Testing of the Lockheed Martin C-130J Hercules II is catching up on its delayed start, with rapid expansion of the flight envelope to all-new limits.
The first four test aircraft have amassed more than 220 flight hours on 60 sorties. Eventually, nine aircraft will be involved in the programme, which is due to cover 14,040 test hours, with a scheduled completion in September 1997.
The flutter envelope has been cleared up to 37,000ft (11,300m) at 160kt (300km/h) calibrated air speed, 30,000ft at Mach 0.705 and 19,000ft at Mach 0.685. Stalling speed with no flap at 32,000ft was determined at 120kt with an angle of attack of between 27í and 29í. With power on and flap deployed at 12,000ft, stall speed was reduced to 60kt. Windmill air-starts of the aircraft's new Allison AE2100D3 turboprops have been successfully achieved throughout a large envelope between 25,000ft and 5,000ft over a speed range of 170-270kt.
Part of the flight-testing has been aimed at seeing just how much faster the aircraft will go with the AE2100s. These are flat rated to 3,425kW (4,590shp) for the C-130J compared to the previous 3,360kW Allison T56-15s. "We knew the aircraft is structurally capable of more," says the test team, "and we had a desire to expand the Vmo [maximum operating velocity] beyond the C-130H envelope."
Flutter testing, therefore, began exceeding the Mach 0.46 limit of the H and aimed for Mach 0.72. "It turned out that the maximum speed of the aircraft was limited by flying qualities, not flutter," says the team.
During one test, the C-130J Mach number was indicating 0.68, whereas that of the chase aircraft was registering 0.70. "We were getting compressibility effects on the pilot tube. When we reached M0.70, all hell broke loose as we hit Mach buffet," says chief experimental test pilot, Lyle Schaefer. Buffeting was "pretty bad," at around 2G, and reverse static stability was encountered.
Despite crew efforts to counter it, "-the nose still came up". The aircraft reached "an uncomfortable" side-slip angle of 37í during the recovery.
Source: Flight International
