Vance
Gyroplane CFI
- Joined
- Oct 30, 2003
- Messages
- 16,464
- Location
- Nipomo,California
- Aircraft
- Givens Predator
- Total Flight Time
- 2400+ in rotorcraft
In an accident thread on the Rotary Wing Forum a CFI asks Antony to explain what Doug, David and Antony wrote about a situation where lift is reduced by descending into turbulent rotor downwash with an over speeded rotor
I am going to make an effort to clarify my opinion on this phenomenon staying inside what I feel is accepted rotor aerodynamics.
Here is a quick review of the most basic gyroplane rotor theory from the FAA publication; The Rotorcraft Flying Handbook.
“ROTOR DISC REGIONS As with any airfoil, the lift that is created by rotor blades is perpendicular to the relative wind. Because the relative wind on rotor blades in autorotation shifts from a high angle of attack inboard to a lower angle of attack outboard, the lift generated has a higher forward component closer to the hub and a higher vertical component toward the blade tips. This creates distinct regions of the rotor disc that create the forces necessary for flight in autorotation. The autorotative region, or driving region, creates a total aerodynamic force with a forward component that exceeds all rearward drag forces and keeps the blades spinning. The propeller region, or driven region, generates a total aerodynamic force with a higher vertical component that allows the gyroplane to remain aloft. Near the center of the rotor disc is a stall region where the rotational component of the relative wind is so low that the resulting angle of attack is beyond the stall limit of the airfoil. The stall region creates drag against the direction of rotation that must be overcome by the forward acting forces generated by the driving region.”
I feel it is fairly well accepted that in order for a gyroplane to fly it has to accelerate air downward.
In my opinion with an over speeded rotor the driving region shrinks and the driven region grows as energy of the over speeded rotor is dissipated.
Most people I know have experience the extra float they get with an aggressive flare on landing. It does not take long for the rotor to return to normal flight rpm. The heavier the rotor and the faster it is turning the more energy is available.
In my opinion an aggressive turn as part of a steep descent near the ground could create a situation where some of the rotor is descending into turbulent rotor down wash.
Under certain conditions I feel this could cause a short term loss of lift.
It appears to me Antony feels this played a part in his gyroplane landing mishap.
I am going to make an effort to clarify my opinion on this phenomenon staying inside what I feel is accepted rotor aerodynamics.
Here is a quick review of the most basic gyroplane rotor theory from the FAA publication; The Rotorcraft Flying Handbook.
“ROTOR DISC REGIONS As with any airfoil, the lift that is created by rotor blades is perpendicular to the relative wind. Because the relative wind on rotor blades in autorotation shifts from a high angle of attack inboard to a lower angle of attack outboard, the lift generated has a higher forward component closer to the hub and a higher vertical component toward the blade tips. This creates distinct regions of the rotor disc that create the forces necessary for flight in autorotation. The autorotative region, or driving region, creates a total aerodynamic force with a forward component that exceeds all rearward drag forces and keeps the blades spinning. The propeller region, or driven region, generates a total aerodynamic force with a higher vertical component that allows the gyroplane to remain aloft. Near the center of the rotor disc is a stall region where the rotational component of the relative wind is so low that the resulting angle of attack is beyond the stall limit of the airfoil. The stall region creates drag against the direction of rotation that must be overcome by the forward acting forces generated by the driving region.”
I feel it is fairly well accepted that in order for a gyroplane to fly it has to accelerate air downward.
In my opinion with an over speeded rotor the driving region shrinks and the driven region grows as energy of the over speeded rotor is dissipated.
Most people I know have experience the extra float they get with an aggressive flare on landing. It does not take long for the rotor to return to normal flight rpm. The heavier the rotor and the faster it is turning the more energy is available.
In my opinion an aggressive turn as part of a steep descent near the ground could create a situation where some of the rotor is descending into turbulent rotor down wash.
Under certain conditions I feel this could cause a short term loss of lift.
It appears to me Antony feels this played a part in his gyroplane landing mishap.