Author Topic: Go Foil Advise  (Read 21524 times)

PonoBill

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Re: Go Foil Advise
« Reply #30 on: September 01, 2019, 06:25:20 AM »
There are lots of near-zero lift tails around--most kite foils are damned close to that. I think the reason they have a foil at all is to keep them from being any sharper than they already are. I've slashed my canopy up enough with stabilizers. Roundness gives me another two seconds before the stabilizer penetrates and starts shredding. Of course, I usually use that to stare stupidly at the coming catastrophe...

Most of the really gruesome pictures of people with foil injuries are from trying to use kite foils to surf with. I think that's how Sam Pa'e got his head cut up. If you have a kite dragging you around it's less likely that you will fall on a foil. In surfing, most of the muscle reactions you've accumulated promote a lovely jackknife effect and drop you onto the foil. Rounded edges mean that causes spectacular bruises but rarely cuts.
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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: Go Foil Advise
« Reply #31 on: September 01, 2019, 07:44:47 AM »
There are lots of near-zero lift tails around

Are there any examples of surf or SUP foils that do not have a front wing that is rightside up (convex up/concave down) and a rear wing that is inverted (concave up/convex down)? 

PonoBill

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Re: Go Foil Advise
« Reply #32 on: September 01, 2019, 11:35:34 AM »
No. but there are plenty of kite wings that look like near-zero lift. Jet aircraft foils look like zero lift, they're generally symmetrical, it's angle of attack that makes them lift or not. That's one reason they fly well upside-down while slower aircraft with high-lift foils need to point their nose radically up to fly inverted.

You might think that wouldn't apply to hydrofoils since the speed is so much lower, but remember that water is a thousand times more dense than air, and lift is a function of density, foil coefficient, area, and velocity squared. In air the density is variable (altitude and velocity both vary density of the medium) and is at least a thousand times less while in water the density is fixed (water is incompressible at the pressures involved). Kiter foilers routinely go 15 to 40 mph while foil surfers go 5 to 15 (more in short bursts). That's about three times faster on average so nine times as much lift from the same wing.

Wing foilers are already starting to go a lot faster and the specialized foils will be different from what we are using now.
Ponohouse is for sale: http://www.ponohouse.com
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.

supfoo

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Re: Go Foil Advise
« Reply #33 on: September 01, 2019, 08:05:30 PM »
My first foil was a Naish, had an adjustable rear wing, it made a big difference on being able to catch the wave.

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Re: Go Foil Advise
« Reply #34 on: September 02, 2019, 01:31:49 AM »
What are kiters using now?  Is it two cambered wings in our configuration (inverted rear wing) or something else?

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Re: Go Foil Advise
« Reply #35 on: September 03, 2019, 02:10:59 AM »
This is pretty cool to consider in regards to changing/adjusting tail stabilizers.


jondrums

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Re: Go Foil Advise
« Reply #36 on: September 03, 2019, 11:45:40 AM »
yes, that image comes from a pretty good decription of Center of Gravity vs. efficiency here:
https://www.boldmethod.com/learn-to-fly/performance/how-does-cg-affect-aircraft-performance/

notable quote:
"while having an aft CG definitely improves performance, in most light aircraft, the difference in will be a few extra knots of airspeed, and a little better climb rate."

My conclusion from all this discussion is:
we should shift our feet and hips to achieve a center of gravity directly over the front wing center of lift and arrange the tail for a neutral position without lift or downforce in the nominal case.

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Re: Go Foil Advise
« Reply #37 on: September 03, 2019, 12:35:57 PM »
has anyone experimented with shimming a tail to create uplift?  I guess I'll have to try it one of these days.  Might have to learn the hard way why everyone has designed downforce in the tail.

a couple of years ago i made a tail wing that could be attached either way, upward or downward lift.
in my minimally educated opinion-

- awful pitch stability

- slight reduction in drag

- very even foot pressure, mast is almost in between your feet

- no drive in the pumps. i see it as a sort of triangulation of the water flow to create thrust. water is thrown down off the main wing and upward off the tail wing resulting in the board trying to pitch up sharply, which it cannot do if the rider is in control so the only other option for it is to go forward. you may notice in some flat water pumping vids little breaking waves being pushed up behind the foil as it goes along. this is the water being pushed up by the tail wing

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Re: Go Foil Advise
« Reply #38 on: September 04, 2019, 02:17:51 AM »
In regard to shimming, I believe that inverting a cambered wing or stabilizer will always lift downward.  If you then angle an inverted wing enough it can create upforce by deflection.  Kind of like Bernoulli and Newton arm wrestling :).   That would, of course, be a super inefficient way of producing upforce.
« Last Edit: September 04, 2019, 02:36:08 AM by Admin »

