THE PROBLEM WE’RE SOLVING
Autonomous landing has proven to be one of the more difficult aspects of unmanned aviation. There are, of course, many variables involved in landing an aircraft of any kind. In addition, there are potential problems caused by winds, weather, dust, runway incursions and the like. Runway conditions themselves can change; even on paved surfaces, the available traction for braking changes with dust, ice and loose dirt. During a manned-flight, these variables and factors are all controlled for and adjusted for by the pilot. During unmanned flight, the aircraft must have the capability to make split-second decisions both autonomously and in reaction to operator input.
WHAT WE’RE DOING
Latitude has approached this problem with four discrete but overlapping strategies.
The AGL Sensor line of products was Latitude’s first development aimed at this problem set and it was our first commercialized product. It uses laser range-finding to provide very precise altitude measurement during the period of the flight when the aircraft is at its closest to the ground, i.e. during takeoff and landing. Later, we developed and now produce touchdown sensors designed to work on fixed-gear aircraft. These sensors detect the flex of the landing gear and communicate this information to the autopilot allowing it to sense when the aircraft has touched down on the runway–signaling the autopilot to transition the control laws from flying to steering.
Latitude has also designed control algorithms that select among available altitude data (including GPS, barometer, and Latitude’s laser AGL Sensor series), in order to determine sensor reliability, and make autonomous abort decisions if necessary. We have developed control logic allowing maximum performance landing aborts, allowing the abort decision to be made by the autopilot or the operator, all the way down to touchdown.
Finally, in order to provide maximum stopping performance on all surfaces once the aircraft has successfully touched down, Latitude has developed an anti-lock brake system for UAV’s. Once wheel lock-up is detected, the brakes are modulated to maintain control and optimize braking capability.
Currently, both the touchdown sensor and the anti-lock brake system are wrapped up in the main landing gear assembly Latitude now produces for the latest model of the Tigershark UAV.