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Terms like Loft, Contour, Ordinates, Lines, and Layout are likely not the first words that come to mind when you think about designing an aircraft. However without these items, standardizing the production of large numbers of aircraft during WWII would have been impossible. Designing an aircraft is a complicated process, and if you’re reading this it means you’ve either come across these 5 terms, or have an interest in learning more about why they are so critically important.
Very often in general discussions, the terms loft, contour, lines, layout, and ordinates are used interchangeably. At a high level, this is appropriate because all of these terms can describe and illustrate the “shape of an aircraft”. When looking at an aircraft profile as a silhouette, the line that can be drawn around the outside edge is the loft or contour line (figure 1). The straight lines and curves that make up this outside edge are the result of meticulous mathematical calculations that were done by the “loftsmen” in WWII aircraft factories.
Curves are the most difficult shapes to communicate on any engineering drawing, and lofting is the practice that allows for accurate reproduction of curves, and assures that every serial number within a given aircraft model range has an identical profile.
Without loft calculations, the production of accurate tooling and manufacturing would be impossible. If you are familiar with photographs from WWII that show groups of engineers laying on the floor all working on the same massive “drawing” – this is lofting (figure 2). Loft drawings, or layouts, were most commonly done on large sheets of metal or wood, and were made in full scale at a tolerance of no less than 0.007 inches. In his 1946 book “Aircraft Drafting”, Hyman Katz describes the importance of accurate layouts by saying:
“When the layouts have been completed and checked, the loft must then provide templates for all parts and the tools that the shop will need in fabricating all sections of the plane. It is also the responsibility of the loft to furnish any special information relative to the lines or any detail parts of the plane to engineers, tool designers, or shop workers to aid in design, tooling, or fabrication.”
Once the loft was finalized, the wood or metal layouts would then be photographed for use in the factory setting. If you have ever been frustrated by not being able to locate a layout that is listed on an engineering drawing (figure 3), that is because you are actually attempting to locate the huge metal or wood plate that would have been stored in the factory!
During and after WWII Loftsmen and Engineer/Draftsman worked together to create standard engineering drawings that functioned within the loft parameters, assuring that the parts fit exactly, and could easily be mass produced. Using the data from both the loft and engineering drawings, templates could be created, and were stored in the factory to create dies and tooling. There is a great Grumman F6F Hellcat promotional video from 1944 on YouTube that shows a bit of the process of creating templates – see minute 12:53.
So now that we know a bit more about what lofting is, let’s look at an actual example. Because loft data defines the outside line or shape of the aircraft, it makes sense that these drawings would also be called “contour drawings”. Contour is a word that will often be seen in the title block of a drawing indicating loft data. Loft or contour drawings are easy to pick out because they either contain nothing more than large tables of decimals or fractions (figure 4), or a series of concentric lines getting larger or smaller (figure 5).
Determines the lines of an aircraft, and furnishes offsets and ordinates
The outside shape of an aircraft seen from the plan, side, and end views.
The dimensions from the horizontal and vertical center line of the plan to its contour or skin line.
The dimensions above and below the chord plane of the wing to its contour or skin line.
If you are someone who enjoys redrawing historic engineering drawings in CAD programs, then you’ve likely come across the need for the data contained on loft or contour drawings. There is not a week that goes by where I don’t get a question about loft, ordinates, or contours at AirCorps Library. However, my answer is usually not satisfactory because this data is often not available.
If loft data is so crucial, the next logical question is “why can’t I find it on AirCorps Library?”. The simple answer is that most manufacturers didn’t include this data with the rest of the regular engineering drawings. It is my personal opinion that loft and contour data was considered more valuable and more highly classified than regular drawings. Now that we’ve discussed that loft was the basis for everything in the aircraft, it is logical to assume that aircraft manufacturers were keenly aware that if their loft data fell into the wrong hands, it would be the key to reproducing an exact replica of the aircraft in question.
Some manufacturers, like Lockheed, occasionally included bits of lofting data on individual engineering drawings. This happened most commonly for smaller parts and components (figure 6), and extremely rarely for larger assemblies like the wing or fuselage.
There are small selections of loft data included on the microfilm for several WWII aircraft, but it is quite rare to find a complete set of loft/ordinates. At AirCorps Library we always make loft data available if it is found on a set of microfilm for an aircraft. Unfortunately, that means if we don’t have it on the site, it didn’t come on the microfilm.
