Design and developmentEdit
The Il-76 tanker was conceived as long ago as 1968, but the transferable fuel load for the initial version was only 10 tonnes, which was insufficient, so development was shelved. When the higher performance Il-76 became available the tanker project was restarted in 1982 as the IL-78.
In addition to the increased fuel load of the late model IL-76, the IL-78 has two removable 18,230-liter fuel tanks installed in the freight hold, giving transferable loads of 85,720 kg (188,980 lb) (with hold tanks) or 57,720 kg (127,250 lb) (without). Controlled from the gunner station, which is stripped of military equipment, three aircraft can refuel in flight simultaneously from the UPAZ-1A (IL-78) / UPAZ-1M (IL-78M) 26m refuelling pods fitted to the outer wings and rear fuselage. In addition, four aircraft can also be refuelled on the ground using conventional refueling hoses extending from the freight hold. Because of the aircraft's high all-up weight after take-off, which in an emergency would mean landing at weights well in excess of maximum allowable landing weight, the IL-78 has a fuel jettison system with jettison ports at the wingtips.
Soon after the IL-78 passed acceptance tests in 1984, Ilyushin was instructed to design and produce an upgraded version to be known as IL-78M. The IL-78M is a dedicated tanker and cannot be converted back to the transport role easily. Adding a third freight hold tank increased transferable fuel to 105,720 kg (233,070 lb) and maximum take-off weight (MTOW) to 210,000 kg (460,000 lb), necessitating reinforcement of the wing torsion box. UPAZ-1M refueling pods improved maximum fuel flow to 2,900 l/min (638 Imp gal/min). Because the Il-78M is not "convertible", all cargo handling equipment was removed and cargo doors were deleted, saving approximately 5,000 kg (11,000 lb) in structural weight.
Early versions of the IL-78 have the fuselage pod mounted on a short horizontal pylon, but the Il-78M has the fuselage pod suspended from an identical pylon to the wing pods, attached to a short stub wing. This modification was served to isolate the pod from turbulence generated by the fuselage, with the added benefit of commonality with the wing pod/pylon combination. Some IL-78s were produced with Aeroflot colors and civilian registrations, but production IL-78Ms received military markings, registration and color scheme.
The majority of the twenty IL-78 aircraft on the strength of Ukrainian Air Force have been permanently converted to pure transports, freight hold tanks and refueling equipment being removed