Author Topic: tail size (Read 7485 times)

defed · « **on:** June 12, 2010, 05:29:57 PM »

i put my piggott 4' up on a test tower today. it's only about 15' tall, but wanted to see what it did. i made the tail 8"x20" as the book said and mounted it with the 20" vertical. it's a LITTLE bit smaller because i rounded the corners and tapered the front edge back (bottom wide, top narrower) but it's a small taper.

it seems to having trouble turning into the wind. if i get in the tractor bucket, the mill seems to yaw easy by hand, but the tail will flutter back and forth a bit. if i turn the mill out of the wind, sometimes it goes back easy, sometimes it doens't want to move. i had it 180 degrees out of the wind and it didn't want to move at all.

how do i know if it needs a larger tail? just try it and see?

the other thing that may be to blame is the wind is coming from the worst possible angle today. usually it comes from the south west which is wide open, today it's coming north west where there are some trees that have adverse affects w/ this short tower. they are going to get shortened eventually, and the real tower would be well above them anyway.

i hooked wires up to the stator for emergency braking, but unfortunately, it never came close to running away. need to get an anemometer so i can verify the wind speeds. but i can certainly tell they are much high 30' and 50' up than they are at 15' by looking at the trees.

dwpeters12 · « **Reply #1 on:** June 12, 2010, 05:53:24 PM »

I have built the same turbine and am having the same trouble!

Mine is 30 ft. in the air and if i climb up it turns easy if you do it by hand! It just has trouble turning into the wind when it isnt very strong. I think i am going to try a bigger tail.

Hilltopgrange · « **Reply #2 on:** June 12, 2010, 06:22:42 PM »

Hi,
this might seem silly but have you checked the tower is plumb and true? if not the turbine will be climbing a hill to yaw.
Maybe you have just not got enough wind yet, this is perfectly normal, the surest way to cause a calm spell is to raise a turbine!

Russell

defed · « **Reply #3 on:** June 12, 2010, 06:28:17 PM »

here's some pics of it up on the test tower.

defed · « **Reply #4 on:** June 12, 2010, 06:30:11 PM »

i wanted the pics to open in the posting, but apparently i made them to big to do so!

well, i made them smaller and they still didn't open in the posting...can you not do that anymore?

defed · « **Reply #5 on:** June 12, 2010, 06:31:31 PM »

i guess the tower COULD be out of plumb. i'm sure it's not perfect, but i believe it is close, tho i haven't actually checked it lately.

fabricator · « **Reply #6 on:** June 12, 2010, 08:50:29 PM »

The area of the tail seems small to me, seems like I remember the tail should be 20% of the rotor size maybe?

defed · « **Reply #7 on:** June 12, 2010, 09:14:41 PM »

i thought it looked small too, unless Hugh's book has a typo for the tail size, it is the "correct" size.

i think i will take all the turbines in Hugh's book, calculate the tail area vs rotor swept area and see if they all have the same ratio.

ChrisOlson · « **Reply #8 on:** June 12, 2010, 09:50:43 PM »

Quote from: fabricator on June 12, 2010, 08:50:29 PM

The area of the tail seems small to me, seems like I remember the tail should be 20% of the rotor size maybe?

I depends on the length of the tail boom too. You can have a big tail on a short boom and it won't steer the turbine, and you can have a smaller tail on a long boom and it will steer it fine. As far as I'm concerned all these hinged against gravity tail systems have too short of a boom and got the tail too close in back of the blades where it's protected too much - and the result is that they don't steer decent and yaw back and forth every time a little gust hits the rotor.
--
Chris

Boss · « **Reply #9 on:** June 12, 2010, 11:08:33 PM »

Quote

well, i made them smaller and they still didn't open in the posting...can you not do that anymore?

Inline images work in SMF if the url to the image is added via the image icon, Your images were probably added as attachments, thus they are not showing up properly

This image is on my site, I just pasted the image url between the img brackets
B-Man

defed · « **Reply #10 on:** June 13, 2010, 06:28:30 AM »

Boss, i could have sworn i had images show up previously, and i always use as attachments. but then again, i'm on many forums so i could be confused on what works where.

defed · « **Reply #11 on:** June 13, 2010, 06:31:31 AM »

the length of the boom is to Hugh's spec, but what i wasn't sure about was how to mount the tail fin. i sort of centered it, which in theory could be making the tail boom shorter by a few inches. maybe if i have the front edge of the fin on the mounting bar, and let it hang out the back, that would lengthen the effective length of the boom.

DamonHD · « **Reply #12 on:** June 13, 2010, 07:58:40 AM »

defed: we just changed the way that images work here, so likely your memory is right AND we're different to (some) other SMF boards!

