On Wed, 13 May 2009 15:10:26 -0500, Jim Logajan wrote:

Honeywell has such a system for big aircraft:

http://www.honeywell.com/sites/aero/...rs3_C91E0E6C1-
A71D-06B3-97EC-617A9F35BEC1_H33815F58-00F1-0786-C716-E0431B6C7F21.htm

Honeywell advert on this link (contains embedded PDF):
http://www.flightglobal.com/pdfarchi...0-%200862.html

A twenty-two year old advert

Some Googling has turned up another system that was used on 707s called
STAN, which stood for "Sum Total and Nose". It was reported to work well.

I'm not surprised that this has been done but it obviously hasn't caught
on and that is surprising. It has found use in other industries: "many
excavators and forklifts have integrated weighing equipment".

I'm studying for a Bachelor of Aviation degree and my lecturer was able
to list a bunch of incidents and accidents which were caused by the crew
entering the wrong weight, so it appears that there is a safety case for
such a system. Weight and cost are the two things that would prevent this
from "going mainstream", but this doesn't seem to be a job that requires
heavy or expensive components.

I've come across a few other threads discussing this system, and I think
this quote gives the best explanation for why we don't see this system on
more aircraft:

"The issue is that you need to certify the thing, or you can't use it for
any flight crew annunciations. So, to certify it, you need to be able to
guarantee performance. And, if you can't certify it, you can't take any
credit for it being there. Still a potential safety improvement, but not
nearly as cost effective as beating on the flight crew and dispatches to
make sure they actually put in the real weight."

Definitely worthy of investigation by enterprising homebuilt
experimentalists. Strain gauges are not that expensive, but do require
careful attention to physical attachment and interface electronics.

No certification hurdles in the homebuilt arena