When it was launched at the 1990 National Business Aircraft Association show in the USA, the PC-XII was offered as a high-performance, low-operating-cost corporate/utility aircraft. Now, Pilatus is working with other large single-turboprop manufacturers Cessna and Aerospatiale to modify the certification rules so that the aircraft can be operated commercially under instrument-flight-rules (IFR) conditions.
This would immediately open up the potentially lucrative air-taxi and light-commuter markets in which the PC-XII, because it presents a unique mix of size, performance and operating cost, would effectively have the market for new aircraft in its category to itself. Pilatus product manager Ed Flohr denies, however, that the PC-XII is a "niche" product. "We can compete with a range of aircraft because of our differential advantages of cost and size."
Canada already allows commercial use of single-engine aircraft in IFR conditions, and the USA is expected to follow with Europe a belated third, possible even fourth, behind Australia. "We're optimistic," says vice-president of engineering, Oliver Masefield, "that we'll have these approvals in the medium term, maybe within a couple of years."
Meetings with the joint US Federal Aviation Administration/European Joint Aviation Authorities working group have included a recent presentation of the PC-XII at Amsterdam's Schiphol Airport. "We wanted to show them the real thing," says Flohr, clearly confident that the aircraft's rugged design, and special safety features such as the wide centre-of-gravity range, and engine exhaust inlet de-icing system, will have a positive effect.
So far, 44 customers have ordered the PC-XII, with the USA accounting for 80% of sales. Five aircraft, have been sold to the Royal Flying Doctors in Australia, representing the first break from the present customer base, which mainly consists of owner/operators. "The USA is obviously the main market at the moment," says Flohr, "but we're beginning to mount a stronger marketing campaign in the rest of the world."
PRODUCTION RATE
Deliveries began in mid-1994, and amounted to ten aircraft by the end of March. The production rate will reach 26 aircraft this year, rising to 36 in 1996. Flohr sees, a medium-term sales potential, for 50 aircraft a year. Although there are "no hard figures" on the possible market size for the PC-XII, he adds that, "we think there may be a requirement for more than 600 aircraft".
The PC-XII is priced at $1.95 million, and there is an escalation clause to provide for inflation. This is for a standard aircraft, the price rising to around $2.2 million for the version tested by Flight International, which was equipped with electronic flight-instrument system (EFIS) flight displays for the co-pilot, global-positioning-system navigation and executive interior.
The price compares with that of the Aerospatiale Socata TBM700 turbine single, which is smaller, but cruises faster. In performance and seating capacity, however, the main competitor for the PC-XII remains the Beech King Air B200/300. Here, the single-engine design of the PC-XII gives it an advantage, yielding operating costs which Flohr believes will be only 60% those of the King Air.
The battle between the PC-XII and a twin-engine design such as the Beech raises the question of single-engine safety: "We have to prove that a single-engine aircraft is as safe as a twin," says Masefield. He draws a parallel with the extended-range twin operations (ETOPS) over-water rules which now allow twin-engine transports to cross the Atlantic every day. "The state of the art of turbine engines is such that the Pratt & Whitney Canada PT6, with an average 100,000h between in flight shutdowns, can be considered reliable enough for single-engine commercial passenger operation." He adds that, while the PC-XII was not originally considered for single-engine commercial IFR use, "...we are delighted that it may be able to compete in this market".
Swiss certification of the PC-XII was delayed by six months, to March 1994. "We decided that modifications were needed shortly after the first prototype flew in May 1991," says Masefield. "We could not get satisfactory handling at very high lift coefficients. By December, we had established that a revised wing was necessary." A stick pusher would also be added, along with ventral strakes below the rear fuselage. The empennage also needed revision at the fin/tail-plane junction.
CHANGES
The changes were necessary to meet the FAA's FAR 23 certification requirement for a 61kt full-flap stall speed at maximum take-off weight that is demanded for single-engine aircraft.
Adding the stick shaker/stick-pusher system protects against sudden stall departures, improving flight safety. "Going for a pusher was a major decision," says Masefield, "but we're very pleased we went ahead because now we have full flying effectiveness right up to the stall." He adds that "...we virtually had to re-write the book on FAR 23 stick-pusher performance...the rules have become much tighter, and we wanted the stall to be spot-on at 61kt [110km/h]".
