Airtest — Piaggio Avanti

Rinaldo Piaggio SpA has produced 51 aircraft types and over 6,000 engines since 1915, and is currently involved in the manufacture and refurbishment of Tornados, G222s, Falcon 2000s, P.166 pusher turboprops, and AMX fighters. Avanti development began in 1982, and Learjet was briefly a partner in the project from 1983 until 1985. The prototype first flew in 1986, with FAA certification in 1990.

Say them in the same breath: “Ferrari, Armani, Pininfarina, Piaggio.” One glance at this Italian thoroughbred’s styling tells you it is indeed something special. Have you ever seen such smooth air-teasing compound curves on a fuselage? You could be forgiven for thinking its construction is all composite but, apart from a few extremities, it is not, and so has avoided the certification woes suffered by many users of these materials. Its primary structure is formed from large aluminium sheets stretched and butt-jointed in a jig, then strengthened from the inside to make the smoothest, cleanest, most curvaceous body air molecules have ever parted for.

The Avanti’s unusual (and widely patented) mid-wing, three-flying-surface concept was optimised to minimise drag and fuel consumption at jet speeds, while keeping the main spar and engines behind the cabin maximises internal space, reduces noise, and allows a wide C of G range. The small, high-aspect-ratio straight wing has a special rear-loaded “natural laminar flow” aerofoil designed by Ohio State University and refined in 4,600 hours of wind tunnel testing. Its panels are milled from solid aluminium to form a super clean surface. To these Genoa-built airframes are mated mainly Sikorsky and Edo manufactured composite foreplanes, stabilisers, nosecones, tailcones, nacelles, flaps, Delta fins, and gear and baggage compartment doors.

The miniature front wing (which is not strictly a canard because it has no control surfaces) has five degrees of anhedral to prevent its wake interfering with the wing’s airflow. This forward wing maintains stability while generating around 10% of the total lift, enabling the main wing to be 35% smaller than normal. Its incidence was selected to ensure it stalls before the mainplane, guaranteeing a nose drop at high angles of attack, helped at the other end of the aircraft by a pair of ventral Delta fins which also aid yaw stability.

The three-spar wing mates to the rear bulkhead with the main gear legs. It has single slotted Fowler flaps outboard of the engines and split flaps inboard. The foreplane also has plain slotted flaps and all units operate in unison, with interlocks to ensure symmetrical deployment. The tiny T-tail is swept for maximum effectiveness. Working in the normal way, it too is optimised for minimum cruise drag, when it produces only the slightest downforce, dispensing with both stick shaker or pusher. Controls are manual and balanced for lightness, the ailerons having completely sealed gaps. All three axes have electrical trim tabs.

The PT6 powerplants are 1,485shp (1,110kW) units flat-rated to 850shp (635kW), fitted with particle separators and installed as pushers in low-drag, area-ruled nacelles to minimise overwing airflow disturbance. Their five-bladed counter-rotating Hartzell props eliminate the “critical engine” and are optimised to work in turbulent airflow from wing and engine exhaust while generating a low external noise footprint, making the Avanti acceptable at jet-banning airfields. Wing and fuselage tanks carry 1,488 litres of fuel with optional single-point pressure refuelling on the lower right fuselage side (without this the gravity fuel port is way above the wing). In this easily accessible lower panel are also convenient engine oil and hydraulic fluid quantity annunciators.

Weighing 3,456kg empty, the Avanti’s 5,262kg maximum ramp weight allows a pilot, six 77kg passengers, and 59kg of baggage to be carried the full published 1,400nm (2,593km) maximum range at 305kt (565km/h) with IFR reserves. (Using 40% bigger 1,200shp (895kW) engines, the heavier and more expensive Beech Starship 2000A carries the same six passengers in a lower, slimmer cabin more slowly over a similar range). Interestingly, the Avanti cruises faster than the King Air 350, the Starship, or even the Citation II, and nearly as fast as the Citation V or Beechjet, yet its fuel flow is lower even than the King Air’s, three-quarters that of the Starship’s or Citation II’s, and barely more than half the Citation V’s or Beechjet’s. And the Avanti’s cabin is bigger than any of its competitors’.

Entry to the low-slung aircraft is up two small steps in the bottom half of the door. The cockpit is partitioned from the cabin and the tapering forward roofline makes it slightly difficult to enter, but two ceiling handholds, folding cushions, and a metal flap over the central console help. The pilot’s seats are low, semi-reclined, and comfortable, while the big wraparound windscreens give excellent panoramic visibility. The roof is clear and the wide grey instrument panel is shaded by a deep glareshield. A lower sub-panel holds system controls, gear switch, and four-needle flap gauge, with circuit breakers on the sidewalls.

Collins avionics and instruments include a three-screen EFIS (electronic flight instrument system) supplemented by conventional instruments for the left pilot, with just round dials on the right. A five-tube system is optional. Two columns of gauges supply engine information; to their right are a double stack of annunciator lights, the radios, and the third, MFD (multi-function display) CRT. The narrow center console holds fuel gauges and controls, engine levers, the small flap selector, and the area navigation system.

