de Havilland DH.60 Moth
Обозначение DH.60X повторно ввели для следующего варианта, сделанного в 1928 году с мотором Cirrus III мощностью 90 л.с. (67 кВт). Эта модель получила новую тележку шасси с колесами на полуосях вместо сквозной оси. К концу года собрали
403 самолета Moth. Кроме того, лицензию на производство купила австралийская фирма "General Aircraft Company" и две финские компании - "Government Aircraft Factory" и "Veljekset Karhumaki". Финские ВВС получили 22 Cirrus II Moth. Массовое производство DH.60X закончилось в сентябре 1928 года. Появились новые модели, но по спецзаказу построили еще несколько таких самолетов. Один хранится в летном состоянии в Фонде Шаттлуорта в Олд-Уордене.
Хотя мощность моторов машин DH.60 увеличили на 50%, масса самолета также сильно возросла. Для компенсации этого увеличения массы и замещения сократившихся поставок моторов Cirrus де Хэвилленд решил разработать собственный двигатель. В 1927 году его компания обратилась с соответствующей просьбой к майору Фрэнку Халфорду - создателю мотора Cirrus. Так появился мотор Gipsy мощностью 100 л.с. (75 кВт). Он положил начало целому семейству легких авиадвигателей с этим именем и открыл новую страницу в истории машин Moth. Новый мотор собрали в июне 1928 года и облетали на DH.60X. Переделанная силовая установка улучшила и без того неплохие характеристики аэроплана. Модификацию с новым мотором обозначили DH.60G, но по очевидным причинам ее назвали Gipsy Moth. Прототип мотора Gipsy позже установили на один из гоночных монопланов DH.71, который должен был участвовать в авиагонках 1927 года на Королевский кубок, а впоследствии этот самолет использовали для рекордных полетов.
Первый серийный DH.60G с пилотом В. Л. Хоупом выиграл королевские авиагонки 1928 года, показав среднюю скорость 169 км/ч. Еще несколько Gipsy Moth установили ряд новых рекордов. Испытания на надежность проводились в течение девяти месяцев с конца декабря 1928 года. DH.60G выдержал их с триумфом, проведя в воздухе более 600 часов и пролетев в общем счете 82 076 км без единой поломки.
С этими замечательными показателями аэроплан DH.60G стал постоянным участником дальних перелетов. В историю авиации вошли эпохальный одиночный 20-дневный перелет Эми Джонсон в мае 1930 года от Кройдона до Дарвина, Австралия, на аэроплане DH.60G Jason (ныне хранится в лондонском Музее наук), перелет Фрэнсиса Чичестера по тому же маршруту, а также его последующие полеты над Тихим океаном. А также множество других перелетов. Среди DH.60 была пара гидропланов с одним большим центральным поплавком и двумя малыми подкрыльевыми вспомогательными поплавками. На одном из них стоял мотор Gipsy, на другом - Cirrus Hermes I мощностью 105 л.с. (78 кВт). Было облетано несколько экземпляров версии купе, но этот вариант не снискал популярности.
Всего фирма де Хэвилленда до 1934 года построила 595 серийных DH.60G. Еще 40 самолетов собрала во Франции фирма "Morane-Saulnier" под названием "Morane Moth". Полторы дюжины машин сделала американская фирма "Moth Aircraft Corporation", 32 самолета - фирма "Larkin Aircraft Supply Co. Ltd" в Австралии.
Хотя многих устраивало то, что DH.60G был выполнен из древесины, некоторым покупателям требовались самолеты более прочной и ремонтопригодной конструкции. Для этого де Хэвилленд создал в 1928 году DH.60M с каркасом фюзеляжа, сваренным из стальных труб. В Британии собрали 535 таких машин, еще 40 выпустила фирма "de Havilland Aircraft of Canada", 10 сделали в Норвегии, 161 аэроплан построила фирма "Moth Aircraft Corporation" в США. Большое количество машин DH.60M поступили в ВВС Великобритании, Канады, Ирака и Швеции, а также в норвежскую армию и датскую морскую авиацию.
