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Aviation History
1910
1910 - 0058.PDF
pn There is thus created a wake (commonly called the ffic- tional wake) behind the boat, consisting of a column of water flowing after the boat, but at a lesser velocity, and this frictional wake will come into existence whether the boat itself be propelled or towed. Inasmuch as the wake in question has any velocity at all, it represents a certain amount of energy, which will be lost unless means are taken to utilise it, and the simplest way of making use of the frictional wake is to place the propeller in such a position that it can act upon it, that is to say, behind the boat. Pulling ». Pushing. In such a position the effect of the propeller in action is to bring the wake to rest, so that, assuming the con ditions to be suitable, it is possible for a boat to be propelled without a column of water being actually pro jected rearwards from the propeller, the slip in this case being neutralised by the wake, or, in other words, the abutment for the thrust being established by taking momentum out of the water instead of imparting momentum to the water. It must, of course, be understood that the power which set the wake in motion was derived indirectly from the propeller itself, and that there is no suggestion of getting work done without the expenditure of a corresponding amount of energy. On the other hand, however, it does show very conclusively that a boat can, theoretically, be propelled with less horse power than it can be towed, because in the former case the energy which the boat puts into the wake is retrieved. The Wake from a Flyer. , When it comes to applying this argument to a flying machine, the same conclusions are not necessariJy deduced, because the conditions are different. A bi plane, for instance, is very unlike the hull of a boat, and the skin-friction of the air upon a decently smooth surface is not comparable with that of water, so that in any case the presence of an appreciable frictional wake seems to be a matter requiring experimental demonstra tion. Even if the wake exists, moreover, it does not JC J^NJTARY 22, I910. necessarily follow that a propeller is better than a tractor screw on these grounds alone, because with the latter arrangement the slip from the screw itself might be turned to advantage by its action upon the aeroplane surfaces by increasing their virtual velocity. Tractor Screws v. Propellers in Practice. These points, however, need a considerable amount of experimental evidence before they can be decided one way or the other, and in the meantime there are con struct ional con s i dera tions to be taken into a c c o u n t which are quite suffi cient to throw the balance one way or the other. In the R.E.P. mo n o plane, for instance, the presence of a tractor- screw direct- coupled to a little engine perched up on the nose, of the machine, is as simple an arrangement as anyone could wish for, considered purely from a mechanical point of view. In biplanes it is more convenient to put the engine somewhere else, and this position is commonly such as to facilitate the use of one or more propellers. " Flight ' Copyright Photo. On the R.E.P. monoplane the propeller forms a four-bladed tractor-screw in front. VOS ANGELE5 FLYING MEETING, IN pur issue' of last week we were able to give details regarding the' wonderful height record made by Paulhan and the speed records of Curtiss. After these per formances, perhaps the most noteworthy flight was that of'Paulhan on Friday of last week, when he flew across country to San Pedro and manoeuvred above the fort and 'the harbour at a height of about 900 ft. Altogether he flew some 20 miles during 35 mins. On coming down Paulhan stated it would have been easy for a fleet of aeroplanes to attack the harbour defences, and destroy the city too. He said it would have been easy for him to have carried up 375 lbs. of dynamite, and with a sufficiently powerful motor he could have gone up to a height of 10,000 ft., when it would have been impossible for any gunner to hit the machine, as it would then appear such a small speck in the sky. On the previous day Paulhan carried two passengers on his Henry Farman machine for a short distance. On the Friday Curtiss took up Lieut. Paul Beck, who during the flight attempted ito drop bags of sand representing bombs from a height of 250 ft. He failed, however, to hit the marks by from 15 ft. to 25 ft. In a speed test between Curtiss and Paulhan the former covered a mile and a half in 2 mins. 12 sees., while ' Paulhan took 2 mins. 48 sees, for the same distance. In a match on the jSth over 10 laps, 16 miles, Curtiss was timed in 23 mins. 43! sees., while Paulhan's time was 25 mins. 5^ sees. On Monday Paulhan set out to beat the endurance record, but stopped after covering 75 miles in ih. 55m. 27fs., mainly owing to a misunder standing with regard to the course he was following. On Tuesday Paulhan made another long flight across country, and this in spite of the fact that a very heavy wind was blowing. At.one time it was felt that it would be impossible to do any flying, but in the afternoon the Henry Farman machine was brought, and Paulhan started off, after making a, preliminary circuit of the Aerodrome, in the direction of Arcadia, some 23 miles away. On arrival there, he was at a height of 1,000 ft., and manoeuvred over the race track. He then started off on the return journey, and, having the wind against him, gradually rose to a height of 2,130 ft., where calmer currents prevailed. Naturally this spectacular flight evoked great enthusiasm among the spectators, and on landing Paulhan was carried shoulder high across the aerodrome, Madame Paulhan accompanied her husband during a cross-country flight of 22 miles on Wednesday, which lasted ^ mins. 54
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