When restoring a WWII aircraft, the only way to gather the necessary lofting information when an official contour drawing is not present is to 3D scan the area of the aircraft in question – something that we do regularly at AirCorps Aviation. If you have an interest in the incredibly technical (but fascinating) world of 3D scanning, check out the two blog posts written by our in-house 3D scanner Stefan Hokuf. The first discusses what 3D scanning is, and the second outlines different types of scanning, and what to know before having a part scanned.
Because loft, ordinates, and contour questions are so common, I wanted to write this blog not only to explain what it was, but also to outline what loft data we DO have on the AirCorps Library website. The chart below outlines the available loft, contour, layout, line, and ordinates drawings for different aircraft, illustrating just how much is (and is not) available. Each part number in the charts below is linked and will take you to the given loft or contour drawing (if you have an active AirCorps Library membership).
Ordinates for Boeing B-17 Flying Fortress |
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Part Number |
Description |
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Contours – Inboard Wing |
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Contours – Cockpit and Fairing |
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Rib Contours Stabilizer |
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Ordinates Empennage Rib |
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Fairing Ordinates Top Gun Replacement |
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Ordinates Stabilizer Rib |
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Ordinates Wing Rig |
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Rib Ordinates Vertical Tail Surface |
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Lines Rear Gun Enclosure Fairing |
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Lines Fin Fairing – Station 8-11 |
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Ordinates for Boeing PT-17 Stearman |
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Part Number |
Description |
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Ordinates – NACA 2213 Airfoil 60” Chord |
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Ordinates for Chance-Vought F4U Corsair |
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Part Number |
Description |
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Lines and Ordinates – Body Group Fuselage |
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Lines and Ordinates – Fuselage – Cockpit Cabin – Windshield and Sliding Section |
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Lines and Ordinates – Fuselage – Cockpit Cabin – Windshield and Sliding Section |
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Lines Bod Group Fuselage F4U-1 |
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Windshield Lines |
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Lines Cockpit Cabin – Sliding Section |
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Lines Center Section – Air Duct Internal |
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Ordinates for Curtiss P-40 Warhawk / Kittyhawk |
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Part Number |
Description |
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Loft Lines – Engine Cowl Allison Y-1710 F3R Body Plan |
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Ordinates Wing Bulkhead and Jig Section |
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Fuselage Ordinates |
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Ordinates – Engine Cowl (PGW-R1830-13) |
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Ordinates – Wing Bulkhead and Jig Sections YP-37 |
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Lines Radiator Fairing |
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Lines Landing Gear Cowling |
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Lines Fuselage Stabilizer Fairing |
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Lines Fuselage |
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Lines Cowl |
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Basic Cowl Lines |
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Lines Layout Oil Cooler and Carburetor Entrance Duct |
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Lines Layout Keel Fairing |
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Fuselage Structural Layout |
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Fuselage Structural Layout |
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Ordinates for Douglas A-24 Banshee (SBD Dauntless) |
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Part Number |
Description |
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Wing Lines Drawing and Master Diagram |
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Ordinates for Douglas DC-6 |
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Part Number |
Description |
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Loft Data Index |
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Ordinates for North American Aviation B-25 Mitchell |
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Part Number |
Description |
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Ordinates NA-62 Wing Outer |
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Ordinates NA-62 Wing Center |
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Ordinates – Empennage |
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Ordinates – Fuselage Stringer |
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Ordinates – Fuselage |
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Ordinates – Fuselage Stringer |
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Ordinates – Fuselage |
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Layout – Outer Wing Flap and Flap Slot Lines |
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Ordinates for North American Aviation P-51 Mustang |
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Part Number |
Description |
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Ordinates P-51D – Wing |
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Accessing the loft and ordinates drawings linked in the table above requires a membership to the AirCorps Library website. Membership is either $9 per month or $75 per year, and gives access to over half a million WWII era engineering drawings on top of the ones listed here, and over 12 thousand aircraft technical manuals.
I hope you’ve enjoyed this deep dive into the world of lofting. If you have any additional questions that I did not answer, please feel free to reach out to me directly at: estera@aircorpsaviation.com
Great article about lofts, etc. I would add one little lesson I learned early at Boeing. The White Model took precedent over drawings, lofts, and contours. The white model was built up of plywood sections cut to the loft sections then filled with plaster (hence white model) and smoothed. Before CNC machining the molds for stamping, stretch forming sheet metal, and making fixtures were developed from making a cast from the white model. Since it was what was actually produced the white model was the final authority if there was a discrepency between the loft drawings and the white model.
Great read Ester, lots of interesting info for those of us that geek out on old airplanes.
