The Mil Mi-24 is a large helicopter gunship and low-capacity troop transport produced by Mil Moscow Helicopter Plant and operated from 1972 by the Soviet Air Force, its successors, and over thirty other nations. In October 2007, the Russian Air Force announced it would replace its 250 Mi-24 helicopter gunships with 300 more modern Mi-28s and possibly Ka-50s by 2015.
During the early 1960s, it became apparent to Soviet designer Mikhail Leont'yevich Mil that the trend towards ever-increasing battlefield mobility would result in the creation of flying infantry fighting vehicles, which could be used to perform both fire support and infantry transport missions. The first expression of this concept was a mock-up unveiled in 1966 in the experimental shop of the Ministry of Aircraft's factory number 329 where Mil was head designer. The mock-up designated V-24 was based on another project, the V-22 utility helicopter, which itself never flew. The V-24 was similar in layout and configuration to the UH-1A Huey, with a central infantry compartment that could hold eight troops sitting back to back, and a set of small wings positioned to the top rear of the passenger cabin, capable of holding up to six missiles or rockets, with a twin-barreled GSh-23L cannon fixed to the landing skid.
Mil proposed the design to the heads of the Soviet armed forces, and while he had the support of a number of strategists in the armed forces, he was opposed by several more senior members of the armed forces who believed that conventional weapons were a better use of resources. Despite the opposition, Mil managed to persuade the defence minister's first deputy, Marshal Andrey A. Grechko, to convene an expert panel to look into the matter. While the panel's opinions were mixed, supporters of the project eventually held sway, and a request for design proposals for a battlefield support helicopter was issued. The development of gunships and attack helicopters by the US Army during the Vietnam War convinced the Soviets of the advantages of armed helicopter ground support doctrine. This had a positive influence on moving forward with the development of the Mi-24. Mil engineers prepared two basic designs: a 7-ton single-engine design and a 10.5-ton twin-engine design, both based on the 1,700 hp Izotov TV3-177A turboshaft. Later, three complete mock-ups were produced, along with five cockpit mock-ups to allow the pilot and weapon station operator positions to be fine-tuned. The Kamov bureau suggested an army version of their Ka-25 Hormone ASW helicopter as a low-cost option. This was considered but later dropped in favor of the new Mil twin-engine design. A number of changes were made at the insistence of the military, including the replacement of the 23 mm cannon with a rapid-fire heavy machine gun mounted in a chin turret, and the use of the then-under development 9K114 Shturm (AT-6 Spiral) anti-tank missile.
The core of the aircraft was derived from the Mil Mi-8 (NATO reporting name "Hip"): two top-mounted turboshaft engines driving a mid-mounted 17.3 m five-blade main rotor and a three-blade tail rotor. The engine configuration gave the aircraft its distinctive double air intake. Original versions have an angular greenhouse-style cockpit; Model D and later have a characteristic tandem cockpit with a "double bubble" canopy. Other airframe components came from the Mi-14 "Haze". Two mid-mounted stub wings provide weapon hardpoints, each offering three stations, in addition to providing lift. The load-out mix is mission dependent; Mi-24s can be tasked with close air support, anti-tank operations, or aerial combat.
The body is heavily armored and can resist impacts from .50 caliber (12.7 mm) rounds from all angles, including the titanium rotor blades. The cockpit is an even more heavily armored titanium tub and can resist impact from 37mm cannon rounds. The cockpit and crew compartment are overpressurized to protect the crew in NBC conditions.
Mi-24D cockpit Considerable attention was given to making the Mi-24 fast. The airframe was streamlined, and fitted with retractable tricycle undercarriage landing gear to reduce drag. The wings provide considerable lift at high speed, up to a quarter of total lift. The main rotor was tilted 2.5° to the right from the fuselage to counteract dissymmetry of lift at high speed and provide a more stable firing platform. The landing gear was also tilted to the left so the rotor would still be level when the aircraft was on the ground, making the rest of the airframe tilt to the left. The tail was also asymmetrical to give a side force at speed, thus unloading the tail rotor.
A modified Mi-24B, named A-10, was used in several speed and time to climb world record attempts. The helicopter had been modified to reduce weight as much as possible, and among the measures used was to remove the stub wings. The speed record over a closed 1000 km course set on August 13, 1975 of 332.65 km/h still stands, as does many of the female specific records set by the all female crew of Galina Rastorgoueva and Ludmila Polyanskaia. On 21 September 1978 the A-10 set the absolute speed record for helicopters with 368.4 km/h over a 15/25 km course. The record stood until 1986 when it was broken by the current record holder, a modified Westland Lynx.