FLIGHT TEST: Raytheon T-6 Texan II - A better Texan

With the B version of its T-6 Texan II, Raytheon Aircraft aims to tap demand for a more advanced turboprop trainer offering a fighter-style cockpit

Since winning the Joint Primary Aircraft Training System (JPATS) competition, Raytheon Aircraft has delivered over 200 T-6A Texan IIs to the US Air Force and Navy - roughly one quarter of the planned US buy of 782 aircraft. The T-6 has also been selected for the NATO Flying Training in Canada programme, where 26 are in operation, and the Greek air force has taken delivery of 45 - the first 25 almost identical to the US version and the last 20 modified to provide a weapons delivery capability with simple sight and freefall munitions.

Raytheon believes there is pent-up demand for a basic trainer equipped with head-up display (HUD) that can perform roles previously requiring higher performance and more expensive aircraft. In an effort to expand the Texan's capabilities, the company has embarked on a self-funded avionics upgrade and developed the T-6B. Modifications are limited to cockpit avionics and corresponding systems.

Evolved from the Pilatus PC-9, the T-6 was tailored by Raytheon to meet the specific requirements of the JPATS programme. The roomy cockpit is designed to accommodate pilots of both sexes from the anthropometric 5th to 95th percentile. To facilitate operations at low altitude, several enhancements were made to increase survivability in the event of a birdstrike. Canopy thickness was increased to prevent a 1.8kg (4lb) bird from penetrating to cockpit at 270kt (500km/h). Wing and vertical and horizontal stabiliser leading edges were modified with an additional spar to prevent catastrophic loss from bird impact. Flight control surfaces were modified to improve the PC-9's already good flying qualities. As well as numerous modifications to aid maintenance and shorten turnaround times, a vapour-cycle air conditioner and onboard oxygen generation system were incorporated. But although the T-6 looks like a PC-9, the only parts they share are the three landing gear tyres.

Upgraded avionics

The heart of the T-6B's CMC Electronics-supplied integrated avionics is two mission computers, mounted aft of the cockpits and linked to the avionics by separate Arinc 429 and 1553B databuses. Like Embraer's competing EMB-314 Super Tucano, the T-6B has a single embedded global positioning/inertial navigation system (GPS/INS). The T-6A's conventional-looking liquid-crystal round-dial instruments are replaced by three 127 x 178mm (5 x 7in) colour flat panel multifunction displays (MFDs) located on the lower portion of the instrument panel, each in a portrait format.The front cockpit has a Sparrow Hawk HUD, with dual combiner panes and 25¼ field of view. An up-front control panel (UFCP) for data entry sits just belowthe HUD. Rounding out major changesto the cockpits are hands-on-throttle-and-stick (HOTAS) control grips and a data transfer module.

The T-6B is not a finished product, but a platform to show prospective operators what is possible. Although the aircraft has all the look and feel of a finished product, only a partial list of advanced capabilities was active when Flight International was invited to fly it at Raytheon's production and test facility in Wichita, Kansas. Before the T-6B flight with Raytheon test pilot Andris Litavniks, I was familiarised with the standard T-6A cockpit. The A model's instrument panel is well arranged, with primary flight instruments in a classic "T" configuration. Individual LCD instruments are of a good size and quick and easy to interpret. Familiarisation with the A model complete, I strapped into the Martin Baker MkUS16LA zero/zero ejection seat in theT-6B's front cockpit. The B model's cockpit layout is identical to the A's, apart from the HUD and instrument panel. Electric seat height adjustment let me attain the design eye position, referenced by visible HUD symbology. Rudder-pedal placement was easily adjusted with a manual crank, and the HOTAS stick and power control lever (PCL) fell readily to hand.

Start procedure

As befits a trainer, the engine start procedure was easy. With only internal electrical power on the aircraft, the PCL was moved forward from "Cutoff" to the "Start Ready" position. Momentary actuation of the starter switch initiated the start process. The power management unit (PMU) almost immediately supplied fuel for light off and monitored the start process. At 60% N1 the PCL was advanced to the idle position. Peak inter-turbine temperature (ITT) was 771¼C (1,400¼F), well below the 1,000¼C limit.

The aircraft generator was placed online and I found the UFCP easy to use, facilitating entry of radio frequencies and ATC transponder code. After checking operation of the belly-mounted speedbrake and setting flaps to the take-off position, I released the parking brake for taxi to Beech Field's runway 18. Once clear of the parking apron, I found the T-6B's nosewheel steering allowed me to track taxiway centrelines easily and accurately. GPS satellite reception on Raytheon's ramp was poor, and the aircraft was stopped before reaching the active runway to allow the INS to perform a GPS-aided alignment. Once stopped, a full-up alignment took only 1min 47s.

