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 Post subject: Bad trim, what to look for
PostPosted: Mon Mar 30, 2015 2:48 pm 
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Joined: Wed Sep 06, 2006 5:12 pm
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Location: S.P.I. TX. / Canon City Co.
Heading for the coast and would like an explanation of symptoms of bad trim, what to look for and how to shim the rear wing, My boards only have a front foot hook for control while starting so basically riding strapless. Starting with the rear wing at aprox 2 degrees negative AOA, front is zero to the mast and mounting surface of the board.
So, whats it going to feel like with too much negative or not enough? how to tell if its foot position or trim etc. ? which do you adjust first? How to tell if the board to front wing angle is correct?


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 Post subject: Re: Bad trim, what to look for
PostPosted: Mon Mar 30, 2015 4:03 pm 
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Joined: Wed Oct 16, 2002 1:00 am
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Location: Denmark
Denisesewa wrote:
Heading for the coast and would like an explanation of symptoms of bad trim, what to look for and how to shim the rear wing, My boards only have a front foot hook for control while starting so basically riding strapless. Starting with the rear wing at aprox 2 degrees negative AOA, front is zero to the mast and mounting surface of the board.
So, whats it going to feel like with too much negative or not enough? how to tell if its foot position or trim etc. ? which do you adjust first? How to tell if the board to front wing angle is correct?


Good question :thumb:

There is, IMO, not one correct angle, as it can be individual what one prefer, and how the board is used.

If you got too much negative, the board will "pop out" of the water too easy, almost no matter what you do and how much weight you have on your front foot, if the hook is too far rear.

In this case, you could move the hook forward, as then the hydrofoil will be quite stable and in trim.

When you learn to ride faster, you might prefer a lower or positive angle on the rear wing.

For the first attempts, where I asume you only got a limited amount of inserts, I would just put the hook far forward, and go out and try :naughty:

If it still pops out by itself, you just shim the rear wing up a bit, till it feels right.

So front hook far forward (you can always stand in a wide stance if the rear wing has too much aoa)
And then trim aoa up (or less negative) if it tries to "fly" too easy, even with a normal not wide stance.

8) PF


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 Post subject: Re: Bad trim, what to look for
PostPosted: Mon Mar 30, 2015 4:09 pm 
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Joined: Wed Sep 06, 2006 5:12 pm
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Location: S.P.I. TX. / Canon City Co.
Great info, Thanks PF !!


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 Post subject: Re: Bad trim, what to look for
PostPosted: Mon Mar 30, 2015 8:20 pm 
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Joined: Sun Feb 24, 2008 6:15 pm
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Location: France
As PF wrote one of the benifits of a front foot hook only is that you can place your rear foot where you want to find the set ups center of lift, knowing that it is also safer to learn with.
For me finding this simply means you have equal weight on both of your feet when flying.
I use EP 817 profiles and like you have 0° front chord line which if I rember correctly equals 4° positive.
And I do the same for the rear of course, profile inverted thus 0° chord line again equals 4° negitive for a delta T of 8°
Then based upon if you like a wider stance or not you can adjust your foot hook placement.
I once read a rule of thumb that 1° AoA change on stab can change center of lift 4 cms using epp817.
Another concept is that more delta T equates to more stabiliy but at the cost of drag.
So the inverse, less delta T less drag but more sensitive.
All that said and not at all 100% sure of these points,
I know maniac guys who shim with 1/10 mm shims and swear they can feel the differance, I sure can not.
It is good to be prepaired with shims to match your hole diameter and fuse width in different thicknesses or I know guys who use alu cans, plastic found on the beach for the high teck approach.
If I understand correctly you are going to be where there are experienced pilots, ask then kindly to test your creations.
R H


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 Post subject: Re: Bad trim, what to look for
PostPosted: Mon Mar 30, 2015 8:29 pm 
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Joined: Wed Sep 06, 2006 5:12 pm
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Location: S.P.I. TX. / Canon City Co.
Will do Rev, Thanks for all the help.


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