Lifting body

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The lifting body is an aircraft configuration where the body itself produces lift. It is related to flying wing which is a wing without a conventional fuselage. A lifting body is a fuselage that generates lift without the shape of a typical thin and flat wing structure. A flying wing seeks to maximize cruise efficiency at subsonic speeds by eliminating non-lifting surfaces. By contrast, lifting bodies generally minimize the drag and structure of a wing for very high supersonic, hypersonic flight or spacecraft re-entry. Both designs pose challenges for controlled, stable flight.

The Martin Aircraft Company X-24 built as part of a 1963 to 1975 experimental US military program
The Martin Aircraft Company X-24 built as part of a 1963 to 1975 experimental US military program
X-24A, M2-F3 and HL-10 Lifting bodies (NASA)
X-24A, M2-F3 and HL-10 Lifting bodies (NASA)

In 1921 pioneering aviator and aircraft designer Vincent Justus Burnelli patented the simple concept of an airfoil shaped airframe to increase the lift and load capacity of aircraft. [1] Despite a number of business and political setbacks, Burnelli continued to refine and license his designs making a number of refinements to the concept up until his death in 1964. [2] [3]

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[edit] Development

Aerospace-related lifting body research arose from the idea of spacecraft re-entering the Earth's atmosphere and landing much like a regular aircraft. Following atmospheric re-entry, the traditional capsule-like spacecraft from the Mercury, Gemini and Apollo series had very little control over where they landed. A steerable spacecraft with wings could significantly extend its landing envelope. However, the vehicle's wings would have to be designed to withstand the dynamic and thermal stresses of both re-entry and hypersonic flight. A proposed solution eliminated wings altogether: Design the fuselage body itself to produce lift. The Space Shuttle implements some of the proven lifting body principles, although it's design relies more on the delta wing concept.

NASA's refinements of the lifting body concept began in 1962 with Dale Reed of NASA's Dryden Flight Research Center. The first full-size model to come out of Reed's program was the NASA M2-F1, an unpowered craft made of wood. Initial tests were performed by towing the M2-F1 along a California dry lakebed at present-day Edwards Air Force Base, behind a modified Pontiac Catalina [4]. Later the craft was towed behind a C-47 and released. Since the M2-F1 was a glider, a small rocket motor was added in order to extend the landing envelope. The M2-F1 was soon nicknamed the "Flying Bathtub".

In 1963, NASA began experimenting with heavier rocket powered craft carried aloft by and dropped from under the port wing of a B-52 aircraft. Of the Dryden lifting bodies, all but the unpowered NASA M2-F1 used an XLR-11 rocket engine as was used on the famous Bell X-1.) A follow-on design designated the Northrop HL-10 was developed at NASA Langley Research Center. The X-24A and X-24B lifting body designs were based on the M2 concept originated in 1957 by Alfred Eggers of NASA Ames Aeronautical Laboratory. The M-2 competed in the design of the Space Shuttle.

A major instability problem with these designs was discovered during the course of flight testing and was determined to be induced by air flow separation whereby the air stream would become very turbulent, causing loss of control and lift. The HL-10 attempted to solve part of this problem by angling the port and starboard vertical stabilizers outward and enlarging the center one. Air flow separation caused the crash of the Northrop M2-F2 lifting body. The successor Northrop M2-F3 added a third (central) vertical stabilizer to the aerodynamically flawed M2-F2 design in an attempt to correct the flow separation instabilities.

The X-38 program, developed under leadership of NASA Johnson Space Center, built an incremental series of flight demonstrators pursuant to the proposed Crew Return Vehicle (CRV) for the International Space Station. The X-38 was a lifting body based on the outer mold line of the X-24.

[edit] Aerospace applications

Lifting bodies pose complex control, structural, and internal configuration issues. Lifting bodies were eventually rejected in favor of a delta wing design for the Space Shuttle. Data acquired in flight test using high-speed landing approaches at very steep descent angles and high sink rates was used for modeling Shuttle flight and landing profiles.

In planning for atmospheric re-entry, the landing site is selected in advance. For reusable reentry vehicles, typically a primary site is preferred that is closest to the launch site in order to reduce costs and improve launch turnaround time. However, weather near the landing site is a major factor in flight safety. In some seasons, weather at landing sites can change quickly relative to the time necessary to initiate and execute re-entry and safe landing. Due to weather, it is possible the vehicle may have to execute a landing at an alternate site. Furthermore, most airports do not have runways of sufficient length to support the approach landing speed and roll distance required by spacecraft. Few airports exist in the world that can support or be modified to support this type of requirement. Therefore, alternate landing sites are very widely spaced across the U.S. and around the world.

