There's only one Antonov An-70 and Flight International's test pilot was the first Westerner to fly Ukraine's four-engined military transport
Peter Henley/KIEV
There are several persuasive reasons to fly the Antonov An-70. Little is widely known about it in the West. It is the product of a leading aircraft manufacturer from the insular days of the former Soviet Union now keen to penetrate the Western military market. It is a fly-by-wire, widebody freighter; it has four "propfan" engines each with multi-bladed, contra-rotating propellers; and its 12-wheeled main undercarriage enables it to operate from unsurfaced strips. Flight International was invited to fly theAn-70, although it had completed only about 120h of a projected 1,200h development programme. Because there is only one An-70 in existence, the prototype is worked heavily in the certification programme at Antonov's flight test facility near Kiev, Ukraine. It was, therefore, a considerable privilege that Flight International's pilot was the first Westerner to sample the aircraft's flying qualities.
Additional interest has been generated by theAn-70 because years of debate have sought a consensus in defining a European Future Large Aircraft (FLA) - yet here is an aircraft, designed in 1989-90 to meet a Soviet air force specification, which provides some of the major capabilities envisaged for the FLA.
The An-70 is short, stocky and purposeful in appearance. The volume of its fuselage is immediately apparent. It is expected to be big enough to contain any significant NATO portable battle equipment or battlefield vehicles. The rear fuselage has clamshell doors and a hydraulic ramp for the loading of airborne despatch of troops and freight. It is intended that paratroopers be despatched in four simultaneous sticks - two over the ramp and two from a pair of personnel doors, one either side of the forward hold (not the more usual real side doors); this concept delivers the maximum number of troops for each pass over a dropping zone.
There is provision for lightweight decking to be fitted, when required, about 3m (10ft) above the main hold floor to carry light freight. There are two cranes on overhead rails running the length of the hold to facilitate loading and unloading boxes or pallets of cargo.
The manufacturer predicts that the An-70 will have a short take-off and landing (STOL) performance (with up to 35t of payload) comparable with that of the FLA, the Lockheed Martin C-130J and Boeing C-17. The maximum predicted payload, for a conventional take-off, at 47t, is 15t greater than the FLA, more than twice that of the C-130J and about 8t less than for the C-17. A particularly interesting comparison is that of cruise speed (in knots, true air speed) where the An-70 is quoted at 405kt (750km/h) against 390kt for the FLA, 340kt for the C-130 J, and 445kt for the C-17.
The spacious cockpit is approached up a steep set of steps from the cargo hold. There is a large, wide centre console between the pilot's seats and a set of six electronic flight instrument system screens span the instrument panels so that each pilot has two side-by-side screens in front of him, while two are at the forward end of the centre console where they are intended to display engine parameters or system synoptics.
This prototype's cockpit is configured to meet the Russian air force requirement for a five-man crew: two pilots, navigator, flight engineer and radio operator. The installation of the avionics hardware and the positioning of systems control panels has, however, been deliberately designed for flexibility. Customer requirements for two or three crew operation could easily be accommodated, Antonov claims.
The pilot seats are of typical military pattern with a fitted parachute. They are tolerably comfortable, have fold-away armrests and are adjustable for reach and backrest angle. Exploiting the generous floor space available, they have been mounted on a curved floor rail so that the seats slide through an arc backwards and outwards making them exceptionally easy to get into and out of.
The control wheels are small and almost square with a hand grip moulded into each vertical edge. These "wheels" are mounted on a sleeved column that protrudes towards the pilot's midriff from the lower edge of the instrument panel. Fly-by-wire technology allows them to be small (because of the low and consistent control forces) and requires relatively small control movements (about 45º either side of neutral for roll control and some 150mm (6in) total movement fore and aft for pitch control). The rudder pedals similarly have little travel and are conveniently adjusted for reach by an electric motor controlled by a switch on the cockpit side panel close to each pilot's elbow.
The field of view is generally excellent with a large, deep glazed area, but there are no upper side windows to help at high angles of bank when the field of view is cut off by the upper frame of the side windows; such aircraft attitudes could reasonably be expected when operating a military tactical transport aircraft. Each pilot can easily see the wingtip, engine nacelles and propellers on his side of the aircraft. A customary eye position indicator on the central windscreen pillar eases seat adjustment to the optimum position for individual pilots.
Although this prototype has the cockpit labels and legends in Russian script, it was not a totally alien environment because most of the flight instrument symbology conformed with Western convention. An exception was the attitude information. Although the aircraft symbol was a cranked wing, common on US instrumentation and therefore familiar, in this case the symbol itself moved in roll and pitch, whereas in conventional presentations the horizon moves. I found my reaction to this form of presentation was not instinctive and would much have preferred the conventional symbol. Modern technology, however, can provide redemption as the presentation software can readily be changed to suit customer preferences.
