SBD Dauntless (US Navy dive bomber)

To update the thumbnail of this WIP thread, I placing here the latest image of the model described here:


_____________________________ Original contents of the initial post __________________________

I started to work on a new model: Douglas SBD Dauntless, a dive bomber introduced to the U Navy service in 1940. My goal is to recreate in the 3D the real airplane, preserving all proportions and dimensions.

I will begin this thread with some posts about preparing the reference drawings. When they contain errors - you will have much more work later, so it is very important to find good, detailed scale plans.

Initially I decided to use for this purpose detailed scale plans from the monograph published by KAGERO in 2007 (Authors: Krzysztof Janowicz, Andre Zbiegniewski, ISBN: 978-83-60445-25-9). It contains SBD Dauntless plans in scale 1:48, traced by Krzysztof Lukasik. They are quite detailed (up to the rivets on the aircraft skin). During the initial verification I did not find any flaws:

All the key locations of the fuselage are in the same place in the side view and the top view. The proportions of the length and the span of the top view is correct: 0.787. (This ratio comes from 996/1266. According the dimensions specified in this monograph, the length of the SBD-3 fuselage was 996 cm [32’ 8”], while the wing span of all the Dauntless versions was 1266 cm [41’ 6”]).

This good impression disappeared, when I compared side views of two different Dauntless versions: SBD-3 and SBD-5:

According the monograph data, SBD-5 fuselage was 4 inches (about 10.1 cm) longer than SBD-3. (The SBD-5 and SBD-6 fuselage was 33’ long. Most probably it has slightly different engine cowling and the propeller. The airframe after the firewall was the same in all Dauntless versions). However, in this monograph they have the same length!!

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(Continued from the previous post)

Maybe the textual data contains an error? In such a situation I try to find an “official”, archival drawing of the aircraft. They do not show many details, but contain the key dimensions. I have found on the Internet a BuAer Navy drawing of the SBD-5, from 1944. From its front view you can read the precise wing span: 41’ and 6 [SUP]5[/SUP]/[SUB]16[/SUB]". From its side view you can read the exact length: 33’ and [SUP]1[/SUP]/[SUB]8[/SUB]". This BuAer drawing isn’t an ideal source: it does not contain such details as panel seams. You can also find here some manual errors, made by its draftsman. While the aspect ratio of the top view matches the span and length specified in the dimensions, the actual fuselage length on the side view is somewhat shorter. (The positions of the wing and horizontal tailplane match in the side and top view match each other. It seems that the part of the vertical tail contour was shifted). On the other hand, the BuAer top view is a little bit asymmetric, and the firewall line is moved forward a little.
The good news is that the wing and the tailplane arrangement on the KAGERO plans and the BuAer drawing match each other:

Then I compared the side views of these drawings (I marked the correct fuselage length measured on the BuAer top view in red):

Thus, I can conclude: never trust the scale plans! I need a better reference, to fix these drawings.

On the next week I will describe how I verify these drawings using photos.

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Great start Witold, looking forward to seeing the next posts and progress of this beauty of plane (alrady subscribed to the thread). Although I’m more of a jet aficionado this is one of the few WWII planes that I like.

tommy1441, thank you! I will do my best to deliver an interesting article…

Hi.
Are these the scale plans you will be working from and the same as those you mention published by KAGERO?

I am not sure If I properly understand your question (did you want to write “are” instead of “and” in the middle of the sentence above?). On the pictures above you can see smaller, somewhat “degenerated” (because I needed a greater BW contrast for these pictures, to better show my point) scans of the plans published by KAGERO. I am going to use them only if they are correct - that’s why I do this verification.
So far:

  • I have found an inconsistency in the KAGERO plans;
  • I used older drawings from different source for the comparison;
  • I have found significant differences in their side views;

Now, to determine which of these “witnesses” is right (maybe none?), I need a kind of “hard” evidence: the photos. I will show this “confrontation” after tomorrow!

yes that’s what I meant! Thanks for answering.

The plans above are not very detailed and so open to some artistic interpretation I guess.

There are a great many websites with photos to help you imagine how the aircraft fitted together, but identifying exactly which aircraft and its history could be difficult.

]That is really what my question meant.

For instance, the wings are turned upwards and there is no front view in the plans. Nor is there a view of the underneath, perhaps due to the war time censorship images of those parts were not kept?

I am interested to see what you will do and look forward to your next post.

