B-26 Engineering Data/Technical Information (From Martin's Own Blueprints)

[Maty12]

Hello all!

I decided I need a place to compile all my findings from analyzing the many technical drawings I scanned from the Smithsonian's microfilm collection. It would be pretty difficult to find a more confusing aircraft to research or model, because of decisions made by Martin, the USAAF/USAF, and persistent myths that get repeated very often, and I want to spare any future researchers/modelers from getting confused or stumbling upon incorrect info. I plan on uploading some spreadsheets at a later date to replace my outdated and incorrect table found elsewhere on this forum. They will be:
-A table of all stations for the fuselage, wing, ailerons, wing flaps, nacelle, fin, rudder, stabilizer and elevator, detailing what parts were located where for each B-26 model.
-A table describing the production models listing serial numbers along with who's been converted into what.
-A table showing how many different versions of each subassembly existed, and what models used which.
-A table listing all B-26-MA and B-26B squadron assignments as best I've been able to find.
-A table describing the "B-26 Skeletons", a concept I'll explain later in this post and which I think will be very helpful for any future modelers and kit builders.

First things first: Defining Terms
Talking about the B-26 is by its very nature confusing, so I will do my best to avoid using conflicting terms. I will also be doing my best to use the language used in the technical drawings. I will also avoid using fractions when talking about dimensions because I find them annoying and they're harder to use in 3D modeling software.

Production Models
-B-26: the term I'll use for the rest of this thread when referring to all models of the aircraft, or nonspecific models.
-B-26-MA: the term I'll use when referring to the first production model, of which 201 were built. Martin and the USAAF just call this the B-26, which makes thing confusing. People (myself included elsewhere) usually call it B-26-MA, and while I have not found any official use of this name and the B-26 predates the USAAF's use of production suffixes (-MA, -MO), a way to refer to specific models is needed for clarity's sake so it'll have to do.
-B-26A: the term Martin uses to describe the A and A-1 models, because they are identical other than the engine
-B-26B: the term Martin uses for all short wing B-26B models (B-26B-MA through B-4), but only the short wing models. The Tail Section assembly was significantly redesigned to accommodate the new twin-gun turret, but the empennage stayed the same (with the exception of a new rudder with broader ribs from 41-17704 onwards). This new tail assembly made the fuselage 0.5" shorter than the previous models, at 698". The last 141 B-26B-4s may have had the "B-26B-1" waist gun positions installed at the factory. All B-26B-4s had a new longer landing gear strut that was mounted lower on the fuselage, I'm still researching its specifics as the only drawings I've found seem to contradict photographic evidence.
-B-26B-MA: the term I'll use to refer to the first production block of the B-26B, of which 308 were built. Again the same problem as the B-26-MA necessitates adopting unofficial terminology.
-B-26B1 Quick Fix (QF): Martin's term for the long wing B models fitted with the same manual turret as the short wing models (B-26B-10-MA & B-15-MA). Despite changes to the Aft Fuselage assembly to accommodate the new fin and waist gun positions, the most parts of the B-26B's tail section and its overall contours were maintained. I'll describe the long wing modifications in more detail in the Skeleton section.
-B-26C Quick Fix (QF): Martin's term for B-26Cs fitted with the same manual turret as the short wing models, effectively making this term interchangeable with "B-26C-5-MO" since that is the only production block it applies to. This production block was also the only one to retain the waist gun position from the B-26-MA and is often seen with the waist gun position of the "B-26B-1".
-B-26B1 Permanent Fix (PF): The tail section was once again redesigned to accommodate a Bell M-6 tail turret, as was the rudder for better streamlining with the turret's canopy. Stabilizer, Elevator and Fuselage Aft Section stayed the same. These modifications reduced the B-26's length from 698.5" (58' 2.5") to approximately 675" (56' 6"). Includes blocks B-26B-20 through B-55)
-B-26B1: Martin's term for all long wing B blocks. USAAF Tech Orders sometimes refer to this model as the B-26B-1, which is very confusing because of the...
-"B-26B-1": A term often used to describe B-26B-MAs bound for the MTO that were modified by Martin's Omaha Modification Center to be more combat capable. I'm not sure this term was contemporary nor who it was used by.
-B-26C Permanent Fix (PF): To the B-26C as the B-26B1 PF is to the B-26B1. Includes blocks B-26C-10 through C-45.
-B-26C, B-26F, B-26G: Pretty straightforward, Martin's terms for all C, F, and G production blocks. F and G models are also called "Twisted Wing" or "Drooped Fuselage", because the wing and everything attached to it (nacelle and landing gear) was rotated 3.5 degrees to increase takeoff performance. I don't know what point they were rotated around, but suspect either the center or bottom of the Center Wing's Rear Spar. I'm not very knowledgeable on the F and G models. Sharp-nose (not shark-nose, as sometimes stated, sometimes called Revised Leading Edge) ailerons may have been introduced on the 51st B-40-MA, I am not sure whether any B-26Cs had those. Starting with the B-26F-2 the M-6 tail turret was replaced with the M-6A, which had a canvas cover instead of the semi-spherical plexiglass cover of the M-6.

