Area rule
The area rule describes the optimal course of the cross-sectional area of a supersonic missile along its longitudinal axis . The area rule applies to the transonic range (approximately from Mach 0.8 to 1.2). A slightly modified form of the area rule applies to higher speeds, since the influence of Mach's cone must then be taken into account when shaping the shape .
The Haacksche Ogive , an elongated, spindle-shaped body, is considered the ideal shape of a supersonic missile . In aircraft, the cross-sectional area of the fuselage is added to that of the wings. If the area rule is not observed, this increase in the cross-sectional area at supersonic speed generates an additional shock wave which drastically increases the air resistance of the aircraft and, under certain circumstances, prevents it from reaching supersonic speed. According to the area rule, the fuselage cross-section must theoretically decrease by the value that is added to the cross-sectional area by the wings. This avoids the creation of an additional shock wave.
history
The rule was discovered by Otto Frenzl between 1943 and 1944 during the development of the Ju 287 jet bomber at Junkers and officially confirmed on March 21, 1944 as patent no. 932 410.
It was also presumably independently rediscovered in the USA in 1952 by Richard T. Whitcomb of the National Advisory Committee for Aeronautics (NACA) and published in 1955 and is often incorrectly ascribed to him alone. Another discoverer is Wallace D. Hayes in his dissertation at Caltech in 1947.
In the early 1950s, the first fighter planes with fuselages that followed this rule were built. In the USA this was, among other things, the F-102, where the rule was not followed from the prototype, but only after a redesign after 1954, while in Switzerland the FFA P-16 was one of the first aircraft to feature the The rule was followed from the start, took off for the first time in 1955.
application
In practice, aircraft constructed according to the area rule have a fuselage constriction in the area of the wings . In aircraft with elongated fuselages such as the Concorde , this " wasp waist " can hardly be seen, but in supersonic aircraft with a short fuselage it can usually be seen clearly (as in the Convair F-106 or the Je-152 ).
The F-106 Delta Dart , a further development of the F-102 Delta Dagger , shows a "wasp waist" shape due to considerations of the area rule
A NASA Convair 990 with anti-shock bodies on the back of the wings
Visualization of the boundary layer separation with and without anti-shock bodies
Behind the engines of this Tupolev Tu-95 you can see two large arched nacelles (for the main landing gear).
literature
- Werner Heinzerling: Wing sweep and area rule, two fundamental German patents in aircraft aerodynamics. German Museum Munich ( PDF; 9.86 MB ).
- Supersonic area rule according to Robert T. Jones . In: NACA Report 1284 . ( PDF; 540 kB, (English) ).
Individual evidence
- ↑ Horst Lommel: Junkers Ju 287. The world's first jet bomber and other swept wing projects. Aviatic, Oberhaching 2003, ISBN 3-925505-74-1 , p. 24
- ↑ Patent DE932410 : Low- resistance design of high-speed aircraft, including those with displacement bodies lying outside the aircraft outline . Registered on March 21, 1944 , published on September 1, 1955 , applicant: Junkers, granted to MBB , inventors: Heinrich Hertel , Otto Frenzl , Werner Hempel .
- ^ Georges Bridel: Swiss jet aircraft and jet engines. , Schweizerische Bauzeitung, year 94, 1976, issue 24, June 24, 1976, page 367