I allowed myself to rearrange the key issues from your post into two groups (it allows me to make a more coherent answer):

Well, these KAGERO plans are very detailed! They contain plenty of all views in 1:48 scale - top, side, bottom, front, rear - of each SBD version (14 A4 sheets). I show here just their simplified fragments to follow the “fair use” rules.

Yes, but it is also a great fun for a modeler like me :). I already collected over 1000 photos of various parts of this airplane (over half of them comes from a friend of mine, who personally took detailed photos in three US air museums). The decision about selection a particular historical airplane will come much later - when I decide about the painting scheme.
[SUB]For example: the painting of my La-5F model (pilot: capt. I. Sytov, 5th GIAP, summer 1943) forced me to read plenty of the source materials (in Russian), including two or more books about VVS in general and the 5th GIAP in particular. But it still is based on many assumptions.[/SUB]

Ah yeah!!

I thought you would need some more information then just the plans you have shared here.

After looking at some of your excellent work I tried it myself but was dissatisfied with the results I got.

I found older aircraft more suitable and so more interesting to model in this way.

You are right the Dauntless is a very painterly subject and using Blender results in a painted sort of result.

" much better than the contours of the detailed KAGERO drawings from 2007 …, which most probably are based on the drawings made by previous authors:"

Don’t be too hard on the poor draughtsman.

Drawings are made for many different reasons and are not expected to produce a nice picture.

At least the KAGERO drawings show the position of the panels.

The BuAer fits the photo so well are you sure it was not taken from the same aircraft??

I think the plane in the photos has a different shaped wing to the originals and the landing gear and nose cowling are from one design and not the original configuration.

I think I remember seeing a documentary which explained that the US often altered wartime aircraft by moving the engine forward and by just adding a different tail or other parts with no real concern about the overall design.

The Dauntless had its bomb load capacity increased and the landing gear had to be changed, but not the bomb launcher it seems, which resulted in the engine being moved forward and other changes.

I am sure. Could you see the date at the bottom of BuAer drawing? 1 June 1944. The airplane from the photo analyzed in my previous post is the restored SBD-5 from CAF, and this photo was taken no earlier than in 1990. (I suppose that it was made in this century). So the time difference between these two pieces od information is over 50 years!

It would mean that this is not the SBD-5 at all. See more pictures of this restored CATF plane, compare them to this photo of a historical SBD-5 (from VMSB-231):


You can also compare it to other WWII photos of SBD-5 you can find on the web. Let me know where are these differences you have mentioned (in the engine cowling or wing shape), because I cannot see any of them. The only differences I can see here: this airplane from VSMB-231 has removed tailwheel leg cower, and has a Yagi antenna under the wing.

Yes, but in subsequent versions (it happended, for example, to P-47). All such changes are well-know in the scale modeling sommunity. None of such significant change happended to Dauntless

I have impression than you mix Douglass Dauntless with its successor - Curtiss Helldiver. All Dauntless versions had the same landing gear and the airframe. As I noted on the drawing there were minor differences in engine cowling details, but they were not significant. All SBD versions used subsequent releases of the same Wright R-1820 engine, which power has been increased from 1000 HP in 1940 to 1200 HP in 1943. The bomb capacity had increased from 1500 lb (SBD-2) to 2000 lb (SBD-5) due to more powerful engine. It is not a siginificant increase of the gross weight, and the landing gear designed for extremely hard carrier landings easily cope with such additional loads.

Yes, you are right. I meant it as a question and was probably thinking of the Helldiver.

That is a far better photo with the ’ feel ’ people at the time wanted. It seems to me the modern one at the top of the page has a dark line around it.

The exhaust passing through the cowling shows there are some differences. Perhaps the cooling flaps are just not visible in the older photo.

As I wrote a week ago, I am working on a better drawing of the SBD-5. It is based on more than 1000 various photos. Below you can see the first version of the side view (click it to see the high-resolution version):

http://wjaworski.pl/blog/sbd/0003-01.jpg

This is not an ultimate drawing: I suppose that it will be updated during my work, following the new findings about the airframe shape and/or details. The dotted lines mark the rivet seams, but size and spacing of these dots does not match the real rivets. I prepare these plans to build a model: that’s why I removed the outer wing section and horizontal tailplane. For these parts the most important drawing is the top view. To build them, on the side view I need the precise contours of their key sections (i.e. their airfoils as well as the incidence angles and spar locations). I draw three profiles: first of the wing root, then the root of the outer wing section, and then the wing tip. Two different sources specifies different wing tip profiles: NACA-2409 (Performance Test Report, 1942) or NACA-2407 (BuAer drawing, 1944). However, the bottom contour of the NACA-2407 seems to be a little concave. Because I did not observe such an effect on the photos, I decided to use the thicker airfoil of NACA-2409. I still have to verify this detail when I build the wing. The airfoils of the tailplane were specified nowhere. I copied its root airfoil from a photo.