Fuselage Group
-Nose Cone: Martin uses both this term and Nose Turret to refer to the Plexiglas nose cone, I prefer the former.
-Forward (Fwd) Fuselage: Martin's term for the forward fuselage assembly, which extends from station 33 to station 230.75. Contains the nose gear and the bombardier, pilot, co-pilot, navigator and radio operator's stations.
-Pilot's Enclosure: Martin's term for the cockpit canopy.
-Center Fuselage: Martin's term for the center fuselage assembly, which extends from station 230.75 to station 434.25. Contains the wing center section, the forward bomb bay and the aft bomb bay.
-Rear Fuselage: Term I'll use for the entire aft fuselage assembly, itself made of two large assemblies, which includes the entire fuselage from station 434.5 onwards and the tail turret.
-Deck Turret: Martin uses this term, Dorsal Turret and Upper Rear Turret to refer to the Martin 250CE electric turret located at station 460.25.
-Tunnel Gun: Martin's term for the ventral gunner's position. The gunner fires a .30 cal (sometimes replaced with a .50 cal) out of the camera hatch which extends from station 512.25 to station 548.375. This gun position as well as the camera hatch were deleted from the B-26B-10-MA onward.
-Waist Guns: Also called Side Guns in early Martin drawings & documents, there were three or four main configurations:

Most if not all B-26-MA through B-26B-MA were modified with fittings for 2x .30 cal machine guns at station 499 1/4, firing through the camera side windows (which was located between stations 486 1/4 and 512 1/4), one on each side. B-26-MA crews were only provided with one gun to attach to either of these positions in the tunnel position, something the 22nd BG quickly remedied on their aircraft. These mounts were frequently upgraded to hold .50 cals in the field, with additional rectangular sighting windows and sometimes wind deflectors added. B-26Bs may have already come with waist guns, it's not 100% clear to me, or what caliber they were if they did.​

The "B-26B-1" configuration was similar, with changes to the windows that allowed them to close with the guns in place, and with the now .50 cals being mounted slightly aft at station 500 11/16 on a new platform. The additional windows were now circular. There may have been another configuration with the old camera windows, it's hard to tell from photos. It's also hard to tell if the windows were enlarged or not. Sometimes it looks like the old windows were kept but are now part of a bigger removable hatch? This configuration can be seen on this 50 Hour Inspection instructional video using a B-26C-5-MO.

From the B-26B-10-MA & B-26C-10-MO onward the waist gun windows were moved aft (to between stations 512 1/4 and 548 3/8) and significantly enlarged, with new hatches that slid upwards on tracks. There was also a single circular sighting window above the waist gun hatches. I do not know the exact location of the gun mounts.
​

-Aft Fuselage: Martin's term for the assembly that extends from station 434.25 to station 581.375. Contains the deck turret and waist and/or tunnel gunner's compartment (depending on the model). The fin attaches to the top of this section.
-Tail Section: Term I'll use for the assembly that extends from station 581.375 onwards. Contains the stabilizer's center section and the tail gunner's station.
-Fuselage Tail Cone: Removable endcap for the tail. Extends from station 693 to station 698.5 on B-26-MA & B-26A, or station 670.75 to station 698 on the B-26B. B-26B1s, Cs, Fs and Gs did not need tail cones.

