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Aviation History
1971
1971 - 0064.PDF
FLIGHT International, 14 January 1971 59 1 note. The whole system (and particularly the latter feature) is one of those devices to whose advantage many pilots are initially quite blind, or rather deaf, until they have used it a while, from then on they are unable to understand how they lived so long without it. The stalls of the two aircraft in the blown launch or landing configuration differ in that the Buccaneer flies up to its limit with positive longitudinal stability, though this reduces near the stall if wing-tanks are fitted, and the stall occurs with no worthwhile warning. An abrupt but small pitch-up and wing drop occurs and is instantly amenable to standard corrections. The angle-of-attack indi cator shows about 29 units, 20 units being the datum for the landing and around 10 units the figure for flight at about 400kt. Similar numbers apply to the Phantom, though for no very good reason the approach datum is 19.2 units. At 22.3 units a rudder-pedal shaker of dubious value is triggered off, around 25 units uncommanded wing rocking may occur and can exceed ±30° of bank if the pilot makes no rudder corrections; at higher angles-of- attack the rocking ceases and after 25 units a longitudinal reversal becomes apparent;-the aircraft is considered to be stalled around 27-28 units, when some yaw divergence may be felt. As both aircraft have little or no classic buffet warning in this configuration, the angle-of-attack indicator is particularly valuable. Angle-of-attack has been quoted in units because the indicator is common; as the diagram might imply, however, the units do not have a common value. Lateral control during the approach is influenced by the adverse yaw experienced with aileron deflection. The Phantom has an aileron and spoiler combination; ailerons, drooped 16.5° for the approach, can move 30° down or 1° up, on the opposite wing the spoiler can move upward through 45°. The combination does not, however, eliminate adverse yaw, so roll-control is augmented by a very suc cessful aileron-to-rudder interconnection system which operates whenever flap is lowered and commands a rudder deflection of up to 15° in the direction of, and proportional to, lateral stick displacement. The Buccaneer goes to no such lengths. Aileron deflects up to ±17° around the droop angle of 25°, adverse yaw is just as apparent but it is left to the pilot to apply co-ordinating rudder deflections in a manner reminiscent of that needed for the Tiger Moth. Controls The different design philosophies are manifest on a smaller scale in the longitudinal controls. At first sight both appear to be conventional all-moving tailplanes which can be expected to become increasingly powerful and sensitive at high EAS. The Buccaneer is designed for this region near the ground, so, as one of a number of ways of avoiding oversensitivity, it keeps tailplane area to a mini mum at high speed and employs a tailplane flap to restore power at low speed. This surface acts as a conventional flap does on a wing and at the same time balances the strong nose-down pitching moment of the aileron droop, to which movement„ it is directly related. To suppress tailplane stall the undersurface of the tailplane leading- edge is blown in the same way as the wing, and here the analogy with a slat finds concrete expression in the fixed slat added to the leading-edge of the Phantom tailplane. It is found only on the two variants with drooped ailerons, and on the F-4E where the e.g. has been moved forward by the addition of the Vulcan gun. No other devices are used on the Phantom tail since, with all its eggs in the supersonic basket, it must retain a large tailplane area for manoeuvre in the high stability regime which is induced by the aft shift of the wing centre-of-pressure at supersonic speeds. Performance comparisons are simplified by the similarity of the empty weights and fuel loads, providing the Phantom's four Sparrow missiles, which are reckoned as basic equipment, are not included in the empty weight. Minimum launch speeds are similar at, for example, a lowish weight of 43,0001b, 19,500kg, they are 120kt for the Buccaneer and 122kt for the Phantom; the contribution of reheat is illustrated by a jump to 136kt if it is not lit. For airfield operation the Phantom reheat halves the unreheated take-off ground run of 4,000ft, 1,220m at 50,0001b, 22,700kg. At the same weight the blown Buccaneer is midway at 3,000ft, 910m, thanks mostly to a lower unstick speed of 144kt against the Phantom's 165kt with and 174kt without reheat. An unblown take-off is possible on the Buccaneer at reduced aileron droop and flap angles but the ground run, despite the thrust increase, is increased to 3,700ft, 1,130m by the higher unstick speed of 175kt. At a typical landing weight of 33,0001b, 15,000kg, the Phantom angle of attack of 13° generates a CL of 1.08 against the Buccaneer's 1.25 at 10.5° and results in approach speeds of 130kt and 124kt respectively. It is instructive to compare the Sea Vixen at this weight and to see that a 25 per cent increase in wing area to 650ft2, 60m3, requires a speed lkt higher than that of the Buccaneer. So maybe it's all worthwhile. • Above. Phantom landing-on. The large flaps keep the speed down against the high power setting needed for BLC blowing. Below, Buccaneer at touch down—the drooped ailerons are prominent
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