Center of gravity

[Bennie Vorster]

Ok, next question.

How do I check and set the center of gravity on my BB.

and do I do it with full tanks or not?

[Mogas]

Hi Bennie
Here is the CofG for my BB, ZU-DZI.
Adapt to suit your BB if you wish but you should have a good understanding of it if you do it yourself. If not, please get an AP to do it.
C of G range is as quoted from Kitplanes for Africa.
Also note that if your aerie has a nose wheel, use a negative figure for the arm as it will be forward of the datum.

[Morph]

Bennie,

you cant use this spreadsheet as is. I have asked Monty to supply us with the correct arm values for the nosewheel version

[Smiley]

Just pick the plane up at the leading spar...! If it falls forward you fly, if not, put your parachute on....

[Morph]

Alteratively you can measure them yourself. The datum is the leading edge of the wing. I understand you have to get the plane into a flying attitude, i.e. set the plane up with blocks of wood etc so that the belly of the plane is level, left to right front to back (as per Monty's instructions)

Drop a plumb line (piece of string with a weight) from the leading edge to the ground on both sides of the fuse and draw a line using chalk. Now measure the distance in mm from this line backwards to the centre of the main wheel. Put this value in the spreadsheet. Do the same for the other main wheel (it should be the same, I don't know why Mogas has 60mm on the one and 87mm on the other. Then measure forward to the middle of the nose wheel and put this value in as a negative.

Measure the distance from wing leading edge to the back edge of the flapperon (they have used 1290mm). If it is different change the values in the calculations in cells J26, j37 and J47

weigh the plane in this attitude using 3 scales (preferably) but if you only have 1 scale you will need two blocks of wood with exactly the same height as the scale. Support two wheels with these blocks and weigh the third. Then move the scale to the next.

I would weigh it with no fuel empty, then with one and then two people. Then full fuel at max all up weight with 1 and 2 people. This is neccessary to show you how the CG will change as you are flying and using up the fuel.

[Mogas]

Arms were measured. Yes Morph, there is a difference in the main wheel arms. I used actual arms rather than data from Monty.

[Morph]

I forgot we are talking mm here and the difference is 27mm, my challenger was done in inches and in the back of my mind I was thinking how can the one wheel be 27inches i.e 685mm further back than the other

[Morph]

Here is the spreadheet from Monty with measurements for the average tricycle version Explorer