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How Sir Alan Cobham surveyed by seaplane a route to the inland lakes of Central Africa


MOORING SIR ALAN COBHAM'S VALETTTA at Marseilles (Marignane Airport)

MOORING THE VALETTTA at Marseilles (Marignane Airport) which was reached on the second day of the outward flight. One member of the crew was in charge of all mooring, and also of the maintenance of the aircraft. Including Cobham, who acted as pilot-navigator throughout the whole flight, there were six men on board the Valetta. The other four acted individually as mechanic, wireless operator, cinematographer and photographer. Although each man had his own duties, he assisted, when required, in other tasks.

WHEN Sir Alan Cobham climbed into the cockpit of the Short Valetta seaplane to begin his flight to Central Africa, he took charge of the largest twin-float convertible aeroplane in the world.

Although the aircraft was almost new — having done only about thirty or forty hours’ flying since the completion of her trials — she was facing a flight of nearly 12,500 miles. Her Certificate of Airworthiness was only five days old and many features of her design were novel.

As she lay at her moorings on the River Medway on July 22, 1931, she represented a great experiment in air transport. Her three engines speeded up readily when Cobham opened the throttles. He gave a final look round, waved and moved out across the water. The aeroplane responded perfectly to the controls and rushed into the wind, rose on the the step of her floats, and took off for Bordeaux, her first port of call. The task that lay before Cobham was complicated and arduous. His earlier pioneer flights (see the chapters “Cobham’s Pioneer Empire Flights” and “Cobham’s Pioneer Empire Flights - 2”) had shown the difficulties and dangers of surveying new air routes. Disaster had often threatened him, and on one occasion his sole companion had been killed by a shot. Yet the main feature of such flights is not danger or excitement; they are merely the incidental accompaniments. The main feature of a survey flight is unceasing hard work.

Before the flight begins it must be organized in every detail. During the flight there is an exacting routine to be followed, a ceaseless check of engine performance, and a critical appraisement of adjustments and alterations. When the flight has ended it must be reported upon in great detail, so that not one of its lessons is lost. The flight to Lake Kivu and back well illustrates the immensity of this threefold task. The route itself was not simply a route to be followed; it was a route to be criticized. While flying along it Cobham had to decide what possibilities it offered for future regular air services. Where it presented alternatives he had to consider the relative merits of this way or that way, and to advise accordingly.

The route, moreover, had been chosen because of its diversities. At different stages it presented entirely different conditions and problems. On the first stretch, across the English Channel and down the French coast, the aircraft would encounter the flying conditions associated with the Atlantic seaboard; the next stage would take her to the Mediterranean, which is notorious for its bumpy flying. The passage of the Mediterranean was a 2,000-miles’ test of seaworthiness.

On reaching Egypt the aircraft was to turn along the valley of the Nile, where her behaviour in restricted river waters could be tested. The long stretch of river work provided unique opportunities for judging her handiness in such difficult conditions as those of the Nile in flood.

A totally different test would be provided in southern Egypt and northern Sudan — the test of extreme heat. In those regions ground temperatures of 120 degrees or so are not uncommon. The slightest inefficiency in engine lubrication could not fail to show up clearly in such conditions.

The final stages of the route, the mountainous regions of central Africa, would provide a final challenge, by demanding good performance at high altitudes. Up to 10,000 feet or so easy control would be necessary to negotiate in safety the high mountain passes.

Apart from appraising the value of the route the main object of the flight was to test the potentialities of a new type twin-float seaplane. The Valetta, with her authorized all-up load of 23,000 lb. and approximately 1,500 total horsepower, was to be carefully criticized in every particular.

She was built as a seaplane, but could be quickly converted to a landplane by taking off her floats and putting on a wheel undercarriage ; she was the largest machine then built on which the scheme had been tried. Her span was 107 feet, her length 70 ft. 5 in. and her height 25ft. 5in. Her tare weight was 15,612 lb., giving a maximum permissible load of 7,388 lb.

To fill her tanks to capacity required 490 gallons of petrol and 50 gallons of oil. She maintained a cruising speed of about 100 miles an hour, and in all ordinary conditions of wind had a range of 500 miles. Her three engines were of the Bristol Jupiter XI F type.

