Adding more blades

[fungus]

Hi,

Just a quick question; when you increase the number of blades does the RPM increase or decrease?

[force9BOAT]

decrease

[ghurd]

One is a nightmare for a computer to figure out. 2 is hard for you to balance, for you.

That's a big part of why 3 blades are common.

[ghurd]

And it relates relates to the alternator.

So 6 blades is not always twice as good as 3. And 3 is not always better than 6.  When everything matches up resonably well.

Things should balance.

I made some crappy PMAs that do better with a 5-blade 20" fan blade than a 28" 3 or 4 blade of reasonable efficiency.  

Either way, my crappy PMAs can't be fixed with different blades. The PMA is still crappy.

Changing the blade count may help, but it won't fix a bad PMA.

Sounds like you are where I was, you are looking for some power in no wind.

It ain't there to be found.

Do not try to get power below 5MPH, or it will be a crappy PMA. Make that 6, maybe 7MPH for smaller PMAs. (directly from the expert on crappy PMAs)  

:/

[dinges]

You could try visiting Alton Moore's windcalculator.

http://www.alton-moore.net/wind_calculations.html

You can calculate yourself to death with that thing. I know I've spent many an hour using it. I love that calculator!

Peter.

[rotornuts]

At the risk of starting to sound like one of the grumpy old men I'll say, Google search the board returns 646 hits for the search "blade numbers".

This is a good example of where a search is in order before the question is asked.

Mike

[wdyasq]

I might resemble that remark!

Ron

[oztules]

Peter

I notice that it asks for the no. of blades, but takes no notice of them

On its's default it gets @.5mp/s. (first line) 27rpm for 2blades, 5blades,20 blades.....

@3mp/s 161rpm for 2 blades, 10 blades 20 blades.....

It seems that it does not take the blade count... into account.

"You can calculate yourself to death with that thing."....Hmmm only if you want the same answer for different blade no's

Try Ed's calculator. From memory it does work out the correct value for the change in blade count.

.............oztules

[oztules]

No Peter,

my copy of Eds calculator (2001) does not reflect a change in rpm for a change in blade no. either.... so where to next.... I've searched the two best programs for this data that I'm aware of or am able to access. Warlock has a calculator which may resolve this, but it is too big for me to ascribe to its suitability for this quandry. (2Mbytes....over 3000 seconds for me to download.... at best.).. so I cannot help any further.

So far the answer from the two most referenced blade design programs to date is not in agreeance with what I believe is the truth..... answer so far is a banana.

(Rotor and wyd....not so quick to condem... which info is correct... the blade programs with their myriad of impressive looking figures, or the usually espoused ( and I feel correct) more blades less speed in same wind.... perhaps he should ask directly....... perhaps not, he may find no information, just grumpy old men.

Banana eating primate.......oztules

[SmoggyTurnip]

Those calculators seem like they

don't take the blade count into

consideration but they do. The

reason they give the same RPM is

that you give it a TSR - that means

it will always give you the same

RPM for a givn wind speed. The cord

width is what changes when you change

the number of blades.  More blades mean

thinner blades but by definition the rpm

will be the same for a given TSR.

.

[oztules]

Thanks for the clarification SmoggyTurnip. Well pointed out. It was right in front of me and I passed straight over it.

now more learned primate.....oztules

[Norm]

  Ditto on that G !

 For the benefit of Newbies...its frustrating !

 Just the difference of a 3mph and a 6mph wind

is amazing ...to a novice this would seem simple

 ...twice the power a 3mph it would take twice

the time to do a job that could be done with a

6mph wind.......Wrong !

...if it take all day to charge a battery with

a certain size windmill in a 6mph wind,,,,

  then the same windmill in a 3mph wind would

take about a week to charge the same battery...

other variables also enter into this...which

could/would make it even worse or impossible

and even knowing this the wind keeps gently

blowing and spinning those dang little pinwheels

....there's energy there ! LOL

                  ( :>) Norm

[wdyasq]

"Banana eating primate.......oztules"

And used cape salesman... Can I get a two for one deal on the capes?

Ron

[oztules]

You might be surprised to know this, but usually 1 cape can do two people. The first one to use  it (quickly becoming safely ensconsed in a pine box) simply passes it on down to the second....economy and recycling......

It's odd how batcape salesman and funeral directors seem to form a symbiotic business relationship.

Failed blade calculator user and Marketing Guru.......oztules