Wing Group
-Center Wing: The section of the wing located inside the fuselage. The spars in this section are connected to station 230.75 and station 346.25 by shear webs and are straight and of constant section, perpendicular to the direction of flight when viewed from above. This section extends 46" from the fuselage centerline, to wing station 46.
-Outer Wing: The panel that makes up most of the wing. This section extends from station 46 to station 364 and can be divided into Nose Section, Main Wing Section and Trailing Section. The Nacelle and Wing Tip attach to this section.
-Wing Main Section: The section of the Outer Wing between the two wing spars, that the nose and trailing sections attach to. To this section attach the nose section, trailing section and landing gear.
-Wing Nose Section: The section of the Outer Wing forward of the forward spar, which is itself built of several smaller sections. Contains the landing lights, running light and deice boots (if fitted).
-Wing Trailing Section: The section of the Outer Wing aft of the rear spar, which is itself made of two sections. The inboard section contains the wing flaps, while the outboard holds the ailerons.
-Wing Tip: The section of the wing extending from station 364 onwards. It contains navigation lights and the pitot tube, as well as one of the aileron hinge brackets in the long wing models. Deice boots are also be attached to this section if installed.

Engine/Nacelle Group
-Nacelle: the term Martin uses to describe the entire nacelle assembly, including the engine hood. Stations are measured along the thrust line, with station 0 being the intersection of the centerline for the propeller blades.
-Engine Hood: the term Martin uses to describe the engine cowling. It is split into five (5) components: two (2) upper panels (which include the carburetor ducts), two (2) side panels and one (1) lower panel (which contains the oil cooler duct). Extends from station 6.6 to station 53.59 (for the upper panels) or station 54 (for the lower panel). These panels are attached to the engine via two mounting rings.
-Desert Cowlings: the term the B-26B manual uses for the engine hood upper panels fitted with enlarged air intakes to allow for installation of air filters. These were fitted to "B-26B-1s" and all production models from the B-3 to the G-25-MA.
-Venturi Cowl: the term Martin uses to describe the section of the nacelle aft of the engine hood and forward of the firewall (station 104.25), with holds the engine's accessories including the oil tank and oil cooler. It is split into five (6) panels: two (2) upper panels, two (2) center panels and two (2) lower panels. The two (2) fairings for the tailpipes are also a part of this unit and are located between the center panels and the lower panels. The upper panels extend from station 53.59 to station 103.65, the center panels from station 54 to station 114.74, and the lower panels from station 54 to station 103.65.
-Tailpipe: Martin's term for the exhaust stacks.
-Rear Nacelle: the term Martin uses to describe the assembly that extends from station 103.65 onwards. This section attaches to the wing outer panels and contains the landing gear doors.
-Nacelle Tail Cone: Martin's term for the removable endcap for the nacelles that extends from station 229.25 to station 262.16 on short wing models and from station 218.13 to station 262.16 on long wing models.

Skeleton
A WIP version of this is available here: B-26 Skeletons. See reply #12 for notes and instructions on it.

So, with that out of the way, what the hell is a B-26 Skeleton? Simple, it's what you get when you combine the smallest amount of information required to describe the airplane's geometry. For scale modeling, it's useful to figure out lengths and distances when modifying kits. For 3D modeling, it's a very helpful tool in order to accurately place all the subassemblies. These are still WIP but I plan on sharing the blender files for them once they are complete. Currently missing are the main landing gear, the nose gear doors and all other doors, the tail turrets, the wing flaps and the ailerons. I also have yet to add the arcs for the tips of the wings, stabilizer and fin. I also have yet to make a skeleton for the non-Quick Fix B1 & C or the B-26F & G, the latter two because I have very little information on then.

I will now use the skeletons as a visual aid to explain how the B-26's wings and empennage were enlarged. Black represents the B-26 and B-26B, while orange represents the B1/C Quick Fix. It's important to remember that Martin's priority was reusing as many components as possible, and keeping the attachment points the same.

