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Author Topic: total geek out post on the GL210  (Read 1536 times)

jondrums

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total geek out post on the GL210
« on: September 22, 2020, 10:54:35 AM »
Yes, foil brain is in full effect even after 3 years foiling for me.  I'm stuck in my house with nothing else to do, so I'm trying to understand the inner workings of foil wings.  I've been using my GL210 as a reference wing.  Hopefully through all this, I can help identify opportunities for improvement (which I think there are still many).

I traced out the foil section profile using paper and scissors and translated it to digital in order to run it through XFOIL software and study the polars.  I had one of my friends operate XFOIL since this isn't (yet) my specialty.  We picked some speeds to look at.  First impressions are that this foil section seems pretty draggy in comparison with more typical glider wing and hydrofoil profiles designed for similar Reynolds numbers.  It is certainly much better than the IWA type section.

I also carefully measured wing twist, so a future analysis could include those effects.  The outer third is pitched negative a bit probably to keep the tips from stalling in dynamic maneuvers.

Before you ask - I WILL NOT post or share the foil cross section.  If you want it that bad, you're going to have to buy your own wing and trace it yourself.  Imitation is flattery, but copying exact is theft. 








supfoo

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Re: total geek out post on the GL210
« Reply #1 on: September 22, 2020, 04:58:27 PM »
Thanks for reminding me why I dropped out of engineering in collage!  ;D

steamroller

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Re: total geek out post on the GL210
« Reply #2 on: September 22, 2020, 06:47:01 PM »
cool!...did you calculate the Mean Aerodynamic Chord for the wing or just use the one measurement for Chord at the Root in your analysis?

steamroller

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Re: total geek out post on the GL210
« Reply #3 on: September 22, 2020, 07:06:31 PM »
and thanks for NOT putting everything out there...XFOIL is definitely the way to go...the equations cannot be worked with analytically...the math is way to complex...everything has to be done numerically in order to make any sense if it all :D

SUPdad

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Re: total geek out post on the GL210
« Reply #4 on: September 23, 2020, 06:55:50 PM »
Thanks for reminding me why I dropped out of engineering in collage!  ;D

Love that comment! ;D

Curious about the washout at the tips. Wondering if the newer style HA wings are generally using washout and if that helps keep the wing flying when a tip comes out of the water.

SUPeter

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Re: total geek out post on the GL210
« Reply #5 on: September 24, 2020, 04:26:38 AM »
I've played around a bit with washout and find the largest benefit being a more gradual modulation in lift.  Instead of the foil turning on and off with regards to lift while small changes in angle of attack are made, the changes in angle of attack are widenened and the onset of lift is slowed.  At higher speeds,  the outer sections of the wing can turned off limiting the amount of lift we need to fight to hold down.  As far as making the wing less prone to aeration when wing tips breach, I'm not sure.  Theoretically, less negative pressure at the wing tip means less air drawn in.  It could help?
« Last Edit: September 24, 2020, 04:29:17 AM by SUPeter »

SUPeter

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Re: total geek out post on the GL210
« Reply #6 on: September 24, 2020, 04:45:23 AM »
One question remains: 
Does the actual wing template/profile remain the same from root to tip or does it change.  Another way of stating this is are they using geometric washout or aerodynamic washout? 
Aerodynamic washout- same wing profile throughout length of wing.  wing ends twisted down9negative)
Geometric washout-  Wing profiles change from root to tip.  no twisting. 

It would be fun to play with both methods.  I have only used Aerodynamic washout.

jondrums

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Re: total geek out post on the GL210
« Reply #7 on: September 24, 2020, 11:41:48 AM »
cool!...did you calculate the Mean Aerodynamic Chord for the wing or just use the one measurement for Chord at the Root in your analysis?

I used the chord at the root.  mean aerodynamic chord is about 80% of the chord at the root.

