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Aviation History
1994
1994 - 2407.PDF
TP REPORT Bell Boeing to test fix for V-22 buffet GUY NORRIS/BEVERLEY HILLS BELL BOEING IS to flight-test aerodynamic modifica tions to the V-22 Osprey tilt-rotor later this month, aimed at improv ing handling qualities and elimi nating a degree of tail buffet discovered during flight tests. The modifications consist of forebody vortex-control devices, or strakes, attached to the upper fuselage. It is expected that the strakes will alter the airflow char acteristics around the aft end of the aircraft, particularly during high angle-of-attack (alpha) manoeuvres. Test pilots Thomas MacDonald of Boeing and US Navy Cdr Peter Levoci said, at die 38th Society of Experimental Test Pilots (SETP) Symposium in Beverley Hills on 22- 24 September, that load buffet was induced at speeds of 180kt (335km/h) in wind-up turns to 2.5g. "We're breaking new ground all the time," says Levoci, who adds that the Bell Boeing team is also looking "...at some alpha lim iting in the flight-control law to prevent incursions into that area [high alpha]." The test team has also encountered some pilot- induced oscillation and high workloads in controlling the V-22 in die lateral axis. Despite some misgivings, the test pilots praise the V-22's hand ling qualities in general and say that flying the tilt-rotor in vertical take-off and landing mode is "...dramatically improved, espe cially in ground effect". In conversion mode, when the prop-rotors are tilted from verti cal to horizontal mode, a set of autoflaps has been developed to ease a "pronounced pitching moment," which occurred during die transition. The V-22 nose moved "down and aft" in pitch, while converting from vertical to forward flight and vice-versa for re-conversion. The autoflaps work through die auto matic flight-control system (AFCS). In die near term, the No 2 and No 3 test aircraft will undergo "risk-reduction" envelope expan sion. Medium-term tests will include more high-alpha flying, external-load carrying and reject ed-take-off testing. More aircraft, will be introduced into the test programme by the end of 1996. These will be used to complete envelope expansion, for investiga tion of AFCS coupled modes and in more operational testing. • VISTA team wants vectoring engine THE US AIR Force and flight-test specialist Calspan are mounting "a major effort" to have a thrust-vectoring engine installed permanently in the Lockheed NF-16D variable-sta bility in-flight simulator test air craft (VISTA). The initiative is one of five steps to have been targeted by the VISTA team as providing future growth potential for the aircraft. Calspan's Karl Hutchinson ar gues that fitting die aircraft perma nently with a thrust-vectoring powerplant "...would increase die simulation capability". He notes diat die recent success of the X-31, F-18 High Alpha Research Vehicle and F-16 multi- axis thrust-vectoring (MATV) programmes make the inclusion of a thrust-vectoring capability a vital requirement for the future. Immediate modification prospects include a variable-feel side-stick for die front cockpit alongside its vari able-feel centrestick. "This is already designed and will probably be installed in sup port of [Lockheed/Boeing] F-22 system testing," says Hutchinson. The safety pilot's conventional F- 16 sidestick controller in the rear cockpit will remain unaffected. Other proposed growth steps include a move to programmable cockpit displays. • US Army arrows in on Longbow glitches MCDONNELL DOUGLAS Helicopter Systems is working to correct several of what US Army test pilots call "deficiencies and shortcomings" in its AH-64D Longbow Apache. Some 16 deficiencies and 73 shortcomings have been identified by the pilots during an intensive preliminary airworthiness evaluation covering 75 flying hours and 50 sorties in day and night condi tions. The US Army declines to specify the problems, but one of the test team says: "They are things like glare from multi function displays." Army test pilot Maj Patrick Garman says: "To date, ten deficiencies and 24 shortcomings have been cor rected. We are scheduled in December to evaluate the aircraft again and eliminate the rest." US Navy to remove F-14D missile-launch restrictions THE US NAVY is expected to lift restrictions on the Grumman F-14D missile-launch- envelope, imposed after fears that the aircraft's newly-developed dual chin pod (DCP) would cause potential separation problems. During technical evaluations of the dual pod, containing a Martin Marietta infra-red search-and-track sensor and tele vision-camera set, some vibration was noted, which "...indicated a more restrictive missile-firing envelope", says US Naval Air Weapons Center (NAWC) test pilot, Lt John Einhorn. Concerns were voiced that changes in the flow field beneath the F-14D would increase missile pitching and yawing moments. "We were especially worried about the pitch-up of missiles," says Einhorn. An NAWC test programme was used to demonstrate separa tion of AIM-54C Phoenix and AIM-7F/M Sparrow missiles in various conditions, ranging from Mach 1.5 and 30,000ft (9,000m) at 3g for the AIM-54 to Ml.6 and 37,000ft at over \g for the AIM-7. "The dual chin pod did cause more nose-up pitch and more outboard yaw," says Einhorn, who adds that, after launch, the mis siles made a "close pass to the radome and DCP". The test programme concludes that the "...DCP has an effect on trajectory, but does not affect safe ty". It says that the F-14D missile firing envelope will be expanded as a result and will be "equivalent to the F-14A/B". USN test teams at Patuxent River, Maryland and Point Magu, California, are work ing on a continuous programme "to look at the impact of the DCP on air-to-ground stores". The investigation follows "some interesting effects" on Mk82 weapons during separation tests at NAS Patuxent River. • FLIGHT INTERNATIONAL 5 - 11 October 1994
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