P-750 XSTOL

The XSTOL’s roots go back to the 1950’s when the Fletcher aircraft company designed and flew the piston-engined FU24 ‘crop-duster’. It was an aerial agriculture aircraft with a difference as it possessed a tricycle undercarriage, the pilot sat in front of the ‘hopper’ and its wing featured the outer wing dihedral; characteristics that live on today in the PAC750. The aircraft subsequently began production in New Zealand in the 1960s and evolved through the next decade to a larger version equipped with a turbo-prop and known as the ‘Cresco’. The next major step in the evolutionary process saw the fitting of the 750HP PT-6 engine in 1992 and the renaming to the ‘Cresco 750’. This aircraft was the immediate predecessor to the PAC750 and its latest manifestation, the XSTOL.

In half a century and over 600 airframes, many lessons can be learnt in aircraft production. The PAC750 XSTOL has evolved from its Fletcher heritage and its design reflects a rugged mixture of the features required to get the job done. Yet these looks are most certainly deceiving as the aircraft is no longer confined to an aerial agriculture role. It is designated a ‘utility’ aircraft and that term is as broad as the tasks that are met by the modern XSTOL.

The aircraft has a proven record in parachuting, spraying, fire-fighting, freight, aerial survey and aero-medical roles. Such versatility is afforded by the aircraft’s ability to operate off the shortest, most rugged airstrips to serve remote communities and a rapid climb to altitude to facilitate more jump sorties per hour than its competitors. Its broad side door, 1000lb capacity cargo pod and highly flexible Centre of Gravity envelope make the aircraft an ideal freighter.

The aircraft is a workhorse and looks as such, yet looks can be misleading. The aircraft to be flown for the Air Test is configured in a 10-seater passenger capacity and is enroute to south-east Asia as a personal aircraft. Comfortable leather seats, generous headroom, large windows and the very acceptable cabin noise levels from the turbo-prop make this aircraft a real option for passenger operations. Its interior can come in a variety of options to suit and today’s demonstrator pilot Guy Stevenson explains that they have even been decked out in an impressive corporate interior; the choice is yours. From the outside the XSTOL may not suggest such a role, but once inside it is easy to understand its suitability. After flying it, one is most certainly convinced.

Brut Bearing.

At first glance, the XSTOL looks to be a brut, able to take whatever is pitched at it. This perspective is further underpinned by an engine/airframe combination that is one of the cheapest and simplest to operate. Yet, on closer examination, the features that give it this brutish bearing each have a very valid design reason that grossly outweighs any aesthetics.

This is no more evident than in the wing and aerofoil design. It has a thick section that affords its high lift characteristics and short field performance. The upward raking of the outboard wing offers enhanced lateral stability and the large single slotted flaps spanning the inboard section facilitate a stall speed of a mere 58 knots at max weight. As a result, at MTOW of 7,500lb this aircraft has a certified take-off roll of only 220m and 364m to 50 feet! Coming back to earth that landing roll is a mere 166m. It is easy to see why the ‘X’ is for extra in STOL. But don’t be fooled, this aircraft will cruise comfortably at 140 knots indicated.

The wings sit relatively low and the fuel cap location is well thought out with remote drum refuelling in mind. The undercarriage reflects years of ‘ag strip’ operations, while the large cargo pod not only boasts 3 side doors for easy access, but a tailgate to the rear for loading longer items. For passengers and or freight, there are large double doors on the rear left hand side. These doors can be substituted with a factory installed skydiving door for those who choose to disembark prematurely.

For the crew there are gull wing crew doors on both sides of the aeroplane. These doors are designed to ‘blow off’ if opened in flight to permit rapid egress should there be an emergency during parachute operations. Once seated, the pilot has an excellent outlook both ahead and to the sides through generous glazing.

The cockpit is well equipped with a very clean and orderly layout. Immediately apparent is a large ‘stick-style’ control column. It has a distinct military feel to it and is home to the push-to-talk switch as well as elevator and aileron trim. There is new generation glass on the centre panel encompassing avionics and a moving map, while conventional toggle switches for systems line the lower edge of the panel. Engine instruments line the top of the panel and have a digital display surrounded by an arc of LEDs. The arc of lights commence as green and become amber when operating limits are exceeded. While this is the same as a conventional dial, its placement and illumination permits a ready reference for power settings without having to drop the eyes back into the cockpit. This is ideal for low level and critical short field operations.

The cabin is well appointed. While this particular aircraft is destined for predominantly passenger operations, the side walls boast discreet freight rails and placards for maximum loads in the different zones. The XSTOL can also change between roles readily by stowing the seats in an aft compartment, freeing the aircraft up to become a dedicated freighter. This aircraft is as much about versatility as it is utility.

Taking Flight.

