Technical Report 1/75
The Caspar ACV Research Project Report No 3 on the drag of Air Cushion Vehicles over land
H S Fowler
Howard first gives an overview of the accepted theory of ACV drag and its components over land and water. He then looks at skirt friction drag over ground terrain of various types.
The 1974 experiments carried out by towing ACV Caspar are presented and drag measurements presented. ACV HEX-3 was also used in 1974 for static airflow experiments and towing trials over soil and grass. The experimental data is used to discuss drag as percentage of craft weight over different terrain at low speed and different cushion flow rates.
This is useful for considering skirt drag for ACV at below hump speeds, or hover platforms when being moved.
Technical Report 5/75
The Caspar ACV Research Project Report No 4
Program 1 The Multicell skirt, a summary
This report summarises the present state of knowledge of the multicell skirt as it is understood in Canada. A description of this type of skirt system is given. This is followed by discussion of the stability of this type of skirt stationary and in motion, Its drag characteristics and ability to operate over obstacles is discussed. This discussion includes trials with the HEX-1 ACV. Finally, aspects of design and fabrication are discussed.
Technical Report 3/77
The Caspar ACV Research Project Report No 5
The Multicell skirt with a cell-sealed perimeter and central pressurised cavity
(The hollow wall and pressurised cavity concept) in over land operation
H S Fowler
This report discusses the ‘Hollow wall and pressurised cavity’ skirt which is a development of the general multicell skirt discussed in Report No 4 where smaller conocal cells are distributed around the periphery of the cushion.
This concept was an attempt to improve the stability characteristics of the basic multicell system initially developed in France. Based on a model and three vehicles it is concluded that this system has similar characteristics to the basic multicell system and so really needed a fundamental redesign of the geometry to be practically useful.
Technical Report 1/78
The Caspar ACV Research Project Report No 6
The use of a non-dimensional quantitative description of lift airflow applicable to any ACV
H S Fowler
Methods of describing lift airflow quantitatively are reviewed, and an improved system is drived which accounts for cushion pressure and vehicle size, a non-dimensional hover gap, vehicle planform and atmospheric conditions.
It is shown that effective hover gap is related to terrain roughness and porosity, and to the mode of operation of the vehicle. Existing vehicles of known adequate performance are seen to be in well-defined groups subject to this relationship, which is discussed briefly in connection with skirt drag.
Technical Report 2/78
The Caspar ACV Research Project Report No 7
The development of a system and equipment for terrain porosity measurement
H S Fowler
The influence of terrain porosity on the operation of and ACV is discussed with regard to its ability to hover over the terrain, and to the drag resisting its motion. This discussion is used to examine an existing terrain classification system, and to propose modification to it specifically for ACV operation.
The design, construction and calibration of a system for measuring this porosity are described, and an appendix gives such field test results as are available, with corresponding drag data for an ACV over the same terrain.
Technical Report 2/73
J R Stallabrass and T R Ringer
This Is report from the Low Temperature Laboratory of NRC and was also presented in a paper to the 7th CACTS Conference in June 1973.
An ACV in operation can blow water droplets from the water surface during breakup season which then turn to ice when they hit the vehicle structure and then build up. Ice accretion can also occur from blown snow melting on hot surfaces then dripping onto cold part of the structure. Ice accretion adds weight to the ACV and can affect its performance.
The aim of this report is to give understanding on the mechanisms to allow designers to configure craft to minimise the problem.
Technical Report 2/74
A Method of controlling ‘Skirt Buzz’ in light air cushion vehicles with peripheral bag skirts
H S Fowler
The vibrations of peripheral bag type skirts of light air cushion vehicles were investigated. A theory is proposed, which enables buzz frequency to be calculated with reasonable accuracy, and on the basis of which a cure for the vibrations is proposed. The successful application of this cure to a half-scale model and two actual vehicles is described.
