The Craft
The craft is a very large flying boat having a wingspan of 3.0 Km and a wing chord of about 32 m. A conventional NACA wing section is used having a thickness/chord ratio of 18% (maximum thickness of 5.76 m.) This means there is ample space within the wing for the reflector sheet, equipment, crew facilities, etc. Thus there is no fuselage in the conventional sense though there are tail booms at regular intervals across the wing span to carry elevons².
Fig.1 is a longitudinal cross section of the craft showing the general arrangement.
When afloat buoyancy is provided by fully submersible floats at 30m spanwise intervals attached to the bottom end of 5m high pylons carrying the wing. The floats themselves have only a small excess of buoyancy over their share of the craft weight, and the pylons have a much lower waterplane cross-section than the floats, thus the whole vessel will float with the float/pylon junction substantially at trough level. The value of this arrangement arises particularly in the event of a long swell running spanwise. In this case, if the floats had surplus buoyancy, several adjacent floats could be out of the water simultaneouslythus putting a considerable load on the mainspar and making it unnecessarily heavy. In flight, because the entire craft weight is (in principal) evenly distributed spanwise, there are no significant bending moments in the spar, thus the spar weight is much reduced compared to conventional aircraft. In practice the spanwise weight distribution is modifed over the units of span between each float so that the bending moment due to uploads from each float (when afloat) is equal and opposite to the bending moment in flight due to the local inequality of weight distribution.
One craft is constructed from 99 similar spanwise units, each of which is effectively a 30m span flying boat having a main central float and a further small float at the stern to provide fore and aft stability. These units are joined wing tip to wing tip t o build up the 3Km span. The craft wing tips are completed by units which are effectively half a normal unit as far as the float but then terminated with a short wingtip unit carrying the main door providing access to the spanwise roadway in the craft. One craft deploys a reflecting area 2.97 Km x 8.5 Km to make up 25 Km² of reflecting area. Thus the operational unit is a squadron of four craft who are able to put down the 100 Km² estimated to be required.
The multiplicity of similar units required enables mass production techniques to be used from the start, thus greatly reducing the total cost. A further benefit is that much of the test flying can be done with a craft consisting of say five units. With such a unit all the aero- and hydro-dynamic aspects can be cleared.
Propulsion power is provided by possibly as many as 101 turbo-prop engines evenly distributed across the span on pylons above the wing. This would give the easiest weight distribution. The number of units is however in no way critical and wil depend largely on availability and pricing considerations. The total maximum power requirement is currently estimated at 40,000 kilowatts.
On board power will be provided by a number of small diesel generator sets (possibly around 100KW) evenly spread over the span.
It will be noted that the span has been limited to 3 Km. There is no structural reason for this limitation. For example if the span was 12 Km and the length of the reflector strips was kept the same then only one craft would be needed to provide 100 Km² of reflecting area. This would be a cheaper solution but (as will be seen later) the craft’s cycle of operation requires a number of 180° turns both airborne and on the water. For practical purposes the time for the air turn (about 1.5° bank) is proportional to the span: for 3 Km span the time is about 5 ½ mins): longer times than this are considered excessive. The maximum bank angle that can be used is defined by the fact that the airspeed at the inner tip must be safely above the stalling speed while the speed of the outer tip is defined by the power available. The 1.5° bank angle is based on 55 knots (inner) and 110 knots (outer).