Hi all,
I've already posted about my B-26 research efforts elsewhere in the forum, but I figured it was about time to make a thread for my model itself since it's starting to take shape. For those who haven't seen that thread, I spent the last six months or so scanning microfilm rolls I purchased from the Smithsonian. I have yet to finish categorizing them fully, but have simplified that process for the future (mainly, going through each individual drawing to note all of its details as I was originally doing is not important for modeling purposes, all that is needed is placing the drawings into the folders that correspond to the subassemblies the drawings correspond to).
Types of drawings:
There are more types, but these are the ones relevant to the model in its current phase.
Martin had specific company names for parts of the B-26, which sometimes match industry-wide terms. There is no official name for some parts as long as it gets the idea across. A rear spar is sometimes called that and sometimes called an aft spar.
The model is currently a collection of different assemblies combined as best I have been able to based on mounting points and information from the general assembly/arrangement drawings. The individual assemblies' positions may change as the model progresses and more data is found. Because the thrust line and fuselage centerline are at an angle to each other and their precise centerpoint isn't marked on any blueprints, all distances in the model are approximate, specifically to within thousands of an inch. Data for the model comes from:
The drawings are in varied stages of legibility, and there is nothing either I or the Smithsonian could do about that, it's the state the original rolls were in. Some are blurry, but worse of all some are just very badly faded, to the point where barely any dimensions can be worked out. Fortunately for some of these, there are also contour drawings that can be used in conjunction with the ordinates. If an ordinate isn't on the line, then I have read at least one digit wrong, or (in the fully legible drawings) the draftsperson has made a copying error. These copying errors range from the copier mistaking similar-looking numbers, switching digits around, copying a line twice without noticing, or sometimes just writing down a number whose origin cannot be traced. Because this is a 3D model, ordinates in the wrong place can also be easy to spot even without contour drawings if a single ordinate is very far from any of the ordinates that were next to them on the original table.
The fin:
The fin is the most complete assembly so far, and the only one where I've modeled the ribs and the spar. I had a brief scare at first because my spar was not lining up with any of the ribs... only to then read the drawing's description again and realize what I had actually built was the Stabilizer's fwd spar. Even with that fixed though, the fin has caused me plenty of headaches. The fin's theoretical stations are parallel to the fuselage centerline, and are measured from 0 to 145.5. The fin's theoretical root is at station 34. That's where the straightforwardness ends. The angle for the fin's spar is not mentioned anywhere in the diagrams and it is not fully vertical. Many of the ribs do not mark the distance where they attach to the spar in their diagrams either, and because of all the angles involved, any values mentioned are rounded. The lowest rib in the fin is the only one that gives attachment information and an angle. It is angled 1d 30' 33" from horizontal, because the top of the fuselage is angled upwards towards the rear in order to accommodate the tail gunner. The other ribs provide no information.
The assembly drawing for the entire fin and the frame drawing for the spar give other dimensions that lead to the calculation that the spar is angled 1d 21' 58" from vertical. However, the spar's drawing also states that most of the ribs meet the spar at an angle of 88d 30', the complement of which is 1d 30'. I don't really know what to do with that information. Angling the spar 1d 30' from vertical results discrepancies in the magnitude of quarter inches in parts where the distances are provided to the thousand of an inch, and I don't think anyone would ever approximate 1d 21" 58" as 1d 30", when the logical approximation is 1d 22". 1d 30' is also not an approximation of the 1d 30' 33" measurement from the bottom rib, as this again results in discrepancies that are too large given the precision of other measurements, and would also be the incorrect way to approximate. My current hypothesis is that for whatever reason Martin decided to angle most of the ribs 88d 30' from the spar, which itself is 1d 21' 58" from vertical, meaning the ribs are almost parallel to the fuselage centerline & stations, but not quite, and almost perpendicular to the spar but not quite. I don't know why they would ever do this and have yet to finish testing the results of this hypothesis. In the current model they are parallel to the fuselage centerline and stations.
Extra tidbits about the fin:
What's next:
I plan on modeling the stabilizer differently, because it occurs to me that using measurements that are rounded to the thousand of an inch that then almost match the theoretical airfoil makes less sense than modelling the airfoil and then cutting slices of it and doublechecking the numbers. The wing and all control surfaces will also follow a similar approach. The landing gear has individual drawings with basically all the info necessary to model them, but the main gear's drawing for some reason had only one mostly illegible copy within the 5,513 drawings that I scanned. The nose gear's drawing is more legible, and it has at least two other duplicates, one of which is fully legible, so it can be modeled with ease.
