Large one blade prop, am i nuts to consider it?

[zubbly]

hey guys!

just starting to wonder if i am going a little bonkers      LOL!

this is just an idea for now. but i may just do it depending what you fellas think.

hopefully my 7.5hp conversion will be going up soon. i have a 12 foot diam prop for it. it was actually made to replace the smashed prop from last years tower crash, and it was for the 3hp conversion.  i know it will be small for the 7.5hp, but it will give me what ever it can for now.

the crazy idea.........

i will likely make a larger prop, and making props are a lot of work and require lots of good lumber which is expensive. the idea to cut back on material and labour is to make a one blade prop. ok, now you can all say i am nuts, i may agree.

i have only seen one attempt on this board last year where someone made a replica of a maple tree seed. i wish to make it according to altons blade program. balance will not be an issue as it can be easily done with a counter weight close to the hub.

are there associated problems with vibration as in 2 blade props?  does anyone see any benefits or serious problems associated with doing this? the blade may be in the 8-10 foot length giving a swept area of 16-20 feet. the one blade would be sandwiched between heavy plate steel and well constructed with laminating the wood.

i like experimenting but don't want it to be a total loss from unforseen problems that i do not know exist.

ok, what are your thoughts?

LOL!

zubbly

[A6D9]

I say be careful do your research and have fun.

Just think it thru, if the great zubbly wants to set a goal, the great zubbly should accomplish his goal.  

[Flux]

They never seem to have been accepted so that may be a clue.

They are best suited to very high tsr and the vibration issue associated with high speed would rule it out from my consideration. If I had to try it , it would be with a servo yaw scheme. I am sure the thing is worse than 2 blades during yaw and probably by quite a lot.

I suspect you tolerate higher speeds than I can from the speeds you quote for your conversions so you may not find it quite so offensive, but in any machine free to yaw ( with a tail) 3 is the correct number for me.

I have to admit that I haven't tried so no first hand experience.

flux

[hvirtane]

I think that vibration would be a quite big problem with a one blade prop.

Why don't you make the prop with two blades with a worm gear to direct it to the wind and furling with an upward hinge? We have developed a special method to make special blades really easily and cheaply:

http://www.fieldlines.com/story/2005/12/29/205319/65

- Hannu

[whatsnext]

I would say that it would not work at all and that all the problems associated with two blade props would be compounded. As everyone here should know by now there are two types of balance, static and dynamic. Static balance is very easy to reach with almost any design. Dynamic balance of a one blade prop will be impossible without cancelling your power. You want the dynamic loads applied evenly around the hub and if you can figure a way to do this with one blade please let us know. Find a video of a super ultralight indoor freeflight model plane and you'll see how the center of rotation is not in the same place as the center of static balance, just like on a maple seed, so your tower will have to be very flexible or it will tear apart. So, to answer your question. Yes you are nuts.

Respectfully, John...

[willib]

Zubbly , i have done this

last winter some time... when working on my 9 inch blades ( 12 inches center to tip), when i only had one to work with that was compleated  at the time,

it wasnt really vibration as much as a severe wobble, due to one blade spinning .

i just could not imagine the forces on a single blade , of a larger size as you are proposing.

if you're gonna make one , then make two more  like the first one, thats all..

is the conversion back from the shop yet?

[zubbly]

hey guys!  

thanks for all the info and the confirmation i am nuts  

i was just thinking out loud trying to save some $ on lumber and lots of time.

balance i didn't see as an issue, but never thought about the wobble it would create.

i did have a very good experience where a 9 foot 2 blade basically tore the base apart of one of my gennys.  if 1 blade would be worse, then i totally forget the idea.

3 blades are the best, and all the 3 bladers i made have been kind to me.

talk about a quick wake up    LOL!

thanks guys

zubbly

[wiredwrong]

I was just wondering if you had seen the one bladed ceiling fans? it almost looks to me like it may make a good downwind machine, but I too would think that it may have trouble when it turn to track the wind.

[inode buddha]

I say, that's interesting. Look at how they balance motorcycle engines, its almost like tuning some electronics. I'm thinking almost in musical terms here, see a single massive counterweight would balance out the first major (even) harmonic at a given RPM. Kinda like the crankshaft from a bus engine. But what if you added counter-shafts with weights; and gear the counter-shafts to both an even and an odd harmonic? Yeah you might need to add a foot or so to the prop blade to make up for the mechanical inefficiencies; but would the gain of a wider RPM operating range make up for it?

Just thinking out loud here. And hey, its OK to be nuts.

[Countryboy]

Hi Zubbly,

  Don't knock something until you have tried.

  My advice would be to build a small 1 bladed prop as an experimental piece.  Heck, just let it be a lawn ornament type windmill, just so you can get an idea of what kind of vibrations (or other problems) it will have.

  Once you've tried it and have some hands on experience, then you can decide if you like it, or if you should flush the idea.

  To counter the argument about static and dynamic balancing, please think about the tires on your car.  Static balance is the old bubble balancers.  Dynamic balancers are the new spin balancers.

  When dynamic balancing a tire with a spin balancer, you add weights to one specific diameter, the rim.  Even if the dynamic imbalance is at a different diameter, you CAN balance the tire so it spins without vibration.

  I think the vast majority of vibration problems you would encounter with a one bladed prop would be due to improper balancing.  Balanced correctly you should have minimal vibration problems with it.  (However, it is going to be a difficult task to properly balance.)

[nothing to lose]

When I was making barrel blades from 35gal plastic barrels I tried a couple one bladed rotors. I think it was about the same time as the Maple seed was tried and probably what gave me the idea to try one blade.

I did not like mine but you might be abe to make it work better.

