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Aviation History
1970
1970 - 1361.PDF
WORLD AEROBATICS '70 Aerobatic technology THE WORLD AEROBATICS CHAMPIONSHIPS began on schedule last Wednesday. July 15. The first programme, the known compulsory sequence, was scheduled to be completed on the following day. Practice had been a little interrupted by a slow- moving front and earlier by high winds but all pilots had an opportunity to practise, once in the local area and once over the airfield. At the time of going to press, preliminary results were not available but a glimpse of some of the competing aircraft revealed some interesting developments. An unknown quantity at the World Aerobatic Championships is the Akrostar, a brand-new European competitions aircraft. It was designed by Arnold Wagner, the Swiss aerobatic champion, who is a Swissair captain, and uses a unique system of control interconnection between elevator, ailerons and flaps. The idea is to boost the lift coefficient in various flight con ditions. When the stick is fully back, ailerons and flaps droop —the flaps half the amount of the ailerons. This increases the wing camber and provides more lift when pulling positive g. Similarly, when the stick is fully forward, ailerons and flaps "droop up." With a completely symmetrical-section wing, lift available in inverted flight is therefore the same as in erect flight. For turns, the flaps also move half the amount of the ailerons so that the aircraft effectively has full-span ailerons with the inner section (the flaps) constantly in the engine slip stream. Stirring the stick seems to make just about everything move but Wagner claims that no complex control linkage is required. A system of interconnected flaps was fitted by Mr Wagner to the KZ8 which he recently sold to Bob Mitchell. The idea was borrowed from the model aircraft world. The Akrostar is fitted with a 220 h.p. Franklin engine and Wagner claims that although the aircraft stalls power-on at 65 k.p.h., it will continue climbing at full power at this speed (or perhaps "mush" upwards) at 700ft/min, 3.5m/sec, and still with lateral control. The measured thrust from the Hartzell constant-speed propeller is 1.0341b. 4.6kN, for an all-up aero batic weight of 1.3231b, 600kg, which compares with the Zlin's 6601b, 2.9kN of thrust and all-up aerobatic weight of 2,0721b, 940kg. Wagner has also designed the engine's unique inverted wet-sump lubrication system. It is fed by two pumps and an extra sump has been fitted to cope with inverted flight. The Akrostar has epoxy spars and ribs and is covered with plywood skinning. Operating limits are + and —8g with ultimate limits of + and — 12g. The epoxy construction means that fatigue is not a problem. In a normal competition sequence, Wagner reckons to pull +7g and — 5g. Wagner sought advice on the aerofoil from Professor Eppler, who designed the wing section for the Phoebus and SHK gliders. The design parameters were processed by the computer at Bolkow and the outcome was virtually identical to Eppler's predictions. The result is a wing of symmetrical section with no dihedral and slight sweepback and mounted at zero angle of incidence. The aircraft was built by Wolf-Hirth GmbH. It was paid for mainly by Jo Hoessl, the German champion who is flying it at the world championships in addition to Wagner. The total cost is estimated as £15,000, of which £9,000 was taken up with building and the remainder in research and development. Heading picture: the Wagner-designed Akrostar showing the virtually constant section of the wing from root to tip. Above, stick left on the Akrostar, showing full up aileron with the interconnected flaps up half the amount of aileron deflection. Below, the aircraft has its landing gear placed well forward which helps to give some of the drag necessary when pointing vertically down Above, the French team has a CAP 20 on its strength. Built by Co operative des Ateliers Aeronautiques de la Region Parisienne (CAARP), the aircraft is descended from the Piel Emeraude and is powered by a Lycoming Al 0-360 engine. Below, the Russians have a tail- wheel version of the Yak-l8P at Hullavington, designated PS. It is otherwise similar to the tricycle-gear PM
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