Flight Mechanics Preliminaries

1
Flight Mechanics - Preliminaries

• Center for Aerospace Systems Design Engineering
• Department of Aerospace Engineering
• IIT Bombay, Mumbai 400076

2
Aircraft Come in All Shapes
What makes them fly?
3
Contents

• Principles of Flight
• Airfoil
• Wing
• Wing Horizontal tail
• Flight Mechanics?

4
Why Airfoil ?
Drag
Airfoil Shape that offers very low drag
5
Airfoil Lift, Moment Thickness, Camber
Sign convention
V?
6
Lift Moment
Fixed ? V? Some MRF
dL/d? dM/d? are constant over a range of ?
7
Watch out ! CP and AC
L1 L M1 M - L x1
(dM1/d?) (dM/d?) (dL/d?) x1
8
Lift Moment
Lift 0.5 ? V2 C a ? Moment 0.5 ? V2 C2
d Moment is about 0.25 C
9
Flat Plate
More than that for airfoil

• Lift 0.5 ? V2 C a?
• Moment 0.5 ? V2 C2 d d 0

10
Lift Moment

• Lift 0.5 ? V2 C a?
• Moment 0.5 ? V2 C2 d d gt 0

11
Lift Moment
Lift
?
Drag
Moment (Pitching)
V

• Lift 0.5 ? V2 C a?
• Moment 0.5 ? V2 C2 d d lt 0

12
Airfoil / Flat Plate
Moment is about 0.25C
Moment does not change with ? Lift increases with
?
13
Airfoil
Moment is about 0.25C
Moment does not change with ? Lift increases with
?
14
Equilibrium Stability
Unstable
15
Aerodynamic Center
Point about which Moment does not change with
? 0.25 C for an Airfoil. CG w.r.t. Aerodynamic
Center ? Stability
16
Flat Plate ? Strip of Paper

• How to make a strip of paper fly?
• AR is large ? Like a flat plate airfoil
• h 0 ? M0 0 ? X 0
• X 0 ? Neutral
• For stability
• h lt 0 ? M0 gt 0 ? X lt 0
• X lt 0 ? Stable

17
Lets Fly a Strip of Paper!
Stable
18
Lets Fly a Strip of Paper!
Stable
19
Lets Fly a Strip of Paper!
Stable
Hinge line of elevator
20
Wing
21
Wing
22
Wing
23
Lets Fly a Wing!
24
Wing Horizontal Tail (No Fuselage)
25
Vertical Tail?
26
Vertical Tail? Dihedral?
?
27
Flight Mechanics?
Thank You
28
Equations of Motion

• Rigid body dynamics
• Aerodynamic forces moments modeled

29
Decoupled Equations
30
Decoupled Equations
Lo Longitudinal, LD
Lateral-Directional
31
http//www.casde.iitb.ac.in sudhakar_at_aero.iitb.ac
.in
Thank You
32
Airfoil, Flat Plate Or Strip of Paper
L W L X Mo 0 X - Mo/L
33
Control Surfaces
Ailerons
Elevators
Rudder
34
Elevators - Pitch
35
Ailerons - Roll
36
Rudder - Yaw