The time had come to take the PAC 750XSTOL into the air and see if it delivers as much in flight as its design offers to the operator. The obvious red fuel selector on the centre pedestal is easily accessible from both seats. Engine start is very simple which is no surprise to anyone who has operated the PT6-34 and in no time we are sitting at idle awaiting the camera ship. Bring the propeller out of feather we move off and taxi using the direct linkage nosewheel steering that is very simple to manage. Pre take-off sequences are very straight forward, lending themselves to the rapid turn-around of spraying and jump operations.

Lined up and cleared for take-off the power lever is advanced against the brakes to have a first up look at the short field performance with three on board and a 1200lb fuel load. Soon after brakes release, the airspeed indicator comes alive and the aircraft feels ready to fly. At around 40 knots and 80 metres the nose lifts off and we take to the sky. Accelerating to 60 knots, the aircraft is climbing at well in excess of 1000fpm and we level off at the thousand foot mark before the far end. Impressive!
With the nose down and cruise power set, we set course for the training area to meet the camera ship. The aircraft has quickly accelerated to 140KIAS and it easy to see why this aircraft easily boasts a cruise TAS of 160 knots while burning just under 200lph, offering 5 hours endurance with no reserves.

Best of all, the aircraft feels so very easy to fly. Initially, the nose attitude was deceptively low, but once the great forward view was accepted and the aircraft was trimmed, it just sat there. In the cruise it felt as docile as a slab-winged Cherokee making it very easy to fly. Conducting upper airwork revealed much of the reason why; the aircraft has phenomenal low speed handling.

It should come as no surprise that any aircraft possessing such an aerial agriculture heritage and short field performance is at home in the low speed regime. Yet having cruised at a good pace in this comfortable and relatively quiet cabin, one forgets about the ‘workhorse traits’ of this aeroplane. Furthermore, its rate of roll is very pleasing and the entry is as crisp as you could ask for, rolling from limit turn to limit turn in the opposite direction in only a couple of seconds.

Stalling the aircraft is impressive at the other end of the spectrum. In both clean and approach configurations, the aircraft displayed text book pre-stall buffet before developing a minimal rate of descent. A slight tendency to drop a wing was easily countered and despite endeavouring to stir the control column around its pivot while stalled, the aircraft remained fundamentally controllable. Recovery was conventional with power and attitude, but why stop there? Maintaining a relatively high nose attitude and advancing the power lever, the XSTOL actually accelerated beyond the stall and climbed away at 60 knots. The main effect to counter was the strong torque as the PT-6 powered up. Through all of this manoeuvring and engine handling, the tell tale LEDs continued to steer me towards the correct power settings without having to drop the eyes and hunt for numbers. In terms of performance, this facilitates the XSTOLs impressive take-off and landing figures, but for everyday operations it infers a very high margin of safety in the low speed regime for anyone flying the aeroplane.

Established in the circuit area, the aircraft’s stability made it simple to fly in the pattern. Furthermore, its broad speed envelope made it very easy to fit in with the lighter aircraft traffic. One can imagine that whether number two to a Tomahawk on final, or being sweated upon to keep the speed up on an ILS, the XSTOL is able to fit in with ease.

Flying around a 90 knot base and 80 knot final, the aircraft has a heap of margin over the stall. Once trimmed, it sits on speed and on slope with minimal pilot input right down to the flare. The back pressure to enter the flare is quite significant and some old hands put in a measure of aft trim on short final to assist. Even so, the stick force is very manageable and the aircraft touches down on its broad track undercarriage without event. Lifting a lever on the power lever, it is pulled back through Beta range and into reverse. From touch-down to full stop, I’d estimate it was less than 100 metres. Even a flapless approach and no reverse is very miserly with the runway. Circuit after circuit, the aircraft performed predictably and right on the money before departing for the return to Bankstown.

Enroute, it was hard to get over how straightforward this aeroplane was to fly, yet how much it had to offer. In all phases, it was very stable, but not at all heavy on the controls. Slowing down, entering the GAAP and conforming to the circuit could not have been easier, yet this aircraft has genuine performance to offer. The XSTOL goes a long way towards actually defining the term ‘utility’ in relation to aircraft.

Looks can Deceive.

Having Air Tested the PAC 750XL, one comes away with a mixture of impressions beyond the tremendous capability of this aeroplane. It is without doubt an aircraft you MUST fly to fully appreciate. To assess it based upon the book figures and appearance would tend to collar the aircraft into a stereotype workhorse role. It is so much more.

While the XSTOL is undoubtedly multi-task capable it is not to be tarred merely with its crop-duster heritage or exceptional short field performance. This is a comfortable and impressive passenger aircraft too that is very simple to fly well. Those qualities that have evolved through necessity serve to complement its all round performance.

In the PAC750 XSTOL is an aircraft capable of a multitude of tasks, operating out of virtually any airfield you can nominate. This is a very well thought out aeroplane grown from decades of experience. It possesses a blend of performance and versatility that enables it to achieve its goals where others often can’t. It may look like a brut on the ramp, but there’s a finely tuned machine lying beneath. And yes, looks can deceive.

(c) Owen Zupp. October 2009