Mouse Posted May 19, 2015 Share Posted May 19, 2015 Hi there The model in question is a parkzone sport cub and i am having great problems setting the c of g correctly. when i try to set it with the plane upside down (as i was shown to do by a member of my local club) i just cannot get it right, the c o g always seems to be to far forwards or to far back, no matter how small the movements of the battery are, i have even tried four differnt types of battery. However if i turn the plane the right way up and support the wings from underneath the c o g is on the right spot and if i use a differnt battery i only need to move it a small amount to obtain the correct c o g. Is it o.k to do it this way and why does it make a differance what way up the plane is, most of the items on the internet show planes both ways up with the same c o g. Help please Bill. Quote Link to comment Share on other sites More sharing options...
KingKade Posted May 19, 2015 Share Posted May 19, 2015 If the cub you have is a high winger, you balance it right way up.... If its a low winger i would turn it upside down...... Quote Link to comment Share on other sites More sharing options...
KingKade Posted May 19, 2015 Share Posted May 19, 2015 Reason? Im sure someone else could explain better... If a high winger is upside down, all the mass is above the wing so small movements throw the weight to one side of the balance point...thats why youhave to turn a low winger over...... Btw balance point is different to c of g.... Someone help!!!!! Edited By KingKade on 19/05/2015 14:20:42 Edited By KingKade on 19/05/2015 14:21:41 Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted May 19, 2015 Share Posted May 19, 2015 Posted by KingKade on 19/05/2015 14:16:29: If the cub you have is a high winger, you balance it right way up.... If its a low winger i would turn it upside down...... What he said...... Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 19, 2015 Share Posted May 19, 2015 mouse Remember the CofG is a 'point' within the structure of the plane so if you try to balance a high wing plane upside down you are pivoting about a point below the CofG. In this state it is unstable so will topple either forward or backward. Balance a high with plane the right way up and the CofG is below the pivot so it is stable. If it is nose heavy the plane will simply balance slightly nose down and vice versa. So it is entirely logical to balance a high wing plane the right way up but make sure it does balance with the fuselage level. Now if you want balance a low wing plane like a Spitfire then it has to be done upside down! Hope this helps. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted May 19, 2015 Share Posted May 19, 2015 Thirded what he said! Reason: the CoG is a three-dimensional point in space, it has height as well as fore/aft, side-to-side. So, you need to put the 3D location of the CoG below the point of support by your fingers. The point will be somewhere in the cabin, so you need to have the "somewhere in the cabin" lower than your fingers! Hence for the cub, which is high-winger, support the model right way up. If you try to do it upside down then you are not only balancing the aircraft you are effectively balancing a pole on your fingertips at the same time! BEB Quote Link to comment Share on other sites More sharing options...
Pete B Posted May 19, 2015 Share Posted May 19, 2015 The C of G of a model isn't exactly a position on either the top or underside of a wing. It is almost always hidden deep within the fuselage. We look for the position where it balances in the fore-and-aft balance sense. By trying to balance the model with the C of G higher than the pivot, it will tend to fall one way or the other. If you suspend the model so the C of G is lower than the pivot, it's much easier. With a high winger, finding the C of G with the model inverted is about as easy as finding the C of G of an egg by standing it on its pointy bit..... Pete ps Blimey, I was a bit slow there..... Edited By Pete B - Moderator on 19/05/2015 14:38:06 Quote Link to comment Share on other sites More sharing options...
Bill_B Posted May 19, 2015 Share Posted May 19, 2015 Mouse, I should give that particular club member a wide berth in future! Quote Link to comment Share on other sites More sharing options...
Mouse Posted May 19, 2015 Author Share Posted May 19, 2015 Thank you all for the replys, and the explaintions. I did wonder why you would balance a plane upsidedown, especialy as i want to fly it right way up (joke). Bill_B, comment noted and agread with, just waiting for the wind to drop now. Mouse. Quote Link to comment Share on other sites More sharing options...
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