Standup Zone Forum

The Foil Zone => Foil SUP => Topic started by: SanoSlatchSup on August 12, 2020, 08:11:56 AM

Title: Can We Talk Stabilizer Geometry?
Post by: SanoSlatchSup on August 12, 2020, 08:11:56 AM
Flat stabs, anhedral down stabs, stab tips curved up, stab tips curved down, stabs mounted on the bottom of the fuse, stabs mounted on the top of the fuse...wth?  Can someone please help make up my mind as to which shaped stab I want to use when and where.

I get the size and AOA thing and all, but all these different shapes and mounting location reasons has me scratching my head as to what it is they're all specifically designed to do differently, and maybe even more importantly for my Axis selections in the future (I currently have accumulated the 390, 400, and 440)...why that is. TIA.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: jondrums on August 12, 2020, 09:00:10 AM
Going from gofoil flat stab (18N) to the new 14.5 upturned tips made a noticeable difference in railing turns.

It is my view that directional stability will come from all vertical surfaces - and related to both the projected area of the vertical surface and the distance from the turning center.  Super hard to know where the turning center is, so that's a bit of a mystery.  But I do think part of the confusion around tail profiles is because the mast is placed differently on different foil brands/setups.  If the mast is further forward with respect to the turning center, then I'm guessing people are going to really want vertical tips on the tail and vice-versa.

We have to have a mast, so it would be nice to get the directional stability from the mast we already have to have rather than rely on upturned tail tips which add drag.  That means the mast would need to be a bit further back on the fuse.  But then, directional stability will vary with depth in the water as the mast area changes dramatically.  So, hard to know if that's a good solution.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill on August 12, 2020, 09:10:24 AM
I'm equally confused. I know how they are supposed to work, but the reality and the current designs don't match up to theory. Wings aren't making much more sense either. There's at least a hundred years of research into hydrofoils but getting my hands on real data and designs is not easy. I've found one practical book on hydrofoil design. Everything else I've dug up is either irrelevant or covers issues we'll never have. I don't plan on going over 60mph with my foil.

My take is that there isn't any science behind current designs for our use--it's just cut and try. The only thing I've seen recently that made sense to me is some of the Moses wing designs, but they look like they would amputate rather than cut if you fell on them.

Screwing around with stabilizer incidence angle has made my foils a lot more stable in pitch, but my front foot is now on the handle, well behind the footstrap mounts.

I'm not good enough yet to really feel any difference in turning ability with various stabilizer shapes. My wing sizes are going down fast though. Yesterday I was on my new 860 and I convinced myself that I really should have bought the 760. My 440 stabilizer looks almost as big as the wing. The GoFoil Kai used to look impossibly small to me, it's 1200cm*2. The same approximate size of the Axis 900 and 860, and the Kai is much thicker, with a higher foil coefficient. That's just weird to me, though I know velocity is much more important than area, and I'm generally going a lot faster than I used to be.

