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 Post subject: Re: best way to reduce interference drag?
PostPosted: Tue Jul 01, 2014 2:38 pm 
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Joined: Wed Nov 20, 2002 1:00 am
Posts: 911
Location: rhode island
To be honest, i was about to confess that i may have "over stated" my position and seek forgiveness before peter bailed me out
:)

in hydro applications external corners are sometimes used to reduce drag by promoting separation (i.e. planning boats and surfboards and the trailing edges of control surfaces)

sometimes its a way to increase projected area and improve lift.



for your sail plane.... I agree. it doesn't look like much of a fillet.
my guess is that they decided to spend their money on other aspects of the design
i bet they can live with it.
-bill


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 Post subject: Re: best way to reduce interference drag?
PostPosted: Tue Jul 01, 2014 2:41 pm 
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Joined: Sun Sep 04, 2011 5:37 pm
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Peter_Frank wrote:
...

Can be seen on many gliders, take a look at the classic Discus, here the duo version:
...

8) PF


Peter -- can you afford to buy me one of those , "Please" ?
I promise to fly it a LOT, and clean & shine it every , (so often) !! :D

Like zfennell said , i could Live with a bit of extra drag !!

Bille


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 Post subject: Re: best way to reduce interference drag?
PostPosted: Tue Jul 01, 2014 10:19 pm 
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Joined: Tue Mar 11, 2014 10:02 am
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Location: Poland
Edge19 wrote:
Funny, I was watching this video the other day and noticed very quickly, cavitation. Weather it's because the foil is close to the surface, lower pressure has caused it like Bille said! but it is very noticeable. I tried to see where it formed from, I took some screen shots and it looks like it came from a wing tip.....
You can see it at 3.29

Cheers

https://vimeo.com/88175084

IMO it is rather ventilation of the foil tip, that travels with the foil sometimes hundreds of meters from the catch of the air.
Cavitation would cease in less than one meter. First sign of cavitation is a high pitch sound you can hear somtimes at speed and that's the sign to improve your foil surface/setup.
But looking back at the wake, you will not see any bubbles, as they are tiny and disappear very quickly.
High pitch sound comes from collapse of milions of these bubbles. :cool2:

Cheers
Tad


Last edited by flying grandpa on Wed Jul 02, 2014 8:58 pm, edited 1 time in total.

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 Post subject: Re: best way to reduce interference drag?
PostPosted: Wed Jul 02, 2014 8:43 am 
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Joined: Mon Dec 30, 2013 2:47 pm
Posts: 33
Been watching loads of vids on cavitation it's a very interesting topic. Super cavitation is incredible could be a way forward but getting to that point could be a problem with drag initially.

Now this getting back to it! If you hear this sort of high pitch sound you know what's happening down below..... Turn up the volume lol :lol:

Cavitation in Hydrofoil at EPFL: http://youtu.be/U7UgMxMsws0


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