Page 25 - Theory and Design of Air Cushion Craft

10 Introduction to hovercraft

because I didn't know enough to be able to work out the probable duct and other
losses and the sort of power that would be required.
Then one Saturday evening I thought I would have a look at using air curtains.
A simple calculation looked all right on a power basis, and so that Sunday I
made up an annular jet using two coffee tins, and found that the air did follow
the 'predicted' path and that there was a 'predicted' gain in lift - very exiting.

Cockerell secured the assistance of a fellow boatbuilder in constructing a working
model of the type of craft envisaged. This was used as a test model for several years
and is now in the Science Museum in London. In December 1955 Cockerell applied
for his first British patent covering lift by means of peripheral annular jets.
Until 1956, air cushion technology was considered to have military potential and
was put on the list of projects which had public information restrictions when it was
offered to the British Government for development sponsorship by Sir Christopher
Cockerell. At this time, study was centred on investigation using free flying models.
For the next two years he made the rounds of industry and government departments
with remarkably little to show for it. The shipbuilding firms said 'It's not a ship - try
the aircraft industry', and the aircraft firms said 'It's not an aircraft - try the ship-
builders'. Three engine manufacturers said 'Not for us, but if you want your invention
taken up, remember to use our engines'. However, he did receive valuable encourage-
ment from Mr R. A. Shaw of the Ministry of Supply, and eventually during 1957 the
Ministry approached Saunders-Roe who accepted a contract to undertake a feasibil-
ity study and to do model tests.
The Saunders-Roe design team who undertook this initial study also formed the
nucleus of British Hovercraft Corporation's technical staff later in the 1960s. Prior to
involvement with hovercraft they had for many years been engaged in the design and
construction of flying boats and hydrofoils. It was precisely because of this background
of 'fish and fowl' expertise that the hovercraft principle was enthusiastically pursued.
Christopher Cockerell in the meantime had approached the National Research
Development Corporation (N.R.D.C.) who also realised that hovercraft were likely to
became a revolutionary new form of transport and through them, a subsidiary
Company known as Hovercraft Development Limited (H.D.L.) was set up in January
1958 with Cockerell leading the research group as Technical Director.
The report of the Saunders-Roe feasibility study was favourable, as a result of
which N.R.D.C. placed a further contract with the company for a programme of work
which included the design and manufacture of a manned development craft desig-
nated SR.N1 (Fig. 1.9). This historic craft was completed on 28th May 1959. On July
25th 1959, in its original form, it crossed the English Channel from Calais to Dover
with Christopher Cockerell on board to mark the 50th anniversary of the first cross-
channel flight by Bleriot in an aeroplane.
Although the first cross channel operations on relatively calm water were very suc-
cessful, the craft performance, manoeuvrability, seakeeping quality and propulsion
efficiency were very poor. The craft had an air gap over the ground of about 100 mm
whilst the lift power, at about 36.7 kW/t, was rather high. The efficiency of the air jet
propulsion used was low, and manoeuvrability was so poor that the pilot was unable
to handle the craft in a stable manner. The SR.N1 was built in an aviation factory, and
aviation engines, equipment, structures and construction technology were used. For