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Flight Test: X'Air Hawk 912

PUBLISHED: 14:58 04 January 2016 | UPDATED: 15:14 04 January 2016

Flight Test: X'Air Hawk 912

Flight Test: X'Air Hawk 912

KEITH WILSON (C) SINGLE USE ONLY

Don't be fooled by its boxy appearance and amazingly low price — here is a very efficient little kitplane with fine handling and rocket-like climb performance

With its light and powerful controls, the Hawk is a sprightly little aircraftWith its light and powerful controls, the Hawk is a sprightly little aircraft

As I taxi the Hawk out slowly onto the strip, I suddenly realise that the forth coming flight will be a first for me: this will not just be a flight test but also a maiden flight, as this particular aircraft has never flown before!

In fact this report is very different from most flight tests, as the subject aircraft was actually built in the same hangar where my Jodel D.9, Buzz lives. Consequently, I’ve been able to watch it coming together and have seen just how much care and attention its builder, John Anderson has put into its construction. I was not perturbed−and actually rather honoured−when John asked me if I’d take the Hawk aloft on its maiden flight and perform the flight test programme required by the Light Aircraft Association.

For far too long, if you said ‘microlight’ to the average pilot they incorrectly envisaged a hang-glider on wheels powered by a second-hand lawn mower engine. Generally considered to be noisy, draughty and just barely able to fly fast enough or high enough to kill you, microlights were mostly viewed as less than satisfactory and best avoided. However, about twenty years ago a new breed started to appear. These lightweight machines−almost invariably powered by a Rotax engine and fitted with a three-axis control system−had a maximum all-up weight of 450kg and, due to their good power-to-weight ratios and low wing loadings, pretty impressive performance.

The cockpit combines nicely positioned traditional dual control sticks with a 21st century multifunction displayThe cockpit combines nicely positioned traditional dual control sticks with a 21st century multifunction display

The X’Air Hawk is an excellent example of this type of machine. It has been around for a few years now, with a global population in excess of 400, and although perhaps not as well-known as some other ultralights, the type is becoming an increasingly common sight in UK skies, with 24 on the UK register. Although most Hawks are powered by a Jabiru 2200 engine, the subject of this flight test, G-CGVS is fitted with an 80hp Rotax 912UL and features a shorter wing and redesigned wingtips.

As usual−and even though I’d actually watched it being built−before commencing the preflight inspection, I stood back and studied the aircraft from a distance. Not only does doing this lend perspective to the size of the fin and tailplane but it might just reveal something you miss, up close. In the case of the Hawk, the immediate impression is that this is an aircraft in which form has followed function, for aesthetically it lacks any pretension towards elegance. Indeed, the nose seems almost unnecessarily blunt (although I believe that this is because when it was originally designed the engine was a Jabiru 2200, resulting in its somewhat stubby appearance).

The overhead trim handleThe overhead trim handle

However, the Hawk does look not only eminently practical but reassuringly robust. I found this encouraging, because I’ve always maintained that although beauty is only skin deep, ugly goes right to the main spar. Predominantly fabric covered and featuring a wide cockpit with a windscreen that runs from the cowling to the wing and a relatively short wheelbase/narrow track undercarriage, the Hawk resembles the Rans S-6 Coyote . Despite its ‘ultralight aircraft’ classification, my impression is that it is very much a proper aeroplane. Having watched John putting together the quickbuild kit (an estimated 500hr is required) I was impressed by both the design and quality of construction.

The fuselage is constructed primarily of aircraft grade aluminium, with steel and stainless steel brackets used at all critical load areas. It is covered with Mylar, as are the constant-chord, strut-braced wings.

The flaps are of considerable span but fairly narrow chord, while the tips carry gracefully upswept winglets. The tail is a very neat unit and consists of a mildly swept-back fin and broad-chord rudder, a large tailplane and separate elevators. The tailplane has two bracing wires on either side and there is a dorsal strake faired into the fin, while underneath the tail is a ventral hoop that functions as a tail bumper. The elevator is actuated by pushrods, and the ailerons by a combination of cables and pushrods, while the rudder and pitch trim use cables. There is a single trim tab on the port elevator. A neat feature is the use of zips to hold the many inspection panels closed.

notched flap quadrantnotched flap quadrant

In common with many ULAs, the engine is the ubiquitous Rotax 912. This turns a three-bladed, ground-adjustable carbonfibre Kiev prop via the usual Rotax 2.27:1 reduction gearbox. There’s a landing light in the intake for the radiator.

