The British Caproni triplane
In the photographic archives at the RAF Museum we hold a series of photographs of a somewhat bizarre-looking aircraft in RAF colours. They are triplanes, meaning they have three sets of vertically stacked wing planes.
One triplane in British service is well documented. The Sopwith Triplane was a successful fighter aircraft but it had only a short career with the Royal Naval Air Service (RNAS), later part of the Royal Air Force, until replaced by the better-known Sopwith Camel. The Triplane formed the inspiration for the German Fokker Dr.1. As the aircraft of the Red Baron this became the most famous aircraft of the First World War.
These are all small fighter aircraft. What we are looking at is something of a very different magnitude. This is the enigmatic Caproni Ca.4 heavy bomber. The first thing to catch the eye is the three large wings, each around 30m (98 ft) wide. An open central nacelle was attached to the middle wing, containing a pilot and machine gunner, and a single rearward (‘pusher’) engine at the rear. Two forward-facing (‘tractor’) engines were installed on either side with a machine gunner positioned behind it.
The Ca.4 was derived from the Ca.3 biplane bomber, which was used in great numbers by the Italians, French and Americans. Half a dozen of these Italian bombers were delivered to the RNAS and later flown by No. 227 Squadron, based in Taranto, south Italy. From there they would have been used for anti-submarine patrols.
As said, there were only few triplanes used by the RAF. The reasoning behind such a configuration is that the increase of wing surface leads to greater lift. That in turn allows an aircraft to increase its climb rate or carry a heavier load. The downside is more drag, and thus lower speed, and obviously an increase in structural complexity.
Looking at these Capronis, the number of cable and struts is bewildering. Fitters and riggers, the ground crews at the time, would have had nightmares keeping such aircraft airworthy.
With three powerful Liberty L-12 engines, each producing 400 hp, the Caproni could carry up to 1,450 kg (3,200 lb) of bombs in a separate nacelle between the landing gear. This made it the heaviest bomber used by the Allies, surpassing even the British Handley Page O/400.
The British Capronis did not see any action on the frontline. I’m not sure this was because it was needed as a patrol aircraft over the Mediterranean, or if there was no need for a heavy bomber on the frontline in north Italy. In any event, the Armistice in November 1918 also meant the end of RAF service for the Capronis. It is likely they were handed back to the Italians, or sold for scrap.
The Italians continued to use the Ca.4, also for commercial flights. Its more remarkable legacy lies in the foundation of one of the most remarkable aircraft designs in history, the 9-winged Caproni Ca.60. This enormous flying boat was designed to become a 100-passenger transatlantic airliner, but the project was far too ambitious at a time of post-war recovery.