Так как де Хэвилленд теперь строил свои собственные моторы, разработка двигателей и планеров шли параллельно. В 1931 году появился мотор Gipsy II мощностью 120 л.с. (90 кВт). За ним последовал перевернутый двигатель Gipsy III, благодаря которому улучшился обзор из кабины и изменились обводы передней части фюзеляжа модификации DH.60G III, впервые взлетевшей в марте 1932 года. Построили 30 таких самолетов. Мотором Gipsy Major IIIA мощностью 133 л.с. оснащали версию Moth Major, выпущенную в 87 экземплярах.
Вершиной развития DH.60 стала версия DH.60T Moth Trainer с мотором Gipsy II, предназначенная для военного применения. 8се заказы на нее поступили от зарубежных военных. 40 машин поступили в Бразилию, одна - в Китай, шесть - в Египет, пять - в Ирак и 10 - в Швецию. Всего собрали 64 экземпляра, включая два тайно проданных в 1931 году в неуказанную страну.
de Havilland DH.60G Gipsy Moth
Тип: двухместный учебно-тренировочный аэроплан
Силовая установка: поршневой мотор Gipsy I мощностью 100 л.с. (75 кВт)
Летные характеристики: максимальная скорость 158 км/ч на уровне моря; крейсерская скорость 138 км/ч на оптимальной высоте; начальная скороподъемность 152 м/мин; практический потолок 5500 м; дальность полета 470 км
Масса: пустого самолета 436 кг; максимальная взлетная 750 кг
Размеры: размах крыльев 9,15 м; длина 7,30 м; высота 2,80 м; площадь крыльев 22,60 м2
Полезная нагрузка: летчик и пассажир в открытых кабинах
Flight, June 1929
BRITISH AIRCRAFT AT OLYMPIA
DE HAVILLAND AIRCRAFT CO., LTD.
FOUR complete machines will be exhibited on this stand, i.e., the D.H. "Hawk Moth" with "Lynx" engine, a standard "Gipsy Moth" land 'plane of the open type, a "Gipsy Moth" coupe, and a "Gipsy Moth" seaplane.
Of the three "Gipsy Moths" to be exhibited one, the coupe "Moth," will be of the earlier form of De Havilland construction with plywood covered fuselage, and wooden wings. The other two "Gipsy Moths" will be of mixed construction in that they will have the latest type of D.H. welded steel tube fuselage and wooden wings.
The metal fuselages of the two open "Gipsy Moths" make use of steel tubing, chiefly of square section. In the front portion, from the fireproof bulkhead to the pilot's cockpit, struts as well as longerons are of square section, and the joints between them are made by fishplates and bolts. In the rear portion of the fuselage a slightly different form of construction is employed. Here, as in the front part, the longerons are of square section, but the struts in the side bays are of round section and joined to top and bottom longerons by welding. Throughout the fuselage diagonal struts are employed for the bracing, forming Warren or N girders without bracing wires. In the "Moth" metal fuselages the covering is fabric, which is carried on light fore and aft stringers. With these general remarks on the form of construction employed in the various types of "Moths," we may turn to the general features of the three machines to be exhibited.
The "Gipsy Moth" open land 'plane is a two-seater biplane designed for use as a training machine and for club and school work, as well as for private ownership. The cockpits are roomy and very comfortable, and large windscreens ensure the exclusion of draught from the cockpits. In the pilot's cockpit a dashboard with black cellulose finish carries air speed indicator, altimeter, tachometer, oil pressure gauge, inclinometer, and, if required, a watch and holder. A de Havilland Patent airspeed indicator on the starboard strut is also a standard fitting. If desired, the Hughes Mark III aperiodic compass can be fitted in front of the control lever. Above the instrument board is a small shelf to take maps, gloves and other small articles, while map cases are fitted within easy reach of the left hand. Behind the pilot's cockpit there is a large luggage locker in which suitcases can be stowed. Speaking tubes, of a new light type, including mouth and earpieces, can be fitted.
The controls of all "Moths" are very light to operate, and the machine responds immediately to the smallest touch. A spring-loaded elevator permits of trimming the machine to fly "hands off" at all speeds and throttle openings, and an adjustable spring on the rudder bar counteracts propeller torque. The ailerons are operated by the well-known de Havilland differential ailerons, which, in addition to reducing the load on the stick, minimise yawing due to lateral control. Ball races are employed throughout in the controls, and all pulleys have been eliminated and replaced by levers. No cable touches any part of the structure throughout its length, and the chance of a cable fraying is, therefore, reduced to a minimum. The rudder bars are fitted with adjustable pedals to suit pilots of different heights. Dual controls are fitted, but the forward control stick can be removed in a few seconds.
