Is there a fulcrum placement formula?

[Mat]

I'm wondering because I am attempting to desighn a simple plane and I didnt think my plane would easily come close to balancing at the calculated CG. Is there a formula where you can put in the weight of your electronics and see if it will balance a an aproximate spot without adding weight?

[kdwzagi]

Is there a formula where you can put in the weight of your electronics and see if it will balance a an aproximate spot without adding weight?

hi

i think you will have to build it to find out, if the plane is of a conventional layout then the centre of the battery is normally in front of the c of g a little

there is a simple formulae for balance but without building the plane i don't think it will help you much

weight*distance=weight*distance

ie 10g 100mm from the fulcrum will balance with 5g at 200mm


but if your designing something a bit wacky then you will just have to build it and see

if you need a c of g calculator try mine in the modeling science section

all the best

[Mat]

So if your plane without electronics/ motor balanced on th cg and the motor weighs 2 oz and the battery is 6 oz your would put the motor 6 in front of the leanth back that the batery is? Do you center the battery, wouldn't the father away half of the battery weigh more because it has more distance to move and same with the motor. would the units of inches work for this.

Also the plane I am making is a flying wing and the cg came out fairly differtnt then on the palos rc webpage calculations.

[FlyByMike]

You'd put the motor 3 times further away from the CoG than the Batt; or put the batt 1/3 closer to the Cog than the motor. Maybe the pic helps. (Imagine a teeter-totter situation :) )
-Mike
ed: change dimensions & mispelling

[Andy W]

It's a lot easier to install components that cannot be moved (i.e. motor, servos, and possible the Rx), then place the model on balance points at the CG, and move the battery around on top of the fuselage until you get it to balance. Mark the spot with tape, and figure out a way to get it to mount inside at that location.
..a

[Mat]

I cant belive I made that simple math mistake!
Would the would you just fing the approximate cg of the motor and is the cg of the motor at the 3in forward in the picture.

[FlyByMike]

I cant belive I made that simple math mistake!
Would the would you just fing the approximate cg of the motor and is the cg of the motor at the 3in forward in the picture.Mat,
If I understand you correctly, yes, the CoG of the motor would be at the 3" place in the pic. And the same way for the batt- the CoG of the batt would be 1" from the plane's CoG.
-Mike

[kdwzagi]

hi

your first post asked for a formulae to calculate the balance point

this has just been posted on another forum

http://www.electrifly.uk.com/Keith/k@r/MikeRollsDesignspreadsheetsAug03Vtails.xls

there is a part of it that that lets you input the weight and position of your servo's and other stuff to get the balance correct

i havn't tried it myself so if it works can you let me know

all the best

kev