Although this cockpit is for five crew members, control of the Russian Elektro Automatika flight instrument system (FIS) was via controllers in front of each pilot. As is usual with such systems, displays may be switched to any screen to compensate for a screen failure or merely for convenience. Each screen measures 200 x 200mm and the presentations are clear and easy to read. The main displays show aircraft attitude (the ADI); angle of attack (AoA) in an arc to the left of the screen; airspeed in a vertical ribbon calibrated in km/h at the left of the ADI; a rate of climb and descent indicator (RCDI) calibrated in m/s and a barometric altimeter calibrated in metres, both to the right of the ADI. The altimeter setting subscale and a g indicator are at the bottom edge of the screen while a space at the top is for emergency and warning legends.
The navigation display screen has a compass rose, course information, prevailing wind, ground speed, true airspeed and drift. Barometric and radio altitude are shown and en route navigation displays - for example inertial navigation or terminal approach displays can be superimposed on the basic compass display. As with most modern systems, there is an extensive menu of engine parameters (for example, power lever angle, turbine temperature, engine oil, pressure and temperature, high pressure turbine speed and vibration) and system synoptic pages (configuration, fuel, hydraulic, electric, doors and hatches).
The An-70 is not equipped with a head-up display (HUD), but could have the equipment installed later. This prototype had an angle of attack indicator, a sideslip indicator and two electric cooling fans mounted on top of the glare shield. These items would not, of course, be fitted to a production aircraft.
Starting the Progress Zaporozhie (Ukraine) D-27 engines was automatic and initiated by the flight engineer via a controller in the overhead electrical system control panel. The auxiliary power unit, housed in the port undercarriage sponson, provided bleed air to start the first engine. Starting all four took 2min 10s. The engine parameter displays were clear and easy to read, but of such large scale that use of the screens was uneconomical. Smaller, more compact and better arranged displays would allow more information to be absorbed from one screen with less need to scan.
Because of the early stage in the An-70's flying career, Antonov's chief test pilot, Alexander Galunenko, took the left seat and I the right. There is a nosewheel steering control on both sides of the cockpit, so I was able to taxi out from the ramp to the runway. The steering wheel fitted comfortably into the palm of the hand and exercised precise steering control. Large angles of nosewheel deflection, required for tight turns were not as easy to make, however, as would be the case with a tiller or larger spoked wheel with a knob such as the C-130's. The foot controlled wheel brakes have steel discs and are powerful and progressive. The parking brake lever is on the centre console by the captain's right knee and was more easily applied by him than the co-pilot.
The first take-off, by Galunenko, demonstrated the An-70's short field capability. The all-up weight was 92t, against a maximum design weight of 172t, of which 12t was fuel and 15t test equipment. Antonov's test field is about 450ft (140m) above sea level, the temperature was 23ºC, and there was a light surface wind; the weather was excellent.
To preserve engine life during the extensive development flying programme, the power used for take off was maximum continuous (about 85% of full power). The power levers were set by the air engineer to maximum continuous while the aircraft was held stationary by the wheel brakes. From brakes-off the aircraft accelerated rapidly and was controlled directionally using the rudder pedals and not the nosewheel steering.
The reference speeds for the weight were V1/Vr 108kt and a V2 (safety speed) of 125kt. The aircraft was therefore "on risk" from rotation until it had accelerated to 125kt. If an engine had failed, it would have been automatically shut down and its propeller feathered; if it had been an outboard engine failure, the opposite outboard engine would have had its power reduced automatically so that directional control could be maintained until V2 was reached. The need to reduce power in this way would clearly be more likely with a full power take-off.
The aircraft unstuck cleanly and climbed maintaining maximum continuous power. The undercarriage was retracted using the lever placed rather quaintly at the top of the central windscreen pillar and completed its travel into the wheel walls with a loud "clonk" - probably from the nose wheels. Once the aircraft was established in the climb, I flew it manually to an altitude of 25,000ft.
A quadruplex-redundant fly-by-wire system is used for the An-70's primary flying controls. There is a fifth, separate, hydraulically operated system on constant standby, as a final back-up. Particular attention has been paid to making the system resistant to battle damage and electronic jamming. Provision is also made for physically jammed controls. The requirements are met partially by making the control surfaces in several segments. For example, the rudder is divided into three panels and the elevators into four. If one or more segment were jammed or damaged, the control surface would remain effective, with reduced authority, provided one serviceable segment survived.
