Rocket-powered target drones from Van Nuys

In my previous post about unmanned air vehicles that I saw at the Western Museum of Flight during my visit there in January 2020, I offered brief details on three Radioplane/Northrop-built UAVs preserved at this museum, the MQM-57 Falconer and MQM-36 Shelduck derivatives of the prolific MQM-33 Quail target drone family, and the NV-144 prototype jet-powered reconnaissance UAV. However, one Radioplane-built UAV on display at the Western Museum of Flight that I virtually overlooked happened to be one of just a handful of rocket-powered UAVs to be designed and built in southern California, the Radioplane AQM-38. Having recently gotten a copy of the book 50 Years of Target Drone Aircraft (published in 1985 by the very company that built many of southern California's most notable 20th century drones besides the Firebee) and done some brief yet painstaking research into the genesis and early development of the AQM-38, I now have the opportunity to dedicate this post to telling the story of rocket-powered unmanned aerial vehicles developed by the Radioplane Division of Northrop in the 1950s.

A trio of XKD4R-1s on their towing platforms at the Naval Air Missile Test Center (NAMTC) in Point Mugu, southern California, January 1957.

In March 1955, Radioplane proposed an air-launched rocket-powered target drone under the company designation RP-70, which used molded plastic in its construction and had a sharply pointed nose, with longitudinal stability provided by three forward control fins (one on top of and two on the sides of the forward fuselage) and a horizontal stabilizer mounted below the ventral vertical stabilizer. Power was provided by a single 37 lb (0.16 kN) thrust Aerojet 530NS35 solid-fuel rocket motor with a burn time of 530 seconds, and the RP-70 had a length of 9 feet 6 in (2.90 meters), a wingspan of 5 feet (1.52 meters), a diameter of 12 inches (30 cm), a weight of 305 lb (138 kg), a top speed of Mach 0.95 and a service ceiling of 60,000 feet (18,300 meters). After launch, the drone would rely on autopilot to remain on a constant heading and altitude for a flight endurance of 9 minutes, with a bright flashing light in the tail utilized to facilitate visual tracking. For recovery, the RP-70 was equipped with a parachute system. The Navy assigned the designation XKD4R-1 to the RP-70, and the first XKD4R-1 drones were built and first flown in late 1956, with deliveries to the Naval Air Missile Test Center (NAMTC) at NAS Point Mugu in January 1957. The main launch platforms for the XKD4R-1 wer the Douglas F3D Skyknight all-weather jet fighter and McDonnell F3H Demon jet fighter, both of which could fly at the subsonic speeds that the XKD4R-1 attained. A handful of XKD4R-1s were manufactured but the drone was not approved for series production despite exhibiting satisfactory performance.

Left: An AQM-38A (RP-76) on display at the Western Museum of Flight, photographed by me on April 17, 2021.
Right: An AQM-38A under the wing pylon of an F-89 Scorpion.

Months before the XKD4R-1 began flight testing, in early 1956 Radioplane proposed a variant of the RP-70 to be used by the US Army for surface-to-air missile training, the RP-76. Despite having the tail empennage, rocket motor, and flight duration of the RP-70, the RP-76 differed in having a blunt nose section to house the Luneberg lens, straight wing/rocket exhaust fairings, and the dorsally mounted forward control fin moved to the underside of the forward fuselage. The Luneberg lens was designed for radar reflectivity augmentation, and the RP-76 also utilized a Northrop RPTA-1 tracking aid system, necessitating elimination of the bright flashing light in the tail developed for the XKD4R. After being launched from an aircraft, the RP-76 was be controlled in flight by autopilot with an optional override by radio command, and recovery of it was done by a two-stage parachute system.  The Army awarded Radioplane a contract for full-scale development of the RP-76 in June 1957, and test flights of RP-76 began in early 1958, with deliveries of service test drones to US Army units commencing later that year, and the first successful hit against an RP-76 by a Nike Ajax surface-to-air missile taking place on September 18, 1958 at the Red Canyon Guided Missile Range near Carrizozo, New Mexico. Series production of the RP-76 began in late 1959, by which time the drone had been cleared for operational service, and launches were conducted from the Northrop F-89 Scorpion all-weather fighter but also the RP-77DL mothership variant of the RP-77D turboprop-powered target drone. 

