By Joseph R. Chambers
Monographs in Aerospace History Number 19
The NASA History Series
National Aeronautics and Space Administration
Office of Policy and Plans
NASA History Division
The worldwide deployment of remotely piloted vehicles (RPV’s) by military forces has dramatically increased. Several factors, such as elimination of threats to human pilots in hostile environments, cost-effectiveness for certain missions, and stealth for some applications, have stimulated the use of RPV’s. The field-launched Exdrone RPV has proven to be an extremely effective battlefield option for the U.S. Marine Corps. During Operation Desert Storm, Exdrone was pulled from a research and development program. The Exdrone was pressed into reconnaissance service to find attack routes through Iraqi defenses, thus allowing a rapid ground advance into Kuwait. The NASA Langley Research Center made a critical and timely contribution during the development of the Exdrone that enabled highly successful deployments of the vehicle.
In the mid-1980’s, prior to the involvement of Langley, BAI Aerosystems, Inc. manufactured the Exdrone RPV in accordance with a technical specification generated by Johns Hopkins University Applied Physics Laboratory. This version of the Exdrone was for an earlier mission (jamming of communications) that required high dash speeds, therefore, the configuration was not optimized for the low-speed flights that are necessary for extended reconnaissance missions. In fact, at slow speeds the vehicle was extremely difficult to fly and several crashes occurred during field trials simulating the reconnaissance task.
In response to an urgent request from the Marine Corps in 1988, Langley conducted wind-tunnel and flight tests of the Exdrone to determine how the vehicle could be modified to enhance the flight characteristics in low-speed flight. Changes to the wing airfoil, control surfaces, wing leading edge, and vertical tail that were recommended by the Langley staff resulted in a configuration with outstanding low-speed flight characteristics. The changes were incorporated into the BQM-147A Exdrone. The modified vehicle was an immediate success in reconnaissance missions in Operation Desert Storm.
The overall aerodynamic configuration of the Exdrone has not been revised since Langley’s study; however, the vehicle payloads and mission applications continue to be upgraded. The latest vehicle is referred to as the Dragon Drone. As technological innovations continue to evolve candidate payloads into smaller, more efficient packages that are suitable for small RPV’s, the Dragon Drone’s capabilities will likewise continue to be upgraded. The nucleus of the concept, however, remains the modified configuration that owes much to the improvements recommended by Langley’s insightful researchers and their problem-solving efforts.
BAI Aerosystems, Inc. (BAI) of Easton, Maryland initially manufactured the Exdrone air vehicle in the late 1980’s in accordance with a technical specification generated by the Johns Hopkins University Applied Physics Laboratory (JHU-APL). JHU-APL’s delta-wing configuration was powered by a tractor propeller propulsion system. This configuration was effective for an earlier mission for jamming of communications that required high dash speeds, therefore the configuration was not optimized for the low-speed flights that are necessary for extended reconnaissance missions. During evaluation for potential reconnaissance applications, the U.S. Marine Corps found that the vehicle exhibited poor stability and control characteristics and had a tendency toward severe lateral-directional instability near the stall, which resulted in numerous crashes.
At the request of the Marine Corps in 1988, exploratory wind-tunnel and flight-test investigations of the Exdrone were conducted at the Langley Research Center by flight dynamics specialists under the lead of Joseph L. Johnson, Jr. Lead researcher for the study was Long P. Yip.
Results of wind-tunnel tests of the baseline Exdrone configuration in the Langley 12-Foot Low-Speed Tunnel identified several aerodynamic deficiencies that contributed to the unacceptable low-speed flight characteristics experienced in the Marine Corps evaluations. For example, longitudinal control was insufficient to trim the Exdrone to the high-lift conditions required for low-speed flight. Yip recommended an increase in the chord of the elevator and thereby provided almost three times as much lift for low-speed flight. To cure a wing-dropping tendency at high lift, Yip recommended a leading-edge “droop” modification to the outer wing panels. Increasing the rudder area and the size of the vertical tail solved deficiencies in directional stability and control. The original configuration displayed a bad combination of lightly damped rolling and yawing motions (sometimes called Dutch roll), but Yip eliminated this motion by increasing directional stability with the increased vertical tail and by adding wingtip skids. The wingtip skids also provided better flow over the ailerons and served as landing skids, which replaced the original drag-producing wire skids.
Langley researchers Long P. Yip and David Fratello with modified Exdrone during flight-test evaluation.
