Yakovlev Yak-25

The Yakovlev Yak-25 was a Soviet military aircraft, an early turbojet-powered interceptor aircraft designed by the Yakovlev OKB. The designation was later reused for a different interceptor design.^[1]

Tasked by the Council of Ministers in a directive issued on 11 March 1947, with producing a straight winged fighter similar to the earlier Yak-19, but powered by a Rolls-Royce Derwent V, OKB-115 swiftly produced the Yak-25, which blazed several trails as the first Soviet fighter with a fully pressurised cockpit, air conditioning, jettisonable canopy, and hydraulic airbrakes on the fuselage amongst other innovations.^[1]

Development

The Yak-25 closely followed the Yak-19 in layout if not in detail. The straight wings, though similar in planform, were fractionally larger and much thinner (9% t/c throughout), using laminar flow sections. To provide enough cord for the retracted landing gear the root cord was sharply increasted at the root edge. Dihedral was 0, but incidence was the usual 1 degree in early Yak jets. The ailerons were for the first time hydraulically boosted, though they lacked the tabs showen in most drawings. The CAHI flaps were also hydraulically powered. The vertical tail unit differed from the Yak-19 in being swept back at 40° on the leading edge, while the horizontal tail was swept back at 35 degrees. The lower rudder had a separate electro-hydraulic power unit which could split it open into left/right halves serving as an airbrake. This would be triggered automatically by a dangerous rise in dynamic pressure sensed by the pitot/static systems.^[1]

The Derwent V engine was attached to the rear of the centre fuselage in a manner similar to the Yak-19. Though the fuselage had a different non-circular cross-section from the Yak-19, a similar double bulkhead directly behind the wing allowed the rear fuselage to be completely removed, giving access to the engine for removal or maintenance. Internal fuel capacity was 875 liters (192.5 gallons), supplemented by Yak's standard 200 liter detachable tip tanks which first appeared on the Yak-17. The undercarriage was very similar to the Yak-19.^[1]

The cockpit was very similar to the earlier Yak jets, though the Yak-25 was pressurized using an air-cycle system based on engine bleed. The single aft sliding canopy was powered. The bullet-proof front windscreen was 57mm thick, while 8mm of armor protected the pilot from behind. The ejection seat was an improvement over the Yak-19, with a longer stroke gun, and leg restraints. Armament was also improved, with three NR-13 cannon, each with 75 rounds.^[1]

Testing

The Yak-25-I was given callsign "yellow 15", and had a number "2" painted on the airbrake rudder. It was flown in factory testing by Anokhin between 31 October 1947 and 3 July 1948. The second prototype, Yak-25-II, with callsign "55" and the number "2" on the rudder, differed only in minor respects, such as an increase in cord on the split-rudder airbrake.^[1]

Flight tests followed quickly, and showed that the Yak-25 was easy to fly, and had exceptional performance and maneuverability for a straight-wing aircraft. Unfortunately it soon became clear that the laminar flow section used for the tail unit was totally unsuitable, with extremely severe buffeting setting in at 500 km/h (310 mph). Test pilot L.L. Selyakov reporting that the buffeting was so bad that he was thrown about the cockpit, banging his head on the canopy, and the needles fell off all the flight instruments. To cure the buffeting the tail unit was replaced with one using a NACA 004 aerofoil section^[2]. Worse yet, the rival swept-wing MiG-15 had superior performance. Yakovlev was never again to build a single-engine fighter superior to the rival aircraft coming from Mikoyan, though neither was Lavochkin. Development was halted, but two of the prototypes were used for test and development purposes.^[1]

Surprisingly, the Yak-25 never received a ASCC reporting name or USAF type number despite being known to the west at the time.^[1]

Experimental work

According to Ing V Kondratyev, in 1948 the third prototype Yak-25 was used to test a "fixed zero-track undercarriage", which was being designed for the Yak-50, and for the big twin-engined Yak-120 interceptor (which would later receive the reissued designation Yak-25, though it was unrelated to the original aircraft).^[1]

Further development, replacing the straight wing with one of 35° sweepback, was undertaken as the Yak-30.^[1]

Yak-25E

The Yak-25E (Eksperimentalnyi) was the Yak-25-I specially modified to be towed by a Tupolev Tu-4 strategic bomber. This came in response to a proposal by the headquarters of Long Range Aviation, calling for a method of towing short-range jet fighters, code-named Burlaki (barge hauler). The Tu-4 was to be fitted with a towing winch from which a cable deployed equipped with a special connector on the end. A long tube projected from the nose of the fighter with a harpoon-like connector on the end. After take-off the pilot steered this harpoon into the coupling on the end of the tow cable, and shut down his engine, allowing the bomber to tow him as a glider. If enemy fighters attacked the bomber, the Yak-25E pilot would simply restart his engine, disconnect from the bomber and engage them in combat.^[1]

The system was tested, but not adopted. A major reason for the rejection was that it required the fighter pilot to remain seated in his cockpit without heating for endless hours while traveling with the bomber. Worse, after combat the fighter would have little hope of returning to friendly territory, let alone its base, unless it could find a Tu-4 to hook up to. Production aircraft would have used Klimov RD-500 engines.^[1]

At the same time the Soviets were developing the Yak-25E, the U.S. Air Force was experimeting with a similar system known as Project Tom-Tom. The U.S. system would have employed either a specially modified F-84 or a XF-85 Goblin parasit aircraft. Early attempts differed by attaching two fighters to the bomber's wingtips. Later plans called for a parasite aircraft to be stowed internally within the belly of a B-36.^{[citation needed]}

Specifications

General characteristics

• Crew: 1
• Length: 8.66 m (28 ft 5 in)
• Wingspan: 8.88 m (29 ft 1 in)
• Height: ()
• Wing area: 14.0 m² (151 ft²)
• Empty weight: 2,285 kg (5,027 lb)
• Max takeoff weight: 3,535 kg (7,777 lb)
• Powerplant: 1× Rolls-Royce Derwent V centrifugal compressor turbojet, 15.6 kN (3,500 lbf)

Performance

• Maximum speed: 982 km/h (530 kn, 610 mph)
• Range: 1,100 km (590 nmi, 690 mi)
• Service ceiling: 14,000 m (45,931 ft)
• Rate of climb: 37 m/s (7,260 ft/min)
• Wing loading: 163 kg/m² (34 lb/ft²)
• Thrust/weight: 0.45

Armament

• Guns: 3 × 23 mm (0.906 in) Nudelman-Rikhter NR-23 cannon, 75 rpg

See also

• Project Tom-Tom
  

Comparable aircraft

• Dassault Ouragan
• Lavochkin La-15
• F-84
• XF-85 Goblin
  

Related lists

• List of military aircraft of the Soviet Union and the CIS
  

References

• Gordon, Yefim (2005). OKB Yakovlev: A History of the Design Bureau and its Aircraft. Hinkley: Midland. 
• Gunston, Bill. Yakovlev Aircraft since 1924. London, UK: Putnam Aeronautical Books, 1997. ISBN 1-55750-978-6.