Chyetverikov MDR-6

1937-43: 44 built.

The Chyetverikov MDR-6 was a 1930s Soviet Union reconnaissance flying-boat aircraft, and the only successful aircraft designed by the design bureau led by Igor Chyetverikov. It first flew in July 1937, as a two-engined high-wing monoplane, built in all-metal stressed skin construction. The prototype had two M-25 radial engines replaced in production (20 ordered) by M-63 engines from 1940 to 1941. They were withdrawn from service in 1942, plagued by structural problems. Despirte of this Chyetverikov tried to correct these issues and made several advanced prototypes until 1945, but none were greenlighted for production.

This seaplane was developed as a long-range naval reconnaissance aircraft by OKB-45 under Chief designer I. V. Chetverikov and manufactured 1940—1942 at the Plant No. 31 (Taganrog). Her first flight happened in the summer 1937 and it started operation from the end of 1940 and stayed in service until 1946. Sources diverged, but Russian sources points out 44 grand total.

Development

About I.V. Chetverikov

Igor Vyacheslavovich Chetverikov (born January 25, 1904, Kuznetsk, Saratov, deceased 1987, Leningrad) was a Soviet aircraft designer, candidate of technical sciences (1951), and engineer-colonel. At 16 he worked as a stoker on steamships on the Volga. In 1926 he graduated from the workers' faculty of Saratov University and in 1928 from the faculty of water communications of the Leningrad Institute of Railway Engineers. With V. L. Korvin-Kerber he worked in Sevastopol on the MDR-6 (Che-2) naval reconnaissance aircraft. In 1938 he also worked in the design bureau of the Marine Experimental Aircraft Construction of D. P. Grigorovich, and after his arrest with French engineer P. Richard.

With the departure of P. Richard for France. The MOS Design Bureau became the Central Design Bureau of TsAGI, headed by Chetverikov. In 1933, G. M. Beriev was appointed chief designer of the Design Bureau, and Chetverikov organized his own design bureau at the Department of Construction of Gliders and Aerosleds (OSGA) at the Naval Research Institute. In 1935, Chetverikov's bureau received a base in Sevastopol for tests and her was transferred to the State Aviation Administration of the Navy. Her developed the the MDR-3 naval long-range reconnaissance aircraft, submarine aircraft (SPL) and ARK-3 Arctic reconnaissance aircraft as well as the MDR-6 (Che-2), only of his models to be produced.

From May 1942 to 1946, he headed the experimental plant No. 458 and organized vankovo (now Dubna) workshop for the evacuated plant No. 30. In 1947, he developed the TA-1 transport amphibian and by late 1948, his design bureau was closed and he was transferred to teaching at the Leningrad Military Aviation Institute. On August 21, 1967 as an engineer-colonel he was discharged. He died in 1987.

Initial design

The Che-2, originally named MDR-6 was a marine long-range reconnaissance aircraft and Soviet flying boat, as well as a twin-engine monoplane with removable wheeled chassis, as a semi-amphibian, when based on shore. This was specified in 1938 and the winning design was Created in OKB-45 under the leadership of I. V. Chetverikov, making its first flight in the summer of 1937. Production started in 1940 at Plant No. 31 in Taganrog with the first delivered undergoing state tests with success by September 1940).

Production

With the transfer of the plant focusing on the LaGG-3 in the spring of 1941, production of the MDR-6 was transferred to Plant No. 30. However, in October it was in turn was forced to evacuate and all its assets were moved by rail and trucks to Chkalovsk, in the Gorky Oblast. There was however no free production space locally and it took time to reset producion. By May 1942, what was left of the Plant No. 30 was returned to its original location and became the "Experimental Naval Aircraft Plant No. 458". The last 5 were assembled there by the end of the year, from the existing parts. This hectic production explains widely different figures, some being as low as 27 or as high as 44, which seems the case of most Russian sources. They probably integrate very different prototypes as well (see variants).

Design specifics

MDR-6 production 1940

General conception

The center section was sharply curved from the fuselage and boat-like belly and connected by fairings. The two engines were installed at the wing bending points, at the ends of the center section, significantly raised above the wing chord to heave propellers clearance. The wing panels were trapezoidal with elliptical tips. Underwing floats were non-retractable, placed under racks with braces, and later struts. Further variants tested retractable floats to regain extra speed.

