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Old Dec 15, 2011, 12:12 AM
RCHN #202
Dowquest's Avatar
United States, CA, El Cajon
Joined Nov 2007
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If some of you are having trouble getting this calculator to do what you need due to forward sweep, or more complex designs, here are a few other calculators.
http://www.geistware.com/rcmodeling/cg_calc.htm#cg
http://www.geistware.com/rcmodeling/cg_super_calc.htm
http://www.scaleaero.com/CG_Calculator.htm
http://www.weflyrc.org/cg_calculator.htm
http://fwcg.3dzone.dk/
http://www.tailwindgliders.com/Files.html - scroll down and find the excel file
http://scherrer.pagesperso-orange.fr...glish/mce.html
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Old Dec 16, 2011, 09:58 PM
Living to Build'em and Fly'em.
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I've got a question for you, here's the wing design:
I'm building a wing with a balsa center that's 3 &13/16th inches wide, (blunt-nosed, like The Bizz) where I'm pitting all the electronics. The wings are foam (but not epp- their standard packing foam because the epp isn't available here) and I've added a balsa Trailing edge for secure fitting of the ailerons, as well as on the wingtips (5/16th).

The question is this... When measuring for the wingtip length, do I count the aileron as well?

It's about an inch wider at the wingtip, than it is at the end closer to the center.
The wings are 25" long, Center Cord is 11" at the Trailing edge balsa strip (12" LE-->TE, measuring the airfoil template.),with the outer wing tip being 6 1/2" to the TE balsa strip, and 8" counting the longer aileron section at the tip.

I'm new to the slope fighters, and I'm not sure if I should count the aileron because it's a control surface, but does add weight....
This is a powerless slope fighter.
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Old Dec 16, 2011, 10:28 PM
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Quote:
Originally Posted by Mr.GFC View Post
I've got a question for you, here's the wing design:
I'm building a wing with a balsa center that's 3 &13/16th inches wide, (blunt-nosed, like The Bizz) where I'm pitting all the electronics. The wings are foam (but not epp- their standard packing foam because the epp isn't available here) and I've added a balsa Trailing edge for secure fitting of the ailerons, as well as on the wingtips (5/16th).

The question is this... When measuring for the wingtip length, do I count the aileron as well?

It's about an inch wider at the wingtip, than it is at the end closer to the center.
The wings are 25" long, Center Cord is 11" at the Trailing edge balsa strip (12" LE-->TE, measuring the airfoil template.),with the outer wing tip being 6 1/2" to the TE balsa strip, and 8" counting the longer aileron section at the tip.

I'm new to the slope fighters, and I'm not sure if I should count the aileron because it's a control surface, but does add weight....
This is a powerless slope fighter.
Yes, you consider the control surfaces.
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Old Dec 17, 2011, 03:38 PM
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Thank you very much.
I'm assuming then, that I'm counting the length of the main cord + the aileron (12"), then the wingtip + the the extended length of the aileron (8").
This would give me a CG of 7" at the Cord, using 18.4%...
I'm calculating this-->
24 3/16ths" X2 for wing length=48 3/8ths... + the center pod of 3 13/16"= 52 3/16ths", with the 12" Root chord, 8" tip chord, and 11" sweep in Distance.
Once I have the wing balanced, if I need to add ballast for stronger wind conditions, it would be inserted at the CG of 7", or more toward the nose?
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Old Jan 23, 2012, 06:39 PM
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OK, so I'm building a flying wing out of 3/4in. blue foam using a KFm2 airfoil. Should I set the CG at 35-38% as for normal KFm2 wings or just set it at 25% for the usual flying wings
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Old Jan 26, 2012, 12:15 PM
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cg for wing

Quote:
Originally Posted by flipflop View Post
OK, so I'm building a flying wing out of 3/4in. blue foam using a KFm2 airfoil. Should I set the CG at 35-38% as for normal KFm2 wings or just set it at 25% for the usual flying wings
I found that setting it forward, sets the wing up for crashing. It needs to be set between 20% and 25% to get the flight characteristics stable. I set the differential to P1-40%, P2-55%, P3-70% for elivon control. The same for Elevator control.
I'm flying with the Elivons in P2, more that P1, and the Elevator seems to work just fine in P1.

P=Switch position for the % of movement.
I set the max movement so that at 100% movement, it's just under the distance where the servo starts to bind.
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Old Feb 05, 2012, 05:55 PM
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Ok, I'm not an engineer and I truly respect those that are. Here is my question.

Is locating the CG the same for a flying wing as for a delta wing plane with rear stablizers. I can only assume that the CG for the entire plane would also be the same as just the wing regardless whether it had tail feathers or not.

