Embraer’s Executive Vice President of Executive Jets Luis Carlos Affonso unveiled more details of the fly-by-wire (FBW) systems that will control the company’s next airplanes—the Legacy 450 and Legacy 500. The 500, a mid-size jet and the 450, a “mid light” jet, to use Embraer parlance—will be the smallest business jets to use FBW systems. Instead of the conventional cables and pulleys of a mechanical flight control system, the FBW system in the 450 and 500 uses digital commands from onboard computers to generate movements of the airplane’s ailerons, elevator, rudder, and thrust levers. Autothrottles will be standard in both models.
While Parker Hannifin will provide the hardware and software, Embraer developed its own control laws for the FBW system. These include both normal and limit flight envelope conditions. In the normal flight envelope, “soft limits” are +30 degrees/-15 degrees for pitch, 33 degrees for bank angle, and a 1.1 Vs minimum flight speed. Embraer calls these “soft limits” because pilots can still command attitudes beyond them—but continuous stick pressure is required. The limit flight envelope imposes hard limits, and prevents the airplane from exceeding limit G-loads, airspeeds, and stall angles of attack. This means that the pilot can fly any pitch or bank angle, for example, provided that G-load and controllability limits are observed. In an emergency climb situation, Embraer says that with full aft stick the airplane will pitch up as quickly as possible, always observing maximum normal structural load factors, until the angle-of-attack limiter kicks in, preventing a stall and yet allowing the airplane to achieve best rate of climb, assuming full power.
There are other helpful aspects to the control laws, Embraer says. A pilot can command and maintain a 45-degree bank angle, for example, but once the control stick is released, the airplane will return to a 33-degree bank. Moreover, the angle-of-attack limiter allows lower margins over the airplanes’ stall speeds, which consequently lowers takeoff and landing speeds and distances.
Affonso said that Embraer was “designing a pilot’s airplane” in that “we leave everything to the pilot, unless you go beyond the airplane’s limitations. Bob Hoover would be able to do one of his rolls in an Embraer 450 or 500, because he never exceeded normal flight loads.”
Affonso also said that the 450 and 500 will do away with Embraer’s signature ram’s-horn control yokes, in favor of side sticks. The $18.5 million Legacy 500 should be certified by late 2012; the first of the $15.5 million Legacy 450s is due to be delivered in 2013.