On 25 November 1911, at Windermere, Waterbird made the world’s first successful flight to use a ‘stepped’ float, only achieved by embodying Edward Wakefield’s two years of persistent experiments. The pilot was Herbert Stanley Adams.
The history is here.
The concept of the stepped float was described by Gertrude Bacon, who flew at Windermere in July 1912, in her book All About Flying, published in 1915:
‘The lower surface of the hydroplane float, instead of being all of one piece, changes or ‘steps’ abruptly to another level. The main object of the steps is to help the float to become ‘unstuck’. There is a great tendency for water to hold on to an object lying flat upon it. Lay the palm of your hand flat on the water and feel the resistance offered when you lift it straight upwards. The step allows the air to come in underneath the under surface of the float, and so does away with this suction effect.’
In early Sunderland flying boats, the hull step was an abrupt one, but in the Mark III it was a curve upwards from the forward hull line. The Mark III was the definitive Sunderland variant with 461 built, of which 35 were built at White Cross Bay, Windermere between 1942 and 1944.
‘It was a clergyman, the Rev. C. M. Ramus, who first suggested the hydroplane, in 1872, and he drew the attention of the Lords of the Admiralty to his experiments and their results [for warships] but the scheme as a whole was abandoned.’ – Flight magazine, 22 February 1913. ‘So far as one can gather, the patent, which was taken out in 1906 by Albert Edward Knight, is the first patent on record relating to “stepped” hydroplanes’ [for boats]. – The Aeroplane magazine, 4 September 1913.
On 28 March 1910, Henri Fabre made the first successful flight from water, near Marseilles. However, his float was not stepped but was arranged with the flat part underneath, with a curved upper surface, so as to generate lifting force when moving on water or in air.
Glenn Curtiss flew from water on 26 January 1911, at San Diego Bay, California. Waterbird’s float was of a Glenn Curtiss-type, but the Curtiss float had been designed to ride through waves of the sea, shaped so that it would tend to rise on the surface and was flat-bottomed, not stepped.
‘The hydro part of the mechanism consists of a float, which in order to avoid the resistance of water suction, is made step-wise at its base, unlike the flat bottom of the American type.’ – Kendal Mercury and Times, 22 December 1911.
On 11 December 1911, Edward Wakefield successfully applied for patents to cover stepped floats and their method of attachment. The object was ‘to provide an aeroplane with means for enabling it to alight, float and travel along the surface of water and to rise again therefrom’. Wakefield had combined features of construction in a novel way.
The development of Waterbird’s float, as depicted in the video clip below, was: built in May 1911, with the additions of a single step in September 1911, a second step in November 1911, and a tapering stern later.
‘The hydroplane float is 12 feet long by 2 feet wide by 1 foot deep, the sides are of ¼” mahogany, the bottom of 22 gauge aluminium and the top covering of Willesden waterproof canvas. Wooden lattice girder frames are fitted internally 8″ apart to stiffen up the float and a centre longitudinal of wood runs centrally from bow to stern inside. Wood beading is used at the corners inside to ensure watertightness. No watertight compartments are at present fitted but Mr Wakefield says he can fit seven with about 15lbs extra weight. The weight of the float is about 96lbs, but with a new one under construction should weigh only 70, this latter has a duralumin bottom on which the sea has no bad effect. Two steps occur in the bottom of the hydroplane, one at about half way of 4″ and the other 8″ from the stern of 3 ½”. The float is attached to the machine by a rubber spring 3 point suspension, the struts being of steel tubing.’ – Lieutenant Arthur Longmore, who test-flew Waterbird for the Admiralty on 20 January 1912.
The original Waterbird float has survived and is at the RAF Museum Reserve Collection.
On 14 March 1912, Wakefield entered into a contract with the Admiralty for floats and undercarriages, or royalties, and to convert Admiralty Deperdussin M1 (a monoplane) into a hydro-aeroplane, which he achieved within four weeks from delivery.
Today, all seaplane floats have steps.