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Old Apr 11, 2013, 12:26 PM
InceCreations
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Quick build thermal flying wing

Hi there,

I was recently intrigued by sea-gulls thermalling above the city, realy amazing how they do this !!

This gave me the idea to try and build my first non powered flying wing.
I'm targetting at an easy thermaller, easy in a sense that it goes up easily

I was thinking on a DEPRON construction method like the FZ3-PT with following specs.
Span 1800mm
Airfoil RAE100
Root 220mm
Tip 150mm
Sweep 20°
Glass covering
AR : 10
All flying weight ca: 700gr
3,6 oz/ft3 cubic wing loading
21 gr/dm2 wing loading (6,8 oz/ft2)
The DEPRON construction method I use is only good for symmetrical, no washout wings: so that my limitation here.

When looking at the attached diagram: my wing would be INSTABLE ?
What do you think?
Any tips for me ?

Vincent
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Old Apr 11, 2013, 05:33 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,251 Posts
Hi Vincent,this is a small 60cm Depron chuck glider I made a while ago.The wing is one piece on the bottom surface with the top taped on,a balsa spar just behind the l/e to give a foil shape.To get some washout I taped the leading edge ,then pinned it down through the spar with a couple of wedges under the tip.por on the trailing edge and the twist is locked in.I've since made one as a full one piece,folded at the l/e.
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Old Apr 11, 2013, 07:19 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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Quote:
Originally Posted by vincent123 View Post
....Span 1800mm
......
AR : 10
.....
The DEPRON construction method I use is only good for symmetrical, no washout wings: so that my limitation here......
For that sort of wingspan an AR of 10 is a little high. Some work on optimizing the AR for ALL AROUND performance was done some years back and presented in one of the Soartech journals.

Bottom line was that you want to maintain an 8'ish inch chord to keep the reynolds numbers up in a more friendly area. It also had other repercussions pertaining to speed range that I don't recall at the moment. Given this you'll likely find that you arrive at a more effective all around model if you go for around an AR of 8. Even 9 would take away a bit of the small size issue penalties. And as a bonus it makes it easier to build in a goodly amount of wing area into a fairly compact size of model.

A symetrical wing is fine. You will get the required reflex to be stable by using a slight up elevon trim. So the wing will not be unstable (it's described as "stable" or "unstable", not "instable".) if you go with a balance point of around 17 to 20% of the MAC and use some up trim to balance the glide. Final trim and elevon reflex amount can be set thru flight trials but in any event you do NOT want to get too close to 25% MAC or the wing will suffer from marginal or zero pitch stability.

You really need to figure out how to add in some washout though. It would be far better if you did.

I'm guessing that the method of forming the wing section is to fold the Depron over at the leading edge and glue the trailing edge. If so then you should be able to induce some washout by letting the trailing edge pieces slip a little while you twist in the washout and then glue the joint to lock it into place. Until you glue that back seam shut the wing can twist like this quite a lot. You just need some sort of wedge to act as a jig to hold it while you glue the top to the bottom along the tailing edge. Try it with some card stock bent around a dowel or scrap "spar" to see what I mean.

How will you get the model up to altitude? Electric motor assist or a high start? Or something exotic like aerotow?
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Old Apr 12, 2013, 01:56 AM
InceCreations
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Joined Jul 2009
720 Posts
Hi Bruce,

thanks for your nice support here!

Indeed, my idea is to fold depon 3mm and glue the TE.
A washout is good you say, how much should I aim for?

In any case, I need a wedge as you mentionned, also for having 2 wing halves with the same washout, at the end of the process ...

Why is 25% of MAC not a good idea, do you have some links about that issue ?

I was thinking to launch it with a bungee ...
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Old Apr 12, 2013, 02:03 AM
InceCreations
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Joined Jul 2009
720 Posts
Quote:
Originally Posted by Stupot46 View Post
Hi Vincent,this is a small 60cm Depron chuck glider I made a while ago.The wing is one piece on the bottom surface with the top taped on,a balsa spar just behind the l/e to give a foil shape.To get some washout I taped the leading edge ,then pinned it down through the spar with a couple of wedges under the tip.por on the trailing edge and the twist is locked in.I've since made one as a full one piece,folded at the l/e.
Hi Stu,

nice jet looking glider !