As we lined the aircraft up on the runway, I turned on the trim aid device (TAD). The digital TAD uses altitude, airspeed, engine torque and pitch rate to set rudder trim to counteract propeller-induced yawing, common to all powerful turboprop trainers. The TAD is designed to reduce pilot workload, but not to totally negate the requirement for proper rudder and trim use as speed and power levels change.

The PCL was advanced until 30% torque was indicated on the engine display indicator (EDI) on the right-hand MFD. As well as engine instrumentation, the EDI displays warning, caution and advisory messages in the lower quarter of the display. Initial acceleration was brisk as the PCL was pushed to the forward limit. The PMU monitored ITT and set 100% torque on the Pratt & Whitney Canada PT6A-68 for the ambient conditions.

Moderate right rudder was required during the take-off roll, to counter torque from the four-bladed, 2.46m (2.0ft) -diameter Hartzell constant-speed propeller. At 85kt indicated airspeed, light aft stick was needed to rotate to a 10¼ nose-high lift-off attitude. The T-6B left the runway 20s after brake release and a ground roll of 500m. Pitch forces, as gear and flaps were retracted during acceleration to a climb speed of 140kt, were easily countered with pitch trim.

Initially the T-6B was levelled off at 2,200ft (670m) to stay below the KC-135 traffic pattern for McConnell AFB. Once clear of the tankers, a 140kt climb was held to 11,000ft for transit to the working area due east of Beech Field. The PMU maintained maximum allowable power during the climb, which took less than 3.5min.

Litavniks had used the flight management system to draw the working area on the tactical situation display (TSD), shown on the left MFD, which allowed me to steer directly to it. During the cruise to the area at 245kt, fuel flow was 565lb/h at 293kt true airspeed. In addition to our working area, the planned route of flight and local airfields were also shown on the TSD. While not operational for my flight, CMC will provide a digital moving map to aid navigation and situational awareness.

Entering a loop

After several clearing turns in the working area, I lowered the Texan's nose and aligned it with a section line to enter a loop. At 250kt indicated and full power, I initiated a 2.5g pull. The nose tracked smoothly during the pull, with the TAD adjusting rudder trim as the aircraft slowed. At the top of the loop I decreased backpressure as airspeed had decreased to about 75kt, rather less than desired. Once nose-low and on the entry heading, I allowed the T-6B to again accelerate to 250kt for an entry into another loop. This time the initial pull was at 3.5g, which gave a more comfortable speed of 110kt over the top. During these manoeuvres, I found the stick forces for the mechanical elevator to be low and linear with applied g. The Texan is provisioned for anti-g suits, a welcome capability for an aircraft with a 7g load limit, although Litavniks and I did not wear them for our flight.

Crisp control

Roll control is via mechanical ailerons, and at 200kt a series of aileron rolls were performed. Full aileron deflection yielded roll rates in excess of 200¼/s in both directions. While rolls could be performed without co-ordinating rudder, proper use yielded crisper rates. With little practice, the precise roll control offered by the T-6B allowed me to perform crisp four-point rolls. The final aerobatic manoeuvre performed was a cloverleaf. This is much like a loop except that instead of pulling wings level over the top, a rolling pull is initiated to change aircraft heading by 90¼ from the entry heading. During this manoeuvre I found the T-6B's pitch and roll control forces well harmonised, a great quality for any aircraft, especially so for a basic trainer.

We then performed three stalls to evaluate the T-6B's low-speed flying qualities. All stalls were entered at 12,000ft, and with 414kg of fuel, aircraft gross weight was 2,926kg. At idle power (0% torque) and in a clean configuration, the aircraft was slowed at 1kt/s. At 93kt and 15.9 units of angle of attack (AoA), the stick shaker activated. Further slowing the aircraft caused the nose to drop slightly, the aircraft's defined stall point, at 86kt and 18 AoA. The stick was held full aft and the aircraft settled into a slow wings-level descent. The T-6B has 250mm stall strips located at 48% span to improve handling characteristics during the stall. Although the rudder could have been used to counter the minor wing drops during descent, the ailerons gave excellent roll control even in the stalled condition. Lowering the nose and advancing the PCL to fly out of the stall regained normal flight conditions.

