I'm helping a chapter member do the initial weight measurements on his
plane. I think we have everything except what point should be used for
the seat positions. I didn't see it addressed in the weight and balance
section of AC 43.13.

What point along the seat is considered the center of a sitting person?
I know an inch or two either way won't make a bunch of difference, but
we might as well start with the best number achievable.

Thanks

On Jan 31, 2:14*pm, "Paul Dow (Remove CAPS in address)"
> wrote:
> I'm helping a chapter member do the initial weight measurements on his
> plane. I think we have everything except what point should be used for
> the seat positions. I didn't see it addressed in the weight and balance
> section of AC 43.13.
>
> What point along the seat is considered the center of a sitting person?
> I know an inch or two either way won't make a bunch of difference, but
> we might as well start with the best number achievable.
>
> Thanks

Use the guy's belt buckle. It's pretty close.

Dan

Or you could weigh the aircraft without the pilot. Then with the pilot. Take the difference in the tailwheel weights and multiply it by the distance between the tail wheel and main mounts. Divide the product of the calculation by the pilot's weight. The result will be the distance from the main mount to the pilot seat.

See paragraph B in the W&B calculation near the bottom of the following link:
http://www.soaridaho.com/Schreder/Schreder/Soaring_Aug_1976_HP-18.html

Wayne
HP-14 6F
http://www.tinyurl.com/N990-6F


> wrote in message ...
On Jan 31, 2:14 pm, "Paul Dow (Remove CAPS in address)"
> wrote:
> I'm helping a chapter member do the initial weight measurements on his
> plane. I think we have everything except what point should be used for
> the seat positions. I didn't see it addressed in the weight and balance
> section of AC 43.13.
>
> What point along the seat is considered the center of a sitting person?
> I know an inch or two either way won't make a bunch of difference, but
> we might as well start with the best number achievable.
>
> Thanks

Use the guy's belt buckle. It's pretty close.

Dan

"Wayne Paul" > wrote in message
m...
Or you could weigh the aircraft without the pilot. Then with the pilot.
Take the difference in the tailwheel weights and multiply it by the distance
between the tail wheel and main mounts. Divide the product of the
calculation by the pilot's weight. The result will be the distance from the
main mount to the pilot seat.

See paragraph B in the W&B calculation near the bottom of the following
link:
http://www.soaridaho.com/Schreder/Schreder/Soaring_Aug_1976_HP-18.html

Wayne
HP-14 6F
http://www.tinyurl.com/N990-6F


--------------new post begins---------

Remember to first level the aircraft.

Assuming that it is not an original design, there should be a recomended
datum line specified for that purpose.

(Also, please use the axle positions rather than the undercarriage mounting
positions.)

Peter

wrote:
> On Jan 31, 2:14 pm, "Paul Dow (Remove CAPS in address)"
> > wrote:
>> I'm helping a chapter member do the initial weight measurements on his
>> plane. I think we have everything except what point should be used for
>> the seat positions. I didn't see it addressed in the weight and balance
>> section of AC 43.13.
>>
>> What point along the seat is considered the center of a sitting person?
>> I know an inch or two either way won't make a bunch of difference, but
>> we might as well start with the best number achievable.
>>
>> Thanks
>
> Use the guy's belt buckle. It's pretty close.
>
> Dan


Seconded.

In a seated position this works out pretty well.

--

Richard Lamb
http://www.home.earthlink.net/~cavelamb/

Thanks for the replies everyone.

The scales were borrowed, so it would be difficult to get them back
again to do the measurements. That procedure makes sense though.

The belt buckle idea seems pretty good. The seats don't have much
recline, so my big butt / fat head should balance each other out.

Paul

I had asked another friend this question, and he's a member of our
chapter, and the one in Hartford. Joe Gauthier (EAA Homebuilt Council)
is also a member of the Hartford chapter, and Joe agreed that the belt
buckle method was what should be used if we couldn't use the 'weigh the
pilot while the plane's on the scales' method.

Thanks again.
Paul

On Sun, 31 Jan 2010 16:14:32 -0500, "Paul Dow (Remove CAPS in
address)" > wrote:

>I'm helping a chapter member do the initial weight measurements on his
>plane. I think we have everything except what point should be used for
>the seat positions. I didn't see it addressed in the weight and balance
>section of AC 43.13.
>
>What point along the seat is considered the center of a sitting person?
>I know an inch or two either way won't make a bunch of difference, but
>we might as well start with the best number achievable.
>
>Thanks

anthropomorphically a seated pilots cg is about an inch aft of his
belly button.
as dan says use the location of his belt buckle. you wont detect the
difference.

Stealth Pilot