Forward swept: the wing angles forward from the root. Benefits are similar to backwards sweep, also it avoids the stall problems and has reduced tip losses allowing a smaller wing, but requires even greater stiffness to avoid aeroelastic flutter as on the Sukhoi Su-47. The HFB 320 Hansa Jet used forward sweep to prevent the wing spar passing through the cabin. Small shoulder-wing aircraft may use forward sweep to maintain a correct CoG. Some types of variable geometry vary the wing sweep during flight: Swing-wing: also called "variable sweep wing". The left and right hand wings vary their sweep together, usually backwards. Seen in a few types of military aircraft, such as the General Dynamics F-111 Aardvark. Oblique wing: a single full-span wing pivots about its midpoint, so that one side sweeps back and the other side sweeps forward. Flown on the NASA AD-1 research aircraft. Sweep variation along span The angle of a swept wing may also be varied, or cranked, along the span: Crescent: wing outer section is swept less sharply than the inner section, to obtain a best compromise between transonic shock delay and spanwise flow control. Used on the Handley Page Victor. Cranked arrow: aerodynamically identical to the compound delta, but with the trailing edge also kinked inwards. Trialled experimentally on the General Dynamics F-16XL. M-wing: the inner wing section sweeps forward, and the outer section sweeps backwards. Allows the wing to be highly swept while minimising the undesirable effects of aeroelastic bending. Periodically studied, but never used on an aircraft. W-wing: A reversed M-wing. Proposed for the Blohm & Voss P.188 but studied even less than the M-wing and in the end never used. Asymmetrical On a few asymmetrical aircraft the left and right hand sides are not mirror-images of each other: Asymmetric layout: the Blohm & Voss BV 141 had separate fuselage and crew nacelle offset on either side to give the crew a good field of view. Asymmetric span: on several Italian fighters such as the Ansaldo SVA, one wing was slightly longer than the other to help counteract engine torque. Oblique wing: one wing sweeps forward and the other back. The NASA AD-1 had a full-span wing structure with variable sweep. Tailplanes and foreplanes The classic aerofoil section wing is unstable in pitch, and requires some form of horizontal stabilizing surface. Also it cannot provide any significant pitch control, requiring a separate