MASS AND BALANCE HELP NEEDED.

[falconp1]

Hi Guys.

Can any of you clever fellows out there please inlighten me as to how you go about doing mass and balance.

I have a fixed wing three axis Condor that is very simillar to a Beaver 550. The thing is that i can only measure the mass of the aircraft from three points. That would be the left and right wheel and from the small wheel that the tail boom rests on. This is what stumps the guys that have conventional tri gear. There is obviously a different formula for this. If im missing anything else please inform.
Any help will be appriciated.

[Morph]

The first thing you need is to know where the datum is, i.e. what is the standard point that you measure from for this model. Bushbaby's use the leading edge of the wing, others use the tip of the nose. Then you need to know what the recommended safe CG limits are, wrt the datum.

The rest is a simple calculation.

This spreadsheet works in mm. Enter the values in GREEN

First measure the distance from leading edge to trailing edge of the wing and insert this as MAC in mm

Enter the scale reading in KG and the distances in mm from the datum for the 2 wheels and the tailboom point. Enter these distances in mm into the ARM blocks. A negative number means the measurement is ahead of the datum, i.e. front wheel, and a positive is the weight is behind the datum. The aircraft should be in flying attitude and empty of fuel and humans

Then measure the distances from the Datum to the seats, Luggage box, Fuel tanks etc. Use a center point of the tank, seats etc. Enter the distances in mm in the Orange cells.

Now you can simply add the weight of the humans and luggage, (Red) and fuel in liters, (blue) for a minimum config and a maximum config. The rest will calculate itself.

[falconp1]

You,re a star Morph.

[Morph]

This spreadsheet will work for any fixed wing aircraft, nose wheel, taildragger.

The difference comes in with the ARM measurements, and the weight. A nose wheel will have a negative arm for the front wheel, and the distance from datum to front wheel will be short. The tail dragger will have a positive arm and a long distance to the tail. Enter these values right and the formula will work for any aircraft.

As I said, you just need to know, what the safe CG is wrt DATUM or % of MAC, and the POH or specification should give you this.

Here is an example of a Challenger, tricycle gear aircraft, but also stands on it's tail when empty

Left Wheel 94kg X 2286mm(90inches)
Right Wheel 99kg X 2286mm(90inches)
Tail 15kg X 5486mm(216 inches)

in this case the datum is the tip of the nose