The de Havilland "Gipsy" engine is neatly faired in in the nose of the fuselage, and is mounted direct on bearers on the fuselage sides. All accessories such as filters, magnetos, carburettor, etc., are readily accessible by opening the quickly-detachable cowling. The starting of the engine - one magneto of which is fitted with an impulse starter - usually follows a single swing of the propeller, and it is not, therefore, considered necessary to fit the cockpit hand starter with which the original "Moths" were equipped.
The "Gipsy-Moth" petrol system is very simple and provides for direct gravity feed from tank to carburettor. The petrol tank is of streamline form and carried in the top wing centre section. It has a capacity of 19 gallons, which gives the machine a range of 4 1/2 to 5 hours at cruising speed. A simple float-operated petrol gauge is fitted above the tank in a position in easy view of the pilot.
The land undercarriage of the "Gipsy-Moth" differs from that of the older models in that it is of the split axle type, with wider track and increased ground clearance. The landing shock is absorbed by a rubber block unit in the undercarriage legs, the compression rubbers being in series, the natural hysteresis of the rubber, combined with the friction obtained from the "Ferrodo" lined pistons sliding in the outer casing, provides sufficient damping.
The main dimensions of the standard "Gipsy-Moth" are: Length o.a., 23 ft. 11 ins.; wing span, 30 ft.; width with wings folded, 9 ft. 10 in. The tare weight is 962 lbs., and the load carried may be made up normally as follows: Two occupants, 320 lbs.; 19 gallons of petrol 140 lbs.; 2 gallons of oil, 19 lbs.; luggage to make up maximum gross weight 309 lbs. Gross weight for normal Certificate of Airworthiness 1,750 lbs. For the "Aerobatics" C. of A. the maximum permissible gross weight is 1,550 lbs.
Normally, nothing like 300 lbs. of luggage will be carried, and a fair average gross weight to take is 1,350 lbs. At this weight the performance of the "Gipsy-Moth" is as follows: Maximum speed near ground 103-105 m.p.h. Full speed at 5,000 ft., 100 m.p.h.; cruising speed at 1,000 ft., 85-90 m.p.h.; stalling speed, 40 m.p.h.; length of run to take off, 80 yards; landing run, 100-120 yards; rate of climb from ground, 700 ft./mins.; time to 5,000 ft., 9 mins.; time to 10,000 ft., 21 mins.; absolute ceiling, 18,000 ft.; cruising at 80 m.p.h., the petrol consumption is approximately 4 1/4 gallons per hour, which gives a working range of about 320 miles.
The "Gipsy-Moth" seaplane is, except for its undercarriage, identical with the land 'plane, with wooden wings and steel tube fuselage. Consequently the description given above of the land 'plane will cover the seaplane also, except for the details of the undercarriage. The "Gipsy-Moth" seaplane is equipped with two Duralumin single-step floats, specially constructed for it by Short Brothers, of Rochester. These floats, although remarkably light, are naturally a little heavier than the wheels of the land machine, and consequently the seaplane version has a slightly greater tare weight. It speaks well for the aerodynamic design of these floats, however, that in spite of the extra weight, the performance of the seaplane is but very slightly inferior to that of the land 'plane.
When running on the water, the Short floats of the "Gipsy-Moth" throw up remarkably little spray, even at speeds just below the planing speed, and altogether the "Gipsy-Moth" seaplane is remarkably "clean" on the water. No water rudders are fitted to the floats, but in spite of this the machine can be manoeuvred quite well with the air rudder while the engine is running.
The tare weight of the "Gipsy-Moth" seaplane is 1,070 lbs., and the permissible gross weights for the two classes of C. of A. are the same as for the land 'plane, i.e., 1,750 lbs. for the "normal" and 1,550 lbs. for the "Aerobatics."
Following are the performance figures for the "Gipsy-Moth" seaplane :- Full speed at sea level, 98 m.p.h.; full speed at 5,000 ft., 92 m.p.h.; cruising speed at 1,000 ft. 75-80 m.p.h.; stalling speed, 43 m.p.h.; time to get off 13-15 secs.; rate of climb from sea level, 480 ft./min.; time to 5,000 ft., 14 mins.; time to 10,000 ft., 40 mins.; absolute ceiling, 13,000 ft. An amphibian undercarriage for a "Gipsy-Moth" is described under the exhibits of Short Brothers.
