FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1934
1934 - 0970.PDF
FLIGHT. SEPTEMBER 20, 1934. THE AIR BRAKE: This is a trailing edge flapextending from one engine nacelle to the other. It is divided into two halves and operated by levers and atorque tube. (Flight Photo.) same difficulty to bring the machine into a small aerodrome. In order to make this possible air brake flaps have been fitted. These take the form of. split trailing edge haps over the central portion of the wing, extending from one engine nacelle to the other. When closed, the flaps lie snugly against the main wing surface. They are operated by a simple torque tube and levers. Designed for long-range flying (the distance from London to Baghdad is about 2,550 miles), the " Comet " is provided with very large petrol capacity. The three tanks are all carried in the fuselage, one of 128 gallons capacity in the nose, another of no gallons capacity approximately over the centre of gravity, and a third, of 20 gallons, just aft of the cockpit. The latter tank is used for trimming purposes. As petrol is consumed the forward tank begins to empty, and to keep the machine from being tail-heavy a small quantity is taken from the rear tank, which is farther from the e.g., and therefore works on a longer "leverage." In addition, the elevators are provided with a spring-loading device for trimming purposes. The tail- plane itself cannot be adjusted for incidence. The "Office" Accommodation is provided in the cockpit for a crew of two. They are seated one behind the other, and have dual controls so that they can take turns at piloting. A well- equipped instrument board is placed in front of the for- ward seat, and can be seen, by craning slightly, from the back seat also. The flying controls are of the usual type, with a plain " stick" for elevator and ailerons. A large wheel to the right of the front seat operates the under- carriage retracting gear. On the left is a lever which operates the air brake flaps fitted under the central trailing edge portion of the wing. Wheel brakes are connected to the rudder bar for steering on the ground. A transparent roof over the cockpit encloses the occupants. Flying control surfaces are of usual type, with a form of Frise aileron operated by the patented de Havilland dif- ferential method. The ailerons are mass-balanced by lead distributed along the leading edge of the aileron. Rudder and elevators have the usual bob-weight mass balances. In the rudder and elevator controls a mechanism has been inserted to give a very low gear ratio at small angles of movement of the control surfaces and an increasingly greater ratio for larger movements. This has, of course, been done in order to provide lightness of control and eliminate violent response to small movements ol 'the controls at high speed. Engine mountings and undercarriage attachments form almost the only metal parts in the "Comet." Welded steel tube construction is used for the engine supports, and the undercarriage wheels are carried en steel forks with telescopic limbs. The wheels are raised and lowered by a worm gear, or rather by the use of '' overgrown '' bolts and nuts, the "nuts" forming cable drums for the operation of the gear. Thus when the '' nuts '' are rotated by cables from the cockpit, they draw the '' bolts '' upwards, shorten one member, which forms one side of a triangle, and thereby raise the triangle and with it the wheel. The movement is explained in two diagrams. As the worm gear is self-locking, no danger arises if the machine should land with the wheels not quite in the '' fully down '' posi- tion. The Dunlop wheels are provided with brakes, which can, as already mentioned, be operated separately via the foot bar. They can be locked " on " together for parking. Instead of a tail wheel there is the usual tail skid, which is thought to offer less air resistance and which helps to pull the machine up when landing. The power plants fitted in the "Comet" are de Havil- land " Gipsy Six " engines, specially modified for the pur- pose of the MacRobertson Race. By using a modified cylinder head, valve rocker gear and piston, the overall height of the engine has been slightly reduced, the com- pression has been raised from 5.25 to 6.5, and the engine works satisfactorily on standard service fuel to D.T.D. 224 specification. In order to take advantage of the use of the Hamilton controllable pitch airscrews fitted, the normal speed of the engine has been increased to 2,350 r.p.ra. At the maximum of 2,400 r.p.m. the engine develops 224 b.h.p. on the bench. In the air this is slightly increased owing to the small degree of "boost" obtained by the high forward speed of the machine. A new crankshaft has had to be made to get an appropriate hub fixing for the Hamilton airscrew. The high pressure required (about 100 lb. /sq.in.) to operate the pitch control of the propeller is obtained from the usual engine pumps through duplicate oil relief valves. It does not affect in any way the normal lubrica- tion system. The standard arrangement of alternative hot or cold air supply for the carburetters has been re- tained in case adverse weather conditions are encountered during the race. Warm air, if required, is taken from the vicinity of the cylinders through a flame trap. A special coupling is provided on the rear end of the crankshaft for driving a rotary vacuum pump used to operate the Sperry gyro compass. Data But few data relating to the "Comet " are available. The dimensions and areas are shown on the general arrange- ment drawings. The gross weight is in the neighbourhood of 5,2^0 1b. As the quantity of fuel carried is 258 gallons, a little "guessing" puts the tare weight, fully equipped, at something like 3,000 1b. Should this be approximately correct, the ratio of gross to tare weight is 1.75. In other words, the machine carries 75 per cent, of its own weight. CANTILEVER TAIL SURFACES: A tall skid Isused instead of a tail wheel on account of its smaller drag. It is fully castering, and helps to shorten therun after landing. (Flight Photo.)
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