While drawing the side view you still have to think “in 3D”. That’s why you can see around this silhouette some auxiliary sketches: the front view of the engine cowling, and the contours of the center wing section. I draw the latter element just to mark the exact position of the first rib of the wing. It was hidden inside the fuselage. Note that this airfoil was a specific modification of the NACA-2415 shape: the part of the wing that houses the main landing gear was reshaped. In the effect, the leading edge of the center wing section has a small downward inclination.

On the next week I will present side views of two earlier Dauntless versions: the SBD-2 and SBD-3. I will discuss where are the differences in the length of the SBD-5 and SBD-3, 4, as well as the mystery of the “missing 7 inches” of the SBD-2.

Within two weeks I will present the corrected/verified top view.

Excellent drawing Witold Jaworski! Thanks for sharing.

Something I noticed is that you have n’t included a scale and did n’t say how you were drawing it??

Thank you! Answering your questions:

I do not need to draw the scale for the drawing I will place as the background image in Blender: the length of this ariplane is as specified on the BuAer drawing: 33 1/8 '. I just need a drawing that preserves all the proportions of the original. Technically - ths is a SVG drawing, created in Inkscape. Internally it happened that 3 drawing units = 1 inch in the real airplane, but I can scale the drawing uints as I wish (this is vector drawing).

There is no hidden magic in creating such a drawing: just comparing and reconciliation of many photographs (taking into account the perspective distortion). Below you can see the random set of the photos (this B/W I use to check the propeller location, because the rest has too strong distortion, the color photo is one of the three that I used to trace the ribs on the fin):

I started with engine cowling, then continued with the center of the fuselage: for example, it took me more than three days to determine the longeron locations. (Fortunately, the bulkhead locations were specified in the Technical Manual). As I wrote, the drawing is not finished. It has been just “stabilized” enough to be presented here. (For example, today I made small updates to two upper longerons).

Thanks again for sharing your work Witold Jaworski!

Tremendous pilot!

Here are some links to the recent 70th Anniversary of what they were all about.

http://www.communistpartyofireland.ie/r-fascism.html

http://www.neweasterneurope.eu/articles-and-commentary/1601-photo-report-the-may-9th-celebrations-in-berlin

http://www.avante.pt/get_img?NrArticle=135417&NrImage=103

Thinking about smith123’s question about the methods I used to trace the plans, I decided to write more about it, as well about some tips and tricks of this process:

In this post I will show you how do I create Dauntless side views. First I used the “semi-orthogonal” photo of the SBD-5 as the reference to draw the side view of this version. This is the most important picture, because it provides reliable “general reference”:


Then I used many other photos and sketched fragments of the other views to complete the side view details (note the multiple guide lines on these pictures):


Note the large B/W photo that I used to verify the shape of the propeller hub and engine cowling. I could not compare it with other areas — the cockpit canopy, for example — because its perspective (barrel) distortion was too intense.
However, when the barrel distortion is moderate, we can revert it! See for example this side photo of another Dauntless version: the SBD-3:


First I identified the undeformed fragment of the fuselage (in this case — around the firewall and the windscreen) then fitted this part of the photo into the drawing. Then, comparing the lengths of this photo and the side view, I concluded that it has a moderate barrel distortion. From the history of this design I know that the SBD-3 and SBD-5 had different engine cowlings. The other parts of their airframes had the same shape. This means that I could use the existing SBD-5 drawing from the firewall to the fin as the reference for the unwrapping process of this SBD-3. Then I unwrapped this photo using the GIMP. (Speaking more precisely – its “Lens Distortion” image filter. You can find all the details of this process in this book).


Note that this operation “flattens” only the airplane contour that lies on the symmetry plane of the fuselage. All protruding elements, like wing and horizontal tailplane remain deformed. But it’s OK, I need this just this contour. While drawing, I will compensate the small remaining deformation of the bulkhead lines. (For example, the leading edge of the NACA cowling from this photo should be a straight line, but it is a very flat ellipse).
Of course, it is always better to prepare more than one of such “flattened” pictures, to minimize inevitable errors:


NOTE: these two SBD-3 photos depict training aircraft, without the telescope gunsight. Such a gunsight was protruding through the windscreen in the combat airplanes.

