Torsion axle location and rating questions.

[Cary Winch]

Andrew makes a great point. That is a common discussion point when doing weight and balance on aircraft. Many prefer to use the prop spinner for the datum point so all the math is additive. I have a plane that the weight and balance is done from the wheel spindles. It will drive you to drinkin when doing a weight and balance. My cg on that plane is 7" forward of the spindles!

Cary

[Corwin C]

We worked on weight & balance charts on an old WWI vintage airplane (I can't remember exactly which one.) I didn't understand why the reference point was 32" in front of the spinner (completely ahead of the airplane) until I had figured it a few times. The designer had done this so that all of the variable mass points on the aircraft landed at convenient to multiply locations. It made it so a proper weight and balance could be done almost in your head.

Now back to your regularly scheduled program...

I'm using the center of the ball on my calculations so everything will be positive numbers.

[angib]

I'm using the center of the ball on my calculations so everything will be positive numbers.

And when you're halfway through, you'll decide to lengthen the tongue and you'll realise why that designer chose a distance in front of the spinner....

[Corwin C]

'Tis true ... no matter how much I think it through, the plan will undoubtedly change. I'll throw a rock out in the yard and measure from there...

[LarryJ]

I'm using the center of the ball on my calculations so everything will be positive numbers.

And when you're halfway through, you'll decide to lengthen the tongue and you'll realise why that designer chose a distance in front of the spinner....

Is this why the spreadsheets measure from the back? I've been trying not to hijack this thread but through-out I've been trying to figure out the pros/cons of using either the coupler vs back.

[angib]

Is this why the spreadsheets measure from the back? I've been trying not to hijack this thread but through-out I've been trying to figure out the pros/cons of using either the coupler vs back.

It isn't that important - if you use the back, you'll later decide to lengthen the trailer by six inches - that's Sod's Law for you.

The only thing that is always useful is to put the measurement datum at, or beyond, one end - adding up positive and negative numbers will always cause mistakes in the end.

I'll throw a rock out in the yard and measure from there...

And when you get there, you'll find a local aircraft designer is already using the same rock for that purpose....

[Corwin C]

I'll throw a rock out in the yard and measure from there...

And when you get there, you'll find a local aircraft designer is already using the same rock for that purpose....

AH Ha!!! ... I AM the local aircraft designer !!! I'll use the same rock and be happy about it.