Every time I try to convince myself that i know what I'm doing with this stuff I look at the variety of current designs and realize I'm clueless.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: bigmtn on August 12, 2020, 10:04:00 AM
Sano, I have no idea. But I can tell you I didn't notice a huge change between the 400 and 370 stab. But the 460 flat stab, gave me a whole different feeling. So I'd pick that one up next. 390 pumps great, but feels really slow compared to the 460. My general feeling with the 900 is 370 surf, 390 winging, 460 downwind. But haven't tried the 460 with the 900 yet. Only downwinding with the 1000.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill on August 12, 2020, 10:08:43 AM
The biggest change in stabilizer I've felt is the 340 shimmed to two degrees. Feels like no drag but it's still stable. I don't know if it helps turning or not, but it feels very loose and skatey, especially with the short fuselage. I should try it with the ultra short.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: tarquin on August 12, 2020, 10:21:21 AM
Not much help but foils are very speed and weight related. A foil that works at 5 kts doesn't work as well at 15 kts. Then you change the angle as well, then you break the surface with it and re enter causing airation and just expect to get perfect laminar flow again. It's amazing they work at all.
 The Americas cup teams and IMCOA 60s are having to develop new computer programs to design foils as existing programs just dont work. Some have turned to F1 teams to use there programs and simulator tech. Mercedes excels in this domain.
 You can see some very different foil shapes and placement in the IMOCA boats. So there is still no right answer. Some will perform better in light air and some better in heavy airs.
 So I guess for the stabilizer some will be better for turning and some will be better for going fast.
 What you want in a foil wing is a soft outer that compresses as speed and pressure increases making the foil thinner. This gives you good lift and low speed and a thinner foil for higher speed. Not easy to do though. You want a foil to flex at the right spot and speed as well. Again giving better shape for high speed. If a curved foil straightens it becomes longer, mainly for avoiding box rules. Also a highly cambered foil that flattens as speed and pressure increases.
 I very much doubt the companies making the foils are using the sort of tech the americas cup or IMOCA boats are using. So I think there is a long way to go for surf/sup foiling.
 No I dont foil.
 But i think my next build may just have foils.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin on August 12, 2020, 10:29:35 AM
Within Axis there is a drop below the 400 from chord at 90 to 80 so the 390 is actually quite a bit smaller than the 400.  The 390 feels a lot faster to me with the wing than the 400 or 370.  Why I am not sure.  I had heard that the 390 had zero incidence which was supposed to have been significantly lower incidence than on the other stabilizers.   The 390 appears to have an incidence (angle in relation to the fuselage and in our use also the mast plate and in many instances board base and deck) of -2.5 degrees so still negative incidence.  I don't have any of the other tails any longer to check those.  Those may have even more negative incidence which might be the explanation for what I am feeling.  It may also be that 390/80 is just a really nice size for me on a certain group of front wings. 

I would be very hesitant to apply a blanket "this design/angle/size works" to anything other than a specific wing and stabilizer.  If something feels off in that closed system then adjust.  Fuselage length is definitely a factor as well. 

Title: Re: Can We Talk Stabilizer Geometry?
Post by: SanoSlatchSup on August 12, 2020, 09:55:08 PM
Thanks all, some really interesting and great responses...much appreciated.

The reason I asked was that having been a GF guy up until a few sessions ago, it was pretty easy to figure out what they were going to do, as it was pretty much just a choice in size because the two shapes of each profile (Maliko/Kai & 18W/N) were basically the same...and having so many to choose from with Axis (one reason I switched) I suddenly found myself with analysis paralysis in trying to figure out which different stab (400, 440) I wanted to try with the 900 instead of the 390 I'd been running with it.

Yes, I could just throw one on and try it, but that's not my personality, I like to do something with a reason and purpose, so having a little idea of what was what with the various designs was intriguing to me. So since I'm really liking the 900/390 combo compared to any of my old GF setups, on occasion when I really stomp on it, I'll sometimes feel the stab sort of fall off or "break through the ice" as a friend of mine described feeling with the GF GL180/18N instead of his normal Iwa/Maliko he just loves.

Also at times I'd get a high speed bobble just setting up a turn, or a pretty good slip/wiggle coming out of those higher speeds turns. When things were slowed down a little bit, it was solid as a rock. But because I kinda like trying to stand on the gas at times, I felt that I needed a little more wing in then rear, but then didn't want to change the overall straight line flight too much adding more lift, so went on the wth do all these different wings do search.

So I've come to the conclusion that with the AOI differences, the foiling from middle to tips, and chord differences to the three, and for what I'm looking for...I'm going to just throw on the 440 first, try it, see what it does, paddle in, and throw the 400 on, rinse and repeat. Cuz I'm still lost on all of it, and just gonna go do the scientific "try and fly" model to discovery. :D


Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill on August 12, 2020, 11:45:38 PM
Well, while you're at it, start farting around with shimming the stabilizer. I have a couple of different angle measuring devices, and occasionally walk around measuring everyone's foils/stabilizer incidence angle. A lot of the combos I've checked are in the 5-degree range. The 390 is about -4.7 degrees to the wing. Admin insists on checking to the fuselage and to the baseplate, neither of which makes any sense to me, but he's nuts, so I don't argue anymore, because he'll insist on explaining it to me. I think that's called Adminsplaining.

