The plane from a legend

The "Modelist-designer"magazine, august 1977.

From these words begin articles and memoirs on plane ANT-25, or as it was quite often named, RD (a record of range) . Among many Soviet planes ANT-25 is one of the most well-known. Its history began December, 7, 1931 when under K.E.Voroshilov's offer the decision on construction of the special winged machine for record flights on range was accepted. Its creation was assigned to a department of test aircraft construction of the Central Institute of Aero-Hudrodynamics (CAHI). The unique machine was projected by a team of P.O. Sukhoi. Andrey Nikolaevich Tupolev supervised over all works. RD was conceived and constructed  as all-metal  one-engined monoplane with low mounted wing of very big length. The relation of its wing span to a chord exceeded 13!
It was necessary to gain the maximal aerodynamic quality, which is the relation of lifting force to the drag. We shall notice, that the wing of planes of that time incured frequently half of resistance of all aircraft. Before RD there was no aircraft with narrow and long consoles. Naturally, a wing of such unusual form was uneasy for design . Researches in this area have made the whole chapter in a history of Soviet aerodynamics. Constructed as a result of theoretical calculations and numerous tests, the wing appeared easy and strong enough to place in it fuel which weight, by the way, made impressive size of 32 % of the take-off weight. It not only has released a fuselage from tanks, but also has facilitated a design as weight of fuel created unloading a wing: the pressure from the aerodynamic forces directed from below upwards, decreased a cargo working from the top downward.
Among the theoretical works concerning RD construction, especially interesting and significant there were researches on vibration of a design. In the literature on aircraft construction of that time there were instructions that at the big length a wing there are special vibrations or flatter. This phenomenon arose, as was found out, at the speed of the flight exceeding some critical speed strictly determined for the given design. Builders of RD plane were afraid, that because of the big lengthening this size covered appears very small. Carefully it was necessary to study the phenomenon. In the CAHI experimental - aerodynamic department was created special "flatter group". A method of its calculation did not exist yet. However it was clear, that there were two ways to the solution of this problem : the first, testing, at which the special case, RD wing, would be investigated only and measures of flatter prevention  were specified; or the second - development of the general theory of the phenomenon and on the basis of its results, suitable for any special case. In the beginning of 30th years  M.V.Keldysh and to his colleagues made possible to solve a problem of flatter in a general view.
In the completed design the wing of the record plane looked so: Basic elements - three   longerons and stringers. The cross section of every half-wing consisted from 18 tubular ribs. First two longerons are connected by six tanks located between them (the pilot could switch a feed to any tank) and form a powerful caisson. To the third auxiliary longeron aileron was suspended  with axial and flettner indemnification. Its each half consist of four sections, fitted by a cloth. Fuel tanks have equipped with drain mouths under a wing. Their valves opened special explosive devices.  Covering of a wing (except for a zone of a caisson) for rigidity have executed firstly from goffered aluminium, and after tests have covered it by lacquered cloth as speed and range of flight appeared below requested because of the increased drag of a wing. Inside have placed packages with emergency products, sleeping bags, tent, backpacks, a ski and other equipment which could be necessary at an emergency landing. With retracted landing gear the plane had an opportunity to land safely  on water and to keep swimming for some time . For this purpose inflatable cylinders from the rubberized fabric were stipulated. Junction of wing  with a fuselage have closed by streamline. In area of joints of consoles with centrplane to the first longeron the main landing gear with oil-pneumatic amortization fastened. Everyone was supplied with two coupled wheels in the size of 900*200 mm. They for the first time in practice of Soviet aircraft construction retracted and extended with the help of electrical mechanism. Gear was powered by a cable attached to the cylinder.  In the extended position gear fixed with the spring lock. In a flight  wheels were half-deep in a wing, and the external part for reduction of frontal drag and  unguided tail wheel, were closed by cowls.

The fuselage consist of two parts: a lobby executed at the same time with centroplane, and a tail of the monocook type. A covering of a fuselage was smooth, duralumin, with semicircular headed rivets. A cross set - from  repoussed frames. Through all tail part passed four longerons located atop of a covering. In a forward compartment was placed the V-shaped engine of A.A. Mikulin design AM-34,  750 hp, forced later up to 874 hp. There were no such a motors abroad yet.
About reliability of engine AM Valery Pavlovich Chkalov after flight on island Udd wrote: the most captious person could not find in it any lack. The crew was convinced, capacity of the motor appears sufficient for take-off from the ground  this 11-tonns giant. There was no any slightest doubt in reliability of work of the motor. Anybody from us was not occurred with an idea, that the motor can hand over and the plane will go on an emergency landing. And you know, we flied above such places where the emergency landing was impossible.
Behind the engine - the cabin with the folding canopy, equipped with all necessary instruments for flights in complex meteorological conditions. Under legs of the pilot was small tank for the control for fuel consumption. Right behind a pilot seat passed a centroplane caisson  in which was located reserve oil tank from which it was possible to fill up with the manual pump a main tank. Behind a joint of forward and tail parts of a fuselage was equipped places for navigator and the second pilot, and because of narrowness the second should be arranged on reserve tank with water.
Fin was carried out at the same time with a tail part of a fuselage. On it have established units of fastening of a rudder  and  the stabilizer with a changeable angle of attack which covering was goffered. Consoles and fin incorporated on onboard ribs and were stretched by tapes of the streamline form. To the stabilizer the elevator with flettner was suspended, consisting of the two halfs connected by an axis.

