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Aviation History
1988
1988 - 2732.PDF
after the first, was more severe, and Goode found that if he pulled more than -2g an attack of giddiness would strike immediately, "Obviously there is no hope of performing an unlimited level competition sequence with this kind of restriction," Goode said. Goode believes he is not alone in having had such problems, but suspects fears of licence withdrawal, particularly from those who fly for a living, have dissuaded some pilots from speaking out, so that the real extent of the problem is unknown. Theories differ as to why it occurs. Flight interviewed three specialists and received three different opinions. "There is nothing in medical literature on this, and I have researched it several times," says Dr Richard Rihn, aerobatic pilot and medical director of As g-\oc and vertigo appear to place physiological limits on positive g and nega tive g manoeuvrability, how will aerobatics develop? Michel Dozieres, research manager at French firm Mudry, thinks that, aside from flying styles, it can go two ways: designers can drive down the price of aero batics or drive more technology into the aircraft. The effect of the former would be to attract more people into the sport whereas the latter would turn competition aerobatics into a Formula 1 car racing-style event need ing substantial sponsorship for support. His company has joined the trend to composite structures with plans to develop a composite wing for the wooden Mudry CAP.230 (a type flown by the French team at WAC '88). He suspects that the CAP.230's roll rate of around 300 deg/sec is about 40 deg/sec slower than it might be because of wing deformation. The wing, if built, may be offered as a retrofit to the all-wood CAP.230. Another change to the CAP.230 under consideration is a more powerful engine. Dozieres says that currently available engines would not enable the CAP.230 to retain its present certification category, so this would be offered as an option. The Soviets continue to lighten the Su-26M to bring down the wing loading—it was seen to begin to stall in tight manoeuvres at WAC '88. Aerodynamic changes may be made to the fuselage, and the carbon wing continues to be inspected with ultrasound every lOOhr, says Smolin. On future Soviet plans, Flight has obtained details of a new design being proposed by Yakovlev, which, if built, may replace the Su-26M in competition in about four years' time. The aircraft is to be offered in two-seat and single-seat versions as the Yak-56 and Yak- 57, and will share the same airframe. This is being made possible by the development in the Soviet Union of a new lightweight engine from the Ivchenko stable, says chief WAC '88, with a longstanding interest in the effects of g. Dr Rihn's theory is that high negative g can cause an inner ear rupture, and that it is this damage that leads to the vertigo. The view is reinforced by the fact that the symp toms are aggravated by head movement, Dr Rihn says. A second theory comes from John Firth, a consultant neurosurgeon at University Hospital, Nottingham, England, aerobatic pilot, and president of the FAFs medical committee. He has examined Goode as well as a number of other pilots and believes that the forces on the brain during manoeuvres may cause haemorrhages in the brain stem. A third specialist, interviewed in England by Flight, but who declined to be named, ; next designer Sergei Yakovlev. The 300 h.p. eight-cylinder unit, whose air-cooled cylin ders are arranged in a double cruciform layout, will weigh 150kg, Yakovlev says. The 360 h.p. Vedeneyev engine in the Su-26M (limited to 340 h.p. by the propeller) weighs some 220kg. Smaller and lighter than the established mid-wing Yak-55, the new aircraft will have a lighter wing loading and need to pull less g than the Su-26M. Maximum take-off weight is expected to be under 650kg, giving a wing loading of 65 kg/m2. Aerodynamic features are "secret" and windtunnel tests are not yet complete, but Yakovlev reveals that full-span ailerons will work as flaps and be linked to elevators, a system used by some Western aircraft. A modified Yak-55 has been flight-tested to prove the system works, and a version of this aircraft may go into production next year. Yakovlev wants the new Yak-56 and Yak-5 7 to be the most advanced aerobatic aircraft, and holds out the possibility of export to the West for $50,000 if it is produced in significant numbers. Yakovlev expects the design will have to compete with a new rival from Sukhoi, however, before production can go ahead. In the USA, Henry Haigh, the new World Aerobatic Champion, has been developing an unconventional aircraft called the Ratsrepus 360. Haigh claims that this is a "radical departure from anything built so far". Its 93in-diameter geared propeller, driven by a 360-h.p. engine built from Lyco ming parts, will produce static thrust greater than the aircraft's 1,2001b weight, giving good vertical penetration without the need for high airspeed. Although the nature of future devel opments is uncertain, it is sobering to reflect that Haigh won this year's men's World Championship in an aircraft modified from one which first flew 12 years ago, which is of all-wooden construction, and which has just 200 h.p. He built it himself. suggested the possibility of damage to the otolith organs, small membranes of calcium on top of hairs and embedded in jelly that act with the ear's semi-circular canals to provide balance. The view of this last source is that there is not enough evidence to choose between the theories and that fresh research is needed. The difficulty in mounting research in the USA is that only the military have the neces sary test facilities. Research has not yet focus- sed on sudden changes from high negative to high positive g, but some negative g data is emerging, says Dr Rihn. But any test which would expose a subject to risk of phys iological damage is likely to be considered unacceptable, says the English source. Any reluctance of affected pilots to talk openly about the problem would also be an obstacle. Pilots defend the sport's safety level. "I don't believe there has ever been a fatality in a World Championship," says Heuer. Firth stresses that there is no evidence that dizziness has ever been serious enough to have caused an accident. He believes weather minima at contests probably protect competition pilots from g-induced dizziness, whereas those at risk are airshow pilots flying in rough weather. In Dr Rihn's view, the only people who could be affected are the "cream" of pilots or those who return to competitive flying too enthusiastically after a layoff. But though the pilots interviewed by Flight have a cautious respect for the effects of high g, the view persists that a link between the phenomenon and high negative g has yet to be proven. If there is a link, how can pilots protect themselves? The advice of Rihn and other experts is to build up g levels slowly over a number of flights, and to avoid excessive practice. More simply, high g could be avoided altogether by flying a relatively slow aircraft. Smolin, who, like other Soviet pilots, pulls high g, is enthusiastic about the performance of Price's 10 Dash 300 biplane: "That is a good aircraft". In fact, there is evidence that the Soviets may move away from high-£ manoeuvres. A design proposed by Yak, which might replace the Su-26M in competition, would be cleared to just lOg and -8g, says Sergei Yakovlev, chief designer at the Soviet enter prise (see box). "It is a question of the pilot, not the airframe," Yakovlev says. Goode, a skilled aerobatic pilot of a Yak- 50, advises against practising hard during turbulence, which could create transient levels of over -lOg. He suggests keeping the head facing forward on entry to a manoeuvre. Firth stresses that if a pilot runs into the problem he or she should seek medical advice and that abstinence from any type of flying for a couple of months may be neces sary. Reassuringly, he adds that all the cases he has investigated have settled down and are "benign". There is no suggestion that either of the phenomena poses a serious safety threat to the sport. C 30 FLIGHT INTERNATIONAL, 24 September 1988
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