The Overall Lengths of the Douglas SBD Variants

Since 2015 I have tried to determine the true length of the early SBD Dauntless versions (the SBD-1, -2, and -3). There was something wrong with the source of this information: the original BuAer performance data sheets. You can find there different lengths of the SBD-2 (32’ 2”) and the SBD-3 (32’ 8”), while the differences between these variants cannot explain the reason of such a longer fuselage in the SBD-3. The other sources repeat these figures without any reflection. Fortunately, last month I found in the SDASM resources two interesting drawings of the SBD-1. One of them is a general arrangement diagram, which clearly specifies its overall length (and how it was measured):

Figure 116-1 The overall length in the general arrangement diagram of the SBD-1

As you can see, the overall length the SBD-1, without the spinner, was 32’ 1 ¼”. This agrees with the BuAer data sheet for the SBD-2 from November 1942, since they rounded each dimension up to the nearest inch. (For example: this BuAer sheet specifies the wing span as 41’ 7”, citing the general arrangement diagram which provides a more accurate dimension: 41’ 6 ¹/₈”.) According the general convention in these drawings, the small transparent blisters of the running lights are excluded from these overall dimensions (see this post, Figure 111-5, and this post, Figure 109-12).

The BuAer data sheet from August 1942 treats the SBD-3 and the SBD-4 as a single variant, thus I assume that it provides the overall length of the SBD-4. Using the available blueprints, I concluded that it was 32’ 7 ¹³/₁₆”, which BuAer rounded up to 32’ 8” (see this post, Figures from 108-4 to 108-6). The sole reason of this difference is the length of the Hamilton Standard Hydromatic propeller, used in the SBD-4. Its central “hub” was longer than in the Hamilton Standard Constant Speed propellers, used in the SBD-1, -2, and -3. Basing on these facts, we can safely conclude that overall length of the SBD-2 and -3 without the propeller spinner was the same as the SBD-1: 32’ 1 ¼”.

What about the length with this spinner mounted? I did not find any explicit dimension, so I still have to rely on my estimations from the previous year (figure below corresponds to Figure 108-7 from that post):

Figure 116-2 Profile with the old propeller (as used in the SBD-1, -2, and -3)

Now, thanks to the SBD-1 arrangement diagram, we know the overall dimensions up to the B baseline (compare figure above with Figure-116-1). In this post you can see that I approximated this length as 32’ 1.5”, +/- 0.3”, so the true value 32’ 1.25” lies within declared error range. According to the data from the same post, the difference between B and C dimensions can be estimated as 42.38” – 37.66” = 4.72”. Let’s round this distance to 4.75”. (Although I suppose that the overall error range for this value is smaller than the error range of the estimated overall length, this 4.75” still lies safely within these limits.) This gives the overall length of the SBD-1, -2, and -3 with the spinner = 32’ 6”.

Below I am providing the length of each Dauntless version, according to their general arrangement diagrams:

• SBD-1:  32’ 1 ¼ ” / 32’ 6”;
• SBD-2:  32’ 1 ¼” / 32’ 6”;
• SBD-3:  32’ 1 ¼” / 32’ 6”;
• SBD-4:  32’ 7 ¹³/₁₆”;
• SBD-5: 33’ ¼”;
• SBD-6: 33’ ¹/₈”;

All these dimensions do not take into account the transparent covers of the running lights. Length in italic are the estimated lengths with the propeller spinner. Note the minor difference in the lengths between the SBD-5 and the SBD-6 (0.15”). I copied this dimension from the SBD-6 general arrangement diagram attached to the BuAer performance data sheet from 1944. It is repeated (as 33’ 0.1”) in the SBD-6 “Erection and Maintenance Manual”. What is interesting, minimally differ from the Douglas blueprints. One of them is the overall length. I cannot explain these variations.

Everything would be fine, unless I checked the alternative dimension chain in this SBD-1 drawing (below it is marked in red):

Figure 116-3 The overall length of the SBD-1 and the alternative dimensioning chain

When you sum up these three red dimensions, you will obtain 386 ³/₁₆”. This does not agree with the blue overall length drawn above (385 ¼”)! The difference is close to 1 inch (precisely: ¹⁵/₁₆”). One of these two lengths is wrong. Which one? Let’s check similar arrangement diagram of the SBD-5:

Figure 116-4 The overall length of the SBD-5 and the alternative dimensioning chain

In this case the sum of the red dimensions matches the blue overall length (396 ¼”). The redesigned engine compartment in the SBD-5 was 11” longer than the SBD-1, so you can see this difference in the overall length and in the red dimension on the left (91 ⁹/₁₆” in the SBD-5 vs. 80 ⁹/₁₆” in the SBD-1). The middle dimensions (22’ 10 ¹³/₁₆”) of the red chain are identical in both variants. But there is an interesting difference in the third red dimension. In the SBD-5 this is 29 ¹⁴/₁₆”, wile in the SBD-1 it was 30 ¹³/₁₆”. The difference is ¹⁵/₁₆” – precisely as the difference between  the alternate SBD-1 lengths!

In the rudder assembly I found that the 29 ⁷/₈”, listed in this SBD-5 arrangement diagram, is the chord length of the rudder:

Figure 116-5 Rudder assembly: chord dimension

I suppose that the SBD-5 and SBD-1 used the same rudder. (Behind the firewall, the geometry of both variants was identical). However, behind the lower tip of the rudder trailing edge there was additional 1” of the tail cone:

Figure 116-6 Details of the SBD tail cone

I signalized this detail in one of my previous posts. However, it was not dimensioned in this assembly drawing, so in that time I could only estimate its length to about 1”.

Now it seems that the partial dimension from the SBD-1 general assembly diagram provides the accurate distance from the rudder hinge to the running light base, so this additional length span is ¹⁵/₁₆”. For unknown reasons, it was not included in the overall length, specified in the general arrangement drawings!

In fact, these general arrangement diagrams are also misleading in other dimensions. There was an error in the overall wing span specified in the Douglas drawings (see this post, figures from 109-12 to 109-15).

Conclusion: because of these errors in the original Douglas blueprints, none of the widely published SBD overall dimensions is true. Below I am providing the updated values for each variant of this aircraft. Although the wing span was the same in all Dauntless versions, I am repeating it just for the reader convenience:

• SBD-1:  wing span: 41’ 3.2”, overall length: 32’ 2.19” / 32’ 6.9”;
• SBD-2:  wing span: 41’ 3.2”, overall length: 32’ 2.19” / 32’ 6.9”;
• SBD-3:  wing span: 41’ 3.2”, overall length: 32’ 2.19” / 32’ 6.9”;
• SBD-4:  wing span: 41’ 3.2”, overall length: 32’ 8.75”;
• SBD-5: wing span: 41’ 3.2”, overall length: 33’ 1.19”;
• SBD-6: wing span: 41’ 3.2”, overall length: 33’ 1.19”;

The wing span is measured between the running lights bases on the wing tips. Fuselage lengths are measured between the spinner tip and the running light base on the tail cone.

If you want to check accuracy of any existing scale drawing or plastic kit, use the well-documented partial dimensions, shown in Figure 111-7 and 111-8 in this post. I suppose that the overall dimensions will be always wrong, due to confusing Douglas general arrangement diagrams.