The 4000 wing is made from conventional metals, but its shape is advanced and is a major contributor to the airplane's capability. The span is just under 62 feet, and the sweep is a moderate 28.4 degrees. And the wing is big with 531-square feet of area. All of those contribute to the airplane's excellent performance, but the airfoil shape is probably most important. The airfoil is an advanced supercritical design that delays the onset of the Mach shock wave and moves it aft on the wing. That means that when the wing is flying at its high-speed cruise of Mach .82 the inevitable shock wave that develops as air accelerates to pass over the wing is minimized and so is drag. The airfoil is quite thick at its leading edge and forward section, which intuitively seems wrong for low drag, but that is key to high-speed cruise. The thick forward section also reduces structural weight because tall spar webs can be employed, and the extra space allows all fuel to be carried in the wing.
The wing has four degrees of dihedral, but most of it is in the inboard section. Like many advanced wings, the thick inboard section sweeps up dramatically while the outboard portion thins rapidly and levels out. The airfoil is able to deliver the low-speed performance without need for the weight and complexity of leading edge slats. Stall speeds are low enough that typical Vref final approach speeds are around 115 knots.
Much of the excellent low-speed performance of the wing comes from long-span flaps that extend over most of the trailing edge. The rather short ailerons are purely mechanical with no hydraulic boost, but their roll authority is augmented by spoilers that, after a small aileron deflection, join in to increase roll authority. There are three spoiler panels on each side, and two are used for inflight roll augmentation and speed brakes, and all six pop up automatically on touchdown or during an aborted takeoff to keep the airplane on the ground.
The elevator is also operated only with pilot muscle and the control forces are at an appropriate level for smooth maneuvering without a lot of effort. But, with so much thrust available, rudder forces after an engine failure are high and human strength just wasn't going to do the job. Most powerful jets have hydraulic boost for the rudder but the 4000 goes a step further with full fly-by-wire control. That means that rudder inputs by the pilot send electrical signals to a computer system that calculates the desired rudder movement, while multiple hydraulic actuators are then commanded to move the rudder.
The 4000 sits low on trailing link main landing gear, a first for the company. The main gear retracts into the intersection of the wing and belly fairing and is completely enclosed by gear doors, which is not the norm since most jets leave the wheel well uncovered when the gear is retracted. The gear is robust enough to make the best of my less than ideal landings, but more importantly, it allows for a high landing weight that is just 6,000 pounds below max takeoff weight.
The nosewheel tiller uses steer-by-wire technology and it is very smooth, making it easy to taxi the 4000 and maneuver on the ramp. The company chose to stick with tradition and did not include any nosewheel steering authority through the pedals, but the rudder is so effective that there is little or no need to use the tiller during the early part of the takeoff roll, or for rollout on landing.
Like many recently designed jets the 4000 fuselage sits atop its wing so there is no compromise in cabin space. This intersection demands a large fairing to control the high velocity slipstream at cruise, and in the 4000 the fairing doubles as a space to locate landing and taxi lights, fuel servicing panel, ducts and wires, and many other system elements that are kept outside of the cabin. The brakes use brake-by-wire technology so that no high-pressure hydraulics are routed inside the cockpit. When you press on the brakes you send an electrical command to computers that modulate hydraulic pressure to the carbon brakes. Some early brake-by-wire systems worked great for high-speed stops, but were grabby at taxi speed, but those issues are gone in the 4000. It's easy to make smooth stops from any speed without practice. And the carbon brakes are designed for 1,200 landings before replacement.
But it is with the fundamental airplane systems that Hawker Beechcraft has gone all out to raise the 4000 above the midsize jet level, to rival the very long-range large cabin jets in system redundancy for long, over water flights. For example, the electrical system meets all of the split bus isolation requirements of any recently designed transport airplane, of course, but it also has at least four sources of power generation. Big oil-cooled alternating current generators on each engine promise very long life compared to the typical starter-generator on midsize jets. Added to that is a generator on the APU that can start and run up to 35,000 feet in case both engine-driven generators are lost. If things really go bad there is a fourth generator powered by the hydraulic systems that can keep the airplane going to reach a suitable airport.
