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Aviation History
1980
1980 - 0941.PDF
900 FLIGHT International, 22 March 1980 Letters Avgas: study of alternatives needed SIR—The latest Avgas price increases mean that I pay £2-06 a gallon for my Aztecs while at the same time paying £115 a gallon for car fuel. A few years ago the UK Civil Aviation Authority and the oil com panies met to discuss the use of auto motive fuel for light piston aircraft after the question had been raised by a manufacturer converting car engines for aviation use. Apparently the meeting established that little difference existed in the respective properties of the two fuels. The CAA suggested to the oil companies that a few tests be made to make the automotive fuel acceptable for avia tion use. Hut these tests were not proceeded with however, as the main advantage being sought was a lower lead content and it had already been established that the lead contents were similar. The practise of using automotive fuel in aircraft has been going on in small airfields for years with aircraft owners bringing out drums of their own fuel for their weekend flying. Companies overhauling these engines do not report any difference in their condition. I unfortunately do not have any information at the moment on whether the engines run any better on automotive fuel or whether it caused the same problems as the new Avgas (100LL as opposed to 100/ 150) with burnt valves, cracked heads and broken rings. Now that supply and cost has become a problem I think the whole subject should be examined very quickly. CAPT JOHN TURNBULL Edinburgh Air Services (Chief pilot Edinburgh Airport and managing Scotland director) Braking-action measurement evidence SIR—The article Braking action: how good is good? by Colin Gordon (Flight, February 23) appears to be mislead ing in certain respects. • Background history. The author's understanding of the background to friction measurement systems seems to be a little confused, in that the Mu-meter and a skidometer are not the same thing, and were not developed in the UK in 1930. The Mu-meter was developed in 1S67, and entered service for use on airfields in 1968. Its officially approved use has since become worldwide, finding appli cation in more than 40 Countries. • Sideways Force Co-efficient. Measur ing friction by using side force co efficient, as the Mu-meter does, could tell the pilot more than a measure ment based on fore and aft limited slip only. Fore and aft limited slip method does not take into effect any degree of cornering force which con trols directional stability. • Mu-meter tyre pressure. The Mu-meter tyre pressure of 10 psi has nothing to do with tyre wear; it was established in order to enable the equipment to sense aquaplane con ditions at a moderate and safe towing speed. • Correlation with aircraft.- With the Mu-meter, positive correlation with many aircraft has been established and computation of stop-distance against Mu-meter reading is possible provided that the many other factors affecting this are taken into account. • Mu-meter results. The Mu-meter does not lead authorities to believe their runways never fall below the level of "good." It clearly picks out surfaces requiring attention, or which can create hazards for other reasons. The FAA has specified the Mu-meter for its current major airport classifica tion programme. • Saab friction tester. To state that the Saab friction tester is basically an aircraft-type anti-skid controllable sys tem is incorrect. The Saab has a fixed 15 per cent slip ratio governed by a transmission system. Most anti-skid braking systems work on sensing any deceleration of the wheel which is greater than normal, and instantly relaxing the braking, this process cycling many times a second. Aircraft braking systems tuned to operate around the maximum "u" condition in effect produce a slip ratio of 5 per cent to 15 per cent (the Mu-meter has what is approximately equivalent to a 13*2 per cent slip ratio). • Data presentation. The description of the Saab friction-tester data presen tation also largely applies to Mu- meters with automatic printout units, including average friction computa tion facility. • Braking action code. It would only be possible to dispense with estab lished tables of braking action if one type of ground friction measuring equipment was used universally, and the aircraft were equipped with manuals relating braking action to the measurements obtained from this one type of vehicle. It is only on snow and ice that a 0-4 and above reading is "good." On wet surfaces it is 0-5 and above. • Correlation graphs. Before a state ment can be made that the numbers given by the Saab are accurate and representative, quantitative-trials data evidence should be available to sup port it. Numerous graphs are available relating Mu-meter readings to various aircraft stop performances. These authenticate the use of the equipment. V. A. BENNING (Mechanical equipment manager) ML Aviation White Waltham \erodrome Berks IMTSB wrong on San Diego? SIR—The US National Transportation Safety Board (NTSB) is wrong in some of its conclusions about particular San Diego area airmisses. Your article (Flight, January 16, page 218), taken from this report says that neither of the general-aviation aircraft in two reported nearmisses were in contact with ground control. In fact, in one of the instances, the general-aviation pilot was in contact and had been given a discrete transponder code to squawk. In this particular incident, the NTSB did not investigate, but merely asked the Federal Aviation Administration to get a statement from crewmembers. The NTSB did not check flight re corders nor measure visibility, nor seek statements from passengers. Neither did it do a radar track until Aopa asked for it. Even then, the NTSB indicated it was incomplete. I am not being critical of your edit ing, but rather suggesting the NTSB should have been more thorough be fore issuing statements. CHARLES SPENCE Aircraft Owners and Pilots Association 7315 Wisconsin Avenue Washington DC 20014 USA ITTBRIEF The Devon Aircraft Research and Re covery Team wants to hear from any one who was a member of 67 MU (maintenance unit) that operated at St Eval and Taunton in the Second World War. The team is preparing a full unit history, and would also like to contact people who had experi ences with aircraft crashes or salvage in Devon and Cornwall and served with either the ARP, Home Guard, St John Ambulance, fire service or police. Write to chairman A. Robin Hood, "Elmbrook," 31 Church Road, Barton, Torquay, S. Devon TQ2 8PN
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