Report

INTRODUCTION TO STABILITY AND CONTROL STABILITY SUMMARY Axes, Moments, Velocities – Definitions Moments and Forces Static Longitudinal Stability Tail Effects Wing Effects Static Margin Directional Static Stability Vertical Tail Wing/Body Lateral Static Stability Vertical Tail Wing Sweep TRADITIONAL AIRCRAFT CONTROLS (All moving) Elevators Ailerons 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 maneuverable C-5, C-17, B-52, Passenger airplanes Maneuverable Aircraft—very easy to move Not 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 Lw Lt cg Ma.c. xac xt xcg SMcg = 0 = Ma.c + Lw (xcg – xac) – Lt (xt) CRITERIA FOR LONGITUDINAL STATIC STABILITY Aircraft is not moving in pitch! 1. CM,0 > 0 2. ∂CM,cg / ∂ a < 0 LONGITUDINAL STABILITY—TAIL EFFECTS Tail aft of cg is Stablizing Canards are Destabilizing Increase stability (more negative CMa) by Lifttail St Longer moment arm Larger tail LONGITUDINAL STABILITY—WING EFFECTS Wing 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 +b x V Design Considerations (Main Contributor) y + Ncg Lv Top View • Vertical tail aft of c.g. is stabilizing • To increase directional stability -- Vert. tail further aft -- Vert. tail bigger (or add another) Wing/Body Contribution to DIRECTIONAL STATIC STABILITY x +b Lw/b V Design Considerations y - Ncg - Ncg Top View - Fuselage area forward of the cg is directionally destabilizing - That’s why aircraft have tails! Vertical Tail Contribution to LATERAL STATIC STABILITY Design Considerations V -L z Rear View y - 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) Wing Sweep Contribution to LATERAL STATIC STABILITY x Positive wing sweep is stabilizing +b V V y Less lift y More lift z Top View Rear View