Imagine an airplane — or house or car or spouse, for that matter — that you have loved for decades but over those years you have wished for some changes and improvements in key areas. The Hawker line of business jets has been admired by legions of pilots and passengers for more than 40 years, and it continues to be a huge success. But many want more of the good things the Hawker delivers, and that’s why there is a new Hawker 4000. The new 4000 does everything the Hawker is famous for, and a lot more.
Cabin comfort has probably been the most consistent strength of the Hawkers over the years and that was the starting point for the new 4000. To make the cabin even more comfortable the 4000 has a flat floor throughout, and six-foot headroom making it comfortable and easy to stand and move about.
The big 4000 cabin — one of the first of what we now call the super-midsize business jets — also has the room for a full capability galley, and a large, comfortable and private lavatory. At 25 feet in length, the 4000 cabin intrudes on the domain of the large cabin business jets.
Over the years pilots and passengers have had a love-hate relationship with the Hawker baggage compartment that is located in the forward cabin. Passengers liked the ability to access their stuff in flight, but loading the bags through the cabin door can be a hassle. The 4000 resolves that issue with a big baggage compartment located aft of the lavatory. The crew can load the bags through a low and easy to reach hatch in the tail cone without a ladder, but passengers can still access their gear in flight through a door in the bulkhead aft of the lavatory. This is not new to business aviation, but has previously been reserved for only the truly large cabin jets.
Over the decades the Hawker was refined and increased in range and performance to become a transcontinental airplane under all but the strongest headwinds. But everybody wants more range so that domestic trips are never a question, Hawaii is always within reach from the west coast, and crossing the Atlantic is routine. So the new 4000 has 3,000 nm of range even when flying at high-speed cruise of Mach .82.
But cruise range is more than simply how many miles you can fly at optimum cruise altitude with the fuel available. The usable range calculation is the result of how much runway you need with the fuel weight on board, and how fast you can climb to the fuel-thrifty optimum altitude. The new 4000 has both excellent climb capability and among the shortest runway requirements in the category.
When the runway is long and the air temperature cool all jets can live up to their maximum range potential, but the real world of business jets takes them to some pretty short runways in challenging parts of the world in terms of elevation or terrain considerations. An interesting example is Hilton Head, where the runway is just 4,300 feet long and the weather is usually warm, at least when most people want to be there. Since all business jets have a required minimum runway length that accounts for an engine failure at the worst possible point in the takeoff profile, the actual takeoff weight of the airplane is critical. If there is not enough runway available, takeoff weight must be restricted so the airplane can stop on the pavement after an engine failure, or continue safely on the remaining engine. That means fuel or passengers, or both, must be left out to comply with the takeoff requirements on a short runway. Warm temperatures complicate the situation by cutting into the power potential of the engines and by reducing the lift production of the wing.
But at the short Hilton Head runway with six passengers on a warm 30° C (86° F) day, the Hawker 4000 can carry enough of its total fuel to fly to San Francisco against the historic 85 percent probability winds. This is an impressive performance for any midsize jet, super or otherwise.
Another challenging, but very popular, destination is Aspen, where the 7,815-foot elevation robs jet engines and wings of performance. The problem is particularly acute in the summer when warm temperatures amplify the loss of performance. But a Hawker 4000 crew can load six standard 200-pound passengers and depart Aspen on a 90° F day and cruise at high-speed Mach .82 to Teterboro or White Plains near New York City. Again, historic winds are considered, and again, this is a trip beyond the capability of most business jets.
A key to the Hawker 4000 range is its climb capability that gets it to fuel-saving altitude quickly. After a maximum weight takeoff the 4000 can be through 35,000 feet in 13 to 14 minutes, and be at 41,000 feet in under 20 minutes. And that is climbing at 280 knots at the lower altitudes, and transitioning to Mach .76 to .78 above 30,000 feet. That means the 4000 is going toward the destination at about 440- to 450-knots true airspeed in the climb. That is faster than many midsize and smaller jets cruise.
