Of floats and boats

by Dr. Marshall Michel
86th Airlift Wing historian

Up through World War II, seaplanes were an integral part of virtually all the world’s navies and many commercial airlines. Seaplanes offered a number of attractions. They had the capability to operate and recover from any area where there was water and the ability to be catapulted off of small warships far out to sea for artillery spotting and reconnaissance. They could then be recovered to be used again.

In the 1920s and ’30s, before the development of monoplanes with retractable landing gear, seaplanes developed rapidly and, for a time, were the largest and fastest aircraft in the world.

There were two types of seaplanes: the flying boat, where the main source of buoyancy was the fuselage, which acted like a ship’s hull, and the floatplane, essentially a land plane with pontoons mounted under the fuselage that were the only part to come into contact with water.

Floatplanes normally carried two floats, but when higher performance was desired some had a single float under the main fuselage and two small floats on the wings – at least one very successful fighter, the Japanese Zero floatplane, performed well in the early days of the Pacific War.

Both designs had disadvantages – the flying boat required a large, deep hull to keep the propellers out of the water, and the floatplane’s floats presented a great deal of drag.
The ideal combination would have been a seaplane with a slender land plane fuselage, but without floats. To that end, in an attempt to drastically increase the seaplane’s performance, the British Blackburn Aircraft company designed the B.20 reconnaissance seaplane.

At first glance, the B.20 seemed to be a floatplane with a large center float for obtaining adequate propeller clearance on the water for the fuselage. It also had two smaller floats near the wing tips for stability and a high wing with twin 1,700 horsepower engines.

But all was not as it seemed. The unique feature of the B.20 was that once in flight, the main float retracted upward and fitted into a “notch” to create a streamlined flying, but slender boat-type fuselage, and the wing floats folded outward to become the wing tips. Thus, in flight, the Blackburn B.20’s appearance was very close to a normal airplane. Operational versions were to have two .30 caliber machine guns in the nose, two in a dorsal turret and four in a tail turret, and to carry four 500-pound bombs or depth charges in wing cells.
The B.20 generated enough interest in the British Air Ministry for it to authorize the construction of two prototypes. The first B.20 prototype flew for the first time in March 1940 and the retractable float system worked well – indeed, perfectly – while initial tests showed a significant improvement in performance over normal reconnaissance flying boats.
But the next month, during a high speed test run, the prototype B.20 came apart. Apparently it was caused by aileron flutter, a common phenomena with newly-developed aircraft caused by an aileron that starts oscillating violently up and down as the air traveling over its surface moves it back and forth; this phenomena can cause the aileron to separate, with disastrous results.
Three of the five B.20’s crew were lost and development ceased as Blackburn’s resources were dedicated to more mundane projects for the war effort.Blackburn proposed a floatplane fighter (B.44) based on the same drag reduction concept, but the rapid wartime development of long range land planes and the construction of large numbers of airfields meant the compromises that came from being able to float and take off from the water – excessive drag and weight, which translated into reduced bomb loads, speeds and ranges – were too great, and seaplanes gradually took on a much reduced role in military maritime operations.
For questions or comments, contact Dr. Michel at marshall.michel@ramstein.af.mil.