The second stall was in a take-off configuration, flaps set to take-off and gear retracted. The shaker again activated at 15.9 AoA, this time 85kt. The stall-defining initial nose drop again occurred at 18 AoA, now 78kt. Lowering the nose and advancing the power allowed the aircraft to fly out of the stall. The final stall was in a landing configuration, flaps full and gear down. Shaker activation and nose drop were at 80kt and 74kt, respectively. As with the previous stalls, control in all three axes was good even at speeds below the stall. Recovery from the last stall was made by maintaining the stalled pitch attitude and advancing the PCL to power out of the stall at a constant altitude.

Debate about the applicability of spin training continues in many circles, but the US military required the ability to teach spins in the JPATS aircraft. The Texan II has been spun in upright and inverted conditions, but with a 15s inverted flight limitation, only upright spins are allowed operationally. With gear and flaps retracted, a 140kt climb was initiated to 16,600ft for entry into the first of two spins. With 386kg of fuel onboard, the T-6B managed a climb rate of over 2,500ft/min from 12,000ft.

First spin

The first spin was entered by applying full aft stick and full right rudder when the shaker activated. The first turn of the spin was with the nose above the horizon, while the second and subsequent turns had the aircraft in a 40-60¼ nose-low attitude. Stabilised yaw rate was about 150¼/s, with little wing rock. Application of full left rudder stopped the yaw after a quarter turn, and placing the stick slightly forward of neutral immediately broke the stall. A 4g pull levelled the aircraft at 13,000ft, just 3,600ft below the entry altitude.

The second spin was to the left, with rudder application delayed until 5kt slower than the shaker activation speed. This time the spin was allowed to continue for six turns. Full opposite rudder stopped the yaw rate in one and a quarter turns, and slight forward stick again broke the stall. The aircraft was recovered to level flight just 5,000ft below the initial entry altitude. During my initial US Air Force pilot training in the T-37, getting four spins on a training sortie was all that could be expected. The turboprop T-6's good climb rate, combined with the low altitude lost during spin manoeuvres, makes it an efficient spin trainer. In all probability the Texan will "spin out" its students before running out of gas.

Having experienced many facets of the Texan II that made it the trainer of choice for the US military, it was time to try the B model's upgraded avionics. Using the left MFD, simulated Mk82 225kg freefall bombs were loaded on the aircraft. Flying over open pasture land, the "MRK" button on the UFCP was used to designate a simulated target as we overflew a small pond. The air-to-ground (AG) avionics master mode was selected via the thumb switch on the stick. HUD symbology changed from the navigation mode to a CCIP (continuously computed impact point) weapons delivery display. The CCIP display was similar to that in a fourth-generation fighter, a bomb fall line extending from the flightpath marker (FPM) to the pipper.

With the avionics tracking target location, the T-6B offered a real-time no-drop scoring (NDS) system. The instructor can track the students aiming down the chute before weapon release via a HUD repeater display on any of the rear cockpit MFDs. The T-6B has no active air-to-ground ranging system and aircraft barometric altitude and manually entered waypoint elevation are used to determine bomb range. The avionics system calculates the bomb's impact point and relays scored position as well as circular error of probability for multiple deliveries.

Our diving deliveries simulated only Mk82s, but the system can also simulate rockets and machinegun fire. As well as CCIP, Raytheon plans to add a continuously computed release point mode to the T-6B's air-to-ground capabilities.

Air-to-air training

Although not in the same speed regime as an F-16 or F/A-18, the T-6B offers a number of air-to-air (AA) training capabilities. During the flight I was able to look at the AA master mode, again selected with a stick-mounted thumb switch. The lead-computing optical sight display on the HUD mirrored that seen in an F-16 orF/A-18. Air-to-air ranging is accomplished using retical matching to manually input target aircraft wingspan. Desired range can be changed between 700ft and 1,400ft with a PCL switch. A continuously computed impact line (CCIL) gunsight display is also available in the AA master mode. Onboard avionics can present a simulated target aircraft in the HUD to train pilots in air-to-air tracking tasks.

The open architecture of the avionics suite allows for any number of upgrades. Of the many potential additions, Raytheon plans to develop an airborne synthetic tactical radar for ground-mapping practice, a synthetic electronic warfare display and, with the addition of a datalink, a rangeless air combat manoeuvring instrumentation (ACMI) capability. A synthetic air-to-air radar display could be used to present ACMI data for actual intercept training, or for practice against a virtual target.

Throughout the flight, in visual meteorological conditions, I could evaluate the HUD and centre MFD as primary flight displays (PFDs). The HUD was easy to use, with needed data such as flightpath angle, airspeed and altitude readily available.

