Mirage IV - Design
Developed in the wake of the Suez crisis (1956), the Mirage IV was a two-seater, twin-engine supersonic bomber having an effective range of up to 4,500 km with in-flight refueling. The Suez crisis in October 1956 prompted France to look into setting up a "strategic intervention force", equipped with nuclear weapons. Soon after General Charles de Gaulle came into office, in June 1958, he said France was to single-handedly develop what he called its "dissuasion of aggression" weapon. The scheme involved an aircraft first, and a ballistic missile later. The Mirage IV was chosen.
The length of the aircraft was 20.42 m, the wing span was 11.28 m. The exterior similarity between this strategic bomber and the Mirage III was noteworthy, in particular the wing design, which was of the delta-type in the Mirage tradition. In fact, besides the scale effect, the air-friction heating was very different. Although its aerodynamic specifications were very similar to those of the Mirage III, its structure, layout and equipments demanded specific developments. Temperature differences during rapid acceleration or deceleration imposed constraints which had to be taken into account when determining the dimensions.
Whereas the Mirage III could only withstand Mach 2 for a few minutes, the Mirage IV needed to hold that speed for much longer than the 20 or so minutes required for the temperature to stabilize throughout the outer structure and inner casings housing the equipment, petrol and hydraulic liquid. Every component, therefore, needed to undergo a full thermal assessment. French equipment manufacturers fulfilled virtually all the requirements.
The wing of the aircraft, based on the wing of the Mirage II, was triangular in shape with a sweep angle of 60 ° along the leading edge. The relative thickness of the profile varies in scope from 3.8 to 3.2%. This was the thinnest wing that was ever produced in France for a military aircraft. The wing had no curvature on the toe and twist. On the toe of the wing there was a saw to improve stability at large angles of attack. There was no anti-icing system on the wing. The heating system was provided only for engines and windshields of the cabin. In the design of the wing there were three main side members.
The volume limited by spars formed a trapezoidal tank-compartment. The wing sock near the root part was also used as a tank. In the triangle between the front and central spars, from the front, there are: a tank, compartment of the air brakes and the rack compartment with a strut of the main chassis. Mechanically machined parts were used for spars, and mechanically milled panels for cladding. Auxiliary elements underwent chemical etching to minimize weight loss.
All along the tail part of the wing were elevons - two on each wing, which were used for longitudinal and lateral control. Elevons and rudder were driven by electrohydraulic servo drives. From the cockpit, the mechanical wiring went to servo control surfaces, deflecting the surface to the desired angle.
The fuselage contours were broken only by two lateral air intakes. A feature of the fuselage was the lack of an armament compartment. The bomb was half-buried in the lower surface of the fuselage, and after its dropping, there was a depression. The space occupied by the bomb was covered with a concave skin. After the bomb has been dropped, a minor balancing violation occurs, which was compensated by the transfer of fuel to the corresponding tanks. To isolate the design of the tail section of the fuselage from the afterburner chambers, there was a tube of titanium separating the chambers from the fuselage, then there was a casing made of heat-resistant fiberglass and, finally, a special rubber coating. Flight tests showed that the temperature of the tail section rarely exceeded 60°C.
The keel installed in the tail of the fuselage has a structure consisting of anterior spar, ribs and a rear spar closing the caisson. The keel was joined by seven lining with seven corresponding fuselage frames. A plate closing the flange, together with two milled paneling panels, forms a 500-liter storage compartment. For the keel, the same sealing system was used as for the wing. A sock and a rudder were attached to the keel design. The rudder was equipped with a yaw dampener.
The fuel system consists of the right and left parts feeding the respective engines. There was a connection between the tanks of the left and right parts, and possibly the power crossover of the engines. Feed pumps were duplicated, and one pump could provide aircraft flight on a subsonic or supersonic cruising mode. Expendable tanks were the left and right front tanks of the fuselage, in these tanks the fuel from the other tanks arrives in the given order. The airplane could be refueled in flight.
The chassis consists of two main racks with trolleys and a bow rack with twin wheels. The pressure in the pneumatics of the main pillars was approximately 12 kg / cm2, so that it could use the existing NATO take-offs. The pressure in the tires of the front landing gear of the chassis was 8 kg / cm2. The cylinder of turn of a rack carries out a role of a damper shimmy and simultaneously provides centering. The nose post was retracted.
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