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.