First off, the wings. Martin kept the center wing and the wing main section's geometry the same, though the parts themselves were not kept. The nose and trailing sections were replaced with ones with longer chord at station 364. The new trailing section was significantly larger and responsible for the most noticeable change in the wing's shape. Since Martin had to redesign this section anyway, they switched from split flaps to slotted flaps as recommended by NACA. The old wing tip was replaced by a new unusually long unit which extended from station 364 to station 426. This made each wing 36" longer, for a total increase in span of 72" or 6'. Keeping the main section's contours meant the nacelles needed much less extensive redesign.

For the empennage, Martin had less constraints. As such, they essentially just extended the old units at the bottom. The fin and rudder grew 20", while each stabilizer and elevator grew 24.25".

While the old fin was held in place only by two bolts at the spar and a row of screws attaching its lowest rib directly to the skin of the upper fuselage, the new fin's lowest rib was now recessed and a new hinge bracket & bolt was attached to a bracket near the leading edge. As such, the fin now had three attachment points, wish the resulting skirt receiving a rubber strip at the interface with the fuselage. The lower section of the rudder was redesigned to still fit in the old fairing at the top of the tail section (note that the orange and black lines intersect at the bottom of the rudder trim tab's trailing edge). The main priority for Martin was keeping the rudder's attachment points the same, particularly the torque tube contained in the aft fuselage.

The theoretical rudder hinge's centerline was thus kept, while the fin spar and nose of the rudder gained a distinct break/angle in their lines. It's worth noting that with this change Martin also changed the datum for the fin's stations from a line tangent to the fuselage centerline to the theoretical base of the fin, which used to be station 34 (which was also the same between all models). So while the fin gained 20", one must subtract 14" from the short-wing B-26s' stations to find the corresponding stations and ribs on the long wing models. Most of the fin's ribs were reused.

The Stabilizer was trickier to modify because three mounting points had to be kept: the front spar, the rear spar and the elevator torque tube. Martin also wanted to avoid reshaping the fuselage frames entirely if possible. The solution was an extension that had constant section between the two spars, with only the nose ribs tapering. The elevator was a much easier affair, with Martin extending its bottom and then simply "cutting" (reshaping) the ends of the trim tabs so that they lined up with the pre-existing fillet from the B-26B. A new fillet and the two bulkheads that held the stabilizer's spars were some of the very few changes made to this section.

B-26B Tail (note that the angled/cut section ends at the elevator):

B-26B1 "Quick Fix" Tail (angled/cut section continues into the elevator, rounding off into the trailing edge with an arc of radius 5"):

Hope y'all find this informative!
-Matt

 

[Maty12]

Correction/addendum to my original post, which I've since edited:

I said the fin was attached to the fuselage via two bolts at the spar and a row of rivets attaching the lowest rib to the top of the fuselage. That rib was actually attached to the fuselage via forty 1/4" screws according to the E&M manual. This makes sense to me, as the unit has to be easily removable for repairs/replacement. The bolts were 5/8" units.

Also according to that manual, the wing outer panel is attached by four 1/4" bolts, two at each spar, and also by 3/8" bolts at the crest of each corrugation.

The stabilizer outer panels are attached by four 1/4" bolts each, two at the front spar and two at the rear spar.

 

[Greg Boeser]

Great info, Maty!

 

[Maty12]

Great info, Maty!

Thanks, Greg!

 

[Juanita]

Excellent work Matt.
It is always very interesting what is uncovered when you 'deep dive' into the technical aspects of an aircraft.
Your research will be very valuable to other folks who study this aircraft type.

Juanita

 

[Maty12]

Excellent work Matt.
It is always very interesting what is uncovered when you 'deep dive' into the technical aspects of an aircraft.
Your research will be very valuable to other folks who study this aircraft type.

Juanita

Thank you, Juanita!

