Blade Drag As The Basic Problem Of Vertical Axis

[IntegEner]

In reading through some of the posts on VAWTs, Darrieuses, eggbeaters, vertical axis turbines, etc. it has become clear to me that something must be said about the parasitic drag of the blades. On all wind turbines but especially these verticals, the blades, no matter how carefully designed with well-studied profiles and how smooth their surfaces, are subject to parasitic drag. When the blades are moving straight into the teeth of the wind nothing can reduce this quite substantial drag on even the best designed blades except creating the blades to be thinner. Somehow they have never been thin enough.

All the kings horses and all the kings men of the past history of wind energy studies at all the Government Labs and in all the large companies involved with this work have not come to terms with this simple concept. It might have something to do with the extensive borrowing of aerodynamic work from aeronautics, in which wing drag in the age of supersonic flight has never been very high on the list of things to write home to Mom about. In wind energy it surfaces as a much more important part of airfoil design.

There is no use in rebutting comments such as these or in making these comments seem out-of-the-mainstream. This is basic truth of the type that will become well known one way or another. Until recently, even I didn't fully understand the importance of these statements. In putting together some hardware of my own, I saw with my own eyes the disastrous flutter on the leading edges of my small vertical axis wind rotator as the blades turned around on their rotation into the wind. I could see immediately that this was an important cause of all vertical axis troubles. I could see that what I was witnessing and what I had learned from all my contact with the technology were two different things.

It is like a completely new chapter is yet to be written in all of wind energy. The blades on wind turbines have not been taking into account sufficiently the presence of parasitic drag.

Anthony Chessick

www.integener.com  

[windstuffnow]

  A few observations on my own over the years.  The wing design of small aircraft, such as the ultralight and experimental, has offered a considerable amount of insight for the vertical machines.  I've had the opportunity to fly a number of these machines over the years.  Some are quite "slipery" through the air and some just aren't.  The basic difference is wing design.  The enclosed wing gives you lots of speed but it takes a bit of speed to get you off the ground as well.  This includes some with a high camber.   Two of them I was really impressed by by their lifting ability as well as controllability at extreemly slow speeds.  The difference was both of them were single surface wings with a large curve in the wing forming the airfoil.  One was a 24ft wing span and would come off the ground at 22mph fully loaded ( around 600 lbs ).  In the air it was very difficult to stall, and I do mean difficult.  If you had any power at all ( even idling the engine) you could pull the stick back to your lap and it would simply buffet.  Although you were loosing altitude it did not stall and nose over.  I could land this thing in a 50 ft square area and turn around and climb out clearing 50 ft trees.  Anyway, after downloading the NASA software and checking lift for a number of wing variations I found these wings have an extreemly high lift in low winds.  Thus the Lenz turbine was born.  Clean, sleek,enclosed and smooth airfoils are great in high speed applications but don't take advantage of the slower speeds (and wind) that they could.  I also believe this design would work very well in Horizontals as well.   This wing design suffers in higher winds or tip speeds but most of us see 6-20 mph winds most of the time anyway.

  In ending, parasitic drag is more promenant in high speed wings which is where the darrieus type verticals could use some help, the slower units the parasitic drag is barely neglegable and I would be more concerned with other aspects of the design.  Just my opinion based on observations...

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[windstuffnow]

  A few observations on my own over the years.  The wing design of small aircraft, such as the ultralight and experimental, has offered a considerable amount of insight for the vertical machines.  I've had the opportunity to fly a number of these machines over the years.  Some are quite "slipery" through the air and some just aren't.  The basic difference is wing design.  The enclosed wing gives you lots of speed but it takes a bit of speed to get you off the ground as well.  This includes some with a high camber.   Two of them I was really impressed by by their lifting ability as well as controllability at extreemly slow speeds.  The difference was both of them were single surface wings with a large curve in the wing forming the airfoil.  One was a 24ft wing span and would come off the ground at 22mph fully loaded ( around 600 lbs ).  In the air it was very difficult to stall, and I do mean difficult.  If you had any power at all ( even idling the engine) you could pull the stick back to your lap and it would simply buffet.  Although you were loosing altitude it did not stall and nose over.  I could land this thing in a 50 ft square area and turn around and climb out clearing 50 ft trees.  Anyway, after downloading the NASA software and checking lift for a number of wing variations I found these wings have an extreemly high lift in low winds.  Thus the Lenz turbine was born.  Clean, sleek,enclosed and smooth airfoils are great in high speed applications but don't take advantage of the slower speeds (and wind) that they could.  I also believe this design would work very well in Horizontals as well.   This wing design suffers in higher winds or tip speeds but most of us see 6-20 mph winds most of the time anyway.

  In ending, parasitic drag is more promenant in high speed wings which is where the darrieus type verticals could use some help, the slower units the parasitic drag is barely neglegable and I would be more concerned with other aspects of the design.  Just my opinion based on observations...

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