I will detail my process of modeling the pilot's enclosure in a future reply and will share more progress as it happens.
Best,
-Matt
I've already posted about my B-26 research efforts elsewhere in the forum, but I figured it was about time to make a thread for my model itself since it's starting to take shape. For those who haven't seen that thread, I spent the last six months or so scanning microfilm rolls I purchased from the Smithsonian. I have yet to finish categorizing them fully, but have simplified that process for the future (mainly, going through each individual drawing to note all of its details as I was originally doing is not important for modeling purposes, all that is needed is placing the drawings into the folders that correspond to the subassemblies the drawings correspond to).
Types of drawings:
There are more types, but these are the ones relevant to the model in its current phase.
- Assembly- Drawing of a part with multiple views and dimensions.
- Installation- Same as Assembly but with less or no dimensions (much less useful). These are instructions on attaching a part to the aircraft and are sometimes the same drawing with only the text modified.
- Installation & Assembly- Usually a combination of both in the same drawing, sometimes identical to an installation drawing.
- Casting/Molding- Similar to Assembly in utility, full of dimensions. Meant to be used by factory workers to make an individual part out of metal.
- Frame/Rib Assembly- Assembly drawing of one specific frame or rib of the aircraft. Full of dimensions, as well as instructions on were bolts and rivets go and how to bend she sheets of metal.
- Ordinates- Tables of number coordinates with a guide drawing, meant to represent the outline of specific parts or large assemblies. Numbers are rounded to the nearest thousand of an inch where practical (such as the pilot's enclosure), or to the nearest hundredth of an inch where the table is too large (such as for the overall fuselage and engine nacelles). The rows of an ordinates table form the outline of a cross section at a specific distanced measured either from the most forward point of the assembly, from its horizontal centerline, from its vertical centerline or an external reference.
- Contours- Meant to go with the Ordinates drawings. The contour drawings overlay the several cross sections formed by the ordinates over each other, lining them up.
- Skin- Diagrams for the skin of the aircraft, common for complex shapes such as the tips of the wings and stabilizers. These are the only drawings that measure the dimensions to the outside of the skin of the aircraft. Dimensions for the internal frames can be obtained by removing the skin thickness, which is always stated in the diagram.
Martin had specific company names for parts of the B-26, which sometimes match industry-wide terms. There is no official name for some parts as long as it gets the idea across. A rear spar is sometimes called that and sometimes called an aft spar.
- Fin- Refers to the vertical stabilizer.
- Stabilizer- Refers exclusively to the horizontal stabilizer.
- Empennage- Refers to the combination of the fin and stabilizer, sometimes including the rudder and elevator.
- Venturi- Refers to the intake for the oil cooler.
- Venturi Cowl- Refers to the section of the engine nacelle that houses the oil tank, oil cooler and exhaust stacks.
- Engine Hood- Refers to the engine cowling. It includes the Carburetor Intakes and the Venturi.
- Navigator's Turret- Refers to the astrodome assembly, which does not have any armament.
- Turret- Refers to both powered and unpowered gun positions.
The model is currently a collection of different assemblies combined as best I have been able to based on mounting points and information from the general assembly/arrangement drawings. The individual assemblies' positions may change as the model progresses and more data is found. Because the thrust line and fuselage centerline are at an angle to each other and their precise centerpoint isn't marked on any blueprints, all distances in the model are approximate, specifically to within thousands of an inch. Data for the model comes from:
- Ordinates tables for the fuselage (Station 33 through 658 1/2, missing tail turret and nosecone), the pilot's enclosure, the nosecone itself, the engine nacelle and cowlings, the propeller spinners, and the fillet around the fin and stabilizer.
- The skin drawings for the tips of the wing, fin and stabilizer (of which the wing has the least useable information).
- The theoretical outline of the wings and stabilizers based on general assembly/arrangement drawings.
- The vertical stabilizer, made from the diagrams for the individual ribs and spar and aligned using the aforementioned assembly drawings.
The drawings are in varied stages of legibility, and there is nothing either I or the Smithsonian could do about that, it's the state the original rolls were in. Some are blurry, but worse of all some are just very badly faded, to the point where barely any dimensions can be worked out. Fortunately for some of these, there are also contour drawings that can be used in conjunction with the ordinates. If an ordinate isn't on the line, then I have read at least one digit wrong, or (in the fully legible drawings) the draftsperson has made a copying error. These copying errors range from the copier mistaking similar-looking numbers, switching digits around, copying a line twice without noticing, or sometimes just writing down a number whose origin cannot be traced. Because this is a 3D model, ordinates in the wrong place can also be easy to spot even without contour drawings if a single ordinate is very far from any of the ordinates that were next to them on the original table.
