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Aviation History
1925
1925 - 0625.PDF
OCTOBER 1, 1925 THE NEW HANDLEY PAGE W.9 "HAMPSTEAD Three Armstrong-Siddeley "Jaguar" Engines ALTHOUGH very similiar in general outline to the HandleyPage W.8F, the new Handley Page biplane, which will be commencing its flying tests at Cricklewood this week isreally a totally different type of machine in that its power reserve, and consequently performance, are considerablygreater than those of the W.8F, of which the W 9 or -HT\?rPotead>" may be Said t0 be the loglcal development.±ne W.8F type has given excellent results in the Congo but no machine is so good that it cannot be improved, and foruse by Imperial Airways a more liberal power reserve and higher cruising speed were deemed desirable, with the conse-quence that, m the " Hampstead," the total power has been increased by something like 300 h.p. Not only so, but to giveimmunity from forced landings, a three-engined machine should have its three power plants all of the same power, sothat if one stops the total power is reduced by one-third only. When the central engine is of greater power than the two wingengines this condition is not, of course, fulfilled, as in that case stoppage of the central engine means losing perhaps40 per cent, of the power, instead of 33 per cent. From the scale drawings of the Handley Page " Hamp-stead " it will be noted that the span is somewhat greater than that of the W.8F, the general arrangement drawings of whichwe published in our issue of May 1, 1924. This increase is due entirely to a lengthening of the centre-section, as the outerportions of the wings are identical with those of the W.8F, with which, in fact, they are interchangeable. The lengthening ofthe centre section was decided upon in order to get the three propeller discs clear of one another, as it was found in theW.8F, in which the large disc of the front propeller overlapped considerably the two smaller discs of the wing propellers,that the latter were apt to suffer from flutter, owing to the slipstream from the central propeller striking the tips of thetwo wing propellers. In the " Hampstead " the three propeller discs, it will be seen, clear one another by a con-siderable margin, and thus there should be no trouble from this source. In other respects the " Hampstead " is similar to the W.8F, except for such changes as are due to the fitting of different types of engines. A very neat engine mounting has been designed for the central Armstrong-Siddeley " Jaguar " engine, in the form of short tubes running from the engine bulkhead to the standard cup-shaped engine plate of the Armstrong-Siddelev Jaguar." These tubes are so arranged as to triangulate the structure and at the same time all meet on four points on the engine bulkhead, so that the removal and replacing of an engine is a very simple matter. The two wing engines are mounted virtually each on a single interplane strut, this being the front strut, from which the engine plate projects laterally outwards, and is braced by a sloping strut from the bottom plane to the outside of the engine mounting, and by a hori- zontal tripod of steel tubes meeting on the rear interplane strut. The two wing engines are left entirely uncowled, as it is considered that the excellent accessibility thus gained more than outweighs any saving in head resistance that might be effected by elaborate streamline cowls. Each wing engine has its oil tank mounted behind it, but as in the W.8F, the petrol tanks are slung underneath the top plane, above and slightly inside the engine, so that direct gravity feed is avail- able. The quantity of petrol carried is about 250 gallons. The cabin of the Handley Page " Hampstead " has seat- ing accommodation for 14 passengers, seven on each side of the cabin, with a gangway down the centre. In addition there is aft of the cabin a large luggage compartment, as the 14 passengers do not by any means represent the whole of the available paying load. The windows of the cabin are in the form of triplex glass, and are designed so as to be raised or lowered. Further ventilation is provided by two tubes running throughout the length of the cabin, one on each side. These tubes, incidentally, form the net-racks pro- vided for light articles, and form the diffuser box for the fresh air which thus, instead of coming from one point in the cabin, niters through throughout the whole length and on both sides. Air is forced in through these tubes by short feeder tubes projecting laterally outside the fuselage and having their outer ends turned forward, and for each feeder tube there is a valve which can be opened or closed by the passengers so as to regulate the supply of fresh air. For winter flying the cabin is heated from air muffs surrounding an exhaust pipe, and the amount of hot air admitted (at floorlevel) can also be regulated by the passengers themselves. On the front wall of the cabin is a set of instruments, includ-ing air speed indicator, clock, and altimeter. Here also is an emergency signal by which passengers can summon thespare pilot or engineer in an emergency, a small sliding panel in the front wall giving access to the pilots' cockpit. Thispanel is smaller than in the older machines and is not now intended as the normal entry of the pilot, who reaches hiscockpit from outside by a ladder of steel tubes permanently built on to the machine. Against the possibility of themachine being used for night flying, the cabin is lighted by three roof lights which should enable passengers to read orwrite during the journey should they feel so disposed. It might be argued that carrying 14 passengers with atotal power expenditure of 1,155 b.h.p. is scarcely a com- mercial proposition, as it represents a power expenditure of82-5 h.p. per passenger, but in this connection it should b e realised that in addition to the 14 passengers there is anavailable paying load of something like 700 lbs. Actually the paying load of the " Hampstead " is 3,220 lbs., whichfigure does not include fuel, oil, or crew, so that the actual paying load is just under 3 lbs./h.p. Another factor whichshould be taken into consideration in this connection is that the machine cruises at just over 100 m.p.h. on very littlemore than half the total horse-power. Purely^from the fuel economy point of view, it would probably pay to fly normallywith only two engines running at slightly less than their full power, as this would give a better fuel consumption perhorse-power; but against this must be set the fact that by normally running two engines nearly all out the reliabilityand life of the engines would probably be seriously impaired. It would, therefore, seem that although the fuel consumptionper horse-power will be somewhat higher, it will pay in the long run to fly normally on all three engines, but with themthrottled down to 60 per cent, or so of their full power. By doing this the engine reliability should be very materiallyenhanced, and the life of the engines should be greatly increased. The good power reserve has, of course, many advantageswhich should be taken into account before hastily assuming that the machine cannot be a commercial proposition. Forinstance, with full load and all three engines running, the estimated rate of climb, at ground level, is 720 ft./min.This excellent rate of climb, combined with the relatively low climbing speed, should give an extremely good climbingangle, so that the " Hampstead " should be able to get off from quite a small aerodrome. It is further estimated thatwith full load and only two engines running, the ground level rate of climb will be 220 ft./min. which, if not spectacular,will, at any rate, enable the machine, should this become necessary for any reason, to get out of a reasonably largeaerodrome with one engine out of action. Finally, it is esti- mated that with full load and two engines stopped the rateof descent would be about 280 ft./min., which corresponds roughly to a gliding angle of 1 in 20. This would mean thatin still air the machine would be able to cross the Channel with but one engine working, provided its altitude at thestart was a little more than one mile, say about 5,500 ft. Normally a machine would not, of course, commence aChannel crossing with two engines out of action, but the figures do help to show that by flying at a reasonable altitudethe simultaneous failure of even two engines—which is an extremely unlikely occurrence—would not prevent themachine from reaching land safely. The question of monoplane versus biplane in three-enginedmachines has not yet been settled. It would appear that if one wants a low landing speed the biplane arrangement is tobe preferred, since it is difficult to get out of a full size wing the high lift necessary to give a low landing speed -with thenecessarily more heavily-loaded monoplane. On the other hand, in large machines it might be possible with the mono-plane type practically to bury the two wing engines inside the wing, and thus save a not inconsiderable amount ofhead resistance. Something of the sort has, of course, been done in the three-engined Junkers monoplane, recentlyillustrated in FLIGHT. Against the possibly greater aero-dynamic efficiency of the monoplane must be set the greater wing weight, which is inevitable in the cantilever monoplanestructure, and, taking it all round, there does not seem any 625
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