I should have more to post soon, still working on the skeletons and do want to make a post with more general information using actual dimensions

-Matt

 

[Maty12]

Hi all,

Wanted to explain why I haven't updated this thread. I've been trying to use CADsketcher in Blender as well as regular mesh to make the skeletons, and these seem to disagree quite a bit at times. Martin's drawings have also been giving me a hard time, so it will be a while before I can provide information on things such as the arcs that make up the contour of the fin and rudder tips. In the meantime, there is information I can give:

The B-26 is a particularly confusing airplane for any modellers, because different dimensions are measured from entirely different planes of reference, the location of which is often not explained, and sometimes the plane itself isn't even mentioned. Dimensions for the overall airplane, the landing gear, the nacelle and the wing are all taken from the thrust line, while dimensions for the fuselage follow its centerline, and dimensions for the empennage have their own reference plane parallel/perpendicular to the stabilizer's chord plane. The location of these planes is completely ommited from the general arrangement/3-view drawings and has to be figured out from blueprints which often times don't appear relevant at all. The only drawing which shows the location the thrust line is the boresighting diagram for the guns, and the stabilizer from the drawings for the elevator torque tubes and empennage change diagram for the B1. That being said, here is that information:

Reference Planes (from CL Fuselage)
Thrust Line Plane	Value	Notes
Angle	1​	From CL Fuselage
Fuselage Station of Intersection	453.52​	Approximately 453.451" in Thrust Line Plane
CL Propeller	143.58​	Measured in Thrust Line Plane, from point above start of CL Fuselage when CL Thrust is horizontal. This is the Reference Datum for the Engine Nacelle's Stations
Wing Chord Plane	Value	Notes
Angle	4.5​	From CL Fuselage, 3.5 from CL Thrust. All wing dimensions not measured across Chord Plane are measured in Thrust Line Plane
Fuselage Station of Leading Edge	218.58​	Approximated to 218.128" in Thrust Line Plane
Height above Thrust Line at Root	19.9​	Measured at Leading Edge. Approx. 24.0039" above CL Fuselage
Wing Sweep (in inches)	56​	Leading Edge and Trailing Edge both have 56" of sweep (positive and negative, respectively), resulting in perfectly centered 1/3 taper from Root to Tip
Height above Thrust Line at Tip	28.5​	Measured at Forward Spar (12% of Chord)
Stabilizer & Fin Reference Plane	Value	Notes
Angle	0.5​	Positive from CL Fuselage, Negative from CL Thrust
Fuselage Station of Intersection	*​	Intersection of Elevator Hinge CL along Ref Plane and Fuselage CL. Elevator Hinge is 36" aft of Forward Spar at Station 20.75, where Forward Spar is Fuselage Station 581.375
Stabilizer Root Station	32.5​	Above Ref Plane
Stabilizer Zero Sweep Line	60%​	There is Zero Sweep along Elevator Hinge (60% of Chord)
Fin Root Station	34​	Above Ref Plane
Fin Tip Station	145.5​	Above Ref Plane
Fin Sweep (Inches)	6​	Forward Sweep of Rudder Hinge from Root to Tip (55% of Chord)

If anyone wants clarification on these, let me know.

I'd also like to make a retraction. I get my information about specific models/production blocks from Tannehill and Baugher, and update it whenever I find either documentation, original drawings or photos that contradict that information. As such, some things have yet to be corrected. There are also things I'm still researching.

I was under the impression that there was more standardization that there really is between the B1 and C models, as most places list these as being the same, so figured the Bell M-6 tail turret was introduced with production block 20 for both the B1 and C models, but there are photos of B-26C-10s and C-15s with the turret. It is unclear to me when this change occurred in the Omaha production line. I will update the original post once I know more.

There is also the question of the nose gear. Any list of B-26 models will say that the nose gear strut was lengthened by 6 inches starting with the B-26B-4. For a very long time, I thought this was incorrect, as in my mind a longer strut would need a longer wheel well, and clearly the wheel well never changed size. I figured the entire gear assembly was simply moved forward and lower. Photos and measurements I got from Pat Rodgers confirmed that the mounting point was indeed moved, but I somehow missed the obvious until recently: it was also lengthened, and the new position allowed this. This is pretty obvious if one compares photos of the old gear to the new one. On the early models, the gap between the bottom of the oleo strut and the top of the wheel is very small, while on later models that gap is very large. The part that was lengthened was the half-fork that holds the wheel.
I don't have drawings for this version of the landing gear. I do have drawings for what's apparently a third version, which might be the version used in the B-26F/G (I have yet to confirm this), which is longer and mounted lower but not further forward. I do not have much information about this setup. The half-fork is angled backwards either 1" or 2.5 degrees, one of the two.

