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VTOL UAVs: Pilotless Rotary-Wing Aircraft

September 11, 2007  By Blair Watson

In the 1981 action film “For Your Eyes Only,” James Bond is a passenger on a helicopter that is taken over via radio control and flown violently by the sinister Blofeld.

279-vtolIn the 1981 action film “For Your Eyes Only,” James Bond is a passenger on a helicopter that is taken over via radio control and flown violently by the sinister Blofeld. After tearing out some wires, Bond regains control of the JetRanger, and then deftly scoops up the wheelchairbound villain with one of the helicopter’s skids and dumps Blofeld down a gasworks chimney.

Radio-controlled (RC) helicopters are not only part of Hollywood make-believe, they have been a reality in aviation for nearly 90 years. Small, RC rotary-wing aircraft that are sold in hobby shops and flown in public air displays are part of the family of Vertical Take-Off and Landing Unmanned Aerial Vehicles (VTOL UAVs). Various companies, including some in Canada, have developed VTOL UAVs for military, commercial and other uses.

The concept of an unmanned air vehicle dates back to the late 15th century. In 1488, Leonardo da Vinci described his aircraft design as “Non il volo umano” (“Non-human flight”). More than four centuries later the forerunner of the modern UAV was the Hewitt-Sperry Automatic Airplane, which was developed during and after World War I. Elmer Sperry’s invention had its first successful flight on March 16, 1918, but after the war ended in November, the US military withdrew its support of pilotless aircraft for a decade.

Although Germany developed the first fully controllable helicopter by 1936 – the Focke Wolfe Fw 61 – and unmanned aircraft such as the V-1 Flying “Buzz” Bomb by 1944, the Nazis did not pursue work on pilotless, rotary-wing aircraft, nor did the Allies. However, both sides developed unmanned, fixed-wing airplanes during World War II (e.g., drones were used to train antiaircraft gunners).


Enthusiastic amateurs did pioneering work in the 1950s to create valve-based control units for RC aircraft. Initially, the units were rudimentary on-off systems, but over time they incorporated increasingly complex systems of relays to control speed and direction. The transmitted information was encoded by varying the signals mark/space ratio (known as pulse proportional). The sophistication of radio control increased further with the development of metal reed switches that resonated with a transmitted signal and operated one of a number of relays.

Advances in transistor technology in the 1960s led to fully proportional servo systems for RC vehicles, including aircraft. By the 1980s, electronics had become cheap, small, and light enough to make multichannel, fully proportional radio control possible and widely available. Work on miniaturization and other technologies continued, resulting in radio control of small machines of 21st-century designs, including rotary-wing aircraft that weigh less than half a kilogram.

Canadair was the first company in this country to develop VTOL UAVs larger than hobby RC helicopters. Its CL-227 Sentinel, which had a bulbous, hourglass shape, was designed to provide a surveillance capability using a pilotless aerial platform. Because of its shape, the CL- 227 was nicknamed the “Peanut.” The first prototype was powered by a Wankel rotary engine, while the second had a Williams Research WR- 34-15 turboshaft engine.

The Sentinel’s first flight was in 1978, with subsequent flight testing in Canada, the US and at sea. It had two co-axial rotors at its mid-body, a sensor turret on the bottom, and a ring-shaped landing skid around its base. The CL-227, which had a datalink range of 20+ km, could be operated tethered or untethered.

The successor to the Sentinel was the Canadair CL-327 Guardian, one of the most advanced VTOL UAVs in the world. The Guardian’s missions include surveillance, reconnaissance, communications relay, environmental inspection, border patrol, drug enforcement, target acquisition/designation, battle damage assessment and electronic warfare. The 1.84m-high, 350-kg CL-327 has GPS and inertial navigation systems, and can be equipped with electro-optics/infrared sensors, synthetic aperture radar, and active electronic surveillance measures. The surveillance system can freeze, pan, and rotate images, and when the GPS nav system is used, the Guardian can geo-locate a target to less than 60 metres. The CL-327’s video is real-time, and its digital datalink system employs C-Band for enroute and over-target operations and L-Band for launch and recovery and redundancy.

