Andrew Doyle/MUNICH
Scheduled to appear at Paris, the Antonov An-70 is competing for the European common medium transport aircraft requirement, for which it is now known as the An-7X.
The German Government tasked DaimlerChrysler Aerospace (Dasa) with conducting a technical evaluation of the An-70 to see whether it could fulfil the European Staff Requirement (ESR) for a common tactical airlifter.
Dasa found it would be possible to "Westernise" the Ukrainian aircraft to meet European Staff Requirements. In reaching its conclusions, however, Dasa had not been able to flight test the aircraft to confirm data supplied by Antonov. Dasa concedes that the amount of data available was limited, but points out that the flight test data confirmed the results of extensive windtunnel testing.
In terms of payload/range capability the propfan-powered An-70, with its 132t maximum take-off weight (MTOW) and payload of 35t, would meet the requirements, although Antonov is still working on improvements. "They are still short of their design goal but, with the existing powerplant, they achieve the ESR," says Claus Frey, the Dasa evaluation team leader.
The flight certification procedures being used for the An-70 correspond to European Joint Airworthiness Requirements (JAR) 25 standards. Frey says the An-70 is a "conventional design" as far as stability and control is concerned, and redundancy assures safe operation following any failure considered to have a greater than 10-9 probability of occurring.
While a significant part of the An-70's flight envelope has yet to be explored, the risk of any required modifications to the aircraft's configuration is considered "minor".
Short take-off/landing (STOL) performance was also found to be satisfactory, with a 1,060m (3,500ft)-long runway required at a take-off weight of 112t and at ISA+15 conditions. The aircraft comfortably meets the ESR requirement of a 1,500m field length at a take-off weight of 120t, and is capable of a non-STOL landing at its maximum take-off weight of 132t.
Dasa looked at aerodynamic data derived from over 14,000h of windtunnel tests, using 22 models, which showed the An-70 would have a stall speed in the landing configuration of 132kt (245km/h), against the ESR requirement of 140kt. Maximum speed, at Mach 0.73, slightly exceeds the ESR stipulation of M0.72, while the An-70's cruising speed is M0.68. Also compliant is the type's initial cruising altitude of 31,000ft (9,450m) and maximum cruising altitude of 40,000ft. "We were quite confident that the development of the aircraft with these goals is achievable in the way that Antonov designed it so far," says Frey.
Unusual propfans
Dasa also paid close attention to the aircraft's unusual contra-rotating ZMKB Progress D-27 propfan engines, rated at 9,700kW (13,000shp) for take-off. The D-27 does not yet meet specific fuel consumption targets, and Dasa found the technological risk in achieving this to be "medium".
The contra-rotating fans yield an efficiency gain of around 10% compared with conventional turboprops, but the units are 300-600kg (660-1,320lb) heavier and require the engine to be made longer, with a corresponding increase in bending moments. They are also louder, with Chapter 3 noise standards only "marginally fulfilled", says Frey. Their modular design, however, is good for maintainability, he adds.
German aero-engine company MTU found that mandatory changes that would have to be made to meet the ESR requirements, including the introduction of a full-authority digital engine control for the D-27 and an integrated engine monitoring system. Work would also have to be carried out to minimise the use of hydromechanical control systems, lengthen the hot section life of the D-27, and introduce a prop synchronising system. Overall, the German company classifies work to Westernise the powerplant as "low risk".
The An-70's basic systems offer a "high degree of redundancy", says Frey, with ESR requirements "fulfilled in most subsystems". Required modifications in this area would include the introduction of a fuel-jettison and in-flight refuelling capability, both of which allow the aircraft to be used in the tanker mission.
The "flotation" capability of the landing gear on soft surfaces falls 27% short of the ESR, and Dasa suggests lengthening the axles on each wheel pair to better spread the aircraft's weight, although "further investigation is necessary".
Also required would be digitally controlled braking and steering. In the electrical system, PVC insulated wiring would have to be replaced with Western qualified wiring, and a DC ground power connection introduced. The auxiliary power unit, meanwhile, was found to be too noisy, and the fact that the unit's jet blast is directed towards the rear cargo ramp is a cause for concern.
The cargo-handling system was deemed capable of accommodating all general air freight requirements, though the on-floor mounting system would have to be replaced with a floor-integrated system. "We have to check that the floor structure below (the cargo deck) allows for the installation of both systems," says Frey. He adds that "an ESR-compliant loadmaster station layout needs to be defined".
Airdrop hazard
Dasa proposes that the rear clamshell doors be split in two to allow the lower sections to fold inwards, so not to represent a hazard when air-dropping. This is because using "Eastern" procedures, troops would be air-dropped using short static lines from the forward side door, whereas Western forces would require the ability to drop from the rear side door.
Dasa recommends that prospective Western customers for the An-7X should evaluate CIS procedures for air-dropping to see if they could be applied by Western air forces.