Will provide more info when I can,
-Matt

*I am not sure of this exact measurement anymore, but in general it's not very useful. It's far better to locate these assemblies through their attachment points instead of a theoretical reference line. (Revised May 24th 2024)

 

[Maty12]

Hey all,

Been a while! I've been bouncing between 3D modeling, going through technical drawings, researching individual aircraft and units, and reading in general. I have a lot I want to post but I have to get my thoughts in order for a lot of it, so for now let's just go with more corrections!

Corrections (Text has been updated)

3.1- Correction of B-26B & B-26B1 Quick Fix sections regarding Waist Guns​

I originally wrote that the waist guns were changed on the last 141 B-26B-4s in the assembly line. I don't remember where I got this info from, I thought it was Tannehill but it isn't (though he also has incorrect info on the waist guns). The last 141 B-26B-4s may or may not have had "B-26B-1" style waist guns installed at the assembly line instead of at a modification center. I need to clarify that this is a different setup from the larger and further aft waist guns that seem to show up on the B-26B-10-MA and B-26C-10-MO as block-standard features. All photos of B-26B-4s seem to show the "B-26B-1" style waist guns, as do most B-26C-5-MO photos, though others seem to show the earlier camera windows suggesting to me that at least on the B-26C-5-MO these were still a modification. More detail under 4.​

3.2- Correction of B-26B, B-26B1 & Tail Cone sections regarding length of B-26B Fuselage​

The B-26B, B-26B1 QF & B-26C QF's fuselage length is not identical to the preceding models (698.5") as I had originally written, it is in fact 0.5" shorter at 698".​

3.3- Correction of B-26C Quick Fix section regarding Tail Turret​

Changed wording to "possibly some B-26C-10-MOs" as I have not found any photos that show B-26C-10s with the QF tail, and currently find it more likely that all B-26C-10s used the Bell M-6 turret instead.​

3.4- Addition of Waist Guns section​

Added the following brief section describing the different Waist Gun (called Side Guns by Martin) configurations of the B-26:
-Waist Guns: Also called Side Guns in early Martin drawings & documents, there were three or four main configurations:

Most if not all B-26-MA through B-26B-MA were modified with fittings for 2x .30 cal machine guns at station 499 1/4, firing through the camera side windows (which was located between stations 486 1/4 and 512 1/4), one on each side. B-26-MA crews were only provided with one gun to attach to either of these positions in the tunnel position, something the 22nd BG quickly remedied on their aircraft. These mounts were frequently upgraded to hold .50 cals in the field, with additional rectangular sighting windows and sometimes wind deflectors added. B-26Bs may have already come with waist guns, it's not 100% clear to me, or what caliber they were if they did.

The "B-26B-1" configuration was similar, with changes to the windows that allowed them to close with the guns in place, and with the now .50 cals being mounted slightly aft at station 500 11/16 on a new platform. The additional windows were now circular. There may have been another configuration with the old camera windows, it's hard to tell from photos. It's also hard to tell if the windows were enlarged or not. Sometimes it looks like the old windows were kept but are now part of a bigger removable hatch? This configuration can be seen on this 50 Hour Inspection instructional video using a B-26C-5-MO.

From the B-26B-10-MA & B-26C-10-MO onward the waist gun windows were moved aft (to between stations 512 1/4 and 548 3/8) and significantly enlarged, with new hatches that slid upwards on tracks. There was also a single circular sighting window above the waist gun hatches. I do not know the exact location of the gun mounts.
​

3.5- Correction of Tunnel Gun section​

Nothing incorrect here, I just forgot to state that the camera hatch and tunnel gun were deleted from the B-26B-10 onward, replaced by the new waist gun windows. Also, this gun was originally a .30 cal, but was frequently switched to a .50 cal in the field and as part of the "B-26B-1" mods.
​

3.6- Corrections to Wing​

Renamed Main Wing to Wing Main Section to keep nomenclature consistent, added running light to list of Wing Nose Section components and deice boots to Wing Tip components.
​

3.7- Correction of Fin paragraph in Skeleton Section​

I incorrectly described the modifications done to the fin's attachment points, stating that a new bolt was added near the fin's leading edge. The new bolt was indeed added, but the fin is no longer attached by screws on the bottom rib. The bottom rib of the fin is now no longer at the very bottom of the fin, making the (now three) bolts the attachment points. There is a small strip of rubber between the fin's new "skirt" and the fuselage. All rudder ribs were also redesigned to change their contour, with the lower ribs also having their chord shortened.​

Future updates: the experimental low-drag landing gear doors that almost got implemented, aileron trim tab changes, comparing different general arrangement/3-view drawings.

