Tip weight formula? Can a formula be developed perhaps using half the weight of the lines and then adding an equal amount of tip weight? Then could a percentage of the line weight added to the tip weight? Would the plane then need to balance at something outside the center line of the plane? Granted the 'formula' would not be exact but it might provide a good and safe starting point. It seems this might be better than "add x amount of pennies". So a penny for your thoughts.
Can be :-)
Question is how exact answer you expect. It will give you number little under 1oz and for the security and with respect of material selection you will come to real weight little over 1oz. And it will be good and safe starting point. :- ))))))
Exactly like LINE-xx program will tell you line rake. It is also “some” useful number. Both methods are very scientific, but both miss reality.
I have formula which works to some extent, but since tip weight needs also subjective tuning, then no “computerized” method gives good answer.
Here are some thoughts:
Tip weight must counterbalance the weight of the fuselage. It is mounted inboard of center of lift, because center of lift is approximately an inch right of the geometrical center of wing because of circular path of the model (outer wing is quicker).
The same is necessary to do for wing and tail.
The problem is, that we use asymmetric flaps, and therefore position of center of wing depends of amount of extended flaps. But the tip weight is important in corners, so we have to calculate it with flaps extended to corner – and that is point which depends on personal preferences (or abilities).
Position of center of lift also depends on yaw.
We have also lines, but lines in corner does not follow model so quick, so they does not change the result so dramatically. For example when I tried thinner lines on my trimmed model, I had to do many changes, but tip weight was the same after retrim. I switched from 0.40 mm line to 0.36 what makes theoretical difference 5g/2.
So for me … The best way I found is to calculate center of lift in corner with respect of “my” corner radius and flaps chord/are asymmetry. Then I add weight to put the CG to that point. It is still too little, but model is yawed little and it is enough to balance lines also in level flight. For example – my fuselage including rudder needs 21g … my wing asymmetry needs 9g … and my real tip weight measured by scale in center of symmetric wing is 29g
However it is good to start trimming with little heavier tip and subtract during trimming. So I would say, make it short and use 1oz