On both SBD-3 photos you can see that the engine cowling is somewhat shorter than in the SBD-5. In fact, in the specifications you can find that these versions had different overall length: - SBD-5: 33’ [SUP]1[/SUP]/[SUB]8[/SUB]”; - SBD-3: 32’ 8 ” (in some sources I also saw 32’ 8 [SUP]4[/SUP]/[SUB]5[/SUB]”) However, on the scale plans authors attribute this difference to the longer propeller hub of the SBD-5 (It used different propeller: Hamilton standard hydromatic). Others did not bother about the different lengths of the SBD variants, and draw the profiles of all Dauntless versions alike.

Following the findings on the unwrapped photos I analyzed many other archival pictures. Below you can see the conclusion:


It seems that in the SBD-5 the engine, together with the NACA cowling, was moved slightly forward. All other bulkheads remain in the same places. This modification shifted forward the center of gravity. I suppose that this correction improved some handling characteristics that changed after the doubling of the rear guns. (The second gun in the rear was introduced in 1942 to the SBD-3 as the “field” modification. It shifted the cg backward).

In my next post I will finish the side view matter, delivering you the complete side views of the SBD-3, SBD-2 and SBD-1 variants. I will also write about other non-existent length difference, which you can find in the books about the SBD Dauntless.

In addition to the side view of the SBD-5 presented in one of my previous posts, I have prepared side views of the earlier Dauntless versions: SBD-2 and SBD-3:


(Here are the links to the high-resolution profile images of: SBD-2, SBD-3).

When you look into Dauntless specifications, you will find that all its models have the same span, but they often differ from each other in the length. This is a typical case, because the wing geometry determines the aircraft behavior. Thus, once “debugged” in the prototype (the stall characteristics etc.) it remains unaltered between subsequent versions. The fuselage shape is not so important, so it is often modified. In the effect, the length of the airplane often vary between subsequent versions.

In the previous post I described how the photos confirmed the different length of the SBD-5 (33’ [SUP]1[/SUP]/[SUB]8[/SUB]”) and the SBD-3 (32’ 8”), listed in their specifications. The reason was the different engine mount, modified in the SBD-5. The same sources specify the length of the SBD-2 as 32’ 2”. This is something strange, because I cannot find any evidence of this significant, 6 inch difference between SBD-3 and SBD-2 on the photos!

The SBD-3 was a “quick and dirty” adaptation of the SBD-2 to the recognized requirements of the modern war. Douglas added armor plates to the pilot and gunner seats, self-sealing fuel tanks (reducing their capacity), doubled the rear guns. All the key elements of the design: the airframe and the engine, remained the same. Where is there the modification that changed the overall of length of the SBD-3 by 6”!?

I started to look for the sources of this information (the subsequent publications copy their specification data from the earlier ones, up to an ultimate source document). Ultimately it seems that it comes from the BuAer Performance Data Reports. There are two of such documents, created in 1942: one for the SBD-2 and one for the SBD-3. On their last pages you can find the measured airplane dimensions. The difference is there: LENGTH, LEVEL: 32’-8” in the SBD-3 report, and LENGTH, LEVEL: 32’-2” in the SBD-2 report. (Unfortunately, they did not specified the length on wheels for the SBD-2, so there is no double-check). Note that all other dimensions are the same. I speculated that the reason of these differences lies in the propeller spinner: it was often removed. If the tested SBD-3 had this spinner, and the SBD-2 didn’t — what was the eventual difference? I tried to check this option, but it shortens the fuselage length by less than 4”.

What’s more interesting: the only survived SBD-2 is owned by the National Navy Aviation Museum in Pensacola. On their web page the owner specifies the length of this airplane as 32’ 8” — the same as the SBD-3! Thinking further about it, I noticed the manual corrections of typing errors in other SBD performance data reports. So I have following hypothesis:

  • The SBD-2 and SBD-3 had the same length: 32’ 8”, as specified by the owner of the restored SBD-2 (NAM in Pensacola);
  • The typist of the BuAer Performance Data Report made a mistake (most probably —deciphering the handwritten measure results he/she read “2” instead “8”). The authors of the first publications about SBD Dauntless used this source, and the others used their publications. So the initial error was multiplied;

Thus I assumed that the SBD-2 length specified in Performance Data report is wrong. Basically it was the same as the SBD-3. It also applies to the SBD-1:


(Here is the link to high resolution profile image of the SBD-1). The only external difference between the SBD-1 and SBD-2 is the larger air scoop on the top of the engine cowling.