Absent some active system for controlling the stabilizer, 5 degrees seems like a hell of a lot. I've settled on shimming to two degrees. This makes for some very radical changes that take a while to get used to, but I like the end result. I've tried 0 degrees. Not great, though I might be able to get used to controlling the foil pitch with my back foot.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin on August 13, 2020, 12:46:38 AM
Well, while you're at it, start farting around with shimming the stabilizer. I have a couple of different angle measuring devices, and occasionally walk around measuring everyone's foils/stabilizer incidence angle. A lot of the combos I've checked are in the 5-degree range. The 390 is about -4.7 degrees to the wing. Admin insists on checking to the fuselage and to the baseplate, neither of which makes any sense to me, but he's nuts, so I don't argue anymore, because he'll insist on explaining it to me. I think that's called Adminsplaining.

Absent some active system for controlling the stabilizer, 5 degrees seems like a hell of a lot. I've settled on shimming to two degrees. This makes for some very radical changes that take a while to get used to, but I like the end result. I've tried 0 degrees. Not great, though I might be able to get used to controlling the foil pitch with my back foot.

Here comes some Adminsplaining :). 

The method of measuring angle mentioned in the vid below (Bill does something similar) is useful provided a few things. 

1.  Nothing moves at all between the foil and the stabilizer measurements.  Your caliper is rock solid (no flex) or wiggle. That means no  measuring on a beach with the board moving or on a floor unsecured.  It is way too easy to slip a degree or four in a game where you are counting on fractions of a degree.  That is why we were unable to reproduce a measurement.  In the vid below he has it really well clamped down and has a flex free caliper and accurate measuring tool. 

2.  Most importantly, for this method to be useful you need to have a target number (difference between front and rear wing angle) that is known good for a given system (specific front wing and and specific stabilizer).  Trying to apply a generic number (2 degree difference for instance) to any foil combination would be silly.  In the vid below George mentions one system that he knows is correct at a 2 degree difference and another that is correct at a 4 degree difference.  He says that the range for that one is 3.8 to 4.2 degrees with 4 being the sweet spot.  That is a very tight range which requires very specific tools and previous knowledge of that desired range. 

My point to Bill was that we were meeting neither of the above points.  :)

George also mentions that what you are really trying to do is to adjust based on what you are feeling for a given system.  That makes sense to me.  What is the specific issue that an individual is trying to address?  It is likely going to be very different for each of us even on the same foil set.  Since we are only adjusting stabilizer angle (incidence) in this scenario all you really need is an accurate measure of that single angle as a start point and again as a measure of the change that you have made.  It is easier and more accurate to measure that single angle then to try to get a relative angle between two foils.  Check out two posts down.  This is a very easy way to measyre shim angle with only a cell phone camera.  Washers may also be too coarse of an adjustment in many instances.  A single thin washer can make a 2 degree change on some foil systems.  Some angle markings on the fuselage at the stabilizer would be a nice idea. 

https://www.youtube.com/watch?v=jTCyag5N_vE
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin on August 13, 2020, 01:11:16 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

(https://cdn.shopify.com/s/files/1/0076/2006/7439/products/miiiddlakffnpble_1296x.png?v=1585096587)

(https://cdn.shopify.com/s/files/1/0076/2006/7439/products/ddjobpeicnbnbmgh_1296x.png?v=1585089015)

(https://cdn.shopify.com/s/files/1/0076/2006/7439/products/bjfolljmjncpmkdg_1296x.png?v=1585089015)
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin on August 13, 2020, 01:33:07 AM
This free online tool is an easy way to measure shim angle:

Please note that Axis is measuring these shim angles in relation to the horizontal axis of the fuselage.

https://www.ginifab.com/feeds/angle_measurement/

Below is an example using the Axis shim as an example.  I also showed the same online tool being used with a cell phone image of a mounted 390 tail with no shim.  You just need to level and weight the fuselage to get an accurate and very replicable baseline reading.  This is the incidence of the stabilizer.  In this example it is -2.5 degrees.


Title: Re: Can We Talk Stabilizer Geometry?
Post by: Dwight (DW) on August 13, 2020, 04:43:39 AM
We (and a local buddy) bought into the Delta video a few years ago and bought those tools.

Tried it on original Naish with tilting tail. All we learned was we didnít know shit. The factory setting was best.

My buddy, whoís heavy, kept trying to find more lift on every foil he owned with the delta method.  All he got was confused and never was successful in making anything better than the factory setting.

Fast forward to my first foil with factory shims, Armstrong, and everyone says just use the +1 shim for max speed. Donít use the 0 shim, itís too much drag and lift. Sounds backwards, but WTF, I have already proven to myself, I cannot do better than the manufacturer, so +1 it is and it is wonderful.

Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin on August 13, 2020, 06:16:59 AM
Fast forward to my first foil with factory shims, Armstrong, and everyone says just use the +1 shim for max speed. Donít use the 0 shim, itís too much drag and lift. Sounds backwards, but WTF, I have already proven to myself, I cannot do better than the manufacturer, so +1 it is and it is wonderful.

The language can be confusing.  It sounds like Arstrong labels their shims opposite to Axis with -2 for instance providing the most downforce.  With Axis the -1 shim has less downforce than the + 1.   

If so, what you wrote above would make sense if a particular combo was feeling draggy.  Then adding a degree to the tail would reduce its negative angle and it would provide less down pressure and less drag. 
Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill on August 13, 2020, 10:17:04 AM
I modified one set of my calipers to do this, but it's only 6" jaws, so it only works on a limited number of wings. I could buy some cheap 12" calipers, or make some other carrier for the angle detector, but the model airplane incidence measuring tool showed up at the UPS store while I was in the middle of making a carrier--I don't remember ordering it, but obviously I did (if you know me, you aren't surprised by this). It's the same tool Mark Ribkoff uses. He's the one that got me started on this kick.

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. The angle to the fuselage or the baseplate might be interesting in some fashion, but it's nothing I really care about.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: soepkip 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...
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin 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.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin 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. 
Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill on August 14, 2020, 08:14:26 AM
Well that started off as a great arguement and then wandered into la-la land.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: jondrums 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)
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin 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. 

Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill 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.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin 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 :)

Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill on August 15, 2020, 10:58:39 AM
Yeah, no.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: jondrums 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
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin 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.  :)
Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill on August 15, 2020, 05:09:40 PM
Oh my god.

Nope, nope, nope not going there.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin 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. 
Title: Re: Can We Talk Stabilizer Geometry?
Post by: container 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.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: container on August 16, 2020, 10:58:19 AM
 11 degrees of twist from root to tip and no fuselage to act as a datum!?
Title: Re: Can We Talk Stabilizer Geometry?
Post by: jondrums on August 16, 2020, 05:23:04 PM
container - we keep waiting to hear how it rides! When do we get the report?
Title: Re: Can We Talk Stabilizer Geometry?
Post by: container on August 18, 2020, 11:59:31 AM
Its awesome, feels completely different to an elliptically loaded foil but well and truely served its purpose. It was designed and built to answer one question- will a very small(area), very high aspect, very highly loaded foil with bell shaped lift distribution and a shitload of wing twist behave in a predictable and satisfactory way.  YUP.  Mk.2 flying wing tuna tail is going to be a fkn WMD
Title: Re: Can We Talk Stabilizer Geometry?
Post by: jondrums on August 18, 2020, 02:53:20 PM
I assume you rode it with a tail/stabilizer?
Title: Re: Can We Talk Stabilizer Geometry?
Post by: container on August 18, 2020, 02:58:02 PM
Yeah with my usual tail setup.  It wasnt designed with positive pitch stability in mind so it was really the worst of both worlds, drag from a tail wing and downforce from the tips in line with the centre of lift. Still went great, and gave a brutally effective answer to my question
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Beasho on August 29, 2020, 07:35:25 AM
Here comes some Adminsplaining :). 
The method of measuring angle mentioned in the vid below (Bill does something similar) is useful provided a few things. 
https://www.youtube.com/watch?v=jTCyag5N_vE

I am late to the discussion.  While I like the video I think George from Delta Hydrofoil is measuring the angle relative to the Chord line not the ZERO lift Angle of Attack (AOA).

On a Symmetric foil the Chord = ZERO Lift AOA.  With a Cambered foil, flat bottom curved top Cessna wing or Maliko foil, the Zero Lift AOA can be Negative Five Degrees or more.  So these angles can all be shifted by +5 degrees by the Camber of the specific foils.

https://en.wikipedia.org/wiki/Zero-lift_axis

Here is an image of Negative Angle of Attack = Zero Lift = No Downwash.  The Stabilizer lives in this downwash.  Even if the Stabilizer were at ZERO degrees relative to the front Wing and was Symmetric it effectively creates down force. 
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Beasho on August 29, 2020, 07:59:20 AM
Said another way:  There is a Lot Going on with wing Camber, Lift, Horseshoe Vortices (Downwash), AOA and Stabilizers.

