lower wing, while the Hanriot HD-1 had dihedral on the upper wing but none on the lower. In a cranked or polyhedral wing the dihedral angle varies along the span. (Note that the description "cranked" varies in usage.Benoliel, Alexander M., Aerodynamic Pitch-up of Cranked Arrow Wings: Estimation, Trim, and Configuration Design, Virginia Polytechnic Institute & State University, May 1994, retrieved 31 March 2012 See also Cranked arrow planform.) Gull wing: sharp dihedral on the wing root section, little or none on the main section, as on the PZL P.11 fighter. Sometimes used to improve visibility forwards and upwards and may be used as the upper wing on a biplane as on the Polikarpov I-153. Inverted gull wing: anhedral on the root section, dihedral on the main section. The opposite of a gull wing. May be used to reduce the length of wing-mounted undercarriage legs while allowing a raised fuselage, as on the German Junkers Ju 87 Stuka dive bomber. Cranked or canted tip: tip section dihedral differs from the main wing. The tips may have upwards dihedral as on the F-4 Phantom II or downwards anhedral as on the Northrop XP-56 Black Bullet. The channel wing includes a section of the wing forming a partial duct around or immediately behind a propeller. Flown since 1942 in prototype form only, most notably on the Custer Channel Wing aircraft. Wings vs. bodies Some designs have no clear join between wing and fuselage, or body. This may be because one or other of these is missing, or because they merge into each other: Flying wing: the aircraft has no distinct fuselage or horizontal tail (although fins and pods, blisters, etc. may be present) such as on the B-2 stealth bomber. Blended body or blended wing-body: a smooth transition occurs between wing and fuselage, with no hard dividing line. Reduces wetted area and can also reduce interference between airflow over the wing root and any adjacent body, in both cases reducing drag. The Lockheed SR-71 spyplane exemplifies this approach. Lifting body: the aircraft lacks identifiable wings but relies on the fuselage (usually at high speeds or high angles of attack) to provide aerodynamic lift as on the X-24. Some designs may fall into multiple categories depending on interpretation, for example many UAVs or drones can be seen either as a tailless blended wing-body or as a flying wing with a deep centre chord. Variable