FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1926
1926 - 0417.PDF
June 24, 1926 Supplement to FLIGHT FLIGHTENGINEERING SECTION Edited by C. M. POULSEN June 24, 1926 CONTENTS Aircraft Performance. By J. D. North, F.R.Ae.Soc Compression Rubbers. By G. H. Dowty, A.F.R.Ae.S., A.M.I.Ae.E. Duralumin. By Leslie Aitchison, D.Met., B.Sc, F.I.C., M.I.A.E. Technical Literature PAGE 57 60 62 64 OUR CONTRIBUTORS Mr. J. D. North deals this month with a number of different subjects, from that of '" tail plane interference " and drag, undercarriage drag, slip-stream effects, etc., to such general subjects as ad hoc research and *' amateur enthusiasts." His thoughts on ideas for improvement, which " starting soundly enough, are advanced by amateur enthusiasts to extremes outside the intentions of their original sponsors," will certainly be read with interest, although possibly not with complete agreement. Mr. North's advocacy of the slotted wing for racing aircraft is worthy of very serious attention in connection with the Air Ministry's new scheme for high-speed development. Finally, the last passage but one of the present article might usefully be kept in mind : '" There is not much probability of making a com- plete aeroplane with a better lift/drag ratio than the best infinite span wing." Mr. G. H. Dowty, who is. we understand, connected with the Gloucestershire Aircraft Company, contributes a very useful article on compression rubbers. The type of under- carriage employing rubber blocks working in compression is rapidly gaining favour, and has already proved itself a very useful type, in which simplicity is combined with hard- wearing qualities to quite a surprising extent. Even in the design of such a simple mechanism, however, knowledge is required, and the advice given by Mr. Dowty should be of assistance. It may be recollected that Mr. Dowty has made rather a speciality of undercarriages, and that he read a paper on oleo undercarriages before the Institution of. Aeronautical Engineers. Dr. Leslie Aitchison ceals at some length with the subject of the corrosion of Duralumin and its prevention, and the impression formed after reading his article is that Mr. Oswald Short was right when, in the first number of THE AIRCRAFT ENGINEER, he stated that the word '" corrosion " has a more fearsome sound than the word " rust," although they are really the same thing, and that while we have come to accept the one as being not very serious, we incline to overrate the importance of the other. With proper precautions there does not seem to be any reason to be unduly alarmed about the corrosion of Duralumin. AIRCRAFT PERFORMANCE, By J. D. NORTH, F.R.Ae.S. (Continued from page 55.) There still remains, apart from those items already enume- rated, the empennage and the undercarriage as contributories to the total drag, in the case of the fin and rudder these are of symmetrical section normally at Zero lift, except for the effect of race rotation in the slip stream. Omitting the consideration of the latter point, the profile drag coefficient of fin and rudder should not exceed 0-004 to 0-0045 for a braced structure, or 0 • 006 to 0 • 008 for an unbraced cantilever arrangement. Similar figures should apply to the profile drag coefficient, of the tail and elevator. If a braced structure of the usual type (monoplane tail and vertical surface) is used an added drag coefficient of 0 • 002 to 0 • 003 will usually cover the external bracing. These surfaces are generally of very low aspect ratio and small in relation to the body on which they are mounted. For this reason plan form (as distinct from plan proportions) may have some influence both on profile drag and interference. Profile drag is also affected by the grading off of thickness towards the tips, from which some small advantage is usually to be obtained. It is not difficult to understand that these end effects may influence profile drag on surfaces where the ends are a signifiV cant proportion of the span. Interference on tail planes (often discussed as " tail plane efficiency ") has been noticed for many years ; careful wind channel work will reduce it to a low figure (or alternatively will give a high "' tail plane efficiency "). The actual forces on the tail plane can be determined from the equations of motion. On stable aeroplanes it will be found that over a large part of the flight range a downward force on the tail plane is required for equilibrium. At first sight this would seem very detrimental, as, in addition to the tail plane drag that of the main planes is increased by the lift having to exceed the weight. Actually, however, the tail plane is working in the downwash from the main planes and a regenerative system is formed. A reference to Fig. 14 will show that where the lift/drag ratio of the tail plane is greater than the cotangent of the downwash angle, the com- ponent of the tail reaction along the flight path is up-wind. I have not personally seen any analysis which showed an absolute up-wind drag for a tail plane, but the regenerative effect is there to diminish the drag. Examination of several aeroplanes indicates that tail plane drag averages about 5 per cent, of the total drag. Characteristic figures for just stable machines are 6 per cent, on climb, 4 per cent, on top 362a D
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