Designing of the plane was completed in the beginning of 1932, and in June its construction began. Two samples, test and the doubler, subsequently converted in ANT-25-1 and ANT-25 were created almost simultaneously. Exactly in one year the first has risen in air. After it the doubler began flights with the engine of M - 34R (that is with a reducer) . In comparison with test plane the doubler had some constructive differences. Use of the engine with a reducer has caused change of the form of a cowl. In a cabin of the pilot for the best view have increased canopy glass area. Have increased the area of fin, established different by the form rudders supplied with servo-compensators.

The aircraft was still not finished, but it was already possible to speak about it as about one of especially oustanding achievements of  Soviet aviation science and engineering. In 1934 ANT-25 has established some records of the USSR and a world record of range of flight on the closed route.
Long-distance flights have begun June, 30, 1934. This day the crew  of pilots M.M.Gromov, A.M.Filin and navigator I.T.Spirin established USSR record for the range of flight. ANT-25 has flown 4465 kms for 27 ? 21 minutes. In one month the same pilots have improved a record; for 39 ? 1 minutes  6559 km  were covered, but this result also existed not for long. In September, flying on a triangle Moscow - Ryazan - Kharkov, a crew of Gromov for 75 ? has covered a distance of 12 411 kms, considerably  exceeded a world record of French pilots Bossutro and Rossi. For this oustanding achievement to the commander of the plane to pilot Gromov, the rank of the Hero of Soviet Union was given. The new record route Moscow - Franz Josef land - Petropavlovsk - on - Kamchatka was soon determined. For this flight the plane - doubler was converted with the improved M - 34R engine  with a tunnel water radiator. Two-bladed the wooden propeller was replaced after a series of researches by 3-bladed metal with the pitch angle adjustable on the ground. For cabin adjustable heating an  exhaust pipes have connected to the pipeline laid inside a fuselage.
There were mounted double controls of plane intended for the control of aircraft during change of pilots. A forward part of a cabin of the navigator was closed by transparent canopy with the solar cource gauge. A radio-compass ring eventually was mounted after all  on the bottom of the fuselage and  made rotary.
To find a position of the plane now it was possible by transmittions of any two radio stations.

July, 20, 1936 modernized RD has made test flight up to Petropavlovsk - on - Kamchatka with crew of  V.P. Chkalov, G.F.Bajdukov and A.V.Beljakov. At the organization of so distant flight it was necessary to undertake special safety measures. In particular, Northern and Pacific fleet have received the order to allocate the on duty ships, Glavsevmorput' has prepared land resque teams. Flight has passed successfully. Having dropped a pendant above Petropavlovsk - on - Kamchatka, the crew has decided to turn on a route to Nikolaevsk-on-Amur. However it was not possible to reach it . Handicap became a strong rain and a fog. Crew flew just in several meters abowe water. The emergency radiogramm was sent with the order  to land as soon as possible. But where?.. At last have seen a strip of the ground - the island Udd. Here, on a sandy shallow, Valery Chkalov, showed the greatest skill and landed red-winged aircraft. ANT-25 stayed in air 56 ? 20 mines and has covered 9374 km. All world admired with this heroic flight. Our government highly estimated courage and skill of the Soviet pilots, to all members of crew the rank of the Hero of Soviet Union was given.
After flight on island Udd Valery Pavlovich wrote: the aircraft sucsessfully passed all tests... The plane easily climbed and obeyed the pilot. The machine perfectly behaved both in a fog, and in clouds, and in conditions of various air streams, and in mountain district of Yakutia, and at various temperatures. In general flight opportunities of the plane appeared fine.
Nevertheless, this flight allowed to estimate some dangers which trapped aircraft of similar type. In particular, serious difficulties were caused with an icing of a fuselage, wings and especially the prop. That is why by designers was in an extra hurry developed in CAHI  the first Soviet de-ice system on the prop.
On natural logic of events the winged champion was included in number of the Soviet exhibits of the World aviation exhibition in Paris in November, 1936 and made there exclusive success.
And in the meantime, aspiring to the decision new, even more complicated problems, the crew has addressed to the government with the request to permit a flight by the route Moscow - North Pole - Northern America. A report of Chkalov, Belyakov and Baydukov was heard at special session of the government and has received kindness.

... In the early morning June, 18, 1937 in 4 h. 5 min. in the Shchelkovo air station was taken start of this unprecedented flight. The way laid to the north. Somewhere below under wings for the first time in the world four Soviet researchers drifted in polar ices: I.D.Papanin, E.T.Krenkel', P.P.Shirshov and E.K.Feodorov. Further - a novel route, ice and ice... Above Canada the plane has got in a cyclone. It was necessary  to bypass it. Flied at height of 4000-4500 m. Pilots lost forces. It was necessary to be replaced  each hour. Oxygen remained a little. Above Pacific ocean stocks of it have run low. It was necessary to fall to the ground. At last, after 62 hours of flight has pilots so Portland. June, 20 in 19 ? 30 mines Moscow time ANT-25  landed at the airfield Baraks near citiy of Vancouver. Unprecedented in a history of aviation non-stop flight, that tooked 63 hours and 25 minutes  was finished here. Above ocean and ice there were covered 9500 km, some thousand from them - in blind flight.
Names of heroes appeared on the pages of newspapers and magazines of all the world. And after only three weeks the crew of the Hero of Soviet Union of M.M.Gromov has made one more flight to America through North Pole. The Soviet pilots have established thus a new world record of range. The plane was in air 62 ? 17 mines, having overcome distance of 11 500 km.
These historical flights have shown to all world not only courage, boldness and skill of our pilots, but also a high level of Soviet aircraft designers.

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