SHORT BROTHERS, LIMITED
THREE complete machines will be exhibited on the stand of Short Brothers, of which, however, but two will be Short machines, the third being a de Havilland "Gipsy-Moth," for which Short Brothers have designed an amphibian undercarriage. The two Short machines will be the "Singapore I" on which Sir Alan Cobham made his flight to the Cape and back, and the second will be a Short "Mussel" light seaplane.
Reference has been made to the fact that on the Short stand there will be exhibited a "Gipsy-Moth" with amphibian undercarriage. This machine is the property of Mr. John Scott Taggart, of radio fame. Short Brothers have designed for him an amphibian undercarriage, which consists of a single float placed centrally under the fuselage, two wing tip floats, and a retractable land undercarriage. The main and wing tip floats are of normal Short design and construction, with duralumin as the material.
The landplane undercarriage consists of a large-diameter transverse tube carried in bearings inside the central float and having on it, near the centre, a worm wheel. A worm on a sloping shaft which reaches into the pilot's cockpit and there terminates in a crank handle engages with this worm wheel, and rotates the horizontal tubular shaft. At each end of the transverse tube is a steel tubular fork, both members of which are telescopic and carry the wheel. When the transverse shaft is rotated the forks move forward and up until the wheels are clear of the water. The transverse tube itself is a cantilever beam, and may also have to resist a fair amount of torsion under certain conditions of landing or taking off. It has, however, been found that the tube stands up to the work quite well, and the amphibian undercarriage, although adding a certain amount of weight, increases enormously the choice of landing "grounds" available.
The central single-float arrangement has not been tried to any great extent in this country, but in the United States of America it is preferred to the British twin-float system. The lateral stability at rest is established, as in a flying-boat, by the outboard floats, and we understand that during tests from the Medway, at Rochester, the amphibian "Moth" was found to handle well on the water. A water rudder is fitted to the heel of the central float, and when the machine is used as a landplane the rudder, which is sprung, serves as a- tail skid, the normal tail skid of the "Moth" not coming in contact with the ground.
Flight, April 1930
AIRCRAFT FOR THE PRIVATE OWNER
IT seems almost unnecessary to have to give any details of the Moth, for it is probably the most popular and most widely-used light aeroplane in the world today.
Actually it can be said that the Moth made the light aircraft movement in England, and, in fact, in many parts of the world, but at the same time it must be borne in mind that it was the "Cirrus" engine which first made the Moth possible. Apart from its use in clubs for instruction, and by some 137 private owners in this country alone, the Moth is widely used by the Air Forces of the world for communication flights and for primary training.
It is available in many forms, such as a landplane fitted with a normal wheel undercarriage, which, as a standard, is of the divided-axle type and stands a remarkable amount of rough use; as a seaplane with twin floats; for use on snow with skis, and lastly as an amphibian with the single central float type of undercarriage with wheels which may be lowered when landing on land, as has been developed for the Moth and such like aircraft by Short Bros., of Rochester.
The Moth is a small single-bay machine with two cockpits in tandem, and if desired may be fitted with a Coupe top which practically turns it into a cabin machine. The engine most fitted now is the "Gipsy," but a very large number have been sold with "Cirrus" engines, and also the Armstrong-Siddeley "Genet," this latter was the type used for a display of advanced aerobatics and inverted flying at the R.A.F. Display at Hendon.
The Moth has lately been redesigned with an all-metal fuselage, but retaining the wooden wings which are, of course, designed to fold very easily.
The Moth is now being built under licence in America and France, and the De Havilland Co. have works in Canada, and Australia, while agents are to be found in nearly all countries.
Flight, July 1931
The alterations to the normal metal-fuselage "Gipsy-Moth" which have been made in producing the new "Moth Trainer" consist mainly in shifting the rear lift wire attachment to the forward wing root, in order to give free exit from the front cockpit, in increasing the cockpit areas, in fitting four doors, and in taking the exhaust pipe away from the side and pointing it downward under the nose
ECONOMY in flying training equipment is the key-note upon which the design of the new Moth Trainer, recently produced by the De Havilland Aircraft Co., Ltd., is based. The normal metal-fuselage Gipsy Moth was already fairly suitable for training purposes, and the modifications necessary to make it entirely suitable for modern training requirements were not of a far-reaching nature from the constructional point of view. Consequently the De Havilland Company has been able to put on the market, at really low cost, a new training type suitable for modern conditions. That this is no idle claim is proved by the fact that the new Moth Trainer is available at prices below ?1,000, the actual price varying according to the additional equipment which it is desired to fit, and which is optional.