On this flight Cobham acted as pilot-navigator throughout the journey, with no relief pilot; but he carried five assistants. Bell, of Short Brothers, was in charge of the maintenance of the aircraft, mooring and so forth; Spencer, of the Bristol Aeroplane Company, acted as mechanic; Parish, of the Marconi Company, was wireless operator; Bonnett, of the Gaumont Company, was cinematographer; and Russell was photographer. Although each member of the crew had his own duties, he assisted as and when required in other work.

A considerable equipment had to be carried, much of it for test purposes. Among the marine items were an anchor, extra mooring lines, a special collapsible rubber dinghy, a special stainless steel mooring bridle and two drogues (sea anchors).

Advance Preparations

Engine spares and tools comprised about 300 items and weighed about 230 lb. There were nearly 100 lb. of aircraft spares and tools, some 40 lb. of wireless spares, and about 250 lb. of photographic gear. In addition, a complete set of engine-lifting gear was carried for use in emergency.

Before taking off from the Medway, Cobham had been engaged for several months in the preliminary organization. Supplies of fuel and lubricating oil had to be laid down for the outward and return journeys. Along part of the route he was able to draw petrol supplies from the stock of Imperial Airways; but special depots had to be arranged in certain parts of the Mediterranean, and extra stocks in Uganda. Much thought was given to the question of moorings, for it was essential that they should be available immediately the aircraft alighted, even if she were not strictly on time. The local methods of mooring at every alighting place had to be considered and approved before the flight began.

Advance preparations therefore included the selection of exact alighting places; the notification to the Government concerned of the intended visit; the finding of the right authority and the obtaining of the necessary permission in every instance; the cooperation at each alighting place of a named individual who would be personally responsible for the provision of mooring facilities; and precise arrangements as to fuel and oil supplies.

Only after all this business had been settled satisfactorily could Cobham take his place at the controls of the seaplane to begin the flight. As soon as the machine was in the air another exacting routine began, for every detail of the aircraft’s performance had to be noted and recorded.

COBHAM’S AIRCRAFT IN FLIGHT near Rochester, Kent, on his return from Africa. The survey flight began on July 22, 1931, and ended on September I of the same year. Some 12,300 miles were covered in 128 flying hours without a serious hitch. The object of the flight was to test the aircraft as well as survey the route.

The more obvious particulars that were required included the dates, times of departure and arrival, the exact number of miles flown and the weather conditions between the various ports. Not so obvious were such items as the engine revolutions throughout the flight, with a log of the speeds; petrol and oil consumption; oil temperatures ; details of loads carried; the behaviour when taking off and alighting; and the condition of the water.

The general handling qualities of the aircraft in the air and on the water had to be criticized; also her behaviour in coming up to and leaving her moorings, and when moored up. Apart from such technical matters as the amount of noise and vibration, trim, flexing of structure and response to controls, details had to be given of any defects that might reveal themselves. Any replacements or adjustments to the aircraft or to the engines had to be noted, with the relevant times.

A specially interesting feature of the Valetta was that her floats were fitted with water rudders, giving her better control on the water than perhaps any other craft of her time. Nobody knew better than Cobham the importance of being able to approach moorings with precision, despite strong winds and contrary currents.

On the flight to Lake Kivu, when Cobham found that it was possible to steer the Valelta on the water with accuracy down wind in almost a gale, he must have recalled his earlier flights, and the many difficulties which he had faced in manoeuvring in narrow waters. There was, however, little time for such slightly different routes. The be abandoned because of bad Lake Kivu. The next day the on Lake Kivu because of the reminiscences, for on such a flight the pilot-navigator has no respite, especially if he is responsible for the whole expedition.

Good weather favoured the opening stages. The 500 miles from Rochester to Bordeaux (Hourtin Seaplane Base) were flown in less than five and a quarter hours. The next day the Valetta flew to Marseilles (Marignane Airport), a distance of 370 miles. The following day, July 24, saw two stages accomplished: to Ajaccio (Corsica) and on to the African coast at Tunis. The day’s total was 585 miles.

Value of Water Rudders

On July 25 the African coast was left for Malta (Calafrana), 270 miles; and the following day another two stages — to Corfu, and on to Athens — were flown. The 698 miles that day had been covered in six hours eighteen minutes.