My 1 barrel blade did not seem to have much vibration and ran "OK".  I had found I could cut the barrel more towards one end and the shape would push the blade forward away from the tower and into the wind, an angle forward and not straight outwards. Being the plastic barrel blade was a little flexable I used that to my advantange. The conter weight was near the hub but outboard some like the root of a blade and just a little forward. At low RPM Low wind the blade leaned more forward but was turning slower so balance was not as critical as at high speed and worked well. At high speeds when winds were good I had a combination of centrifical force and wind presure pulling/pushing the blade straight. At the higher speeds then with the blades closer to straight outwards I was more balanced Dynamically with the counter weight. The counter weight if needed could also be set up to move forward at low RPM and to the rear at high RPM by centrifical force thus keeping the blade in balance Staticaly and Dynamically I think. As I recall I did try mounting the counter weight to a thick piece of barrel side so it would also straighten out at high speed when the blade did. Been so long now.

Although mine was only about 30" blade or so for a 60" sweep, 5', plus a few inches added by the hub it worked "OK" but I did not like it and had little interest in it and went back to 2 and 3 blades. I thought 1 blade looked goofey myself and preffer the looks of 3. Also I think I needed a larger blade when using only 1 than I did when using 3. I am certain I got far more power with 3 the same size as only one, which makes sense of course. With a larger blade I needed more material and a barrel only has so much usable side for length. I think I had some minor problems maybe but I don't remember what they might have been, must not have been very serious ones.

It's been along time and I forgot most the details on the 1 blader now. I think if you had a real interest in trying it, a smart guy like you could make it work if it will.

[stevesteve]

Have you seen Ben's experimental version:

http://www.gotwind.org/latest_experiments.htm

There's a movie clip and it looks pretty smooth!

[willib]

Did i mention that mine did Not have a counterweight  

[whatsnext]

I have to say that that video doesn't really tell much. If that is as fast as it spins it would put out no usefull power and since such a small prop bolted to such a thick tower you wouldn't see the problems until it was too late. This is something I don't understand about this board. It is my understanding that this is supposed to be a forum for practical RE devices and yet many of us act like 17th century explorers who pretend that there is no base of referrence from which to guide us. A one bladed prop is no more original than a two, three, or four bladed one and has been tried many times. The problem with them is that there is no way to balance the forces that the prop generates while spinning. Since we know the forces are not directly porportional to RPM they become problematic to overcome. This is one reason why you don't see any because it's not like it's never been thought of before. So what would be the point of spending time, which is limited, to just "try it"? If the Dans had a category that was something like "Ideas from people who just don't trust the engineers and scientists that came before us" then this "try it" attitude would be well placed. I just don't get it here.

Just my 2 cents, John..

[TomW]

John;

Remember, it is not acceptable to say "it will not work" to any idea regardless of how retarded or unworkable it is or has been shown to be.

Never tell baby no it might force reality on them.

You can not think outside the box effectively until you know what the hell is inside of it. Simple fact.

Any more I usually just watch because for health reasons I cannot do much building.

T

[RP]

"Remember, it is not acceptable to say "it will not work" to any idea regardless of how retarded or unworkable it is or has been shown to be."

Thanks a lot Tom.  Now I have to clean the soda off my monitor and change my shirt.

;-)

[whatsnext]

Sorry Tom,

Every once in a while I get tired and think to myself "hey, logic should prevail" and, being tired, I share my thoughts with others. I really need to learn.

John...

[Ungrounded Lightning Rod]

Actually you can get static and dynamic balance of a one-blade prop with no problem.

What you CAN'T do is balance the WIND LOADING.  It will be centered far off-axis and will wobble the mill big-time.

I've been trying to think of ways to get the blade to tilt and balance ala the spin of a maple seed (where it tilts back so the dynamic imbalance fights the off-center load) but that would take modeling to even check.

[whatsnext]

I just assumed that "wind loading" would be part of the dynamic balance equation seeing as how it's the wind spinning the prop. Sorry I wasn't more specific.

John..

[Ungrounded Lightning Rod]

"Dynamic balance" is a well-defined technical term referring to the distribution of mass around the axis.

[whatsnext]

Unless you are looking at the entire system and not just the rotating mass, which I was, in which case using the term would be perfectly acceptable and is done so commonly in engineering texts. Not that it really matters because the point was all along that a one bladed prop would have unbalanced force around the hub which would appear as a static balance issue once the blade was in motion. It just isn't a good idea but anyone who chooses to try it can find out for themselves instead of using their time productively.

John...

[rotornuts]

Can't be any crazier than that.

Dynamic balance isn't impossible to overcome but uneven loading of the rotor is a problem that needs a solution.

After the things I've tried making a single blade a downwind machine with a teetering hub is a start in my mind. The next step is to have the counter balance side produce a load even if it's drag but preferably lift. Large wide fat airfoil root. 1/3 blade length counterbalance side, 2/3 of the large blade side to produce lift or something like that.

Mike

[wdyasq]

Just put a signature line on that they can't understand - that raises concern. But, don't mention safety, it might hurt their ego. And heaven forbid on't sugest they do a bit of research.

Ron

[Gary D]

Zubbly, a thought from an uninformed/ inexperienced jerk here.... Dan's 10 footer hits cutin at 150rpm about 7 mph. So at 28 mph it would hit the 600 you were looking for(allowing voltage to rise). If your 12 foot set has a slightly higher tsr, you might get the same results at approxamately the same windspeeds? Havent a clue on how a fixed resistance will drag down your rpm's tho (uninformed), but if it spins, it will create heat... Have fun experimenting! Unwelcome/useless poster rooting for you! ;-D Gary D.