Area Rule - Applications

Applications

The area rule was immediately applied to a number of development efforts. One of the most famous was Whitcomb's personal work on the re-design of the Convair F-102 Delta Dagger, a U.S. Air Force jet fighter that was demonstrating performance considerably worse than expected. By indenting the fuselage beside the wings, and (paradoxically) adding more volume to the rear of the plane, transonic drag was considerably reduced and the original Mach 1.2 design speeds were reached. The culminating design of this research was the Convair F-106 Delta Dart, an aircraft which for many years was the USAF's primary all-weather interceptor.

Numerous designs of the era were likewise modified in this fashion, either by adding new fuel tanks or tail extensions to smooth out the profile. The Tupolev Tu-95 'Bear', a Soviet-era bomber, has large bulged landing gear nacelles behind the two inner engines, increasing the aircraft's overall cross section aft of the wing root. Its airliner version has been the fastest propeller-driven aircraft in the world since 1960. The Convair 990 used a similar solution, adding bumps called antishock bodies to the trailing edge of the upper wing. The 990 remains the fastest U.S. airliner in history, cruising at up to Mach 0.89. Designers at Armstrong-Whitworth took the concept a step further in their proposed M-Wing, in which the wing was first swept forward and then to the rear. This allowed the fuselage to be narrowed on either side of the root instead of just behind it, leading to a smoother fuselage that remained wider on average than one using a classic swept wing.

One interesting outcome of the area rule is the shaping of the Boeing 747's upper deck. The aircraft was designed to carry standard intermodal containers in a two-wide, two-high stack on the main deck, which was considered a serious accident risk for the pilots if they were located in a cockpit at the front of the aircraft. They were instead moved above the deck in a small "hump", which was designed to be as small as possible given normal streamlining principles. It was later realized that the drag could be reduced much more by lengthening the hump, using it to reduce wave drag offsetting the tail surface's contribution. The new design was introduced on the 747-300, improving its cruise speed and lowering drag, with the side effect of slightly increasing capacity on passenger flights.

Aircraft designed according to Whitcomb's area rule looked odd at the time they were first tested, (e.g., the Blackburn Buccaneer), and were dubbed "flying Coke bottles," but the area rule is effective and came to be an expected part of the appearance of any transonic aircraft. Later designs started with the area rule in mind, and came to look much more pleasing. Although the rule still applies, the visible fuselage "waisting" can only be seen on a few aircraft, such as the B-1B Lancer, Learjet 60, and the Tupolev Tu-160 'Blackjack' — the same effect is now achieved by careful positioning of aircraft components, like the boosters and cargo bay on rockets; the jet engines in front of (and not directly below) the wings of the Airbus A380; the jet engines behind (and not purely at the side of) the fuselage of a Cessna Citation X; the shape and location of the canopy on the F-22 Raptor; and the image of the Airbus A380 above showing obvious area rule shaping at the wing root, which is practically invisible from any other angle.

Read more about this topic:  Area Rule