VOL. 18, NO. 11 J . AIRCRAFT NOVEMBER 1981 History o f Ke y Technologies AIAA 81-0491R Historical Development of Aircraft Flutter I . E Garrick an d Wilmer H . Reed II I NASA Langley Research Center, Hampton, Va. Introduction Work in flutter has been (and is being) pursued in many EROELASTICITY, and in particular flutter, has in- countries. As in nearly all fields, new ideas and developments A fluenced th e evolution o f aircraft since th e earliest days in flutter have occurred similarly and almost simultaneously of flight. This paper presents a glimpse of problems arising in in diverse places in the world, so that exact assignment of these areas an d ho w they were attacked b y aviation's pioneers priorities i s often i n doubt. Moreover, a definitive historical an d their successors u p t o about th e mid-1950s. Th e emphasis account would require several volumes; yet we hope to survey is on tracing some conceptual developments relating to the some o f th e main developments i n a proper historical light, understanding an d prevention o f flutter including some an d i n a wa y that th e lessons learned ma y b e currently useful. lessons learned along th e way. It is recognized that detailed documentation of flutter Because it must be light, an airplane necessarily deforms troubles has nearly always been hampered by proprietary appreciably under load. Such deformations change the conditions an d b y a reluctance o f manufacturers t o expose distribution o f th e aerodynamic load, which i n turn changes such problems. th e deformations; th e interacting feedback process ma y lead From our present perspective, flutter is included in the to flutter, a self-excited oscillation, often destructive, wherein broader term aeroelasticity, the study of the static and energy is absorbed from the airstream. Flutter is a complex dynamic response o f a n elastic airplane. Since flutter involves phenomenon that must i n general b e completely eliminated b y the problems of interaction of aerodynamics and structural design o r prevented from occurring within th e flight envelope. deformation, including inertial effects, at subcritical as well The initiation of flutter depends directly on the stiffness, and a s t critical speeds, i t really involves al l aspects o f only indirectly o n th e strength o f a n airplane, analogous t o aeroelasticity. I n a broad sense, aeroelasticity i s a t work i n depending on the slope of the lift curve rather than on the natural phenomena such as in the motion of insects, fish, and maximum lift. This implies that the airplane must be treated birds (biofluid-dynamics). I n man's handiwork, aeroelastic no t a s rigid body bu t a s n elastic structure. Despite th e fact problems o f windmills were solved empirically four centuries that the subject is an old one, this requires for a modern ago in Holland with the moving of the front spars of the airplane a large effort in many areas, including ground blades from about th e midchord t o th e quarter-chord position vibration testing, use of dynamically scaled wind-tunnel (see th e article b y Ja n Drees i n list o f Survey Papers). W e no w models, theoretical analysis, an d flight flutter testing. Th e recognize that some 19th century bridges were torsionally aim of this paper is to give a short history of aircraft flutter, weak an d collapsed from aeroelastic effects, a s di d th e with emphasis o n th e conceptual developments, from th e Tacoma Narrows Bridge i n spectacular fashion i n 1940. Other early days o f flight t o about th e mid-1950s. aeroelastic wind-structure interaction pervades civil After a long career a s research scientist an d manager, I . E Garrick retired from NACA/NASA i n 1972. H e remains active a s Distinguished Research Associate o f Langley. H e i s th author o f numerous publications in areas of aerodynamics, aeroelasticity, and aeromechanics, has served on many advisory councils, an d ha s lectured extensively. Mr . Garrick served fo r a year a s th e second Hunsaker Professor o f Aeronautical Engineering a t MIT. Hi s 1976 AIAA vo n Karman Lecture dealt with th e topic: "Aeroelasticity—Frontiers an d Beyond." Among hi s awards ar e th NASA Exceptional Service Award, the Langley Scientific Achievement Award, and the AIAA Sylvanus A. Reed Award. He is a Fellow of the AIAA. Wilmer H . Reed II I from 1972 t o 1980 wa s Head o f th e Aeroelasticity Branch which operates th e Langley Transonic Dynamics Tunnel, a national facility dedicated exclusively t o research an d