The Poundswick Hovercraft
|In 1967 a new school society called
the Technical Activities Group was set up under the
guidance of Mr. K. Moorby (Metalwork) and Mr. M. F.
Russell (Physics) to cater for pupils who wanted to learn
more about how the knowledge of the scientist is combined
with the applications of the technologist.
The group's first (very ambitious) project was to build a two-seat hovercraft which was entered into a national competition sponsored by the Daily Express and B.P. It was 18 feet long, weighed over 1000lb and was powered by three 197cc Villiers two-stroke engines. It was all home-built, including the propellers which were hand-carved by a particularly talented pupil.
In April 1970 the following article appeared in the School Council Publication Project Technology. It describes the hovercraft in some technical detail and I have reproduced the text and photographs in full.
Poundswick High School's
In this candid and unpretentious account K.
Moorby, Head of Technical Studies
of reference were simple - to build a craft capable of
travelling at 30 m.p.h. over land and water and capable
of carrying two adults, yet safe enough for operation by
the boys themselves. The total available funds amounted
to £50 and knowledge was limited to the basic principles
of hovercraft operation.
Since the ages of the pupils involved in this project were, at the time of building, only 13 -15 it was felt that they could not be expected to appreciate the more difficult mathematics of air flow calculations and the design of fans and propellers. In consequence, our mathematical treatment was limited to four approaches. These were:
1. Consideration of craft area in relation to the expected cushion pressure and the overall weight of the craft.
2. Consideration of the top speed of propellers of different sizes operating at various rev/min.
3. Simple moment calculations which assisted in the balancing of the craft.
4. Calculations to estimate the buoyancy of the craft.
The design was planned in stages which permitted modification at various stages of the construction, in the light of experimental trials. This technique appealed to our younger boys and provided a suitable link between experimental science and technology.
Our initial design was based on the assumption that an adequate lift can be obtained at a pressure of 10lb/sq.ft. and that the width of the craft had to be no greater than 6ft. 3in. so that it could be removed from the building. This restricted the shape of the hull to an unconventional 6ft. 3in by 14ft. Weight was kept to an absolute minimum except where safety demanded additional strength.
This provides accommodation for two adults sitting side-by-side. As the money available for this project was extremely limited, the comfort afforded to the operators is negligible.
CONSTRUCTION OF THE CRAFT
TRIALS AND EXPERIMENTS
Experiments were carried out using manometers to measure air cushion pressures under various conditions. Stroboscope techniques were used to determine fan and propeller speeds. In addition an investigation of the water absorbed by various buoyancy materials was carried out in order to determine the most suitable material on a cost versus effciciency basis.
FIRST PUBLIC APPEARANCE
With a deep roar, the lift engine easily lifted the gross weight of half a ton and then, very smoothly, the power of the two 197cc thrust engines sped the craft across the school fields, to the accompanying applause of the many friends and parents gathered to watch the maiden run.
Suddenly disaster loomed up in the shape of a goal post directly in the path of the oncoming craft. Safety drill had been carried out in simulated conditions and it was with confidence that we waited for the craft to slide to a halt, the lift engine having been cut. It was not to be. The craft kept on a collision course and the inevitable happened. With a crash, the work of months wrapped itself round a very strong 4in. x 3in. upright and pieces of hovercraft flew off in all directions.
A rush to the scene confirmed the worst. The goalpost had carved into the bows for a depth of 3ft. 6in. and had reached the cockpit. The occupants had escaped with minor shock. With a wry smile the driver said "It's not so bad sir, we'll soon fix it". And they did. Back to the school it was carried, repair work commenced almost immediately. What drives twelve boys, two members of staff and several parents to work until midnight rebuilding a severely damaged hull? Such was their enthusiasm that by the next day it was clear that the craft would be ready to compete in the Daily Express Air Rider competition at Harlow only forty-eight hours after the crash.
After this success the reliability and the appearance of the craft were improved and we have given many demonstrations at various schools and shows. The pilots became very proficient and could manoeuvre the craft easily and safely.
The craft was recently demonstrated before the Manchester Regional Group of Project Technology, under rather unusual conditions - 8pm on a November night involved obvious difficulties. Headlights were fitted to the craft and goalposts indicated by marker beacons. This is possibly one of the few occasions that a light hovercraft has performed during the hours of darkness.
Since some of the boys involved in the construction are now 17 years old, it is probable that we shall carry out more involved experiments to test the correlation of theory with practice in the design of light hovercraft. This is a subject offering much scope and, judging from the arguments in amateur hovercraft circles, the answers are by no means clear!
|If any Old Poundswickians who worked
on the hovercraft would like to add their recollections
of the project to this page, please get in touch.