Left: An AQM-38B (RP-78) under a wing pylon of an F-89 Scorpion, late 1962
Right: An RP-76-4 target drone under a wing pylon of an F-89 Scorpion, circa 1961

In parallel with design of the RP-76, in April 1956 Radioplane envisaged a supersonic variant of the RP-76 for the Air Defense Command of the US Air Force, the RP-78, which had the same airframe and guidance system as the RP-76 but was designed for a top speed of Mach 1.25. The RP-78 had a service ceiling of 78,700 feet (24,000 meters) and a range of 44 miles (70 km), and the top speed and altitude for which for the RP-78 was designed meant that this drone utilized a slightly more powerful solid-fuel rocket motor generating 100 lb (0.44 kN) of thrust. The RP-78 began flight tests in 1960, but by then the US Air Force had lost interest in the RP-78 in favor of the Ryan Firebee, so the US Navy took over the RP-78 program, and the operational deployment of the RP-78 with Navy units commenced in October 1962, with the F-89 being used as the launch platform. Radioplane in April 1960 proposed another supersonic derivative of the RP-76 to be used by the US armed forces and NATO member states in Europe, the RP-76-4, which began test flights in December 1961. The RP-76-4 was 11 feet (3.35 meters) long with a wingspan of 4 feet 4 in (1.32 meters), a top speed of Mach 2.25, a service ceiling of 80,000 feet (24,384 meters), and a 200 lb (0.89 kN) thrust solid-fuel rocket motor. It differed from the RP-76 and RP-78 in having delta wings and a conventional dorsal vertical stabilizer as well as anhedral horizontal stabilizers, and it had an endurance of four minutes over a range of 62 miles (100 km) under rocket power and 30 minutes in controlled glide mode. Over 20 test flights of the RP-76-4 were made by 1964, and despite its stellar flight performance, no production orders for this advanced drone followed. When the US Defense Department introduced a new designation system for missiles, unguided rockets, and drones on June 27, 1963, the RP-76 and RP-78 were designated AQM-38A and AQM-38B respectively (ironically, the RP-78 had not been assigned a Navy designation prior to 1963). Production of the AQM-38 ended in 1968 with more than 2,400 targets built, and the AQM-38 itself remained in operational service until the mid-1970s.

References:

Botzum, R.A., 1985. 50 Years of Target Drone Aircraft. Newbury Park, CA: Northrop Corporation (Ventura Division) Publishing Group.

Taylor, J.W.R., 1963. Jane's All the World's Aircraft 1963-1964. New York, NY: McGraw-Hill.

Taylor, J.W.R., 1965. Jane's All the World's Aircraft 1965-1966. New York, NY: McGraw-Hill.

From land-based patrol bomber to firefighter: PB4Y-2s for Hawkins and Powers Aviation

I have long been familiar with the post-World War II use of the Martin JRM Mars giant flying boat as a firefighting aircraft, while reading about how aerial firefighting has come to be one of the many niches of the C-130 Hercules tactical transport in its peacetime non-military capacity, having remembered watching the local news back in June 2002 of the crash of one C-130A firefighting aircraft in Mono County, eastern California. During my visits to the Yanks Air Museum in Chino in the past, I saw a Consolidated PB4Y-2 Privateer languishing in the boneyard section of the museum, the first time I encountered this aircraft in person after seeing photos of this aircraft in several aviation books. While helping Joe Baugher update several webpages about US military aircraft, it transpired to me that a handful of Privateer aircraft were repurposed for use as firefighting aircraft by Hawkins and Powers Aviation not too long after being retired from service with the US Navy. Even though the Hawkins and Powers firefighting company was based in Wyoming, the history of PB4Y-2 operations with this company is worth discussing because the PB4Y-2 was built in San Diego, California, like the B-24 Liberator and PB4Y-1 navalized version of the B-24.

A PB4Y-2 aerial firefighting aircraft (ex-BuNo 59701, civil registration N6884C) in flight over Reno, western Nevada, in 1976. Note the Hawkins & Powers serial number 127 on the nose of the aircraft. 

Several books have been written about the operational career of the PB4Y-2 Privateer in the early 1950s (by which time PB4Y-2s in active service were redesignated P4Y-2 despite the P4Y designation having been applied to the Consolidated Model 31 Corregidor flying boat), but the story of the conversion of a handful of PB4Y-2s to aerial firefighting planes began in 1959, when several PB4Y-2s were declared surplus and earmarked for scrapping in the summer of 1958. The US Navy had retired its PB4Y-2/P4Y-2 fleet from service in 1954, but the US Coast Guard continued to operate several ex-USN Privateers in the search-and-rescue role (designated P4Y-2G) until 1958. In the second half of 1959, eight PB4Y-2 aircraft (BuNos 59701, 59882, 66260, 66261, 66300, 66302, 66304, and 66306) were acquired by aerial firefighting firm Christler & Avery Aviation of Greybull, Wyoming and seven were converted to aerial firefighters, necessitating modification of the bomb bays to carry 18,000 lb (8,164 kg) of fire-retardant chemicals, while the R-1830 Twin Wasp radial piston engines were replaced by Wright R-2600 Twin Cyclones. These aircraft, which were called Super Privateers, had short-stack exhausts which protruded around the circumference of the engine nacelles. The PB4Y-2 with BuNo 66261, while allocated the civil registration N7682C and the serial number 13 by Christler & Avery Aviation, was never converted to aerial firefighting configuration and instead used as a spare parts airframe to support the the PB4Y-2 firefighter fleet, which began firefighting operations in the western US in 1960. Meanwhile, Christler & Avery Aviation changed its name to Avery Aviation in 1961, and it was eventually bought out by Hawkins and Powers Aviation in 1969. The PB4Y-2s with BuNos 59701, 59882, 66260, 66300, 66302,  and 66304 were allocated the new serial numbers 127, 126, 123, 124, 121, and 122 by Hawkins and Powers, which also received one PB4Y-2 with civil registration N6813D (ex-BuNo 59876) that had been previously operated by Cisco Aircraft and another PB4Y-2 with civil registration N6816D (ex-BuNo 59792). Even before the purchase of Avery Aviation by Hawkins and Powers, one PB4Y-2 in use by Avery Aviation with civil registration N7974A (ex-BuNo 66306) was lost in an accident on July 22, 1968, when it hit a mountain near McGrath, Alaska, while en route to a forest fire, killing all four people aboard. 

