www.PSFmagazine.com | March-April 2019 | 23 22 | March-April 2019 | Powered Sport Flying by Stephanie Gremminger Blade regions in vertical autorotation descent Force vectors in vertical autorotation descent Gyroplane Review Gyroplane Jeopardy! Who hasn’t dreamed of being a contestant on America’s most watched game show, Jeopardy?! We had a little Jeopardy fun at the 2019 Illinois Ultralight/Light Sport Safety Symposium when we played a round of Gyro Jeopardy, so we thought we would bring you our home edition so you could play along. This will be our first installment of the game. In true Jeopardy fashion, you would have to answer in the form of a question, but not in this version, since some of the questions would be pretty long! Let’s get started Alex! Audience, please do not shout out your answers. Let’s reserve that for our contestants. FOR 25 POINTS: WHAT POWERS GYROPLANE ROTORS IN FLIGHT? The rotor is not powered by the engine, it is made to spin by aerodynamic forces, through a phenomenon called autorotation. Now what causes the rotor to spin, or ‘autorotate?’ The simple explanation is that the wind passing through the tilted rotor disk gives it its power. Think of those maple seeds that spin as they fall. The air is the only thing that makes them spin—and if they weren’t spinning, they’d fall faster. FOR 50 POINTS: DURING AUTOROTATION, THE ROTOR DISK IS DIVIDED INTO THREE REGIONS. NAME THEM. The stall region includes the about 25 percent of the inboard portion of the blade radius. Because the inner portion of the blades are moving slower, the relative wind angle of attack on the inner portion of the blades is above the stall angle of attack – stalled and not contributing to upward lift. The driving region comprises about 45% of the middle portion of the blade radius. The total aerodynamic lift vector in this region is mostly upward but is inclined slightly forward of the axis of rotation. This forward inclination provides forward pull to drive or pull the rotation of the blade forward. The driven region is nearest to the blade tips and normally consists of about 30 percent of the rotor disk. The total aerodynamic lift vector in this region is also upward but inclined slightly aft of the rotating axis. This aft inclination tends to hold back the rotation of the rotor blade. (See image on facing page, upper left.) When the rotor rpm increases to the point where the aft pull of the Driven region balances the forward pull of the Driving region, the rotor maintains that rpm. The three regions are constantly adjusting their areas according to the load on the whole rotor. Different loads require changes in the rotor disk Angle of Attack and subsequently the Angle of Attack of the relative wind on the rotor blades and the lift vector inclination. Therefore, the Rotor rpm is also adjusting to find the new balance point of the Driving and Driven blade regions. Both the Driving and the Driven regions are creating the upward lift which supports the aircraft in flight.
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