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Aviation History
1931
1931 - 1133.PDF
FLIGHT, OCTOBER 23, 1981 THE BRAUN RELATIVE ALTITUDE METER INVENTED by a young Austrian engineer, Hans vonBraun, this new instrument was given its preliminarytests recently over the Tempelhof Feld, Berlin, inone of the machines belonging to the Deutsche Luft Hansa. Its origin, like many great inventions before, was largely the result of chance, Herr Braun happening one day to come across an article in a journal describing the work of the French Professor Jolly on the mutual attraction of bodies. It will be realised that the practical difficulties to beovercome were rather formidable, as the gradual reduc- tion in weight as a body is removed from the surface ofthe earth is so very small as to require extremely sensi- tive apparatus to determine it. Not only so, but theinstrument, which Herr Braun has termed a " relative altimeter," but which we prefer to call a " relative "altitude meter, is mainly intended for use fairly close to the ground, i.e., for giving accurate indications when theordinary barograph, set to indicate altitude above sea level, fails to give the information desired.The Braun relative altitude meter makes use of the earth's attraction of bodies, which attraction varies, ofcourse, with the distance from the earth's surface. In the work of developing the instrument to the point whereit is regarded as a practical piece of equipment, Herr Braun has been assisted by Diplom-Ingenieur Erwin Stern,and several years have been spent in experimentation and development work. The experimental model recentlytested was found to be very sensitive, and gave readings on the dial when the aircraft passed through bumps. [Itwould be interesting to know whether these readings were due to the sudden change in distance from the earth'ssurface, or whether they were caused by the acceleration and deceleration of the machine.—ED.] What the Brauninstrument indicates is altitude above the surface imme- diately below, and not height above sea level. Thus, infeggy weather the pilot is warned of an approach to hilly or mountainous country, a warning which the ordinaryaltimeter cannot give. The principle of the Braun relative altitude meter maybest be followed by a reference to the accompanying diagram. The instrument consists of a cross pendulumwhich is driven at a speed of about 1,200 r.p.m. by an DIAGRAMMATIC RE PRESENTA- TION: Me is the indicator dial. Gl, G2, G3, and G4 the weights carried on arms of cross pendu- lum. F is the spiral spring and T the revs, indicator. The electric motor is shown at M. F R.P.M ^ V T J f) electric motor. The pendulum arms carry at their endsweights which are acted upon by gravity and by centri- fugal force. A spiral spring is connected to the pendulumarms in such a manner that when the arms close up or spread out the spring is contracted or expanded. Highly geared to the pendulum arms is the pointer ofthe indicator dial. This dial is divided into 100 divisions for each 5-m. (16-ft.) difference in altitude. This partof the dial is to be regarded as the " vernier " reading. A vertical scale indicates simultaneously the altitude in500-m. (1,600-ft.) divisions. The spring tension and the speed of revolution of thecross pendulum with its weights remaining constant, the only variable is the weight of the weights Gl, G2, G3 andG4. This is influenced by altitude, and the very minute increase or decrease in weight causes the pendulum crossarms to contract or expand, this very slight change being communicated, magnified manifold, to the pointer of thedial. The principle is simple, but its carrying into effectmust have presented many problems. For example, unless the speed of rotation of the pendulum arms is absolutelyaccurate and constant, the readings must become in- accurate. Or, if the spring tension varies due to expan-sion or contraction caused by a difference in temperature, the readings would, presumably, also be upset. In the experimental model the drive is by an electricmotor driven by a 6-volt accumulator. A variable re- sistance is incorporated so as to enable the speed of themotor to be regulated to a nicety. The weight of the experimental model is stated to be approximately 8 kg.(17 lb.), including accumulator, but it is expected to re- duce this weight to some 3 kg. (7 lb.) in the productionmodel. THE BRAUN RELA- TIVE ALTITUDE METER: Front view of the actual experi- mental model. 1063 0 2
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