In the mid-1960s, the US Air Force launched the Sandpiper program to modify some Beechcraft AQM-37 supersonic target drones with hybrid fuel rocket motor system using a solid grain fuel and liquid oxygen because the liquid-fuel rocket motor used to power the AQM-37 used dangerous hypergolic propellants. In 1968-1969, flight tests of the Sandpiper were conducted and they were so successful that the USAF in the early 1970s initiated the HAST (High Altitude Supersonic Target) program, later renamed HAHST (High Altitude High Speed Target), for a production target drone based on the Sandpiper configuration, and the designation XAQM-81A was assigned to the HAST/HAHST program. However, technical difficulties meant that a definite configuration for the HAST/HAHST program was not settled upon until the late 1970s. By this team, the USAF deemed Beech's offer for a full-scale development contract too expensive, and thus called for competitive bids for HAHST development from the aerospace industry. Among the submissions for the HAST/HAHST competition was a proposal from Teledyne Ryan, the Model 305 Firebolt, and in December 1979, the the XAQM-81A development contract was awarded to Teledyne Ryan, with an order placed for nine XAQM-81As.
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| An AQM-81A Firebolt on display at the March Field Air Museum in Riverside, California, photographed by me on December 17, 2022 |
The XAQM-81A Firebolt had the same layout and airframe as the AQM-37, particularly the slender delta wings and triangular vertical fins at the wingtips, but it mainly differed in having a single 1,200 lb (5.3 kN) hybrid-fuel rocket motor built by Chemical Systems Division (CSD) of United Technology which used IRFNA (Inhibited Red Fuming Nitric Acid) as the oxidizer for the solid grain fuel. The thrust of the rocket motor could be adjusted in flight to alter speed and altitude to give interceptor pilots a more flexible and realistic target. The air inlet below the fuselage of the Firebolt utilized a ram air turbine that pressurized the IRFNA oxidizer before delivering it to the thrust chamber of the rocket engine, and it also provided electrical power for the drone. The XAQM-81A was 17 feet (5.18 meters) long with a wingspan of 3 feet 4 inches (1.02 meters), a fuselage diameter of 13 inches (33 cm), and a weight of 1,230 lb (560 kg), and it had a top speed of Mach 4.3 and an endurance of five minutes. The F-4 Phantom II served as the launch platform for the AQM-81A, and after being launched from an F-4 at a speed of Mach 1.5, the Firebolt would ignite its rocket rocket to reach an altitude of 103,000 feet (31,400 meters) at speeds exceeding Mach 4. The XAQM-81A Firebolt could fly a pre-programmed course and/or respond to guidance commands from the ground, and it was equipped with a parachute recovery system to enable either a soft landing or a mid-air retrieval by a helicopter, the latter via the Mid-Air Retrieval System (MARS). The US Navy version of the Firebolt, the AQM-81B (erroneously listed in a few sources as "AQM-81N"), had the same mode of launch and performance characteristics as the planned production AQM-81A but differed in incorporating the Navy's AN/USW-3(V) ITCS (Integrated Tracking and Control System), radar augmentation for ground tracking requirements, and flotation gear for recovery over water.
The XAQM-81A began flight tests on June 13, 1983, at Eglin AFB in Florida. Even before the Firebolt began its flight test program, the number of Firebolt test vehicles had been increased to 21 drones, including six each of the AQM-81A and AQM-81B. In July 1984, test flights of the AQM-81B began at Point Mugu NAS in southern California, by which time the Air Force had began service tests of the Firebolt. Flight tests of the AQM-81 continued until the fall of 1984, by which time more than twenty flights had been conducted. Although the AQM-81 exhibited outstanding performance during its flight test program, it was not ordered into production because the Air Force and Navy realized that the unit cost of the AQM-81 was far more expensive than the simpler AQM-37.
References:
Munson, K., 1988. Jane's World Unmanned Aircraft. Coulsdon, UK: Jane's Information Group.
Wagner, W., and Sloan, W.P., 1992. Fireflies and other UAVs (Unmanned Aerial Vehicles). Arlington, TX: Aerofax.
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