Raytheon AIRCRAFT joined forces with Pilatus in 1990 when it identified Pilatus' PC-9 trainer as a viable candidate for the $7 billion US Joint Primary Aircraft Training System (JPATS) competition. This contest was to select an aircraft for primary training of pilots for both the US Air Force and Navy, with the aim of saving both the services billions of dollars over the life of the programme, compared with the costs involved in continuing the traditional methods of individual training by each service using its own aircraft and equipment.
When Raytheon undertook preliminary design studies, the result was an aircraft which strongly resembled the PC-9. Although Raytheon evaluated all the existing aircraft with potential for development to meet the JPATS specification, the PC-9 became the obvious candidate. Starting with a proven type eliminated the initial-design phase and, once the suitability of the basic design had been confirmed, allowed Raytheon to concentrate on the task of modifying the PC-9 into the Beech MkII to meet the JPATS requirements and make the aircraft a strong contender to be the winner of the competition - and at attractive acquisition and cost-of-ownership prices. (A full description of the Beech MkII appeared in Flight International, 4 - 10 September.)
The PC-9 was known to have excellent spin characteristics, and Raytheon was determined to maintain these qualities while concentrating on changes to the powerplant and systems. To this end, the PC-9's Pratt & Whitney Canada PT6A-62 turboprop of 860kW (1,150shp) - flat-rated to 710kW - was replaced by a PT6A-68. This change enabled the Beech MkII version to meet the JPATS performance requirements at much reduced rated power (820kW flat-rating instead of the thermodynamic 1,270kW), thus increasing time between overhauls. (Raytheon predicts 4,500h between overhauls and an airframe life of 18,000h, which equals only three or four scheduled overhauls in the life of each aircraft. The engine installation is specifically designed to allow hot-section inspections without engine removal). A considerable operating bonus derived from down-rating the engine is the ability to fly at full throttle without time limit.
Raytheon's modifications to the airframe to meet the JPATS requirements include cockpit pressurisation to 0.24bar (3.5lb/in2) differential - in line with usual military design practice. The one-piece windscreen and canopy are new, the stretched acrylic being able to withstand a 1.8kg birdstrike at 270kt (500km/h). The entire canopy is strengthened to cope with the pressurisation: it is hinged along the starboard side and is secured by two handles on the port side. A canopy-fracturing miniature detonating-chord is included, running down the centreline and round the outside edge of each main transparency. The chord operates automatically upon ejection, but firing can be initiated by a T-handle on the ground if the canopy cannot be opened in an emergency. Should the chord fail to work during an ejection sequence, each seat has a substantial spike at the top of its spine to shatter the canopy before the pilot's head reaches it. While redesigning the canopy, Raytheon also bowed the sides outwards, allowing room for the pilots (particularly the instructor in the rear seat) to move their heads outwards and have an improved downwards view.
The ejection seats chosen for the MkII are the Martin-Baker MkUS16LA zero altitude/zero airspeed version. Martin Baker tailored the seat to meet Raytheon's needs - such as reducing the width of the "top box" thereby improving the rear-seat occupant's field of view either side of the seat in front. This, combined with Raytheon's mounting of the rear seat higher (giving the instructor a straight line-of-sight over the aircraft's nose), and the already-mentioned reprofiling of the canopy's sides, provides the rear-seat occupant with an excellent field of view for a tandem-seat trainer.
No personal-survival pack is provided, but each seat does have its own emergency-oxygen bottle, automatically triggered on ejection (with a manual override handle). Normal oxygen is produced by an onboard generator (thus eliminating ground recharging between sorties) and supplied via a regulator and mask. By the pilot's right thigh, there is a standard-pattern manual over-ride handle for separation from the seat, if this fails to happen automatically.
Other important improvements to the PC-9 airframe wrought by Raytheon included strengthening the wing to withstand +7 and -3.5G, with revised skinning to leave the top and bottom main-spar caps visible for easy crack detection, a larger ventral fin to improve directional stability, and single-point pressure refuelling for the 500kg-capacity wing tanks (about 3min to fill and 6min to de-fuel), although the overwing refuelling points are retained. A US Government requirement is that the MkII has to be US Federal Aviation Administration-certificated to FAR Part 23 Aerobatic Category.
By far the most innovative feature incorporated in the MkII by Raytheon is the trim-aid device (TAD). The installation of this device stems from the criticism often levelled at single-engined turboprop training aircraft, that the propeller effects are a burden to a student who will enjoy the torque-free characteristics of a jet aircraft throughout his or her front-line service. It has been claimed that countering the propeller effects on a standard PC-9 leads to a yaw-trim workload equal to four times that needed to trim in pitch or roll: in other words, every change in power or speed needs a rudder trim to keep the ball in the centre.
