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Aviation History
1961
1961 - 0652.PDF
Controllability in handling—demonstrating compliance with British Civil Airworthiness Requirements Section D2.8, paragraph II THIS is a story of flight-test routine—a story of the flying thatprecedes delivery to an airline of a new aircraft variant, in thiscase the Herald Series 200. It was September last year whenHandley Page announced that six Heralds had been ordered by Jersey Airlines, and that they would be 200-series aircraft. These areextended by 4/in in front of the wing and have a gross weight in- creased to 40,0GGlb. As related on page 665, the first is to be de-livered in the late summer, dressed in the airline's new Charles Butler-designed livery with a sun-yellow flash and fin. No great changes in handling characteristics were expected as aresult of the fuselage stretch, but an extensive fiight-test programme was necessary to convince the ARB that the Herald's stability andcontrol were not impaired by the associated forward movement of the e.g. A lot of development flying, leading to tail-surface modi-fications, was devoted to ensuring tnat passengers could be seated at random in Series 100 aircraft. A similar aim is being followedin developing the 200. Moving passengers up and down the fuselage at intermediate stops to adjust the loading is popularneither with airlines nor with travellers. In aerodynamicist's terms the extended fuselage has brought thee.g. forward by 1 per cent of the standard mean chord. Some wind- tunnel tests were carried out on a model of the new fuselage, but theeffects were shown to be negligible. Any adverse changes could, it was anticipated, be ameliorated by the forward shift of e.g. A testschedule was agreed with the ARB on the basis of that used for the Series 100 aircraft, and when the aircraft first flew on April 4 theHandley Page test team were ready to go ahead with a programme which, it was expected, would last about two months. At the end ofthis time the first 200 should be awarded a special-category Certi- ficate of Airworthiness, leaving only about a week's production testflying to obtain a normal C of A for the first production aircraft. In this account the part of the programme concerned with per-formance testing is necessarily glossed over; the small differences that occur between 100- and 200-series aircraft are the result of the1,0001b increase in maximum weight and not of the extended fuse- lage. These differences will largely disappear when the Series 100 iscleared, as intended, at the same maximum weight of 40,0001b. From a handling point of view the aspects that are now beingexamined in test flights from Woodley concern the stall, flying at minimum control speeds, stability and sideslips. Conducted over awhole series of configurations, tests under these four broad headings establish the handling behaviour of the aircraft. In the stall, for example, there are two aspects to be examined:the manner in which the aircraft handles and the speed at which stall occurs. On the Series 100, the stall is innocuous and there is no wing drop. British Civil Airworthiness Requirements, the bible fora 11 flight test and experimental work, demand that if wing-drop does PROVING TH Test-flying Techniques on the Aircraft occur it must follow the pitching-forward of the nose, and must notexceed a bank angle of 20 . As the Herald's wing was originally designed to give good stalling characteristics it was difficult tovisualize any deterioration in performance with the extended fuse- lage, and the 200 behaves, if anything, slightly better. What was notexpected was that stalling speed with flaps down would be a few knots lower than previously; at a typical weight of 33,5001b Vso is63kt. The stalling programme is formidable, each stall being carried outat four e.g. positions, four configurations (clean, flaps deflected 5 and undercarriage up, flaps at take-off position and undercarriagedown, and flaps and undercarriage down), and at three different aircraft weights. To determine the speed at which stall occurs, eachis performed five times in each configuration. Then there arc stalls in turning flight to be investigated, power-on stalls, dynamic stallsand stalls with one engine inoperative—a total of 600 altogether With the aircraft ballasted at the right e.g. position and at theright weight the technique is to trim-out at a speed 40 per cent above the expected stalling speed, and then to reduce speed at aboutikt/sec until the aircraft stalls. During this period out-of-trim forces, control angles and aircraft attitude are measured on a tracerecorder. Stalls in turning flight are carried right through until full breakaway occurs; it has been demonstrated that the Herald rollsout of the turn on all occasions. Quite extreme attitudes are some- times developed during investigation of the stall with power on.This may also be the case in dynamic stalls, in which the airflow separation point is approached appreciably faster than at lkt./sec,and with some g loading on the aircraft. Less stringent conditions are attached to the behaviour in the latter case, but there muii stillbe no violent wing-drop. The Herald stall programme has been carried out at convenientheights between 6,000 and 12,000ft, height lost in recovery ucing measured and recorded. One aspect of stall performance is th.it theconfiguration does not lend itself to providing natural, aerodymic stall-warning, and a stick shaker is fitted to provide this infoi nartificially. As experience is gained in the flight-test programr. device is set to operate between 5 and 10 per cent above the s"speed in each configuration. What happens if there is sudden and complete failure cpowerplant, particularly when the aircraft is taking off? Thi ion this °Jje
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