axial alternator offset

[Raptorman670]

Hi Guys the Hugh Piggot book says to have the yaw pipe to the right of the alternator. There are a few I have seen that the yaw pipe is to the left of the alternator. What is the difference pros and cons between left and right? I am in the the process of building one not sure which way to go.

     Thanks Dave

[oldculett]

Hugh has switched sides in his books.  In 'How to Build a Wind Turbine', and before, they swing to one side, and in his new book 'A Wind Turbine Recipe Book', they swing to the other.  I believe this was because in the old version, if it yawed hard enough, the blade could possibly hit the tower where in the new version, it's much less likely.  Another way to do this with the original setup would be to have the blades spin in the other direction.  Just my understand.  Oldculett

[Flux]

Yes that is right. Under most site conditions the machine is likely to experience greater gyroscopic forces as it goes hard into yaw as it furls compared to coming back into the wind after a gust.

If the worst case is as it goes into furl you are better off with the blades trying to lift away from the tower as the tips pass the bottom, this is safer than the tips being thrown towards the tower at the bottom.

Under some conditions with turbulent wind the tail can yaw the thing to cause the opposite effect so although  the best condition normally is for the gyro forces to bring the blades clear of the tower as it goes into furl it probably won't be the best case for all conditions.

In real life it is best to have enough clearance to the tower for all conditions but statistically you are probably better off having the offset such that the blades lift from the tower as it goes into furl.

Some may argue that there other factors but from my experience this question of tower strike is the only issue and if you can be sure nothing is going to strike the tower you can have the offset either way. As pointed out, if you reverse the prop rotation it has the same effect as changing sides for the offset so if built conventionally it may be safer with a reverse rotation blade.

Flux

[Sly]

Hi all,

Can somebody simplify for me please so I understand. Here is the information on my turbine:

Otherpower 10', looking at it from the front i.e. at the prop:

Tail pivot is to the left

Stator to the right

Prop rotation is clockwise

There are no clearance issues at all but I am just curious, would counterclockwise rotation have been better for furling purposes?

Also if tail pivot was to the right and stator to the left what would be the prefered rotation?

I just want to know for future builds (Ah Yes there will be others....)

Thanks and much appreciated.

sly

[Flux]

"Tail pivot is to the left

Stator to the right

Prop rotation is clockwise"

In this case it throws the blades towards the tower as it furls. If this is the most rapid yaw moment then it would be better to reverse the prop. If you want to keep clockwise rotation then mount the alternator to the left.

This preference is based on the worst case being caused by a yaw as it furls. On turbulent sites anything can happen but there seems to be some general agreement that reversing things from the conventional gives you a better chance.

Flux

[Dave B]

 As expected, here is my comment on this and the reason why I have changed my blade rotation to counter clockwise looking at the blades from upwind and the rotor offset is to the right from this view also. This link http://usa.errachidia.org/video-precession-1-IEwAry0GARw.html  showing the precession experiment shows that a counter clockwise rotation would assist the furling if the offset is to the right. If the offset were to the left and the rotation remained counter clockwise you can see that the "yaw" rotation would fight against moving to the left and would want to move forward or stay into the wind.

 I have experienced this and I think others may have also. The darn thing just does not seem to want to furl properly even though you worked very hard to duplicate a proven design. Hugh has changed his ways and states the previous advantage of the blades swinging out away from the tower in turbulant winds when furling. This is an advantage too I agree.

 Unfortunately it is a project to change this if the original Dan's or Hugh's plans were originally followed. Reversing the offset or carving new blades may not seem worth it to those who have not experienced any problems. This affect will be more apparent for larger diameter blades both for possible flexing of the blades and the larger gyroscopic forces will accentuate the precession effects shown also. My problems have been solved by changing from the original offset VS. blade rotation.  Dave B.  

 

[Flux]

I thought Dave would come back on this one.

I certainly agree that I would use the other rotation in any future design.

I am still not convinced that changing the rotation solves the seeking problem, it may well help the get the thing furled quicker and perhaps transient changes in yaw may be enough to get it furled when it otherwise wouldn't .

I have built machines with the conventional rotation that do furl ( not entirely convinced that all proven designs do especially if you change the load conditions).

It may well be that the critical offset is less with the reversed rotation.

When you see a machine with offset and no tail running upwind at full power for many minutes I think you are forced to believe that the seeking force depends on other things than gyroscopics to hold it in the wind.

I do at least agree that changing every factor that helps is a good idea and starting from scratch I would put the offset on the other side for the tower strike reason and for the fact that it may help in other ways.

I based all my furling ideas on the Lucas Freelite but I have to confess that over the years I have changed the offset to the other side but I can't deny that my furling works better than the original Freelite.

Can anyone remember which way the offset is on the SWWP angle governor?

Flux