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Sunday's Windgen design - what do you think? | 12 comments (12 topical, editorial)

Re: Sunday's Windgen design - what do you think? (3.00 / 0) (#7)
by kitno455 on Mon Apr 11th, 2005 at 07:10:42 AM MST
(User Info)

dont bother with the second prop. the first prop is going to chew up the air near the root especially, and unless you have a masters or better in aerodynamics, you are not going to be able to figure out how to size and shape the rear blade so that it turns at the same speed as the front one. basically, one blade will be trying to turn faster than the other, and the slow one will be acting as an airbrake, not a windmill. put your force into your alternator, not spinning another fan. put six inch longer blades on front prop, and it will work better.

i did see a big one that worked this way, but all blades were the same, and they had a huge space between them.

also, it has no furling system at all.

allan

Re: Sunday's Windgen design - what do you think? (3.00 / 0) (#8)
by PHinker on Mon Apr 11th, 2005 at 07:37:31 AM MST
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Actually, ballparking this would be pretty easy. Let's say you set up the front blades with a TSR of 4. Benz says that the most you can take out of the wind is 60% (I know, it's 59.3 but we're ballparking here). If the wind's blowing 10 mph and your front blades are good but not great (slow the wind 50%) then the downwind blades should see a windspeed of 5 mph or so. So, front blades TSR 4, downwind blades TSR 8 should give you a good place to start at least. Also, if you set the downwind blades up to 'cone' you can get some decent furling for free.

Paul

[ Parent ]

Re: Sunday's Windgen design - what do you think? (3.00 / 0) (#9)
by kitno455 on Mon Apr 11th, 2005 at 07:49:05 AM MST
(User Info)

nah. the betz equations assume smooth air. turbulence and screw caused be the font blades throws this completely off. no point in even trying.

also, how is flexing the rear blades going to cause furling if the front blades are fixed? the fronts will overspeed, and the centrifugal psuedoforce will keep the rear blades out. the best you can do there is that the rear blades will act as a drag on the fronts, but i doubt that will stop overspeeding. again, this thing has no furling.

long thin shaft like that between your flapping airbrake and your over-speeding blades? fatigue and broken shaft within the first couple gusty storms.

allan

[ Parent ]

Sunday's Windgen design - what do you think? | 12 comments (12 topical, 0 editorial)

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