Douglas O-46A (oz6136)

About this Plan

Douglas O-46A. Free flight scale model for rubber power. JD McHard's super-scale Douglas O-46A. Scale is 1/16.

Quote: "Rubber powered flying scale models are rare birds these days, but there is a certain satisfaction in knowing that the motor will start first time and having started, will flap the prop over silently. Then to see the model soar effortlessly into the air with no exhaust and diesel oil ruining that smart paint job!

The O-46A was selected as a prototype for several reasons. The fuselage is long, giving reasonable distance between motor hooks. The tailplane is of such a size as to need litle enlargement to produce a stable machine. The position of the wing is perfect for satisfactory performance and the fixings are very adaptable to knock-off mountings.

The machine was originally in service with the US Army Air Corps from 1936 until the beginning of the recent war. It became affectionately known as the 'Flying Razor', chiefly because of its very narrow fuselage. As the service designation indicates it was an observation ship and it fulfilled roughly the same role as the Meteor 9 does today, though at a more leisurely pace!

The odd device on the fuselage side is the insignia of the 22nd Observation Squadron, Brooks Field, Texas, used during World War One by the 135th squadron flying SPADs! The background is blue, surrounded by a yellow outer band. Stars are white and the comet tail starts as red and merges into yellow and then white at the extreme tip. (On the original model the colours of the tail are reversed, but this boob remained undiscovered until after the photos were taken!)

A motor tube is used on the model, to act as a building jig and also strengthen the finished fuselage. It minimises the risk of writing off the fuselage when the motor breaks! Formers have sharp inner edges and rubber whips around as it unwinds; by using a motor tube the life of the rubber motor can be prolonged considerably, particularly with such a narrow fuselage as the 0.46A.

This and many other novel constructional features of the McHard model are fully detailed in the building instructions which are issued with each full-size APS plan. Readers will note the close wing rib spacing and almost scale stringer positions on the fuselage which have been used .16 produce a model capable of winning flying contests as well as exhibition prizes.

Correct colouring is with fuselage and struts in dark blue and the wings and tailplane in orange-yellow. To keep the weight down to a minimum for best flying performance, it is advisable to use coloured Modelspan, rather than colour dope. However, the original 0.46 model manages consistent 90 second flights in spite of its all-up weight of 71-1/2 oz, of which no less than 1-1/2 oz can be attributed to use of colour dope and fitting sundry oddments to improve the scale detail and appearance.

The rubber motor consists of eight 30 in loops of 3/16 flat strip, pre-tensioned by the 'White' method, and this gives quite a realistic snappy climb after take-off. 3° downthrust was required on the original and a little sidethrust may be found necessary. To bring the centre of gravity forward to the right place, it is best to add ballast beneath the cowling surface so that it will be discreetly hidden. The propeller shaft is so arranged that three or two-blade airscrews can be interchanged in experiment to find the best performance."

Direct submission to Outerzone.

Quote: "Hi Steve, I was just checking your site for Douglas O-46 plans and realized I had a scan you did not. So here you go."

Update 10/08/2017: Added PDFvector plan tracing, also article pages, thanks to hogal.

Update 28/8/2022: Added supplement file Motor Tube Notes, thanks to Ted Avey.

Supplementary file notes

Article pages.
Motor tube notes.
PDFvector plan tracing.

Corrections?

Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction