It is important for stable flight that you have checked the "center of gravity" (CG) of a plane before it goes up in the air. 

1) A lot of times, the manual will tell you where the CG of the airplane. What does one do if there is no manual for the plane ? How do you check the CG (where on the wing would you try to hold and lift it up) ? Is the rule of thumb to go for the highest point on the top part of the wing ?

2) Assuming one got the CG wrong, normally what do people do to fix it ?

NB: Just stimulating some discussion that will help beginners 

Or is this question better framed as "how to determine leading edge for any given model/wing" ?

here's SOME NICE INFO
http://www.rcpowers.com/forum/blog.php?b=98


http://www.dailymotion.com/video/x7gwlx_noseheavyverticalstabilizers_tech

http://www.youtube.com/watch?v=NZtqZ2UhnDg&eurl=http%3A%2F%2Fwww.rcpowers.com%2Fforum%2Fblog.php%3Fb%3D98&feature=player_embedded

For Rc normal types you can't go wrong by taking an initial CG of 33% of chord.
Note this is for parallel chord wings - for tapered wings take mean average chord.



For freeflight - rubber or pylon type FF power - its about 50%.

if anybody wants to know more - give some specific examples and I 'll
take my best shot.


Here's another point for the sake of discussion - I,ve always wondered
if I have a sharply raked back rudder hinge line - will application
of left or right rudder also give some up elevator effect ?

Couple of my experience in designing an airplane wing with ease of CG balancing in mind.

1, Make your wing chord larger. Its is easier to balance a plane with wider wing chord than a plane with shotter wing chord. This is a simple concept - Imagine you are standing on a tight rope.. it would be better to balance yourself with a long pole in your hand than a short one.

2, Make the airfoil slightly thicker - relative to the model size. I do not have a hard number for the %age of thickness but I usually go with my instincts. - usually it would be about 10% of the chord length. I have noticed that thinner airfoils will have wing incidence issues and thicker ones are more forgiving.

-Ismail

CAN ANY ONE GIVE ME THE INFO ON CG OF A RC PLANE...??

[Admin Note]: Merged with existing discussion on CG

guys,
We usually talk about CG in terms of the balance wrt to the wings. What about the balance along the fuselage (nose to tail)?
Is it important?
How to check?

Pankaj

Yes, hold model nose to tail and check that both wings are balanced and level

Quote from: saikat on July 11, 2009, 07:25:17 AM
For Rc normal types you can't go wrong by taking an initial CG of 33% of chord.

Hi saikat,

Can you explain me this point clearly since I could not get it clear. I mean the text "intial CG of 33% of chord".

For example, the Chord length is 6", wing span is 36" and the fuse lenght is 24" then what will you be CG? Can you try and let me know? (I mean for parallel chord wing - Gliders/SPADs)

Hi to all,

Here is a link to check CG of your RC plane with TWO simple techniques... It is really easy.

http://www.rc-airplane-world.com/balancing-rc-airplanes.html

I am sure it is very simple and useful technique.

Regards
Srihari

What he means is that if you install the motor, battery etc, and the wings, mark out 1/3 of the wing chord from the leading edge (in hour example, 2" from front). then lift the model exactly at these points on the wing tip using things that are very small and blunt. The model should be balanced with just about 3-5 degree inclination towards the nose.

Thanks Pankaj, I understood.

Good and free application for calculating CG.
http://home.arcor.de/d_meissner/W_Laengs4_V26.zip

Center of gravity is generally at 25-35%. It can be found by balancing plane's wing on fingertips on vertical axis.

Question is should center of gravity be considered to lie on the wing's surface or somewhere below the wing and in the fuse. This is for a high winger plane.

If you consider both roll and pitch axis then COG will always lie in the fuselage. But the CG rarely changes for the roll axis hence we generally check CG only on the pitch axis, by balancing plane's wing on fingertips.

So for a easy star if the motor's thrust line is to be adjusted to pass thro the CG, then, should the CG be considered to be on the wing surface or in the fuse ?

In the fuse. But why do you want to change the thrust angle, the default angle works good.

Here is the Great Planes CG balancer, it is available here (http://www.greatplanes.com/reviews/gpmr2400-man.html), however a closer look, you can DIY easily. Here is the pic

$$..better to build one i guess 

@ Vector (Amar?) , augustinev : I could have bought or built the stuff, but currently I am running low on vitamin-M and vitamin-T.

@ SLS: I had fixed my motor pod after a crash and subsequently lost stock prop inflight. A 6x4E prop (which should normally fit onto easy star) would not fit on mine. Then i realized that the thrust angle was incorrect. Went thro corrective operation of the motor pod. I have not yet flown the plane after repairs as I was not 100% sure. But with these diagrams I think the thrust line is almost correct w.r.t. the original thrust line. Can be sure only after I fly again.

It looks good just toss it at 50~60% throttle for the first flight and you should be fine