Author Topic: Can We Talk Stabilizer Geometry?  (Read 3311 times)

soepkip

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Re: Can We Talk Stabilizer Geometry?
« Reply #15 on: August 14, 2020, 03:16:19 AM »
PS:

Here are the two printable shims that Axis offers (+/- 1 degree).  I do wish that they would sell these.

https://axisfoils.com/collections/foil-parts-accessories/shim

I added the two shim files to my cart and it seems I have to pay for them...

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Re: Can We Talk Stabilizer Geometry?
« Reply #16 on: August 14, 2020, 03:29:19 AM »
I see this on the order page:  These files are free for download, just add to cart and proceed as if you were shopping online. At the checkout page you'll be provided with a downloadable link and a copy will be sent to the email you provided.

Maybe drop them an email.
« Last Edit: August 14, 2020, 03:31:59 AM by Admin »

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Re: Can We Talk Stabilizer Geometry?
« Reply #17 on: August 14, 2020, 03:58:45 AM »
The purpose of the incidence angle is to push the front wing into an angle of attack that increases the lift. That's completely a function of the angle between the stabilizer and the wing.

Agreed but it is not just the angle.  The amount of downforce is determined by the stabilizer size and shape as well.  Two stabilzers at the same negative incidence may have very different downforces but using the delta system they would be treated as equal.  Similarly the amount of front wing lift depends on the specifics of that wing.  That is why measuring both to obtain a single difference number is only valuable in a closed system (specific wing and stab) and when you know the number you are trying to hit.  The problem with what were seeing people doing with these tools on the beach was that they had come up with a number (2 degrees difference) that they felt would be good on all closed systems.  I think that is a mistake.  Since we are only adjusting the stabilizer angle and since we have no real target number for any Axis foil combo it makes sense to me to simplify the stab measurement as much as possible.  Measuring the front wing is tricky but measuring a tail angle against a level fuselage/mast plate is easy. 
« Last Edit: August 14, 2020, 04:03:11 AM by Admin »

PonoBill

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Re: Can We Talk Stabilizer Geometry?
« Reply #18 on: August 14, 2020, 08:14:26 AM »
Well that started off as a great arguement and then wandered into la-la land.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

jondrums

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Re: Can We Talk Stabilizer Geometry?
« Reply #19 on: August 14, 2020, 11:39:33 AM »
can I take it further into la-la land?  :P

I can say with absolute certainty that installing your tail wing upside down does not work.  After I got out to the break this morning and bailed off the first two wave attempts I realized that I did exactly this.  Tried a few more waves just for science and the foil was unrideable for me.  (this was GoFoil 14.5 tail with short pedestal)

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Re: Can We Talk Stabilizer Geometry?
« Reply #20 on: August 15, 2020, 01:28:08 AM »
Well that started off as a great arguement and then wandered into la-la land.

Wait, we don't agree yet? 

Measuring the front wing is possible but without working up a really stable measurement scenario (above) it is going to produce junk info.  It is also irrelevant without a target angle difference (and as far as I know none of those are available).  Without that we are left just making adjustments to the stabilizer angle.  You can do that by feel or by measuring your incremental stabilizer adjustments directly. 

Neil Pryde has a very cool adjustment feature on this windsurf foil system:  https://www.neilpryde.com/products/flight-f4-evo

I plopped their 3 sample adjustment images (which they have labeled Neutral Down and Up) onto the online protractor mentioned above.  Of course the names are unimportant but what they are calling Neutral is -3 degree incidence, Up is Zero degree incidence and Down is -6 degree Incidence. 

« Last Edit: August 15, 2020, 02:47:45 AM by Admin »

PonoBill

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Re: Can We Talk Stabilizer Geometry?
« Reply #21 on: August 15, 2020, 09:13:40 AM »
I don't know why I'm even trying, but what the hell, I type fast.

The stabilizer affects the wing. All the fuselage is doing is holding the wing and stabilizer. The action of the stabilizer is a function of the incidence angle operating like the elevator in an airplane, plus any lift caused by the foil and AOA of the stabilizer. The lift of the stabilizer is a complex calculation that changes dynamically as the stabilizer AOA changes and it doesn't yield a result we can change other than swapping out stabilizers. But we can change the stabilizer incidence angle easily, and record what changes we tried if we know the angle of the stabilizer relative to the wing. There's no particular trouble measuring the wing angle, either with your visual protractor or with an incidence gauge. The wing's centerline is just a line drawn between the center of the leading edge and the center of the trailing edge, easily found with V-blocks at both ends of the gauge (or notches in a set of calipers). And a shaky platform is no big deal as long as it can't move in the direction of the pitch. Not hard to do with a five-foot board, the nose of the board would have to move an inch to change the angle by one degree assuming the tail is fixed (tan 1degree * 60 inches).