The fuselage had well-streamlined shapes with a front tier transverse, rear tier pointed and all cross-sections curved. There were no flat surfaces. The guiding idea of the designer was to reach maximum compression of the fuselage to achieve the smallest possible midsection and least weight. The bow was extremely short, which urged the fitting on splash guards. The whole fuselage was indeed lightweight, barely within minimum strength standards, even to the detriment of belly strength. This was the main issue for a flying boat and it showed in tests and operations.

The design was all-metal, albeit fabric covered the ailerons, rudders, and tail section of the wing consoles. The hull used stressed skinned aluminium just 0.8 mm with attachment stringers with a step 120 of 150 mm and a wing skin up to 2 mm. The riveting was completely flush or hidden for the best performances. The tail unit was single-fin with stabilizer attached to the air keel with V-shaped struts. There was a wheeled chassis used to move it on land or in winter but not fitted on the hull as a true amphibian.

Engine

The MDR-6 started with M-63 engines for serial production. There was a significant wing span in proportion. Other engines were tested for further models, ending with the VK-107A engines rated for 1650 hp on the 1945 MDR-6B5. Flight weight was 5,600 kg, up to 6,450 km gross for a top speed at sea level of 338 km/h and range of 2,650 km. Initially satisfactory in behaviour it soon became clear this needed to be improved tocompete with the float version of the DB-3 bomber. This led to modifications designated A, and later B 1 to 5 until 1946.

Armament

The crew was of just 3-4 dependng on the configuration, with three ShKAS machine guns in two firing mounts and up to 12 bombs not superior to 1,000 kg total weight on underings racks, each capable of supporting 400 kg. The defensive armament was revised in 1944 but never made it into production.

Specifications Che-2 1940
Crew:	3+3 passengers
Dimensions:	15.73 x 19.4 m (51 ft 7.25 in x 63 ft 7.75 in)
Wing area:	52.3 m2 (562.97 sq ft)
Weight: Light	4,100 kg (9,039 lb)
Weight: Gross	7,200 kg (15,873 lb)
Propulsion:	2× Shvetsov M-63 radial 821 kW (1,100 hp) each
Top speed:	360 km/h (224 mph, 195 kn)
Cruise speed:	220 km/h (137 mph, 119 kn)
Endurance:	2,650 km (1,647 mi, 1,431 nmi)
Ceiling	9,000 m (29,530 ft)
Armament	7.62-mm ShKAS machine bow, 12.7-mm UBT machine dorsal, 1t bomb load

Variants

At least nine modifications were united under the Che-2, in some cases differing greatly in size, shape, engines, and essentially representing new aircraft. The base design was roughly the same, a flying boat and high-wing monoplane with cantilever wing panels of the "seagull" type, first seagull cantilever wing in USSR, found ideal for seaplanes albeit already tested by the I-15 fighter to improve the pilot's view and a reverse seagull in the Stal-7 aircraft.

The development of the MDR-6 project started in 1936 withtwo M-25 engines, also tested on the ARK-3 and in the summer of 1937, a protortype was completed with M-25E and M-62 engines, going through all factory and state tests, being accepted for production with M-63 engines (1100 hp takeoff power). Howebver soon before production was stopped after facilities were transferred out of german control, the Che-2's showed serious weakness of its "boat design" on the main frame with severe noise and vibrations due to the close propeller blade tips to the hull. The fuel system was rushed and improperly mounted, leaking heavily and there were countless other issues.

MDR-6-A (1940), MDR-6 B (1941)

MDR-6A

Two prototypes, almost similar but different from the type N were presented respectively in late 1940 and mid-1941. They kept the M-105 engines but the wing consoles were significantly reduced to regain speed, and the floats on the MDR-6A were retracted flush into the wing, as on the MDR-6B (later B1) they protruded slightly. On both the tail unit was spaced apart and canopy and turret shapes were changed. The defensive turret was moved behind the rear step. The construciton remains of a semi-monocoque with a frame made of pressed and rolled sections. The MDR-6A floats were able to fit between the wing spars when retracted in box-shaped racks, electrically activated with a worm gear. On the B1 the floats were larger and thus protruded from the wing.

The M-105 engines were smaller than the M-63, with radiators still suspended under the center section and they were aesthetically more pleasing overall. They looked right, were faster at 454 km/h at 6000 m and still carried three ShKAS LMGs plus four 100-250 kg bombs. The MDR-6-A was designed by late 1939 and by 1940-1941 passed all factory tests and later state tests. But production never started.

