Retaining the Original Airframe and Systems
The Eclipse 500 evolved from the late 1990s' five-seat Williams V-Jet II. That experimental aircraft was commissioned by Sam Williams of the turbine engine company that bears his name and built by Burt Rutan's Scaled Composites in Mojave, Calif. The V-Jet II was conceived as a technology demonstrator intended to show off Williams' revolutionary 700-lb.-thrust FJX-2 turbofans that promised record low manufacturing costs and ultra-high fuel efficiency. Williams envisioned a twin-turbine VLJ that could replace light piston twins such as Beech Barons.
Raburn bought into the concept with great passion, ultimately founding Eclipse Aviation to bring it to fruition. Using the basic V-Jet II concept, Eclipse Aviation developed the all-aluminum Eclipse 500. Raburn chose aluminum over composites for the airframe because it was more efficient to fabricate and assemble parts for mass production. His dream was to build the Eclipse 500 in unprecedented quantities, thus making possible an $837,500 price tag.
Raburn raised hundreds of millions of dollars that he invested in new avionics technology, drag-cheating aerodynamics and high-volume manufacturing equipment.
Eclipse Aviation was the first U.S. civil aircraft manufacturer to use friction stir welding (FSW) to join aluminum parts. The process is used extensively for the pressure vessel and it eliminates about 60% of the mechanical fasteners in the airframe and slashes labor hours. Conventional mechanical fasteners are used exclusively to join nose and aft fuselage components. Pino and Holland intend to move one of Eclipse Aerospace's FSW operations to Poland.
Oliver Masefield, Ph.D., lead engineer on the program, tapped Ian Gilchrist at Seattle-based Analytical Methods Inc. to design the Eclipse 500's high-speed, laminar flow airfoil that was inspired by the NACA 65000-series wings of some 1950s' era U.S. Air Force fighter jets. The 144.4-sq.-ft. Eclipse wing has an 8.9:1 aspect ratio, a leading edge with no sweep and is tailored for good high-lift characteristics at low speed. Its drag divergence Mach number is 0.68, well above the aircraft's Mach 0.64 redline. That characteristic enables the aircraft to cruise efficiently all the way up to Mmo and it assures positive pitch stability at high speed. However, the junction between the deice boot and wing upper surface is not conducive to laminar flow, thus the wing has more drag than the wind tunnel predicted.
Functionally, the aircraft can be divided into four areas: (1) Avio IFMS avionics suite (see avionics sidebar), (2) thrust control (see engine sidebar), (3) essential systems and (4) mechanical flight controls.
Most normal systems are controlled through dual aircraft computer system boxes tied into the Avio IFMS, making it one of the most integrated avionics and control systems ever installed in a business jet. Systems that are controlled by the Avio IFMS include engine fire extinguishing, fuel, electrical, electronic circuit breakers, environmental, pressurization, ice protection, normal landing gear operation and exterior lights.
Essential systems not controlled by the Avio IFMS include the batteries, certain stand-alone circuit breakers, oxygen, emergency gear extension, cabin pressurization dump and the emergency locator transmitter.
The mechanical flight controls include the ailerons and elevators that are actuated by side-stick controls, a rudder that is operated by foot pedals and electrically actuated trim tabs and trailing edge flaps operated by switches.
The side-stick controls free up knee room and make it easier to climb into and out of the crew seats. The lower instrumental panel has slide-out multifunction keyboards that extend toward the pilots' knees and control CNS functions, FMS programming and EFIS reversionary modes, among other functions.
Masefield was no fan of spring or servo tabs, devices that are used to reduce control force. As a result, the Eclipse 500 has relatively hefty roll control effort at high speed. Unless spring or servo tabs are fitted to the Eclipse 550's ailerons, it too should have relatively heavy roll control forces.
Brushless DC linear actuators are used to move the trim tabs and flaps. They also operate the nose and trailing-link main landing gear and air-conditioner ground vent doors. Tamagawa Seiki now supplies these components and they have proven to be highly reliable and are virtually maintenance free.
The wheel brakes are hydraulically actuated by the rudder pedals. There is no anti-skid system and the twin PW610F-A turbofans produce considerable idle thrust after landing touchdown. The nosewheel steering also is mechanically operated through the rudder pedals, providing up to 15 deg. of steering authority. The nosewheel will free caster beyond 15 deg., thus differential thrust and braking can be used to turn tightly in confined areas.
The Eclipse 500 was one of the first light jets to use separate batteries for engine start and for avionics and systems power. The architecture prevents power surges to the Avio IFMS and supports a true split bus electrical distribution system after engine start. There are 127 electronic circuit breakers that are controlled through the Avio IFMS. There also are mechanical circuit breakers for the left PFD and left aircraft computer system, plus some optional equipment.
The 22-amp/24-VDC sealed, lead-acid batteries are mounted in the nose bay to offset the weight of the engines. This results in relatively long electrical cables running aft to the engines' 200-amp/30-VDC starter/generators. In addition, battery heater blankets are needed to assure optimum battery performance. Even so, the start battery works hard to crank the engines for start. Battery-only engine starts are allowed only at oil temperatures above 5C/41F. GPU-assisted engine starts are allowed only at oil temperatures warmer than -20C/-4F. Below that oil temperature, engine starts are not permitted.
Each engine has its own fire detection loop and fire extinguisher bottle. Some other FAR Part 23 light jets only have one fire bottle for both engines. The Eclipse uses a proprietary fire extinguishing agent called PhostrEx, a phosphorus tri-bromide compound that catalytically binds with essential combustion ingredients to poison the flame chemistry. It's ozone friendly, but once used it's also highly corrosive unless washed away from engine parts with fresh water. Early PhostrEx bottles were prone to leaking and replacement canisters were not readily available. Eclipse Aerospace redesigned the bottles to prevent leaking and relocated the filler ports to the top of the canisters. With these modifications, the PhostrEx bottles on the Eclipse 550 should be problem free.
The 8.33 pressurization system is fully automatic. The IFMS provides a landing field elevation input so that no crew input is required. A vapor cycle air-conditioner cools the cabin and engine bleed air furnishes the heat. Dual zone temperature controls are provided for the cockpit and cabin.
Pneumatic deice boots on the wing and horizontal tail leading edges provide ice protection. Anti-ice protection for nacelle inlets is provided by engine bleed air and electrical heaters protect the probes and windshields.
There is a 40-cu.-ft. oxygen bottle in the nose bay. The crew has quick donning, on-demand flow oxygen masks and the passengers have constant flow, drop-down oxygen masks available for use in case of cabin depressurization.