The Avanti PT6s’ two-lever control is nearly jet-simple. The power levers move from idle forwards to maximum power or aft to max reverse, while the combined propeller and condition levers run from cut-off through feather, ground idle, and flight idle to max rpm. Selecting start on the right starter/generator quickly raises rpm to 13%, when the condition lever can be slid forward two notches to ground idle. The maximum ITT (inter-turbine temperature) of 1000°C is rarely approached, and the starter automatically disengages at 45% rpm. Switching on the right generator recharges the battery within thirty seconds, and selecting 65% rpm on this engine gives sufficient power for a cross-start. Avionics and hydraulics can then be activated, pressurisation set, flaps run to mid, and auto-feather (a no-dispatch item without which Vmca increases from 100 to 128kt) turned on for takeoff.

Taxying is a little more challenging. The twin nosewheels steer through the rudder pedals with two ratios (taxy gives 50° of authority and takeoff reduces this to 20°) selected by a control wheel button. The taxy setting is rather sensitive, with a slight lag, and my over-controlled efforts were not helped by a strong, gusting tailwind snatching the pedals from side to side. It might be better to use the takeoff ratio on the straights to reduce the wiggles. The multi-disc, carbon-fibre brakes are very effective and, with an anti-skid system still under development, pedal travel has been chosen so a good long push is needed for maximum effect. Since reversed pitch can throw up debris, the easiest way to keep speed under control is to select one (or both) of the props to feather from time to time.

With half fuel and six occupants our takeoff weight was around 4,500kg, giving a 103kt (190km/h) rotate speed. Selecting steering to takeoff, and condition levers to max rpm, I advanced the power levers to 1,000ft lbs torque, released the brakes, and continued increasing torque to its maximum 2,230ft lbs. Acceleration was impressive and, once rolling, we left most of the prop noise behind. Rotation speed came up after just twelve seconds and perhaps 600 metres in the 50° 1021 HPa conditions with 15kt (28km/h) of headwind (ISA zero wind balanced field length at top weight is just 870 metres, although the takeoff distance to 50ft after engine failure can be much longer at high density altitudes). While it took a reasonable pull to attain ten degrees nose up, the controls immediately impressed me once we were airborne. We quickly reached the 140kt (260km/h) single-engine climb (blue line) speed while the gear and the slower moving flaps retracted silently and without trim change. Once clean, initial climb is made at fifteen degrees nose up and 160kt (295km/h) until the pitch is lowered to a 200kt (370km/h) cruise climb for passenger comfort, when the rate settles to around 2,500ft/min all the way to the stratosphere.

The maximum continuous power of 2,230ft lbs and 2,000rpm is maintained to around 25,000ft by carefully advancing the power levers from time to time. Thrust is limited above this altitude by the warranty ITT maximum of 780°C. Although auto-synchronisation is available as an option, no prop resonance was noticeable during our flight. The Avanti can climb straight to FL 410 from takeoff at max weight, but temperature can sometimes reduce its power-limited climb capability a little. Time limited our sortie to FL 310, which we reached just fifteen minutes after takeoff, despite a couple of intermediate level segments.

All controls are delightfully light, making the Avanti a real pleasure to hand fly. Pitch stability in the climb was just positive (confirmed by noticing only small pitch changes throughout the speed range). Elevator travel is a mere 14° (half the normal range) and its force is just right at 200kt (370km/h) IAS, light enough for good manoeuvrability without undue sensitivity. Roll stability is similarly minimal, with exceptionally light ailerons and an astonishing (and truly Italian) near aerobatic 150 degree per second roll rate. The Avanti’s yaw stability, even without the damper engaged, was good throughout the flight. The Collins APS-65 autopilot/flight director’s simple controls range along the glareshield and, while the aircraft is certified under FAR part 23 for single-pilot operation without needing a type rating, neither the yaw damper nor the autopilot need be serviceable for despatch.

Leaving max continuous power set and lowering the nose, the cruise speed soon built to 240kt (445km/h) Indicated Airspeed (IAS) (0.66 Mach), giving a 380kt (705km/h) True Airspeed (TAS) with 250kg per hour fuel flow in a -50°C (ISA -3) Outside Air Temperature (OAT). The excellent aerodynamics make noise levels very low and, while prop rpm can be reduced to 1,800 for economy, neither vibration nor sound change much. The small wing’s high loading gives a smooth ride through turbulence without appreciable flexing. Noise levels, while not quite jet-quiet, are impressively low, even in the aft cabin and roomy, stand-up, flushing lavatory. The Avanti’s competition-beating six-foot-wide interior is roomier than in even some long-range, mid-size exec jets. The 1.75 metre ceiling and lack of a spar crossing the floor allow easy movement around the whole area, while both the 41cm aisle and thoroughly comfortable leather and fabric upholstered, swivelling, reclining armchairs are wider than usual.