From Athens the route lay over the Mediterranean again to Alexandria, via Mirabella (Crete), the mileage of the two stages being 592, flown in five hours eleven minutes. A feature of this part of the flight was wireless reports from the Imperia, lying at Mirabella. The Imperia is Imperial Airways’ depot ship and wireless station lying permanently at Mirabella. She gave the Valetta her bearings about every half hour, so that despite low cloud the seaplane found Alexandria Harbour only half a mile off course. At Alexandria there was a day’s halt, the first since the flight began.

On July 29 the stretch from Alexandria to Luxor was flown, with stops at Cairo and Asyut. The value of the water rudders was apparent at all these places. It was found possible to make complete circuits in the river regardless of wind or current, with all three engines ticking over and control given by the water rudders alone. Native dhows sailed out to midstream at Luxor, to do the refuelling; the fact that they were able to make fast to the Valetta's mooring without fouling her wings with their sails was a point in her favour.

The next day, July 30, was the hottest of the flight, for on arrival at Aswan it was found that afternoon shore temperatures had been 120 degrees for many days. Between Aswan and Wadi Haifa the highest oil temperatures reached during the flight were recorded.

On the 400-miles’ stretch from Wadi Haifa to Kareima, which was flown on July 31, a short cut across a great bend in the river was attempted; but a dust storm arose and made visibility so poor that it became necessary to find the river again, and use it as a guide, as there was no horizon. When an aviator is flying low over desert in a dust storm the horizon disappears. The twin-float seaplane, however, could fly safely some twenty to fifty feet above the water, with the banks just visible, for in this way she always had an emergency alighting place below her.

At Kareima a 12-knots current made mooring difficult; buoys were dragged under water by it; so officials fixed other buoys on top of the ones that sank. The surface buoy to which the Valetta made fast was really the fourth, three other buoys being hidden under water.

THE OUTWARD AND RETURN FLIGHTS were over first attempt to fly from Katunguru to Lake Kivu had to weather in the mountain pass between Lake Edward and pass was successfully negotiated but no landing was made previous day’s delay.

Next morning, August 1, disclosed the fact that another buoy had been tugged under water, for the mooring bridle was sloping at an angle of forty-five degrees, and the seaplane’s floats were acting as a buoy to support the mooring. Apparently the scouring action of the Nile at that time of the year is so great that any chain or cable holding a buoy is apt to be buried by the silt. It was difficult to get away in such conditions, but the take-off, for Atbara, was good.

Another dust storm was negotiated by flying low again over the river. When Cobham reached Atbara he decided to push on to Khartoum before alighting. Sixty miles farther on, however, visibility became so bad that it was decided to turn back to Atbara. There was no mooring; so the seaplane dropped her anchor and, despite a thirty-miles-an-hour wind, the anchor held.

The weather was good for the next day’s run to Khartoum where, because all exposed controls were covered with sand, a day’s halt was made for overhaul, cleaning, greasing and oiling. The difficulties from extreme heat were now over. Although the seaplane was still approaching the Equator, the weather became cooler each day after Khartoum had been left behind.

Two stages were flown on August 3, from Khartoum to Kosti and from Kosti to Malakal. Fog caused a late start next day. When it cleared visibility was unusually good and, after having landed at Shambe, the Valetta flew on to Juba.

Beyond Juba the flat country gave way to hills, and mountain ranges appeared on the horizon. A 240-miles’ stage on August 5 took the seaplane to Butiaba, on Lake Albert, 2,037 feet above sea level. The day’s run was completed by flying on to Port Bell, and then to Entebbe, both situated on Lake Victoria, at an altitude of 3,726 feet. A day was spent on overhaul work at Entebbe, in preparation for the high altitudes of the pass over the mountains to Lake Kivu.

On August 7, flying west along the Equator, the seaplane made for Lake George and alighted in the Kasinga Channel at Katunguru, on the south bank, for refuelling. Then an attempt was made to fly on to Lake Kivu the same day. After having left Lake Edward, however, the seaplane met with bad weather up the mountainous valley of the Ruchuru River.

Lifted 3,000 feet by Up-current

The pass over the mountains to Lake Kivu is only seven or eight miles wide, and the mountains —then partly hidden by mists and cloud — are badly mapped. Some of the volcanoes rise to 15,000 feet. Petrol began to get low, storms arose and visibility got worse. There was no alternative but to return to Katunguru and try again.

