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Aviation History
1964
1964 - 0555.PDF
Air-Cushion Vehicles FLIGHT International supplement, 21 February 1964 KAWASAKI KAG-3 Performance Results The main body of Mr Ando's report is concerned with a description of the results of two trials which took place during February and May of 1963. These are referred to from now on as the winter and summer trials. After the winter trials the KAG-3 was modified (details of the modifica- tions are shown on the general arrange- ment). Subsequently, improved per- formance was recorded during the summer trials, even though the measured thrust of the outboard motor was lower than in the winter. A graph summarizes the performance results. It should be noted that the measured drag is the overall drag of the craft minus the drag of the screw strut. Likewise, measured thrust is the gross thrust of the power- plant less the drag of the screw strut. The report makes no attempt to explain the trend of the measured drag curve but an explanation will be attemp- ted here. In order to do this we must first understand the different contribu- tions to the measured drag. The hydrodynamic drag of the floats is composed of wave drag and profile drag (skin friction plus form drag), whereas the aerodynamic drag can be separated into profile drag (aerodynamic skin friction plus form drag) and in- duced, or lift dependent, drag. The characteristic hump in the drag curves, which occurs at between 20 and 30km/hr (llkt and 16kt), is caused by the large contribution of the wave drag to the measured drag in this region. Prevailing wind speed is assumed to be fixed so that an increase in water speed produces an equivalent increase in air speed. When the craft travels at water speeds in excess of the "hump" speed the wave MEASURED THRUST IN FULL THROTTLE OPERATION, 2Jin PITCH SCREW DURING WINTER TRIAL DURING SUMMER TRIAL DURING WINTER WITH 2 CREWMEN (UPPER,FOLLOWING WIND. 1-5-2-5 m/sec ROWER.HEAD WIND 3-5m/scc DURING SUMMER TRIAL WITH 2 CREWMEN DURING SUMMER TRIAL WITH I CREWMAN 1UPPER,FOLLOWING WIND 1-5-2 5 m/sec (LOWER,HEAD WIND 3-5m/sec 40 60 WATER SPEED tkm/hr) 80 Comparisons of measured thrust and drag during summer and winter KAG-3 Data The following particulars are quoted as received. Overall Dimensions Length ... ... 5.88m Beam (including tailplane) 6.14mHeight 1.63m Main Wing Area 9.6msChord 3.58m Span 2.68m Aspect ratio 0.75 Section profile NACA 6409 Design incidence ... ... ... 6deg Floats Each float has a half-body shape; the inside surface is flat and vertical. Length 5m Each beam 0.5m Tailplanes A pair of tails is a "separated Vee-tail" type. Each expanded area 1.6m1 Dihedral angle 35deg Sweepback in 25 per cent chord ... 30deg Taper ratio 0.615 Section profile (in the free stream dir- ection) NACA 0009 Location of eg. 40 per cent chord of main wing (2 crewmen) 42.5 per cent chord of main wing (I crewman) Powerplant Engine An outboard engine Merc. 800 full gear shift Propeller Water screw, pitch 23in WeightWeight empty 540kg Weight loaded 690kg Seats 2 Fuel 6gal Materials Major parts of the structure light aluminium alloy Float skin (except for the bottom) Fibreglass re- inforced plastic (F.R.P.). Float bottom skin (Sandwich structure of "F.R.P. + plastic foam + F.R.P."). Performance Maximum water-speed 85km/hrNormal endurance ... ... ... 40min SUMMARY OF TEST RESULTS OF KAG-3 Body-fram e plan t j 1 Powa i Perfmnc e | Stabilit y Aerodyn Hydrodyn Aerodyn Hydrodyn Sea-worthiness Structur e Strength Payload per cent Engine Screw Screw-strut excellent excellent satisfactory almost satisfactory not satisfactory almost satisfactory not satisfactory — excellent -—• Ci_ 5= 1.2, L/D > 11.4. Ci_ is larger than expected from most kinds of model tests. We ") High-airborne (nearly 99%) would obtain L/D > 16 for larger future vehicles. runs were achieved very L/D = 5.0 at the hump speed, and higher at the top speed. These are also better than ex- | sured drag to weight waspected from model tests. J reduced to one-tenth or less The vehicle ran very smoothly even in the wind of about lOm/sec, when the aerodynamic 1 It was found that dynamic lift was large enough to support the vehicle gross weight. 1 behaviours of KAG-3 were The vehicle is satisfactorily stable in yaw and roll. In some cases vehicle experienced I with only self-powered "porpoising" motion, which was suppressed. J model. The vehicle can run with full power in the sea where the waves were 6 per cent or higher of the vehicle length. Although wave impacts were much less than in case of conventional planing boats, still seemed to exceed the passenger comfort limit. The float beam must be made much narrower; this situation requires some air cushion even in the take-off run. Major parts such as floats, main wing and centre body were sufficiently strong, and justified the design criteria based on thatof flying-boats. Payload is very small for the gross weight. The main reason is the over-weight of the side floats, whose outer skin is through- out made of thick F.R.P. Larger future vehicle will carry the payload of about 30 per cent gross weight. Screw-shaft horsepower is much less than the catalogue power. Propulsive efficiency of the screw itself seems to be excellent. At high speeds (70-80km/hr), the screw-strut seems to cause water drag of about 50-60kg, which amounts to about half of the screw thrust at this speed. 30
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