7/31/2019 Aiframe of a Subsonic Vehicle1

1/13

AIRFRAME OF A SUBSONIC VEHICLE

7/31/2019 Aiframe of a Subsonic Vehicle1

2/13

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.

7/31/2019 Aiframe of a Subsonic Vehicle1

3/13

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

7/31/2019 Aiframe of a Subsonic Vehicle1

4/13

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:

7/31/2019 Aiframe of a Subsonic Vehicle1

5/13

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.

7/31/2019 Aiframe of a Subsonic Vehicle1

6/13

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.

7/31/2019 Aiframe of a Subsonic Vehicle1

7/13

PRELIMINARY DESIGN

Step3: Material selection:

Static

Fatigue

Fracture toughness

Step 4: Fastener and repairability

Fastener selection

Adequate edge margin

Joint or splice requirements

7/31/2019 Aiframe of a Subsonic Vehicle1

8/13

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

7/31/2019 Aiframe of a Subsonic Vehicle1

9/13

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.

7/31/2019 Aiframe of a Subsonic Vehicle1

10/13

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

7/31/2019 Aiframe of a Subsonic Vehicle1

11/13

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

7/31/2019 Aiframe of a Subsonic Vehicle1

12/13

DESIGN PARAMETERS

AIRFRAME MATERIAL PROPERTIES :

High strength to weight ratio Light weight

Corrosion resistance

Non flammable High quality

7/31/2019 Aiframe of a Subsonic Vehicle1

13/13

FUSELAGE STRUCTURE

DIFFERENT TYPES OF STRUCTURES USED FORFUSELAGE AIRFRAME CONFIGURATION