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Author Topic: Douglas O-46B Observation Plane / CP 39-785 (1939)  (Read 1688 times)

Offline circle-5

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Douglas O-46B Observation Plane / CP 39-785 (1939)
« on: July 18, 2018, 03:09:41 pm »
Here's a model of a 1930s Douglas Aircraft Observation Plane that I am unable to identify.  Does someone in the vast SPF knowledge base know what it is?
« Last Edit: July 25, 2018, 09:11:07 pm by circle-5 »

Offline Skyblazer

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #1 on: July 18, 2018, 04:51:18 pm »
Very interesting find! It seems to be the Douglas proposal for the same Specification that produced the Curtiss Owl (the O-52 was C-416-1, so perhaps this may have been C-416-2 JUST a hypothesis here).
« Last Edit: July 18, 2018, 04:57:26 pm by Skyblazer »

Offline circle-5

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #2 on: July 19, 2018, 11:55:23 am »
Very interesting find! It seems to be the Douglas proposal for the same Specification that produced the Curtiss Owl (the O-52 was C-416-1, so perhaps this may have been C-416-2 JUST a hypothesis here).

Good educated guess I hope some evidence will eventually confirm that.  It was not customary for Douglas to omit an ID nameplate of some sort on their models.  They were clearly not thinking of the problems this would cause me, 80 years later ... :)

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #3 on: July 19, 2018, 12:36:28 pm »
Could this model has been (intentionally) lacks the wing struts?

Similarity to Curtiss O-52 is striking - and wing's planform "asks" for struts.

There were some Douglas high wing observation's types - but none of them have been as clean and elegant 8-)

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #4 on: July 19, 2018, 01:03:02 pm »
From above or three quarters view, very similar to the Westland Lysander, minus the strutts.  I know it is not but the similarity is there.

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #5 on: July 19, 2018, 01:28:58 pm »
From above or three quarters view, very similar to the Westland Lysander, minus the strutts.  I know it is not but the similarity is there.

And minus the fixed undercarriage of Lysander. ;)

We could think about this Westland aircraft, as about obsolete - and as about mass-produced and widely-used at the same time. No Douglas or Curtiss "observation" aircraft could rich similar "popularity".

Offline circle-5

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #6 on: July 19, 2018, 03:39:23 pm »
Could this model has been (intentionally) lacks the wing struts?

Similarity to Curtiss O-52 is striking - and wing's planform "asks" for struts.

There were some Douglas high wing observation's types - but none of them have been as clean and elegant 8-)

The model is generally well preserved (for its age) and shows no evidence there ever were any struts this was a fully cantilevered wing design.  I imagine the wing support structure was intrusive inside the cockpit, but the absence of struts gave the crew an unimpeded view of the ground below.

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #7 on: July 20, 2018, 08:14:41 am »
The model is generally well preserved (for its age) and shows no evidence there ever were any struts this was a fully cantilevered wing design.  I imagine the wing support structure was intrusive inside the cockpit, but the absence of struts gave the crew an unimpeded view of the ground below.

I think, that wing planform could be a clue - with widest airfoile in the middle of the wing (where struts could be attached), and narrower - near fuselage. Please, compare it with Westland Lysander.

The size of model could be a reason, why struts have been omitted - either they too thin for being produced in appopriate scale or too weak to be touched by viewers.

In my humble opinion, struts itself wouldn't be so bigproblem for observation.

Offline Jemiba

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #8 on: July 20, 2018, 10:18:47 am »
In my humble opinion, struts itself wouldn't be so bigproblem for observation.

Certainly not, but they weren't necessary, see the Cessna Model A (1927), Lockheed Vega (1927), or Renard R.17 (1931).
The wing planform may be no indicator for the need of struts here, it's the leading edge, that's drawn in and just as in
the Lysander the reason probably just was the pilot's view.
And looking at that prop on the model, I really don't think, that the struts were just omitted, because of sorrows, that
they could be damaged. A simple piece of steel wire would have been much stronger, than those prop blades.
I have full confidence in the preciseness of that, certainly long gone modeller here !
It takes a long time, before all mistakes are made ...

Offline circle-5

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #9 on: July 20, 2018, 02:06:07 pm »
I agree with Jemiba.  It would not have been a problem to include struts (the model is quite large) since much smaller details are shown.  See attached photo note metal prop detail, side window angle, etc.  These models were made to generate sales and several manufacturers were competing for just one customer.  Everything had to be accurate.  If Douglas factory drawings are ever found (there is likely a copy at the National Archives), the absence of struts will be confirmed.

As for struts impeding the view, successive short flights in a Cessna 172 and 177 will reveal how much of a difference it makes not to have these things in the way.  And neither the 172 or the 177 are observation planes!

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #10 on: July 24, 2018, 07:34:06 am »
Dear circle-5!

Do you have estimation of scale for this model? Perhaps, the propeller diameter could be a key to this subject?
And could you be so kind to  tell it's overall size?

Thanks in advance!

I wonder, what's the origins of such display models in USA, when their initially became common as presentation of company poropsals to the armed services?

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #11 on: July 24, 2018, 10:37:26 am »
Dear circle-5!

Do you have estimation of scale for this model? Perhaps, the propeller diameter could be a key to this subject?
And could you be so kind to  tell it's overall size?

Thanks in advance!

I wonder, what's the origins of such display models in USA, when their initially became common as presentation of company poropsals to the armed services?

This late-1930s Douglas Observation Plane concept model measures 27-1/2 inches wingspan x 20 inches length (698,5mm W x 508mm L).  Without knowing the dimensions of the original, I don't want to speculate on the scale could be around 1/18 or 1/20.  Yes, this was likely a presentation model for the Army Air Corps, as part of a proposal package from Douglas Aircraft in Santa Monica.  Now we use 3D renderings, but models were the only way to show a 3D representation of the airplane back then, until (approx.) the 1980s and even later.

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #12 on: July 24, 2018, 07:09:38 pm »
Most interesting photos of that model!

Once I saw it I had to go back into my records and seek out information on the competition, which was CP 39-785, Type Spec C-416, analysis date of 8-14-1939. This CP eventually resulted in the building of the O-52 - another fine target for Air Corps planners still fighting WWI.

There were a substantial number of entries for the competition, with Douglas itself entering at least eleven different possibilities, apparently labeled D-1 (for the O-46A seemingly as a comparison for the other designs), up to at least the D-11. Of these entries, the Air Corps only analyzed three - the D-2 (O-46B), the D-11 (O-46C) and the D-5 (also labeled the O-46B for reasons I will hopefully logic through here).

The D-11 is immediately written off our list as it was a 3-place, tricycle landing gear entry. However, the D-2 and the D-5 appear to be basically the same except for the D-2 having an R-1690 engine and the D-5 having an R-1830.  On that basis the weights, speeds, ranges, etc. all differ. The  wingspan and area are the same. Both had retractable "conventional" landing gear and a fixed tail wheel and were fitted with a 3-blade constant speed propeller. The D-2 had a propeller diameter of 11' and the D-5's was to be 11.5'. Due to the larger engine and propeller - and perhaps other items - the D-2 had a wing loading of 22.7 and D-5 one of 26.5.

The Air Corp's analysis stated that spin recovery was questionable on ALL the analyzed Douglas aircraft, including the existing O-46A (labeled D-1). The Air Corps gave the D-2 a score of one (1) for its possibility of meeting the required guarantees, but the D-5 received a six (6). Lateral control for the D-2, D-11 and D-5 was deemed to be marginal at low speeds, although maneuverability was determined to be satisfactory.

Engineering analysis deemed that the D-2 (and thus the D-5) had good vision and was a simple design. But the stress analysis was not acceptable as shear stresses from direct shear and torsion had not been considered. The tail wheel was overloaded and the main struts were non-standard with no provisions for skis. There was insufficient data for determining the potential for field maintenance to the cowl. Once again, the Safety Characteristics for the D-2 were determined to be the same with regard to questionable spin recovery as for the D-1 (O-46A), but worse by an Order of 3.

Regarding the fuselage structure, it was a semi-monocoque with formed bulkheads, flange section stringers, Alclad cover flush joints and flush rivets. 

Endurance for the D-2 and D-5 at Operating Speed was calculated to be 2.25 hours and a ferrying range of 700 miles. Service ceiling for the D-2 was 26,100', and that for the D-5 was estimated to be 27,800'.

High speed for the D-2 at 4,000' was guaranteed to 227mph, with 258mph for the D-5. Operating Speed for the D-2 was guaranteed to be 199mph. For the D-5 it was 225mph.

Length and span were exactly the same for both entries - 33' 11" and 45' 8" respectively. Numbers for both the airfoil shape and chord are the same and reflect the trapezoidal shape of the wing.

Empty/gross weights for the D-2 were 5221lbs/6988lbs respectively, and for the D-5 they were 6020lbs/7557lbs.

Based on all the analyses performed by the AAC, the time period, etc., I'm going to declare that the pictured model represents the D-5 simply because of the potential of the larger engine - but it could be the D-2. Length and Span are identical for both entries.

Below are drawings from the AAC analysis clearly showing the wing shape plan view and the fuselage front view, both of which fit the model exactly - including no strut. And there is no mention of a wing strut in any of the analyses for these aircraft. Finally, I've included two photos from my collection of a model of the aircraft that were identified as the Douglas entry for CP 39-785.

Respectfully submitted,

Alan Griffith


« Last Edit: July 24, 2018, 07:23:51 pm by ACResearcher »

Offline circle-5

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #13 on: July 24, 2018, 07:52:39 pm »
Most interesting photos of that model!

Once I saw it I had to go back into my records and seek out information on the competition, which was CP 39-785, Type Spec C-416, analysis date of 8-14-1939. This CP eventually resulted in the building of the O-52 - another fine target for Air Corps planners still fighting WWI.

Oh well ... I was really hoping for more details <sigh>.

Just kidding this is awesome everything I ever wanted to know and more!  All speculation is now confirmed, from its connection to the O-52 to the absence of wing struts.  The photos you posted show the same blemishes on the model.  As I suspected, it's likely to be unique.  Thank you very much Alan, I never expected that anybody would have such a wealth of data about this airplane.

Would a moderator kindly change the title of this thread to:  Douglas O-46B Observation Plane / CP 39-785 (1939) or something equivalent ...  Thank you!


DONE !
« Last Edit: July 25, 2018, 12:21:18 am by Jemiba »

Offline Skyblazer

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Re: Douglas O-46B Observation Plane / CP 39-785 (1939)
« Reply #14 on: July 25, 2018, 02:26:43 am »
WOW. Sure wish we had more of that kind of research on this forum!
Thanks a bunch, ACRsearcher for this most enlightening description.

I have a slight problem with the "O-46B" designation being used in the topic's title without quotes, as I gather this (as well as the "O-46C") were never seriously considered for order, nor were they actual derivatives of the O-46A (and if ordered instead of the Curtiss proposal, would likely have been O-52 themselves). These were just working designations, just as it would be wrong to say that "D-2", "D-5" and "D-11" were actual Douglas designations for the proposals (this particular reflection somehow also sheds some light over my earlier interrogation about duplicate H- designations by Hughes, which were probably also just working designations for a particular program and not proper model designations).