Hi Ester,
First, thanks for your interest in and appreciation of aircraft draftsmen and draftswomen and the artwork that they produced.
I was an aircraft designer/drafter and then design engineer for years. My career spanned the time between manual drafting (drawing board) and CAD. I was considered quite proficient at both. I never worked in a Loft Group but worked with their products extensively to develop the engineering for finished parts and installations.
As Shawn Murphy noted, there was always a tooling master model built that was intended to represent the loft in 3-dimensions. The ones that I remember were full size and had many master lines scribed on them. Although they looked like plaster, I think the tooling guys used some kind of cement to make them because they were hard like concrete not soft like plaster.
Here is a list of lofting-related materials that I used to learn about lofting, etc. This is intended mostly to give people that are also interested in the subject additional resources for study and appreciation. Air Corps Library has the Navy Bureau of Aeronautics set of 4 booklets prepared by the International Textbook Company that are also very good.
Aircraft Lofting articles in Aero Digest magazine:
“Lofting Problems of Streamlined Bodies” by Carter M. Hartley (Chief, Lofting Dept.) and Roy A. Liming (Charge, Lofting Mathematics), both of North American Aviation,.
Part 1 – Dec 1941
Part 2 – pp 180, Jan 1942
Part 3 – pp 151, Feb 1942
Part 4 – pp 210, Mar 1942
Part 5 – pp 126, Apr 1942
Part 6 – pp 249, May 1942
Part 7 – pp 164, Jun 1942
Part 8 – pp 209, Jul 1942
Part 9 – pp 234, Jan 1943
Part 10 – pp 130, Feb 1943
Part 11 – pp 183, Mar 1943
Part 12 – pp 200, Apr 1943
Part 13 – pp 160, May 1943
Part 14 – pp 205, Jun 1943
Part 15 – pp 309, Jul 1943
Part 16 – pp 197, Aug 1943
Part 17 – pp 193, Sep 1943
Part 18 – pp 204, Oct 1943
Part 19 – pp 230, Nov 1943
Part 20 – pp 176, Dec 1943
Part 21 – pp 74, Apr 1, 1945
Part 22 – pp 71, May 1, 1945
Part 23 – pp 66, Jun 1, 1945
Part 24 – pp 74, Jul 1, 1945
“Airfoil Development and Structure within the Camber Surface”
Part 1 – pp 66, Nov 1, 1945
Part 2 – pp 64, Dec 1, 1945
Part 3 – pp 56, Jan 1946
Part 4 – pp 47, Feb 1946
Part 5 – pp 76, Mar 1946
Part 6 – pp 76, Apr 1946
Part 7 – pp 78, May 1946
Part 8 – pp 76, Jun 1946
Part 9 – pp 107, Jul 1946
Part 10 – pp 72, Aug 1946
Aero Digest is held by many larger libraries, particularly engineering libraries. It may not be out on the shelves since it went out of print in 1957, but is usually available from the reserves on request.
Aircraft Lofting and Drafting Books:
Practical Analytic Geometry with Applications to Aircraft; Liming, Roy A.; MacMillan, New York, 1944
Mathematics for Computer Graphics; Liming, Dr. Roy A.; Aero Publishers Inc., Fallbrook, CA, 1979
Aircraft Descriptive Geometry Vol 1; Vaughn, Walter; Aircraft Publishing, Glendale, 1941
Aircraft Lofting; Nelson, William; McGraw-Hill, New York, 1941
Ship and Aircraft Fairing and Developments For Draftsmen and Loftsmen and Sheet Metal Workers; Rabl, S. S.; Cornell Maritime Press, Cambridge, MD, 1941
Aircraft Drafting: Parts 1- 3; Brimm, Daniel J., Jr.; International Textbook Press, Scranton, 1940
Aircraft Drafting; Katz, Hyman H.; MacMillan, New York, 1946
A Manual of Aircraft Drafting; Svensen, Carl Lars, M.E.; Van Nostrand, New York, 1941
Aircraft Layout and Detail Design; Anderson, Newton H.; McGraw-Hill, 1946
Aircraft Detail Design; Meadowcroft, Norman; McGraw-Hill, 1942
Aircraft Template Development; Gentle, Ernest J.; Aero Publishers, Glendale, 1942
Drafting for Engineers; Svensen, Carl Lars; Van Nostrand, New York, 1927
Engineering Drawing; French, Thomas E.; McGraw-Hill, New York, 1941
Most of these are occasionally available from used book sellers on the Internet.