Technical Report 1/73 (139 pp)
The Control and Guidance of Light Air Cushion Vehicles
German & Milne, Montreal, with Robert Trillo Ltd, Brockenhurst, England, and Jones, Kirwan and Associates Hagersville, Canada
This report documents a study of the control and guidance of light ACVs below a weight of 2270 Kg. The work was completed as NRC Contract 028-2545 as part of a programme to improve the understanding of control for light ACVs. This was relatively early days for these craft and the time the designs were very varied, from direction of cushion air to open propellers and rudders to ducted centrifugal, or axial fans.
The report predates the report prepared by Howard Fowler in 1979 here, and the Stability and Control of Hovercraft – Notes For Commanders Guideline from 1980, here. The three reports together provide a valuable resource for designers.
Contents
Figures
Conversion Chart
R W Helm, Bell Aerospace Canada Textron
Canadian Aeronautics and Space Journal, Vol 33, No 1, March 1987
An overview of the development of LACV 30 for the US Army, the procurement, and the performance in service in six major operational exercises in 1983 to 1987. A total of 12 craft were delivered to the US Army in the initial phase and in total 26 craft were in service in 1987, a significant amphibious capability.
Canadian Experience with Air Cushion Vehicle Skirts
P A Sullivan, University of Toronto, and D Jones, Jones Kirwan Associates
Canadian Aeronautics and Space Journal, Vol 39, No 1, March 1993
Canadian developments in air cushion skirts are discussed, with emphasis on the authors’ experience. Early field trials with two European skirt systems, a multicell and a loop-segment system are reviewed. Both are shown to have deficiencies,
A simplified version of the loop-segment skirt developed for use on large platform cushions is described. Although this skirt is attractively simple to build and maintain, and although it has been used successfully on small high-speed craft, it is shown to have significant dynamic limitations. A hybrid cellular-segmented skirt is proposed to circumvent these limitations.
Results obtained from model tests of components of such a skirt are presented together with some field test data obtained from a recreational craft. It is suggested that hybrid configurations may be the appropriate path for most skirt systems. This includes use of a bag geometry to obtain the responsiveness necessary for comfort at high speed.
An interesting part of this paper is the discussion of response hysteresis of segmented skirts in roll or pitch.
Progress Report on Bertelsen Research and Development of an Air Cushion Crawler All-Terrain Vehicle
W R Bertelsen, Bertelsen Inc
Canadian Aeronautics and Space Journal, Vol 33, No 2, June 1987
The ACV is an exceptional amphibian, but it is not, nor is any other existing craft a true All-Terrain Vehicle. Using the best elements of and ACV in an Air Cushion Crawler Tractor a true ATV can be obtained.
A conventional crawler drive train will propel two tracks as pressurised propulsive pontoons. The key to a successful ATV is in perfecting efficient, durable, sliding seals to allow the belt to move in its orbit around the track unit and maintain its internal pressure.
After deriving the adequate seal, a 12-inch wide by 86-inch-long endless rubber belt was fitted with bilateral seals and side plates with interna guide wheels fore and aft with a 21-inch wheelbase.
From the experience of this approximately one quarter scale model, full scale Air Track Crawlers, true ATVs of any capacity can be produced.
Jetrider SES 300 Passenger Ferry Development
Ola Gullberg, Karlskronavarvet AB, Sweden
Canadian Aeronautics and Space Journal, Vol 35, No 2, June 1989
This paper presents the research and development work carried out to build the first two surface effect ships at Karlskronavarvet AB. The two passenger ferries, each with a capacity of 300 passengers and a continuous speed f 42 knots are now operating between the cities of Helsingborg in Sweden and Copenhagen in Denmark.
Special attention is given in the paper to the hull design, hull and air resistance at different speeds and trim angles, the propulsion system, the Ride Control system, the lift fan drive system and finally roll stability characteristics.
In the last sections the experience gained from the operations is reported. Despite a very tight schedule for the two vessels with very little time for maintenance, so far only one or two departures have been cancelled for technical reasons. The need for future development especially concerning propulsion systems, Ride Control systems, and skirt design and maintenance are dealt with in a special section. The problem of very short lifetime for the bow finger seals is highlighted.
Finally, a new SES passenger ferry design is presented. This new SES with a top speed of over 50 knots and a passenger capacity of 450 is now under construction and will enter service next summer on a 130-mile-long route between Sweden and Denmark.
