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Teaching Basic Aerodynamics. Mel Burkart, MCFI 2008 FAA Flight Instructor of the Year St. Louis Flight Standards Region. Lecture Content. Glider Aerodynamics Effect of Controls Low and High speed flight Thermaling Approach and Landing Stall, Spin and Spiral Dives
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Teaching Basic Aerodynamics Mel Burkart, MCFI 2008 FAA Flight Instructor of the Year St. Louis Flight Standards Region
Lecture Content • Glider Aerodynamics • Effect of Controls • Low and High speed flight • Thermaling • Approach and Landing • Stall, Spin and Spiral Dives • Limit Load Considerations
Analysis of Accident Data 6 Year Summary Average Fatalities = 6 - Average Accidents = 32
Analysis of Accident Data 6 Year Summary
How to Correct/Reverse Trend • Teach your student a basic, simplified way to understand and apply basic aerodynamics in a high stress environments. • Takeoff • Approach and Landing
Lift / Drag Formula L = CL S P/2 V2 D = CD S P/2 V2
Lift / Drag Formula L = CL S P/2 V2 D = CD S P/2 V2
Lift & Airspeed Relationship • With constant Angle of Attack: • Doubling the airspeed quadruples wing lift • Increasing airspeed by 1.4 doubles wing lift • Increasing airspeed by 1.2 gives 40% increase in wing lift • Conclusion: Relatively small increase in airspeed yields substantial increase in lift.
Speed, Lift, & Turning Flight: • Which wingtip is faster in turning flight - the outer wingtip or the inner wingtip? • What effect does this speed differential have on the lift the inner wingtip and the outer wingtip produce? • Is this effect related to overbanking tendency in a glider?
Airspeed, Lift, & Load Factor • If the stall airspeed in a 1 ‘G’ wings-level is 30 knots (at Maximum Gross Weight)… • Then what is the maximum load factor that can be produced at 60 knots? • Doubling airspeed quadruples wing lift potential, and so: • 4 ‘G’s is the maximum possible before stall if flying at 60 knots’ airspeed in this glider.
What Does This Mean? • In any glider, if you cannot remember the rough-air speed or the maneuvering speed, then: • Limiting airspeed to no more than 2 times the wings-level 1 ‘G’ stall speed will keep flight loads at or below 4 ‘G’s. • On the other hand, flying at 4 times stall airspeed means that you have the power to induce 16 ‘G’s! • 16 ‘G’s is well beyond the capability of the glider to withstand. • These are practical aerodynamic considerations.
Practical Drag ConsiderationsDrag Versus Airspeed [With Illustrations From TheFAA Glider Flying Handbook]
Parasite Drag Parasite Drag – any surface which deflects or interferes with the smooth airflow around the glider.
Is Parasite Drag... • Intuitive? • Or is it ... • Counter-Intuitive?
Parasite Drag & Airbrakes • What type of drag do airbrakes generate? • Induced drag? • Or Parasite drag? • What happens to airbrake parasite drag if airspeed is doubled? • Airbrake parasite drag quadruples! (Reference V squared)
With Airbrakes Full Open: • What happens to airbrake drag if airspeed is doubled? • Airbrake drag quadruples! • What happens to airbrake drag if airspeed is increased by 40%? [e.g. from 50 to 70 knots] • Airbrake drag doubles! • What happens to airbrake drag if airspeed is increased by only 20%? [e.g from 50 to 60 knots] • Airbrake drag increases a whopping 40%!
Airbrake/Parasite Drag Questions To Ask... • With airbrakes full open, what is the sink rate of your training glider at 50 knots? • With airbrakes full open, what is the sink rate of your training glider at 65 knots? • With airbrakes full open, what is the sink rate of your training glider at 80 knots? • So… If you find yourself too high on final, what can you do to get down? • Deploy full airbrakes and increase airspeed!
Induced Drag & Parasite Drag Induced Drag – airflow circulation around the wing.
Is Induced Drag... • Intuitive? • Does it make sense to the aviation newcomer that induced drag is very low at high speed, and very high at slow speed? • Or is Induced Drag Counter-Intuitive? • Most newcomers choose counter-intuitive. • So, what simile or metaphor can we use to model the concept of induced drag?
The Wing’s Magic With Illustrations From TheFAA Glider Flying Handbook And The Web
As the Angle Of Attack Increases • The CL (Center of Lift, a.k.a. the Center of Pressure) moves forwardon the wing • At high angle of attack, the main lifting force is far forward on the wing • The higher the angle of attack, the further forward the CL moves.
