In 1931, the Soviet Military Revolutionary Council decided that a long-range bomber was needed for the Air Force, and in August that year it set up a commission to establish the design requirements. It was decided that none of the TB class aircraft was suitable, so the commission proposed a more streamlined, single-engined design with a slow-running engine in order to reduce drag and to save fuel. Tupolev was instructed to prepare proposals.
The proposals were approved in December, and Tupolev set up a team headed by Pavel Sukhoi to design the aircraft around a Mikulin M-34 engine. The designers set out to achieve a still-air range of 13,000km/8,078 miles, while Tupolev guaranteed that a minimum of 10,000km/6,214 miles would be possible. It was given the designation ANT-25RD (Rekord Dalnosti, or long-range record), and the military designation DB-1 (Dalnii Bombardirovshik = long-range bomber). The design was finalized as a single-engined, low-wing monoplane with a very high aspect ratio of more than 13:1 - span was 34m and chord was 2.62m. The spar was in two sections, with the flanges manufactured from steel achromatized tubes. A third spar was mounted to the rear of the (wing) chord. Duraluminium braces were fixed between the spars and were part of the load-carrying structure, as were the riveted fuel tanks, seven metres long, which were mounted in each wing. The wing surfaces consisted of corrugated metal.
The fuselage was made of two sections: forward, the front was monolithic and integral with the wing, while the rear was a monocoque of oval sections. The tailplane was also corrugated. The undercarriage retracted by folding backwards into the wing; the wheels were solid discs rather than the usual spoke versions; and the suspension featured oleo-pneumatic shock absorbers. The tail wheel was covered by a spat to minimize drag. The large, three-blade propeller could have its pitch adjusted, but only on the ground. It measured 3.9m/12.8 feet, from tip to tip.
Exhaust gases were used to heat the cockpit. The pilot sat on a canvas-covered seat directly behind the engine. Behind him, on the wings’ centre spar (and over the integral fuel tanks), was a bed for crew rest. Then came the navigator who was provided with a sextant and observation hatch to allow him to fix position by star/astral readings. He also doubled as radio operator, so the aircraft’s radio equipment was mounted alongside the navigation area. Last came the second pilot, with a simplified instrument panel and full controls. With no forward visibility, he could only fly on instruments and served only as a backup, and short-term relief, for the first pilot.
The ANT-25 was equipped with the latest developments in blind flying instruments for its time, including an artificial horizon and a turn and bank indicator. It also featured an early gyro magnetic compass, a solar course indicator, and a radio transceiver with a range of up to 5,000km/3,107 miles. To improve the possibilities of evacuation time in the event of ditching, inflatable rubberized bags were fitted which would increase buoyancy.
Work began on the first aircraft at the TsAGI/ZOK on 7 December 1931. Completed in June 1932, it was then disassembled and brought by road to Monino where it was reassembled and readied for flight, fitted with a 750hp Mikulin M-34. On 22 June 1933, the ANT-25 made its first flight, piloted by Mikhail Gromov, which lasted for just over an hour. In September, the original Mikulin engine was replaced by an uprated version which gave 874hp.
The test results proved to be disappointing. The second aircraft, which was constructed in August/September at Monino, made its first flight on 10 September, again flown by Gromov. This was fitted with the uprated M-34R engine, which gave 900hp. It showed that the ANT-25’s range in still air would not exceed 11,000km/6,835 miles. So Sukhoi and his team looked again at the design, and decided that the corrugated surfaces on the wings and tailplane might be increasing the aircraft’s drag coefficient. They decided to cover these surfaces with linen, using a special needle which was fed into machined holes on the riser surfaces. The corrugated ‘valleys’ were filled with lightweight balsa wood, and the new wing surfaces were varnished as was the engine cowling. The propeller was then highly polished, all with the aim of reducing drag.
It worked. Test flying began again in summer 1934, and noticeable improvements in performance were evident right from the start. Tupolev and Sukhoi were quickly convinced that 13,000km/8,078 miles could be achieved. In August a thorough pre-flight preparation began, which included the crew spending long periods flying in cloud, flying the proposed route in a Polikarpov U-2 training aircraft, and locating possible emergency landing strips en route, and trying them out. The next training session was a triangular Moscow-Ryazan-Tula circuit, a distance of 520km/323 miles, which was to be flown as many times as the aircraft’s endurance would allow.
Early in September, Mikhail Gromov took off from Monino, near Moscow, accompanied by crew members Aleksander Filin and Ivan Spirin. Because it was necessary to chart strictly the aircraft’s track, it was decided to fly at minimum speed and at low altitude; 200m/656 feet was chosen for the sector to Ryazan. About an hour into the journey, they encountered fog and the engine began to lose power. Gromov decided to jettison fuel and to seek a landing spot. To jettison he had to switch off the engine or face a possible explosion. Fuel jettisoned well from the right tank, but only a thin trickle came from the left. But he landed the aircraft on a wet field and despite the wheels digging in up to the axles, the aircraft did not nose in.
