Darrieus - how big is too big?

[electrondady1]

oop's , sorry mike , i've been home with a virus all week . guess your comment was going over my fevered head.i'll try to pay attention from now on!

shawn

[rotornuts]

No problem shawn. That's just the kind of thing I do all the time.

Mike

[windstuffnow]

  Mike,

    I like it !   It's going to be an interesting machine.  How are you going to lay out the wings?  what size are you going to make it?  Lift on the outside or inside?

    I didn't find that airfoil in my data base but found one similar.  ran it in the nasa sim and it has real good lift qualities.    Making the camber a bit deeper increases lift at lower speeds as well... depends on how your going to use it.

    Here is my theory on inside lift.... See if I can create a mental picture...  Let's say your a pilot sitting slightly behind the wing.  You want to pull the plane into and out of a loop, what happens?  Don't think about an engine helping you through... don't need it.... looped gliders before plenty of power from mother nature.  Does it stall?  Can you do a loop in a tail wind?  The big difference here is the amount of energy thats available to make the "loops". Were working with low energy so the design has to enhance what's there.   Inside lift works with the machine in the direction its spinning, outside lift fights the machine.   An HAWT works similar to "outside" lift.  Part of the lift goes into spinning the blades, part goes into loading the bearings and tower.  If you've ever taken a small lift type turbine and held it in your hand you can feel the force against you when the designed tsr is reached... make it work for you not against you.  

Looking forward to hearing you matched the betz !

.

[rotornuts]

I was working on a mental picture of inside and outside lift myself.

The way I looked at it was I imagined if I had a lever attached at a pivot point with a length of rope attached to the free end what would work better? should I pull the rope away and slightly ahead of the pivot point like an outside lift unit or should I pull the rope across the end of the lever ahead of and towards the pivot like an inside lift machine? In my mind crossing the pivot ahead of center will work way better so I'm in agreement with you on that one. I think to get the best out of these things they should be inside lift.

The GOE 435 I think will make a good starting point. I like the rounded leading edge and the thickness ratio. I'd like to try my hand at tubercles again but I've found them difficult to make beyond something crude. I have this Idea in my head that the open backs on your blades are serving two purposes, assisted startup and low wind performance and ensuring that little lift is produced on the outside of the blade when flying into the wind. The last point could help to explain the successfull into the wind fight. Despite the drag being produce by the backside the lift generated on the inside of the blade is in excess of the drag even at negative AoA's. I'd like to see if I can reproduce that effect using tubercles to produce a favorable pressure distribution on the inside of the blade all the way through the into the wind swing.

I'll likely try my hand at foam and fiberglass again but I'm really tempted to use a frame and skin style for ease of construction the move to a fiberglassed blade if I like the results. I think I'll go with at least two feet diameter this time as 12" doesn't produce enough startup torque for even experimental purposes, I think it skews the results.

I'm still in school doing my first year machinist apprenticeship and CNC operation so it will be a while before anything flies.

I'm always inspired by your designs and your appreciation for simplicity and all you guys with lathes and milling machines seem to have the most fun so I thought I'd join the club.

P.S. I'd like to thicken up the inside of the GOE a bit which would effectively increase camber. By inside I mean the underside of the wing because I will actually use it "upside down" so the bottom becomes the lifting surface, lifting towards the inside of the unit. I like the Cambered profiles because I have this vision in my head of an uncambered wing dragging its tail around.

I have to think more on this though cause I have this nagging in the back of my head saying I should maybe try it the way it was intended to fly and just reverse the swail at the trailing edge. Part of the reason I liked the GOE 435 though is the fact that it looks symetrical so other than the camber it should fly the same upside down and when you consider a Vawt flies an arc is it reasonable to assume the blade is effectively appearing uncambered to the wind? Questions I need to someday asnswer.

Mike