Also, if any of y'all have info or photos that support or contradict anything I've said here, please contact me so I can update this further.

Stay tuned,
-Matt

 

[Maty12]

Photo of B-26B-10-MA 41-18272 PN-Q "Murder Inc" and B-26C-5-MO 41-34683 PN-V clearly showing the difference between the waist gun positions fitted to the C-5 and B-10 models, courtesy of the American Air Museum In Britain. Murder Inc's left waist gun hatch is in the closed position. Note the difference in shape, size and location of the window, as well as the size and number of sighting/scanning windows above the waist gun.

 

[Aeroweanie]

Can you share your model? I'd love to run it in CFD

 

[Maty12]

Can you share your model? I'd love to run it in CFD

Sorry, I don't currently have a model. There are ordinates for most of the fuselage and nacelle, and I have a partially-modeled empennage (not attached or complete). With the wing especially I have very little, and with the gear I only have wheels.

 

[Maty12]

Been a while since I've posted here, so I have a two-in-one update this time:

First up, I'd like to highlight a little detail that people rarely notice: the leading edge of the B-26's wing! Martin documents claim that the wing is a NACA 0017-64 airfoil of 168" chord at the root tapering to a NACA 0010-64 airfoil of 56" chord at the tip. There's two problems with that:
1- The chord at the tip is NOT 56". It's hard to say what it is however, since the leading edge isn't straight.
2- The airfoil is not symmetrical outboard of the landing lights

Image 1: Leading Edge at the landing light, compare white line (straight leading edge) to orange line (ordinates for landing light cover).

Image 2: Theoretical airfoil at Wing station 365 (in gray) compared to actual rib at station 365 (in orange).

Image 3: Top view comparing theoretical wing with 56" chord at tip (in orange) to the actual wingtip ordinates (gray shape) and new theoretical leading edge (in black)

Image 4: Notice how the straight red line drawn from the nacelle to the wingtip does not match the actual leading edge in this photo of Kermit Weeks' B-26, 40-1464. They start to diverge in front of the landing light.

Image 5: You can actually notice this in photos once you know what to look for, though it's harder if the airplane is painted. In this photo of 40-1361, follow the border between the highlight and shadow at the leading edge of the wing. The line is lower outboard of the landing lights!

So, why is the wing shaped like that? Why isn't this documented? I can't fully answer these questions, but I stumbled across some drawings that tell part of the story: Martin drawings SK-9283 and SK-9285 are labeled as Leading Edge Slats, and show the same shape as above, but with slots/gaps for airflow that are absent from the final aircraft. I can't share the drawings, hence me using my 3D model as an example. These are the same setup used in the Lockheed Hudson and other aircraft. I do not know why Martin ultimately decided against the slats/slots, but they did not change the shape of the wing after doing so, leading to the shape we see above. The slats would have spanned from station 262 to station 364.

On a tangentially related note, I forgot about the skeletons entirely until recently, so I figured it's best to share what I have for now and issue corrections later if needed. They can be found here: B-26 Skeletons

