1/72 Otto Doppeldekker
DECALS: Home printed
REVIEWER: Stephen Foster
NOTES: Plans via Steve Cox of IPMS WWI SIG and other internet sources


Gustav Otto was a Bavarian engineer who established a factory for building aircraft in Munich in the years just before WW1. Unusually for German designers he focussed on pusher machines, and according to contemporary British sources these were copies of Farman designs. In fact this was a little unfair as it would be more accurate to say that he was inspired by the Farman designs as his machines were considerably different in outline and construction. Whereas most contemporary machines were built with wooden frames, Otto used steel. This was a very marked innovation for the time as was his use of elevators rather than wing warping which was common on most contemporary French and British designs. The engine was mounted on a platform above the rear of the nacelle and was an Argus of 100hp, again a more powerful plant than most of its non-German contemporaries. However the basic design went through many variations over time, as did many other contemporary designs, as Otto tried to refine and improve the basic idea. There were variously machines with four fins and rudders, twin two-wheel undercarriage units and various shapes to the nacelle. One photograph shows an Otto without any nacelle at all as on the Bristol Boxkite, with the pilot sitting fully exposed in the front of the aircraft and the passenger equally exposed behind. It would seem that by 1914 the design had settled to something like what I have tried to represent in my model, but I cannot be certain of all the details as there is little reliable information published in English. Otto was also the owner of the Ago company which built the C class of aircraft which was the subject of another scratch build that I have posted on this site.

An interesting part of the story of this design involved Flying Instructor Bruno Büchner who organised demonstration flights to rally interest in aviation in South-West Africa, then a German colony, now Botswana. He was given a biplane from the Pfalz-flugzeugwerke, caller Doppelfalz, and told that after completing his displays he was to fly overland to East Africa (also a German colony at the time - now Tanzania), to give shows there. In May 1914, Büchner, his wife, and a newspaper reporter arrived in Swakopmund with the Doppelpfalz. He assembled and tested the plane at the coast and flew to Windhoek. Conditions were far from ideal - the air was too thin at that altitude and the aircraft was not really suitable for a tropical environment. It was therefore decided that Büchner should not fly to East Africa. He continued to performe at a few shows in the South-West colony and undertook what was for those days long distance flights to Usakos and Karubib, carrying post bags and even a passenger. Eventually, the party arrived in Lüderitz by train. The shows ceased in July when he had the aeroplane shipped in crates to Dar-es-Salaam.

Büchner heard about the outbreak of the First World War in Zanzibar Harbour. He returned to Dar-es-Salaam met the cruiser Königsberg. On arrival he offered his aircraft to Oberstleutnant Paul von Lettow-Vorbeck, the commander of the defence forces in German East Africa. Von Lettow-Vorbeck ordered Büchner to undertake a scouting mission in the direction of Zanzibar and Bagamoyo. Flying along the coast he spotted two gunboats which immediately opened fire and was wounded in the arm. On landing, the plane struck deep sand and somersaulted. Büchner was thrown clear but injured; he arrived at his base late in the evening and utterly exhausted. While he was still in hospital, another officer, Leutnant Henneberger, had the plane repaired and took off. However, when he was attempting to land the aircraft clipped the tops of palm trees and crashed killing the pilot even though the plane was only lightly damaged.

After his recovery Büchner was ordered to fit floats to his plane and to support the Königsberg, which was then lying disabled in the Rufiji Delta. The aircraft was rebuilt and sheet-metal floats were attached. It was then found that there was insufficient petrol available, and the project was cancelled. The inventive Büchner fitted the aircraft's engine to a small-gauge railway goods truck and, with this much admired Schienen-Zepp(Rail-Zepp[elin]), undertook two goods transport trips to the inland town of Morogoro. Following the occupation by the British, Büchner and his wife were interned.

The military service career of these aircraft at home seems to have been limited to reconnaissance on the Eastern front by a very few machines. The Army did not like them because they were considered to be badly constructed and the Navy ordered several but these seem to have suffered from poor construction too. However some machines do seem to have been employed at least in the early months of the war before they were withdrawn from service. 

I started as usual by making a mould for the fuselage nacelle using the standard push-mould technique. The frame of the fuselage was thin rod and a simple instrument panel added with a couple of dials was from card. A compass from a thick piece of rod was cut and mounted on the port side of the fuselage, together with a control column, rudder bar and some seats. A fuel tank was made from laminated card - this fits under the engine platform in the rear of the nacelle. A gravity tank which was under the top wing was made from a cocktail stick. The engine was constructed from laminated card for the sump and rod for the cylinders with various bits of pipework from thin rod or stretched sprue.  The radiator was 40 thou card with the front and rear scribed to give a pipe effect. The propellor was carved from 60 thou card. The engine platform was made from card and rod and glued to two strips of Evergreen strip on the sides of the nacelle and top of the lower wing. This can only be fitted after the lower wings are in place.

