Recent content by Jean Claude

  1. Jean Claude

    Articulated rotor blades

    Hinged three-bladed rotor like C30 avoids the drag vibrations but unfortunately not "ground resonance". Hinged two-bladed rotor restore drag vibrations, now transformed into cyclic differences in individual centrifugal forces, and keeps the serious downside of ground resonance
  2. Jean Claude

    Engine power for a ultralight

    Yes, undoubtedly
  3. Jean Claude

    Engine power for a ultralight

    Words and definitions changes depending on the messages. For example when you say that in vertical descent the speed forward is zero. Since "forward" speed refers to movement, then "forward" is below in a vertical descent and forward speed is the speed of descent.
  4. Jean Claude

    Engine power for a ultralight

    The aerodynamic definition of "lift" is the force perpendicular to the direction of the speed. So, in vertical descent, the rotor has zero lift, just a vertical drag, and L/D = 0
  5. Jean Claude

    Electric Pre-Rotator

    If 200 rpm of the electric spinner seems sufficient to you, why do not they seem sufficient to you with the mechanical spinner, since then the thrust of the propeller and the gripp of the wheels discharged by the rotor, do not yet create problem ? 200 rpm instead of 300rpm requires only 44% of...
  6. Jean Claude

    Engine power for a ultralight

    Yes, but my words were "To cancel the impact speed ..." During this phase of slowing down, the state is no longer "steady" and the helicopter can use part of the kinetic energy of a heavy rotor, while the gyro cannot: A heavy rotor don't help him
  7. Jean Claude

    Engine power for a ultralight

    During a gliding descent, aircrafts are not like a brick which regularly increases its speed of fall during the descent. To say that the descent is stabilized means that the potential energy is dissipated as it goes. To cancel the impact speed of a helicopter when descending vertically, it is...
  8. Jean Claude

    Engine power for a ultralight

    The minimum mass for the helicopter concerns the mass of the blades, not that of the load. It is simply a matter of giving the pilot enough time to reduce the collective pitch before the Rrpm decreases below that the stall of the blades. The rotor of a gyroplane does not have this concern...
  9. Jean Claude

    Engine power for a ultralight

    Certainly. And today, a 12 Hp engine weighs about 8 kg and it allows to takeoff in less than 300ft , rise at 600 ft/mn and flight 50 mph in cruise.
  10. Jean Claude

    Engine power for a ultralight

    The rotor adds about 5 kW of profile drag, which requires a more powerful and heavier motor, which requires a more solid structure, and more fuel. This additional weight now increases the induced drag which ... etc, etc. It's just a "snowball effect" PS Thank you for making me discover this...
  11. Jean Claude

    Engine power for a ultralight

    A FW can fly with much less power. My JCD03 of 175 lbs and span 23 feets was powered by a 12 hp SOLO engine and a propeller 28 inchs rotating at 5800 rpm. But my calculations always gave more than 35 hp for a gyro.
  12. Jean Claude

    Rotor blade chord

    Entering the characteristics of MTOsport (392 kg) in my spreadsheet, I obtain a maximum L/D of 3.7 at 29 m/s At this moment, Parasitic drag = 360N Rotor profile drag = 426 N Induced drag = 250 N
  13. Jean Claude

    Rotor blade chord

    I also can't post an Excel file, while I did in the past A possible formula for profile power when forward speed is nul is: P = ¼ Cd.ρ.c.ω^3. R^4 with Cd = 0.011 So, when ρ = 1.225 kg/m3, c= 0.18 m R= 3.5 m and ω = 36.6 rd/s, then Profile power = 4400 w, let's say 4800 w at 20 m/s forward
  14. Jean Claude

    Rotor blade chord

    This is only true for an FW, but false for a gyro because the profile power of a rotor keep almost constant . In my opinion, relying on the cD min of 8H12 measured in a wind tunnel with low turbulence, H. Dudda underestimates the drag of the rotors . Thus, to justify the power absorbed in...
  15. Jean Claude

    Rotor blade chord

    Just change Cd*S from 1 (with no fairing) to 0.35 (about clean) at 50 mph allows 25% power less in cruise. Are you sure that everything is done to avoid the separations of the flow behind the pod?
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