Development of the project product “240” (В-24) began after the release of the Resolution of the Council of Ministers of the USSR and the Central Committee of the CPSU on May 6, 1968, in the Experimental Design Bureau of Mikhail Mil. Test aircrafts (OP-1 and OP-2) were ready in a year. A significant part of the units and assemblies was unified with the Mi-8 and Mi-14.
Test helicopter had a common front two-seat cockpit (so-called greenhouse) with dual controls. The crew consisted of a pilot and an operator, with side-by-side seating. Further the crew was additionally manned with a flight engineer. In the middle part of the helicopter, there was a cargo cabin, accommodating up to 8 people of the landing force. The right and left sides of the cargo cabin were equipped with double doors with top and bottom flaps. The opening windows were equipped with pintle mounts for firing during the flight from individual weapons. Both cabins are sealed, boosted by engines.
From the very beginning, the equipment of the crew included specialized flight armor helmets and bullet-proof vests. Armour-plating of the cabin represented by the frontal armored glass, armored crew seats, local armored plates on the sides of the cabin, and the hood of engines.
Due to the unreadiness of the weapon complex “Shturm” it was decided on the first aircraft to install the complex K4B of the helicopter Mi-4 – “Falanga-M” missile with a manual guidance system and the machine gun mounting NUV-1 with the machine gun A-12,7, four beam holders for NUR or unguided bombs.
Factory tests began on September 15, 1969 (test pilot G. V. Alferov). The construction of a prototype series of ten helicopters began Immediately. At the end of 1970, two aircraft were upgraded – to improve stability at speeds of more than 200 km/h the helicopter was equipped with a wing with negative V-12 degrees and an extended cockpit already with longitudinal seating of pilots. Thus, by 1971, the appearance of the helicopter, widely known throughout the world, shaped. The first serial helicopters Mi-24A (make “245”), made in this shape, with manual guidance of missiles “Falanga-M”, became operational for experimental service.
Mi-24A were built in a plant in the city of Arsenyev. Almost 250 aircraft were manufactured, which entered service for army aviation structures, in separate helicopter regiments of the Soviet Army combined arms armies and landing and assault brigades. Based on the Mi-24A, the training modification of the Mi-24U (ed. “244”) with full-fledged dual control was developed.
Mi-24B (make “241″) received a new machine gun mounting USPU-24 with machine gun YakB-12,7 (4500 rds/min), missile complex “Falanga-P”. But finishing the helicopter was suspended and made fundamental changes – the cabin was redone in tandem, with the tail rotor with the transmission was installed from the Mi-14 – the pusher screw became the puller screw, which dramatically increased the efficiency of directional control. The helicopter was named “Mi-24V”, or the make “242”. But due to unfinished complex “Shturm” helicopters with a new cockpit had to be equipped following the Mi-24B type, and this “intermediate version” entered series production. It took 8 years to finalize the Mi-24V. In 1976, the helicopter was officially taken into service and was the most mass-produced helicopter. The letter “G” in the designation was skipped. It was named Mi-24D (make “246”).
The Mi-24 is built according to the classic single-rotor scheme with a five-blade fully articulated rotor main rotor and a three-blade tail rotor.
Non-retractable three-leg landing gear with steerable nose leg.
The fuselage nose contains two-seat cockpit following the tandem scheme: The operator pilot is located in a separate front cockpit, the aircrew commander (pilot) is behind him, the commander’s cockpit is raised 0.3 m above the operator’s cockpit for the convenience of viewing, the flight engineer can be placed on a folding seat in the cargo cabin behind the cockpit. The crew is located in sealed cabins, equipped with air conditioning or life support system (for the Mi-24R helicopters), to prevent the ingress of contaminated air and radioactive dust a slight overpressure is maintained.
The cockpit, engine oil tanks, the main transmission, and the hydraulic tank are armored with steel plates. The pilot’s chair is armored, folding with armored headrest, the operator’s chair is not armored, windscreens are armored, flat and heated, equipped with wipers and spray system (alcohol), side convex glass is organic, not armored.
The central fuselage section consists of a cargo cabin, which can accommodate up to eight paratroopers, and a rear cone-shaped part for equipment and cleaning niches of the main landing gear.
The transmission and the dual control system are the same as in the Mi-8 helicopter.
The shaft of the main rotor is inclined to the right by 2,5 °, which helped to significantly reduce the angles of rolling and sliding the helicopter in flight, unavoidable for all rotary-wing aircraft with single-rotor design, thereby improving the accuracy of shooting from fixed weapons. One of the main features of the helicopter is a 6.75 m² wing with negative lateral dihedral -12°, which provides up to 30 percent of lifting force, depending on speed and other factors. The first prototypes had side wings located at right angles. To improve lateral stability at high speeds, it was decided to install wings with negative lateral dihedral. Later, vertical pylons with guides for anti-tank guided missiles were installed at the ends of the wings. Hence the helicopter got its distinctive silhouette.