If you're thinking that the angle of the baseplate is important in all this, realize that with the board in the air the rider shifts weight to trim the foil to a stable angle where the elevator effect and lift of the stabilizer are balanced by the weight pressing the wing down. Having the nose of the board tipped up or down doesn't affect what that stable angle is, it's purely a function of the lift and incidence angle of the stabilizer. If you want the board to be flat when the foil is trimmed you shim the baseplate, which is just shimming the board angle relative to the baseplate and has no effect on the foil's trim angle.
« Last Edit: August 15, 2020, 09:17:09 AM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

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Re: Can We Talk Stabilizer Geometry?
« Reply #22 on: August 15, 2020, 09:44:38 AM »
We don't disagree on most of that.  The angle of the baseplate is the angle of the fuselage which by definition determines the angle of incidence for anything static (individually) that is affixed to it.   That is the easiest angle (stabilizer incidence) to measure.  That doesn't negate the importance of the relationship of the stabilizer to the front wing, we just gain nothing by measuring it.

But now we have come full circle and this is where we usually start again.

Stevenson is going to be fun today :)


PonoBill

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Re: Can We Talk Stabilizer Geometry?
« Reply #23 on: August 15, 2020, 10:58:39 AM »
Yeah, no.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

jondrums

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Re: Can We Talk Stabilizer Geometry?
« Reply #24 on: August 15, 2020, 12:41:51 PM »
I'm a little lost, but I think I agree with Pono that angle of the baseplate doesn't matter.  All that should matter for how the system performs is the relative angle of the stab to the wing.  angle of the baseplate or fuse is not really a factor in my opinion

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Re: Can We Talk Stabilizer Geometry?
« Reply #25 on: August 15, 2020, 03:40:03 PM »
Measuring stabilizer angle against the fuselage angle is the best and most accurate way to make and confirm your stabilizer adjustments.  The fuselage and baseplate are parallel in our our instance (lucky us) so if the baseplate is set on a level surface (simple to check) you can get an accurate stabilizer measurement in relation to a level surface with no special tools.  Your results will also be 100% repeatable and accurate once changes have been made.  That is the extent of it. 

Using the Delta method, should you have the correct tools and brace well you will end up with a single number.  Lets say we are measuring an Axis Foil set and lets use the resulting value of 5 for instance.  That will be the degree difference from the angle of the front foil and the angle of the stabilizer.  So you have the number 5.  What do you know?  Nothing.  You have the number 5 which will inform no action.  From there you can reduce or increase the stabilizer angle.  You could have done that with no measurement at all.  All you have done is find the most complicated way to establish a baseline number to adjust from.  The easiest way to establish a baseline measurement is the most direct one.  Simply measure the angle of the only element that you will adjust. 

As I mentioned before, the only reason why the Delta measurement would be valuable is if you have supplied knowledge of known good settings taken using that method.  If you don't it is an exercise in window dressing.

Incidence is always measured as the angle of a fixed foil (or other fixed element) in relation to a horizontal fuselage.  Always.  In airplanes that angle sets the angle of attack (which is a relationship to flow) while the wheels are still on the ground.  That is where this reference comes from.  Both the stabilizer and the front wing have an incidence angle.  The difference between those two angles is, of course, the same angle difference that is used in the Delta method. Lets say the front wing has a positive incidence of 2 and the rear wing has an incidence of negative 3.  There is you 5 difference.  Of course if the front angle was positive 10 and the back was positive 5 you would have the same resulting 5.  Without supplied reference it is a useless number.

I have no problem if someone disagrees but do tell me what you are going to do with your prized number 5 that you couldn't have done with no measurements at all.  :)
« Last Edit: August 15, 2020, 04:03:34 PM by Admin »

PonoBill

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Re: Can We Talk Stabilizer Geometry?
« Reply #26 on: August 15, 2020, 05:09:40 PM »
Oh my god.

Nope, nope, nope not going there.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

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Re: Can We Talk Stabilizer Geometry?
« Reply #27 on: August 15, 2020, 05:55:48 PM »
Ughh, no.  That was a massive dodge :)

Do tell me what you are going to do with your prized number 5 that you couldn't have done with no measurements at all. 

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Re: Can We Talk Stabilizer Geometry?
« Reply #28 on: August 16, 2020, 10:44:17 AM »
hold on to ya zimmer frames. why dont we move the stabilizing down force out to the main wing tips, sweep the wing tips aft so the stabilizing force is aft of the centre of gravity- the red mast in this case- and chop the fuselage off all together. problemo solvo.

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Re: Can We Talk Stabilizer Geometry?
« Reply #29 on: August 16, 2020, 10:58:19 AM »
 11 degrees of twist from root to tip and no fuselage to act as a datum!?

 


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