Flying wing CG calculator - Page 9 - RC Groups
 This thread is privately moderated by z80, who may elect to delete unwanted replies.
Aug 27, 2012, 08:26 PM
Registered User
Quote:
 Originally Posted by z80 I wrote a little CG calculator for flying wings. If you have a HTML 5 browser supporting the canvas object you will get a little image of the wing too. http://fwcg.3dzone.dk Bug reports and suggestions are very welcome.
This thing is awesome. So I just put the full wing span?
 Sep 05, 2012, 09:50 PM Registered User question please, what are MAC lines and what do they illustrate? Thank you. Last edited by rimshotcopter; Sep 05, 2012 at 09:58 PM.
 Sep 05, 2012, 10:11 PM Registered User Kinda wondering that myself. The mac lines look interesting but thats it for me. Mean aerodynamic chord. Heck I don't know. Tom
 Sep 05, 2012, 10:17 PM Envies his own avatar The MAC lines stand for Mean Aerodynamic Chord. They are used to determine the average (mean) chord of the wing. If the wing is rectangular (no sweep and no taper from root to tip), the MAC is the same as the geometric chord. When there's constant sweep and/or constant taper involved, the MAC can be geographically "calculated" by extensions of the root chord and tip chord and the intersection of diagonal lines from one to the other. If the wing is ellipsoid or of varying taper, the process of determining where the MAC is located is more complicated. Does this make sense?
 Sep 05, 2012, 10:19 PM Registered User Man I was just guessing. I don't understand yet but give me time. I'll learn. Tom
 Sep 05, 2012, 10:21 PM Registered User Thank you, makes sensor but now that I have the name (Mean Aerodynamic Chord), I can do more research.
 Sep 05, 2012, 11:57 PM Envies his own avatar
Sep 30, 2012, 08:53 PM
Registered User

# Flying Wing CG

When using the wing CG calculator.....do you include the elevons in the measurements?

I apologize if this has been answered...couldn't find it in the posts.......
Thanks
Ralph Matile
Sep 30, 2012, 09:07 PM
Registered User
Quote:
 Originally Posted by rpm3 When using the wing CG calculator.....do you include the elevons in the measurements? I apologize if this has been answered...couldn't find it in the posts....... Thanks Ralph Matile
This was shared with me: https://www.rcgroups.com/forums/show...postcount=1589

I am not sure about this calculator but it would seem correct to include the elevons.
Sep 30, 2012, 09:59 PM
Registered User

# Thanks rimshot!

thanks...I thought I hadn't, but rechecked and had included them in the measurements.....I'm a few weeks away from a test flight at the pace i am going (SLOW)....looking forward to trying this hacked pico....if i keep it as light as i think....its going to have "way enough" power....
Ralph Matile
 Nov 21, 2012, 02:19 AM Registered User This is what I do I dived the Main wing by 5 like 10 /5= 2 then I add that on to the center wing works every time :+J
 Nov 22, 2012, 02:59 AM Registered User can someone please help me to calculate the centre of gravity of this wing, though its given in this plan i need to show workings on how i calculated it. Here is the plan: http://fadmuker.co.uk/html/meat_eater_plan.html
Nov 22, 2012, 07:01 AM
The original Flying Pigs Sqd.
I found this the easiest CG calculator for a flying wing. It's a simple Excel file, and shows you the formula as well as has a working formula in the spreadsheet. Just enter the measurements (either in centimeters or inches, but don't mix!) as indicated.

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Nov 29, 2012, 10:48 PM
Envies his own avatar

# CG determination for a delta-winged plane

To determine the proper center of gravity for a delta-winged plane, you must first figure out the length of the Mean Aerodynamic Chord (MAC). This is accomplished using the geometric method:

1. Determine the length of the root chord. That's the front-to-back length of the center of the wing. On the Meat Eater, there's a small cut-out for the motor. I'd just ignore that.

2. Determine the length of the tip chord. That's the front-to-back length of the tip the wing. On the Meat Eater, there's an extension at the wing tip that's rounded in the front and swept back to a point at the rear. It's pretty small, so I'd just ignore that too.

3. Draw a line forward from the front of the root chord line that's the same length as the tip chord.

4. Draw a line rearward from the rear of the root chord line that's the same length as the tip chord.

5. Draw a line forward from the front of the tip chord line that's the same length as the root chord.

6. Draw a line rearward from the rear of the tip chord line that's the same length as the root chord.

7. Connect the ends of those extended lines diagonally.

8. The two lines will cross somewhere near the center of the wing. This location is the MAC.

9. Measure the distance from the leading edge to the trailing edge at that point, and you'll have the length of the MAC.

10. Multiply that length by 0.80, and that will be the center of gravity location as measured from the trailing edge (which is usually easier than measuring from the leading edge).

That should give you a good, rock-stable starting point for your maiden flight. Make sure you have lots of "up" elevon travel available--particularly if the airfoil does not have built-in reflex. Your elevons will have to provide the reflex by themselves. If the elevons seem ineffective and/or the plane requires lots of forward stick to fly level inverted, nudge the center of gravity rearward, but do so a little at a time. Each time you move it rearward (by adjusting the battery rearward, or by removing nose weight, or by adding weight to the rear of the plane), you should find you need less reflex in the elevons to fly level when the plane is upright.

The example pictured below is for a plane called a Meat-Eater. While it's not a "perfect" delta, the cut-off nose and the tips are small enough that I think their differences are negligible.

--Rocky

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Last edited by rockyabq; Nov 29, 2012 at 10:53 PM.
Dec 05, 2012, 06:36 PM
clark ross

# delta cg

i have been locating the cg on a delta using the the flying wing formula
they always turn out nose heavy. what am i doing wrong?
cr73