Hawker 850 XP Delivers Risk Free Improvement

However, as with all things in airplane design, there is a tradeoff when wingspan grows. Each increment of wingspan lengthening increases the bending loads on the wing root, and thus requires more structural strength to carry the loads. The issue is a matter of leverage. For example, if you hold your driver at the end of the grip, it will feel heavy. Pick up the same golf club near the center of the shaft, and it feels lighter. Your hand is absorbing the increased bending moment of the full length of the club shaft.

The increased moment, or leverage, of a longer wing multiplies the loads on the center of the wing, particularly when the effects of turbulence are considered, as they must be. At some point the loads of a long wing would be so great that the center of the wing would need to be far too heavy and thick to be efficient. That's why wings are a compromise between the aerodynamic efficiency of long span and the structural requirements to carry the bending loads.

But properly designed winglets can deliver many of the aerodynamic benefits of greater span with only a fraction of increased strain on the wing structure. The interaction of the winglet with the high-pressure air that flows out from under the wingtip is very complex, but in general, the air behaves as though the wing continued for a greater span. That's one of the reasons the most efficient winglets angle outboard.

Aviation Partners Inc., an aerodynamic design firm specializing in winglets that also created winglets for the Boeing 737 and other jets, turned its attention to the Hawker a few years ago. The people at Raytheon Aircraft, Hawker's parent company, considered making a deal with Aviation Partners, but decided to create their own winglets for new airplanes. Raytheon has experience with winglets on the Beech King Air 350 and also had the opportunity to optimize the Hawker winglet design for new construction airplanes without compromise that may be required to fit them to existing airplanes.

The Hawker 850XP winglets are made from high strength composites with a metal leading edge. Each winglet is 30-inches tall and angles outboard so its tip extends one and one-half feet further out than the previous Hawker wingtip, adding three feet to the total wingspan. The winglet does not require any ice protection, and it is faired into the wing in a continuous sweeping curve. A new lens covers LED position lights that have an expected life of at least 5,000 hours, which is important because it is the norm to turn on the nav lights whenever power is on the airplane, which is the way a Hawker awaits its passengers with the auxiliary power unit (APU) running to heat or cool the cabin.

The winglets on the 850XP use a "supercritical" airfoil with a deep cusp on the outer surface, which is the surface that corresponds to the bottom of the wing. A supercritical airfoil is one that minimizes the shock wave that forms when an airfoil reaches its "critical" Mach number. Critical Mach is the speed of the airplane at which air, accelerating to flow over and under the airfoil, reaches transonic velocity and a shock wave forms. The sonic shock wave generates enormous amounts of drag, almost as though a wall were stretched across the airfoil. A supercritical airfoil suppresses the transonic shock wave with its shape, which features a quite flat upper surface and a deep cusp on the lower surface near the trailing edge. The high-pressure air expanding into the cusp rejoins air flowing over the upper surface at the trailing edge in a smooth manner that prevents the shock wave on the upper surface from growing.

The addition of winglets to the 850XP called for minor internal wing structural changes that have not added inspection or maintenance requirements. In fact, a variety of small airframe improvements enabled Hawker to extend the basic inspection interval of the airplane from 300 to 600 hours.

If the winglets perform as expected, the 850XP should climb quicker and fly further, and it does. At maximum certified takeoff weight the 850XP climbs to 39,000 feet in two minutes less than the model 800XP it replaces. Once level in cruise, the 850XP is as much as five knots faster, and because the extra speed comes from reduced drag, not more thrust, range goes up more than 100 nm.

Combining quicker climb and faster cruise improves block speeds, but really pays off when flying into a headwind. The winglets add four percent to the 850XP's still-air range, but can add more than 25 percent range when going upwind. For example, the 850XP can fly nonstop between Teterboro and San Francisco, a distance of 2,225 nm, with NBAA IFR fuel reserves against 57 knots of average headwind. That equals Boeing's prediction of 80 percent worst case. The Hawker 800XP could make the trip nonstop against only 58 percent worst-case winds. That's a 27 percent improvement.

The other noteworthy improvement to the Hawker 850XP is the addition of the Collins integrated flight information system (IFIS) to the Pro Line 21 cockpit. A computer file server unit with cursor controls gives 850XP pilots the ability to show Jeppesen charts on either of the two big 8-by-10-inch flat panel displays in the middle of the panel. It also shows enhanced map overlays, and en route real time radar and other weather information from a variety of providers.

The Collins Pro Line 21 system is a complete digital electronic system. What that means is that there are fewer wires and much smaller avionics boxes to handle all navigation and communications tasks. The various elements of the system communicate on digital buses, so in the 850XP there are a tiny fraction of the wires that you would find in a Hawker of a few years ago. And the system qualifies for operation in all international airspace as new requirements take effect.

Performance and the added safety of advanced avionics are very important, but what has made the Hawker line such an enduring success is the comfort of the cabin. And the 850XP has some improvements there, too.

The Hawker cabin is 5 feet 9 inches high and 6 feet wide, so even tall people can move around easily, and many can stand upright. Most Hawkers are completed with five articulating chairs and a three-place couch. The couch has been one of the most popular features of the airplane. The one rap on the Hawker cabin has been that all luggage must be stored inside, but that isn't much of an issue anymore. The forward baggage area now has 33 cubic feet of space because avionics boxes that used to take up space in the compartment have now become so small they are mounted in the nose or other out of the way areas. In the 850XP, Hawker moved the couch from the right rear of the cabin to the left, and that opens up the rear baggage compartment to 16.5 cubic feet. The aft lavatory remains the same comfortable size, and is fully enclosed and private.