One unique feature of the display not found in high-performance aircraft's HUD is the display of a climb dive marker (CDM) as well as an FPM. The FPM was about half the size of the CDM, which was similar in size to FPMs in other aircraft. At low speeds, sizeable crosswinds and resultant high drift angles render the FPM difficult to use for many tasks. The CDM was essentially a drift-caged FPM, and was my primary flightpath control indicator except during manoeuvres for approach and landing, when the FPM helped to manage the sizeable Kansas crosswinds. The HUD's airspeed and altitude displays were round-dial-like to show trends, with a centre digital readout. Although I prefer tape-type displays for airspeed and altitude, the round-dial HUD displays were clear and easy to interpret.

The head-down PFD, displayed on the centre MFD, was not as usable as the HUD. The PFD's location below the UFCP is lower than optimum on the instrument panel. The display itself was readable even in direct sunlight, but its layout could be improved. Space allocated to each of the six flight instruments on the PFD was compromised by the large horizontal situation indicator (HSI) compass rose on the bottom half of the display.

The five other instruments - attitude director indicator (ADI), airspeed indicator, AoA, altimeter and vertical speed indicator (VSI) - are all presented in the upper half of the display. As with the HUD, these instruments are all round dials, and the ADI is smaller than I would have expected for a trainer aircraft. The use of tape-type displays for airspeed, altitude, AoA and VSI, and/or a smaller HIS, would allow for a larger ADI. While I found the head-down PFD adequate, I much preferred flying the aircraft by referencing the HUD.

Simulated failure

Before returning to Beech Field, Litavniks simulated an engine failure by setting 6% torque on the engine. We were several miles north of El Dorado, an uncontrolled airfield east of Wichita. I immediately established a 130kt glide and turned towards the field. We arrived overhead the field at 3,000ft, in an ideal "high key" position. The gear was lowered overhead the runway, and a left turn to "low key", downwind abeam the desired touchdown point, was started. The flaps were lowered to the take-off setting, and 120kt held until halfway round the final turn.

The T-6B's good glide ratio and fine flying qualities made energy management easy, and once reaching the runway was assured, the flaps were set to landing and 110kt held until touchdown. On the runway I advanced the PCL, applying right rudder as the engine spooled up for the return leg to Beech Field. A touch-and-go and full-stop landing at Beech Field again reminded me why the Texan was the JPATS winner. With just one hour at the controls, I was able to grease on the final two landings despite strong crosswinds.

Although the T-6A is a competent primary trainer aircraft, Raytheon's decision to develop an upgraded avionics package has served to highlight the Texan II's unrealised potential. The aircraft's open-architecture avionics and dual mission computers should provide the foundation for the incorporation of a large number of tactical training capabilities. The HOTAS switches and HUD are representative of those found on current operational fighters, with the HUD proving itself to be a most capable PFD.

Although the Texan is not a high-performance aircraft, the tactical training capabilities it can offer should allow it to perform tasks previously requiring more expensive platforms. Raytheon is launching a world tour for the T-6B in the new year, and interested parties will sample first-hand the aircraft's promise while further guiding its development.

Rivals compared

	Embraer                 EMB-314                Super Tucano	KAI                     KT-1        Woongbee	Pilatus              PC-9M	Raytheon             T-6B              Texan 11
Length	11.3m	10.3m	10.14m	10.2m
Wing span	11.14m	10.6m	10.19m	10.2m
Crew	2	2	2	2
Powerplant	1 x P&WC	1 x P&WC	1 x P&WC	1 x P&WC
	PT6A-68A	PT6A-62A	PT6A-62	PT6A-6
Power	@ 1,250shp	@ 950shp	@ 950shp	@ 1,100shp
Operating empty wt	2,420kg	1,901kg	1,725kg	2,512kg
Max take-off wt- clean	3,160kg	2,540kg	2,350kg	3,062kg
Max take-off wt- stores	4,918kg	3,311kg	3,200kg	N/A
Landing distance	550m	396m	700m	580m
Load factors – clean	+7g/-3.5g	+7g/-3.5g	+7g/-3.5g	+7g/-3.5g
Maximum speed	320kt	350kt	320kt/M0.65	316kt/M0.67
Max range/endurance	1,667km/5h	1,535km/4h	1,670km/4h	N/A
Max climb rate	4,750ft/min	3,500ft/min	4,090ft/min	4,500ft/min
Max operating altitude	35,000ft	38,000ft	38,000ft	31,000ft

MICHAEL GERZANICS / WICHITA, KANSAS

Source: Flight International