Engine access is adequate. You could say that the absence of a small hatch to check the oil and coolant is remiss−or you could equally claim that this arrangement ensures that you have no excuse for not also checking the important coolant hoses, particularly as the top cowling is only secured by ten Dzus fasteners and can be quickly removed.

centre console mounting radio and mag switches etc; and rudder pedals sporting heel brakescentre console mounting radio and mag switches etc; and rudder pedals sporting heel brakes

The fuel is carried in a single tank behind the passenger seat, the filler cap sitting under a zippered flap on the starboard side. The tricycle undercarriage uses bungees for shock absorption, and consists of three currently un-spatted wheels (spats are included in the kit) suspended from rugged looking aerofoilshaped alloy struts. The nosewheel is fitted with a 3.50 x 6 tyre and steers through the rudder pedals, while the mainwheels are fitted with 4.00 x 6 tyres and hydraulic disc brakes.

Access to the cockpit is excellent. The very large doors open forwards a full 180° and the sills are agreeably low. Settling onto the comfortable seat, I notice just how large the cockpit is−and it feels even bigger, as it features a lot of transparencies. The windscreen is tall, the doors are about eighty per cent clear Lexan and the roof is fully glazed. Each door is held closed by two simple but sturdy latches. There are air vents built into the doors, but personally I’ll always prefer a full DV panel on at least the pilot’s side, and preferably both.

The pilot has his own well-placed control stick (many microlights employ a shared centre-stick arrangement) and although there is no provision for altering the position of the sturdy-looking rudder pedals, the seats adjust fore-and-aft.

With its light and powerful controls, the Hawk is a sprightly little aircraftWith its light and powerful controls, the Hawk is a sprightly little aircraft

A neat feature is that there are two throttles, allowing the P1 to fly with either hand. There are a number of different options that provide operation of the hydraulic wheel brakes, including a centrally mounted floor lever or independent pedals.

The trim lever and four position flap selector are both located in the roof. At first I found the flap lever a bit awkward, although I soon got used to it. However, its operation is counter-intuitive as having pulled down on the T-bar to take it out of the detent (there are four settings: 0, 10, 20 and 35°), you push it forward to extend the flaps and back to retract them. Now, more than fifty years ago, a comprehensive study at the US Aero Medical Laboratory concluded that far too many aviation accidents were occurring through misidentification of controls. A similar study also took place in the UK around the same time, and between them, these two programmes produced a number of innovations. These included using differently shaped knobs and handles for different controls (i.e. a wheel-shaped knob for the undercarriage and an aerofoil-shaped handle for the flap lever) as well as delineating the throttle, prop and mixture controls with both different colours and different shapes. The US study also recommended that (where applicable) all controls should be forward for takeoff, switches should be ‘up’ for ‘on’ and that rotary knobs should rotate clockwise to ‘increase’. It was also recommended that the controls should move in the correct direction (i.e. the undercarriage lever should move upwards for undercarriage retraction). This is all good, solid stuff−and I just don’t see the benefit of changing it now.

After what seemed like a ridiculously short ground roll it literally leaped off the runway and clawed itself skywardAfter what seemed like a ridiculously short ground roll it literally leaped off the runway and clawed itself skyward

Pitch trim is manual, operated by a lever in the roof. There is no position indicator. On the plus side I liked the way it was impossible to misidentify the choke−a fault I find regularly in Rotax-powered machines. There is also no carb-heat control: apparently, the carb is located where it stays warm enough from residual engine heat to preclude the possibility of carb icing. All the exposed cables and bellcranks reinforce the impression of a design in which form follows function. The instrument panel is very wide and provides more than enough space for a fairly comprehensive instrumentation fit. In this case it is dominated by a Brauniger Alpha Multi-Function Display and also features a vertical-card compass, a nice big slip ball plus standby analogue ASI, analogue oil and cylinder head temperature gauges plus fuel quantity and pressure, and a voltmeter. Although all of this information (and more) can be displayed on the Brauniger alone, as John is the X’Air dealer for East England and Victor Sierra is his demonstrator, the idea is to show that either analogue or digital panels are an option−and there’s certainly enough room. There is also a sight-gauge for the fuel tank behind the seats, but I have to say I really didn’t care for it, as it’s not easy to read. The baggage bay is also behind the seats: it can take up to five kilos and is zippered closed.

