Sojka Spreads Its Wings

September 2005
By Henry S. Kenyon

Developed for the Czech army, the Sojka III unmanned aerial vehicle (UAV) is a tactical reconnaissance platform designed to serve echelons at or above battalion level. The aircraft can be assembled in the field quickly and launched with a rocket assist.
Czech program highlights contributions to European unmanned aircraft development.

A new NATO partner nation has entered the international unmanned aerial vehicle market with a multipurpose surveillance platform. Designed for tactical operations, the robot aircraft can carry a variety of sensor packages and can provide real-time battlefield information via a datalink.

Ongoing military operations in the Middle East and Central Asia have proved the efficacy and combat utility of unmanned aerial vehicles (UAVs). Though several nations such as the United States, Germany and Israel have developed and maintain large numbers of UAVs, over the past two decades many other nations have produced their own platforms for internal use and for export. The growing numbers of robot aircraft now available allow customers to select from a range of models designed to meet specific operational needs.

One example of the alternatives in the marketplace is the Sojka III, developed by the Czech Air Force Research Institute (VTUL a PVO) in Prague. The Sojka program began in the early 1980s to meet Czech Ministry of Defense requirements for an unmanned aerial target for helicopter combat training. According to Jiri Nohyl, a VTUL a PVO systems developer, the platform’s operational requirements changed in the 1990s to that of a daylight reconnaissance UAV. Named for a bird, the Sojka (jay) system has been in service with the Czech army since 1998.

Powered by a rotary engine, the UAV is made of fiberglass and lightweight carbon and aramid composite materials. The aircraft is 3.78 meters (12.40 feet) long with a wingspan of 4.5 meters (14.75 feet). Launched from a truck-mounted rack via rocket assist, it has a maximum speed of 210 kilometers (130.5 miles) per hour and a cruising speed of 180 kilometers (111.85 miles) per hour. The Sojka has an operational endurance of four hours and a maximum ceiling of 4,000 meters (13,100 feet).

The UAV uses a belly skid or a parachute to land. Nohyl notes that the parachute also can be used as an emergency recovery system if the engine fails, or it can deploy a deceleration bag—an air bag—to soften the impact of a parachute landing. An onboard safety system shuts off the engine and deploys the parachute if it detects any malfunction in the flight control system. The UAV’s mission can be terminated by a command from its groundstation.

The aircraft can be readied for launch in 45 minutes and prepared for a second mission in less than 40 minutes after landing. The UAV and its control shelter can be packed and ready to move within 30 minutes of landing, Nohyl explains.

Designed to provide brigade-level tactical reconnaissance, two Sojka units are in service with the Czech army. Each unit consists of six UAVs, one ground control station, a launcher truck, a transport and maintenance container, and an off-road recovery vehicle. The recovery vehicle also transports the crew and is used to locate launch and landing sites in the field. It is equipped with a special trolley to move the UAV to a launch point or for recovery.

The Sojka does not have a satellite communications link, but it is equipped with standard radio systems, Nohyl says. Data gathered by its sensor systems is processed and sent to the groundstation, which transmits it across the Czech army’s ground forces tactical command and control system. Although this system can share information with NATO and allied systems, Nohyl emphasizes that the Sojka’s sensor feeds cannot link with coalition force networks.

Sensor packages are housed in the front of the aircraft. The most common equipment arrangement consists of a charge coupled device video camera on a stabilized mount and an infrared linear line scanner for high-resolution imagery. Optional sensors include a digital camera system mounted in a stabilized gimbal and an X-ray sensor. In addition, VTUL a PVO engineers have test fitted the aircraft with a radiation detector, Nohyl says.

A video switch, videocassette recorder and a video datalink are a standard part of the sensor package. Nohyl explains that this is the video and camera arrangement that the Czech army uses most. The UAV’s recovery parachute is housed in a bay located in the center of the fuselage. The autopilot and fuel tank are located behind this area.

The Sojka is controlled from a ground control station housed in a portable shelter. It contains positions for a pilot, payload operator and commander. The pilot can use a manual control panel or a computer-based navigation system to direct the aircraft. Two screens provide real-time video from the aircraft, and a second monitor displays trajectory planning and graphic telemetry data. A portable control panel allows the pilot to visually launch and land the Sojka while standing outside of the control shelter. The shelter also can be used for operator training and mission simulation via software run through the operational equipment.

Nohyl notes that the control system currently does not have an automated take-off and landing feature; however, the system allows the UAV to be flown in semi- and fully automatic modes. A global positioning system transponder provides navigation capability to the craft. Additional data such as flight parameter graphics, trajectory planning, system status updates and post-mission analysis are displayed on the control system.

Flight plans can be pre-programmed before launch or while the UAV is in flight. Up to four flight plans can be stored in the ground control system’s computer. The pilot can switch between different plans during flight to react to a changing tactical situation. A moving digital map feature provides the UAV’s position location data to the pilot.

Constructed of fiberglass and composite materials, the Sojka UAV features a modular forward sensor bay that can house video and digital cameras. A built-in parachute allows the aircraft to land in rough areas and provides an emergency recovery capability in the event of a flight system failure.
Nohyl explains that the payload operator’s position is designed to maximize the user’s ability to locate, identify and describe a target in real time from a video stream or a still photograph. Reconnaissance data is sent to the commander, whose computer is linked to the Czech army ground forces tactical command and control system. This processed data can then be sent across the network to battalion headquarters. An Ethernet connection in the ground control station links the commander’s computer to the pilot’s and payload operator’s systems.

The Sojka system uses an ultrahigh frequency radio to transmit command and telemetry data and an L-band radio for analog video information. Depending on terrain and weather conditions, the real-time video transmission system has a maximum range of 60 kilometers (37 miles). Nohyl shares that this feature was confirmed during reconnaissance flights at 300 meters (985 feet). Work is underway to transmit video data in the C band, he adds.

Nohyl maintains that the Sojka system has been modernized in an incremental, evolutionary manner. The latest version of the platform consists of a smaller ground control station, a rocket-assisted launcher, a new datalink and a recovery vehicle. The launcher truck also has been modified to carry two partially disassembled UAVs. He adds that the VTUL a PVO also is experimenting with an advanced autopilot that features built-in autonomy systems with the ability to share airspace with other aircraft.


Web Resources
NATO aerospace and aerospace related information node:
The Czech Association of Research Organizations:


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