1

Lecture 7: Stability & Control

Jason Mickey

For AE 440 A/C LectureSeptember 2009

2

S&C Responsibilities

• Select/design/size all control surfaces, e.g. horizontal tail, vertical tail, etc. (sizes to aerodynamics & configuration

• Determine/Ensure static margin range for all flight conditions

• Evaluate longitudinal and lateral stability (suggest needed changes to configuration)

• Specify avionics and any digital control system (weight/size to internal configuration)

• Evaluate dynamic stability (phugoid & short period) and evaluate flying qualities (e.g. with a flight simulator)

3

Control Surface Sizing

• Horizontal tail, elevator

• Vertical tail, rudder

• Ailerons

4

Longitudinal Moments

Raymer, Fig. 16.3

cg cg acw w w f fus

h ach cg t p cg p

M L X X M M f M

L X X Tz F X X

5

Types of Tails

Raymer, Fig. 4.30

6

Tail and Control Surface Sizing

vt W Wvt

vt

c b SS

L Wht W

htht

c C SS

L

(Raymer)

7

Neutral Point

W

PahL

W

hthL

PP

Paachh

LW

hthmacwL

np

qSF

aa

CSS

C

Xaa

FXaa

CSS

CXC

X

aha

ahafusa

(Raymer)

Find such that for all aX 0aMC

8

Elevator to Trim

Find such thatE 0cgM

Raymer, Fig. 16.18

9

Yaw and Roll Moments

wing w a fus acv cg

p p p cg p

N N N a N F X X

TY DY F X X

10

Stability and Handling Qualities

• Static stability

• Dynamic stability

• Handling qualities

11

Stability

12

Cooper-Harper Scale

13

Avionics

14

Samples of Stability and Control from Previous PDRs

15

Tail and Control Surface SizingTable 5.2.1 Horizontal Tail Dimensions

Configuration Area (ft2) Span (ft) Mean Chord (ft)

Pusher 26.75 10.7 2.5

Tractor 22.83 9.13 2.5

Twin-Boom 19.41 7.31 2.5

Table 5.2.2 Vertical Tail Dimensions

Configuration Area (ft2) Span (ft) Mean Chord (ft)

Pusher 12.84 5.14 2.5

Tractor 13.7 5.55 2.5

Twin-Boom 15.07 4.38 2.5

16

Tail and Control Surface Sizing

17

Static Margin

Table 5.41 Power-Off Static Margin (%)

Configuration 1 Pilot 2 Pilots

Pusher 1.93 9.60

Tractor 3.33 6.98

Twin-Boom 4.17 5.99

18

Suggestions for CR

• Determine tail-type(s)• Finish sizing tail and control surfaces• Determine elevator reqt. for takeoff & landing• Determine trim points• Determine static margin range• Investigate static stability• Trade studies, e.g. tail size/location vs. trim

elevator deflection