Control controversy
There will probably always be controversy over the pilots' controls in a fly-by-wire aircraft. Airbus favours a sidestick, Boeing a more conventional looking control yoke. Antonov has decided on a "mini wheel" for the An-70. I have flown the Airbus A319 and A330-200; I found the sidestick easy to adapt to and I liked it. Equally, I found the Antonov's mini wheel pleasant to use and, on balance, think it the better solution for a tactical aircraft likely to be "hand flown" for a much higher proportion of its operational use than an airliner. I suspect that many pilots graduating to the An-70 from earlier generations of tactical transport and cargo aircraft might feel the same. More importantly, however, the wheel was found by Antonov to cope better with the manual reversion - an unlikely eventuality but still possible through battle damage.
This An-70 prototype has a pair of switches in the overhead panel, called "integral" switches. With the integral switches on, the full fly-by-wire is integrated with automatic protection for speed, bank, g and AoA and semi-automatic trim is in operation. With the switch off, the basic fly-by-wire mode operates. For most of the development flying, the basic mode is used as the protection limits will deliberately be exceeded in executing many test points.
With the longitudinal axis integral switch off in the climb, I found the An-70 to have longitudinal static stability similar to a "conventional" aircraft. In this mode, the aircraft has to be trimmed as in a conventional system using the rocker switch on the control wheel until the force is trimmed out. With the integral switch on - ie in the full fly-by-wire mode - briefly pressing the trim switch initiates automatic re-trimming to the new conditions. In either mode the control forces are light and fairly well harmonised, being lighter in roll than in pitch; the rudder forces are very light and deflection is automatically reduced as airspeed increases.
Control in roll is through ailerons and spoilers, and in pitch by elevators mounted on a fixed tailplane. The elevators are interesting because they are divided and hinged mid chord and deflect like a geared flap. At full up deflection, the leading segment is at 28º to the tailplane mean chord and the trailing segment at 50º. Full down deflection is 20º and 40º, respectively. The purpose is to maintain elevator authority at the low airspeeds demanded by the short field approaches and flares.
A maximum rate, emergency descent was initiated at 25,000ft by closing the power levers to flight idle; deploying the airbrakes (the spoilers) and lowering the undercarriage and flaps to 60º at the respective maximum limiting speeds for extension. The resultant rate of descent was off the vertical speed scale, but was about 6,000ft/min (30.5m/s).
At 13,000ft the aircraft was cleaned up and flown in the integrated fly-by-wire mode to check the limits. Firstly, in roll, selecting an angle of bank up to 30º resulted in that angle being maintained, hands off. Between 30º and 45º, the control forces required to increase bank became higher. Beyond 45º the bank angle was automatically reduced to 30º, hands off. Full roll control deflection resulted in a maximum angle of bank maintained at 60º. In pitch the allowed AoA (or alpha) varied with aircraft configuration. Clean, at a mean airspeed of 195kt, increasing alpha by gradually applying full back stick resulted in a warning at about 12º alpha and limiting at 14º. If the alpha was held so that airspeed decreased, a slow rate of descent would result once the minimum safe airspeed for configuration had been reached. A dynamic approach to high alpha or limiting positive g resulted in a stick push to prevent exceeding the limit.
Similarly, stall protection was provided by minimum speed limitations and a gradual descent or ultimately a stick push to prevent a stall. Full stalling trials have yet to be undertaken by Antonov, so it was not possible to investigate the natural stalling characteristics with the protection switched off. These few test points did, however, clearly demonstrate the effectiveness of the protection afforded by the fly-by-wire system. Such protection, and particularly the slow speed and dynamic stall protection, is arguably vitally important in a tactical transport intended to operate at low speeds and low altitude in a hostile environment.
Next Galunenko undertook to demonstrate a short field, maximum effort, landing. It is the attainment of the best possible STOL performance that has defined much of the An-70's design philosophy. Propfans (i.e. multi-bladed propellers) were chosen in preference to turbofans because of propellers' well known advantages on a tactical transport aircraft. That is, quicker responses to power changes, reverse pitch on landing (which slows the aircraft and kills the lift over the wings, enhancing wheel brake effectiveness) and the ability to reverse the aircraft on the ground - all with less chance of foreign object ingestion.
Antonov has exploited these characteristics further by using efficient, curved, relatively short, wide chord propfan blades and employing their slipstream to maintain the laminar flow over the wing once an extraordinary amount of camber has resulted from the sophisticated high lift devices. These devices consist of leading edge slats (deployed with initial extension of flap) complemented by complex Fowler flaps with a maximum angle of 60º - but including a trailing edge segment deflection of 80º. It was realised that boundary layer flow round that curvature could not be achieved without artificial blowing - or using the propeller slipstream. On the An-70 the front propellers have eight blades and the rear six.