The MDR-6B1 arrived in the spring of 1941, passed factory tests and by October 16, both made competitive state tests. If the A crashed near Uglich, the B1 failed all tests de to engine troubles and floats retractation, creating additional drag. The propellers were still too close to the water and the engines ingested way too much seawater spray. Fine-tuning continued and led to a new model.

MDR-6-B2/B3

Both had the same dimensions and wing design derived from the B1, as development. Both first flew in 1943, B2 with M-105 engines, B3 with M-105PF engines. Front radiators had reworked louvers and the floats were even wider and larger and so now did not retracted flush into the wing. The fuselage remained the same, as the position of engines, wings and general construction. Due to the increased weight, the fuselage sat deeper into the water and degraded seaworthiness.

The MDR-6 B3 modification had enhanced armament with blisters for UB machine guns in the tail, a crew of 5 people, 7,200 kg unladen and 8,200 kg gross, with the fuel counting for 1100 kg. Flight performances remainds close to the MDR-6A, but range remained low and did not reached the requested 3000 km.

MDR-6-B4 and B5

The MDR-6 B4 was designed in order to meet range expectation and improved seaworthiness, speed and altitude, in 1944. It ended significantly different from the B3. The fuselage was widened from 1.9 to 2.2 m, made higher of about 0.4 m, with a raised tail and empennage. The rear step was shifted back and the floats were made non-retractable using struts with braces. The larger hull authorized a greater fuel capacity by 2,150 kg. The engines were now VK-107 radials with reshaped frontal radiators similar to the B3, crew of 5, new redesigned MG tail Blisters with better arc, and outside the three UB LMGs, 1000 kg of bombs could be carried underwings. The vertical tail was increased and third keel added, for a final weight of 10 tons. It was tested but not greenlighted for productionl albeit vastly improved.

The next MDR-6B5 designed in 1945 was a development with improved VK-107A engines rated for 1650 hp. It was 0.5 m longer and the pilot's post was moved forward of the the propellers while the center section was increased, and the rest was the same. The engines however now drove four-bladed propellers and the MGs were replaced by three B-20 cannons, nose with 200 rounds and in the electric turret with 300 rounds. Still carrying underwings either four FAB 100-250 kg bombs or two FAB-500. The B5 now topped 5,610 tons empty, close to 11 tons in flight. Because it completed in the summer of 1945, and still passed factory tests it was too late into the war to have ot transferred to state tests and this productionnever took off. The war was over and there was no need for a competitor of Beriev's own projects.

Allthough the MDR-6 design was rational it suffered always from strength issues and engine wearing out by seawater ingestion, as well as being close to sluggish to commands in some situations. Post-war it was believed it had some limited tasks remaining and the Be-6 and M-12 remained viable propositions even with limited speed, and were preferred are more rugged and trusted. The MDR-6 simply did not brought any major advantage over models already in production.

Service

They were used in all 4 fleets from the end of 1940 to 1946. Doctor of Naval Sciences, twice Hero of the Soviet Union V. I. Rakov wrote about his pilot experience:

More unique was the domestic seaplane "CHE-2" designed by Chetverikov. Certainly good in its qualities, it was somewhat capricious when landing. It was impossible to land it at three points at once, as at a land airfield (at sea airfields three points were taken conditionally): touching the water with its tail, it then "plopped" hard with its step. The result was a "suspension" landing, although at a minimum landing speed. The plane had to be landed almost at speed, having climbed out of the corner and only slightly lowering the tail. When landing on a wave, and even worse - on a coast, the metal plane experienced such frequent and loud blows that it seemed as if you were rushing not on water, but on the crests of a bumpy road paved with huge cobblestones. These seemingly sliding, but in fact strong the blows had a very adverse effect on the bottom of the boat"

Until recently, it was believed that not a single Che-2 had survived. However, in 2022, a fairly well-preserved set of Che-2 aircraft wreckage, found by searchers, appeared in the Aviation exhibition of the UMMC Museum in Verkhnyaya Pyshma. It includes the nose and tail sections of the fuselage, engines and planes.

Resources

Books

Donald, David, ed. (1997). The Encyclopedia of World Aircraft. Prospero Books. p. 258.
Gunston, Bill (1995). The Osprey Encyclopedia of Russian Aircraft from 1875 – 1995. London: Osprey Aerospace.
Maslov, Mihail (September 2000). "Un grand hydravion de reconnaissance maritime: le Chetverikov Che-2 (MDR-6A)" Avions.