Soviet Heavy Fighters 1926–1949


On March 11, 1930 the machine was dispatched to perform state trials. Their results, to say the least, were not satisfactory. The official post-test report noted that the aircraft failed to meet the technical requirements in several areas: all-up weight was exceeded by 335 kg, while airspeed at sea level was 14 km/h less than required and 42km/h below expectations at 3,000 m. Time to climb to 5,000 m was 30 minutes instead of 15.3 minutes as per technical requirements. Additionally, demonstrated range of the machine (designed to be a long-range reconnaissance platform) was merely 268 km, while a much lighter and cheaper Polikarpov R-5 could reach 398 km! To add insult to injury, the report noted excessive vibrations of tail surfaces, fuselage and engines, leaking fuel tanks and poor damping characteristics of the landing gear. The navigator’s station allowed decent visibility only when the navigator stuck his head outside the dorsal gun turret. The part of the report summarizing the findings read: “Advantage over the TB-1 – marginal”. That must have hurt, when the hopes were that by scaling down the size of the aircraft and by reducing weight associated with standard bomb load, a design with superior flight characteristics could be achieved. To be fair, the report’s conclusions did mention some of the machine’s advantages: “The aircraft is simple and easy to fly” has “good stability and controllability”, in addition to a short take-off roll (100 – 120 m) and heavy armament.
State trials ended on March 30, and the aircraft returned to TsAGI where all the bugs revealed during tests were to be ironed out. The work took about four months and included raising the wing’s trailing edge by 175 mm, while leaving the wingtips in their original position. This was done to eliminate the vibrations of the fuselage and tailplane, which, as it turned out, were caused by turbulent airflow behind the wing. Engine coolant radiators, originally placed under the wings between the fuselage and engine nacelles (fully retractable in flight), where installed under the engines and fitted at an angle, in hopes of reducing drag. The engines received new cowlings and exhaust manifolds facing upwards. The pilot’s seat was raised 100 mm to improve visibility from the cockpit, while the navigator’s station was fitted with a celluloid porthole in the nose. The forward gun turret was replaced to match the rear one (both were now the TUR-5 models), with the latter receiving a celluloid fairing in front of it. A redesigned ventral turret was fitted to a larger cutout in the fuselage and the main landing gear received 1000x225 wheels and tires. Interestingly, all the changes introduced to the prototype not only didn’t increase its overall weight, but resulted in net savings of some 80 kg.
On 24 July, 1930 the R-6 prototype was once again delivered for further trials to NII VVS (Nauchno- Ispytatielnyj Institut VVS – Air Force Scientific Test Institute). The tests lasted until September 31 and, this time around, the results were much better. The aircraft’s speed at altitudes above 2,000 m increased, as did its service ceiling. However, there was also an increase in landing speed and the time to complete a turn and “figure eight” (by about 5 – 6 s). Test pilots reported better handling characteristics and improved visibility from the cockpit. In general, the aircraft’s performance was thought to “fulfill technical requirements”. This is not to say that the R-6 received a clean bill of. The report mentioned a host of issues: the aircraft was still overweight, engine mounts were not rigid enough causing excessive engine vibrations, upward-pointing exhaust stacks blasted exhaust gases straight into the cockpit, engines splashed oil all over radiators and main landing gear, the windshield was too flimsy and struggled under pressure of high-velocity airflow, the cockpit was lashed by howling wind caused by uninsulated fuselage design. In addition, the aircraft didn’t carry the required WOZ IV radio and had no provision for intra-crew communications.

CiezkieSowieckie zd6

 Most of the issues were resolved fairly quickly, except the engine mounts whose design wouldn’t change until full-scale production began. As an added bonus, the designers decided to increase the forward-looking porthole in the navigator’s station and replaced celluloid with Triplex glazing. After the work had been completed, the machine was once again handed over to the NII VVS for follow-up testing. The trials lasted until October 17 and focused mainly on the tactical use of the R-6. Based on the test results, the Air Force commanders were keen to establish the machine’s role in a future war. The results must have been satisfactory, since several documents drawn in their wake offer statements like “dives well at 60 degree angle”, “heavy armament”, “easy to control in Immelman turn, stable, normal loads on flight controls”. The Air Force concluded that the R-6 could be employed as a long-range reconnaissance platform, bomber escort and a multi-seat fighter (the latter, unfortunately, only in a very limited scope). It is worth mentioning, however, that the question of what role exactly the R-6 was assigned by the Air Force, is not immediately clear from the available NII documents, which quite often contain contradictory statements. One of the documents clearly states that the machine was not suitable as a multi-seat fighter due to its “limited maneuverability and heavy weight”, but then goes on to say that the R-6 “…can be used as a multi-seat fighter to conduct long-range air-to-air engagements against heavy bombers”. The reason for those inconsistencies might have been the fact, that the R-6 would not stand a chance in a dog fight not only against single-engine fighters, but also typical light or medium bombers. It was only lumbering heavy bombers that could be potentially engaged by the “air cruisers”. Nonetheless, the overall conclusion of the report following state trials was summarized in one sentence: “The aircraft is cleared for full-scale production”.

 

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