The third phase of flight tests has begun on the Boeing/NASA X-36 tailless-fighter research aircraft at Edwards AFB, California, after "exceptional" agility was proved in its first two flight phases, says the test team.
By the end of September, the X-36, a 28%-scale remotely piloted vehicle, had accomplished 10h 54min of flight time over 22 sorties. It had also reached maxima of 4.86g, 40¹ angle-of-attack, 177kt (330km/h) airspeed and 20,500ft (6,250m) altitude. The first phase, from mid-May to late July, covered eight flights totalling 4h and verified control software, ground station, data system and air-data calibrations in preparation for more aggressive testing in Phase II.
This second phase looked primarily at "elevated g agility", with thrust vectoring on and off, says Boeing. The third phase, expected to cover ten fiights, will demonstrate the agility of the X-36 at lower speeds and dynamic pressures, at around 1g and speeds below 100kt. The thrust-vectoring system, which works in yaw only, will again be turned on and off. A projected fourth phase, still in planning, will explore the high-speed part of the envelope.
Modifications to the X-36 to date include revised software, to "-reduce the aggressiveness of the autopilot", revised aerodynamic-control surfaces and changes to the still-classified thrust-vectoring system, including a "new lateral-directional mixer".
Surprises so far have included the total loss of datalink several times on one flight, later traced to a faulty low-noise amplifier in the datalink ground antenna. Others include the need to modify the nozzle bay, to improve cooling, and to change the climb-out profile, to enable the gear to be retracted at speeds below 120kt after earlier problems which prevented operation at higher speed.
Source: Flight International