The environmental system is also redundant with two independent air cycle machines to condition the pressurized cabin air, and either one can carry the load. The hydraulic systems are also dual and totally independent, so no essential functions are lost after a pump failure. Power transfer units send hydraulic muscle to the failed system without compromise of the operating system. If both hydraulic systems were to somehow fail there are accumulators for wheel brakes after landing. The airplane is clearly designed for global operation.
Pulling all of these systems together is the Honeywell Epic network that monitors and reports the health and actions of just about everything in the airplane on the engine indicating crew advisory (EICAS) display in the center of the cockpit. If a circuit breaker pops, for example, you get a plain language message on the display. Want to know the position of any control surface, including individual spoiler panels, flaps or even gear doors, the system can show you. Every parameter of system operation is available for display to the crew, and is also recorded in the central maintenance computer that reports what went wrong and when. The fix is to exchange a line replaceable unit (LRU) that takes only a few minutes and requires no special tools. It is this combination of monitoring and designed-in maintainability that gives the 4000 a maintenance interval of 600 flight hours.
The 4000 carries the dark cockpit concept to the highest level I have seen so far. The idea is that when everything is normal there should be no annunciator or other lights displayed in the cockpit. In the 4000 even the normal system control buttons are darkened when in normal position. For example, the windshield heats are turned on before takeoff and left on at all times, so the button that controls heat is totally blank, unless you turn it off and then the word "off" lights up. It takes a few minutes to remember that for most switches there is no "on" indication, only a blank button if all is as it should be.
The Epic system in the 4000 uses five flat-panel displays. The screen in front of each pilot is the primary flight display (PFD) with all standard flight instrumentation and navigation progress data. In the center is the EICAS display that continuously shows engine and system status. In between on each side are multifunction displays (MFD) that each pilot controls and can be used to display everything from maps to traffic to system synoptics.
Dual flight management keyboards are in the pedestal and each pilot has a cursor control device at his outboard hand. The CCDs, which have a touch pad similar to a laptop computer, are used to select menus on the MFDs. Dual inertial reference units are standard, which is another unusual feature in a midsize jet, and the IRUs measure very precise attitude and flight path, and also provide independent navigation capability should the dual GPS sensors somehow fail.
The 4000 cockpit doesn't have the snazzy map graphics, chart overlay and satellite weather yet because the company has been concentrating on completing the fundamental system certification, but those features will come along. The system does meet required navigation performance (RNP) standards so the airplane qualifies for operation in any global ATC environment.
To see the 4000 in action we planned a flight from Beech Field in Wichita to Aspen and back. We had two passengers and 7,000 pounds of fuel to bring takeoff weight up to 30,950 pounds, well below the maximum of 39,500 pounds. Available payload with full tanks is 1,600 pounds, so all eight standard seats can be filled. However, the 7,000 pounds of fuel was plenty for a high-speed flight halfway across the country to Los Angeles from Wichita so it was actually a pretty typical fuel load. The fuel planning rule of thumb for the 4000 is to burn about 2,600 pounds in the first hour, 2,000 in the second and about 1,800 pounds an hour after that for an endurance of over seven hours at Mach .82 cruise with full tanks. The temperature in Wichita at 25° C made the required takeoff runway just 3,355 feet.
The Pratt PW308A engines are rated at 6,900 pounds of thrust each, and have the capability to produce all of that thrust up to an air temperature of 37° C at sea level. That means you get full power on the hottest day, and a big chunk of rated power on a hot day at a high elevation airport. The engines are, of course, controlled by full-authority digital engine computers (fadec) so all starting and operating parameters are automatically controlled. However, the 4000 has an autothrottle system as standard -- another midsize first -- so pilot workload is further reduced because the autothrottle maintains the desired airspeed.
For takeoff you engage the autothrottle and advance the levers about halfway, and then the system takes over to set the power. With the high bypass fan design of the PW308 engines, acceleration is very brisk and we were quickly at the 111-knot rotation speed. The pitch response of the airplane is totally predictable and it's easy to rotate to the desired target and hold it. The real challenge is to keep from blowing through the 200-knot airport area speed limit, but the autothrottle helps take care of that by bringing the power back in advance of leveling at the assigned altitude.