Performance-wise, the Guardian has a maximum endurance of 6.25 hours, a time-on-station (at 100 km) of 4.75 hours, and a datalink/operational range of about 200 km. It is powered by a Williams International heavy fuel turboshaft engine (125 shp flat-rated to 100 shp), which results in a maximum speed and altitude of 90 knots and 18,000 feet. Production of the CL-327 began in October 1996, and since then Canadair has marketed the VTOL UAV to various countries. The CL-327 system includes a control station and requires only two personnel for operations. Nominal pilot skills are needed to fly it, and the crew can be trained to operate the air vehicle in just four weeks.

Some VTOL UAVs have the overhead rotor and tail rotor design of most helicopters, while others do not. Bell Helicopter Textron manufactures a pilotless tilt-rotor aircraft called the Eagle Eye Unmanned Aerial System (UAS). Tilt-rotor aircraft can take off and land like conventional helicopters, or in a short distance like STOL airplanes, and once airborne, their engines rotate forward, resulting in a cruising speed typically greater than that of helicopters of comparable size. The Eagle Eye UAS first flew on Jan. 26/06 after receiving certification from the FAA for experimental flight testing, the first ever issued to a vertical-lift UAS.

Bob Ellithorpe, Bell Helicopter’s director of unmanned systems, says the Eagle Eye UAS “will provide military and commercial operators with multiple capabilities ranging from homeland security to pipeline patrol.” Bell Helicopter will deliver 45 Eagle Eyes and 33 ground control stations to Lockheed Martin, where they will become part of the US Integrated Coast Guard Systems program known as Deepwater.

There are not only military, homeland security and commercial applications for VTOL UAVs, but also ones pertaining to search-and-rescue and policing. In March of this year, TGR Helicorp, a New Zealand helicopter firm, began operational testing of a prototype VTOL UAV designed to provide air ambulance/rescue services to climbers on Mount Everest. The Alpine Wasp is a derivative of TGR Aerospace’s SNARK unmanned combat air rotorcraft; modifications include an advanced rotor head and blades optimized for high-altitude operation. The Wasp’s DeltaHawk Engine runs on Jet-A1 rather than diesel to resolve fuel gelling problems in extreme cold.

The Alpine Wasp will be equipped with a five-camera sensor suite mounted in the nose, and transmit video in real time to a virtual piloting station. Flight testing is being conducted in the mountains of New Zealand’s South Island until September. The VTOL UAV will be deployed in Nepal in December and commence in-country testing in March 2008, followed by fee-for-service rescue operations from April 2008. The Alpine Wasp will be able to carry two sick or injured mountaineers.

Police forces in various nations have expressed an interest in VTOL UAVs. In this country, the Canadian Police Research Centre (CPRC) has partnered with Draganfly Innovations Inc. of Saskatoon to explore the use of drone aircraft in assisting law enforcement. Their study involves the Draganflyer Tactical Surveillance Unit (TSU), a small, electric, RC VTOL UAV that can provide police with an aerial view of a building, alley, or other location. It can even be flown indoors.

The Draganflyer TSU, which has onboard electronic sensors, easily and safely maneuvers in an urban environment. It has been profiled on major news networks and is reportedly very easy to fly. Operators can adjust the sensitivity of the controls to whatever suits them, and the TSU’s sensors allow the VTOL UAV to automatically level itself if the operator loses control.

The Draganflyer TSU weighs an astonishing 0.45 kg, thanks to its frame made of carbon fibre and nylon and other lightweight parts. It can fly for approximately 17 minutes per charge and transmits high-resolution, real-time video to a portable station 400+ metres away. The CPRC is working with police agencies to determine the operational advantages and limitations of this unusual Canadian VTOL UAV.


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