Sovereign Hobbies said:

I'm trying to chew this over.

 

Either the entire empenage is moved higher on the B model (which may or may not imply that the rudder is taller) or there's a rabbit off somewhere.

 

 In the back of my mind, something says it was. I'recall if you draw a line from the tailplane to the cockpit on both variants and the line us in different places in relation to the bottom of the canopy

[occa]

Here are the assessments and a few observations re the vertical wing position and the droop effect of the wing kink on the kits that are/were available for the recent decade

 

- The 3 variants of the Condor / SH kits I still own (A-36, P-51 and Mustang I) have all the height of the B/C series, they are all one mm too tall.

 

- The High Planes is the most correct, it has both the right distance between the cockpit sill and the wing and a realistic droop effect of the wing kink.

 

- The Academy is correct re the height too. The droop of the leading edge kink is missing tho, see the Italeri below.

 

- Surprise, the Italeri has the correct fuselage height too. But it has the D wing root.

Also it is missing the droop effect which results that the wing is attached to the fuselage at a wrong angle, same with the Academy.

 

 

[John Thompson]

40 minutes ago, occa said:

I've just checked the 3 variants of the  Condor / SH kits (A-36, P-51 and Mustang I).

They all have the height of the B/C series, they are all one mm to tall.

The High Planes is the only one that is correct, it also has the best rendition of the S-curved lower nose contour.

 

 

I still have to check the Academy later today, will edit this post when I have the result.

 

Thank you, occa - I'm looking forward to seeing your results!

 

John

[occa]

Hi John !

 

I've already added my result for the Academy kit, it's looking good in that matter.

 

Cheers, Martin

[elger]

almost afraid to ask, but any idea about Italeri's fuselage? (let's ignore the wings)

[occa]

8 hours ago, elger said:

almost afraid to ask, but any idea about Italeri's fuselage? (let's ignore the wings)

Ah almost forgot about that one ...

 

Edit:

Done, I also edited my comparison above for better clarity I hope.

[FinnAndersen]

2 hours ago, elger said:

almost afraid to ask, but any idea about Italeri's fuselage? (let's ignore the wings)

IMHO, disregard the Italeri, it's no good at all.

[72modeler]

On ‎10‎/‎8‎/‎2017 at 8:13 AM, occa said:

Here are the assessments and a few observations re the vertical wing position and the droop effect of the wing kink on the kits that are/were available for the recent decade

 

- The 3 variants of the Condor / SH kits I still own (A-36, P-51 and Mustang I) have all the height of the B/C series, they are all one mm too tall.

 

- The High Planes is the most correct, it has both the right distance between the cockpit sill and the wing and a realistic droop effect of the wing kink.

 

- The Academy is correct re the height too. The droop of the leading edge kink is missing tho, see the Italeri below.

 

- Surprise, the Italeri has the correct fuselage height too. But it has the D wing root.

Also it is missing the droop effect which results that the wing is attached to the fuselage at a wrong angle, same with the Academy.

 

 

Occa,

 

Whew! For a minute there, I thought I was the only crazy one! I had some time yesterday and pulled all the kits again. Using the excellent 'wing reference line' in the diagram posted by Colin, I can confirm your and my observations about the wing position. Using that reference point, in 1/72 scale, it is 30" from the WRL to the cockpit sill on the Allison Mustangs and 33" on P-51B/C, given the fact that the wing was dropped 3". Only the Academy P-51 (12401) gets it right for the Allison Mustangs and the venerable Monogram P-51B has it correct at 33" The SH Mustang Mk 1 (72041), MPM P-51/F-6A (72085), and the Condor A-36A (72016) all have the sill at 33", which is correct for a B, as we all know by now, but wrong for an Allison-powered version. I'm still working on the best way to record and present the pros/cons of each of the kits, so that will take a while- plus I've got some house maintenance projects I need to finish for the 'War Department' first!

 

I could use that time building something if somebody would hurry up and release a decent kit...Eduard, c'mon, you can do it!

 

Mike

 

PS: I forgot to mention, and I didn't want all of you out there to think I was pulling opinions and observations out of my hat, but the scale drawings I used when comparing the kits in my previous posts  were the excellent ones in the MMP A-36A monograph as well as the 1/48 drawings from the Accurate Miniatures A-36A kit, reduced to 1/72. They both seemed to compare very closely to the published dimensions. I am not concerning myself with all of the panel lines and inspection panels, as these do vary from drawing to drawing and kit to kit, and I will look at  them when I actually start building. I would think getting a kit that is accurate in shape and dimension is more important to all of us- hope I am correct in that assumption?

Edited October 9, 2017 by 72modeler
added additional information

[occa]

^^ Glad you came to the same results Mike !

 

Here's a page that shows how accurate the HPM looks if built properly:

http://modelingmadness.com/review/allies/us/usaaf/p51/gros51a.htm

 

[silberpferd]

Hi all,

 

Having done a lot of research on the subject, I might give you some clues regarding what is right and what is wrong.