A centre console carries the radio, avionics master, mag switches, starter button and key-operated rotary master switch. There is also a battery isolator set into the floor on the right, while the fuel selector is also built into the floor, on P1’s side.

As in every other mode of flight, the Hawk displayed impeccable manners in the circuitAs in every other mode of flight, the Hawk displayed impeccable manners in the circuit

Positive feel, simple systems

The Rotax started readily and the Hawk trundled purposefully out onto the strip: the nosewheel steering has a nice, positive feel to it. Out at the run-up point, I waited patiently for the engine oil temperature gauge to rise above fifty degrees before starting the power checks. Everything was as it should be−and with such simple systems the rest of the pre-takeoff checks were completed quickly−so after a final glance around the cockpit I rolled out onto the runway and opened the Rotax up to full power. With a power-to-weight ratio of only 5.6 kilos per horsepower acceleration was distinctly brisk, and after what seemed a ridiculously short ground roll it literally leaped off the runway and clawed itself skyward. With the VSI indicating in excess of 1,000fpm and a relatively low forward speed, the angle of climb is impressively steep, even at Vy (speed for best rate, rather than angle of climb). In common with many similar aircraft, it is worth noting that the flap limiting speed is quite low, and if the takeoff is made with the flaps down, care must be taken not to exceed the limiting speed. I do feel though, that with such impressive performance a flapped takeoff would probably be quite a rare event.

Having rocketed up to 3,000ft in less than three minutes I reduced power, retrimmed, and began to feel the aircraft out. As this was the aircraft’s maiden flight I only really intended to briefly check rig and trim, ascertain the stall speed in the landing configuration and then bring it back. While experimenting with the primary controls I noted that for a high-wing aircraft the visibility is quite good, although−as you find with practically all-high wing aircraft−the Hawk is a tiny bit blind in the turn. Another nice touch is the transparent panel in the roof, which allows you to see over the wing in a very tight turn.

To build a good aeroplane, one should simplify and add lightnessTo build a good aeroplane, one should simplify and add lightness

The controls all seemed quite nicely harmonised and authoritative. The roll rate in particular is sprightly, while control in both pitch and yaw is more than adequate. The trimmer is effective. Slowing down to explore the low speed side of the flight envelope revealed no unpleasant traits. Indeed, with flaps down and carrying a reasonable amount of power, the Hawk showed no desire to stall at all. (This may be in part because the flaps sit very close to the fuselage when extended and may well be enhancing lift by deflecting the propwash downwards.) A more vigorous approach to the stall with the engine off produced a positive G-break at just under 30kt, combined with a very slight wing-drop. Time had flown by and, although I’d stayed very close to the field, I reasoned that John was probably getting increasingly itchy to check his baby over after its first flight so reluctantly re-joined the circuit. As in every other mode of flight, the Hawk displayed impeccable manners in the circuit. Application of flap produces a fairly marked change in pitch trim, although this is easily trimmed out. Speed control is good, and the aircraft practically flies itself down final approach. A Vref of 50kt felt about right, for although this is considerably more than the traditional approach speed of 1.3 x Vso (stalling speed) it’s been my experience that as lightweight machines have less inertia they tend to bleed energy quite rapidly. The landing was gratifying smooth and as I turned back towards the hangar John’s grin was as wide as the wingspan!