I cut the wings from bent 40 thou card and put on the ribs from 1mm masking tape, varnished and slightly rubbed down. Before putting on the ribs the wings were sanded to an aerofoil section by thinning the trailing edges and rounding off the leading edges. The shape of the cut-out of the top wing seems to have varied a little, as did the location of the gravity tank. The trailing edge of the lower wing also varied from one machine to another - I have modelled a simpler style but there were also curved ones.  Ailerons were on the top wing only. These hung down when the aircraft was on the ground and the control wires hung loose but as I use copper wire for rigging this would have been impossible for me to reproduce so I left my ailerons in the horizontal position. I also cut the tail surfaces at this stage. 

I joined the lower wings to the fuselage one at a time. This part is critical because the nacelle tapers so the wing to fuselage joint must reflect this or the alignments will be wrong and the model will look horrible. The inner strut holes  go right through the wing because the undercarriage legs will fit into them later. On the top wing the outer holes go right through to mount king posts later. Mark on very carefully the places where the booms will attach to the wings and using the end of a round file grind out shallow grooves that will later take the ends of the booms. The wooden frames that support the engine platform to the fuselage and lower wing were fixed next followed by the supports for the platform. Glue the platform to the supports but do not put on the engine until the platform and supports are painted
I painted the model at this stage. The scheme was overall clear doped linen with black for the engine platform. I also put on the markings on both wings and the rudder. I printed my transfers on clear transfer sheet having first painted the white square backgrounds on the wings. I should have printed the crosses on to white transfer sheet really, but then we can all be wiser after the event. 


The two struts which extend from the leading edge of the top wing to the nacelle were from rod as was the undercarriage. Wheels from the spares box, but they could easily have been made from card discs and rod tyres. The tail skid was made from card, as were the control horns on the flying surfaces. The wing and tail king posts were rod.
Paint all of the struts, booms, king posts and undercarriage black, tyres light grey and propellor natural wood. Leave the propellor and wheels off for the moment.Paint all of the struts, booms, king posts and undercarriage black, tyres light grey and propellor natural wood. Leave the propellor and wheels off for the moment.Paint all of the struts, booms, king posts and undercarriage black, tyres light grey and propellor natural wood. Leave the propellor and wheels off for the moment. Paint all of the struts, booms, king posts and undercarriage black, tyres light grey and propellor natural wood. Leave the propellor and wheels off for the moment.

When the painting and markings were complete  I added the engine and radiator and a fuel pipe from the engine to the fuel tank in the nacelle. I also added the side braces between the sides of the radiator and the platform and a pipe from the rear of the engine to the rear of the radiator - this goes along the top of the engine. There are other pipes on the sides of the egine which can be added now or later. Fixing the wings can be difficult but life becomes easier if you glue the four inner struts into the holes in the lower wing and put small blobs of glue into the inner holes on the underside of the upper wing.  Then gently lower the upper wing and align the struts so that they are vertical. Support the wings while this dries out thoroughly. If this is done properly there should be no problems with alignment and gap between the wings. When the structure is dry the other struts can be added carefully and the structure should be strong enough to allow this procedure to proceed without problems. Many people seem to think that building biplanes in this way is difficult because the structure would be weak but experiences proves otherwise. I cut my booms from florists wire as this is stiff enough to hold the model together and is completely straight, which I do not find is the case with plastic rod. Fix the booms to the lower wing first. I placed the model on a plan so I could align them correctly in the horizontal plane. I then measured from a side elevation of the plans the vertical distance between the trailing edge of the wing and the rear end of the boom. This gives the height of the support that has to be put under the tail end of the boom while the glue dries. I use epoxy as it gives me time to make last moment adjustments and get everything into the correct position before it hardens. The two small bracing struts at the rear of the V were from plastic rod held with superglue. I had drilled a small hole in the base of the rudder and inserted a small pin which I now placed into the V of the lower boom, again with superglue to hold it. Hold the rudder in the correct position while the superglue dries. Then I can add the upper booms to the top wing joints and brought the rear ends to form a V on a small nick cut out in the leading edge of the rudder - this latter joint was superglued. Note that in the horizontal plane the booms converge towards the rear. The boom struts were be measured individually with dividers and cut from rod and put into place with superglue. This structure is strong when it is all in place.

Paint all of the struts, booms, king posts and undercarriage black, tyres light grey and propellor natural wood. Leave the propellor and wheels off for the moment.

For the rigging I used 40 SWG copper wire rolled straight and held in place with superglue. Measure the distances on the model with a pair of dividers and cut each length individually. Work systematically around the model and you are unlikely to miss any. Place the most inaccessible ones first, and leave the most prominent and therefore most likely damaged until last. Glue on the propellor after you have rigged the sides of the booms but before you put in the cross bracing, and the wheels until after you have rigged the undercarriage frame but before you put on the under-wing bracing.


When you have finished you will have a unique model not in that there are a few others around, but I guarantee that most of them will be vacuforms, whereas yours will be truly your own work and therefore unique in that respect.

Stephen Foster

9 January 2017

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