It takes time to work the bugs out of most all-new airplane designs, and the Beechcraft Premier is no exception. The Premier's design goals of being the fastest light jet with the largest cabin cross section were accomplished when it entered service in 2001, but it is now, with the IA version, that the Premier is hitting its stride as a mature design.
The Premier is a pioneer as the first business jet to use carbon graphite epoxy as primary structure. The Premier fuselage is made from carbon fiber while the wing is constructed of conventional aluminum alloys. The carbon fiber fuselage probably saves some weight, but more importantly, it allows for a larger interior cross-section size for a given external dimension because the composite structure is thinner than a conventional metal fuselage. Boeing is using a similar scheme in its new 787 Dreamliner.
The Premier cabin is 5 feet 5 inches high, which provides a half a foot more headroom than other light jets. The extra diameter of the circular cabin translates into an even greater advantage in cabin width, particularly at the floor level. The cabin cross section of the Premier is actually closer to that of a conventional midsize than to the competitive light jets.
However, the size advantage of the Premier was ill used in the original cabin design. Routing of air ducts, wires, controls and other necessary items was not optimized, so they claimed usable cabin space. The headliner with its lighting panels did not maximize the headroom the fuselage structure offered. And the window reveals that surrounded the very large cabin windows were sort of a retro automotive-inspired design that made the cabin smaller, both visually and in reality.
The newly designed interior in the Premier IA now takes full advantage of the potential offered by the carbon fiber fuselage. What Beech did is copy the best of the interior design in its other airplanes and in the competition. The sidewalls are now smooth, one-piece elements that provide maximum shoulder room when seated.
Unlike some other light jets, you can sit upright without your shoulder, or your head, being squeezed inboard by the curve of the fuselage.
The window openings are maximized for visibility and to enhance the spacious feeling of the cabin.
Overhead Beech created a smooth headliner without the protrusions of the original. The environmental duct work that took up cabin space has been redesigned and offers improved temperature control, and soft light washes down the sidewalls from the new headliner. While the original cabin design was dramatic, perhaps even gaudy, the IA cabin is subtle and elegant, with obviously only top grade leathers, wood veneer and carpet.
It is the wing, the wing to fuselage fairing, and the shaping of the aft fuselage that controls drag and gives the Premier its Mach .80 maximum speed and 451-knot high-speed cruise.
The Premier wing is quite small with only 247 square feet of area and a span of 44.5 feet. That equals a moderately high aspect ratio of 8.6, meaning the chord is fairly narrow compared to the span. In general, a higher aspect ratio wing with small area is lower in drag. Additional drag control at high cruise speed comes from the 20-degree leading edge sweep that helps to control the formation of a Mach shock wave when the airplane is operating at nearly 80 percent of the speed of sound.
There are, as always, tradeoffs, and the small, slender wing does add complexity. Because wing loading-the amount of weight carried by each square foot of wing area-is fundamental to stalling speed, a small wing will stall at a higher speed than a larger one. To overcome that the Premier has large Fowler flaps that occupy most of the trailing edge of the wing. The wing is of the "cranked" design, meaning that the trailing edge is straight at the root and then sweeps back to mimic the sweep of the leading edge. With a cranked wing the flaps must be segmented into inboard and outboard sections. The Premier flaps are made from composites and are electrically actuated.
Because the flaps take up so much of the trailing edge of the wing the aileron is quite small, not large enough to provide all necessary roll control on its own. The solution for the small aileron is to augment the roll authority with spoilers. After 10 degrees of aileron travel, the spoilers on the down-going wing start to rise to provide more roll authority. This system is common in virtually all larger jets, but is rare in a light jet, and is transparent to the pilot when flying.
As with most modern business jet designs, the Premier fuselage sits atop the wing so the spar does not intrude on the cabin. This is great for cabin room, but is a challenge to the aerodynamicist to create a fairing that joins the fuselage to the wing with the lowest drag. Because the Premier fuselage is so big around compared to its length, the wing-to-fuselage fairing needs to occupy most of the available fuselage length. Many have commented that the fuselage fairing gives the Premier a "pregnant guppy look," but its design is very state of the art. All modern jet designs have a similar fairing, but it doesn't stand out as much as on the Premier because there is so much fuselage ahead of and behind the fairing. The shape of the Premier fairing never bothered me because I understand its objectives and even appreciate the skill the designers applied, but not all pilots agree. In another improvement to the IA, Beech paint designers have created schemes that minimize the appearance of the fairing and, along with people growing more accustomed to the shape, should help the Premier look more conventional.
The aft fuselage of the Premier is another example of drag control shape that appears extreme because of the short but wide fuselage. Ahead of and inboard of the engine nacelles there are very deep hollows that are called "area ruling." The area rule was developed early in jet design and, in general, states that total area of a body is more important than the shape when it comes to creating drag. In the case of a jet with engines mounted on the fuselage as in the Premier, the presence of the engines increases the area of the aft fuselage. To minimize the drag created by the extra area of the engines, Beech scooped big hollow areas out of the aft fuselage so the total area remains as constant as possible. Many jets apply the area rule near the engines, but the shape is more dramatic in the Premier because of its wide fuselage.