The comfort of the cabin extends forward into the Hawker cockpit. Because the flight management system (FMS) control units are angled out from the center of the instrument panel, the Hawker has the shortest center pedestal I can think of. That means you can get into either pilot seat without a gymnastic maneuver to hurdle the pedestal. Once seated, the standard IPECO crew seats have more adjustments than I can remember, and there is plenty of room for the tallest or portliest pilot.

Whenever I walk around a Hawker, or climb into one, I can't get clichés such as "built like a tank"out of my mind. Is that a cliché if it's true? In the case of the Hawker, it is. The engineers at de Havilland in England, who created the original, must have owned stock in an aluminum company, because they sure used a lot of it. The airplane is so rugged that it is approved for operating from sod and gravel runways, something extremely rare for a jet. And as far as I know, the Hawker is the only business jet to take a hit from a ground-to-air missile and continue to a safe landing.

The extremely conservative design philosophy continues into the systems. The flight controls are the old-fashioned kind of fly by wire, where thick steel cables connect the controls directly to the pilot's hands and feet. If, for example, the primary hydraulic system should somehow fail, you can lower the gear and flaps with a backup system that has its own lines and its own reliable source of power-the copilot on a hand pump. The airplane even has a pitch trim wheel that you can move by hand, or at least watch spin as you use the electric thumb switch. Mechanical trim systems are rapidly disappearing from jet cockpits and though I don't really miss them, its presence in the Hawker is emblematic of a very conservative design philosophy. What the robust structure and straightforward systems really add up to is predictable maintenance and dispatch reliability. The Hawker 800 series has enjoyed good success in the demanding fractional jet ownership programs.

Flying the 850XP is a pleasant combination of the familiar and the new. The ram's horn control yokes, the big air brake handle and the large nosewheel steering tiller all fall to hand. But in the panel are the four big Pro Line 21 flat panel displays and the FMS controls in the center. There isn't a radio tuning knob in the airplane because every bit of data, including frequencies, is entered into the FMS. The Collins system uses a scratch pad entry format, so you type in whatever it may be-a frequency, new nav fix, squawk code-and then use a select key to put the entry in the desired place. I like the way it works. You can start typing as soon as you get a new frequency or whatever without needing to put the cursor in a specific place. The previous version of the cockpit had radio control units with knobs, but they just weren't used so they were eliminated in the 850XP.

The Hawker is one of the few airplanes where you can fill the fuel tanks and the seats and still be within certified takeoff weight limits. A typical 850XP has a basic operating weight of 16,245 pounds, including two pilots, their gear and cabin stores. The tanks hold 10,000 pounds of fuel and that leaves 1,875 pounds for passengers and baggage. At the business jet standard of 200 pounds per passenger, that's more than nine people. For my evaluation of the 850XP we had 5,180 pounds of fuel and two passengers, bringing our takeoff weight to just under 22,000 pounds. The Hawker is not the short field champ of the midsize jets, but on a warm day in Wichita we needed 4,250 feet of runway to balance the field for takeoff.

The nosewheel steering and brakes are exceptionally smooth in the Hawker, so you won't jiggle your passengers' drinks on the way to the runway. The engine computers take care of setting power, so it's levers full forward for takeoff. Should an engine fail, the computers automatically increase the output from the remaining engine, and a rudder bias system driven by bleed air from the operating engine steps on the proper rudder to help you hold the airplane straight. All Hawkers have one unusual flying quality and that is at rotation, where the control yoke feels as though it were connected to the elevator by rubber bands. At Vr speed you haul way back on the yoke and in a second or two the nose rises smoothly. As the nose comes up you move the yoke forward and from then on all control inputs generate a smooth and precise response. The Hawker is not a finger tip flyer, but it is easy to fly smoothly.

Once up and away I reduced power until the word "climb" appeared near the N1 fan speed indication on the Pro Line 21 display and left the levers alone. And climb the 850XP does, going up initially at 3,700 fpm. In nine minutes with air temperature 12 to 14º C above standard, the 850XP was through 26,000 feet and four minutes later we were at 35,000 feet. The unrestricted climb to cruise at 38,000 feet took just 15 minutes. The performance was better than the handbook predicted and better than what I remember from earlier Hawkers. Level at FL 380 the 850XP accelerated to Mach .79 with a true airspeed of 449 knots. The acceleration after level off is also quicker thanks to the winglets. The new winglets do not change the predictable flying qualities of the Hawker at high or low speeds. I made a simulated emergency descent with airspeed right at the Mach limits and with the overspeed warning complaining occasionally, and there was no vibration or any other indication that the winglets were there. At the slow end the winglets may provide a little more lift, but not enough to notice or change maneuvering or approach speeds.

The Hawker has effective and large wing flaps, so typical landing approach speeds are around 115 knots and runway requirement is under 3,000 feet. The Hawker is a very easy airplane to land smoothly and is one of the first, if not the first, jet to have a lift dump system. When the main wheels touch you pull way back on the big speed brake handle and the flaps quickly deploy to 75-degrees down and the spoilers extend. Lift dump really plants the airplane on the runway for braking efficiency, and the drag of the huge flaps means you almost never get the thrust reversers out of idle power before you are turning off. The 850XP is, like the Hawkers that came before, a very effective mixture of technologies. The Pro Line 21 cockpit is on the cutting edge, but the basic airframe is more mature than any other business jet still in production. The basic wing is strong and efficient, but with the new winglets is better. When you look at the panel you could think the 850XP is a newly designed airplane. And with the rakish winglets, you could think the same when you see an 850XP on the ramp. That's what has made the Hawker a great airplane over so many decades. The parts that can be improved have been continuously so, but the solid core of a stout airframe and comfortable cabin have been there from the beginning.