Design of IL-76 aircraft, Kiev

1. technical description of the aircraft

The designed aircraft is a cargo aircraft made according to the type of classical aerodynamic arrangement, a high-plane scheme, and has an all-metal structure of the form of a half-monocoque. This aircraft is intended for operation on routes of short and medium length. On-board systems and units, as well as loading equipment, allow autonomous operation at unequipped airfields for 30 days. The aircraft is equipped with built-in transport equipment that provides autonomous loading and unloading of any cargo, including in containers accepted in the ISO. Ground conveyor systems are used for loading and unloading of cargo on aircraft pallets and in standard containers. A temperature-controlled sealed cargo cabin provides transportation of animals and perishable products. In the nose compartment of the fuselage there is a place for cargo escorts.

The on-board complex, which includes more than 50 processes, automatically collects data on the functioning of on-board systems and equipment, analyzes them and displays the processed information on displays. In case of "abnormal" situations, the necessary recommendations to the crew will be displayed on the screens. Additional data can be retrieved upon request to the computer.

The system optimizes flight modes, provides automated aircraft navigation at all flight stages under any conditions. The electrohydro-remote steering system has three digital and six analog channels that provide reliable piloting, even when exposed to an electromagnetic pulse of a nuclear explosion. The system implements integral control laws that meet the most modern requirements in terms of stability, controllability and comfort, which helps reduce crew fatigue in difficult flight conditions.

Structurally, the aircraft is divided into the following elements:

- caisson-type wing;

- fuselage including sealed cabin for crew and passengers;

- horizontal and vertical plumage;

- power plant with engines of TRDD type;

- LG.

2. purpose and scope

The aircraft was created as an analogue of the Il76 tactical military transport aircraft.

The design is designed for an average annual flight time of more than 3,000 hours, the unit maintenance cost is 810 man-hours per flight hour.

It is possible to transport oversized and long cargoes, self-propelled and non-self-propelled wheeled and tracked vehicles, perishable cargoes and food products.

Almost all types of army equipment and weapons can be transported in the fuselage. The aircraft is able to lift about 20% of the large cargo transported by the strategic transport aircraft An124.

The high technical and operational potential of the aircraft allows creating a number of targeted modifications on its basis with low costs and in a relatively short time, in particular:

- long-range radar detection and guidance aircraft;

- air command post;

- maritime patrol aircraft;

- refuelling aircraft;

- search and rescue aircraft for the naval forces.

3. selection and justification of design parameters

Generation of technical assignment for the project

Technical assignment for the aircraft design is made on the basis of statistical data and contains the following groups of parameters and characteristics: type of air lines, minimum airfield class, weather minimum of landing, geographical and climatic features of flight areas, crew composition and number of flight attendants, equipment composition, comfort requirements, flight-technical characteristics (passenger capacity, mass of commercial load, design flight range, cruising speed and flight altitude, take-off speed, approach speed, landing speed).

Selection and justification of aircraft diagram

Aircraft diagram is determined by mutual arrangement of units, their number and shape. The aerodynamic and technical-operational properties of the aircraft depend on the scheme and aerodynamic layout. A well-chosen scheme allows you to increase the safety and regularity of flights, and the economic efficiency of the aircraft. Selection of the designed aircraft diagram is preceded by study and analysis of the aircraft diagrams adopted as prototypes. The following shall be justified:

position of wing and tail relative to fuselage, as well as selection of their shape;

the location of the engines, their number and type, unless specified in the design assignment;

LG type and location;

Substantiation of aircraft diagram should be performed based on the information given in the literature.

Designed aircraft is made according to normal aerodynamic scheme of high-wing with swept wing and T-shaped swept plumage. Wing mechanization is performed in the form of flaps and TE flaps, interceptors, this will make it possible to improve AC ATL during take-off and landing, during mileage.