So how does the 4000 deliver all of this cabin comfort, speed, range and runway performance? The answer is that it’s not easy. In fact, it proved to be much more difficult than anybody at Hawker Beechcraft — then a division of Raytheon — imagined when the program was announced in 1996. The original and overly ambitious development schedule had the 4000 completed and in service by the year 2000 or early 2001, and that just didn’t happen. There is no one single development issue that accounts for the delays, but it was system development and avionics integration that really stretched out. The airframe structure and aerodynamics development moved along as predicted, but creating an all-new transport category jet that was first to encounter many new FAA certification rules delayed the program for years. The devil was in the details.
To achieve the performance and cabin comfort objectives of the Hawker 4000 — originally named the Horizon until 2005 — the company knew it would need to employ new and advanced technologies. What looked to be the most advanced, and perhaps riskiest part of the program, was the decision to build the fuselage entirely from carbon fiber composites. Beech had pioneered development and certification of composite primary airframe structures with the Starship, a turboprop pusher that missed many of its weight and performance targets. But the Starship program taught the company, and the industry, as much what not to do with composites, as in how to use them.
What the company learned is to use composites where they can deliver the greatest advantages, and to automate the production of those components. Using composites for the fuselage offered the promise of perhaps weight savings, but more important the thinner structure of the carbon fuselage delivers more usable cabin space compared to the outside dimensions of the fuselage. The 4000 fuselage has an external diameter of 84 inches, and the finished interior cabin size is 77.5 inches, so only 6.5 inches is used by the carbon structure, insulation and other wires and ducts that go between the structure and the finished interior. No other jet manufacturer offers comparable measurements, but it certainly appears that the 4000 achieved its goal of having the smallest possible fuselage, and thus the lowest drag, for the greatest usable cabin space. The strength to weight ratio of carbon also contributes to the high 9.6 psi pressurization differential that keeps the cabin at 6,000 feet when the airplane is flying at its ceiling of 45,000 feet.
The fuselage is built in three sections by exotic machines that wrap individual carbon fibers over a mold called a mandrel. The fibers are placed only where they are needed for strength, and their orientation is along the load paths. For example, the machine will wind additional fibers around a window or door cutout to carry the loads transferred by those openings. The complete fuselage sections, mandrel and all, are baked at high temperature to cure the composite. The entire process eliminates unneeded resin that can add useless weight, and assures uniform strength through the production process. The three sections of the fuselage are joined by high-strength metal hoops that are placed so that they provide anchor points to attach the wing to the fuselage. The exterior of the carbon composite is filled and sanded to perfect smoothness.
Is the carbon fuselage lighter? It seems so because a person can lift one end of a fuselage section single handedly. But the company never designed or built the fuselage using conventional metal techniques so there is no certain comparison. Boeing is a believer and is using a similar design for its new 787 for many of the same reasons.
Hawker Beechcraft also uses composite material for skins on the tail. Both the horizontal and vertical tail elements have aluminum spars and ribs that are skinned with carbon material. Composites are also used for fairings and other components in the 4000. In place of the “all composite” mindset of the Starship, the company has clearly learned to employ the material where it makes sense, and can deliver a useful benefit in terms of manufacturing and airplane performance.
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.
We had two brief level offs at lower altitude but at 15 minutes after takeoff the 4000 was climbing through 37,000 feet, despite air temperature that averaged 5° to 10° C above standard. With the autothrottles locked onto a Mach .78 climb speed, the 4000 was going up at 1,800 fpm through 40,000 feet, where the temperature had dropped to standard, and at 20 minutes after takeoff we were level at 43,000 feet despite the two intermediate altitude assignments. Acceleration from climb to high-speed cruise of Mach .82 took barely a minute and we settled on a true airspeed of 471 knots with total fuel flow of 1,800 pounds per hour.