Conclusion from this little investigation (in fact, it took me a few days): do not trust blindly the specified width and wing span of a historical airplane! When you compare the different sources you will find that sometimes these figures are different. Always try to verify available data. The wing span is less error-prone because it usually does not vary between subsequent versions. Remember that the photos are always the ultimate evidence.

In the next post I will present the updated/verified Dauntless top view.

This Monday I finally got the “Instructions for the Erection and Maintenance of the Model SBD-6 Airplane” book – more than 600 pages about the Dauntless, published by Douglas in March 1944. Because of the lengthy title, I will refer to this book as the “SBD Maintenance Manual” or the “Douglas manual”. In spite that it describes the last produced version, it is also usable for the earlier models: as I mentioned in one of the previous posts, the SBD-1 airframe behind the firewall differs only in a few details (the double gun mount, gunsight type, lack of the YAGI antennas) from the SBD-6.

Inside you can find the SBD-6 general arrangement drawings, as well as the stations diagram:

Here are the links to the high-resolution versions: side view (cropped from the page), top and front view, stations diagram. As you can see these Douglas diagrams contain more dimensions than the BuAer drawings. Their chains on the side view allow for verification of the wing location, as well as the wing and tailplane incidence angles. They also allow you to determine the basic “trapeze” around the rudder and the fin. From the front view you can also read the dihedral angle of the outer wing panels (9⁰ 19’).

The dimensions from the top view allowed me to draw the basic trapezes around the wing and tailplane, as well as to determine locations of the aileron and elevator hinge axes. This information, combined with dimensions from the side view, allows for determining the precise location of the firewall, wings and empennage. I used them to verify my scale plans. Sometimes they just confirmed what I determined before (for example — locations of the wing or the last bulkhead). Sometimes they revealed the errors I made. I will write more about it in the next post. So here is the current, updated version of my drawings:

http://wjaworski.pl/blog/sbd/0006-02.jpg

Because of the formatting issues I had to split this image into two parts:

http://wjaworski.pl/blog/sbd/0006-03.jpg
(Click here to get these drawings as a single, high-resolution image). Note that I draw the outer wing panel without its dihedral (it is much easier to build its model using such a “flat” reference). Thus when you check proportions of this top view, its span/length ratio is somewhat greater than the expected value of 41’ 6” / 33’. What is interesting, the dimensions on the general arrangement drawing indicate that the “official” wing span does not include the size of the running lights:


To obtain the “physical” wing span value you have to add 1.5” to each wing. I used similar convention when I matched the fuselage contour against its dimension (33’ [SUP]1[/SUP]/[SUB]8[/SUB]”). These dimension lines are more obscured on the side view, but for the matching purposes I skipped the length of the running light cover protruding from the tip of the tail (1”).

In general, after all these updates I feel more confidence in my drawings. I know which elements come from the explicit dimensions of the general arrangement diagram, which from the photos, and which are based on other drawings or just on an assumption. The only larger element that I was not able to verify is the fuselage width (i.e. its contour in the top view). It is copied from the Douglas drawing. I was able just to verify it at the 9[SUP]th[/SUP] bulkhead (station 140). I have a photo of this bulkhead from one of the Dauntless restorations, so I am sure that it fits properly into the fuselage contour on both views: the side view and the top view. However, I did not verify in any way the curved contour of the tail on the top view.

Frankly speaking, after this experience I am really glad that I am doing such a “slow start” to the modeling by preparing these drawings. It forced me to think twice (or even more times than twice) about every part of this airplane, resulting in better understanding of various nuances of its geometry. Sometimes I had to deliberate over a single line (like the gap between the elevator and stabilizer) for a whole day, watching and comparing hundreds of photos. In the effect I had to move a few lines around it on the plans. It was not a big deal. However, if I already started to build the model, adaptation of such findings would require a lot of work!

In next post I will tell you more on how I used the explicit dimensions from the Douglas drawings. They allowed me to find some flaws in my plans. Description of this case will give you an insight into the errors that you can make using the photos.

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Your attention to detail is an inspiration to me and other modellers. Keep up the good work.

Cheers, Clock.