P-51 Firewall Question

[AHancock51]

Hey again guys, thanks for answering my many questions about the P-51! It'll all make sense quite soon I am planning on building my own P-51B replica (full-scale) and am in the process of designing a steel-frame fuselage. I'm looking at the dimensions and weight diagram for the P-51B, and am using the fuselage dimensions to design my 4130 frame. My question is this, the forward firewall (right in front of the cockpit) is at an angle, I'm curious as to what this angle is. I'll post a screenshot to help you see what I mean. Thanks in advance!



- Austin Hancock

[Ew51]

Hello Austin,

According to the structural repair manual 13 degrees 6 minutes 20 seconds.

Eric.

[AHancock51]

Hello Austin,

According to the structural repair manual 13 degrees 6 minutes 20 seconds.

Eric.

Thanks Eric! Still learning how to read blueprints here, so I most likely missed it, haha!

- Austin Hancock

[The Inspector]

Basically, a blueprint is like a map. Start @ the bottom right corner to find out what the drawing (also called a cartoon by sheetmetal guys) pertains to, also there you will find your tolerances for dimensions, usually +/- .003 in.. Then up to the upper right corner for notes and drawing changes (as things are refined, rather than redraw the whole thing, a change will be made to a portion of the drawing and when they were incorporated into the drawing) Views shown on the drawing may have facing arrows and two matching letters (A-A, B-B, etc.) and a note saying 'see view A-A in C-6' drawings are right to left bottom to top for sections of the drawing so your rotated or cutaway view indicated in A-A can be found in section C-6 of the page you are dealing with. Just like a Gazetteer map book.
Drawing Change Notices (DCN's) will be either attached to or incorporated on the last pages of the entire drawing usually after the parts lists. Advanced Drawing Change Notices (ADCNs) will usually be stapled to the first page of a drawing and tell you the section and view affected, this is a'quick bandaid' to correct the drawings intent until the change can be incorporated, sometimes the guys in the cartoon shop (engineering) will wait until several items need redrawing before they make the changes, this depends on the manufacturer's policies.
Always be sure you are using the latest drawing, see if you can find a book @ the local FBO (or check to see if the info is on'line) that deals with reading blueprints, I've given you the 'fast and dirty' on prints, but once you figure the system out, they are as easy as reading the Sunday Funny Papers.

And, never scale anything from a paper drawing! You have no idea how much the drawing you are using has been reduced to fit the piece of paper you are holding! If you can, use the fulll sized velum master drawing for measurements and dimensions, and the velums will be hard/impossible to obtain since they ARE the master drawings.

[AHancock51]

Basically, a blueprint is like a map. Start @ the bottom right corner to find out what the drawing (also called a cartoon by sheetmetal guys) pertains to, also there you will find your tolerances for dimensions, usually +/- .003 in.. Then up to the upper right corner for notes and drawing changes (as things are refined, rather than redraw the whole thing, a change will be made to a portion of the drawing and when they were incorporated into the drawing) Views shown on the drawing may have facing arrows and two matching letters (A-A, B-B, etc.) and a note saying 'see view A-A in C-6' drawings are right to left bottom to top for sections of the drawing so your rotated or cutaway view indicated in A-A can be found in section C-6 of the page you are dealing with. Just like a Gazetteer map book.
Drawing Change Notices (DCN's) will be either attached to or incorporated on the last pages of the entire drawing usually after the parts lists. Advanced Drawing Change Notices (ADCNs) will usually be stapled to the first page of a drawing and tell you the section and view affected, this is a'quick bandaid' to correct the drawings intent until the change can be incorporated, sometimes the guys in the cartoon shop (engineering) will wait until several items need redrawing before they make the changes, this depends on the manufacturer's policies.
Always be sure you are using the latest drawing, see if you can find a book @ the local FBO (or check to see if the info is on'line) that deals with reading blueprints, I've given you the 'fast and dirty' on prints, but once you figure the system out, they are as easy as reading the Sunday Funny Papers.
And, never scale anything from a paper drawing! You have no idea how much the drawing you are using has been reduced to fit the piece of paper you are holding! If you can, use the fulll sized velum master drawing for measurements and dimensions, and the velums will be hard/impossible to obtain since they ARE the master drawings.

