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Old Nov 29, 2014, 10:36 AM
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Jon Himself's Avatar
United Kingdom, England, Ashford
Joined Jun 2014
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Glider help

Hi, I've been fascinated by wings for a while and had some success with trial and error set-ups however my recent attempt really screwed up my confidence with my knowledge as the 2 meter wing just consistently nosed in (even though my CG was correct and constantly adjusted to suit).

Primarily what I want to do is create an un-powered wing I can hand launch or bungee to do a circuit and land.
I know I could copy a design already built but I do want to further my knowledge on the principals of the wing as opposed to just cribbing what someone has done and have no understanding of why (hope that makes sense)

Any advice would be really helpful.

vvv here's my last wing attempt.
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Old Nov 29, 2014, 11:16 AM
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There are many spreadsheets that use the Panknin formula to find the right combination of twist and CG for a given planform and speed. Are you using one of them?

--------.~.
--------/V\
------//----\\
-----/(------)\
----(^^)---(^^) --Norm
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Old Nov 29, 2014, 12:35 PM
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Jon Himself's Avatar
United Kingdom, England, Ashford
Joined Jun 2014
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No, never heard of it
To be honest all I have been doing is taking the shape, adding a rudimentary foil design and curling up the trailing edges or adding surface controls to experiment with reflex.
Worked really well on the one I threw out of my upstairs window, but not on this one which is twice as large.

I think I've just been lucky up until now - I'll have a look at Panknin formulas, this should give me more purpose in the design instead of hit hit hit miss.
Thanks
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Old Nov 29, 2014, 01:30 PM
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Trial and error will eventually get results but I have found that monkey see monkey do is faster. You can Google for "Panknin twist" and get the article so you can write your own spreadsheet or use one of the many that have been posted with various bells and whistles. I wrote one that also calculates corrections for Reynolds & Maach numbers and weight at altitude. It's kind of unfinished and ugly but for the most part it works. Curtis Suter made a nice one that draws a picture. To use any of the Panknin spreadsheets you'll need some airfoil data. For now you can get the needed data from airfoiltools.com/ but if you decide that you like the geeky side of the hobby you can get the software behind that site for free. Xfoil if you like the old command line interface or XFLR5 if you prefer a GUI.

--Norm
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Old Nov 29, 2014, 02:25 PM
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Knoll53's Avatar
United States, CA, Marina
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Quote:
Originally Posted by Jon Himself View Post
the 2 meter wing just consistently nosed in (even though my CG was correct and constantly adjusted to suit).
Hey Jon. We can get that thing to glide....no problem.

So if it noses in, check that you have 20 degrees up deflection on the elevons. I prefer elevons that are between 1/2 to 1/3rd of the half span in length. Can you post a drawing of what you got or a photo from the top?

If that doesn't work, try moving the CG back. That will certainly work, but at the cost of handling.

Once you've a controllable glide that requires a lot of up elevator to get the nose up, continue to move the CG back until it becomes too hard to fly. Horten designs need a lot of wing twist, like 9 degrees. It is those draggy tips that help with yaw stability.

Set a video camera about 10m away so we see the toss and glide!


Kent
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Old Nov 30, 2014, 08:30 PM
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Hi, thanks for the help.
I've been reading a lot over the past days - what I have created is a wing that wants to pitch violently so is inherently unstable. By gooning around with the CG I just made things worse by moving it backwards, so I understand better now - the process of adding a lot of twist makes sense to me now rather than moving the CG backwards to fix my issue.

Sadly the wing took a harsh dive into the ground and smashed the nose in so I'm gonna repair it with a solid core foam. With those calcs spreadsheet though I'm tempted to put my hand in my pocket and get a nice foam core wing cut on the CNC.

I might try a soft bungee launch as well, looking back on some of the videos my throws are inconsistent.

XFLR5 looks amazing - thanks for all the advice
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Old Dec 11, 2014, 09:16 AM
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Wouldn't putting drooping leading edge cuffs on the outboard third be worth a try?
That would result in lower AOA for the outboard sections and achieve at least a rudimentary "wing twist".
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Old Dec 17, 2014, 01:08 AM
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Ukraine, Crimea, Ordzhonikidze
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Hi!
You have not to change location of CG to balance. It tied to form of wing, its sweep and aspect ratio.
Calculate CG thoroughly, and set it. Balanse only by elevons or twist.
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Old Dec 17, 2014, 04:55 PM
SlingWinger
San Bernardino, California, United States
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Put a tail on it.
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Old Dec 17, 2014, 11:31 PM
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Originally Posted by dayhead View Post
Put a tail on it.
Blasphemer
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Old Dec 17, 2014, 11:46 PM
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Knoll53's Avatar
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he, he, he.....maybe hang gliders could use tails as well

So Jon are we ever going to get a video out of you?
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Old Dec 19, 2014, 10:02 AM
SlingWinger
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Quote:
Originally Posted by nmasters View Post
Blasphemer
Blaspheming can be fun at times.

My Seedwings Sensor (USA) has a vertical tail. That's a start.

I love Nurflugels too. They are a great source of sorrow and joy.

They sure have increased my appreciation of tail assemblies.
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Old Dec 19, 2014, 02:02 PM
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Originally Posted by dayhead View Post
Blaspheming can be fun at times.
Perhaps I should have used an appropriate smiley. I find flying wings to be a more interesting design challenge than "conventional" planes because of the theoretical efficiency that's impossible to achieve without some pretty harsh compromises.

Quote:

I love Nurflugels too. They are a great source of sorrow and joy.

They sure have increased my appreciation of tail assemblies.
Yeah, I think every 4th year aeronautical engineering student should be encouraged to design and evaluate a flying wing for just that reason.

--------.~.
--------/V\
------//----\\
-----/(------)\
----(^^)---(^^) --Norm
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Old Dec 19, 2014, 02:44 PM
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Quote:
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They are a great source of sorrow and joy.
ha, ha, ha......Sorrow-n-Joy will be the name of my next flying wing.


When I hear "tail" I think of an elevator, so the SeedWing is still a pure flying wing in my book. An ATOS with it's tail is something else, although such a token effort at an elevator should be in a special class somehow.
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Old Dec 19, 2014, 10:05 PM
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Originally Posted by Knoll53 View Post
An ATOS with it's tail is something else, although such a token effort at an elevator should be in a special class somehow.
I had assumed that the tails I've seen on Atos' were just pitch dampers and that the movement was just for trim adjustment. Is it actually a stabilator? Whatever the control function it is a pitch damper on a tail arm so it does disqualify the Atos from being called a flying wing while it is attached but I've seen a few pictures where it appears that the pilot left it on the ground so FW on that flight, probably in very calm conditions

--Norm
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