Raytheon's TAD harmonises the roll, pitch and directional trim requirements so that they became about equal. The need to trim directionally is not eliminated, but reduced to a level much more within the bounds of competence for a student pilot. At the same time, this makes the handling characteristics of the primary trainer much more in line with those of the advanced trainer - in the case of the USAF, the Northrop T-38 Talon and, for the USN, the McDonnell Douglas T-45 Goshawk (British Aerospace Hawk derivative). To do this, the TAD computer uses power, altitude, airspeed and pitch-rate inputs and drives the same actuator as those controlled by the pilot.
In harmony with the TAD, Raytheon has introduced a power-management system (PMS) providing a single-lever control for both engine and propeller, thus making flying the MkII even more akin to flying a turbojet - indeed, the system is specifically intended to make handling the PT6A similar to handling the Pratt & Whitney Canada JT15D turbofan. In essence, the PMS is a full-authority digital engine-control system providing torque and temperature limitation, automatic engine starting, and a smooth, linear, predictable power response (shown in graph which compares the power response of the MkII's PT6 with that of the PC-9's).
A JPATS requirement, with political overtones, specified a cockpit capable of accommodating occupants of widely varying stature - in fact between about 1.5m-tall and weighing 48kg (in flying kit) to 1.9m and 110kg.
Not only did this set Raytheon an ergonomic challenge in seat and control adjustments and field of view, it confronted Martin-Baker with the task of making its seats capable of performing safely during ejection while being occupied by a pilot in some instances more than twice the weight of another. The purpose behind this Congressional edict was to demonstrate a strong commitment to equal opportunities and an acknowledgement that future military-pilot training plans would include significant numbers of women. Solving this particular conundrum took more time and money than any other single aspect of the MkII design.
The MkII's avionics are from AlliedSignal Bendix/King with active-matrix liquid-crystal displays. There is a primary flight display (PFD) mounted at the top centre of the panel with a horizontal situation indicator (HSI) below. The airspeed indicator (reading in kt and Mach) is to the left of the PFD, while the altimeter (with sub-scales in milibars and inches) is to the right. Beneath the altimeter and to the right of the HSI are the engine instruments, all predominantly analogue, but parameters such as inter-stage turbine temperature and torque have an analogue scale (to present trends) and a digital readout of the instantaneous value.
The standard equipment includes a global-positioning system (GPS) and the controllers for this, together with those for the radios and avionics, are to the left of the main display. There is an angle of attack (AoA) indicator, a G meter, three attention-getters at the top of the panel and a central warning panel, above the pilot's right knee. There is a row of standby instruments (airspeed, attitude, altitude and turn-and-slip) across the bottom of the panel.
Flying the beech
A prototype Beech MkII (N8284M) was flown across the Atlantic from Wichita, Kansas ,to Farnborough for the air show in early September. Flight International had the chance to fly it while it was in the UK at Air Hanson's site at Blackbushe.
The MkII demonstration pilot was Jim De Garmo, a retired USAF instructor pilot with experience in the Fairchild A-10 and McDonnell Douglas F-4. He and the marketing manager Pat Farley were happy to talk about their aircraft's evolution from the PC-9 and gave me an excellent briefing on flying it. The sortie profile was to escape from the bounds of Hampshire and operate over Wiltshire and Somerset while exploiting the relaxed and reassuring radar service provided by the Defence Evaluation and Research Agency's field at Boscombe Down.
The MkII looks business-like, with a distinctly military posture, despite its cheerful red, white and blue demonstration livery. The pre-flight "walk-around" inspection is much like that for any comparable aircraft. There is a locker with a hatch to the rear of the cockpit and behind the electrical bay on the port side; it comfortably holds a small bag or a military flying helmet and oddments.
Boarding the aircraft is easy, there being a walkway on the port wing root and a foot hold for the rear occupant. Stepping from the wing into the front seat is easier because of the lower "gunwale": no portable steps or platform are necessary. Strapping-in was a particular pleasure for an ejection-seat user as this Mk16 has the excellent single harness for seat and parachute - two shoulder straps and two lap straps in total, plus the two standard Martin-Baker leg restraints fitted just below one's knees. (I understand that the production version will, however, have a different USAF/USN harness arrangement). The field of view from the front seat is excellent and, although one sits above the leading edge, a good view downwards can be had almost vertically ahead of the wing or, at a shallower angle, behind the wing trailing edge. The cockpit has the snug feeling of a good fighter, but is in no way cramped or restrictive of head or elbow movement.
The range of adjustments (including electrical adjustment of the seat vertically) makes it easy to find a comfortable position in easy reach of the controls, with all instruments clearly visible without body contortions. While all major controls are obviously duplicated, there are some functions (such as operating the battery and generator master switches and programming the GPS) which can only be done from the front. The aircraft would normally be flown solo from the front seat.