PonoBill

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Re: Go Foil Advise
« Reply #39 on: September 04, 2019, 05:37:53 AM »
It's actually a common way. Almost any airplane can fly inverted but it flys nose up. Many can also fly knife edge if they have enough power.
Ponohouse is for sale: http://www.ponohouse.com
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: Go Foil Advise
« Reply #40 on: September 04, 2019, 09:03:17 AM »
I found a really interesting article about that which I cannot find right now.  They mentioned that early pilots with low poiwer and very heavily cambered wings were able to fly them upside down for short durations with enough angle.  They switched to symmetrical wings for stunt use because they were so much more efficient when upside down.  Of course, you wouldn't choose and inverted wing to be used primarily for upforce.  I guess the point of that is that shimming an inverted tailwing on foils for our purposes makes sense to (but not past) a neutral position. 

supfoo

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Re: Go Foil Advise
« Reply #41 on: September 17, 2019, 05:54:56 PM »
I received my GL 210 today, after dark, & it was windy & wavey this evening!  Had to go on the Maliko 200 but still had fun. Anyway, the tail is back ordered till next month. Has anyone tried the GL's with the old tails?? I'm wondering what to expect or if I should even try it at all.

paddlur

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Re: Go Foil Advise
« Reply #42 on: September 17, 2019, 09:59:06 PM »
I received my GL 210 today, after dark, & it was windy & wavey this evening!  Had to go on the Maliko 200 but still had fun. Anyway, the tail is back ordered till next month. Has anyone tried the GL's with the old tails?? I'm wondering what to expect or if I should even try it at all.
I just recieved my GL210 couple weeks ago as the GL rears were sold out, but finally tracked one down,and in mean time have been using it with the maliko tail and really like it in small waves,I just recieved my rear 1.5 18W tail but have not tried it yet waiting for a bit more swell to test it but with my weight 225lb the GL210 with the Maliko tail works great for me and itís a stock Maliko not cut down, looking forward to trying the new 18W tail, but was pleasantly surprised how well it worked for me.
Naish kites-mhl lift foils-GoFoil-ASD surfboards fortaleza brasil,Kalama supfoil.

PonoBill

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Re: Go Foil Advise
« Reply #43 on: September 18, 2019, 08:41:40 AM »
Me too. I have the GL tail, but I tried the Maliko tail and liked the way it felt. I'm wing foiling, so this doesn't necessarily translate to surf foiling, but the Maliko tail felt more stable and I could get up on the foil more easily, the GL tail is less draggy, but I needed to power up the foil instead of being able to pump up. I find the same thing happens with the Axis using the 440 tail vs. the 500.

My pumping isn't very effective, but it helps in light wind. The 5M wing makes both wing pumping and foil pumping more effective--I can kind of hang on it and make my feet lighter.
Ponohouse is for sale: http://www.ponohouse.com
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.

Beasho

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Re: Go Foil Advise
« Reply #44 on: September 18, 2019, 09:23:09 AM »
The cut MALIKO tail is about halfway between the two in size.  I was personally very happy with the 420mm cut MALIKO tail combo with both the M200 and IWA.  Pitch stability is a bit more touchy - which has good and bad.  On the good side, its really easy to get it out of the water and to avoid overfoiling.  On the other hand, you have to have your feet right and react fast.

A big thing you have to understand is that the MALIKO tail creates DOWNFORCE!  That downforce is NOT lift - effectively it is like pitching moment pushing the nose up (and the tail down). The tail is negating some of the front wing lift, and on top of that creating drag.   And the worst part is that it seems to be somewhat variable with speed.  So if you take a steep drop at high speed you really have to work to keep the nose down, then when you slow down you need to shift weight to trim up the nose.  With the cut down tail, I didn't feel any of that speed sensitivity - it was much more neutral and didn't require so much work to trim the nose.

The new GL tails seem to be much more neutrally tuned - I don't think they are setup stock to produce much if any downforce.   I haven't tried the new tail with IWA or M200 because the GL wing is so fun as it is.

I am still with Jondrums on this tail issue.  At first I thought the smaller tails DID NOT PUMP well.  But then I used them more, as in 20+ sessions more, and they started to work.  I then had to ask whether it was the equipment or the rider.   

Pono - You were the one that suggested the reason a FLYING WING with NO TAIL may not be as effective as having a tail is because the wild, uncontrolled pitching up/down would actually reduce the efficiency of flying wing only.   

The better we can manage the pitch the more efficiently we can fly without, or with smaller, tails.
« Last Edit: September 18, 2019, 09:24:49 AM by Beasho »