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Aviation History
1913
1913 - 0138.PDF
LfifCMTj FEBRUARY 8, 1913- ENGINE SPEED INDICATORS AND SAFETY. One of the causes contributory to many of the aviation fatalities that have occurred of late, has been that the pilot has not taken suffi cient care to see that his motor is in sufficiently good ivorking trim before starting out. Knowing Mr. G. M. Dyott to be a most reliable and careful pilot, and, moreover, he being especially emphatic upon the point that pilots as a rule do not study their motor to the extent that they should, at the request of the Editor he has here set out his views in writing. By G. THE importance ofa pilot being able to tell at a glance the revo lutions per minute of his motor can hardly be overestimated, and yet comparatively few aeroplanes are equipped with a thoroughly reliable revolution indicator, and but few aviators seem to realise the advantages incurred by their use. Apart from the mere interest which such an instrument affords, it can indirectly be the means of procuring much valuable in formation, which enables the machine to be navigated with far greater precision and safety. Spend a few days at any aero drome, and the following snatches of conversation will probably come to your ears : "I don't know just what the trouble was ; apparently, my engine was working well." "The motor seems to be all right, may be, the propeller is no good." '' Somehow or another I can't get my machine to fly as it used to," &c. &c. All of these re marks clearly indicate a sort of vague uncertainty in the minds of the speakers as to what their respective machines could do. This should not be the case. In connection with the flying of an aeroplane, innumerable variable quantities present them selves at every turn. The one particular variable isundoubtedly the power developed by the motor, and as luck would have it, it is generally the unfortunate motor that gets blamed for every thing. In so doing we often fail to learn a valuable lesson which passes by unnoticed. On one occasion I was carrying a passenger from an aerodrome, 8,000 ft. above sea level; on returning I could not maintain my altitude in spite of the fact that the revolution indicator showed the motor to be working at its normal speed. A gentle gust caught me and but for a quick dive I would have been over. The first impulse was to blame the motor, but I could not do this, for I knew it, at any rate, was not at fault; analysis was thereby simplified, and it opened my eyes to the real nature of the trouble. Without an indicator I would still have been hopelessly at sea, or else satisfied with an entirely wrong explanation. There are some men whose sense of hearing is very much more acute than others, and they contend that it is possible to note the least variation in the running of an engine by sound alone. To an extent this may be true after intimate experience with one particular motor, but even at the best of times a drop of 25 revs, in 1,300 would be hard to detect. A falling off of 50 revs, might be apparent to a well-trained ear, but probably too late to do anything, whereas proof positive a few seconds before might have averted an emergency landing in an uncomfortable place. If the pilot is called upon to fly different types of machines equipped with various motors, the case becomes still more difficult. His ear might be attuned to the variations in hum of a Gnome to-day, but he would be lost behind the hoarse bark of an Anzani to-morrow. When flying a Gnome over broken country in windy weather, one often notices how the sound of the motor will rise and fall, some times almost dying away entirely. Without an indicator my ears would tell me that something was wrong, but with a reliable indication in front of me my mind would be at rest. Smith found that by careful practice he could descend from the roof of his house to the street below by means of a tight rope. His friends, however, continued to use the staircase, as it required less agility and was more reliable. Does not the same line of reasoning apply to the use of speed indicators. Even suppose that after careful practice anyone could train his ear to the least variation in sound would that be a reasonable excuse for not employing a revo lution indicator ? I should say certainly not. In general, then, we might say that if there is any advantage in knowing the exact engine M. DYOTT. speed of an aeroplane, a reliable indicator is the only way of ascer taining it. The question which now arises is whether such informa tion after all is really worth knowing. To those who confine their attention to spasmodic flights round an aerodrome, the value of knowing their exact engine's speed may not be apparent, but take the same man and have him fly 10,000 ft. above sea level one week, then move him to some cold, damp place on the coast, shifting him afterwards to a hot, dry plateau in the tropics, and it would not be long before he would not only realise the advantages, but the absolute necessity of such an instrument if he is to get the best out of his machine with a minimum amount of trouble and worry. Let me illustrate the point at issue by relating a few experiences which have come within my personal observation. October, a year ago, I was flying in New York at a meet. The weather was cold and damp, but the machine had been tuned up and was running perfectly. Three weeks later I was in the tropics,, where the atmosphere was hot and dry, 8,000 ft. above sea level, and considerable adjustments had to be made before I was able to get the engine in good shape to suit the new atmospheric conditions. On> one occasion I had started for an altitude flight when the motor showed signs of slowing up. Immediately I turned round and headed for the aerodrome, and well for me that I did so, for no sooner had the manoeuvre been accomplished when the motor went completely out of business. A long straight vol /»/W just brought me safely within- the enclosure to find my carburettor frozen up stiff and covered with snow. Had it not been for the few seconds' warning given, by the speed indicator I would have been forced to land on very bad ground, may be damaging the machine. Not many weeks later I found myself at sea level again, a very hot place this time, which of course meant renewed engine adjustments. Starting on a cross-country flight one evening I noticed the motor speed gradually dropping, and taking advantage of a natural landing ground came down to find the oil tap closed. My indicator saved a burnt-out motor and an emergency landing that might have been costly. On another occasion I was giving an exhibition flight in Western Pennsylvania, and had the machine ready to start. The engine was set in motion, but I could not get the full 1,150 r.p.m. necessary— only a shade over 1,100. A quick get away was imperative in order to clear a row of trees. Besides, outside, the ground was bad, So ttas was not good enough. The plugs were chaDged, distributor cleaned, and magneto inspected, but all to no avail, the result was the same. Naturally, the people were impatient, and I was sorely tempted to risk it ; but, no, what was the use of going against one's better judgment ? So a further careful inspection was made, and again the motor refused to come up to speed. At last my mechanic noticed that the petrol did not flow freely from the jet. It was evident that it was clogged up, and we proceeded to take it off. Before doing so I looked inside the petrol tank which was new and had not been fitted with a gauge-glass at that time ; it was almost empty, although the last thing the day before it had been filled full. There was no question but what someone had wilfully removed the contents leaving just enough for a three minutes' flight. It is not pleasant to reflect what might have happened. As it was, a new supply of the necessary petrol and off the machine went, showing her full 1,125 on the dial. Experiences sueh as these happen to every aviator, and I there fore contend that since in each special case a revolution indicator was, to say the least, of tremendous service, the argument as to whether information pertaining to the engine speed was worth knowing or not has been answered in the affirmative. There is one more point I wish to bring up before closing, and that is the necessity of having a reliable instrument. Information that cannot be depended on is worse than none at all. I was flying a monoplane a few months ago equipped with a small indicator driven by a belt. I seldom had two readings agree, and usually had to club the instrument into submission before the pointer would move from zero. This led to a jumble of information that was most confusing. Subsequently the instrument was replaced by a. really good one, and in a few flights the following data was obtained :— With a certain make ol propeller of certain dimensions, I found that, with the machine I was flying, I ought to get the engine turning over at 1,150 revolutions per minute at least before leaving the ground. When in the air, if the engine was doing 1,150 or over, I felt that the machine was well in hand. If the indicator showed an engine speed of anything from 1,125 to I>IS°> I n£ui the idea that something would happen, unless by carburettor adjustment I could bring the speed back to normal. The machine could still climb gently, and remain pretty well in hand in fairly good weather,, but all the same, I kept my eyes open for a good landing ground. 138
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