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Essential Tips for Dynamic Stability in Glider Construction and Performance Assessment

This lesson covers key aspects of dynamic stability in glider construction, focusing on essential tips and techniques for optimal performance. Learn the significance of using wood glue or fast-drying epoxy, ensuring symmetrical dihedral and wing sweep, and installing an adjustable tail. Understand dynamic versus static stability with a detailed overview of the five dynamic modes. Explore crucial flight performance assessments and perfect your launch techniques to enhance glider flight stability. Prepare for the next lesson with a quick review of stability concepts.

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Essential Tips for Dynamic Stability in Glider Construction and Performance Assessment

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  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

  4. 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

  5. B-747 Dutch Roll Roll rate Yaw rate

  6. 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

  7. Dutch Roll in the Simulator

  8. 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

  9. Spiral Mode in the Simulator

  10. 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

  11. 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

  12. Short Period in the Simulator

  13. 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…)

  14. Phugoid (Long Period) Mode in the Simulator

  15. 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

  16. 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

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