development i n th e field o f aeroelasticity. Notably, this facility i s used b y th e United States i n develop- ment of practically all its military aircraft, commercial transports, and launch vehicles. At present, Mr. Reed i s Chief Scientist, Loads an d Aeroe'.asticity Division, NASA Langley Research Center. H e joined NACA/NASA in 1948 and holds Bachelor and Master degrees in Aeronautical Engineering from Auburn University an d th e University o f Virginia. Hi s professional experience includes research i n aeroelasticity, wind loads o n structures, damping devices, an d wind tunnel testing techniques. H e received th e NASA Exceptional Service Medal in 1979, holds several U.S. Patents, is a member of Tau Beta Pi, and an Associate Fellow of the AIAA. Presented as Paper 81-0491 at the AIAA/ASME/ASCE/AHS 22nd Structures, Structural Dynamics and Materials Conference, Atlanta, Ga., April 6-8, 1981; submitted April 14 , 1981; revision received July 8 , 1981. This paper i s declared a work o f th e U.S. Government an d therefore i s n the public domain. EDITOR'S NOTE: This manuscript wa s invited a s History o f Ke y Technologies paper a s part o f AIAA's 50th Anniversary celebration. I t i s no meant to be a comprehensive survey of the field. It represents solely the authors' own reconstruction of events at the time and is based upon their own experiences. 897 898 I. E. GARRICK AND W.H. REED III J. AIRCRAFT engineering. The elastic response of an airplane to rough air (gusts o r turbulence) i s a n important aeroelastic problem requiring separate study an d documentation. A s th e phenomena an d concepts have unfolded, aeroelasticity, and flutter in particular, have been the subjects of many survey papers throughout the years. These papers often furnish valuable assessments of the state-of-the-art, give interesting bits of the history, and also furnish numerous useful references. A s i t feasible t o refer t o only a small fraction o f these references individually, w e have included a list of such survey papers separate from quoted references. In particular, we may refer the reader to the outstanding survey papers o f A . R Collar, which emphasize th e British developments, th e most recent o f which, "The First Fifty Years o f Aeroelasticity," came t o ou r attention during th e writing o f this paper. I t wa s Collar's "Aeroelastic Triangle" (1947) that showed graphically that flutter embraced all aspects of aeroelasticity. Fig. 1 Langley's aerodrome, which plunged into th e Potomac River The Early Years, 1903-1919 in 1903. Th e Wright Brothers I n their historic flight, Orville an d Wilbur Wright made Brewer3 on the collapse of monoplane wings. Brewer notes in beneficial us e o f aeroelastic effects fo r roll control o f their his one-page article i n Flight Magazine that a rash o f biplane by the use of wing warping in place of ailerons. They monoplane wings with stays had had "accidents in which the also were aware o f th e adverse aeroelastic effect o f th e loss o f wings break downward" and he remarks that "the greater the thrust o f a propeller, du e t o twisting o f th e blades, b y their span th e more readily will th e wing tips b e twisted"; an d that experiments o n th e performance o f thin propellers having the movement of the center of pressure with speed could put it broad blades. They found that th e propeller ti p under high behind th e attachment point o f th e rear stay, resulting i n thrust loads twisted to partially unload itself. We quote from 1 sudden wing flip. The Papers of Wilbur and Orville Wright : Professor Collar (see Survey Papers, 1958, 1978) ha s stated Orville Wright, i n later life, explained th e that part of the speculation about Langley's airplane disaster nature and function of the "little jokers" to Fred is based on the circumstances that some years after Langley's C . Kelley, wh o states i n hi s book, Th e Wright death the original Langley machine was removed from the Brothers, "After th e Wrights ha d made th e Smithsonian National Museum, modified, an d flown suc- blades o f their propellers much wider an d thinner cessfully a t Hammondsport, N.Y. These modifications, than th e original ones, they discovered that th e which involved substantial changes i n th e wing structure an d performance o f th e propellers i n flight di d no t trussing, s o strengthened an d stiffened th e original structure agree closely with their calculations, as in the a s t o significantly reduce th e probability o f aeroelastic failure.