In the medical evacuation role, Dasa found that with an upper deck floor installed, theAn-7X could accommodate 300 troops, or 95 stretchers and 110 wounded. The additional floor structure could be installed in five hours. However, without the upper-deck floor, the An-7X could handle 174 troops or 96 stretchers.
The An-70 requires two pilots, a flight engineer, navigator and radio operator, but probably the most significant change required for the aircraft is the need for a two-crew cockpit, with the possibility for a third tactical operator.
This is a requirement that closely reflects the proposed cockpit refit for the An-124-210 derivative proposed by Antonov and Air Foyle for the Royal Air Force's short-term strategic airlifter competition.
To meet ESR requirements, a completely new flightdeck would be required, including a wide range of automated systems and a night-vision goggle capability. Another area of concern is that software development for the production aircraft's avionics has not yet begun.
Among the mandatory required actions identified by Dasa are the replacement of CIS military equipment such as the identification friend or foe system and the modification of the mission management system and aircraft integrated monitoring and diagnostic system. The company also identifies the need for exchangeability of avionics components with off-the-shelf equipment, and the provision of software documentation in English.
The flight control system (FCS) uses several unusual features - the horizontal stabilisers are fitted with leading-edge slats, which are deployed automatically when required, the elevators are split into two sections and are double-hinged, while the rudder is double-hinged and split into three sections." You end up with a fairly high number of actuators, but for the primary FCS they use just two types of actuators," says Frey. He recommends an evaluation of the An-70's handling qualities be carried out in the simulator by Western pilots, who could then suggest changes where necessary.
"Fly by tube"
The production An-70 will have a four-channel digital fly-by-wire primary FCS, as opposed to the mixed digital/analogue FCS used in the prototypes. The secondary FCS encompasses two independent flap systems, a leading-edge slat system and 60í blown flaps to boost STOL performance.
The pitch control back-up system uses a hydraulic rather than mechanical linkage to reduce the number of moving parts, which Frey refers to as "fly-by-tube". The methods and procedures used to develop the FCS are "comparable to Western programmes", says Frey, and its high level of redundancy means it is compliant with ESR requirements. But he warns that development of the flight control computer for the An-7X has only just started.
Dasa also determined that the aircraft's digital flap/slat system computer would have to be replaced. It also discovered that components in the FCS would have to be assessed for their maintainability.
Frey and his team also looked at the structure of the An-70, identifying potential weight savings totalling 1,900kg. These included the introduction of composite skin panels and a revised loading system in the fuselage. "You can reduce the [operational empty] weight by 2,000-3,000kg depending on what you want to do," says Frey, but adds "we didn't find any area where we thought that it could be made much lighter."
The aircraft has a design life of 45,000h over 15,000 flights, which meets the ESR requirements concerning fatigue, says Frey. Several aspects of production technology not yet used in the West feature in the An-70. The empennage is constructed using "highly integrated' carbon fibre reinforced plastic (CFRP) techniques. The fuselage stringer and skin joints, meanwhile, are spot welded and hot bonded which, requiring a non-automated process, would be considered uneconomical in the West. Wing manufacture, carried out in Tashkent, Uzbekistan, was not assessed due to lack of data.
For the An-7X, Dasa recommends switching to auto-riveting for the stringer/skin joints and evaluating CFRP winding technology to establish its reproducibility, potential for non-destructive testing and repairability. The company also says that the tooling and technology used in the production of the wing must be assessed in preparation for the possible establishment of a new production line.
Looking at the certification issues, Dasa notes that the manufacturer meets ISO 9000 quality standards, although work will have to be done on harmonising East-West processes and procedures. Well-defined, standardised processes in areas such as materials, parts and information technology will be required, it says, to allow for the second-sourcing of parts from outside Russia and Ukraine.
Only a small fraction of the 1,800h flight test programme for Russian certification has been carried out. Dasa estimates a 3,000h test programme would be required to achieve Western certification, including 2,000h for basic certification, followed by work on areas such as low-level flying and parachute drops.
Enter airtruck
A group of German companies and the Medium Transport Aircraft (MTA) consortium - the Russian and Ukrainian companies building the Antonov An-70 - have formed Airtruck, a German-registered company based at Lemwerder. Airtruck will plan and manage the modification programme required to make the An-70 suitable for Western requirements.
German joint-venture partners in Airtruck include Aerodata, Dasa company ASL Aircraft Services Lemwerder, Autoflug, BMW Rolls-Royce, Bodenseewerk, ESG Elekroniksystem-und Logistic, Liebherr Aerospace and VDO Luftfahrtgerate.
Airtruck says other companies are interested in joining and that the founding partners form a "comprehensive centre of excellence". Airtruck predicts a market of 300 aircraft for the An-7X, 75 of which would be acquired by the German armed forces.
Source: Flight International
