C of G

[Bubbles]

I have been given what l belief to be an old Minimoa Glider. At least it looks like one. It was past around a club l have just joined,from member to member , for a refurb but no one did. No tow hook so guess it was for slope
The ailerons were on bellcranks, with tissue covering, and the wing itself was nylon and old dope. I have stripped and put in modern servos and antique shrink fabric.
I guess the model is 20 plus yrs old from its overall construction and appearance
There is a big chunk of lead in the nose. I have no information on Cof G
The wingspan is 3M and cord 245mm.
So 25%,(a bit far forward) is 61.25 mm and 1/3 is 81.66
I have set my Balencer at 70 mm and with battery and Rx etc in position and with original lead it is still quite tail heavy.
For a test flight would you go for a Balence at 70mm or something else.
If anyone has a Minimoa would be interested to know your CG position from Leading edge.
Many thanks

[chris williams]

If it actually is a Minimoa, then the CG will probably be nearer 50% root chord, because of the sweepback of the outer panels

[Jilles]

Use the calculator of attached link. pick the wing type, say 2 panels for the Minimoa. enter the figures. For Vintage gliders I recommend a 10% static margin. Click and you get the C.O.G location measured from the L/E.
I used this on all my vintage gliders. It will be spot on for the maiden flight.Depending on what you want from the glider make adjustments as you like.
The general rule among model pilots is to set the C.O.G at about 30% or under the main spar. As Chris W already mentioned the sweep or shape of the wing is also critical. The surface area and position of the horz.stab elevator is even more critical.
When building a model plane at 100% scale including the horz. stab/elevator the surface area is at the smaller scale less effective then at prototype scale
By moving the C.O.G a bit more forward then the general rule this problem is solved. The C.O.G calculater includes details of the tail bits and calculates accordingly.


https://rcplanes.online/cg_calc.htm

[Bubbles]

Thanks for replies. Yes looking at the drawing certainly a Minimoa. Only difference seems to be on my wing the aileron is only 12 inches and not full length of outer panel.
Will get out the long ruler and start some measurements for the C of G calculator.

[Bubbles]

As a matter of interest just put the Minimoa together again with new battery and original weight back in place and set my balencer at 122 mm.....ie 50% and Nose heavy.
Adjusting the balencer it is balancing exactly on 105mm, so just over 40%. So maybe that is about right!!

[Bubbles]

Just done the math as they say. Calculator says 120 mm from L E. So about 48%. Very interesting exercise