Windspeed x 88 / ( Dia x Pi ) x TSR = RPM
Windspeed in mph Diameter in feet
An Example:
12mph wind x 88 / ( 6ft prop x 3.14 ) x 6 = 336 rpm
Have Fun Ed Have Fun! Windstuff Ed
Have Fun Ed Have Fun! Windstuff Ed[ Parent ]
Would this formula work for an H-Bar Darrieus? Or is there another more suitable. I'm thinking the unit I'm building (10 ft. diameter x 6.25 ft. high blades) will be happy between 175 to 225 rpm.
Another question, I've read varying opinions about speed control, some say it's needed, others say the Darrieus is self regulating to a degree. I'm going to incorporate speed brakes on this thing anyhow, but was wondering how necessary they really are...
Ted.
This IS fun![ Parent ]
The speed brakes (spoilers) are mounted on the upper struts, deployed by centrifugal force. They will be set to start deploying at 250 rpm. They deploy up into the wind stream so the resultant force is down against the tower. I figured at least I could make RCF work FOR me in that small way. There's a disk brake too in case that fails. And an aircraft type woven cable through each wing, bolted to the torque tube in case both of those fail so the pieces will stay close to the tower.
At 2 lb per blade and 450 rpm TSR 4 I make it 690 lb. (Yikes is right...)
Thanks for the formula - I really like things distilled to the KISS principle wherever possible.
This is a lot of fun - I'll post pics once this thing is done. Hopefully about 2 weeks.
Ted.[ Parent ]
Destructive is right! Something like http://www.fieldlines.com/story/2003/10/29/72741/101
I'll be trying a few different composite blade coverings this week to see if I can get something strong enough that's less than 2 lb. I do a bit a flying too and one of the things that was stressed to us back when I was studying for my license was a good pre-flight on the prop. Cause if a blade flies off during flight the resulting imbalance can cause some pretty bad stuff to happen to the remaining rotating assembly - like a motor coming off for example. Then the C of G moves so far aft the whole thing becomes 100 percent uncontrollable.
I kind of like the larger diameter idea - I am trying a Darrieus first, but I'm planning a 12 foot or so prop model next. If the diameter is big, and the rpm's are controlled the machine can rotate relatively slowly and still capture significant power.
It is a lot of fun!
Lots of Fun as a learned experience to look back on, not necessarily fun at the time. Found out later that a nyloc nut was a replacement for a steel lock nut.. Can't do that on an exhaust system... nylon melts.
Ed Have Fun! Windstuff Ed[ Parent ]
OUCH! Well I guess you're the level-headed type under pressure! Never had a forced landing other than the 1,000,000 times the instructor pulled the power - lots of times under the hood. It's interesting flying along on instruments, keeping your scan, and wondering why there's constant downwards altitude creep... Thankfully never the real thing - yet.
Found this kinda neat program to play around with props: http://www.mh-aerotools.de/airfoils/javaprop.htm
If you click the "The Applet" link on the left, then scroll down to near the end of the page there's directions on how to download a free copy for your PC. Alternatively you can just run it from the web page.
Depending on the various problems that are still waiting to crop up, the HAWT may actually make it onto the pole first, who knows. I liked the downwind turbine on your web site, thinking about something like that but about 12' dia. And an airfoil the same height as the blade's radius for the pole, you know, linked to the rotating head so it pivots around with the turbine and lessens the turbulence downwind of the pipe...
Lots of fun! Ed Have Fun! Windstuff Ed[ Parent ]
