FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1921
1921 - 0647.PDF
SEPTEMBER 29, 1921 appear to have been any trouble due to this cause. Themachine was built during the very hot summer months, and has since been flying or standing in its hangar (a tenthangar at that) during wet spells. Yet so far as we are aware there has been no sign of a deterioration in performancesuch as might be expected if the slightest slackness in the wing fabric had the pronounced effect which has been alleged.One of the greatest difficulties which beset modern designers is that of providing ample lateral control at or near thestalling angle. In the ordinary wing the effect when near stalling angle of pulling down the aileron on the lower sidemay, and frequently does, result in precipitating a spin rather than in righting the machine. The consequence isthat in few machines is it possible to land as slowly as the maximum lift of the wing would otherwise allow. As spinningis a function of the lift coefficient and of the shape of the lift curve near the burble point, it may be expected that highlift cantilever wings would be worse in this respect than the ordinary high-speed wing. Thus the de Havilland Aircraft Co. J>.H. THE D.H. 29 MONOPLANE : Details of the fittingwhich secures the wings to the top longerons of the fuselage. were faced with a double problem, as it were. It is of interestto see how they have solved it. As will be seen from the general arrangement drawings, the wings have a very pro-nounced taper—from approximately 12 ft. chord at the -tfoot to about 6 ft. near the tip. Ailerons of ordinary typeare fitted, and do not appear to have any unusual aerodynamic features, such as being twisted after the fashion of mostGerman ailerons. Nor, it will be seen, do they have any horn balance, as might have been expected in a machineof this size. The manner in which balancing has been provided while at the same time guarding against starting a spin isvery interesting, and is almost ridiculously simple. The control cables are inside the wing, and are attached, at theirouter ends, to a rocker arm lying in a fore-and-aft direction. From this rocker a steel tube runs to a king post on thelower side of the aileron. As will be seen from the sketch, the two arms of the rockerare of unequal length (three holes are provided in the rocker shown in the sketch so as to allow of variation) so that adifferential action takes place by which the aileron which is being pulled up moves through a greater angle than doesthe opposite one in descending. The consequence is that not only is the aileron on the low side not pulled down to suchan extent as to give great resistance without a corresponding increase in lift, but the question of balance is solved at thesame time. It might be added that all controls work in ball bearings, and this fact coupled with the method ofbalancing renders the lateral control of the machine so easy • that we understand that the stick can be pulled over withone finger. The advantage which such ease and nicety of control has for long-distance commercial work is too obviousto need emphasising. Before leaving the subject of the cantilever wing, it isof interest to examine the manner in which it is attached to the fuselage. The simplest way would have been to providesimple sheet-steel plates, as is often done. This, however, has the disadvantage that, in putting the wing back into placeafter it has been removed for overhaul or for any other reason, such relatively thin plates are very easily damaged,or at any rate bent, and have to be bent back to their original shape. By the time this bending has been done a few timesthe plates will have been weakened, and may give way in the air. It is therefore to be expected that a firm like thede Havilland Aircraft Co. would not countenance such a fitting. The one which has actually been used is shownin one of our sketches. There are, it will be seen, two long bolts which run through the wing spar. One of these has aconically-shaped head, and serves to locate the wing in a socket on the top longeron. The other has a forked endand takes the lift by way of a horizontal pin as shown. In order to provide duplication the first-mentioned bolt is alsolocked by the horizontal pin. As the head of the latter projects, the pilot can see at a glance whether or not his wingattachments are in order, and there is therefore not the slightest risk of going up with an unsecurely fastened wingattachment. The whole job is very neat and businesslike, and at once inspires confidence in the detail design, animpression which is confirmed on examination of the whole machine. The ControlsReference has already been made to the aileron control. As regards the elevator and rudder controls, these are ofmore or less standard form, with the exception that at no point do the control cables pass over pulleys or throughfairleads. It has been the bitter experience of many airline firms that the wearing of control cables is a serious item.Wherever it has been necessary to carry a control cable through a guide in the D.H. mono., a length of steel rodhas been incorporated in the cable and works in a substantial • guide, as shown in our sketches. Moreover, the cables donot run direct to the elevator king posts, but terminate on the cranks of a transverse shaft some distance ahead of thetail plane. From these cranks steel tubes run to the elevators, and the hinged joints are surrounded with leather protectorsand well greased, much after the style so familiar on motor cars. There should thus be no trouble with control cableson the D.H. mono.—a fact which will appeal strongly to users of the machines. The tail plane itself is of cantilever construction like thewings, and elevators with horn balances are fitted. The fin and rudder are of the usual de Havilland type. The Undercarriage.After the success which the undercarriage of the D.H.i8's" has had, it was to be expected -that the same type would befitted on the monoplane. Certain modifications have been made, by way of cleaning up and simplification, but funda-mentally the undercarriage remains the same. It has already been stated that the first of the monoplaneshas gone to Martlesham to be tested, and consequently no performance figures are available until these official testshave been made. From the flights that have been made at Stag Lane, with Captain de Havilland himself at the helm,there is every reason to hope that the performance will be very good, both as regards speed and load carrying. Thefollowing figures of weights are of interest. The structure weight of the machine is 2,687 lbs., of which 1,110 lbs. areaccounted for by the wings. The weight of the machine empty, but with water, is 4,200 lbs. What the useful loadwill be depends partly upon the way in which the machine is found to get off and climb, but it may be stated that thestructure has been stressed for a total weight of 7,500 lbs. Whether regarded aerodynamically, or as an engineeringstructure, or as a commercial aeroplane, the D.H. 29 is a highly interesting machine, and Captain de Havilland,with his assistants, of whom one would mention Mr. Walker, chief engineer, and Mr. Hagg, head of the drawing office,are to be complimented upon a very fine production. •.•.*,•• 647
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
