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question please, what are MAC lines and what do they illustrate?
Thank you. 



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? 



Thank you, makes sensor but now that I have the name (Mean Aerodynamic Chord), I can do more research.








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I am not sure about this calculator but it would seem correct to include the elevons. 




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 


Joined Aug 2012
45 Posts

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 



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.




CG determination for a deltawinged plane
To determine the proper center of gravity for a deltawinged 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 fronttoback length of the center of the wing. On the Meat Eater, there's a small cutout for the motor. I'd just ignore that. 2. Determine the length of the tip chord. That's the fronttoback 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, rockstable starting point for your maiden flight. Make sure you have lots of "up" elevon travel availableparticularly if the airfoil does not have builtin 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 MeatEater. While it's not a "perfect" delta, the cutoff nose and the tips are small enough that I think their differences are negligible. Rocky 
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