This is not easy, I am not entirely sure I know what you are asking and if you are asking what I think I may not be able to explain it.
When you pitch a blade to feather you rotate it so that the neutral axis is in line with the wind so that it produces no lift. If you pitch to stall you increase the angle of attack above a critical angle ( typically 15 deg) so that the blade stalls and produces relatively low lift.
For a turbine you have to think of this very differently to an aeroplane, so although it is not immediately obvious the Jacobs machine pitches to feather ( but it never fully feathers).
The Proven machine pitches to stall.
From the operating point of view, the pitch to feather machine need a mechanism that can rotate the blades to something over 45deg and as Dave said you get little reduction in power or speed unless you can get this sort of angle. Depending how you are operating at the control point, your first movement will most likely increase the lift and may have the opposite effect if you are running near stalled. The pitch to feather system reduces thrust and tower loading by extracting less energy from the wind.
The pitch to stall can be achieved by quite a small angle change as most machines are near stall at full rating ( non mppt machines). Wind loading goes up as you are presenting full blade area to the wind and reducing power to the alternator by making the blades inefficient rather than reducing extraction.
Now the bit where I am lost, you seem to be referring to the side furling arrangement, which is not a pitch control mechanism. The simplest way to regard it as reducing power by reducing the effective area exposed to the wind, the frontal area is reduced by the cosine of the angle of furl.
If only life really was that simple it would be a wonderful situation, what really happens is very complex and way beyond my maths to explain. In some parts of the swept circle a blade stays similar to below furling, in other parts it goes into stall and in other parts it comes more out of stall.
The net effect is that if the offset is large it behaves much like the simple reducing area model and power does fall something like the cosine law.
The complication comes from a component that is not predicted by the simple area reduction idea and the blade has a force component that tries to keep it directly into the wind ( some of us have called it a wind seeking force). If the offset is too small this seeking force will defeat the moment of thrust on the alternator offset radius trying to turn it out of the wind and it will never furl. You can take the tail off and it will run upwind and produce power until it burns out. In this destructive mode the wind flow behind the prop will force the tail against the wind to a large angle and those not familiar with this problem will convince themselves it is furling.
The critical offset depends on the blade profile and type of loading so may be very different for different turbines, the Bergey machine will work with an offset well below any home built machine ( I don't know why but it is something to do with the blades as I have been told that changing the blades to wooden home made ones will cause the furling to fail completely).
As I am not entirely sure that this is what you are asking I will leave it at that. If the question is about reversing the blade rotation on a side furling machine the this has been discussed before, it has neglible effect on the furling but has some efrect on blades striking the tower. It affects the direction of the gyro force during yaw and depending on what that does to the friction of the yaw pivot it may marginally affect furling or the critical offset.
It most certainly is not changing the machine from pitch to furl to pitch to stall, it just isn't a pitch control scheme and doesn't work that way.
Flux
