Guy Norris/LOS ANGELES
New Bell Boeing MV-22 Osprey sea trials will be conducted this month to perfect low level hover characteristics and test flight control software that was revised following a narrowly avoided crash during last year's trials.
Tests will take place on a Wasp (LHD) class assault ship to augment sea trials conducted early last year on the USS Saipan (LHA) and in September on the USS Tortuga (LSD) assault ships.
The US Marine Corps says the trials developed day and night launch and recovery envelopes for six of the nine LHA landing spots and both LSD spots. However, two "significant" handling problems were discovered during the first period at sea requiring the changes about to be tested.
One characteristic, pitch up with sideslip, was known before the start of tests. The second, a non-linear lateral control response, was unexpected and tests were stopped until the flight control system [FCS] could be modified, says the USMC. The problem was uncovered when the V-22 attempted to land on spot seven, just aft and left of the ship's island. In winds of up to 25kt (46km/h), the aircraft suddenly rolled to 37° bank while only 3m (10ft) above the deck. Disaster was only avoided because the left rotor was over the water, and full power had been applied to initiate a climb.
Analysis showed that a left lateral trim bias, combined with insufficient FCS port authority and small-displacement control inputs, saturated the lateral control axis.
Following tests in a Boeing simulator and flight trials at the US Navy's Patuxent River test site, the FCS laws were revised to improve lateral handling. Trials on the LSD showed response was more predictable. "In a low hover the aircraft was much better behaved, so we were able to get back to the ship and test it," says the USMC, adding: "this month the test team plans to go out to do landings on an LHD." The LHD deck is wider than the LHAs, and the USMC adds "we have decided not to do any landings next to the island on [an LHA]."
Source: Flight International
