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AIRFRAME OF A SUBSONIC VEHICLE
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SUBSONIC AIRCRAFT
INTRODUCTION:
Subsonic aircraft is an aircraft with a maximumspeed less than the speed of sound (mach 1)
For Subsonic aircraft we can neglectcompressibility effects and the air densityremains nearly constant.
General aviation aircraft, helicopters , and allmodern airliners are subsonic aircrafts.
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PRELIMINARY DESIGN
In order to design all the phases of airframe excludingpropulsion system a knowledge of structural designand an understanding of the load paths is required
The type of analysis used in airframe work are verydifferent in many aspects.
In stress analysis the structural weight savings mustbe paramount for an efficient performance of aircrafti.e; a high percentage of payload is to be obtained
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PRELIMINARY DESIGN
Subsonic aircraft has a simple structure with
stringers of equal size and spacing is
considered.
If either the method or the structure
analyzed is simplified when doing
preliminary sizing cost effectiveness is
increased..this could be shown as:
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PRELIMINARY DESIGN
TYPE OF STRUCTURES: For example it may be possible toconvert the wing box into a rectangular section withparallel shear webs and be symmetrical about a verticalplane.
LUMPING STRINGERS: Reduce the complexity of largenumber of stringers by combining adjacent stringers intoso-called lumped stringers
TYPE OF LOADING: Choose one of the critical or primaryloads from the axial(from bending), shear flow (fromvertical shear load or torsion), or lateral to do the sizing.
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PRELIMINARY DESIGN:
Step 1: Recognize the structural function and configuration of thecomponent:
Wing box, tail box , fuselage barrel
Control surfaces
Joint, splice or fittings Panel with cutouts.
Step 2: Basic loads( static , fatigue , fail-safe , and crash condition loads):
Tension Shear
Compression
Normal surface pressure loading.
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PRELIMINARY DESIGN
Step3: Material selection:
Static
Fatigue
Fracture toughness
Step 4: Fastener and repairability
Fastener selection
Adequate edge margin
Joint or splice requirements
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PRELIMINARY DESIGNStep 5: Compromise efficient structure:
Configuration
Fabrication
Installation and assembly
Fabrication
Design for stiffness requirements (flutter)
Step6: To meet low cost:
Manufacturing and assembly
To meet market competition
Aircraft performance requirements
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DETAIL SIZING
Detail sizing is also called as
Stress analysis is done to support structural
design
Production stress analysis is the most
important factor in determining whether ornot the aircraft will meet the target weight.
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Optimize the design for improved performanceand reliability
Perform a Finite Element Analysis
Generate a Finite Element Model of the structure
Airframe Design
Create a Parametric definition,
Structural Model
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DESIGN PARAMETERS
An airframe designed for a subsonic aircraftcomprises of :
a fuselage structure
a wing structure (consists of a leading edge,trailing edge, an inboard end, an outboardend connected to the fuselage at the inboardend)
spars intervening between fuselage structureand inboard end of the wing ,each sparconsists of airfoil configuration
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DESIGN PARAMETERS
AIRFRAME MATERIAL PROPERTIES :
High strength to weight ratio Light weight
Corrosion resistance
Non flammable High quality
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FUSELAGE STRUCTURE
DIFFERENT TYPES OF STRUCTURES USED FORFUSELAGE AIRFRAME CONFIGURATION