Armann Norheim - Articles and news items
Issue 6 2011 • 8 December 2011 • Armann Norheim, Leader of the ICAO Friction Task Force (FTF)
The history of the world includes many well known inventions which have had a significant influence on technological developments. One of these is the Dynamometer, a device used for measuring force, moment of force (torque) and power. Dynamometers have been a vital and necessary component in instruments that can identify the friction developed between a tyre and the surface it acts upon.The principle used is an invention that is nearly 450 years old. The instrument indicates weight or pressure by making use of Hookes law1 of elasticity which states that “the extension of a spring is in direct proportion with the load applied to it”. In this article we will look into the history of tractive resistance within the transportation sector up to the advent of the jet aircraft. France, 1798Long before the birth of aviation, in the early 1780s Edme Régnier started the development of what came to be known as The Régnier Dynamometer2. Régnier was encouraged by two naturalists (Buffon and Guéneau of Montbelliard) who desired a device by which a man’s strength would be rendered comparable to that of another. The French revolution came, Buffon and Guéneau died and Régnier became inspector of the manufacture of portable arms. In 1796 the physician Coulomb urged Régnier to resume his work in view of the developing industry. Régnier’s Description et usage du Dynamomtre appeared in 1798.
Issue 3 2011 • 10 June 2011 • Armann Norheim, Leader of the IATA Friction Task Force (FTF)
In railroad engineering, the factor of adhesion of a locomotive is the weight on the driving wheels divided by the ‘starting tractive effort’. Adding extra power serves no purpose since there is not enough traction (adhesion, friction) to create useful work. The factor of adhesion which is 25% of the weight on drivers, corresponds to the co-efficiency of friction for steel-on-steel with an oxide surface film of μ = 0.25.Within aviation we are constantly in search of the ‘stopping tractive effort’. The term ‘braking action’ has been used to describe this. It is not an accurate description since its use is not consistent. In the U.S. the term relates to the pilot reports only, within ICAO it has been used for both pilot reports and the reporting of runway surface conditions. A letter is due to be sent out to American States requesting feedback on the subject. In due course, this may result in changes across all levels.
Reporting the conditions of the critical tyre/surface in a way relevant to aircraft performance has been a long sought goal. There have been a lot of challenges for the aviation industry since the first reporting systems emerged and the regulating bodies have their role to play in achieving the goal for a global reporting system. Key players in such a reporting system are the airport ground staff collecting the information and making the assessment and the pilots making judgements based on the information given. The main regulating bodies (ICAO, FAA, and EASA) have several initiatives ongoing addressing these topics.