Economical — and comfortable

Over the next few weeks I put about seven hours on the Hawk while we sorted out a few minor glitches and tweaked the rigging slightly. The specified two-hour cross country gave me an ideal opportunity to assess its performance as a tourer. A cruise setting of 4,700rpm at 3,000ft gave an indicated airspeed of 80kt, the fuel flow being approximately 12 litres per hour. This suggests a range of around 360nm, allowing a typical VFR reserve of thirty minutes’ fuel remaining. Cockpit comfort was good, with adequate ventilation and reasonable ambient noise levels. On the final flight to gather the data required for John to submit a Permit application to the LAA, the aircraft was carefully fuelled so that with flight test observer Tony (suitably armed with kneeboard and stopwatch) joining me, we were exactly at 450kg, with C of G at the mid point. The takeoff (on short but wet grass and with a slight crosswind) was still impressively short at around 100m, while the initial rate of climb was just over 1,000fpm. As we spiralled skyward we initially turned our attention to the general handling, and a couple of steep turns and reversals revealed crisp, authoritative controls with delightfully pleasant stick forces. The control circuits all seemed agreeably light and reasonably frictionless, with low breakout forces.

An exploration of the stick-free stability around all three axes, revealed it to be strongly positive longitudinally, positive directionally and neutral laterally. At a safe height I began slowing down to examine the stall. As we were at MAUW this took a while, as the Hawk is actually slipperier than its boxy appearance might suggest. Furthermore, not only is the limiting speed for max flap extension, Vfe relatively low at 65 knots, but it is physically impossible to even get full flap down at Vfe due to the high forces on the flap lever.

While we waited for the airspeed to diminish it struck me that the glide angle seemed fairly flat, while the minimum sink rate was quite low. As the needle of the ASI finally sank into the white arc, I lowered the flaps to their maximum deflection of 35°. There is no artificial, and only very subtle natural stall warning, but the speeds are so slow and the pitch angle so high that it’s obvious that something isn’t right. Having retracted the flaps to the takeoff setting of 10˚, I increased power for a look at a departure stall. As expected, this manoeuvre did provoke a slightly more vigorous response, although the ensuing stall was easily recovered from with minimal height loss. I doubt that you’d ever need to do a sideslip with the effective flaps fully extended, but just for grins we thought we’d try one. The sink rate is remarkable! The final item on the flight test card was the Vne (limit speed) dive, and while this should−quite rightly−always be treated with a degree of circumspection, on this occasion it proved to be as benign as every other aspect of the Hawk’s flight envelope: this is a very easy aircraft to operate.

After the final landing we taxied back to the hangar, where on shut-down the Rotax stopped with its characteristic ‘clunk’. This is due to the reduction gearbox, and while I fully understand that it is perfectly normal it remains something that I have still never quite got used too.

Superior to a ‘spam can’

It is interesting to note just how much the lighter end of the sport aircraft spectrum has changed over the last twenty years, and particularly in the States, where essentially the same types of aircraft are allowed to weigh up to 600kg. Usually featuring larger cockpits, better power-to weight ratios and lower wing loadings than ‘traditional’ light aircraft, the modern microlight is quieter, more comfortable and offers significantly better takeoff and landing performance and also lower fuel consumption.

Under the enlightened auspices of the LAA these aircraft will continue to evolve and many microlights (now officially referred to as Ultralight Aircraft, or ULAs) are superior in practically every respect to the classic American ‘spam cans’ (typically small Cessnas and Pipers) that most of us learned to fly on. A maxim much favoured by aircraft designers is that to build a good aeroplane one should ‘simplify and add lightness’−an aim that I believe the X’Air Hawk has achieved admirably.

Specification:

X’Air Hawk 912 £32K (Kit Inc Engine and Prop)

Dimensions:

Wingspan – 10.0m

Length – 6.09m

Height – 2.30m

Wing area – 13.9sq m

Weights and Loadings:

Empty weight – 266kg

Max all-up weight – 450hg

Useful load – 184kg

Fuel capacity – 62 lit

Baggage capacity – 5kg

Performance:

Vne – 110kt

Cruise – 80kt

Stall with flap – 34kt

Climb – 1,000fpm

Take off to 50ft – 180m

Landing from 50ft – 180m

Range – 360nm

Engine and Propeller:

80hp Rotax 912UL flat-four driving a Kiev three-blade, ground adjustable composite propeller.

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