Doubts about Deltas

In an article "Wing Shape of the Future", published in the Australian journal Aircraft, Mr H K Millicer, Depl.Ing., M.Sc., A.F.R.Ae.S., who is aerodynamic design engineer in charge of the Aerodynamic and Initial Projects Office at the Government Aircraft Factories, Australia, says that "essentially the delta wing is only a high-speed (M = 1.2 to 1.4) short-range proposition".

Among the disadvantages of the delta wing Mr Millicer lists the need for a great deal of engine thrust to maintain a reasonably flat approach angle, remarking that this feature precludes any engine-off landing at low speeds. There is nothing, he says, that could be done to improve the bad features at the present stage of aerodynamic development unless one returns again to external surfaces such as large fins, high-mounted tailplanes, boundary-layer fences, wing-tip slots, or boundary-layer suctionequipment.

The aeroplane again becomes a familiar Christmas tree, but, even so, it is far more difficult to fly at low speeds than an orthodox aircraft.

"No amount of wing thinness or sweep back appears to delay the compressibility drag rise much beyond the Mach number of 0.87," says Mr Millicer. "It seems that we shall have to be content with cruising at Mach numbers of 0.9 to 0.93 for medium or long-range aircraft for the next ten years or so. Therefore it appears to me that the delta wing configuration is unnecessary… I am firmly convinced that in the next two or three years we shall see a turn away from sweptback wings to very thin wings with either slight or no sweepback at all."

Summing up, Mr Millicer says: "The delta wing emerges as a purely supersonic, short range aircraft with very short endurance. Due to its stability troubles near the stall it is very 'touchy' to handle, difficult to land, dangerous to stall. It should be satisfactory for short-range pilotless missiles or even for short-range manned fighters. But it does not look promising as an economic proposition for a medium- or long-range subsonic transport, bomber or even fighter."

Source: Flight International