The carburettor jets were replaced, and they returned to Monino on the next day. Two days later, they tried again. Thirty-four hours into the flight, they were some 120km/75 miles beyond Ryazan, flying at 3,500m/12,000ft, when a fire started in the starboard engine block, and they began to lose power. Gromov turned back to Ryazan, and began to descend. Thirty-five minutes later they landed beside a river and had to jump out to hold the aircraft so it wouldn’t fall into the water. It turned out that a carburettor float had failed when Gromov switched tanks. It was repaired and they returned to Monino. On 10 September they were off again. By the third night of the journey, they had flown the Moscow-Ryazan-Tula circuit nine times plus a wide range of other sectors in order to avoid boredom, but because of bad weather, they were advised by radio to fly westwards, towards Kharkov in the Ukraine. There they flew another complex sector pattern. They were flying near Kharkov at 4,200m (almost 13,000 feet) when they ran into more bad weather. They realised that fuel for a return to Moscow was doubtful, so they continued to Kharkov, where they landed. There was only thirty kilograms of fuel remaining, perhaps ten gallons! They had covered 12,411 km/7,712 miles in seventy-five hours and two minutes. While this exceeded the existing record of 9,104km/5,657 miles set by French pilots Maurise Rossi and Paul Codos in August 1933 when they flew a Bleriot 110 from New York to Rayak in Syria, Gromov’s flight was not recognised by the Federation Aeronautique Internationale, as the Soviet Union was not then a member of the FAI.
Now that Gromov and his crew had proved that the ANT-25 could beat the record, the government gave instructions to prepare for a long-distance record-breaking flight. It was decided to fly non-stop from Moscow to the United States over the polar icecap and the North Pole.
The winter months were used in preparation for the flight, and the following May the second ANT-25 took off from Monino, this time commanded by Sigismuncl Levanevski. They headed due north, aiming for the Pole. Some twenty hours later, over the frozen Barents Sea, oil began to leak from an engine pipe, and Levanevski decided to return to Moscow rather than face the prospect of a forced landing on the icecap. On his return, Levanevski berated Tupolev and accused him of attempting to sabotage the flight. He also stated that he would never again fly a Tupolev aircraft. He never did, for tragedy followed.
Levanevski also suggested that it was madness to attempt to fly such a long distance in a single-engined aeroplane. Ironically, shortly after Chkalov and Gromov had successfully flown ANT-25s over the Pole to America, Levanevski and a crew of five set out in a four-engined DB-A designed by M. M. Shishmarev in Zhukovski’s Military Aviation Academy, heading for America in an attempt to break the long-distance record. They reported passing the North Pole, and that they were heading for Fairbanks in Alaska. Then they reported the loss of an engine. Two garbled messages followed, but they were never seen again.
Levanevski’s return did nothing to inspire confidence in the ANT-25, and for six months it looked as if no further flights would be allowed. But Georgi Baidukov, Levanevski’s co-pilot, did not share his lack of trust, and he persuaded Valeri Chkalov, perhaps the best known Soviet pilot and well known to Josef Stalin, to support the programme. Previously, he had flown only fighters, and he was reluctant to fly the ANT-25. But after one flight, he was enthusiastic. Chkalov’s intercession resulted in Stalin giving approval for him to undertake a long-range flight within the Soviet Union. A route plan was drawn up: starting from Moscow, the flight would proceed north to Spitsbergen, and then fly east along the north coast to Franz Josef Land, on over the Northern Lands to Tiksi, then south-east to Petropavlovsk-Kamchatski and Nikolaev-Petropavlovsk-Kamchatski-na-Amure (Nikolaev on the Amur river).
All of this had delayed the programme by a year, but on 20 July 1936, at 5.45 a.m. Moscow time, Chkalov, with co-pilot Georgi Baidukov and navigator Aleksander Belyakov, lifted off from Monino and headed north. Fifty-six hours and twenty minutes later, bad weather forced them to land on Udd Island at the mouth of the Amur river. They had established a record, which was recognised by the FAI, of 9,347km/5,825 miles. Udd Island was renamed Chkalov Island by Stalin in commemoration of the event.
With confidence in the ANT-25 re-established, Stalin gave approval to proceed with the transpolar flight to the United States. At first, the plan was for both aircraft to fly with a separation of thirty minutes. The Soviet government set about preparing for the flight by establishing ‘Severny Polus 1’ (North Pole 1), a meteorological centre floating on the polar ice which would broadcast weather reports for the flight from the top of the world.
In the winter months while preparing for the attempt, Baidukov flew the ANT-25 via Cologne to Le Bourget, from where the aircraft was brought by road to the XVth Paris Air Salon at Glahd Palace (November 1936). It returned to Moscow in December, routing through Berlin.