Notes:
1- The engine nacelle of the B-26-MA is 1/8" shorter than that of future models according to Martin's 3-views, with the propeller also being mounted 1/8" forward of future models because of this. I don't know what to make of that. I can and did double-check the lengths for the B-26-MA, but cannot do so for the other models.
2- The neutral angle of the aileron trim tabs changed between models. The tabs are shown in neutral position and also flush with the wing. In general all tabs are simplified in shape and the dimensions are not 100% correct. Their leading edges are also missing, they extend only from the hinge to their trailing edge. I may update all of this in the future.
3- The wing flaps are missing, because they are very complicated and I have yet to fully confirm their mounting location and angle.
4- The nose landing gear for the B-26B1 and C is missing as I do not have enough data on it. The rest of the landing gear is simplified (again, lack of data), but contains the mounting points, full suspension travel, downlocks, uplocks and actuators.
5- In general I have far less info about the long wing models, everything was referenced from 3-views and station diagrams with the only exception being the empennage, which was extensively researched. There isn't even a skeleton for the F and G models because I have practically zero data on them.
6- These are setup so that in edit mode the Global tab gives the dimensions in reference to the Fuselage plane, while the Local tab gives them in reference to the Thrust Line Plane.
If any of y'all have any questions about this, don't hesitate to ask!

 

[Aeroweanie]

Can you post this in STEP or IGES format?

 

[Maty12]

Update: forgot to show photos of the skeletons. Here are some previews of them!

Can you post this in STEP or IGES format?

Blender does not support those natively, but it does support DAE, OBJ and STL. Is this skeleton of use to you? It doesn't contain the plane's actual shape, it's a reference jig.

 

[Maty12]

Revised the first post to correct some stuff:
1- several phrasing changes for clarity,
2- corrected information about B-26C, there were many differences between supposedly equivalent B1 and C production blocks, and no B-26Cs were fitted with the 47" smooth contour wheels as I had previously claimed,
3- corrected information about B-26B1 QF as while most parts from the B-26B tail were kept, a few were changed and so was the overall assembly's part number. I originally claimed the entire assembly was reused,
4- added information about the B-26B's rudder
5- corrected info on sharp-nose ailerons based on my current understanding of them. This is something I am still researching,
6- removed information on the XB-26D and XB-26Es as it is not relevant to the overall post. Will at some point make a full breakdown of the models
7- corrected info on "B-26B-1" to reflect my current understanding of it,
8- corrected the incorrect use of B-26B1 and B-26C. These terms refer to all blocks within their models, with the terms Quick Fix and Permanent Fix being used to differentiate between blocks with the manual tail turret and long chord rudder and blocks fitted with the Bell M-6 tail turret and short chord rudder
9- not a correction but a general note: Martin themselves have no standardized names for the aircraft's assemblies, so really the terminology isn't particularly important

I am still researching what assemblies were fitted to what model, but my understanding is currently incomplete as I only have access to a limited number of drawings and manuals. I'm not too sure what I actually want to do with this thread in the future. I do want to make a complete breakdown of the differences between production blocks at some point in the future

 

[Greg Boeser]

You've bitten off a lot to chew.
Another factor is that once the completed airframes left the factory they were often transferred to modification centers for further work. The result was even aircraft produced in the same block could have different features.
Early aircraft manuals had load and balance charts included, but later, each aircraft had its own load and balance card to reflect the particular configuration of that aircraft. I assume, though I have never seen one, that these cards would be updated every time the aircraft recieved any modification.

 

[Maty12]

You've bitten off a lot to chew.
Another factor is that once the completed airframes left the factory they were often transferred to modification centers for further work. The result was even aircraft produced in the same block could have different features.
Early aircraft manuals had load and balance charts included, but later, each aircraft had its own load and balance card to reflect the particular configuration of that aircraft. I assume, though I have never seen one, that these cards would be updated every time the aircraft recieved any modification.

That's a good point, Greg. There are also times when aircraft were fitted with parts for a different model because they were still interchangeable. Flak-Bait for instance has one "late" style forward bomb bay door on one side and an "early" style bomb bay door on the other, B-26B ailerons are explicitly approved as spares for B-26As (as long as both sides are the same type), B-26A nose cones are approved as spares for B-26-MAs and were routinely fitted on them, and much more.

Generally, I'm not too sure what the end product of this will look like or how extensive it'll really be (if it makes sense to cover each tiny internal change in a block or is better just to say that there were several minor changes, for instance). A list of the major assemblies broken down per model is relatively easy to do, but a complete list of parts is ridiculously impractical and the reason that parts catalogs are so long. A spotting guide to help people identify models from the outside is also an interesting idea, but is tangential and would have a long list of things that are not reliable identifiers due to field mods.