Wow!! This is great stuff, thank you so much for the information! I have always been curious about this, you've given me an awesome introduction to it all. I'll keep referring to this post as I move along I'm sure. It definitely sounds like once one understands how to read them, they become just as easy as doing the crosswords in the paper, haha. Thanks again, wow!!

- Austin Hancock

[The Inspector]

A great book to find and own is, curiously enough, 'How to Read Aircraft Blueprints' (who'da thunk it?) by Albert A. Owens, published in 1940 (things don't change a lot do they?) which should be available either through a major bookseller or online.

You might also want to become comfortable with Cartesian Coordinates which Douglas used forever. Personally, even though I worked on a lot of Renton and Everett tin, I prefer Cartesian for finding locations. It's pretty much the same coordinates used by architects. X, Y, and Z for left/right, front to back, and up and down, then you get into X+/-, Y usually always plus, and Z +/-. Boeing has reinstated (sort of) Cartesian into the 787 but seem to have screwed that up too, confusing X and Z so in and out is now up and down, and up and down is now in and out. (It's amazing more airplane mechanics don't show up @ work toting a 12 Ga. shotgun). Hold your fist out, stick your thumb out X, point ahead Y, and point your middle finger down, Z.

Since the dawn of the jet age, all big U.S. aircraft manufacturers keep the fuselage station locators as positive numbers, that way if they stretch the airplane, the body datum for weight and balance is always positive (example, a DC-9 series 10 is 104 feet long, an MD-80 is 147 feet long, yet the very tip of the radome is station 7 on both, incidentally, all versions of the DC-9 series are built under the same ATC type certificate) it also has to do with swept wing designs and using % of MAC (Mean Areodynamic Chord) to calculate C.G. and weight and balance. I remember in A&P school in Airframe Class having to 'weigh' a DC-4 on paper. That required 'removing' everything forward of the wing leading edge not bolted down (because that stuff was all negative Datum) while recording the location and weight, doing the empty calculations, then adding it all back one part @ a time and working the arm and moment of each piece matematically 'add two sets of manuals @ 7 pounds each @ station minus 58...' no wonder that W&B was more hated by mechanics than blind dating your ex wife, and that was back when a calculator was the guy who was always trying to figure out how to date the waitress-it was all paper and pencil and long division and clouds of invectives, dark, shaded doubts about the engineers parentage and hereditary and sexual preferences.

[AHancock51]

A great book to find and own is, curiously enough, 'How to Read Aircraft Blueprints' (who'da thunk it?) by Albert A. Owens, published in 1940 (things don't change a lot do they?) which should be available either through a major bookseller or online.

You might also want to become comfortable with Cartesian Coordinates which Douglas used forever. Personally, even though I worked on a lot of Renton and Everett tin, I prefer Cartesian for finding locations. It's pretty much the same coordinates used by architects. X, Y, and Z for left/right, front to back, and up and down, then you get into X+/-, Y usually always plus, and Z +/-. Boeing has reinstated (sort of) Cartesian into the 787 but seem to have screwed that up too, confusing X and Z so in and out is now up and down, and up and down is now in and out. (It's amazing more airplane mechanics don't show up @ work toting a 12 Ga. shotgun). Hold your fist out, stick your thumb out X, point ahead Y, and point your middle finger down, Z.

Since the dawn of the jet age, all big U.S. aircraft manufacturers keep the fuselage station locators as positive numbers, that way if they stretch the airplane, the body datum for weight and balance is always positive (example, a DC-9 series 10 is 104 feet long, an MD-80 is 147 feet long, yet the very tip of the radome is station 7 on both, incidentally, all versions of the DC-9 series are built under the same ATC type certificate) it also has to do with swept wing designs and using % of MAC (Mean Areodynamic Chord) to calculate C.G. and weight and balance. I remember in A&P school in Airframe Class having to 'weigh' a DC-4 on paper. That required 'removing' everything forward of the wing leading edge not bolted down (because that stuff was all negative Datum) while recording the location and weight, doing the empty calculations, then adding it all back one part @ a time and working the arm and moment of each piece matematically 'add two sets of manuals @ 7 pounds each @ station minus 58...' no wonder that W&B was more hated by mechanics than blind dating your ex wife, and that was back when a calculator was the guy who was always trying to figure out how to date the waitress-it was all paper and pencil and long division and clouds of invectives, dark, shaded doubts about the engineers parentage and hereditary and sexual preferences.

