Triplane Builder

Articles by Triplane Builder - William (Bill) Woodall

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Why So Few

Historians seem at a loss to explain the short life span and few numbers built for the Sopwith triplane.
Seemingly it was a very competent fighting "scout". It was well mannered and blessed with a fair turn of speed and a fine rate of climb. It did have only one machine gun and its opponents had two, but its ratio between victories and losses was respectable.
One early criticism was the capacity of its fuel tank and therefore its "time on station".
It did seem that triplanes spent a large amount of time being repaired, and some machines were shuffled between squadrons.
Historians place the number at slightly over 150 as the total made by Sopwith and 2 other contractors.
This seems strange. The RFC had wanted the airplane, but then traded their production slots to the RNAS for Hispano-Suiza engines.
The Germans had high a regard for the triplane, but the British rushed the Camel into production as its replacement, prior to its becoming obsolescent.
Sopwith "Pups", which were more obsolescent, continued to be produced after the triplane was discontinued.
The triplane had an unusual construction feature. This was the cabane strut configuration.
Since the mid-wings anchor to these struts, they were made an integral part of the fuselage structure.
This means that most maintenance being done on systems within the forward section of the fuselage was influenced by those struts.
The fuel and oil tanks are impacted by this positioning, and when any damage needed repairing, decisions had to be made. If the tanks could not be repaired externally, the front end of the airplane must be opened up for their removal.
This would mean removing the wings--top, and side shields, nose cowl and propeller. The machine gun and its synchronizer and mounting arches would also need to be taken off, as well as the plan form brace wiring that draws the fuselage sides together. With these things done, the upper longerons could be jacked apart so that the oil and fuel tanks could be un-plumbed and lifted out.
This constitutes a long stay in the maintenance shop, and lots of labor.
I further think that the Sopwith Camel was rushed through design and prototyping to get past these hurdles.
Many writers have cited the fact that the Camel has its engine, pilot and guns as far forward as possible, so that if the excuse for building the triplane in the first place was "visibility for the pilot", that item was certainly discarded.
Why were all of these groupings carried out? It was to make room for the main fuel tank which was now located behind the pilot. This location had a serious effect on the center of gravity of the airplane, and dictated that the other heavy items move forward.
A further consequence was that the main tank could not be operated as a gravity-feed unit. It depended on air pressure from the hand-pump and the wind-driven Rotherham air compressor to force the fuel to the Tampiere valve. When the Tampiere valve is forced to cope with a pressurized fuel flow, its regulation becomes much more sensitive. The possibility that the pilot can inadvertently over-charge the carburetor is very real. Should this occur, the engine can encounter a "rich-stall" condition. Firing ceases for some time before leaning can restore the proper mixture. The Camel was probably the first rotary powered fighter equipped this way. (Other machines-the Pup-1/1/2 Strutter, and triplane had air pressure to assist to their gravity systems.)
Encountering a silent engine during take-off--at a high angle of attack-in a tail-heavy airplane was the novice pilot's recipe for disaster in Sopwith Camels.

One other aside that might indicate the validity of this argument was the negative report made by British air officials on the neat appearing LePere-Lusac fighter that the USAS had designed and built. It seems they objected to the integral cabane strut lay-out as being impractical for a service airplane.

Bill Woodall

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