On August 8 conditions were better, but the pass provided plenty of excitement. A violent up-current suddenly took the machine, without extra throttle, from 8,000 to 11,000 feet, in what appeared to be a matter of seconds; as this rapid rise was into thick cloud, it was necessary to dive steeply to regain visibility. The Valetta answered to her controls perfectly, and a few minutes

later the mountain pass had been safely negotiated.

Because of the previous day’s delays, Cobham decided not to alight on Lake Kivu, but to survey its northern shores from the air, and then return through the pass without having flown to the southern end of the lake. The return through the mountains was difficult and exciting, because of the strong air currents. Good time was made back to Katunguru, where there remained just enough petrol to take the machine back to Entebbe.

Several days were spent at Entebbe as Cobham had other survey work in the vicinity, and this period enabled the seaplane to be overhauled in preparation for her return flight. He took off for Butiaba on August 14, choosing a different route for the return journey because the route possibilities between Lake Kioga and Lake Albert had to be further reported upon.

DETACHABLE FLOATS WERE FITTED to the Valetta, which could thus be quickly converted to a landplane. She was the largest aircraft on which this scheme had been tried. To assist in manoeuvring the flying boat when on the water, rudders were fitted to the floats. The authorized all-up load of the aircraft was 23,090 !b. and a horse-power of approximately 1.500 was provided by her three engines.

The stretch from Butiaba to Juba, on August 16, was one of the few in which wireless communication was difficult, because of atmospherics. At Juba a swift current was running and, after having refuelled, the fliers got away quickly for Shambe. The next day they pressed on to Malakal, and then to Khartoum, where a day’s rest was taken. This was beneficial to the aircraft, which could be inspected thoroughly; and it was essential to the pilot-navigator, who still had more than 4,000 miles to fly. There was no relief pilot, and there was no respite from the strain, for the return flight was as important as the outward flight from the point of view of survey.

On August 19 a flight from Khartoum to Wadi Haifa non-stop was logged as 510 miles in four hours thirty-four minutes, an average speed of about 115 miles an hour. The heat at Wadi Haifa was intense, but after luncheon and re-fuelling the flight was continued to Luxor, another 320 miles, done in three hours three minutes.

Luxor to Asyut, Asyut to Cairo, and Cairo to Alexandria were all flown on August 20. Later in the day, when the fliers were approaching the Mediterranean, a strong wind, haze and bumps made flying difficult. The directional wireless, which had already been most useful, proved its worth once again on the flight across the open sea from Alexandria to Mirabella, on August 22. The Valetta was also in touch with Malta, 900 miles away. Another advantage of radio communication was noted at Mirabella, where nearly all appearances denoted wind from the north, but messages from the airport said the surface wind was west. Without such notification even an experienced pilot might have attempted an across-wind landing.

The Mirabella-Corfu stage was uneventful, but from Corfu to Naples a strong wind was troublesome over the Gulf of Taranto, and clouds covered the foot of the Apennines. A way through was found with some difficulty and a good landing was made in the harbour at Naples. In landing, and again in taking off for Ajaccio, the easy manoeuvrability of the seaplane was impressive.

It was intended to fly on August 29 from Ajaccio to Bordeaux (Hourtin) with only one stop for refuelling at Marseilles, but the weather over the south of France prevented this. Low cloud, rain, and the absence of radio weather reports — it was Sunday — made it scarcely wise to take a seaplane for 300 miles over land, in poor visibility. A stop was made for the night at Cette, and the remainder of the stretch was finished next day in very wild weather.

Bad weather and poor visibility attended the Valetta on the coast of Brittany, but over the Channel the weather improved, and she alighted on Southampton Water on August 31. Flying north to the Thames next day, she kept over the river through the centre of London, and touched down at Rochester.

By having covered some 12,300 miles in 128 flying hours without a serious hitch, Sir Alan Cobham had emerged with honours and had completed another great aerial survey flight.

THE SURVEY AIRCRAFT off the African coast at Tunis. The most varied conditions both in the air and on the water were experienced during the flight. High temperatures, sandstorms, squalls and thick clouds were encountered. On the Nile at Kareima a twelve-knots current made mooring difficult and dragged the buoys under water.

Click here to see the photogravure supplement to this chapter.

You can read more on Cobham’s Pioneer Empire Flights” , “Great Flights” and “Survey in the Empire” on this website.

Cobham’s Pioneer Empire Flights (3)