The Ground-Breaking Boeing Condor UAV

The Condor in flight

In the 1960s as the technology for unmanned aerial vehicles (UAVs) progressed, the USAF initiated two programs that would provide unmanned analogues to the premier airborne reconnaissance aircraft of the day, the Lockheed SR-71 Blackbird and the U-2. Both aircraft had their strengths and weaknesses and the USAF hoped to expand upon their capabilities with adjunct UAV reconnaissance aircraft. The companion program to the SR-71 Blackbird originated from the Lockheed Skunk Works as the D-21/Tagboard reconnaissance drone for the CIA. Possessing the same Mach 3 performance as the Blackbird, the D-21 was originally launched from the back of a modified A-12 Cygnus. However, after a disastrous fourth airborne launch that cost the launching aircraft and one of its crew, the D-21/Tagboard was moved over to the Boeing B-52 Stratofortress as the launching aircraft. After four failed operational missions in which the D-21 was lost, the program was canceled in 1971, at which time the second program which would have been a companion to the Lockheed U-2 was getting under way. Being a large jet-powered glider-like aircraft not too dissimilar in performance to the U-2, in 1971 the USAF initiated the Compass Cope program with Boeing and Teledyne Ryan producing prototypes- Boeing's design being the YQM-94 Gull (Compass Cope B) and Ryan's competing design being the YQM-98 Tern (Compass Cope R). After a competitive evaluation, Boeing's Gull was chosen in August 1976, to which Ryan lodged a protest. It was pointless at that juncture as the USAF canceled Compass Cope in 1977 before any production Gulls were built. 

But it wasn't the end of the story for Boeing's work for a high-altitude, long-endurance (HALE) UAV. The Defense Advanced Research Projects Agency (DARPA) was still interested in the idea of a HALE UAV for strategic reconnaissance. DARPA wanted to go one step further than the Compass Cope program, though. A contract was issued to Boeing for a HALE UAV that could operate for days at high altitudes carrying reconnaissance payloads that ranged for optical camera systems to electronic intelligence collection arrays to even an airborne synthetic aperture radar for all-weather/day-night surveillance. Boeing contracted with Burt Rutan who was using an all-composite structure in his record-breaking long-distance aircraft, Voyager. Boeing's design, aptly named Condor, used a predominantly composite structure with a wingspan of 200 feet, the same as that of the Boeing 747. The fuselage was only 68 feet long but was slab sided to facilitate the mounting of either an ELINT or SAR antenna array. Designed to be disassembled into sections and transported by a Lockheed C-5 Galaxy, the Condor's fully loaded weight was 60% fuel. 

Comparing the Condor and the 747

The wing's airfoil section was extremely efficient and provided natural laminar flow at altitudes in excess of 50,000 feet. Since the Condor was to be autonomously controlled, the wing had to have benign stall characteristics to simplify the control of the UAV. The wing was so efficient that it had twice the lift-drag ratio of the U-2- 40:1 compared to 20:1 for the spyplane. Since the wing would be highly flexible, a fuel transfer system was used to move fuel between wing tanks to reduce flexing in flight. The use of composites resulted in a wing that weighed only 2 lbs/square foot- an impressive feat considering that a commercial jetliner's wing comes in at approximately 30 lbs/square foot. 

The Condor was powered by two Teledyne Continental 175-horsepower six-cylinder piston engines that were superturbocharged for operation at very high altitudes. Each wing-mounted engine drove a three-bladed propeller 16 feet in diameter. Since the propellers were optimized for high-altitude cruise, at lower altitudes they would cause a significant amount of fuel burn and drag- as a result, a two-speed gearbox was used- one gear ratio for low-altitude flight and a different gearing for high altitude cruise. 

The flight control computer of the Condor was groundbreaking in that the Condor was the first UAV designed and flown autonomously without external control input from a remote pilot. Two Delco Magic 3 series computers were used as the brains of the Condor- the Magic 3 series computers were also used in the guidance systems for the Titan II ballistic missiles and the Delta family of rocket launchers. One computer acts as the primary computer with the second one operating in standby and ready to takeover should the primary computer fail. The control software consisted of only 60,000 lines of Fortran code- minuscule when one considers that today's RQ-4 Global Hawk reconnaissance UAV uses several million lines of software code! The Condor's computers were responsible for vehicle functions, flight control, and navigation using inputs from an inertial navigation system (this was in the days before GPS). The computer system was even designed to not only handle inflight emergencies but also prevent an enemy from taking electronic control of the UAV. Should that happen, the system was designed to recognize it was being taken over and immediately direct the Condor back to friendly territory. 

A microwave landing system was adopted to provide control of the Condor during takeoff as well as landing. Using a dolly, once the Condor reached 65 knots, it lifted off the ground and left its takeoff dolly behind. It would take anywhere from two to three hours for the Condor to reach its cruising altitude of over 50,000 feet. At cruise altitude, the Condor cruised at 200 kts, but its all composite construction made it a very small radar target and its piston engines had a very low infra-red signature- so despite its size and apparent leisurely cruise speed, it was a difficult target to track on most radars of the day. Descent for landing took two to three hours as well, and an extendable nosewheel and landing skids were used for landing. To save weight, instead of doors covering the skids and wheel, a replaceable Mylar sheet was used that the skids and nosewheel broke through on landing.

The Boeing Condor today at the Hiller Aviation Museum 

The Condor was developed in secret and its rollout in March 1986 was its unveiling to the world. It made its first flight on 9 October 1988 from Boeing's test facility at Moses Lake, Washington (the former Larson AFB). Since the rules on UAV operations in controlled airspace had yet to be fully written, a manned chase plane had to accompany the Condor during its transit through any controlled airspace. Only eight test flights were made with the last one on 28 November 1989, but the Condor set two world records- one for record altitude for a piston-engined aircraft at 67,028 feet on the fourth test flight and one for unmanned aircraft endurance at an impressive 58 hours, 11 minutes on the final test flight. Given that the test flights occurred over eastern Washington state, it's unlikely any operational reconnaissance payloads were carried, but to this day the exact nature of the payloads to have been carried- or even if they were carried- on the Condor remain classified. With a cost of $300 million, the Condor program did prove the viability of autonomous UAV flight as well as advanced composite construction and ultra-lightweight structures, but it lacking in military flexibility as well as its slow speed resulted in its cancellation after the final test flight. Only one Condor was built and flown, and in 1998 it was acquired by the Hiller Aviation Museum in the Bay Area where it can be seen on display today. It's the largest aircraft to be suspended in an interior museum display in the world. Not bad, even just sitting in the museum it still sets a record!

Sources: Birds of Prey: Predators, Reapers and America's Newest UAVs in Combat by Bill Yenne. Specialty Press, 2010, p20-32. 
Condor photo in the Hiller Museum by Joe May @ Travel for Aircraft- "Photo Funday- Boeing's Condor"