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| Keywords: DAST in Flight Showing Diverging Wingtip Oscillations DVIDS699105.jpg en Two BQM-34 Firebee II drones were modified with supercritical airfoils called the Aeroelastic Research Wing ARW for the Drones for Aerodynamic and Structural Testing DAST program which ran from 1977 to 1983 In this view of DAST-1 Serial 72-1557 taken on June 12 1980 severe wingtip flutter is visible Moments later the right wing failed catastrophically and the vehicle crashed near Cuddeback Dry Lake Before the drone was lost it had made two captive and two free flights Its first free flight on October 2 1979 was cut short by an uplink receiver failure The drone was caught in midair by an HH-3 helicopter The second free flight on March 12 1980 was successful ending in a midair recovery The third free flight made on June 12 was to expand the flutter envelope All of these missions launched from the NASA B-52 From 1977 to 1983 the Dryden Flight Research Center Edwards California under two different names conducted the DAST Program as a high-risk flight experiment using a ground-controlled pilotless aircraft Described by NASA engineers as a wind tunnel in the sky the DAST was a specially modified Teledyne-Ryan BQM-34E/F Firebee II supersonic target drone that was flown to validate theoretical predictions under actual flight conditions in a joint project with the Langley Research Center Hampton Virginia The DAST Program merged advances in electronic remote control systems with advances in airplane design Drones remotely controlled missile-like vehicles initially developed to serve as gunnery targets had been deployed successfully during the Vietnamese conflict as reconnaissance aircraft After the war the energy crisis of the 1970s led NASA to seek new ways to cut fuel use and improve airplane efficiency The DAST Program's drones provided an economical fuel-conscious method for conducting in-flight experiments from a remote ground site DAST explored the technology required to build wing structures with less than normal stiffness This was done because stiffness requires structural weight but ensures freedom from flutter-an uncontrolled divergent oscillation of the structure driven by aerodynamic forces and resulting in structural failure The program used refined theoretical tools to predict at what speed flutter would occur It then designed a high-response control system to counteract the motion and permit a much lighter wing structure The wing had in effect electronic stiffness Flight research with this concept was extremely hazardous because an error in either the flutter prediction or control system implementation would result in wing structural failure and the loss of the vehicle Because of this flight demonstration of a sub-scale vehicle made sense from the standpoint of both safety and cost The program anticipated structural failure during the course of the flight research The Firebee II was a supersonic drone selected as the DAST testbed because its wing could be easily replaced it used only tail-mounted control surfaces and it was available as surplus from the U S Air Force It was capable of 5-g turns that is turns producing acceleration equal to 5 times that of gravity Langley outfitted a drone with an aeroelastic supercritical research wing suitable for a Mach 0 98 cruise transport with a predicted flutter speed of Mach 0 95 at an altitude of 25 000 feet Dryden and Langley in conjunction with Boeing designed and fabricated a digital flutter suppression system FSS Dryden developed an RPRV remotely piloted research vehicle flight control system; integrated the wing FSS and vehicle systems; and conducted the flight program In addition to a digital flight control system and aeroelastic wings each DAST drone had research equipment mounted in its nose and a mid-air retrieval system in its tail The drones were originally launched from the NASA B-52 bomber and later from a DC-130 The DAST vehicle's flight was monitored from the sky by an F-104 chase plane When the DAST's mission ended it deployed a parachute and then a specially equipped Air Force helicopter recovered the drone in mid-air On the ground a pilot controlled the DAST vehicle from a remote cockpit while researchers in another room monitored flight data transmitted via telemetry They made decisions on the conduct of the flight while the DAST was in the air In case of failure in any of the ground systems the DAST vehicle could also be flown to a recovery site using a backup control system in the F-104 The DAST Program experienced numerous problems Only eighteen flights were achieved eight of them captive in which the aircraft flew only while still attached to the launch aircraft Four of the flights were aborted and two resulted in crashes--one on June 12 1980 and the second on June 1 1983 Meanwhile flight experiments with higher profiles better funded remotely piloted research vehicles took priority over DAST missions After the 1983 crash which was caused by a malfunction that disconnected the landing parachute from the drone the program was disbanded Because DAST drones were considered expendable certain losses were anticipated Managers and researchers involved in other high-risk flight projects gained insights from the DAST program that could be applied to their own flight research programs The DAST aircraft had a wingspan of 14 feet four inches and a nose-to-tail length of 28 feet 4 inches The fuselage had a radius of about 2 07 feet The aircraft's maximum loaded weight was about 2 200 pounds It derived its power from a Continental YJ69-T-406 engine NASA Identifier NIX-ECN-31306-fr41-5 2009-09-23 Glenn Research Center https //www dvidshub net/image/699105 699105 2012-10-10 14 20 WASHINGTON DC US PD-USGov Langley Research Center Images from DoD uploaded by Fæ | ||||