I've played around a bit with washout and find the largest benefit being a more gradual modulation in lift.  Instead of the foil turning on and off with regards to lift while small changes in angle of attack are made, the changes in angle of attack are widenened and the onset of lift is slowed.  At higher speeds,  the outer sections of the wing can turned off limiting the amount of lift we need to fight to hold down.  As far as making the wing less prone to aeration when wing tips breach, I'm not sure.  Theoretically, less negative pressure at the wing tip means less air drawn in.  It could help?

yes, look at the very peaky plots of Cl/Cd - washout would help smooth that out a bit I think.  I've seen plots of other cross sections that look a lot less peaky and I'm thinking that would be a lot better.
I believe the typical reason for washout in wings is to generally prevent tip stall on aircraft, meaning that you avoid excursions in roll in hard maneuvers/slow speeds

One question remains: 
Does the actual wing template/profile remain the same from root to tip or does it change.

I believe that the foil section profile remains the same from root to tip, but did not confirm that by tracing the profile, just by inspection

Admin

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Re: total geek out post on the GL210
« Reply #8 on: September 26, 2020, 01:26:01 AM »
Hey Jon,

At $20 it seems like one of these contour gauges may make quick work of section acquisition.  If you wanted to get fancy you could also use it to grid the wing which would show wash, etc.





https://www.youtube.com/watch?v=D-BI1bqXdlI
« Last Edit: September 26, 2020, 01:58:45 AM by Admin »

jondrums

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Re: total geek out post on the GL210
« Reply #9 on: September 27, 2020, 10:06:06 PM »
yeah, I have one of those and tried to use it.  But the problem I had was that I could only get the top and bottom profiles separately - which are hard to reassemble accurately.  Getting the leading edge shape with that tool is difficult.  Cutting and taping cardstock together yields a much smoother and more accurate transcription of the shape and only took 10 minutes or so.

norcom

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Re: total geek out post on the GL210
« Reply #10 on: September 29, 2020, 07:04:14 AM »
Hey Jon,

At $20 it seems like one of these contour gauges may make quick work of section acquisition.  If you wanted to get fancy you could also use it to grid the wing which would show wash, etc.


Heh, I have a couple of those tools. I tried to use them to copy the contour of my GoFoil 18W tail so I can design some 3d printed shims. In short, it didn't work that well.

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Re: total geek out post on the GL210
« Reply #11 on: September 29, 2020, 07:17:37 AM »
Hey Jon,

At $20 it seems like one of these contour gauges may make quick work of section acquisition.  If you wanted to get fancy you could also use it to grid the wing which would show wash, etc.


Heh, I have a couple of those tools. I tried to use them to copy the contour of my GoFoil 18W tail so I can design some 3d printed shims. In short, it didn't work that well.

What went wrong?

jondrums

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Re: total geek out post on the GL210
« Reply #12 on: September 29, 2020, 10:20:07 AM »
the problem I had is that the individual pieces are about 1mm wide, and so it only transcribes points at about a mm interval.  Near the leading edge that isn't enough resolution to get the shape.  Maybe it would be possible to use it several times at different angles, but then when tracing each shape onto paper it is very tough to figure out how to merge the individual profiles back together into a cohesive picture of the cross-section.  cutting/taping cardstock is pretty foolproof and easy

judoChop!

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Re: total geek out post on the GL210
« Reply #13 on: September 29, 2020, 10:28:37 AM »
the problem I had is that the individual pieces are about 1mm wide, and so it only transcribes points at about a mm interval.  Near the leading edge that isn't enough resolution to get the shape.  Maybe it would be possible to use it several times at different angles, but then when tracing each shape onto paper it is very tough to figure out how to merge the individual profiles back together into a cohesive picture of the cross-section.  cutting/taping cardstock is pretty foolproof and easy

another tip is to wrap a wire around the profile section, then just slide it off. Quick & easy. use something malleable like soldering wire.
check out Kazuma here: https://youtu.be/vwvPDhunzZM?t=154

Admin

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Re: total geek out post on the GL210
« Reply #14 on: September 29, 2020, 01:56:46 PM »
the problem I had is that the individual pieces are about 1mm wide, and so it only transcribes points at about a mm interval.  Near the leading edge that isn't enough resolution to get the shape.  Maybe it would be possible to use it several times at different angles, but then when tracing each shape onto paper it is very tough to figure out how to merge the individual profiles back together into a cohesive picture of the cross-section.  cutting/taping cardstock is pretty foolproof and easy

I see.  Maybe a non starter then.  Possibly one of the metal pinned ones would have a higher "resolution".

 


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