Engine starting is a model of elegant simplicity. The throttle is positioned to match a line on the lever with a line on the quadrant: the start switch is selected to AUTO, and the button pressed. At 40% N1 (the compressor speed), the throttle (acting as a fuel cock) is moved to the idle gate. Any abnormality in starting, such as an over-temperature would be detected by the PMS, which would then automatically stop the cycle. The engine having been successfully started, the noise level in the cockpit (even bearing in mind the noise-attenuating effect of the hood and the military helmet) is good and much more like that of a jet-powered aircraft than a turboprop. Although the presence of a four-bladed propeller is patently obvious before engine start, the propeller disc after starting is sufficiently unobtrusive to be readily forgotten. After the ritual of checking the primary flying controls, the flaps and the airbrake (done in the time-honoured way by hand signals, although there is an external jack-plug on the port rear fuselage, should more sophisticated contact with the ground ever be needed), the single seat-pin can be removed from the front of the seat pan and stowed atop the hood locking lever where it is visible both to ground personnel outside the aircraft and to the instructor in the rear seat. (The seat has a total of three pins but the other two are inserted for maintenance, storage, etc.)
Before moving off, the GPS has to be initiated and the rudder-pedal-controlled, hydraulic nosewheel steering selected "on" by using a push-button switch in the top-left portion of the instrument panel. The MkII is designed to be taken off and landed with the nosewheel steering off and, indeed, can easily be taxied with it off, by use of the rudder pedals and differential brake, but the steering is normally used to taxi: it is sensitive and positive and relatively highly geared, tight turns requiring some into-turn brake to lessen the radius.
The foot-operated brakes are progressive and powerful, although requiring fairly high foot forces to apply them hard. At idle RPM, the MkII is quite spritely and requires judicious use of the brakes to contain the taxi speed. Once the aircraft has stopped, the pedals can be held down and locked on by the parking brake which is a T-handle emerging from the panel just to the right of the pilot's right knee.
The take-off from Blackbushe's 1,220m (4000ft) runway was made in good, dry, visual meteorological conditions, with a crosswind of about 10kt from the left. The field is 300ft above sea level and the temperature was 15¡C. The pre-take-off checks were completed, including setting the flaps to 23¡ (they are split flaps, hydraulically operated from a main system pressure of 207bar and electrically selected. The selector, which is inboard of the throttle, is stiff and notchy to use, but acquaintance lessens the burden.
The nosewheel steering was selected off. A torque of 30% was set against the brakes, followed by full throttle upon brake release; the aircraft was easy to keep straight using rudder, despite the crosswind. Rotation was at 75kt and unstick at 85kt. With a positive rate of climb, the gear was retracted. The gear-lever at the bottom left-hand corner of the instrument panel came to hand readily and was easy to use. At 110kt, flap was selected in. The time taken from brakes-off to gear-up was about 14s and the gear took about 4s to retract. Had the crosswind been 15kt or more, the recommended technique would have been to keep the nosewheel on the runway until 85kt.
The configuration changes caused little discernible pitch change. The MkII was climbed at 140kt and, although the climb had to be stepped to meet air-traffic-control requirements, the maker's claim of a 3,000ft/min (15.24m/s) rate of climb to 15,000ft was clearly attainable. The aircraft was easy to trim using the "coolie-hat" button atop the control stick for longitudinal and lateral trim (the button has a central "press-to-activate" portion and moves readily from side to side or up and down as required, quickly and precisely trimming out the loads) while the rudder was equally easily dealt with using the rocker switch neatly installed in the forward face of the throttle grip (rocking to the left relieves left-foot loads and vice versa).
The PMS gave worry-free, push-to-the-firewall-and-forget use of the throttle. The MkII proved to be nicely stable for periods of instrument flying and the instrument scan for both flying and engine instruments easy to make allowing for plenty of "head out of the office" time in clear conditions. My only criticism was that the LCDs were susceptible to washout during changes from shadow to sunlight. De Garmo says that Raytheon's experience to date agrees that there is a need to achieve quicker changes of brightness, and that this will be the case with production equipment.
The all-manual primary flying controls are well harmonised. Roll acceleration and rate of roll are good, while control forces are agreeable in all three axes. The TAD works as advertised at all times, moderating the handling idiosyncrasies expected from a single-engined propeller-driven aircraft. Large changes of power were possible with none of the usual aggravation forthcoming from turboprops. As De Garmo puts it, "all the spikes" are taken out of the spooling up or down of the engine, and the associated propeller pitch changes, leading an imaginative pilot to believe that he could be flying a turbojet - but without being able totally to ignore directional trimming.