The plan to fly both aircraft to America on the same day did not work out, because Chkalov’s engine needed some maintenance. So the engine was removed from both aircraft, and that of the second was fitted on Chkalov’s ANT-25. On 18 June 1937, at 4.04 a.m. Moscow time, Chkalov, again with Baidukov and Belyakov, took off from Monino and headed due north along the 38°E line of longitude. Five hours into the flight, Chkalov noticed an oil spillage, just like Levanevski’s, but he decided to continue. After a while, the spillage reduced. At nine o’clock, Baidukov took over for a four-hour duty, and was soon flying in icy conditions in cloud at 2,600m/ 8,530 feet. When Chkalov resumed control, he climbed first to 3,000m (9,843ft) then eventually to 4,250m (13,944ft) to avoid ice. At this level, oxygen was needed, and there was only enough for nine hours on board. By 11 p.m., Chkalov calculated that fuel burn was higher than planned by about 300 litres/66 Imperial gallons - two flight hours. At 4.15 a.m. on 19 June, the aircraft was heard passing the North Pole by the crew of Severny Polus 1; Chkalov then flew south along the 133°W meridian. By late morning they were into cloud and icy conditions again. Chkalov climbed to 4,850m (15,913ft), then 5,500m (18,046ft). Oxygen was now running short. They had to descend to 3,000m (9,843ft).
They crossed the Canadian coast at 4.15 p.m. and flew on towards Bear Lake. Four hours later, as they crossed the Mackenzie River, they saw the Rocky Mountains and had to climb again. As they flew by Portland, Chkalov discovered that, of the 500 litres/110 gallons of fuel remaining; only about 120/26 could be fed to the engine and this would not be enough to reach San Francisco, their target. So they landed at Vancouver, Washington. There they were met by General Marshall, and, a few hours later, by Soviet Ambassador Troianovski. They had covered a straight line distance of 8,504km (5,284 miles) and a track distance of 9,130km (5,673 miles) in sixty-three hours and twenty-five minutes. It was the first nonstop flight from Moscow to the United States.
They were hailed as heroes both in the United States, where President Roosevelt spent one hour and forty minutes with them instead of the planned fifteen minutes, and where they received a New York tickertape parade, and in Russia, where Chkalov’s home town of Vasilevo was renamed after him. The ANT-25 was disassembled in the United States and shipped back to Russia, and is preserved in Chkalovsk. Chkalov died in an air accident in 1938 in circumstances still regarded as controversial.
Three weeks later it was Gromov’s turn. He added an extra 500kg fuel by leaving off survival gear, including an inflatable boat, a rifle, food supplies, and oil and grease, saving some 250kg/5511b weight. His crew were Andrei Yumashev and Sergei Danilin. After a normal take-off from Monino, things went well for them, although they also had some icing problems. They dropped several markers en route to confirm their track. They passed the Pole some fourteen minutes early and calculated that they had used less fuel than expected. They overflew Prince Patrick Island exactly on their plotted course but ran into bad weather shortly after reaching Canada. In icy conditions, many of their instruments ceased to work, but luck was on their side and they passed through the ice layer. They passed Chkalov’s landing point and flew on by San Francisco, right down to the Mexican border. As they had no permission to overfly Mexico, even though they had enough fuel to reach Panama, they turned back and landed in a meadow near San Jacinto, but only after several low passes were made at about 10m/33 feet to persuade two calves to move, which they did. They had covered 10,148 kilometres/ 6,306 miles in sixty-two hours and seventeen minutes, a record which would last only one year. In November 1938, two modified Vickers Wellesley bombers of the Royal Air Force’s long-range development flight, led by Squadron Leader Kellett, increased the record distance to 11,526km/7,162 miles by flying from Ismailia in Egypt to Port Darwin, Australia.
After their landing, crowds quickly arrived, many looking for autographs. The landowner, obviously a resourceful businessman, was soon charging admission fees; when Gromov allowed him to take the remaining fuel; he poured it into small glass phials and quickly sold it all. They visited Hollywood, where their guide was six-year-old Shirley Temple; then San Francisco, then Washington where they met President Roosevelt. Then back to Le Havre on the Normandie liner, then to Paris where the FAI awarded them the Henri de Lavo medal. And from there back to a heroes’ welcome in Moscow.
Tupolev, the designers, built two ANT-25s. In 1934, the Voronezh production factory received orders from the government to build fifty for the Soviet Air Force. These were improved versions and were redesignated ANT-36. In 1989, staff of the Tupolev Design Bureau built another ANT-25, this time a replica for preservation at the State Aviation Museum, fittingly located at Monino where it holds pride of place.
Some US sources doubt that these flights took place, pointing out that Gromov’s aircraft was unpainted when it arrived in California, and that photos published in Soviet newspapers of the time show it with titles on the side. It must be remembered that Soviet photographs were frequently ‘improved’ by artists before release.