1. Aero Engineering 315 Lesson 39Dynamic Stability

2. Glider Construction Tips • Glider fly-offs Monday, 8 December, 1815-2015 • Use wood glue or fast drying epoxy (flexible) • Make sure dihedral, wing sweep, etc. are symmetrical • Recommend adjustable tail (rubber band and wedge) • Clay ballast/c.g. location • Practice flying your glider • Assess performance (i.e. how straight does it fly) • Perfect your launch techniques

3. Dynamic Stability Overview • Dynamic vs. Static Stability • Lateral-Directional Modes • Spiral • Dutch Roll • Roll • Longitudinal Modes • Short Period • Phugoid • Objectives • Know the 5 modes and how aircraft motion varies with each mode

5. Dynamic vs. Static Stability • Static stability describes • Initial tendency once displaced from equilibrium • Dynamic stability describes • Tendency over a period of time once displaced or excited • Dynamically stable if eventually returns to equilibrium • Dynamic modes involve different motion behavior over a period of time

6. B-747 Dutch Roll Roll rate Yaw rate

7. Lateral-Directional Modes:Dutch Roll DUTCH ROLL: High frequency, lightly damped oscillation. Frequency near human response time, so pilot can aggravate oscillations (PIO). • Named after Dutch skaters • Typically objectionable when |CNb / CLb| < 1/3 • To correct poor Dutch Roll characteristics, increase directional stability and decrease lateral stability Glider Hints • Decrease dihedral • Decrease sweep • Decrease vert. tail height

8. Dutch Roll in the Simulator

9. Lateral-Directional Modes:Spiral SPIRAL: Non-oscillatory mode which primarily consists of a steady increase in roll angle (bank) and yaw rate if unstable. A slightly unstable spiral is acceptable in many aircraft, BUT in your glider it will result in it auguring into the ground… • Typically objectionable when |CNb / CLb| > 2/3 • To correct an unstable spiral, increase roll stability and decrease directional stability • Glider Hints • Increase dihedral • Increase sweep back • Move vert. tail forward • Decrease vert. tail area

10. Spiral Mode in the Simulator

11. Lateral-Directional Modes:Roll Roll rate response to pilot’s aileron command • Measure of how quickly a steady state roll rate is reached • Balances the aileron control power (i.e. how much roll force is generated) against the aircraft’s natural roll damping and roll inertia • Glider Hints • No ailerons • No problems

12. Longitudinal Modes:Short Period High frequency, heavily damped oscillation. Frequency near human response time, so pilot can aggravate oscillations (PIO). • Typically observed as an oscillation with a and pitch attitude, q Glider Hints • Not applicable to glider

13. Short Period in the Simulator

14. Longitudinal Modes:Phugoid Low frequency, lightly damped oscillation - exchange of kinetic and potential energy. Easily controlled by pilot. • Motion observed as an airspeed and altitude variation, and oscillation of kinetic and potential energy • Aggravated by airspeeds faster and slower than trim speed Glider Hints • Change trim speed or launch speed of glider (i.e. launch your glider at trim speed…)

15. Phugoid (Long Period) Mode in the Simulator

16. Well “damped” Lightly “damped” C-5A Short Period response – elevator to a a 5 10 C-5A Phugoid response – elevator to airspeed U 150 300

17. Next Lesson (T40)… • Terazzo Tour—meet at F-4 • Look-ahead: • Lesson 41: quick stability review, Stability and Control Quiz, then course critiques • Lesson 42: course review