Thread: Hawts and Vawts
View Single Post
Old 09-26-10, 05:40 PM   #9
Big Al
Big Al
Join Date: Jul 2010
Location: Scotland
Posts: 31
Thanks: 0
Thanked 0 Times in 0 Posts

Skyl4rk-Thanks your input. I'm in UK where getting suitable airfoils difficult compared with US and OZ/NZ and even then most of what is available is Hawt directed rather than Vawt.Two points of which Caleb ? may be unaware
1/ There is on web what I thought a very good thesis on small wind by Claude Guillaume , Sandra Algazze and Emmanuel Duc on home wind . They favour Vawts and recommend S2027 airfoil which they measure as giving significantly increased O/P over the other airfoils tested-they are also very good on solidity and aspect ratio.
2/ The backshed website is full of really useful information and technical ingenuity to increase O/P . This is mostly Hawt directed but a lot of it particularly on the generating and control side is applicable to Vawts.

I had n't come across KFm foils or coroplast so thanks for the reference.

My initial thoughts on airfoils of the S2027 type was to build it out of 2 thick aluminium strips Rivetted or welded together ) and machine it to the required profile. Altho I have metal working facilities I'm not sure they would easily cope with modifying the profile for a helical blade or the subsequent bending.This is also an expensive approach. My second thought was to use my Hydraulic press and a die to bend thinner sheet to most of the required profile and bonding or riveting this to wood to make up the rest of the profile . Again I suspect not easy. The backshed guys don't seem to worry too much about profile and still get amazing amounts of power but to get Vawts up near Hawt performance I think I'll need to use every trick in the book ( and even Hawts can hardly turn their nose up at a 16% increase in power by using a simpler and more efficient airfoil )

I shall be measuring and logging wind speeds for the next two or three months but will try and move my thoughts along and maybe even do a few experiments over the winter. An initial thought is to make the bottom blade support , a thinnish discus shape (low drag ) with weak spring loaded vanes popping out of this at rest to give a savonius starting effect , the vanes retracting automatically(to cut drag) under wind pressure as the rotor accelerates. I also believe this bottom plate would allow the mounting of a variable pitching mechanism which could do a lot to improve efficiency altho making this simple and reliable is a challenge. However some of the the revered Jacobs turbines had variable pitching on Hawts (much more difficult ) and are reputed to have been reliable.

While I'm logging wind don't expect any great technical progress but will post anything I find of interest. Rgds. Big Al

Last edited by Big Al; 09-26-10 at 05:43 PM..
Big Al is offline   Reply With Quote