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Aviation History
1917
1917 - 0616.PDF
JUNE 21, 1917. [As a number of letters reach us signed with initials only, some of which do not give a complete address, we would point out that such communications cannot be dealt with in our columns. Full name and address, which will not be published, must always be given.—ED.] Notice to Correspondents In General. Applications for commissions in the Royal Naval Air Service should be addressed to the Director of Air Services, Admiralty, S.W. The necessary form and conditions of entry can be obtained from the Secretary of the Admiralty. Applications for commissions in the Royal Flying Corps should be sent to the Director-General of Military Aeronautics, Hotel Cecil, Strand, W.C. Those who wish to enlist in the R.N.A.S. should apply to the nearest naval recruiting station or to the R.N.A.S. Drafting Office, Crystal Palace, S.E. -Skilled mechanics are taken whatever their army classification, but unskilled men are only taken if they are classified Bi, Bz, or Ci. Recruiting for the R.F.C. is closed for the time being, and any enquiries should be made to the Officer Commanding, Royal Flying Corps Depot, Famborough. Enquiries with regard to appointments in the A.I.D. should be addressed to the Chief Inspector, Aeronautical Inspection Department, Hotel Cecil, W.C. 2. C. A. A. (S.W.)- As a rule air screws have their pitch stamped on the boss. When this is not the case it is a matter of some difficulty to find the pitch accurately. It may, however, be found approxi- mately in the following manner : Place the airscrew on a plane surface, such as a table top, with the drawing face downward. The distance C, or the projected width of the blade, is a part of the circumference at the point measured, and the height P of the leading edge of the section above the base line AB is paj^t of the pitch. The pitch is then found by the formula P = -^p. P - pitch, in inches, r «=• the distance from the axis of the boss to the point measured, in inches, and C «= the projected blade width, in inches, *-, of course = 3" 1416. The pitch, thus found is not, however, quite correct, since this method presupposes that the chord of the sections is set at no angle of incidence. In practice this is not usually so, the chord angles being generally greater than the helix angles. The accompanying diagram will illustrate our point. The lines dc, ec, fc and at represent the helix angles, which we have called »], a2, a3, «4 respectively. For the sake of clearness we have shown all the chord angles 3 degrees greater than the helix angles, although this does not necessarily represent general practice. As a matter of fact, there are, we believe, propellers in which, at certain points, the chord angles are actually smaller than the helix angles. The angles Aj-aj, A3-<Zj, A3-OJ, A4-a4, are called the angles of attack, and correspond to the angle of incidence of an aeroplane wing. In our diagram all these angles of attack are 3 degrees, but they may, as we have pointed out, vary along the blade of the airscrew. Near the boss, where the blade has a small velocity, some propellers have sections resembling a stream- line shape rather than an aerofoil section, the blade being here more in the nature of a supporting arm. Consequently in that case the chord angle is the same as the helix angle. If due allowance be made for this angle of incidence over the outer part of the blade and it is assumed that near the boss the chord angle is the same as the helix angle, the pitch may be found approximately. E.D.G. (Ackworth). We cannot say whether you could obtain a commission, You should apply as directed above. M. E. G. (Erith). • / Apply to the R.N.A.S: Drafting Station as directed above when you reach 18. In the meantime you should stay at your work. A. L. C. (Twickenham). The pay of a Flight Sub-Lieutenant, R.N.A.S., is 10s. a day, plus 8s. a day flying pay. The pay of a Flying Officer, R.F.C., is 12s, a day, plus 8s. a day flying pay. C. H. J. (Sutton Coldfield).—Judging from your sketch, the machine in question is a Maurice Farman "Shorthorn." The R.E.8 is a tractor biplane, rather large span, big exten- sions to the top plane, and a big dihedral angle. Planes of high aspect ratio. The Bristol bullet is a fast scouting' biplane. The machine on page 483 of " FLIGHT " is a B.E.2C. C. T. (Catford).—It is not possible from your description, to say what the machines you refer to are. Prob3rt>ly the first mentioned was an R.E. As Gilbert's famous Morane monoplane " Le Vengeur " has been built during the war, it is not permissible to publish scale drawings of it at present. The fins on top of the upper wing of the flying boat perform the function of raising the centre of side area of the machine, thus increasing its lateral stability. . W. D. K. (Sanderstead).—So far as we know there is no easy method for judging the height of aircraft. Instruments are, of course, in existence which are designed to do this, but the rough-and-ready ni^thods sometimes published are worse than useless unless the exact size of the aircraft is known. G. A. M. (N.16).—It is quite possible to stop an airscrew daring a flat glide. This is not, of course, usually done deliberately, since with the majority of engines once"the propeller had stopped it would, not be possible to restart it. Exceptions are machines fitted with some form of starting devices, but we take it that what you refer to is starting the propeller again with the speed of the aeroplane. Where an engine has a very low compression, as in the case of some of the older rotaries, it would probably be quite possible to put the machine into a vertical dive, thus attaining a speed sufficient to restart the propeller. As a " stunt " stopping the propeller is quite a well-known performance. 1st A.M., S. T. M. (R.F.C.).—So far as we know there is no book published dealing specially with " low-power flight." This is chiefly a matter of design, and F. S. Barn well's book, "Aeroplane Design," would probably be found useful in indicating methods of designing an aeroplane. In the first months of 1916 we published in " FLIGHT " a series of articles entitled " A Popular Type Aeroplane Design," which you would also find useful. The issues containing this article are obtainable from the offices of " FLIGHT." B. E. (Larkhill).—For details regarding the Renault engines you could not do better than get the " Wolseley Aero Engine Manual." It can be obtained from " FLIGHT " offices for 5s. 4<2. post free. J. H. G. (Prestbury).—The N.P.L. report for the year 1912-13 containing the stress diagrams of aeroplanes can be obtained from the offices of " FLIGHT." The price is 10s. 6d. post free. 6l6
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