One noteworthy modification contributed by NASA was a sawtooth notch on the wing leading edge near the wingtip. This notch and the leading-edge droop mentioned earlier were an outgrowth of the Langley General Aviation Stall-Spin Program. Yip and his peers had previously recommended the combination to certain general aviation companies for increasing stall departure and spin resistance with a minimal drag penalty. Thus, NASA research to improve light aircraft provided a critical improvement for military applications. As a result of these improvements, the Exdrone is easily flown by inexperienced pilots and very forgiving during training maneuvers.
The results of radio-controlled flight tests conducted by Langley researchers at the Langley Plum Tree Test Site, located in nearby Poquoson, VA, showed that the modified configuration had excellent longitudinal and lateral-directional flight characteristics. The configuration was very maneuverable and responsive to control inputs, exhibited good damping characteristics, and was easily flyable through the stall with no departure tendencies.
The modifications recommended by Langley were endorsed and applied to the Exdrone design, and the overall aerodynamic configuration of the Exdrone vehicle has not changed since these modifications.
In early 1990, approximately 30 of the newly configured BQM-147A Exdrone reconnaissance RPV’s were sent to Operation Desert Storm. The Exdrones were successfully used to map Iraqi minefields and bunkers, which allowed the Allied ground forces to slip through in darkness. During the 1990’s, several hundred Exdrone air vehicles were produced by BAI under contract to the U.S. Uninhabited Air Vehicle Joint Project Office (UAV-JPO). These vehicles were sent to Army and Marine Corps units as cost-effective devices for familiarizing new users with the benefits of tactical unmanned reconnaissance systems.
Throughout the 1990’s, the UAV-JPO directed BAI, the Department of the Navy, and the Army Research Laboratory to test and incorporate numerous payloads and system upgrades for the basic Exdrone aircraft. Some of those upgrades include Global Positioning System (GPS) (Exdrone was among the first military aircraft certified to use GPS for navigation), a communications relay, the Tactical Remote Sensor Suite (TRSS), an infrared and several other versions of down-looking reconnaissance sensors, and a parachute recovery system to protect the higher value payloads.
In early 1997, the Marine Corps provided funds to BAI to create a new configuration of the Exdrone (referred to as Dragon Drone) for the Hunter-Warrior Advanced Warfighting Experiment at Twenty-Nine Palms, CA. Tests performed at NASA Wallops Flight Facility successfully identified and led to the elimination of onboard vibration interference with reconnaissance payloads. A belly-mounted pan-tilt-zoom television camera produced by BAI was then installed into Dragon Drone with several other improvements.
During the Hunter-Warrior Experiment, Dragon Drones proved highly effective in identifying enemy command locations and troop movements at distances of up to 30 mi. Because of the success of the Hunter-Warrior Experiment, the Marine Corps funded the development of other upgrades to the Dragon Drone system, including
The Marine Corps’ success with the Dragon Drone has sparked worldwide interest in the system. BAI Aerosystems, Inc. received the first international order for a Dragon Drone system from the Bahrain Defense Force (BDF) with delivery in late July 1999. A small Dragon Drone system is being leased to the Australian Marines for evaluation. The Ministry of Defense of the United Kingdom is investigating the feasibility of Dragon Drone providing turnkey fulfillment of their tactical UAV requirements. Several U.S. organizations, including the Air Force and Coast Guard, are actively pursuing these systems.
Clearly, the future for the Dragon Drone is bright. As technological innovations continue to evolve candidate payloads into smaller, more efficient packages that are suitable for RPV’s, the Dragon Drone’s capabilities will likewise continue to be upgraded. The nucleus of the configuration, however, remains the vehicle configuration that came from the timely and responsive improvements recommended by insightful researchers at Langley.
An Exdrone undergoes weight and balance tests.
BAI Aerosystems, Inc.
Date in service
Over 500 to date
Remotely piloted vehicle
8-hp 2-stroke gasoline engine, 2-blade wooden propeller
Reconnaissance, communications jamming, and delivery of nonlethal payloads
U.S. Marine Corps and U.S. Naval Air Warfare Center
Wingspan . . . . . . . . . . . . .8.2 ft
Length . . . . . . . . . . . . . . . 6.1 ft
Height . . . . . . . . . . . . . . . 1.7 ft
Wing area . . . . . . . . . .21.4 sq ft
Empty . . . . . . . . . . . . . . . 45 lb
Max payload . . . . . . . . . . 46 lb
Cruise speed . . . . . . . . .90 mph
Range . . . . . . . . . . . . . . . .50 mi
Endurance . . . . . . . . . . . . . .2 hr
Last Updated October 17, 2003
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