An all-wing configuration embodying a straight, or non-swept wing, has been proposed and flown successfully in model sizes. It offers the serious disadvantage that suitable distribution of weight empty and useful load items is difficult and, if proper balance is to be accomplished, most of the structural weight and useful load must be included in the forward 30 percent or 40 percent of the wing, leaving a large volume of space within the wing unusable. Such a configuration results in an unnecessarily large airplane to accomplish a given job and for this reason has not been considered seriously.

The swept-back arrangement exemplified by the various airplanes previously illustrated and described seems to offer the best configuration for a materialization of our all-wing ideal. It can be balanced satisfactorily within quite wide ranges of sweepback, utilizing almost all available volume within the wing for storage of useful load items. It seems to fly satisfactorily in many different configurations and the arrangement is such that large payloads can be carried virtually over the C.G., with the weight empty items so distributed as to cause little variation in C.G. position between the fully loaded and empty conditions.

Weight distribution

As has been pointed out previously, the permissible range of C.G. location is not overly critical in this type of airplane. It is, nevertheless, of great advantage to be able to load the airplane almost at will, without concern as to how the useful load is disposed and the swept-back configuration lends itself most suitably to such loading.

In the case of the XB-35, the useful load, consisting largely of bombs and fuel, can be readily disposed in suitable position about the C.G. While some fuel is located well forward and other fuel well aft of the desired C.G. location, under normal operating conditions the proper balance is readily maintained. In case of failure of one or more engines, it is necessary to pump the fuel from unused tanks to those supplying the remaining engines, but a simple manifolding system provides this facility.

Based on a great many studies of various types and applications of the all-wing principle, some practical limitations may be approximately defined. Where very dense (high specific gravity) payloads are contemplated, such as warheads or similar munitions, quite small units are practical, as demonstrated by the all-wing buzz bombs to which reference has been made. Medium-sized units having a span of perhaps 100 ft. and a gross weight of 50,000 to 60,000 lb., appear entirely practical for medium bombers and freighters. Here again the density of the useful load, both in payload and fuel, is comparatively high.

Airplanes designed to carry people need the largest volume of all. Even individual reclining chair accommodations require a minimum space of perhaps 40 cubic ft. per passenger, which is a density of only about 5 lb. per cubic ft. This is one-half to one-quarter the density of typical air cargo, and only 4 percent or 5 percent of the density of a warhead.

Immediate applications--all-wing aircraft

It may be concluded, then, that the all-wing design is immediately applicable and practical for a number of military and cargo-carrying versions, and that the passenger-carrying aircraft are likely to be of rather large size and, in the immediate future at least, will provide only comfortable seating instead of the more luxurious appurtenances associated with long-range ocean travel.

An airplane of the XB-35 configuration and size can carry 50 passengers in comfort in the existing airfoil envelope with adequate headroom for all, and with vision forward through the floor, and upward if desired. Passenger vision in a flying wing may be more satisfactory than in conventional types if we get used to the idea of forward vision rather than that provided by side windows. The really interesting views are likely to be forward and downward rather than to the side. An airplane like the XB-35 will have cargo space for 40,000 to 50,000 lb. of air freight at a density of 10 to 15 lb. per cubic ft., in addition to the necessary crew and space for 50 passengers.

Future possibilities

Turning now to future possibilities, it seems that considerable further aerodynamic refinement can be made over that already accomplished in all-wing types. Particularly if turbojets are used as the motive power, the minimum parasite drag may be reduced to .008 or less. This value is obtained by subtracting the drag of propeller shaft housings, gun turrets and other military protuberances from the XB-35 configuration and assuming an improved degree of aerodynamic smoothness of the airfoil section. Boundary layer removal and the use of somewhat thinner wing sections may further appreciably reduce this figure.

A maximum trimmed lift coefficient 1.9 for the all-wing configuration seems attainable by methods already suggested and possibly may be further increased by judicious use of boundary layer control in combination with turbojet power plants. It is our opinion that the ratio of C1max to Cd min may be increased to a value of 235 within the not-too-distant future from our present actual achievement of about 130. In contrast, the years of intensive development of the conventional types already passed promise an improvement of less magnitude within a comparable time. In our judgment a trimmed maximum lift of 2.8 vs. a minimum drag of .020 seems reasonable to expect for large, long-range transport and bombardment aircraft of conventional type.

These estimates are, of course, completely arbitrary and controversial. However, if one cares to assume their validity, the following conclusions may be reached. . . . The total minimum profile drag of the all-wing airplane . . . will be from 40 percent to 59 percent [of the drag of the conventional plane]. The power required by the all-wing to maintain the same cruising speed as the conventional will be from 70 percent to 80 percent and, conversely, the maximum range of the all-wing, at the cruising speed of the conventional airplane, will be 143 percent to 125 percent. The maximum range of the all-wing airplane at its best cruising speed will be 158 percent to 130 percent of the conventional, and the most economic speed will be from 125 percent to 115 percent faster.

Under high speed conditions corresponding to full power of reciprocating, turboprop or turbojet engines, where the induced drag is assumed to be 20 percent and the parasite drag 80 percent of the total, the power required to drive the all-wing airplane at the speed of the conventional airplane will be 52 percent to 67 percent and, conversely, the range will be 192 percent to 149 percent of the conventional airplane. The maximum speed of the all-wing airplane at comparable powers will be 124 percent to 114 percent of its conventional counterpart.

Different assumptions of comparative maximum lift and minimum drag values can be made to suit individual opinion, but it is believed that any reasonable assumptions will always result in an advantage to the all-wing configuration of such magnitude as to fully warrant whatever trials and tribulations may be associated with its development. . . .

It is gratifying to those of us who have been working on all-wing projects for years to recognize the increased interest in the type evidenced in Germany toward the end of the war, and more particularly in England and Canada in recent years. For many years we received scant encouragement and often seriously questioned our own judgment, as well as our ability to achieve a successful solution to the many problems involved in the development of this type. The goals and rewards have always seemed well worth attainment, however, and I believe accomplishments to date have justified the effort required.