After a few minutes we asked the flight management system for max cruise and the 4000 accelerated to Mach .83 for 477 knots true on 1,900 pounds of fuel flow. Even at that speed the airplane was moving through the air .251 nm for every pound of fuel burned for a remarkably good specific range. The wing is so efficient at Mach .82 or .83 that very little range can be gained by slowing down, so I doubt many 4000 pilots will, unless they need to stretch for the last couple hundred miles of a very long trip.
The very smooth contours of the carbon fiber fuselage, and the way the windshields have been blended into the sophisticated canopy shape, makes the cockpit very quiet even at maximum indicated airspeeds. The same is true in the cabin where sound pressure levels measure well below that of many other jets. The cabin sound level is so low, in fact, that people from one company that went on a demonstration flight asked if an acoustic curtain could be installed between the fore and aft seating groups because normal conversation from each area could be heard by all. If there is such a thing as being too quiet, maybe the 4000 is approaching that level, but I’m sure most are going to be more than pleased with the very low sound and vibration levels.
Pressurization controls are fully automated with the system consulting the database for both departure and arrival airport elevations. It was interesting to watch the system in action while approaching Aspen as it gradually raised the cabin altitude from the cruise level of around 5,000 feet to smoothly meet the 7,800-feet elevation at Aspen with no bumps in the pressure, nor intervention required by the crew.
For the return trip from Aspen to Beech Field we added fuel to bring the total up to 5,050 pounds so our takeoff weight was 28,845 pounds. It was a beautiful summer day in the Rockies with the temperature at 23° C, which is about 22° C above standard, so the density altitude was very high. Despite the conditions the 4000 needed only 5,060 feet of runway for a balanced field takeoff and we could have easily added enough fuel to fly to any point in the lower 48 states.
This time the controllers kept clearing us higher with no steps and we were at 45,000 feet in 17 minutes after takeoff. Yes, we departed at nearly 8,000 feet, but that is still impressive. With temperatures a little below standard the 4000 quickly accelerated to Mach .82 for a true airspeed of 465 knots on just 1,640 pounds of total fuel flow. At that level we were covering .272 nm for every pound of fuel burned.
Overall the flying qualities of the 4000 are precise and predictable at any altitude or airspeed. The speed brakes are linear, meaning they respond to the amount you move the handle, and can be used at any airspeed or altitude. I tried steep turns and found that with a little practice — and by watching the flight path indicator — I could hold altitude to the required stand-ard. Approach to stalls are a nonevent with loads of power to accelerate away from the stick shaker warning.
Learning to land the 4000 does, however, take a little practice. Unlike most jets, the deck angle on approach is level, or perhaps even a little nose down. To make a good landing you need to make a sort of round out 100 or so feet in the air, and then let the airplane settle. It’s not really a flare, but more a leveling of the attitude. With the confusing visual illusions of the mountains and uphill runway at Aspen for my first landing, I didn’t get it right and banged the airplane on. The automatic ground spoilers did their job and kept the airplane firmly on the runway for an easy rollout. Back on the level land at Wichita I got the hang of the sight picture on very short final and turned in a decent landing. With a little practice, and the long stroke trailing link landing gear, 4000 pilots will be rolling the airplane on. There was a 90-degree crosswind gusting to 18 knots for my last landing and it worked out just fine, so the airplane surely has the capability and control authority to handle demanding conditions.
Hawker Beechcraft has a dedicated team of service reps to smooth entry of the 4000 into service and plans to ramp up production gradually to a rate of about 30 per year. More than 130 are on order, and 2010 is the next available gap in the delivery schedule.
It’s been a long road for the 4000 but in the end the airplane delivers. It was the first airplane to be announced in the super midsize category, and in terms of performance, cabin comfort and system redundancy the emphasis certainly ended up being on the “super.” For everyone who has loved the Hawker and wanted more, the 4000 is the one.