This 600-hour demonstrator had six passenger seats (one of which folds down to make a bed with the sideways facing forward bench), but up to nine are available in a variety of layouts with folding tables, recessed lights, speakers, and ventilation outlets. Many interior options are available within the basic price, and standard equipment includes a wardrobe in the toilet area, a refreshment centre with heated water, and several storage compartments and spaces. A heated, lit, but unpressurised 1.25m³ baggage compartment has been lengthened to 1.95m for skis as well as golf clubs and is loaded through an external door forward of the left propeller.

Normal descent is made at 1,800rpm with enough power to achieve the required angle. Speedbrakes are not necessary because closing the throttles with the props in fully fine gives marked deceleration. Lowering the nose five to six degrees below the horizon to maintain redline speed (Mach 0.67 or 260kt/480km/h) gives a 5,000ft/min descent rate. Undercarriage limit is 175kt, with a maximum of 170 for mid-flap and 150 for full flap. Both systems are silent in operation, rates of travel are slow, and neither causes significant pitch change.

Below 150kt (278km/h) the elevator force reduces until, at about 13° nose up, it again increases shortly before light buffet starts at 112kt (208km/h). At 109kt (202km/h) the nose drops as the forward wing stops flying and, although the attitude can be held level in considerable sink, this now requires a good pull. Full power just flies the aircraft away from the stall. With flaps at mid, the buffet starts at 103kt (191km/h) and the nose falls away at 93kt (172km/h), when the descent rate really builds up. With gear, full flap, and idle power the speed drops off rapidly in level flight, with buffet starting at 95kt (176km/h), and the stall coming at 89kt (165km/h).

Leaving full power, flaps at mid, and gear down, we simulated an engine failure in the takeoff configuration. Auto-feather (used any time the wheels are down) takes three seconds to act as the engine runs down, and the nose must be lowered appreciably to maintain 140kt (260km/h) while retracting gear and flap, but a remarkably good 1,200ft/min climb was possible. Rudder pedal travel is small but the force required is high (approaching the maximum allowable) although it can easily be trimmed out using the center console switches, the whole procedure being as easy as in any jet.

Returning to base, the central MFD screen became very useful, providing instantaneous orientation and range. As we descended through cloud for an ILS, the ice warning caption illuminated on the center panel, confirmed by a glance at a rod protruding from the fuselage side just aft of the left windscreen. Wing de-icing is by engine bleed air, foreplane de-icing is electric, and the intakes have conventional boots. The propellers need no de-icing because they are in the hot exhaust, and the whole of the tail unit lacks de-icing because it has proved capable of normal operation with a full three inches of ice all over it. The “laminar flow” aerofoils have been chosen to minimise the effects of ice, so that complete contamination over the whole airframe only reduces performance by 5%, while increasing stall speed by just 5kt (9km/h).

Despite a 30kt (55km/h) tailwind, the ILS proved relatively easy at 130kt (241km/h) with gear down and mid-flap. Breaking off at 500ft, we circled for a reciprocal landing, approaching at 120kt (222km/h) with full flap (which adds significant drag) and 600 to 700ft lbs torque. Despite its comparatively high approach speed, the Avanti has good stopping performance, with an 870m (2,860ft) quoted landing distance. Landing was simplicity itself even in the “twenty gusting 29kt” (37 to 54km/h) wind, with no need for a conventional flare, since reducing to idle power at 30ft produces a rapid speed reduction, while the high thrust line gives a slight pitch up to stop the descent. Using this technique, the aircraft always touches within a few feet of the aiming point, and the briefest hold-off precedes mainwheel touchdown. Then the power levers can be retarded for max reverse. Brakes are hardly needed for other than the shortest landings, and we stopped in under 900m without them.

Taxying does not require more than idle power, so the engines have normally cooled by the time you are parked, and shutdown is simply a matter of sweeping across the panel from left to right to turn everything off, then pulling the condition levers up and back to cut-off.

Piaggio Avanti

The Avanti is truly in a class of its own. Of course its incredible efficiency does not come cheap. At $US4.68 million (plus options) the basic price is more than you could pay for a run-of-the-mill turboprop; but it is still cheaper than any similarly performing mid-size cabin executive jet (with double the fuel consumption!). This includes several interior options, pilot and engineer training, and free maintenance for two years. From an initial production batch of 54, Piaggio has sold six to the Italian Air Force and a couple to the French carrier Air Enterprise within the last twelve months, taking total deliveries to nearly thirty, with ten (including two for China) expected during this year. In March 1994 the financially troubled company formed a liaison with Grumman to assist marketing and production in the USA and to tender for US Army and National Guard requirements for up to 150 multi-purpose support aircraft.

Watching the visually unique Avanti taxi away across the tarmac, I was reminded that, although this particularly stylish aircraft looks, feels, and performs like a jet from its spacious inside, it happens to be driven by propellers. When its owner could arrive in one of these head-turning Italian bizsprops, who would want an ordinary exec jet?