This is so effective that the resultant airflow can produce a downwash over the tailplane. This airflow is in turn redirected across the tailplane and elevators by giving the tailplane leading-edge devices to restore the required chordwise flow. A corollary of exploiting propwash in this way is that engine power above flight idle on the approach is required to generate a sufficiently powerful airflow.
Furthermore, this minimum required engine power will vary with aircraft gross weight (more power obviously being needed at higher weights). Antonov is establishing the minimum approach power required for any given set of conditions. Eventually a "smart" system will electronically restrict power lever angle reduction by recognising the instantaneous all-up weight. Meanwhile, an arbitrary, but adjustable, mechanical gate is fitted across the rear of the power lever quadrant.
Galunenko was about to use all this technology to demonstrate a STOL landing and approach. The approach was started from a height of 1,650ft. The airspeed was reduced, the undercarriage lowered and the flaps (which have settings at 5º increments between 0º and 40º then at 10º increments to 60º) lowered progressively to 60º. An approach path of about 5º was established using power to maintain 95kt threshold speed (Vat or Vref) down the slope. Minimum power to keep the propwash effective over the wings was ensured by the mechanical gate across the rear of the power lever quadrant. On touchdown the flight engineer whipped the gate to one side and applied full reverse propeller pitch with the power levers. Galunenko applied the wheel brakes and the An-70 stopped within an estimated 300m of ground roll - and was then reversed to therunway threshold.
At this point the plan had been to depart again for air-to-air photographs. Unfortunately the An-70 had an overheat warning on the number two engine and, although an indicator circuit fault was suspected, the aircraft was returned to dispersal for investigation. Once the indicator fault was rectified a second sortie was flown during which the photographs were taken. I flew the take-off. The photography was carried out at a height of about 1,500ft. Here, on a couple of occasions when manoeuvring close to the chase aircraft, the better sideways view in a bank which upper side windows could provide would have been much appreciated.
Propeller vibration
When manoeuvring at 190-215kt, some propeller vibration was evident. No work on propeller synchronising or synchrophasing has yet begun, however, and I would expect vibration to be addressed later in the development programme. One observer on the ramp as the An-70 first taxied out and took off told me that the environmental propeller noise was not bad for a military propfan and there was none of the characteristic scream from the propeller tips that afflicted earlier generations of propfan - presumably because the An-70's propellers are a relatively modest 4m in diameter and the tips do not approach transonic Mach numbers. Certainly in the cockpit, roar from the propellers is clearly audible, particularly at high power settings, but, once again, these are early days in the programme and noise insulation and propeller synchronising could improve things on production aircraft.
Finally, I was entrusted with flying a STOL approach. The procedure was as before and I found the aircraft easy to fly down the approach path at Vat. It was stable, and accurate speed control was not difficult. The light control forces in pitch and roll generated by fly-by-wire meant that the pilot could readily fly the aircraft single-handed and control the power with the other hand. The weather conditions were admittedly ideal, with negligible turbulence and a light wind down the runway, but I would not expect difficulties in much more demanding conditions.
There was, however, a need to maintain a busy scan, transferring one's focus from the touchdown point into the cockpit to check airspeed, rate of descent etc and back outside. In poor weather and at night this scan would become even more hectic and this is why the An-70 (in its tactical military transport role) needs a HUD, so that the pilot can fly the whole operation (and all the other phases of operation) while looking through his windscreen.
Another facet of the STOL approach is that Antonov has so far proved the An-70's abilities up to six approach paths. Realistically, the capability for up to nine or 10 will ultimately be needed and it will be interesting to see how the necessary additional drag will be generated, bearing in mind the necessity to maintain a minimum power on the approach to keep the propwash flowing over the wings.
The An-70 is an impressive aircraft - technologically, in its lift capacity, short field performance and flying characteristics. It seems to fill an obvious gap in the world's inventory of medium to heavy cargo aircraft. It is an ambitious project because it is all new - airframe, fly-by-wire, engines, propellers and avionics. To realise its potential it needs to achieve certification in Russia, Europe and the USA as soon as possible. There is an enormous amount of development work still to do, yet there is only one prototype. Projects of this magnitude usually employ a minimum of three prototypes.
The question with the An-70 is not whether Antonov has conceived a winner but whether the company will be able to raise the cash investment needed to take their winner, to the starting gate in time for the race.
Source: Flight International
