Battery location planning

[radioflier]

I'm in the middle of scratch-building a plane originally designed for glow. How do you plan for the configuration and placement of the battery pack when you don't know exactly where its going to end up? I would like to use the location of the pack to assist in getting the balance point right without adding nose/tail weight.

Ron
:confused:

[Andy W]

You often just don't know until everything else is installed. You can guess by figuring out the weight of the glow model you're planning to replace, and asking other modelers who have this model how it balanced (did they have to add weight)..
..a

[radioflier]

That's what I suspected. My guess is that the battery pack will most likely end up somewhere near the leading edge of the wing since I am replacing the called-for 4-stroke and elimating the fuel tank, throttle servo, and receiver battery pack.

[Norm]

Ron, I try to completely frame up my models before any covering is completed. I then place all the equipment (servos, etc.) where I'd like to put them. With everything installed and the tail feathers pinned on, I balance the model with the battery pack in it. For a low wing plane, I simply lay the battery pack on the bottom of the plane while I balance it. This gets me real close to where the pack will end up, keeping in mind there will be more covering weight behind the CG than ahead of it.

Norm

[Dereck]

Hi Ron
The two medium size conversions I've done - Sig 4*40 and GP CAP 232 - have both ended up with the battery middle point not far off the kit's CG. Talking to other 4*40 owners, nose-heaviness is a real possibility - mine has the fus servos and RX just aft of the wing, for starters and the pack rear end (either 16 or 20 2400) is back under the front end of the canopy. That's with a geared MaxCim 13Y and ESC up front - one of the lighter of its power bracket.

Norm's idea is as good as you're likely to find. Both mine have ply battery trays mounted on rails glued to the fuselage insides - made the rails longer than needed, allowing for sliding the battery on its tray around some to fix the CG of a part built model with all its wood bits pinned or taped in place and the RC gear and so on fitted. Made that tray an inch longer to allow for fine tweaking later, guessed as to where the balance uncovered should be to allow for covering and finished.

If you really want to do it the hard way - get hold of Andy Lennon's "RC model airplane design". Chapter 3 is on how to estimate balance by putting the components over a fus drawing on a plank balanced on a fulcrum under the CG. You then figure an estimate of the structural weights, control runs, glue, covering and stuff.

While doing this, you have to read the book and stay awake too! ;)

I'd do what Norm and Andy W suggest :)

Regards

Dereck