The aircraft is made according to the scheme with a high swept wing. Such a scheme has the following advantages:

- reduction of aerodynamic drag from interference, especially for round fuselage (aerodynamic quality of high-plane is higher than that of low-plane);

- reducing the distance from the fuselage to the ground, which creates a number of operational amenities;

- a good view of the land from the passenger cabin;

- reduction of probability of failure of engines located on the wing due to ingress of solid particles from the runway during take-off and landing.

Engines are arranged on pylons under wing. This engine installation scheme has the following advantages:

- engines unload the wing structure in flight, reducing bending and torque moments from external loads, which leads to a decrease in wing weight by 1015%;

- engines dampen wing oscillations during flight in turbulent atmosphere;

- engines are anti-flutter balancers;

- convenience of replacement of one type of engine with another;

- easy access to the engine during maintenance.

At the same time, this arrangement of engines has its own drawbacks:

- in case of engine failure, a large turning moment is created in the horizontal plane;

- pylon suspension of engines makes it difficult to use TE flaps throughout the wing span.

Caisson tripod wing is spar-shaped, has five sectional flaps and two sectional tripod slotted flap to improve LTX during take-off and landing.

Half-monocoque fuselage made of aluminium alloys. It has 2 doors, on each side, and a rear deflectable wall.

The aircraft has a T-tail unit to take it out of the zone of influence of the jet (compared to the classical unit).

Booster type control system. Six sectional interceptors and single-section ailerons are used for lateral control together or independently. For longitudinal control, a height steering wheel is used, and for balancing - a controlled stabilizer. Track control is provided by rudders.

Five-support diagram of landing gear with nose support is used on the aircraft. Which provides high stability on run and run, good controllability when driving on the ground and effective braking of the wheels due to the lack of hood. The main supports are attached to the fuselage.

The power plant consists of two TRDDs.

Fuel is located in centerplane tank and in root, pre-consumption, service compartments of wing tank of each cantilever. Aircraft fuelling is performed centrally from below under pressure through one aircraft fuelling connector.

Refueling order - wing tanks, center-wing tank.

The air conditioning system is fed by the air taken from the TRDD.

The anti-icing system of the front edges of the wing and the edges of the air intake operates in hot air taken from the engine compressor. The sock of the keel and horizontal plumage are heated by electricity.

Emergency rescue equipment. Cockpit tightness allows emergency landing on the water surface.

Radioelectronic equipment. The aircraft is equipped with a complex of electronic equipment, which allows operation under weather conditions.

Selection of main wing parameters

The main parameters of the wing include the profile and relative thickness C, sweep x 0.25 chord, elongation?, constriction?, the angle of the transverse V wing and the specific load on the wing P, the shape of the wing in the plan Aerodynamic characteristics of the wing and are largely determined by the shape of the wing in plan. Profile parameters (XC, f) and relative wing thickness (C), as shown by aircraft construction practice, depend on the number M of cruising flight - MK

If the designed aircraft has MK < 0.6, then for its wing it is most advisable to use asymmetric ("bearing") profiles with a rounded front edge and with a relatively front (on 20... 30% chord) position of maximum thickness C, which in the root part of the wing can be 15... 18%, and at the end of the wing - 10... 12% chord. For the wings of modern near-sound aircraft, close to symmetrical and asymmetric profiles with a sharper leading edge and with a relatively rear position of maximum thickness Xs = 35... 45% are used. They are characterized by a smoother distribution of pressures along the wing chords, which reduces the local air speed above the upper surface of the wing and contributes to an increase in the critical number of ICRIT flights. For the same reasons, the relative wing thickness of near-sound aircraft with MKRIT = 0.8... 0.9 usually decreases (12... 14% in the root and 8... 9% at the end of the wing). In recent years, the so-called supercritical profiles (double curvature profiles), which, compared to conventional profiles of the same relative thickness, have higher (by 0.08... 0.1) Mkrit values, have also begun to be used for the wings of near-sound passenger aircraft.