A block of airspace between 15,000ft and 20,000ft was kindly lent to us by Boscombe Down for general handling, including stalls, spins and aerobatics. It was De Garmo's suggestion that I tried a loop, firstly with the TAD, and secondly with it switched off. The difference is marked, with large changes of rudder deflection being required to keep the ball in the centre without the TAD and nearly all the hard work taken out during a loop with TAD selected. First, however, the MkII was stalled.
Clean, the stall was approached at 200kt in a nose-up attitude, the natural stall-warning buffet occurring at 87kt and the G-break at 80kt. With full flap (50¡), the approach was at 100kt nose up, the warning at 75kt and the stall at 70kt. In both instances, the ailerons were effective into the stall and any tendency to drop a wing easily countered by either aileron or rudder -the 255mm-long stall strips fitted to the inboard leading edges by Raytheon were seemingly effective in inducing the stall inboard before the tips. In either configuration, there was only a mild nose-down pitch change.
Next, spins to left and right were undertaken. Entry was initiated with full pro-spin control at 60kt power off. The aircraft rolled on to its back before the nose dropped through the vertical and then upwards to establish an erect spin with the nose about 50¡ below the horizon, each turn taking about 2-3s. After three developed turns, full recovery control was applied, leading to a brief increase in rotational speed before full recovery at about 80¡ nose down was achieved. The spin to the right was slightly oscillatory. Recovery from an incipient spin or from an unusual position was promptly and benignly achieved by centralising the controls. The MkII is said not to be sensitive to aileron deflection during the spin. Inverted spins have been carried out during development.
Basic aerobatics were pleasant and easy to fly, 230kt being a good entry speed for looping and rolling manoeuvres. About +4G at the start of loops gives about 120kt over the top - more than enough safely to roll off the top. Full rudder should be applied at about 90kt to stall turn the aircraft and there was little difference in the turn to left or right.
The MkII has an airbrake on the underside of the fuselage centre section about in line with the trailing edge. It is hinged at its leading edge, perforated and hydraulically operated through an electrical control switch on the end of the throttle grip. It can be extended in increments, produces little pitch change, no buffet and only some aerodynamic noise; moving the switch to close the airbrake selects it in to the closed position, one sweep taking about 2s, according to the instrument-panel warning legend. Although there was no opportunity to try it out for this, I imagine that the air brake would be an admirable asset to formation flying.
The PT6A-68 engine is the aerobatic version of the -67, with the addition of an oil-scavenging system for inverted flight. The airframe has a collector tank in the centre section, fed by jet pumps and containing 11.4kg of fuel giving about 45s of inverted flight.
Descent to blackbushe
Descending and returning to the visual circuit at Blackbushe allowed for higher speeds in transit. The MkII is limited to 270kt at low level (310kt at altitude) and it is here that it compared less favourably with its turbojet brethren (the Dassault Alpha Jet is capable at about 490kt and the Hawk about 540kt at low level, for example) in terms of training in agile thinking and high speed navigation. Entry to the circuit can, however, be made in a proper military manner even if not at truly representative speeds. On arriving at the "initials" point at 220kt at circuit height, a level break with closed throttle and airbrake bleeds off the speed to the gear-and flap-extension at limit 150kt on a close, tight downwind with further reductions to 120kt at the start of base leg, 110kt in the turn and 100kt on finals. A touch and go (roller) landing was carried out using into-wind aileron. Despite the crosswind, the aircraft was easy to control, but some use of rudder was clearly essential, casting some scepticism on Raytheon's published claim that a touch and go can be done "feet on the floor".
The subsequent full-stop landing was also a low-adrenaline event using moderate braking and some caution because the MkII does not have anti-skid brakes. This is a slightly surprising omission, particularly as the tyres are narrow-section 12bar units with, I imagine, some potential for bursting if abused.
Fun to fly
The MkII was great fun to fly and is bound to be an appealing aircraft for experienced pilots, flying instructors and students alike. It has excellent handling qualities, albeit in some respects artificially achieved through the TAD. Its PMS, combined with the TAD, convincingly mimic the behaviour of a similar-sized turbojet. The tandem cockpit bestows an ambience much like a single-seater fast jet - but the MkII lacks the low-level maximum speed capability to go with it. It is a strong, safe aircraft, but relatively complex in that it has retractable gear, flaps, an airbrake, pressurisation, ejection seats and a GPS for the student to think about - but simplicity no longer seems to be as desirable a characteristic in a military basic trainer as once it was.
A great deal of perceptive thought has obviously gone into making the Beech MkII the aircraft it is today and it is easy to understand why it was chosen as the winner in the hard-fought JPATS competition.
The Raytheon Beech/Pilatus PC-9 MkII has yet to receive a military designation -
The speedbrake is hydraullically operated
The front (left) and rear (right) cockpits are almost identical
Radio compartment (port side)
The single-point fuelling valves
Radio compartment (starboard side)
Baggage hold with oxygen point
New ventral fin improves directional stability
Source: Flight International