Measurement of CofG

At 16:57 15 January 2012, Dan Marotta wrote:
Thanks for a good technical reply.

Now I just have to check and see if any of my measuring devices have
decimal
inch/cm graduations. Seems most are graduated in 1/16th, etc... Let/s
see... That would be 200 inches long and 2 and 14.4/16 inches high. Oh,

crap! There's that pesky decimal again. I know - I'll make my triangle
2,000 inches long and 29 inches high! Now, if I could just find a surface

on the glider where I can make that fit.

Really, how accurately can you measure 2.9 inches, mark it, and cut it? I

don't have a machine shop. This all reminds me of the old Air Force
adage:

Why would you want to use inches specifically? the ratio 2000:29 could be
inches, millimeters, bananas or ay other unit you might wish to use, that
is why it is expressed that way, works whatever system of measurement you
care to use. A distance of 10000mm with a drop of 145mm would seem to me
pretty easy to set up.

Actually, I mistyped. It's 100:2.9 and, yes, I understand that it's a ratio
and unitless. Still, I don't have any tools which measure nine tenths of
anything, be they banannas, apples, inches, or millimeters. The point I was
trying to make is that such precision as 1/1000th of a degree really isn't
necessary. When I attended engineering school, I used a slide rule, not a
computer, and I learned that close enough is good enough.


"Don Johnstone" wrote in message
.com...
At 16:57 15 January 2012, Dan Marotta wrote:
Thanks for a good technical reply.

Now I just have to check and see if any of my measuring devices have
decimal
inch/cm graduations. Seems most are graduated in 1/16th, etc... Let/s
see... That would be 200 inches long and 2 and 14.4/16 inches high. Oh,

crap! There's that pesky decimal again. I know - I'll make my triangle
2,000 inches long and 29 inches high! Now, if I could just find a surface

on the glider where I can make that fit.

Really, how accurately can you measure 2.9 inches, mark it, and cut it? I

don't have a machine shop. This all reminds me of the old Air Force
adage:

Why would you want to use inches specifically? the ratio 2000:29 could be
inches, millimeters, bananas or ay other unit you might wish to use, that
is why it is expressed that way, works whatever system of measurement you
care to use. A distance of 10000mm with a drop of 145mm would seem to me
pretty easy to set up.

On Jan 16, 8:13*am, "Dan Marotta" wrote:
I like the idea of a "beeping" level which would allow a single person to
complete the operation. *And I *really* like the design of Wayne's "wedge".

Bob, thanks for stating what I've always felt, i.e., the TLAR method is good
enough (2-7/8"). *I was (wrongly) getting the impression that people were
stuck on precision which I couldn't attain. *It would seem pointless to
measure the angle to a gnat's ass and then fly with boots and a heavy jacket
one day and shorts and sneakers the next.

One more time - Wayne, I LIKE the design of your wedge. *I think I'll build
one. *And ask the manufacturer why they don't include at least a drawing for
a device to level the fuselage.

"Bob Kuykendall" wrote in message

...
On Jan 15, 8:57 am, "Dan Marotta" wrote:

Really, how accurately can you measure 2.9 inches, mark it, and cut it?

I think that just on the far side of 2-7/8" would do just fine.

...it looks like 100:2.9 is an angle of 1.6618 degrees. Will a
digital level get that accuracy? *Is that accuracy really necessary?

Most digital levels will offer repeatable measurements to 0.1 degrees,
and I think that that is close enough. In this case I'd feel fine
about a reading of 1.7 degrees. For my fuselage, the exact tailboom
slope is 1.213 degrees, but 1.2 or even 1-1/4 degrees would be fine.

What's the good of a parallel surface if it's not accessible? Why not
make,
say, the arm rest parallel to the longitudinal axis? Then you could simply
place a carpenter's level on the arm rest and, voila!

Thanks, the armrest trick is a good idea, I might adopt that; it would
be useful for people who have digital levels that beep when they're
actually level.

Thanks again, Bob K.

when we did the W & B for my Tetra we used a 24" level and a 1/2" tall
socket, with the level located as required by Bob it was easy to set
everything up on scales. I had my engineer friend do the
math............empty weight came out at 479 pounds!

Brad