_Power plant_—The complete engine or engines in an aircraft, together with propeller or propellers (if any), accessories, fuel and oil tanks and lines, etc. _Powered aircraft_—An aircraft having one or more engines, as distinguished from a glider. _Tailspin_—A spin, so named in reference to the characteristic spiral action of the tail when the airplane is in a spin. _Warp_—To change the shape of something, especially an airplane’s wing, by twisting. To give lift or drop to a wing by twisting it at the ends. _Wind tunnel_—A chamber through which air is forced at controlled velocities, up to several thousand miles an hour, and in which airfoils, airplanes, missiles, scale models of airplanes, or other objects are mounted in order to observe and study the airflow about such objects, as well as the aerodynamic effects upon them. _Wingspan_—The span of a wing, measured or taken between the tips or outermost extremities of either a single-piece wing or a wing that is separated by other aircraft components. _Wing-warping_—The action of warping a wing, or a control system for warping the wings at will. _Yaw_—An angular displacement or motion to the left or right about the vertical axis of an airplane. _Suggestions for Further Reading_ Gibbs-Smith, C. H., _A History of Flying_. Frederick A. Praeger, New York, 1954. Kelly, Fred C. (Ed.), _Miracle at Kitty Hawk, the Letters of Wilbur and Orville Wright_. Farrar, Straus and Young, New York 1951. Kelly, Fred C., _The Wright Brothers_. (A Biography Authorized by Orville Wright.) Harcourt, Brace and Company, New York, 1943. McFarland, Marvin W. (Ed.), _The Papers of Wilbur and Orville Wright, including the Chanute-Wright Letters and other Papers of Octave Chanute_. 2 vols., McGraw-Hill Book Company, New York, 1953. U.S. GOVERNMENT PRINTING OFFICE: 1963 OF—710-606 NATIONAL PARK SERVICE HISTORICAL HANDBOOK SERIES (Price has of National Park Service Publications may be obtained from the Superintendent of Documents, Washington 25, D.C.) Antietam Aztec Ruins Bandelier Chalmette Chickamauga and Chattanooga Battlefields Custer Battlefield Custis-Lee Mansion, The Robert E. Lee Memorial Fort Laramie Fort McHenry Fort Necessity Fort Pulaski Fort Raleigh Fort Sumter Fort Union George Washington Birthplace Gettysburg Guilford Courthouse Hopewell Village Independence Jamestown, Virginia Kings Mountain The Lincoln Museum and the House Where Lincoln Died Manassas (Bull Run) Montezuma Castle Morristown, A Military Capital of the Revolution Ocmulgee Petersburg Battlefields Richmond Battlefields Saratoga Scotts Bluff Shiloh Statue of Liberty Vanderbilt Mansion Vicksburg Wright Brothers Yorktown