Ilyushin Il-40
| Company type | Military aircraft |
|---|---|
| Industry | Aerospace |
| Founded | 1953 |
| Headquarters | Rostov-on-Don , Soviet Union |
| Products | Armored ground-attack aircraft |
Template:Good article Template:Infobox aircraft The Ilyushin Il-40 (NATO reporting name: Brawny) was a Soviet-designed, twinjet, two-seat armored ground-attack aircraft. Its maiden flight took place in 1953, and the prototype demonstrated excellent performance except when firing its guns; the combustion gases disrupted airflow into the engines, causing flameouts or engine surges. Addressing this issue required over a year and led to a significant redesign: relocating the engine air intakes to the aircraft's very front and shifting the guns from the nose tip to beneath the fuselage just behind the nose landing gear. This modification gave the plane a distinctive "double-barreled shotgun" appearance from the front. Production was authorized in 1955; however, only five units were completed before the project was terminated in early 1956 when the Soviet Air Forces abandoned their close air support doctrine in favor of tactical nuclear weapons.
Development
During 1950–51, Sergey Ilyushin initiated design work on a jet-powered ground-attack aircraft intended to surpass the performance limits of piston-engine predecessors. By late 1951, his design bureau had submitted a technical proposal for an armored two-seat aircraft powered by two Mikulin AM-5 axial-flow turbojets, each delivering 2,150 kgf (4,740 lbf) thrust at maximum dry power and 2,700 kgf (5,952 lbf) with afterburner engaged. The government approved this plan promptly in January 1952, commissioning a prototype build.
The Il-40 featured low-mounted wings swept back at an angle of 35°, complemented by a tricycle landing gear configuration. Its twin AM-5 engines were housed in pods adjacent to the fuselage. Consistent with Ilyushin's ground-attack design philosophy, the aircraft's core structure comprised a load-bearing armored shell safeguarding both crew stations, six fuel tanks, and parts of the radio and electrical systems. Armor thickness varied between 3 to 8 mm (0.12 to 0.31 in), with a reinforced 10 mm (0.39 in) bulkhead shielding the pilot from frontal threats. The cockpit glazing was bullet-resistant, and an 8 mm (0.31 in) armored headrest protected the pilot against projectiles from above and rearward angles. The gunner's position was armored with plates ranging from 4–10 mm (0.16–0.39 in) thick. Altogether, the armored shell and bulletproof glass added up to 1,918 kg (4,228 lb) in weight. Both crew members had ejection seats installed for emergency escape. To improve dive maneuverability, three perforated airbrakes were positioned on the rear fuselage—one on each side and one underneath.
Initial armament consisted of six 23 mm (0.91 in) Nudelman-Rikhter NR-23 autocannons mounted in the nose—three per side—each supplied with 150 rounds and protruding into the slipstream. Additionally, one NR-23 was installed in a remotely operated Il-K10 tail barbette carrying 200 rounds; this turret could elevate up to 55°, depress to -40°, and traverse ±60°. The turret’s traverse speed reached 42° per second with an elevation rate of 38° per second. Four small bomb bays integrated into the wings could each hold up to 100 kg (220 lb), while alternatively four underwing racks accommodated bombs up to 500 kg (1,100 lb), 82 mm (3.2 in) TRS-82 or 132 mm (5.2 in) TRS-132 rockets, or drop tanks totaling 1,100 litres (290 US gal) capacity. Standard bomb load was 400 kg (880 lb), extendable to 1,000 kg (2,200 lb) under overload conditions. In such cases, up to twelve TRS-82 or eight TRS-132 rockets could be carried. Two cameras installed in the rear fuselage enabled day and night damage assessment photography.
The Il-40’s first flight occurred on 7 March 1953, revealing no major aerodynamic issues during testing. The center of gravity was somewhat too far aft but caused only minor difficulties during takeoff, landing, and taxiing due to a relatively short wheelbase. The most significant challenge emerged when firing its guns: during initial aerial cannon tests late March 1953, muzzle flashes temporarily blinded the pilot and caused both engines to flame out simultaneously. Although he managed to restart them and land safely, Sergey Ilyushin launched an immediate investigation into these engine malfunctions. Ground trials using high-speed cameras demonstrated that neither muzzle brakes nor flash suppressors mitigated the problem; even firing as few as five to ten rounds from a single gun induced engine hiccups.