The PB4Y-2 aerial firefighting aircraft serial number 124 (ex-BuNo 66300, civil registration N2872G) on display in the outdoor storage area of the Yanks Air Museum in Chino, California, photographed by me on May 19, 2018.

The PB4Y-2 aerial firefighter that I've seen at the outdoor storage area of the Yanks Air Museum, BuNo 66300, was one of 710 production PB4Y-2 aircraft (BuNos 66245/66394, 66795/67054, 76839/77138) ordered in late 1944, of which only 80 had been delivered by October 1945, the remainder on order canceled after V-J Day. The PB4Y-2 with BuNo 66300 was delivered to the Navy on August 31, 1945 and later assigned to storage at NAF Litchfield Park in Arizona from November 16, 1945 until August 1949. By the early 1950s, it was transferred to the US Coast Guard for search-and-rescue duties and converted to P4Y-2G configuration, serving in that capacity until 1958, when it was retired from active service with the USCG and transferred to CGAS Elizabeth City in Elizabeth City, North Carolina, for eventual disposal. BuNo 66300 was assigned the civil registration N2872G when sold to Ace Smelting in 1959, but was eventually spared from the breaker's torch along with a few other PB4Y-2s and sent to  Christler & Avery Aviation for conversion to Super Privateer configuration, receiving the serial number B24 and beginning firefighting operations in July 1960. After Hawkins and Powers Aviation acquired Avery Aviation, the aircraft was given the new serial number 124 in 1970, and it was used by the US Forest Service for extinguishing forest fires in and around Fairbanks, Alaska.

PB4Y-2 serial number 123 (ex-BuNo 66260, civil registration N7620C) crashing near Estes Park, Colorado, on July 18, 2002

Although the PB4Y-2s operated by Hawkins and Powers Aviation had success in putting out forest fires in western North America during their three decades of service with Hawkins and Powers Aviation, their operational career was marred by a few accidents. On July 27, 1972, N6816D was destroyed in flight while on approach to Wenatchee-Pangborn Field in Washington after fighting a local forest fire. On July 18, 2002, PB4Y-2 serial number 123 (BuNo 66260, civil registration N7620C) broke up in flight and crashed near Estes Park, Colorado, while fighting a forest fire in Rocky Mountain Regional Park, killing both crewmembers. The other PB4Y-2s operated by Hawkins and Powers Aviation and US Forest Service were withdrawn from operational service due to old age, and by 2005 Hawkins and Powers Aviation ceased operations. Three years later, the PB4Y-2 that had been given the serial number 124 by Hawkins and Powers Aviation was delivered to the Yanks Air Museum on November 23, 2008. It should be noted that PB4Y-2 serial number 122 (BuNo 66304) was damaged beyond repair after veering off the runway during a takeoff roll at Ramona Airport in Ramona, California, on August 27, 1980. The damaged aircraft was mated with remnants of BuNo 66261 and retained BuNo 66304 due to the fact that BuNo 66261 had been in derelict condition for over 20 years, but Hawkins and Powers had no need for any additional operational use of this aircraft, and the rebuilt PB4Y-2 was eventually given to the National Museum of Naval Aviation in Pensacola, Florida, where it resides today.

References:

Carey, A.C., 2005. Consolidated-Vultee PB4Y-2 Privateer: The Operational History of the U.S. Navy's World War II Patrol/Bomber Aircraft. Atglen, PA: Schiffer Publishing.   

Veronico, N.A, and Ginter, S., 2012. Convair PB4Y-2/P4Y-2 Privateer (Naval Fighters Number 93). Simi Valley, CA: Ginter Books.