As a variant of its normal form as a landplane training machine, the Moth Trainer can also be supplied as a twin-float seaplane, and used for seaplane training (at extra cost, of course), or with skis instead of wheels for winter training in countries where snow-covered aerodromes or frozen lakes are the rule rather than the exception. Moreover, the three types of undercarriage are interchangeable, so that the machine can always be fitted up to suit the season of the year, using the wheel undercarriage in the summer and the ski undercarriage in the winter.
It is, of course, well known that De Havilland service exists in nearly every civilised country in the world, and, owing to the fact that so many of the components of the Moth Trainer are identical with those of the standard Gipsy Moth, purchasers of the Moth Trainer can be assured that spares are always readily obtainable, and at low cost. Thus, not only first cost, but upkeep and maintenance costs, should be low for schools using the new school machine.
Although flying training is the function which the Moth Trainer has primarily been designed to fulfil, it has been specially designed also to carry out many other duties by means of additional equipment, which can be readily fitted without modification to the main structure. These duties include Advanced Training, Fighting Training, Bombing Training, Wireless Training, and Training in Photography. The machine has been considerably strengthened, and as a result the permissible Certificate of Airworthiness weight for aerobatics has been raised from 1,550 lb. (704 kg.) to 1,640 lb. (746 kg.), and for normal flying the permissible all-up weight has been increased from 1,750 lb. (796 kg.) to 1,820 lb. (827 kg.).
These increases in the permissible all-up weight not only enable the extra equipment to be carried, but the Moth Trainer is made nicer to handle, even at the extra weight, by fitting wings of a completely new section, so designed that, although speed and climb are not adversely affected in any way, the stall is less abrupt and the resultant spin is slower.
Among the more important modifications made in producing the Moth Trainer, mention may be made of the arrangement of the lift wires. It will be recollected that in the normal Gipsy-Moth the rear lift wire is in the plane of the rear spars. This means that the wire rather gets in the way if, in an emergency, the occupant of the front cockpit is obliged to leave hurriedly, as, for instance, in jumping with his parachute. There is always a risk that some loose portion of clothing or equipment may catch on this lift wire and cause a delay at a time when every second is likely to count. To avoid this possibility, the rear lift wire in the Moth Trainer has been brought forward to the front spar wing root, where the lower portion of the wire is in front of the front cockpit, and thus right out of the way.
Further to facilitate exit from the front cockpit, a deeper type of door has been fitted, so that the occupant can now very easily step straight out on to the lower wing. These deep doors are fitted on both sides, enabling a rapid exit to be made from either side. This point is of great importance, since it is easy to visualise conditions under which it would be relatively easy to get out on one side of the machine, but impossible on the other. Thus, the addition of the second door may be regarded as a very real safety measure.
The fitting of doors in both sides of the fuselage brought up another problem. The exhaust pipe in the normal Gipsy-Moth runs along the port side of the fuselage. This would obviously interfere with the use of the door on that side, and so in the Moth Trainer the exhaust pipe has been shortened, and is bent down under the nose of the machine. In this position the exhaust pipe is not in the way, and, although the noise is possibly slightly greater when heard from a point outside the machine, in the cockpits there is no noticeable difference in noise.
In a training aircraft, as, indeed, in all aircraft, view is an important consideration, and as the number of aircraft increases, the subject of view will assume greater and greater importance. By careful experiment and the application of experience, it has been found possible, in the Moth Trainer, to make certain detail alterations which have resulted in a much improved view from both seats. The view from the back seat has been greatly improved in an upward direction by cutting away the trailing edge of both top wings at the root end fittings. Biplane construction normally restricts the upward view from the front seat. In the Moth Trainer this disadvantage has been reduced a great deal by the fitting of a mirror at a suitable angle into the engine cowling, immediately behind the engine. This mirror was not in place when our photographs were taken, and is not, therefore, shown in the accompanying pictures. The use of mirrors has also been extended to the pilot in the back seat. A small mirror is fitted at the side of the front windscreen. In this mirror the instructor and pupil can see each other, thus giving a feeling of closer contact.