Looks like a slope glider, does it thermal ?

Vincent
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Old Apr 12, 2013, 04:17 AM
I don't like your altitude
Stupot46's Avatar
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Quote:
Originally Posted by vincent123 View Post
Hi Stu,

nice jet looking glider !

Looks like a slope glider, does it thermal ?

Vincent
No,just a free flight test bed for a stalled project(HoX)

Thinking about the wedge idea,it might be better to make a jig.A strip of ply say 50mm wide with wedges to keep a straight t/e.Otherwise you could have hinge problems.I'll leave it to the more informed to advise on the washout angle.
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Old Apr 12, 2013, 04:46 AM
InceCreations
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Hi Stu,

I found this on the net:
http://www.decker-planes.de/index.ph...art&Itemid=268

Is this model any good, heard from it before ?

Vincent
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Old Apr 12, 2013, 05:58 AM
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Since it's birds you're interested in emulating, why not choose a planform geometry a bird uses when thermaling? For instance, vultures use forward or zero sweep when thermaling. They only sweep the outer wing panels aft when desiring more speed for penetration.
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Old Apr 12, 2013, 07:11 AM
I don't like your altitude
Stupot46's Avatar
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Originally Posted by DT56 View Post
Since it's birds you're interested in emulating, why not choose a planform geometry a bird uses when thermaling? For instance, vultures use forward or zero sweep when thermaling. They only sweep the outer wing panels aft when desiring more speed for penetration.
Inspiration behind the Alula!

Vincent,That is a beauty!Sorry I don't know it,a bit more info here-
http://www.zanonia.de/yoda.php. Maybe Andres or one of the other continental guys may help.
Are you thinking of a kit purchase or a scratch build?
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Old Apr 12, 2013, 07:15 AM
I don't like your altitude
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http://www.rcgroups.com/forums/showt...t=thermal+wing
Scaled down?
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Old Apr 12, 2013, 08:12 AM
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Bern, Switzerland
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Quote:
Originally Posted by DT56 View Post
Since it's birds you're interested in emulating, why not choose a planform geometry a bird uses when thermaling? For instance, vultures use forward or zero sweep when thermaling. They only sweep the outer wing panels aft when desiring more speed for penetration.
There is an austrian guy named Robert whose flying wing models are partly inspired by eagles and likewise birds.

Here in middle europe he has a outstanding reputation as designer of tailless planes.

He sells his planes as kits. I dont know if he ships to US of A.

Here is a Picture of his latest creation, the "eyecatcher 2"



And here you find the site link to the available kits: wing-tips.at
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Old Apr 12, 2013, 08:26 AM
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Zurich
Joined Apr 2006
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Quote:
Originally Posted by DT56 View Post
Since it's birds you're interested in emulating, why not choose a planform geometry a bird uses when thermaling? For instance, vultures use forward or zero sweep when thermaling. They only sweep the outer wing panels aft when desiring more speed for penetration.
Note: as with ALL aircraft with fwd-sweep, the tips are washed-IN and perform a kind of "canard stabilizer" function. This is also true of the soaring Broad Wing Hawk raptors, incl. vultures. And the tails are often depressed to offset this and in accordance with the aerodynamics of deltas and B-2 type "Nurflügel".

L
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Old Apr 12, 2013, 09:47 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
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[QUOTE=ConEx;24700335]There is an austrian guy named Robert whose flying wing models are partly inspired by eagles and likewise

Thanks for posting that.Eye Catcher certainly lives up to it's name.Nice touch on the wing tips.
Some very nice designs on his site,priced ok as well
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Old Apr 12, 2013, 09:59 AM
less is more
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United States, CA, Marina
Joined Sep 2006
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Birds can change their static margin by changing their wing sweep angle. Moving the static margin close to zero with a forward sweep would do a lot to improve thermalling performance.......as long as you have an on-board computer for control of the resulting unstable platform.

Kent
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Old Apr 12, 2013, 04:08 PM
InceCreations
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Joined Jul 2009
720 Posts
Already thanks for the valuable tips and links.
The austrian Roberts site is realy nice.

Not sure if it will be a scratchbuild, with such nice kits around.

Vincent
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