HANDLING QUALITIES FLIGHT TESTING OF HELICOPTERS AT EXTREME LATERAL CENTER OF GRAVITY

This paper addresses the handling qualities of the UH-60A Black Hawk helicopter at several lateral centers of gravity that could result from asymmetrical external fuel loading with the Extended Stores Support System (ESSS) installed. The primary test objective was to determine if normal aircraft operations could be conducted at or below 100,000 in-lbs lateral moment (maximum lateral moment for normal operations) without exceeding the aircraft flight envelope or applying additional flight limitations and restrictions. Additionally, if the maximum lateral moment for normal operations were exceeded, would the pilot be aware of exceeding this limit and what pilot actions would be required to prevent loss of aircraft control. The test consisted of 25 flights with the ESSS configured with 230-gallon external fuel tanks mounted on the outboard vertical support pylons. The aircraft was ballasted for nine different lateral moments ranging from near-mid to 191,000 in-lbs, which is equivalent to an asymmetrical jettison of full outboard 230-gallon external fuel tanks. Tests were conducted in both forward flight at mission relatable airspeeds and low-speed flight at different azimuths. Aircraft parameters affecting lateral control margins that were of primary interest were airspeed, power, load factor, and aircraft gross weight. Test results revealed that in forward, descending, ball-centered flight at low airspeed and minimal power with a right-lateral imbalance, the sideslip limits of the aircraft could easily be exceeded. This was the only limit exceeded while operating at or below the maximum lateral moment for normal operations. At larger than normal lateral moments (150,000 in-lbs, 174,000 in-lbs, and 191,000 in-lbs), five conditions tested resulted in control margin less than 10%. While attempting to stabilize on one test point, a handling qualities rating (HQR) of 10 (aircraft uncontrollable) was assigned. Additionally, during low-speed flight and cross-slope landings, the control stop/limiter was contacted several times.