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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
an ornithopter whose wings move only up and down. In most orthopter designs the lift is generated by a change in the position of hinged flaps located on the wings. When the wings move up, the flaps open; when the wings move down, the flaps close.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.