Shear force and bending moment diagrams due to loads along chordwise direction : Aerodynamic center :- This is a point the chord of the airofoil section where the bending moment due to the components of resultant aerodynamic force (lift and Dr ag) is constant irrespective of the angle of attack. Hence the forces are transferred to this point fot obtaining constant Mac.
Shear center :- This is a point on the airfoil section where if a force acts,itproduces only bending and no twisting. Hence the force is transferred t ransferred to this point and the torque is found. Angle of Attack (max.) = 15.0*, Angle of Attack (Zerolift) = -1.0
SHEAR FORCE BENDING MOMENT : Co-efficient of force at normal direction
Co-efficient of force at chordwise direction:
Therefore, Force per per unit length =
For Linear, Y= 23.05x + 145.39 x
Shear Force: Integrate Eqn.
TORQUE DUE TO NORMAL FORCES AND CONSTANT PITCHING MOMENT AT CRUISE CONDITION: Aerodynamic center :- This is a point on the chord of an airfoil section where the bending moment due to the components of resultant aerodynamic force(Lift and Dr ag) is constant irrespective of the angle of attack.Hence the forces are transferred to this point for obtaining constant Mac.
Shear center :- This is a point on the airfoil section where if a force acts,it produces only bending and no twisting,Hence the force is transferredto this point and the torque is found.
Th lift and drag forces produces a moment on the surface of cross-section of t he wing, otherwise called a torque,about the shea center. Moment about the aerodynamic center gets transferred to the shear center.The shear center on the chord under which it is locates.
NET TORQUE : Then the different torque components are brought together in a same graph to make a comparison. The net torque will be sum of all the above torque (i.e) torque due to normal,force,chordwise force,powerplant and aerodynamic moment.
LOAD ESTIMATION OF WING WING STRUCTURAL LAYOUT
Specfic Roles of wing (mainwing) Structure: The specific structural roles of he wing (or main palne) are :
To transmit : wing lift to the r ootvia the main span wise beam
Inertia loadsfrom the power plants, undercarriage,etc. to the main beam.
Aerodynamic loadsgenerted on the aerofoil, control surface & flaps to the main wing beam.
To react against:
Landing loads at attachment points
Loads from pylons stores
Wing drag and thrust loads
To provide :
Fuel tanks age space
Torsional rigidity to satisfy stiffness and aero-elastic requirements.
To fulfill these specific rules,a wing layout will conventionally componies:
Span wise members (known as spars or beams )
Chord wise members(ribs)
A covering skin
Stringers WING SPAR ARRANGMENT
Basic Function of Wing structural Members The functions of each of these types o f members may be considered independtly as: SPARS
Form the main span wise beam
Transmit bending and torsional loads
Produce a closed- cell structure to provide resistance to torsion,shear and tension loads .
In particular :
Webs – resist shear and torsional loads and help to stabilize the skin.
Flanges- resist the compressive loads caused by wing bendin
SKIN:
To formimpemeable aerodynamic surface
Transmit aerodynamic forces to ribs & stringers
Resist shear torsion loads (with spar webs)
React axial bending loads (with stringers)
STRINGERS:
INCREASE SKIN PANEL BUCKLING STRENGTH BY DIVIDING INTO SMALLER LENGTH SECTION.
React axial bending loads
RIBS:
Maintain the aerodynamic shape.
Act along with the skin to resist the distributed aerodynamic pressure loads.
Distribute concentrated loads into the structure & redistributed stress around any discontinuities
Increase the column buckling strength of the stringer though and restrain
Increase the skin panel buckling strength.
SPAR DEFINITION: The maximum bending moment from precious section was found to be as 897784.51Nm. therefore we define 3 spars with front spar 15% of chord, middle spar 45% of chord and rear spar at 70% of chord. The position of the those spars from the leading edge of the root chord is given below as follows:
STRUCTURAL ANALYSIS AND DESIGN OF FUSELAGE FUSE LAGE STRUTURAL LAYOUT: The fuse lage is the main structure, or body of the aircraft. It prov ides space for personnel, cargo ,controls and most of the accessories. The powerplant ,wings,stablisers and landing gear are attached to it. There are two general types of fuselage construction welded steel truses and monocoque designs. the welded steel truss was used in smaller navy aircraft, and it is still bering used in some helicopter. The monocoque relies largely on the strength of the skin or covering to carry various loads, the monocoque design may be divided into three classes- monocoque semimonocoqu and reinforced shell.
The true monocoque construction uses formers,frmae assembles, and bulkheadsto give shape to the fuselage. However, the skin carries the primary stresse. Since no bracing members are present, the skin must be strong enough so keep the fuselage rigid. The biggest problem in monocoque construction is maintaining enouh strength while keeping the weight within limits.
Semimonocoquedesign oversome the strength-to weight problem of monocoque construction is maintaining enough strength ehile keeping the weight within limits.
The reinforced shell has the skin reinforced by c omplete framework of structural members. Different portions of the same fuselage may belong to any one of the three classes. Most are considered to be f semimonocoque- type construction. The semimonocoque fuselage is constructed primarily of aluminum alloy, although steel and titanium are found in high temp areas. Primary bendings loads are taken by the longirons are supplemented by other longitudinal members known sringers,stringers are more numerous and lightweight than longerons. The vertical structural members are reffersd to as bulkheads, frames,and formers. The heavier vertical members are located at intervals to allow for concentrated loads. These mebers are also found at points where fitings are used to attach units, such as the wings and stablizers. The stringers are smaller and lighter than longerons and serve as fill-ins. They have some rigidity but are chiefly used for giving shape and for attachment of skin. The strong heavy longerons hold the bulkheads and formers. The bulkheads and formers hold the stringers.All of these join together to form a rigid fuselage framework.Stringers and longerons prevent tension and compression stress from bending the fuselage.