Good to know! I will most definitely look for this title, seems that you will be a good reference for me on my project! Thanks again...

[avenger2504]

This has been an interesting thread, not just because of the aircraft side of it but I use x y z co=ordinates all day long in my job as a CNC machinist! For me Z is depth of cut (and to confuse matters can be vertical or horizontal depending on the type of Milling machine) X and Y are normally the table or work piece movements but you also can have 4the axis machines(so a B axis). Don't even want to know about the 5 and even 6 th axis mills, my job's hard enough some days!

[The Inspector]

Yep! Z+down and Z- is up from the zero reference plane. X+ is right of CL and X- is to the left of the CL, used to love explaining to folks how you could be standing in X- holding a mirror and look @ Z+.

[Enemy Ace]

Just curious have you studied the Jurca plans and thought about scaling them up to build your 51B?

[AHancock51]

Just curious have you studied the Jurca plans and thought about scaling them up to build your 51B?

I have in fact thought of that, but from what I've heard, upscaling would be a pretty big task. If it's not though, I'd be willing to try that route!!

[51fixer]

The P-51 series of prints is available from the NASM in microfilm format and from online sources as .tiff images.
Figured you might know about it already.
I have both types.
Firewall on the P-51 is basically 3 chunks of steel plate with a formed Stainless steel bathtub shaped to clear the oil tank in front of the cockpit and another Stainless Steel section along the bottom in front of the wheel well.
The lower portion in front of the wheel well differs from B/C to D as the wing leading edges differed along the inboard end.

[AHancock51]

The P-51 series of prints is available from the NASM in microfilm format and from online sources as .tiff images.
Figured you might know about it already.
I have both types.
Firewall on the P-51 is basically 3 chunks of steel plate with a formed Stainless steel bathtub shaped to clear the oil tank in front of the cockpit and another Stainless Steel section along the bottom in front of the wheel well.
The lower portion in front of the wheel well differs from B/C to D as the wing leading edges differed along the inboard end.

Ah yes, I recently got a hold of the blueprints in .tiff format. Thanks for the info., did not know that's what it's shaping was for!

[51fixer]

The P-51 series of prints is available from the NASM in microfilm format and from online sources as .tiff images.
Figured you might know about it already.
I have both types.
Firewall on the P-51 is basically 3 chunks of steel plate with a formed Stainless steel bathtub shaped to clear the oil tank in front of the cockpit and another Stainless Steel section along the bottom in front of the wheel well.
The lower portion in front of the wheel well differs from B/C to D as the wing leading edges differed along the inboard end.

Ah yes, I recently got a hold of the blueprints in .tiff format. Thanks for the info., did not know that's what it's shaping was for!

To get clearance between the rear of the engine and the oil tank they had to put the rear edge of the tank just a hair behind plane of the firewall.
They cut an opening in the thick steel of the firewall and stamped a thin SS piece into the shape of the rear side of the oil tank so the tank will set against it and be strapped in on the top and front.
Somewhere in the Bald Eagle thread there are pictures of engine changes that show the tank and how it is supported.

[AHancock51]

The P-51 series of prints is available from the NASM in microfilm format and from online sources as .tiff images.
Figured you might know about it already.
I have both types.
Firewall on the P-51 is basically 3 chunks of steel plate with a formed Stainless steel bathtub shaped to clear the oil tank in front of the cockpit and another Stainless Steel section along the bottom in front of the wheel well.
The lower portion in front of the wheel well differs from B/C to D as the wing leading edges differed along the inboard end.

Ah yes, I recently got a hold of the blueprints in .tiff format. Thanks for the info., did not know that's what it's shaping was for!

To get clearance between the rear of the engine and the oil tank they had to put the rear edge of the tank just a hair behind plane of the firewall.
They cut an opening in the thick steel of the firewall and stamped a thin SS piece into the shape of the rear side of the oil tank so the tank will set against it and be strapped in on the top and front.
Somewhere in the Bald Eagle thread there are pictures of engine changes that show the tank and how it is supported.

Oh ok, cool! I'll check out the thread and see what I can find...