Stabilizers Are Training Wheels

Like grandma holding a railing going down a flight of steps we use Stabilizers to make ourselves feel Comfortable flying at our skill level. 

The better we get the less we need them.  The smaller they become and the shorter the length from center of lift to stabilizing platform. 

A flying wing is inherently unstable (typically because the center of mass is behind the center of lift).  We are using Mass shifting instead of control surfaces to manage pitch stability.  Similar to a hang glider.  But we are all still beginners with just a few years of experience. 

2 years ago I took the stabilizer OFF and it flew.  A little bit pitchy but I even managed to pump.  This was only my 3 attempt behind a tiny little boat. 

https://www.youtube.com/watch?v=WpTwOYx0Lho
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin on August 29, 2020, 08:33:55 AM
I am sure that you guys have played with this or similar but this simulator is really interesting.  https://www.grc.nasa.gov/www/k-12/airplane/foil3.html

This is just looking at the properties of a single wing and it still highlights how complex and intertwined these relationships are.  Looking at one element in isolation is interesting but only so valuable.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin on August 29, 2020, 09:03:23 AM
Quote
While I like the video I think George from Delta Hydrofoil is measuring the angle relative to the Chord line not the ZERO lift Angle of Attack (AOA).

That is what he is doing.  He is simply getting the difference between front wing angle and stabilizer angle to use as a basis of comparison (and potentially for adjustment) to known good settings for specific foil/stabilizer combinations. 
Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill on August 29, 2020, 10:13:01 AM
That's all true, but so what? How else would you get a measurement that you can relate to the effect of changing the stabilizer incidence angle?
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin on August 29, 2020, 10:32:31 AM
Measuring both wings in fine but overly complex.  If you are just looking for a basis for adjustment you can just measure the stabilizer incidence first and then again after the change to confirm your adjustment.   
Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill on August 29, 2020, 10:38:24 AM
...and here we are again. You have to zero the gauge anyway, so whether you zero it on the fuselage or on the wing makes no difference in the complexity of the measurements.
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin on August 29, 2020, 11:29:09 AM
I did mine with my camera as earlier.  That is really easy and accurate.  I tried a thin washer to raise (and then lower) my 390 on the 760.  The change was just over a degree in either direction.  Less negative incidence and it was harder to take off and not noticeably faster.  More negative incidence was really draggy feeling.  George was talking about really small changes (within a range of 4/10's of a degree).  Possibly my changes were too large or possibly this is nicely optimized for me as is. 
Title: Re: Can We Talk Stabilizer Geometry?
Post by: PonoBill on August 29, 2020, 02:05:12 PM
I don't really see any big change in speed with lower incidence angles, though the draggy feeling goes away somewhat with bigger wings. The biggest change I see in going from 5 to <3 degrees is the change in foot position--my front foot moves back about 8 inches--and the board is more stable, especially on a close reach.

It's definitely harder to get up on foil, I have to reach much higher speeds for the board to lift. But when it comes up it comes up relatively flat, so I don't have quite as much stalling going on. I'm considering increasing the incidence angle to use the 860 since I have to pump the board and wing like a maniac to get going.

Title: Re: Can We Talk Stabilizer Geometry?
Post by: jondrums on August 29, 2020, 11:17:56 PM
Beasho - check this out
https://www.deltahydrofoil.com/shopfoils/mono-wing-foil-carbon-plate-mount

I've been eyeing this setup lately.  Although I sold my IWA a while back, I picked up a used one cheap to try a tail-less IWA in the waves.  Just waiting to find an old short GoFoil mast cheap next
Title: Re: Can We Talk Stabilizer Geometry?
Post by: Admin on August 30, 2020, 04:07:16 AM
I am sure that you guys have played with this or similar but this simulator is really interesting.  https://www.grc.nasa.gov/www/k-12/airplane/foil3.html

This is actually fairly amazing for an online simulator.  I am sure that it is not 100% accurate but it does allow you to change to water at a constant density (and choose depth) and adjust speed down to our (low) speeds.  You can set foil angles, thickness and section shape to get reasonably close to our usage. 

If you want to check out something like relative thickness and how that effects lift and drag at a variety of speeds and angles this is a nice visual way to do that (and possibly a little surprising).
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