The seats in both cockpits are specially designed to accommodate the Irvin seat type parachutes, in conjunction with which the new Irvin harness of the "quick release and adjustment" type may also be used.
Structurally, the Moth Trainer follows exactly the same lines as the normal Gipsy-Moth. That is to say, the fuselage is a welded steel tube structure, while the wings and tail are mainly of wood construction.
The engine fitted in the Moth Trainer is the Gipsy II, of 120 b.h.p., and the patrol tank forms, as in the older type, the centre-section of the top plane.
For inverted flying the Gipsy II in the Moth Trainer is fitted with the well-known De Havilland scheme, which consists in fitting a tray in the engine sump, which, functioning on the unspillable inkpot principle, prevents oil from flooding the cylinders when the machine is on its back. If desired, the engine can be made to fire in the inverted position by the provision of a mechanical pump, which delivers petrol under pressure to the inlet manifold.
An undercarriage of the divided type is fitted, in which the telescopic legs have shock absorbers in the form of rubber blocks working in compression. Special low-pressure Dunlop landing wheels and tyres are fitted, and, in conjunction with the travel provided by the stroke of the telescopic legs, practically eliminate all risk of minor damage due to heavy landings, such as are inevitable at training centres where pupils are doing their first few hours of solo flying. A special feature is that these wheels run on ball bearings, which require practically no attention, and which eliminate shake and rattle.
It has been said that, in addition to its main function of a flying training machine, the Moth Trainer can be used for instruction in fighting, bombing, wireless, photography, etc. For these purposes the appropriate equipment is added to that used for ordinary flying training, which includes a full range of instruments fitted in each cockpit, and full dual control, with duplication of control column, rudder bar, tail-trimming lever, throttle and ignition switches.
The camera gun is the recognised method of instruction in aerial fighting, and in the Moth Trainer provision has been made for mounting a service type camera gun, with appropriate sight, as shown in one of our photographs.
For instruction in bombing a special bomb rack, carrying four 20-lb. bombs, is fitted under the fuselage. Apart from its use for training, the Moth Trainer can be used for light offensive operations. An example of this was provided by the fleet of military-type Moths supplied to the Government of Iraq some little time ago. These machines were fitted with bomb racks, and carried in addition complete wireless transmitting and receiving equipment, including airscrew-driven electric generator. A Very pistol was also a part of the equipment, while the Iraq machines had, in addition to their already heavy load, to carry an extra 10-gallon petrol tank, a 2-gallon drinking-water tank, and airtight ration containers in both cockpits. An aerial camera was fitted in the floor of the forward cockpit, while the wireless apparatus was installed in the rear cockpit.
The Moth Trainer carries a British Air Ministry Aerobatic Certificate of Airworthiness, allowing an all-up weight of 1,640 lb. (746 kg.). With instructor and pupil both wearing parachutes, all equipment, full tanks, and a camera gun for fighting training, the figure of 1,640 lb. leaves a considerable margin, which may be used for personal gear or special equipment.
The following performance figures relate to the Moth Trainer at a gross weight of 1 1,640 lb.
Full speed at ground level, 106 m.p.h. (171 km./h.); full speed at 5,000 ft. (1,525 m.), 101 m.p.h. (162.5 km./h.); full speed at 7,000 ft. (2,130 m.), 98 m.p.h. (158 km./h.); full speed at 10,000 ft. (3,050 m.), 90 m.p.h. (145 km./h.); stalling speed, 45 m.p.h. (72.5 km./h.).
The length of run to take-off is 160 yards (144 metres), and the time to take-off is 11 seconds.
The length of run on landing is 135 yards (120 metres). The best gliding angle is 1 in 7.5.
At ground level the rate of climb is 730 ft./min. (3.7 metres per second), while the times to 5,000 ft., 7,000 ft., and 10,000 ft. are 8.5 min., 12.5 min., and 22.5 min. respectively.
The service ceiling (i.e., altitude at which the rate of climb is 100 ft./min.) is 13,800 ft. (4,200 metres), and the absolute ceiling is 15,900 ft. (4,850 metres).