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Aviation History
1975
1975 - 0517.PDF
fLIGHT International, 20 March I97S 453 Private SI iu'lr .:•''.r .i''l':'l-'"t•'*'.•-':t M* i*'*..1*'•'i'.nll.ii'<*."';..'1''.i' •• • .i' •' '. ' 'Lit •' '',•' .fiH .r' y .1. .fl' •.. • High wing, low wing FROM time to time Flight is asked to comment on or recommend a type of aircraft. There is rarely a simple answer, as aircraft have so many characteristics, some of which are helpful, and some of which are not so useful, in a particular job or situation. The prospective buyer should look at these characteristics and assess their effect on the applica tion for which the aircraft is to be used. One of the main distinguishing features on any aircraft is the wing position: whether high, low or in be tween. The design values affecting the choice are discussed here; some arc obvious but are included to balance the picture. From the pilot's point of view the prime consideration is the position of the leading edge relative to his eye If it is aft of his eye it poses few visi bility problems, although ideally i1 should be at eye level so that lie can glance back above or below it, as is possible in most modern sailplanes. Most single-engined aircraft, how ever, place the pilot more or less on the e.g., under or over the wing. In these layouts the wing is almost cer tain to be an embarrassment to visi bility in one situation or another. A high wing is a considerable nuisance in the circuit as it blanks off the air field as one turns from downwind to base leg. It also obscures the cone of air space inside the turn, which may be destined to be occupied by a faster aircraft whose pilot's attention is also directed towards the airfield. However, the high wing undoubtedly gives a better view for sightseeing and map- reading. A particularly good example of this layout is the Citabria, which we Team-tested in 1973. Apart from the unobstructed view downwards to each side, the engine is set well below the pilot's eye level, affording a fine view down forward over the nose. Although a low-wing arrangement gives a clear view of the area towards which the aircraft is turning, it can be an irritation when one is flying directly over interesting ground features. Just as the aircraft is near enough for a river or castle to be clearly seen, the wing tends to get in the way and the aircraft has to be re positioned so that a fairly steep turn will temporarily remove the offending wing and bring the landmark into view. The writer has often crossed in teresting country by Turbi or Kitti- wake in a series of such manoeuvres, which can produce a cumulative navi gational error unless the course is cor rected periodically at known land marks. The main danger of a low wing lies in the possibility of letting down on top of another aircraft in the circuit. Top, the runway just visible beneath the high wing disappears completely as the aircraft banks into its approach glide. Below, a low- winged aircraft has to be banked steeply to bring a landmark into view •vum Mi Unless one is under ATC, it is a good idea to check the airspace below by sideslipping to port and starboard be fore and during descent. An accident occurred after one of the King's Cup races as a result of a lower-flying air craft being obscured by a low wing. One particularly difficult machine from this point of view is the Tipsy Nipper, which has a mid-wing so close below the pilot's eye that it cuts out nearly all of the downward view. Two perspex panels are fitted under the wing roots, but these are usually scratched and oily and suffer too much from reflection to be of much assist ance in map-reading. Luckily the con trols of this machine are so light and powerful that it can be effortlessly tipped on to its car if the pilot wishes to have a good look at the ground below. The blanking effect of a low wing may be reduced considerably by placing the pilot as high above the wing and as far forward as possible, a technique which is easier in larger four-scat aircraft. This solution does, however, tend to cause the pilot to sit bolt upright and can increase the frontal area of the aircraft. The low wing, of course, gives unobstructed upwards and sideways visibility, and an aircraft with this configuration is a joy to fly, particularly if fitted with good controls. For positive-g aerobatics it gives a near-perfect view of the air ahead. It is worth noting that for these reasons all the fighters of the Second World War were low- or mid-wing, while just about all of the single- engined observation designs were high-wing. From a purely aerodynamic point of view a high or carefully faired shoulder wing should be most efficient, as the upper surface (which does most of the work of carrying the aircraft) is effec tive over the full span. Just how' much can be gained from such a wing is seen on the Polish Wilga, which has a full - span leading - edge slat con tinuing right across the top of the windscreen. The angle at which this aircraft can be flown has to be ex perienced to be believed. A high wing is much easier to fair into the fuselage and fillets are rarely necessary. On the other hand a low wing is more difficult, especially with a rounded fuselage or one which is tapered for ward of the trailing edge. At high angles of attack, vortices from the wing fuselage intersection tend to trail up the sides of the fuselage (some-
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