Crescent and shallow compound-delta wings

[steelpillow]

The crescent wing was invented in Germany during WWII. When news spread, many other companies produced designs. The Handley Page HP 88 research prototype and the Victor bomber of 1952 are well enough known. Many other designs were studied in the early postwar period, varying from the classic swept crescent to a more or less straight trailing edge in the form of a wide, shallow compound delta. Some lost their tails. This thread is for all these others (please, NOT the later sharply-swept supersonic deltas or modern BWB which includes the fuselage). Some have their own threads here, others do not.

Some that I have found include:

Fairchild M-186 transport. (linked thread)

Breguet Br.978A.(linked thread)

Air Service Training (AST) C.4 High Speed Towed Target. Designed by the Aircraft Division of Air Service Training, Ltd, with a small number built by Brooklands Aircraft Ltd. This one is tailless. Photo on Alamy.

 

[riggerrob]

I suspect that a structural benefit of that extended wing root chord is that it helps conceal/streamline a deep center-section spar.

Modern airliners do the same thing by extending their wing root chords AFT. Leading edges remain essentially straight, with a constant sweep angle. The sweep helps reduce trans-sonic drag when they cruise at Mach 0.9. This longer root chord allows for a deeper, stronger and lighter spar while also changing the flap hinge line to perpendicular to the airflow. Control surfaces are most effective when at right angles to airflow.

 

[steelpillow]

I suspect that a structural benefit of that extended wing root chord is that it helps conceal/streamline a deep center-section spar.

Modern airliners do the same thing by extending their wing root chords AFT. Leading edges remain essentially straight, with a constant sweep angle. The sweep helps reduce trans-sonic drag when they cruise at Mach 0.9. This longer root chord allows for a deeper, stronger and lighter spar while also changing the flap hinge line to perpendicular to the airflow. Control surfaces are most effective when at right angles to airflow.

The key to high-Mach sub/transonic cruise is to minimise acceleration of the airflow over the leading edge, so as not to exceed the local speed of sound at that point. On a swept-back wing, the pressure wave from the inboard section propagates out sideways to slow the air there down. The crescent wing takes advantage of this by reducing the sweep outboard and hence giving higher aerodynamic and structural efficiency. Several of the designs here do straighten the trailing edge, presumably for the reasons you state, which is why I refer to them as more like compound deltas.

Note that these older designs tend to have engines buried in the wing root. Modern types have them moved outboard in pods, and keeping them well forward necessitates moving the junction of inboard and outboard wing sections forward. The modern use of supercritical aerofoils on the root section helps keep the acceleration over the leading edge down, without the need for sharper sweepback than the outer section.