Author Topic: Wing lift or AOA lift?  (Read 17551 times)

jondrums

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Re: Wing lift or AOA lift?
« Reply #45 on: August 09, 2017, 12:05:27 AM »
this is the closest thing I could find to what I was thinking of.  But I was thinking of ejecting water through the holes in the trailing edge of the foil rather than air.  Maybe it only works with air.
https://www.google.com/patents/US3221698

Here's a different idea for passive height control of a foil.  Not what I was thinking, but kind of similar in that it uses a water inlet (pitot tube) on the leading edge for actuation.
http://www.foils.org/taig.pdf

supuk

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Re: Wing lift or AOA lift?
« Reply #46 on: August 09, 2017, 12:59:37 AM »
As we are fairly borderline on lift already I think it would be more appropriate to have height management rather than just scrubbing lift off by introduceing air anywhere as not only will you lose lift but allso efficiency and if you have experiaced a foil cavitating on anything it's not a good feeling!

SURFFOILS

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Re: Wing lift or AOA lift?
« Reply #47 on: August 09, 2017, 04:52:40 AM »
Oh wow, 'borderline on lift' ?
 I see the amazing performance by Kai and all the pro makers and riders to show the opposite.
 They're amazing !
 They can do full airs , 360's and the downwinding is really flying on a puff of wave chop.
 I see the currently available foils as absolute masters of lift.
 Can you explain how that's borderline ?
 Maybe it's the wave power difference around the world.

supuk

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Re: Wing lift or AOA lift?
« Reply #48 on: August 09, 2017, 12:06:37 PM »
Oh wow, 'borderline on lift' ?
 I see the amazing performance by Kai and all the pro makers and riders to show the opposite.
 They're amazing !
 They can do full airs , 360's and the downwinding is really flying on a puff of wave chop.
 I see the currently available foils as absolute masters of lift.
 Can you explain how that's borderline ?
 Maybe it's the wave power difference around the world.

Not so much on proper waves but for open ocean and for small unbroken waves were I have been foiling the drag/lift  ratio is marginal so once your up you really don't want to be eating any energy.

jondrums

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Re: Wing lift or AOA lift?
« Reply #49 on: August 09, 2017, 04:18:06 PM »
I was thinking about wave surfing where getting in early might call for good low speed lift, but as the wave develops and speed increases it might be desirable to spoil the lift.  It may well be that the best way to do this is varying angle of attack through body position - but it is also fun to think about other solutions.

SURFFOILS

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Re: Wing lift or AOA lift?
« Reply #50 on: August 09, 2017, 08:27:18 PM »
I'm with you there Jondrums, the increase in energy from take off to full speed is about 2 seconds due to gravity.  Lift on takeoff isn't what you want as you're trying to move forward not lift.

 As long as you've got enough height in the wave , gravity pulls you down and forward as the foil dictates. With a steep enough wave that drop,due to gravity, is constant and gives constant lift.

 The period of high lift is much longer when you're actually foiling which is what we're after. Low lift and better control are the goals for surf foiling.

SURFFOILS

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Re: Wing lift or AOA lift?
« Reply #51 on: August 10, 2017, 12:52:51 AM »
That last line was confusing...   :o :P ::)

 What I mean, and you can see it in any of the foil videos is that within a sec or two the foil is out of the low lift/speed range on anything more than a minor ripple.
 It transitions very quickly to the high riding speed and lift and there fore doesn't need exceptional low speed lift. By reducing the overall lift coefficient then the lift will be more manageable at higher speeds.
 Rather than looking to specialise on low speed lift which is rarely encountered on waves, low lift at higher speeds is a better focus and a lot of the foil makers are doing that already with more sweep, lower A/R and moving the foil apex back.

 


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