Boeing reportedly initially developed Condor with corporate funds, but there also was support from non-DoD sources. As part of its TEAL RAIN, DARPA supported the flight-testing of the Condor in a military configuration. The first aircraft rolled out in 1986. It was considered a “significant milestone in the development of endurance UAVs. The Condor featured lightweight all-composite and honeycomb structures, autonomous controls, high altitude aerodynamics, and a fuel-economical propulsion system.”78 The UAV was large enough (it had a 200-foot wingspan) to carry a big payload and during test flights it carried about 1,800 pounds of instruments. It was powered by two, six-cylinder liquid-cooled piston engines. The engines had two-stage turbocharging for high altitude operation and a gearbox that shifted the propellers to higher RPM at these high altitudes.
Boeings' Condor, a remotely piloted twin engine aircraft, had a wider wingspan (200 feet) than a Boeing 747 and could operate above 65,000 feet for several davs. Condor reached a maximum altitude of 67,028 feet in a 1988 flight. This altitude record for propeller-driven aircraft set by the Condor was unsurpassed until June 1997, when NASA's Pathfinder UAV reached a record altitude of 67,350.
It was capable of operating autonomously from takeoff to landing, using a flight control program, but communications links allowed a mission to be modified in flight. The Condor reached a record altitude of 67,028 feet in a 1988 flight. This altitude record for propeller-driven aircraft was unsurpassed until June 1997, when NASA’s Pathfinder UAV reached a record altitude of 67,350. The Condor was not inexpensive. It was estimated to cost about $20 million without payload. However, it had a range of 9,000 miles and 2.5 days’ endurance. Because of these capabilities it was viewed as a “cheap satellite” for many applications.
In 1989, the Boeing Condor completed at 141-hour flight test program, in which it set the record for the highest altitude ever achieved by a piston engine aircraft. An unmanned aerial vehicle (UAV), the Condor was designed to complete remote-controlled, high altitude missions. In its historic flight, the Condor stayed aloft for over two-and-a-half days at an altitude of 66,980 feet.
The Condor was built with carbon-fiber composite materials, and had a wingspan of 200 feet. Two custom-built three-bladed Hartzell propellers gave the Condor the boost and durability it needed to reach its unprecedented altitude. Although the Condor was ultimately deemed too large for stealth missions, its record-breaking achievements were remembered for years to come. The Condor spurred huge advancements in aerodynamics, UAV technology, and propulsion, leading the way for progress in military, commercial, and civilian UAV aircraft.
For subsonic flight, a high altitude propulsion unit is significantly larger and heavier for the same output compared to a low altitude unit. To complicate matters further, the high altitude aircraft needs to have a more powerful propulsion unit because it must go faster at altitude in order to support its own weight (maintain wing loading). As a result, the propulsion system will claim a greater fraction of the airplane's gross weight. This trend unfortunately runs counter to the airplane's ability to carry the weight.
The advantage of gas turbine power is that the high specific power (HP / lb) which it can develop allows high speeds and relatively high wing loading to be maintained, which reduces the aircraft's susceptibility to winds and turbulence at lower altitudes and makes for shorter flight times to conduct the mission.
The disadvantages are higher fuel consumption (less range) and the exponential thrust lapse that occurs with altitude. As the air density drops the turbine engine will ingest correspondingly smaller amounts of air resulting in less power and less thrust; this eventually leads to combustor flameout. The power lapse curve typical of turbine engines illustrates this trend. As an example, the Compass Arrow's turbojet engine, capable of over 5,000 pounds of thrust at sea level, would produce only 184 pounds of thrust at 80,000 ft (Mach no. = 0.85) and would be operating on the verge of flameout.
A propeller driven unit powered by a turbocharged reciprocating engine has long been considered attractive power plants for subsonic flight at high altitudes. A propeller provides high propulsive efficiency because of its large capture area, which in turn enables high altitude flight at slower airspeeds and reduced fuel consumption. Because this is an existing technology base of mass-produced automotive and general aviation hardware that can be adapted for this purpose, it is possible to develop a turbocharged power plant with its core engine and turbocharger/intercooler system at much lower cost than a jet engine. Several multiple stage turbo/supercharging systems have already been demonstrated either in high altitude flight or in altitude test chambers.
A three stage turbocharger system was developed by ThermoMechanical Systems (TMS) of Canoga Park CA, a small company with considerable previous background in turbocharger development and engine installations. It was TMS which, under the formerly classified TEAL RAIN RPA technology development program that preceeded Condor in the early 1980's, successfully demonstrated operation of a three stage turbocharged (45 cid 3 cylinder) experimental engine producing 55 HP at 90 kfl simulated altitude in a dynamometer equipped mechanically exhausted chamber. TMS later applied the intermediate pressure and high pressure stage hardware from TEAL RAIN to a ROTAX 912 core engine for demonstration of a two stage turbocharged engine for small high altitude long endurance (HALE) vehicles under the Ballistic Missile Defense Organization's RAPTOR program (an effort to develop HALE RPA's for launch detection of land mobile missiles; the Raptor aircraft and TMS hardware were transferred to NASA's ERAST program in 1995 as BMDO attention was shifted away from airborne surveillance systems to terminal defense.
The Condor powerplant is a Teledyne developed series turbocharged Voyager 300 liquid cooled engine with a rating of 175 BHP at 2800 RPM. Each engine drives a three bladed, variable pitch, 16 foot diameter propeller through a two speed reduction gearbox (2). The Voyager 300 is a six cylinder 300 cubic inch displacement engine utilizing an advanced design high turbulence combustion chamber with 11.4 compression ratio (Z). The engine is capable of providing specific fuel consumption values well below .375 lbs/BHP/hr across a broad operating range and has demonstrated a .355 lbs/BHP/hr cruise capability at 90 BHP/1700 RPM. The turbocharger system consists of two stages, a high pressure (HP) unit and a low pressure (LP) unit, operating in series with both intercooling and aftercooling.
With its high altitude and long endurance, it had global reach, capable of conducting missions ranging from military surveillance to drug enforcement. The Defense Advanced Research Projects Agency (DARPA) supported the flight-testing of the Condor in a military configuration. Potential users looked at the Condor as a cheap satellite with a long dwell time. At $20 million (without payload), Condor would be a cheap supplement to the amount of money now being spent on state-of-the-art satellite systems.
Condor is viewed as a positive example of DARPA’s collaboration with commercial firms. The collaboration between Boeing and DARPA resulted in a very advanced system to meet an identified Navy need to counter Soviet Backfire bombers. The Navy had stated a requirement for 50 units. However, the development fell victim to changing Service demands when the DoD transferred the Navy mission for which the Condor had been designed to the Air Force. The Navy canceled its support for the Program and the Air Force did not pick it up.
Although Boeing reportedly spent more than $100 million of its own funds on the development of the Condor, it ultimately had no buyer and the aircraft was mothballed. The Condor is viewed as the conceptual prototype of the Global Hawk.
According to its engineers, it did not achieve its full potential during testing. They claimed it could have flown more than 23,000 miles (37,000 kilometers), remained airborne for longer than a week and reached an altitude of 73,000 feet (22,250 meters). Originally, the Condor was intended for both military and commercial purposes; however, it could not find a customer. Because of its large size, slow speed and lack of stealth, it was too vulnerable to be used for military operations. It had tremendous civilian potential for weather monitoring and atmospheric research, but at the time the expense of such a vehicle was beyond the budgets of most civilian agencies.
In the long run, Condor laid the groundwork for more successful follow-on unmanned aerial vehicles.
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