Transcript AE315 Lsn30
Aero Engineering 315
Lesson 30
Turn Performance
“Turning” the tables…
Turn Performance Overview
Define bank angle and load factor
Calculate load factor needed to sustain
a level turn at a given bank angle
Calculate initial turn rate and radius for
level turns, pull-ups and pull downs
Turn Performance Definitions
Load factor – Lift/Weight
(measured in g’s)
n = L/W
Bank angle (f) – angle created
by rotating the aircraft about
the aircraft reference line
L
f
Turn rate (w) – radians/second
or degrees/second
Turn radius (r) – feet
W
Level Turns
L sin f
L cos f
Level flight means
constant altitude (no
vertical acceleration)
In level flight, bank
angle creates a specific
load
Example: level turn at
f = 60°
n = 1/cos 60° = 2
In a level turn:
n L 1
W cos f
If bank angle is known,
you can find load factor
and vice versa for a level
turn
Level Turn Load Factor
Level Turn Load Factor
6
4
2
0
10 20 30 40 50 60 70 80
Bank Angle
Level Turns
L sin f
f
L cos f W
L = nW
Constant velocity turn
Stall speed in a turn:
2
L = nW = CLMAX r VSTALL S/2
2nW
VSTALL =
L sin f
r
CLMAX r S
Stall speed increases as n½
Extra pilot care when
performing high bank
angle turns near the
ground
Level Turn Performance
Concepts
For good turn performance we want:
Small
turn radius
High turn rate
To achieve this we should turn with
Low
velocity
High load factor
Note: Turn radius and rate are functions only of
velocity and load factor. A B-52 and an F-16 at
the same airspeed and “g” have identical turn radii
and rates.
Level Turn Design Considerations
To get small turn radius (r) and large turn rate (w)
Maximize “g” loading
Structural considerations (max g for the structure)
Physiological considerations (human g limits)
Aerodynamic considerations (stall limitations)
Minimize wing loading, W/S (n = CL q S / W)
Maximize lift coefficient
High lift devices
Pitch vectored thrust
Maximize thrust-to-weight ratio (T/W)
High “g” creates very high induced drag
F-16 Turn Performance Limits*
Stall limits
Human/aircraft
structural limits
Aeroelastic limits
*F-16 COMBAT AIRCRAFT
FUNDAMENTALS, page 46
Homework #36
An SR-71 is in a 20° banked level turn at
Mach 3.0 and an altitude of 80,000 ft.
Assume the ambient temperature is
390°R.
a.
b.
c.
What is the aircraft’s turn radius in NM?
What is the aircraft’s turn rate in deg/s?
If the pilot increases the bank angle to 45°
while maintaining a level turn at Mach 3.0,
what would the new turn radius be in NM?
What would happen to the aircraft load
factor?
SR-71 Mach 3 80,000 ft
20o bank
r = 118 nm
45o bank
r = 43 nm
10o bank
r = 244 nm
Vertical turns (loops)
Pull-down
WV2
S FR = g r = L +W
g(n+1)
w = V/r =
V
Vertical Portion
WV2
S FR = g r = L
gn
w = V/r =
V
Pull-up
WV2
S FR = g r = L -W
g(n-1)
w = V/r =
V
T
D
Pull-Down
W
L
T
L
D
W
r
L
T
D
W
Pull-Up
5.0 GR
4.7 GR
4.7 GR
r=
V2
gn
4.0 GR
4.0 GR
GR = denominator
term in g’s
3.0 GR
r=
V2
g(n+1)
r=
V2
gn
3.3 GR
r=
V2
g(n-1)
3.0 GR
Next Lesson (31)…
Prior to class
Read text 5.12
Complete homework #36-37
All sections of Fighter Design Project
In class
Discuss V-n diagrams