1. Aircraft Mechanics Alan Altschuler (Mr. A)

2. Forces and Moments on Aircraft Forces – Lift – Drag /Thrust – Inertia Gravitational (weight) Linear and Rotational Momentum – Ground Support Weight Speed-Up – Catapult Slow-Down – Arrestment – Parachute (Drag-chute) – Pressures (self-balancing) Cabin Hydraulic and others (bleed air) Moments – Pitch – Nose up and down – Roll – Left wing tip up with right down, and vice versa – Yaw – Nose left and right

3. Axis Systems on Aircraft Local aircraft (x=aft, y=outboard (usually left), z=up – relative to aircraft (structure) – usually called Body Axes – Thrust is “mostly” negative local x Air stream (x=streamwise flow (positive impinging on aircraft nose) – Wing angle of attack is “mostly” angle between local x and air stream x from pitch (also provided via roll velocity) – Vertical Tail angle of attack is “mostly” angle between local x airstream x from yaw (also provided via roll velocity) – Lift is positive airstream z – Drag is positive airstream x Inertial (z=up relative to earth) – Weight is always inertial negative z Direction Cosines – A method to rotate vectors among axis systems

4. Ground Configuration All axis-systems aligned Z b,a,i X b,a,i Air Configuration All axis-systems mis-aligned here ZbZb XbXb ZiZi XiXi ZaZa XaXa airflow Aligned with airframe Aligned with airflow Aligned with earth

5. Lift curve Bernoulli Angle of attack Camber Bernoulli NACA airfoil

6. Roll – Yaw Coupling Due to asymmetry in the aircraft y-z and x-y planes Can have roll-pitch and yaw-pitch coupling, but symmetry about aircraft x-z centerplane would make these couplings zero. Interesting cases of asymmetry – Single-engine aircraft – Multi-engine aircraft without counter-rotating engines E-2 tail (Hawkeye)Hawkeye – Single main-rotor helicopters – A-10 nose wheel (Warthog/Thunderbolt)Warthog – 2-bladed props Principle axes

7. Inertia Linear Angular – Issue with Most HelicoptersHelicopters – Banking a bicycle – Car Tilting on an unbanked roadway Roadway banking Center of Gravity

8. Ground Configuration

9. Newton’s Second Law F = ma ? – Not really Actually, force equals the change in momentum over time Momentum P = mv In calculus F = dP/dt = d/dt (mv) = m dv/dt + v dm/dt In non-calculus F =  P/  t = m  v/  t + v  m/  t  v/  t = a F = ma + v  m/  t – the second part is the “rocket” part, exhausted gas quickly from the body

10. Lifting Surfaces Wing – Bi-plane wing structures Bi-plane – Winglet Winglet Horizontal Stabilizer (Tail) Vertical Stabilizer (Tail) Canard – X-29 X-29 Fuselage – F-14 body lift F-14

11. Ground Configuration - parked Air Configuration – steady level flight

12. Control Surfaces Elevators Ailerons Rudders Pictures Spoilers Used less often – Speed brakes – Elevons (Space Shuttle)Space Shuttle – “Flying” Horizontal Stabilizers (F-14)F-14 Aka stabilators

13. Landing Gear (Alighting Gear) Main Gear – Metering Pins Metering Pins Nose Gear Tail Gear (DC3)DC3 Parachute/Drag Chute (Space Shuttle)Space Shuttle Tail Hook (Navy)Navy Tow Bar (Navy)Navy Emergencies – USAF – Tail Hook – USN – Barricade1Barricade1 – USN – Barricade2Barricade2

14. Level Turn Increased g’s are need to maintain altitude AND turn simultaneously

15. Coordinated Turn 1-g in the body axis-z direction is generated for passenger comfort. Combined rolling, pulling up when banked, and turning produced a “coordinated turn”. The aircraft actually accelerates down in the inertial-z axis and loses altitude

16. Aero-elastics Static – Lift – Roll – Pitch – Divergence Dynamic – Flutter – Example1 Example1 – Example2 Example2 – Non-aero effect Shimmie Unswept wings (whose chordlines align with the airstream) do not have a negative increment of angle of attack (gliders) Swept wings provide greater area with less frontal area (less drag) Outbd tip deflects up Inbd near fuselage a b airstream elastic axis a & b are chord-lines perpendicular to elastic axis, b deflects up more than a, producing an elastic increment of negative angle of attack in the airstream

17. Sonic Effects Sub-sonic – Center of pressure at approx 25% chord Super-sonic – Center of pressure at approx 40% chord – Wing sweep (F-14)F-14 Pressure distribution

18. Ground Effects Case Study US Navy wanted to perform a test of the E-2C Landing Gear at the Maximum Sink Speed – Sink speed is the vertical component of the landing velocity. This is no fun for the pilot, whose back can be injured. It is very difficult to do due to ground effects. In real life the Navy is concerned with aircraft carrier combined pitch, roll and vertical deck motions when the aircraft lands.

19. “Clean” Upper Wing Air Passage Case Study Often airframe structural analysts are asked to review issues regarding parts manufactured out-of-tolerance. These parts may be scrapped, reworked or used as-is. Sometimes new parts are added, often called “doublers” Aerodynamicists rarely permit violation of the upper cover’s Outer Mole Line (OML), the shape of the wing on the top, but care little about the lower cover’s OML. Typically, no doublers are allowed on the upper cover.