The skin is attached to the longerons,bulkheads,and other structural members and carrier part of the load.The fuselage skin thickness varies with the load carr ied and the stresses sustained at particular location. There are a number of advantages in using the semimonocoque fuselage.
The bulkhead, frames,stringers.and longerons aid in the design and construction of a str eamlined fuselage,they add to the strength and rigidity of the structure.
The main advantage of the semimonocoque construction is that is depends on many st ructural members for strength and rigidity. Because of its stressed skin construction,a semimonocoque fuselage can withstand damage and still be strong to hold together. Loads and its distribution:
To find out the loads and their distribution,consider the different,The main component of the fuselage loading diagram are:
Weight of the fuselage
Engine weight
Weight of the horizontal and vertical stabilizer
Tail lift
Weight of crew,payload and landing gear
System,equipment,accessories Symmetric fight condition,steady and level fight(Downward forces negative) valuesfor the different component weights are obtained from aerodynamic design calculation S.No.
1 2 3. 4. 5. 6. 7. 8. 9.
10. 11. 12
Equipment and Component Nose Pilot (2) cockpit Wing Passenger(3) Passenger(3) Passenger(2) Crew(2) Weight of fuselage sheet Power plant Horizontal Tail Vertical tail
Length from ref. point 0.58 2.02
Weight( N)
Moment
Shear Force
Bending Moment
3933.81 1962.00
2281.609 3963.24
3933.81 5895.81
2281.809 6244.84
To determine the shear force and bending moment diagram for the wing we assume that the wing is a cantilever beam with the root end fixed while the tail end is free. For a cantilever beam the shear force is given by,
Structural analysis of fuselage like thatof wing is of prime impotance while designing an aircraft.as the fuselage is the one which houses the pilot, the power plant and also part of the payload is structural integrity is a matter of concern.while analyzing the fuselage structure the section must be idealized.idealization innolves the conversion of a stringer and its accompanying skin thickness into a concentrated mass known as a born.The shear flow analysis of the fuselage simulating flight condition is shown below..
To above stringer section is uniformly used throughout the fuselage as shown above in order to provide the fuselage the required load c arriying capcity.the diagram showed adjacent is of the idealize fuselage structre.the idealization process is carried out in the following way. STRESS ANALYSIS: IDEALIZATION:
The boom 1 is given by:
Design of miscellaneous Member
Wing fuselage interaction: The 8 seater business jet aircraft has lowing configuration,thus the entire wing structure continues in the way of airplane body. Four pin design concept : This concept is adopted as it the most simple and straight forward method used in horixon 4000 transport,during 1950s.The lift and moment load can be carried between the wing and fuselage by simple shear on the four pins.the drag and t hrust is taken by breather web,this design allws the wing spar and fuselage bulkheads to deflect independently of each other such that no spar moment is directly transferred to the bulkheads.
The wing body juncture produces aerodynamic interference which in turn promotes,flow separation with its attendant higher drag and unstedy buffering.This adverse pressur gr adient and consequent flow separation can be minimized using contoured surface called fillet.
ENGINE MOUNT : A engine mount is frame that supports the engine and holds it to the fuselage or necclle, usually it is made of built up sheet metal, we lded steel tubing. The turbofan engine, “HONEY WELL TFE731 -20”.A typical turbofan engine installation for a low wing aircraft configuration similar to that of t his aircraft is shown below.
The pylon has three spars (longerons) – Upper,middle and lower andthree major bulkheads and is attached to the wingat four primary points. These are two mid spar fittings, an upper link and a diagonal brace. Theattachment pins are secured with “fuse” bolts which are hollow carbon steel devices that
have been heat treated to shear fail at a define load/ in t he landing break way condition (wheels uo landing); the sequence is designed to fail the upper and lower links so that pylon rotates around the mid-spar and upward.The wing pylon design provides considerable lead path redundancy such that an upper link can fail partially or completely, and there is an alternate path lower diagonal brace. The below figure shows the engine mounts.
Empenage design Horizontal stabilizer: The horizontal tail of the aircraft is convetional and consist of a fixed tail box. The horizontal stabilizer is usually a two sapr structure consistingof a centre structural box section and two outer section. The stabilizer assembly is interchangeable (symmetrical airfoil section) as a unit at t he fuselage attach points and the outer sections are interchangeable at the attachment to the center box.
The two basic horizontal stabilizer box construction for modern t ransport are 1. Box construction with spars, closer light rib spacing ( usually lessthan 10 inches) and surface ( may be tapered skins) without stringer reinforcement. Thefeature of design is the low manufacturing cost an high thorsional stiffness require by the flutter analysis, 2. Box construction with spar stronger ribs and surfaces skins with stringer reinforcement skinstringer or integrally stiffned panels is a lighter weight st ructure..
VERTICAL STABLIZER : The structural design of the vertical stabilizer is essentially the same as for the horizontal stabilizer is essentially the same as for horizontal stablizers. Thevertical stabilizer box is a two or multi spar structure (general aviation airplanes usually use single spar design) with cover panels (with or withoutribs). The root of the box is terminated at the aft fuselage conjucure with fitting or splices.