To overcome this issue, it was decided to replace the six NR-23 cannons with four AM-23 guns featuring a higher rate of fire—50% greater—and equipped with 225 rounds each. The gun installation was completely redesigned: guns were consolidated at the nose tip within a dedicated heat-resistant steel compartment featuring a blast deflector chamber directing combustion gases away from engine intakes. Ventilation doors at the chamber’s bottom opened during firing to dissipate gases. However, testing revealed that blast gases accumulated near spent cartridge and link storage areas sometimes ignited spontaneously, occasionally deforming the chamber structure itself. This led to enhanced ventilation for spent casings and introduction of muzzle brakes that effectively resolved these issues.
Due to these armament challenges, State acceptance trials scheduled for July 1953 were postponed. A special commission eventually conducted trials starting on 31 December that year. Following successful manufacturer tests completed in January 1954, State acceptance evaluations took place from 21 January through 15 March. Results were favorable: pilots found the Il-40 easy to fly and sufficiently agile to challenge contemporary fighters such as the Mikoyan-Gurevich MiG-15bis and Mikoyan-Gurevich MiG-17. It also demonstrated clear superiority over existing piston-engine ground attack aircraft like the Ilyushin Il-10M. Nevertheless, flight tests uncovered issues with blast gas ingestion during sideslip firing maneuvers affecting the engine opposite the sideslip direction.
Various solutions were considered for this problem; ultimately Ilyushin advocated for a more radical redesign involving extending engine air intakes all the way forward to the aircraft’s nose while relocating guns beneath the nose behind these intakes.
This configuration change—giving rise to a front profile resembling a "double-barreled shotgun"—also allowed forward repositioning of the nosewheel, lengthening the wheelbase for improved ground handling. Guns were mounted just aft of the nosewheel bay behind a protective shield mechanically linked to steer with the nosewheel; this shield extended during steering movements to guard gun barrels from debris kicked up by landing gear operation. Other modifications included replacing original AM-5F engines with improved Tumansky RD-9V variants, increasing normal bombload capacity to 1,000 kg (and up to 1,400 kilograms (3,100 lb) overloaded), plus adding a rearview mirror for enhanced pilot visibility of rear upper hemisphere surroundings.
Production
Ilyushin initiated the assembly of an additional prototype to test this approach, which received official approval on 16 October 1954 when the Council of Ministers mandated production to commence at Factory (Zavod) No. 168 located in Rostov-on-Don. This improved model was designated as the Il-40P. The Il-40P prototype took to the skies for the first time on 14 February 1955 and entered State acceptance testing on 12 October 1955. These modifications effectively addressed all issues encountered with the previous design, leading to an order for an initial batch of forty units.[1]
By spring 1956, five units had been completed and were undergoing preflight evaluations when the entire project was abruptly terminated on 13 April 1956, with all parts prepared for production being discarded. Shortly thereafter, the Attack Aviation division of the VVS was replaced by the Fighter-Bomber division, accompanied by a significant shift in VVS doctrine. The new strategy abandoned close air support for ground forces in favor of employing tactical nuclear weapons within a nuclear battlefield context.[1]
Prior to cancellation, Ilyushin explored two variants. The first, known as the Il-40K, was designed for artillery observation. This variant incorporated a third crew member positioned in a redesigned forward fuselage. The air intakes were restored to their original location since the guns had been relocated to small wing bomb bays, eliminating the risk of engine ingestion of gun blast gases. The spotter-navigator occupied a heavily glazed compartment at the nose tip, protected by armor and bulletproof glass. Completion of this fuselage was nearly achieved when the program was halted. The second variant, termed Il-40T, was intended as a torpedo bomber based on the Il-40K’s fuselage but featured optically flat glass panels in the navigator-bombardier’s station to aid targeting. This version received minimal development and was discontinued early in its design phase.[1]
Variants
- Il-40 – Initial prototype
- Il-40P – Second prototype plus five production aircraft
- Il-40K – (korrektirovshchik – corrector) – Artillery observation model with three crew members, including a spotter-navigator in a glazed nose cockpit
- Il-40T – (torpedonosets) – Torpedo bomber variant featuring three crew members; navigator located in a glazed nose section with optically flat panels for precise weapon aiming
- Il-42 – A late 1960s attempt to revive the Il-40 concept, ultimately surpassed by the Sukhoi T-8 (prototype Su-25)
- Il-102 – Final evolution of the Il-40/Il-42 series incorporating advanced avionics and engines; also outperformed by the Sukhoi T-8