FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1911
1911 - 0025.PDF
•opposite side to a vertical discharge pipe 6 ft. by 4 ft. in cross section. The electrically driven fan for producing the air current was fixed to the inlet on the west wall of the testing house. In the 4 ft. by 4 ft. duct between the fan and the testing box a Pilot tube was fixed communicating with a water gauge inside the testing room, so that continuous observations of the velocity of the current could be made throughout the test. The other sides of the box were detachable for the purpose of erecting the engine, and were provided with windows for observing the motor. The connections to the throttle and ignition were carried through the side of the box, so that during the test the testing box could be kept closed. Estimation of the Speed of the Motor.—The speed was measured in two ways ; one by the direct reading of a counter at stated =r-E tests. This brake was of the ordinary type, and consisted of a mild steel flanged disc specialty fitted with spring tialances and ball thrust bearincs to work in an inclined potitfcw. End Thrust.— To apply the required endthrustof 175 lbs. a bell- crank-lever was mounted on a shaft in beatings bolted to the testing r0 ^ Kmrt EOCK SU*»OWT. row CCNKWOTOH Fwiia MOTOR TESTIWC OTWA Monnw Fig. 1. The testing plant. <lasai«!M_A»sa««» . Fig. 2. intervals, and the other by an Klliott speed recorder worked from a magneto fixed to the shaft of the engine. The recorder was mounted at the top left-hand side of the switchboard. The time scale of the instrument was 12 in. per hour, and the pen indicated fluctuations of 0'5 per cent, of the mean speed. Estimation of the Brake Horse Power.—The crank-shaft of the motor was connected through a flexible coupling to the shaft of a 50 kilo-watt generator mounted on knife edges, which formed a very sensitive dynamometer. The method of suspension of the generator on the knife edges will be clear from Fig. I. For this purpose the end bearings were provided with hardened steel rings which were in rolling contact with the steel knife edges as shown. As this method of supporting a generator used as a dynamometer is apparently new, it may be stated that the difficulties experienced in constructing and setting up were quite small, and that the device gave no trouble whatever during the 24 hours' test. It was thought that the generator might move endways due to any small axial force on the armature, and to prevent this small rollers in ball bearings were fixed to the frame and in contact with the steel rings on the casing. It was found, however, that this precaution was needless, as there was no tendency for the machine to move endways. The lever of the dynamometer is provided with a dash-pot for damping the oscillations, and a scale pan for the dead load, which was adjusted to the mean torque required. For the purpose of recording the fluctuations of torque, the end'of the lever arm was connected to a cast iron pillar by means of a spiral spring, so that the varying tensions of this spring, recorded on a rotating drum, were a measure of the amount of the fluctuations. As the motion of the lever arm was limited to \ in. it was necessary to devise a multiplying gear (if 6 to I to work the pen. For con venience this pen was fitted so that it should be in contact with the paper on the drum of the speed recorder. The whole arrangement is shown in Fig. 2. By this means it was found possible to obtain a complete record of the fluctuations of speed;and torque throughout the whole trial. Absorption of the Power Developed —For this purpose special resistance mats were used. By using a combination of these mats in parallel, adjusted by means of the switches on the board, it is possible to regulate the power absorbed to ^.th of a horse-power. These mats are not specially air-cooled in any way, and proved perfectly satisfactory for a 24 hours' run. Tests with the Engine Tilted.—Under the conditions of the competition, tests of one hour duration had to be made with the shaft of the engine inclined at an angle of 150 to the horizontal, first with one end up and then the other. As the difficulties of using the generator with its axis inclined would have been considerable, a special water-cooled rope brake was made for the purpose of these rails. The vertical arm of this lever was forked, and carried two J-in. Hoffmann ball bearings, the outer collars of which fitted into a recess in the half of the flexible coupling nearest the engine. It may be noted that these bearings gave no sign of heating when running at 3,500 r.p.m. for 24 hours continuously. The estimation of the petiol and oil was by direct weighing of the supply tanks before and after the trial. At the conclusion of the trial the water conten! of the jacket and radiator was measured, and the loss during the trial estimated. The engines were then taken down and weighed, and afterwards opened up and examined for signs of wear. The Interim Report. With respect to the interim report proper of the Advisory Committee, the eight pages of text is mainly devoted to telling Mr. Asquilh that everything is progressing very satisfactorily at Hushey House, the only actual facts that evolve are the following :— Permeability Tests. In the rubbered fabrics the capacity for holding hydrogen seems to be generally dependent on the weight of rubber in the fabric. It is possible that diagonally doubled rublwred fabric* are superior to parallel doubled, but this cannot be definitely asserted without further investigation. Some samples of proofed silk tested have shown a hydrogen containing capacity equal to that of the best and heaviest rubbered cloths, with a greatly lower weight. The excellence of goldbeater's skin in this respect was shown by the figures previously published, l'aper, sized and unsized, has been tested, but hydrogen passes through it with great readiness. Some tests have been made to determine the variation in per meability with rise of temperature. The rubbered fabrics tested have shown a somewhat rapid increase of permeability, while a proofed silk gave a slightly lower permeability at the higher temperature. The permeability of goldbeater's skin was found to increase slightly with temperature rise. The effect of low tem peratures will also be investigated. Other Tests of Fabrics.—Durability tests have been made by exposure of samples in the open to sun and weather. After weathering, the samples are subjected to tensile and permeability tests. After an exposure of fifty days proofed silk and rubbered cotton fabrics showed a loss of strength not very different in amount in the two materials. The permeability of the rubbered fabrics, however, very greatly increased, while some of the samples of proofed silk showed actually a decreased permeability. One- sample of proofed silk taken down for test on a cold day showed a permeability much larger than that of the other samples, probably due to crumpling at a somewhat low temperature ; when re-exposed in the sun the permeability of this again decreased. Goldbeater's -5
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