Frank.
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Old Feb 06, 2012, 09:56 AM
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Quote:
Originally Posted by countilaw View Post
Ok, I'm not an engineer and I truly respect those that are. Here is my question.

Is locating the CG the same for a flying wing as for a delta wing plane with rear stablizers. I can only assume that the CG for the entire plane would also be the same as just the wing regardless whether it had tail feathers or not.

Frank.
I have found that it needs to be closer to the expert location for it to have stable flight characteristics. I tried setting the CG at beginner/test, but the wing was just not stable. I added 28 grams just in-front of the trailing edge, which moved the CG to 23% and was finally able to get it to stay in the air without wanting to spin when turning.
I have also discovered by comparison, that the Slinger vs my current slope fighter, has a much narrower wing-tip, which makes the Slinger prone to spinning as well.
The plane I built that I'm referring to can be seen here:http://www.rcgroups.com/forums/member.php?u=369624
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Old Mar 21, 2012, 12:40 AM
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I have tried several multi panel CG calculators as "Dowquest" posted.

Trouble is I got conflicting results for a 20% CG setting, between 90-170mm from the nose. My visual guess would put it at around 160mm.

This makes the build difficult to design right. I would have liked to have built with a pre configured ballast option. I will need to maiden the incomplete wing and dial in the correct CG before finalising the build.

Appreciate any advice from people that have tried the various calculators and which one was most accurate for a multi panel flying wing.

These are my measured dimensions of the modified wing cores.
Inner panel: per side (mm) root=260, tip=220, span=190, angle=29 degrees.
Outer panel: per side (mm) root=220, tip=140, span=328, angle=15 degrees.

Pictures of the build are here:
http://www.rcgroups.com/forums/showt...994291&page=27
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Old Mar 21, 2012, 07:29 AM
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Cleansurf,

The links in the post you referenced are all for single panel wings, as far as I could tell.

Flying Wing Calc at my website works for multiple panel wings.
I put your data into the spreadsheet and here is what I come up with:
5% static margin = 146mm aft of the root leading edge.

Just to make sure I got my data correct I went to this website:
http://adamone.rchomepage.com/cg2_calc.htm
and input the information you provided and came up with a balance location with a 5% static margin of 146.27mm.

I had to do some conversions for the leading edge angle vs 1/4 chord angle but they obviously are correct!

That's close enough for me!
Best of luck with your project.

Curtis
Montana
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Old Mar 21, 2012, 07:30 AM
Red Merle ALES
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Oh, a 20% CG setting is the same as 5% static margin, I'm not sure if that's clear to you or not.

Curtis
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Old Mar 25, 2012, 03:29 AM
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CloudyIFR,

Much appreciated.
I've saved your site to my favourites, good info there.
Yours was the pick of the bunch that I did manage to find for multi panel flying wings (nice work).

I did a maiden on the wing today to dial in CG before I can complete the build.
Currently have the CG at 137mm from the nose. I had it back as far as around 146, no big handling issues there, just brought it forward for a safer feel. So looks like yours was pretty dam accurate. One other multi panel CG calc gave me a result of around 80mm.

I could measure my LE angle, but didn't understand how to get the numbers needed in the calc (1/4 chord angle ?).
I don't get this quote from your post sorry, "5% static margin = 146mm aft of the root leading edge."
Could you explain please how to work out the calculator numbers required for the sweep angle.

thanks
Rick
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Old Mar 25, 2012, 08:45 AM
Red Merle ALES
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United States, Mt, Helena
Joined Apr 2002
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Rick,

The leading edge angle is fairly easy to measure.
The distance aft a panels tip is from it's root is easy to measure.

Aerodynamic formulas need the quarter chord angle.

I added a conversion tool just below the wing info, see attached screenshot.

You either need to know the "leading edge angle" or the "distance the panels leading edge tip is aft of the root. The example in the attached screenshot is for you outer panel and in a previous post you had given me the leading edge angle of 15 degrees so I used that and got the quarter chord angle of 11.69 degrees and typed that in above.

Hope this helps. Thanks for the kind words on my spreadsheet.

Curtis
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Old Mar 25, 2012, 11:39 AM
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Wing CG Calculator

This is the CG calculator that I used.

Click Here

It's specific for flying wings.
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Old Mar 26, 2012, 03:01 AM
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Thanks CloudyIFR
that does help.

Mr.GFC,
That is a great CG calc for single panel flying wings. I use to use it a lot too, but have gotten into more complex shapes and had to step it up a notch, which is where CloudyIFR multi panel CG calc comes in really handy.

cheers
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