Earthstar Forums

Actually it is transferable.
Just measure from the nose and you have your aircraft arm.
Happy Flying
Mark

Sent from my iPhone

Hey Guys,

What does everyone use as the datum point for a seat?

I am presently using the center radius point of where the seat bottom and the seat back are formed.

Because of the seat shape... I can only presume this is a standard location point to use for establishing the datum point for use in calculating CG...? Is this a viable assumption on my part?

Thanks for the input...

John
N701SY

Hi John
The human body's centeroid is the belly button.
Happy Flying
Mark
Sent from my iPhone

Hi Mark,



Of course your correct, I knew that already J. I will take a new measurement of the pilot seat arm with me sitting in the plane, and go from there.



Thanks again for the info…



John

But the arm charts already have the seat station specified and shouldn’t have to be re-measured, just as in the fuel tank has it’s location specified. I did find that the nose of my plane sticks out less than the distance to the nose-wheel axle specified in the arm chart, so I used the datum point at an imaginary location about 2 inches out from the nose to make the nose-wheel arm correct, then to the mains. I then assumed the pilot arm and fuel tank arm were correct with respect to the other arms and it all worked out. I used a clean floor and a small framing square to get the axle mid-points down to the floor, drew a line and measured back to the datum point ahead of the nose-wheel and marked on the floor. A plumb-bob to the floor gave me the wing leading edge reference which also was fine. We drill all of our new plane owners and builders to pay attention to w&b and take the time to do it right.

Hi Mark,



I do/did exactly as you described to gather all my measurements.



My fuel tank is installed and secured at the very back of the airframe, wedged tight against the V shape of the aft fuselage tubing, not as shown in the manual apparently being much farther forward.



I will re-measure everything tomorrow and relocate my 0 datum initial point to match the manual’s nose-wheel arm location. Since my mains are swept back, contrary to the manual, I will adjust the main gear arm accordingly.



Thanks Again… sorry, I hope I am not coming off to everyone as the groups dumb pest with all my questions. And I absolutely agree with your last comment



Best Regards,



John

It's always better to ask questions than to wander off into the dark with out any guidance.
Weight and balance problems have been the end of to many good airplanes. Taking care to understand
All the ins and outs of balance is what makes a good plane work.
Happy Flying
Mark
Sent from my iPhone

If this was FB, I'd "like" Mark's reply. ;)

Alan

The pipe/axle doesn't touch the plane. The plane was sitting on a
stiffened pallet like you'd see at a Lowes. The pallet was rolled back
and forth on the pipe.

This wasn't done in a real scientific way. It was pretty much a lark ..
just something to play with :-)

Ed Baker
FlyBoy Acres, LLC
(860) 315-7581 ph


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it's scientific alright :)
pallets' a new word for me, sit on a stack of old heavy beams like them, on the rooftop all the time

Rahul
+91 981 134 0544
Jaipur, India