Author Topic: Which way to furl?  (Read 1023 times)

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Shadow

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Which way to furl?
« on: February 01, 2005, 05:01:46 PM »
Currently building a dual rotor machine, built everything according to Dans 10 foot and Hughs workbook. However I've noticed When facing front of rotor Dans alternator is slightly off to the right, tail off to the left, so when furled the tail will rise up to the right to meet the alternator, Now on mine I've noticed when facing it from the front my alternator is off to the left, tail off to the right, when furled tail will swing to the left to meet the alternator. If both these machines are rotating clockwise will they both furl either way? (His obviously does but will mine?) Everything else is built to plans.
« Last Edit: February 01, 2005, 05:01:46 PM by (unknown) »

Flux

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Re: Which way to furl?
« Reply #1 on: February 01, 2005, 10:56:25 AM »
It will be fine.


Flux

« Last Edit: February 01, 2005, 10:56:25 AM by Flux »

Ungrounded Lightning Rod

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Re: Which way to furl?
« Reply #2 on: February 01, 2005, 01:37:20 PM »
They will both furl.


The only issue with which way they furl with respect to their rotation occurs if they're close enough to the tower and the blade flex or bearing slop that gyroscopic forces might make the blade hit the tower.


If I've got this right:  The problem is greater during furling  than unfurling.  During furling the wind is already strong and the blade is spinning fast, creating strong gyroscopic forces.  Then the wind gusts even higher, the tail pops up and stops opposing the drag on the off-center blades, resulting in an abriupt yaw.  During unfurling the blades will have slowed down, reducing gyroscopic forces, while the tail's ability to yaw the blades back into the wind is limited by the same tilted bearing AND is opposed by the drag on the blades.  So unfurling yaw will be slower.


So you want the gyroscopic forces from the furling yaw to push the blades AWAY from the tower, and are willing to accept the slower unfurling yaw to push them toward it (because it's to a lesser extent and under less extreme conditions).


Gyroscopic forces occur because a force trying to turn the axis of a rotating object acts with the sine of its position.  So it speeds up over part of a cycle, and by the time it's moving maximally it's a quarter-turn around from the maximum accelleration.  Then it decellerates over the next quarter-turn.  So the motion from the force is shifted a quarter-turn with the rotation.


You say your machine is rotating clockwise as you face it from windward, and the alternator is offset to the left in the same view.  That means in a yaw the blade at 3:00 will be pushed toward you (away from the tower), and thus gyroscopic forces will push it away from the tower at the 6:00 position:  Just what you want.  Dan's machine, on the other hand, will have the blades pushed toward the tower.


Of course if your blades and bearings are stiff enough and/or your blades are far enough forward from the tower, it's not an issue.  If it becomes an issue, it will be less of an issue for you than for Dan.

« Last Edit: February 01, 2005, 01:37:20 PM by Ungrounded Lightning Rod »

Shadow

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Re: Which way to furl?
« Reply #3 on: February 01, 2005, 03:28:03 PM »
Whew!.. Thanks guys sometimes these little things can set off an unwarranted panic attack..lol..I worry too much.
« Last Edit: February 01, 2005, 03:28:03 PM by Shadow »

JW

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Re: Which way to furl?
« Reply #4 on: February 01, 2005, 08:32:05 PM »
First off,


 I wanted to give DanB time to weigh in on this matter.


As far as the regards, as to left or right in-clan-in-atation, of(gravity)furling with regards(to left or right with wind direction facing)... Flux is correct 15% wieght offset(difference) means very little, when one considers, the forces encounterd, at deflection of angle of attack(incomming wind forces).


 Yet this is in fact measurable...


What really screws with me is the (air speed at the blade tips/impetus) in relation to an air bearing...


 Think about it this way, Goddard sat on a stool with a bearing axle suspending a bycicle wheel of 24in dia(maybe less). at a given diameter(dia) rotating at a given"rpm". The 'tangental' off-set of the bycicle "axle' would cause Goodard to revolve clock'wise or counter-clock'wise depending on orientation. Hence the birth of the modern gyro..


  The (compound)"tangental' furling angle, with relation to wieght, affects center of g, causing  "yaw"? with relation to given tolerance to weight X force of windspeed. Its my suspition that at max rpm of the rotor, the 'thrust' of inherent discharge(at tip surface) accomodates some sort of "air bearing" that neutralizes the tolerance factor to 1/3rd of in comming wind speed balenced by max alt capacity(rpm), thru some sort of "air bearing effect at the blade tips? depending on load and swept area?


please forgive any misgivings, just having fun postulating...


JW


 

« Last Edit: February 01, 2005, 08:32:05 PM by JW »