Rgds

Damon

eduardomonzon · « **Reply #13 on:** June 14, 2010, 08:40:39 PM »

I had the same problem. I fixed it by doing a new tail twice the height, same width, same lenght. That should be the correct size to comply with the foRMULA where the vane is to be 20% of the area swept. Somebody ought to tell Hugh to fix that. It musto to be a typing error on the manuals

defed · « **Reply #14 on:** June 15, 2010, 06:05:54 AM »

do you have a picture of what it looks like? i was debating making it wider and extending it further back, which would increase the fin size and extend the boom length at the same time.

you are correct tho, the current tail is only 160 sq inches, while 20% of the swept area of a 4' prop is 361 sq in. so double one dimension and it gets close.

defed · « **Reply #15 on:** June 15, 2010, 03:44:24 PM »

i think the answer hit me while i was at work today...the spec for the tail is 8"x20"....if it was 18"x20", that would be 360 sq in, or just about exactly 20% of the swept area of the 4' prop. my guess is the '1' got dropped. there have been a few of that type of typo in the US version book.

Hilltopgrange · « **Reply #16 on:** June 15, 2010, 05:33:59 PM »

The UK metric version is basically the same 20cm x 50cm (7.9 x 19.7 inches) interestingly though the older version in the August 2004 edition gives a size of 18 x 12 inches. Hugh posts here regularly so he might clear this up for you.

Russell

defed · « **Reply #17 on:** June 15, 2010, 08:21:57 PM »

thanks for the info. i left my book out in the barn. tomorrow i will take all the tail sizes and calculate the percent of swept area of each and see if there is a pattern.

defed · « **Reply #18 on:** June 16, 2010, 10:18:46 AM »

i crunched all the #'s and it appears that most of Hugh's tails are about 12% of the prop swept area. some are closer to 15% and the 4' tail is only about 9%. not sure if his tail lengths are meant to compensate, or he just likes smaller tails?

think i will try something in the 20% range and see what it does.

defed · « **Reply #19 on:** June 16, 2010, 12:20:55 PM »

made a new tail today. the blank was 18"x20", rounded the corners, and tapered the front back. it's BIG! i'll post another pic when i get a chance to get the mill back up.

taylorp035 · « **Reply #20 on:** June 16, 2010, 08:37:47 PM »

I once had my 50" with a tail that was too small, and I found that the length of the tail was critical. It think you should mount the piece horizontally instead of vertically. Doing that will increase your length. Maybe a tad larger would help too. My tower is very far off from being vertical, but this tail size worked very well.

Here is mine.

defed · « **Reply #21 on:** June 19, 2010, 10:00:41 AM »

got some fair winds going so i put the mill w/ the new tail back up on the test tower. seems to be yawing really well. the blades will begin turning but i have not gotten more than 5v dc yet. the tower is only 12-15' high so the wind there is not too good. the tops of the trees are really swaying so if only i could get a taller test tower!

still researching weather stations so i can get an anemometer up so i can at least verify what wind i am working w/ at the test tower height. when not using the test tower, i would raise the anemometer closer to what the final tower height would be. at least if i know what winds i am getting at test tower height, i can determine if the mill is spinning up like it should.

Flux · « **Reply #22 on:** June 19, 2010, 03:42:11 PM »

There does seem to be some confusion about this. I have confirmed that Russell is correct in that the original version had a recommended size of 18 x 12".

The other factor is that the boom length does affect things and mounting a rectangle vertically or horizontally on the same length of boom will change the length from pivot to centre of pressure. The little machine is not too critical on furling but changes in the tail effective length will also affect furling.

Normally rectangles are more effective when mounted long side vertical but it may be better to use a longer boom in this case. I suspect going much below the 18 x 12 is not a good idea unless you lengthen the boom but increasing boom length may affect the furling unless the vane material is light.

I have a feeling that part of your trouble may be the low test height, there is often no really useful wind at low level and the smaller tail may work in clean air but even so it ought to track the wind fairly well.

With your specified rectangle size I would make the vane start 3ft from the pivot with it vertical, but I would be inclined to go up to 18 x 12.

Flux

I find that in general a longer tail is more effective than increasing vane size but you have trouble keeping weight down if you increase the boom length too much

defed · « **Reply #23 on:** June 19, 2010, 04:30:03 PM »

true, my test height is not that good. i can see trees swaying like mad all around and hardly any getting to the blades. i have only reached cut in 3 times and maybe only for about 10 mins elapsed time overall. it is yawing nicely now, even at cut in it will track the wind and maintain speed.

the specified boom length is only 28", so as it is, i can't make it start at 3' from the pivot. i have some pics of the new tail i will get on later. trying to reach cut in at least one more time to see if my rectifier is still good after a mishap!

i should note that it looked like it wanted to furl a couple of times, the tail started to turn and lift, but it never got very far due to the weak wind at 12'. but at least if it EVER works at 12', it should work pretty darn well at 50'...generation wise, maybe not furling.

defed · « **Reply #24 on:** June 19, 2010, 04:57:47 PM »

here's the new tail.

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Author Topic: tail size (Read 7485 times)