by eddiema, published
A simple rotor head which uses one or two plastic rulers as a crude aerofoil.
I haven't gotten it to auto-rotate yet and maybe it won't - it is experimental.
This is not intended to ever fly.
I don't know what the critical things are to achieve auto-rotation that is partly why I've made this.
Obviously making a windmill is easy but that problably isn't the same thing.
I'm lacking a good wind source for testing ATM.
My current feeling is the blades will need to be sanded to a better shape.
This is a very low priority project so it may take some time.
There seems to me to be contradictory information on the web regarding blade pitch.
It looks like slightly positive pitch is the norm for fixed pitch rotors.
Shaft bearing assembly to follow.
I tried the zero pitch rulers in front of an industrial fan and seemed to get some auto-rotation.
It was weak and the swirling uneven air-flow may not be causing true auto-rotation.
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Not quite. Yes I've pre-rotated all along.
The last profile I posted is a gyro profile.
No you need positive pitch - usually 1 to 5 degrees. It it wasn't positive they couldn't do stop and drop landings.
The airflow is usually up except during prerotation and landing flare.
I have shelved gryos and will be flying powered parachute instead.
A windmill definitely is not the same as a gyro rotor. One thing you need to know is that a gyro does not start autorotating when it is not rotating yet.
It needs the airflow in the plane of rotation, generated by the rotation itself, combined with airflow through the plane of rotation to get a lift force with a tangential component which drives the rotation.
So first pre-rotate, then get some air to flow up through the rotor plane, and then you will experience autorotation.
Of course you do need a decent airfoil profile to make it work at all.
Zero or slightly downard pitch should work.
Â I'm not an expert in gyros. I've never flown one or had a close look for quite a while. I read some theory and watched a lot of video. I don't think real gyro blades have twist or taper but they are proper airfoils and possible have non-zero pitch (possibly even negative pitch). I haven't found that information anywhere.
(Even when set to zero pitch you get positive pitch when you tip the rotor back and move forwards).
I think the important thing is the retreating blade stalls near the hub.
I've only tried the rulers in front of a fan which is too weak and not a laminar flow.
I also don't think the teeter bolts is needed for auto-rotation but I could be wrong.
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gyrorotorholder3.stl has a 3 degree pitch. This has to be printed standing end on.
gyrohead.stl has holes to take a 3mm pin or something to act as a teeter bolt.
Ideally we'd stick some bearings there but first try will just be a lubed pin.
cy1.stl is a clark-y aerofoil.
cy-sim is a symetrical foil based on the clark-y
cy-sim-pair has two joined foils for printing stability. The also have some mounting holes.
naca8h12-pair uses a common profile used on real gyrocopters.
naca8h12-pair-ccw is a mirror image so it rotates the same direction as big gyros - it may need a reversed hub.
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