It should be borne in mind that all the above measures aimed at increasing the MKrit of flight adversely affect the stiffness and weight characteristics of the wing, as well as lead to a noticeable decrease in the maximum values ​ ​ of the lift coefficient CYmax. Wing sweep is a means of increasing the critical Mach number of flight, increasing wing sweep not only shifts the beginning of the wave crisis at high flight speeds, but also mitigates its flow, reduces the increase in resistance, improves the stability and controllability of the aircraft at near-wave speeds. In addition, wing sweep increases the critical speed of flutter and divergence. However, with an increase in the sweep angle, the Cymax and Kmax wings decrease, and the effectiveness of take-off and landing mechanization decreases. Due to lateral overflows of the boundary layer to the ends of the swept wing, it tends to end disruption of flow at large angles of attack, the result of which may be a loss of transverse controllability and longitudinal instability of the aircraft during landing. Sweep complicates production and increases wing weight.

These circumstances cause the "economical" use of sweep, that is, the angle of sweep of the wing of the near-sound aircraft is usually selected according to the minimum determined by the value of the assigned speed (MK number) of cruise flight.

Wing elongation is a parameter that significantly affects the value of inductive resistance and maximum quality of wing and aircraft. In addition, γ affects the weight and stiffness characteristics of the wing structure.

Subsonic transport aircraft have wings with zero and low sweep. The elongation of such wings lies in a fairly wide range, γ = 8... 12, with large elongation values ​ ​ usually referring to large-sized aircraft with a large design flight range. Increased wing elongation values ​ ​ are sometimes chosen for aircraft with a short flight range due to the desire to improve their take-off and landing characteristics.

For approximate assessment of lengthening of a wing of the designed plane the formula can be used: λ = 10.5 • cos2 χ. Obtained value of extension is corrected on the basis of data on wing parameters of aircraft-analogues.

Wing constriction has a contradictory effect on the aerodynamic, weight and stiffness characteristics of the wing.

The increase in the constriction eq has a beneficial effect on the distribution of external loads, stiffness and weight characteristics of the wing. It also leads to an increase in the construction height and volumes of the central part of the wing, which facilitates the placement of fuel and various units, and an increase in the area of ​ ​ the wing served by mechanization significantly increases its efficiency.

However, the increase in constriction has negative sides. The main of them is the tendency of the wing with a large constriction to the end breakdown of the Stream while reducing the efficiency of the ailerons. Due to the above circumstances, the narrowing of the straight wings of subsonic aircraft is usually filled with a small one and is set to a value of? = 2... 2.5, which provides close to minimum inductive resistance of the wing and high values ​ ​ of CYmax pos.

The angle of the transverse wing V is known to provide a degree of lateral stability to the aircraft. Its value and sign depend optically on the scheme of the aircraft, and for aircraft with swept wings - also on the angle of sweep. For straight wings of subsonic aircraft, the values ​ ​ of the transverse V angle range from + 5 °... 7 ° for the low-wing circuit, to 1 °... 2 ° - for the high-wing. Sweep increases the transverse stability of the wing and therefore sweep wings should be given a negative transverse V. However, layout and other requirements (for example, landing with a roll) can cause a positive V sweep wing. This will entail the installation of automatic yaw dampers in the control system and will require some increase in the vertical plumage area.

Selection of fuselage main parameters

The aerodynamic and weight characteristics of the fuselage significantly depend on its shape and size, which are determined by geometric parameters such as cross-sectional shape extension = 7.82 and fuselage diameter Df = 3.35 m. The extension and length of the fuselage are specified in the subsequent layout of the aircraft based on the conditions for providing the necessary volumes for the crew, passengers and cargo, as well as acceptable arms Lvo Lgo horizontal and vertical plumage aircraft. The extension of the fuselage and its parts (nose and tail) are chosen for reasons of aerodynamics and fuselage weight. When choosing a designed aircraft, we focus on such statistics of modern aircraft.

The extension of the fuselage nose and tail is within the following limits:

; =1,7…2,0; =3,0…3,2.