Chris, have you been giving thought to mechanical braking? I see that back in December, Dan was asking about furling and the shut-down lever, but I was wondering if this was evolving like the rest of the machine
Spar, I did at one point think about mechanical braking but decided not to go with it. The geometry of the furling control mechanism has changed a bit to provide more predictable power control results. Plus my latest machines have hysteresis braking, using the stator. The "problem", if you want to call it that, with the GOE222 is that they will refuse to stall even at 2 TSR. With the wind blowing at 65 mph and 2 TSR, the tip speed is still 130 mph on the blades, which delivers well over 100 amps to a 24 volt bank.
So basically, the furling reduces the swept area which controls power. The hysteresis braking comes on if the system hits 30 volts and prevents the inverter from kicking out due to over-voltage. When the stator brake comes on in high winds it usually only clicks in and out 2-3 times, about 1.5 seconds each time, before the powerful gust dies out enough so the side furling is effective. It applies at 30 volts, releases at 27. That has worked very well with no more problems with the inverters kicking out.
Using the stator for hysteresis braking on a geared turbine is quite effective because of the mechanical advantage the stator has over the rotor thru the gearing.
I keep shying away from mechanical brakes because they're a wear item. I think a mechanical brake would be OK for parking the machine, but for power control in very high winds it just wouldn't last. And even for parking a mechanical brake is not necessary - cranking the tail on the machine and shorting the stator holds it parked even in winds over 60 mph. And cranking the tail and leaving it run in very high winds limits the power to about 500-600 watts due to all the pressure being gone attempting to steer the rotor back into the wind.
So my end conclusion was that spending the engineering time to add a tail cranking mechanism is much more worthwhile than spending it on a mechanical braking setup.
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Chris