The fin:
The fin is the most complete assembly so far, and the only one where I've modeled the ribs and the spar. I had a brief scare at first because my spar was not lining up with any of the ribs... only to then read the drawing's description again and realize what I had actually built was the Stabilizer's fwd spar. Even with that fixed though, the fin has caused me plenty of headaches. The fin's theoretical stations are parallel to the fuselage centerline, and are measured from 0 to 145.5. The fin's theoretical root is at station 34. That's where the straightforwardness ends. The angle for the fin's spar is not mentioned anywhere in the diagrams and it is not fully vertical. Many of the ribs do not mark the distance where they attach to the spar in their diagrams either, and because of all the angles involved, any values mentioned are rounded. The lowest rib in the fin is the only one that gives attachment information and an angle. It is angled 1d 30' 33" from horizontal, because the top of the fuselage is angled upwards towards the rear in order to accommodate the tail gunner. The other ribs provide no information.
The assembly drawing for the entire fin and the frame drawing for the spar give other dimensions that lead to the calculation that the spar is angled 1d 21' 58" from vertical. However, the spar's drawing also states that most of the ribs meet the spar at an angle of 88d 30', the complement of which is 1d 30'. I don't really know what to do with that information. Angling the spar 1d 30' from vertical results discrepancies in the magnitude of quarter inches in parts where the distances are provided to the thousand of an inch, and I don't think anyone would ever approximate 1d 21" 58" as 1d 30", when the logical approximation is 1d 22". 1d 30' is also not an approximation of the 1d 30' 33" measurement from the bottom rib, as this again results in discrepancies that are too large given the precision of other measurements, and would also be the incorrect way to approximate. My current hypothesis is that for whatever reason Martin decided to angle most of the ribs 88d 30' from the spar, which itself is 1d 21' 58" from vertical, meaning the ribs are almost parallel to the fuselage centerline & stations, but not quite, and almost perpendicular to the spar but not quite. I don't know why they would ever do this and have yet to finish testing the results of this hypothesis. In the current model they are parallel to the fuselage centerline and stations.
Extra tidbits about the fin:
- The fin only has one spar. I find this very unusual, especially given that the stabilizer has two, but there genuinely is no forward spar near the leading edge. The leading edge attaches directly to the skin and ribs (which have angled sections that I have yet to model.
- The bottom rib of the fin is the only one that includes the skin thickness in its measurements, as it is exactly .032 of an inch longer and wider than the theoretical fin in a section where the skin is .032 inches thick.
- Most drawings of the fin in my possession list stations both for the short tail and long tail models of the aircraft. Station 145.5 on the B-26 is Station 131.5 on the B-26B1, and so on. The difference is always exactly 14 inches, which is odd given that the B-26B1's tail was 20 inches taller. What gives? Well, when the fin was lengthened Martin decided to change the reference datum from the fuselage centerline to the theoretical root of the fin, Station 34. 145.5 +20 -34 =131.5.
- The fin is one of the only parts of the aircraft to not have round-ish numbers for its stations, the fuselage, wings and stabilizer all use whole numbers, or down to 1/64 of an inch as needed, while some of the fin's stations are 75.854 or 102.927. Why is that? Because of the rudder's hinges, which are exactly 15" and 69" from the top of the theoretical hinge line, respectively. The hingeline which is angled 3.08d degrees from vertical, resulting in hinges at station 130.0035... and 75.8559... . The remaining stations are merely the result of dividing the interval between 34 and 75.854 and the interval from 75.854 to 130.000 evenly into increments of 7.95868..." and 9.024602..." respectively. I do not know why 75.8559 was rounded to 75.854 instead of 75.856.
What's next:
I plan on modeling the stabilizer differently, because it occurs to me that using measurements that are rounded to the thousand of an inch that then almost match the theoretical airfoil makes less sense than modelling the airfoil and then cutting slices of it and doublechecking the numbers. The wing and all control surfaces will also follow a similar approach. The landing gear has individual drawings with basically all the info necessary to model them, but the main gear's drawing for some reason had only one mostly illegible copy within the 5,513 drawings that I scanned. The nose gear's drawing is more legible, and it has at least two other duplicates, one of which is fully legible, so it can be modeled with ease.
I will detail my process of modeling the pilot's enclosure in a future reply and will share more progress as it happens.
Best,
-Matt