Post on 15-Dec-2015
transcript
INTRODUCTION TO STABILITY AND CONTROL
STABILITY SUMMARY
Axes, Moments, Velocities – Definitions
Moments and Forces
Static Longitudinal StabilityTail EffectsWing Effects
Static Margin
Directional Static StabilityVertical TailWing/Body
Lateral Static StabilityVertical TailWing Sweep
TRADITIONAL AIRCRAFT CONTROLS
Ailerons
(All moving)Elevators
Rudder
ALTERNATE CONTROL METHODS
Canards
Spoilers (T1) and Speed Brakes
Wing Warping
Center of Gravity Shift
V-tail (combines pitch and yaw control)
Thrust Vectoring or Asymmetric Thrust
Flaperons (flap and aileron)
Elevons (elevator and aileron)
Ruddervators (rudder and elevator)
AIRCRAFT MOTIONS - ROLL
Roll: what is it?
Ailerons
AIRCRAFT MOTIONS - ROLL
Roll: Motion about the longitudinal (X) axis produced by the ailerons (l moment)
Ailerons
AIRCRAFT MOTIONS - PITCH
Pitch:
Elevator
AIRCRAFT MOTIONS - PITCH
Pitch: Motion about the lateral (Y) axis produced by the elevators (m moment)
Elevator
AIRCRAFT MOTIONS - YAW
Yaw:
Rudder
AIRCRAFT MOTIONS - YAW
Yaw: Motion about vertical (Z) axis produced by the rudder(s) (n moment)
Rudder
STABILITY VS.MANEUVERABILITY (CONTROL)
Stable Aircraft—not very easy to move Not very maneuverableC-5, C-17, B-52, Passenger airplanes
Maneuverable Aircraft—very easy to moveNot very stable (unstable in many cases)Require Flight Control Systems to keep aircraft pointy end forward
F-16, F-22
MOMENTS AND FORCES
Trimmed Flight SMcg = 0
Straight and Level, Unaccelerated Flight (S.L.U.F.) SF = 0
L = W T = D
CONVENTIONAL AIRPLANE
cg
Lw
Lt
Ma.c.
xcg
xac
xt
SMcg = 0 = Ma.c + Lw (xcg – xac) – Lt (xt)
CRITERIA FOR LONGITUDINAL STATIC STABILITY
1. CM,0 > 02. ∂CM,cg / ∂ a < 0
Aircraft is not moving in pitch!
LONGITUDINAL STABILITY—TAIL EFFECTSTail aft of cg is Stablizing
Canards are Destabilizing
Increase stability (more negative CMa) by
Lifttail Longer moment arm
St Larger tail
LONGITUDINAL STABILITY—WING EFFECTSWing a.c. forward of c.g. is Unstable
Decrease instability (lower CMa)
↓ (hcg – hac) Shorter Moment Arm or move c.g. forward
LONG.-STATIC STABILITY - TOTAL AIRCRAFT
Most parameters are fixed once the aircraft is built
C.G. can be moved Cargo location Fuel location Weapons, Stores, etc.
Variable Geometry wings—change cg
CONVENTIONAL TAIL - STABILIZING
F-22
F-16
CANARDS I - DESTABILIZING
Su-35
Long-Eze
CANARDS II - EUROFIGHTER
Vertical Tail Contribution to DIRECTIONAL STATIC STABILITY
Design Considerations (Main Contributor)
• Vertical tail aft of c.g. is stabilizing• To increase directional stability
-- Vert. tail further aft -- Vert. tail bigger (or add another)
Top View
x
y
+ Ncg
+b
Lv
V
Wing/Body Contribution to DIRECTIONAL STATIC STABILITY
Design Considerations
- Fuselage area forward of the cg is directionally destabilizing
- That’s why aircraft have tails!
Top View
x
y
- Ncg
- Ncg
+b VLw/b
Vertical Tail Contribution toLATERAL STATIC STABILITY
Design Considerations
- Vertical tail above c.g. is stabilizing - To increase lateral stability
-- Vert. tail taller” -- Vert. tail “bigger” (more area)
-- Increase Vert. tail lift curve slope (Increase ARvt and/or Increase evt)
Rear View
y
z
-L
V
Wing Sweep Contribution toLATERAL STATIC STABILITY
x
y
+ b
V
Rear View
y
z
Top View
V
Positive wing sweep is stabilizing
Less lift More lift