The Shuttle's delta wing design was driven by these issues. These requirements were further exacerbated by military requirements (the USAF would use the future shuttle for defense satellite payloads and other missions) that extended the Shuttle's flight landing envelope.

Although a lifting body configuration may have been less vulnerable to the wing leading edge failure that caused the second shuttle loss.[citation needed], such a configuration could not meet the flight envelope requirements of both NASA and the military.

Nonetheless, the lifting body concept has been implemented in a number of other aerospace programs such as the Lockheed Martin X-33, BAC's Multi Unit Space Transport And Recovery Device, Europe's EADS Phoenix and the joint Russian-European Kliper spacecraft. Of the three basic design shapes usually analyzed for such programs (capsule, lifting body, aircraft) the lifting body may offer the best trade-off in terms of maneuverability and thermodynamics while meeting it's customers' mission requirements.

[edit] Popular Culture

Much of the general public had never heard of nor seen anything about these lifting body designs until watching the 1970s television show The Six Million Dollar Man. The show's introduction footage showed the M2-F2, piloted by Bruce Peterson, crashing and tumbling violently along the Edwards dry lakebed runway. The cause of the crash was attributed to the onset of Dutch roll stemming from control instability as induced by flow separation. Bruce Peterson survived to fly again and the craft was rebuilt as the M2-F3.

Lifting bodies have appeared in some science fiction works, including the book The Mote in God's Eye and the movie Marooned (Special Effects Oscar Winner) with Gregory Peck and David Jannsen. The Discovery Channel TV series conjectured using lifting bodies to deliver a probe to a distant earth-like planet in the computer animated Alien Planet. Gerry Anderson's 1969 Doppelgänger used a VTOL lifting body lander / ascender to visit an earth-like planet, only to crash in both attempts. In the Buzz Aldrin's Race into Space computer game, a modified X-24A becomes an alternative lunar capable spacecraft that the player can choose over the Gemini or Apollo capsule.

[edit] Body lift

Some aircraft with wings also employ bodies that generate lift. The Short SC.7 Skyvan produces 30% of the total lift from the fuselage, almost as much as the 35% each of the wings produces. Fighters like the F-15 Eagle also produce substantial lift from the wide fuselage between the wings.

Apparently, because the F-15 Eagle's wide fuselage is so efficient at lift, an F-15 was able to land successfully with only one wing.

On the summer of 1983, an Israeli F-15 staged a mock dogfight with Skyhawks for training purposes, near Nahal Tzin in the Negev desert. During the exercise, one of the Skyhawks miscalculated and collided forcefully with the F-15's wing root. The F-15's pilot was aware that the wing had been seriously damaged, but decided to try and land in a nearby airbase, not knowing the extent of his wing damage. It was only after he had landed, when he climbed out of the cockpit and looked backward, that the pilot realized what had happened: the wing had been completely torn off the plane, and he had landed the plane with only one wing attached. A few months later, the damaged F-15 had been given a new wing, and returned to operational duty in the squadron. The engineers at McDonnell Douglas had a hard time believing the story of the one-winged landing: as far as their planning models were concerned, this was an impossibility.

[edit] List of Dryden Flight Research Center lifting body vehicles (1963 to 1975)

[edit] Lifting body pilots and flights

Pilot M2-F1 M2-F2 HL-10 HL-10
mod		 M2-F3 X-24A X-24B Total
Milton O. Thompson 45 5 - - - - - 50
Bruce Peterson 17 3 1 - - - - 21
Chuck Yeager 5 - - - - - - 5
Donald L. Mallick 2 - - - - - - 2
James W. Wood * - - - - - - *
Donald M. Sorlie 5 3 - - - - - 8
William H. Dana 1 - - 9 19 - 2 31
Jerauld R. Gentry 2 5 - 9 1 13 - 30
Fred Haise * - - - - - - *
Joe Engle * - - - - - - *
John A. Manke - - - 10 4 12 16 42
Peter C. Hoag - - - 8 - - - 8
Cecil W. Powell - - - - 3 3 - 6
Michael V. Love - - - - - - 12 12
Einar K. Enevoldson - - - - - - 2 2
Francis Scobee - - - - - - 2 2
Thomas C. McMurtry - - - - - - 2 2
TOTAL 77 16 1 36 27 28 36 221
* Wood, Haise and Engle each made a single, car-towed, ground flight of the M2-F1.

[edit] See also

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