Aerodynamically, the PC-XII now stalls at 59kt with full flaps, "...but we needed a 2kt margin for the stall-barrier system to operate", says Masefield. "It doesn't sound much, but when you convert this to a difference in lift co-efficient, it is a big jump." To achieve the required stall performance, the wings had to be lengthened by 1m to accommodate the larger flaps, which would be necessary. This also meant that the ailerons would have to be moved out, bringing the additional benefit of increased roll power.
Larger flaps meant a total redesign of the flap-extension mechanism. The original flap track system, was removed, to be replaced with a clever system of pivoted levers, which lower the friction and are dirt tolerant for improved rough field tolerance. "We're very pleased with it," says Masefield, "it has been completely trouble-free since the first flight."
WINGLETS
Winglets were added to the extended wing to restore dihedral, bringing the benefit of improved cruise performance at high altitude. "We flew the aircraft both with winglets and without them," says Masefield, "and found that it definitely handled better with them fitted."
The top section of the rudder was redesigned to reduce drag. This now sports a McDonnell Douglas DC-9-type fairing, while the rudder itself, which previously had an angled notch at the rear edge, has been extended right up to the all-moving tail-plane, with a split elevator, for rudder clearance.
All these changes have been added to an aircraft, which Pilatus had already put much effort into refining for the business-utility role. The Stans based company has considerable experience with its earlier PC-6, PC-7 and PC-9 turbo-prop singles, more than 1,000 of which are in service, along with a reputation for quality and ruggedness.
This philosophy has been extended to the PC-XII, resulting in a highly practical aircraft, yet with the refined, airliner-like feel which the PC-XII market will demand. For example, the aircraft is fitted with trailing-link landing gear, providing softer landings as well as good rough-field performance.
The pressurised cabin has a deceptively large volume, and is longer (by 80mm) and wider (by 140mm) than that of the Beech King Air B200. Fitted with the executive interior of the test aircraft, the PC-XII offers ample space for comfortable travel over a 2-3h period. Configured as a nine-seat commuter, space is obviously limited, but is perfectly adequate for short-medium-range trips.
A unique feature is the outsized cargo door at the rear of the cabin, enabling Pilatus to offer the PC-XII as a combi with genuine cargo-carrying ability able, for example, to carry four passengers and 6m3 of freight at the same time. The high-set tail allows palletised loads to be delivered without danger of damage. At 4,100kg maximum take-off weight, the PC-XII can carry a 1,090kg payload a maximum range of 370km (200nm) or fly 3,300km with a 300kg payload on board - about 190km more than the B200. A flat, heavy-load bearing floor is fitted, and recessed cargo-net hooks are provided inside the cabin.
The PC-XII is powered by the most powerful variant of the Pratt & Whitney turboprop, the PT6A-67B, which has a thermodynamic rating of 1,120kW (1,605shp), but is flat rated to 900kW for take-off and 750kW for cruise. It drives a 2.67m diameter Hartzell propeller at 1,700RPM, the combination yielding seemingly effortless power as the PC-XII takes off and climbs over the mountains which surround Stans.
Avionics remain the same and are centred around the AlliedSignal Bendix/King KFC 325 3-axis, automatic flight- control system, with either one or two 100mm EFIS displays. The PC-XII also has a central advisory and warning system to warn, caution or advise on aircraft condition via. An annunciator panel mounted in the lower centre instrument panel.
The PC-XII is the first aircraft to meet the FAA's FAR 23 Amendment 36 crash requirement, which calls for passenger seats capable of resisting a 16g deceleration, and pilot seats with a 21g capability. Masefield admits that cabin-seating flexibility is "somewhat compromised" by the rule, but adds that there are "obvious marketing advantages" to meeting Amendment 36.
While it will not be at the Paris air show in June, the PC-XII will be in evidence at many other venues in Europe and the rest of the world throughout the year. Pilatus evidently hopes that its combination of high performance, ease of handling, flexible roles and good looks will see the aircraft carving itself a healthy slice of the business/utility market.
Source: Flight International