 

I have always been puzzled about the change of fin heigth on the NAA 3 views drawings, between the Allison and Merlin powered Mustangs, until Charles Neely provided me this drawing

 

the 69 9/16" on the P-51B and D drawings is just wrong, and should read 67 9/16", this being also confirmed by working on the full set of microfilmed drawings I have purchased some time ago. I guess at some point someone mistook the "7" for a "9", and the error was was reproduced on subsequent drawings. The Fuselage Refernce Line stayed the same for Allison and Merlin powered P-51s, only the thrust line changed.

 

Therefore, the wing is really 3 inches lower on P-51B/C/D/K Mustangs.

 

 

I hope this helps.

 

Regards,

 

Laurent Boulestin

[72modeler]

6 minutes ago, silberpferd said:

Hi all,

 

Having done a lot of research on the subject, I might give you some clues regarding what is right and what is wrong.

 

I have always been puzzled about the change of fin heigth on the NAA 3 views drawings, between the Allison and Merlin powered Mustangs, until Charles Neely provided me this drawing

 

the 69 9/16" on the P-51B and D drawings is just wrong, and should read 67 9/16", this being also confirmed by working on the full set of microfilmed drawings I have purchased some time ago. I guess at some point someone mistook the "7" for a "9", and the error was was reproduced on subsequent drawings. The Fuselage Refernce Line stayed the same for Allison and Merlin powered P-51s, only the thrust line changed.

 

Therefore, the wing is really 3 inches lower on P-51B/C/D/K Mustangs.

 

 

I hope this helps.

 

Regards,

 

Laurent Boulestin

Laurent,

 

Your photo is worth a thousand words! Thanks for sharing it! Sure wish the kit makers would seek Charles out before cutting molds for any Mustang variant! Your photo also shows the flap position indicator that is often overlooked on Mustang models as well as the fact that the portion of the wing flap that is exposed when down is bare metal. 

Mike

[Bozothenutter]

On 10/6/2017 at 10:27 PM, Dana Bell said:

Why I LOVE the archives - interdesk Materiel Command memo dated 28 August 1942 [sic]:

 

Left by Alec Burton together with the dope on the Griffin 61, this date.  "Dutch" Kindleberger says the Merlin 28 is out for installation in the P-51, but they are going full blast on the Merlin 61.  About all the re-design necessary is to move the wing forward 3 inches and down 1 inch; also, the nose will be dropped a little to give better visibility than in the P-51.

 

If the aerodynamics isn't ruined, looks like they might have a pretty good airplane.

 

The last line may be one of the greatest understatements of the war, even if the repositioning of the wing was slightly different in the production.

 

A later memo on new models of the P-51 notes that the P-51B will be the standard airframe with the Merlin added, while the P-51C will have the Merlin added AND the wing repositioned.  In the end, of course, the wing was moved on both variants....

 

Cheers,

 

 

Dana

So Kindleberger got the measurements mixed up?

But more interesting, was the wing moved forward? (Presumably 1 inch?)

[ColFord]

7 hours ago, Bozothenutter said:

So Kindleberger got the measurements mixed up?

But more interesting, was the wing moved forward? (Presumably 1 inch?)

Not necessarily, the design process for the installation of the Merlin on the Mustang that resulted in the P-51B went through a number of iterations and proposed changes.  Some changes considered proved not to be feasible, or require too great a change in the basic airframe which would have potentially delayed introduction of the Merlin engine Mustang into service and caused substantial disruption to production.

 

If you want to 'deep dive' into the original design and production of the Mustang from the first Allison engine variant through to the introduction of the P-51B/C and conception of the P-51D, then your current best reference is:

P-51B Mustang: North American’s B*****d Stepchild that Saved the Eighth Air Force Hardcover – 9 July 2020

by James William "Bill" Marshall (Author), Lowell F. Ford (Author), Col (Ret.) Robert W. Gruenhagen (Foreword) - supported by input from a lot of dedicated Mustang flyers, maintainers and researchers.

 

The other best and seminal reference on the development of the Mustang is:

Mustang - the story of the P-51 Fighter by Robert W Gruenhagen ( a couple of editions of this classic from late 1970s, some of the information is dated but it still holds up very well for the basics covered.)

 

 

Edited August 22, 2022 by ColFord
Correcting the autocorrect

[Bozothenutter]

@ColFord reading the B*st*rd book as we speak!

[ColFord]

If you enjoy the B*****d book, be happy, lead author Bill Marshall posted today "my next project will focus on P-51D/F/G/J and H. It may or may not touch on combat history, but I will expand on ETO/MTO/CBI from the 'b*****d Stepchild' for entire war - not just up to D-Day." 

 

That project is already well underway and will continue the story and be in a similar format/style and will likely be from the same publisher.  He has lots of material to work with so it will be another huge tome.