Since we're talking electronic sensors...

G'day,

I've been enjoying the AoA thread and it is kind-of related to another
idea which has been floating around in my head since the Emirates near-
disaster a couple of months ago. Basically, an Emirates A340 used every
inch (and a bit more!) of the 12000 foot runway at Melbourne airport
because the crew mistakenly entered the weight as 260 tonnes instead of
360 tonnes.

The question was asked in another forum: why doesn't the aircraft have
sensors in the landing gear so that it knows it's exact weight? It would
also be able to calculate it's centre of gravity if such sensors were
installed.

Yes, I realise the genesis of this question has nothing to do with
homebuilt aircraft BUT to my mind (having no electronic skills or
experience whatsoever) this should be a trivial problem and if such a
system were developed all aircraft, homebuilt and otherwise, would
benefit. Besides, the people with the skills to tackle this problem
reside in this newsgroup

I would be very interested to hear your thoughts!

Michael

"M" == Michael writes:

M The question was asked in another forum: why doesn't the
M aircraft have sensors in the landing gear so that it knows it's
M exact weight? It would also be able to calculate it's centre of
M gravity if such sensors were installed.

M Yes, I realise the genesis of this question has nothing to do
M with homebuilt aircraft BUT to my mind (having no electronic
M skills or experience whatsoever) this should be a trivial
M problem and if such a system were developed all aircraft,
M homebuilt and otherwise, would benefit. Besides, the people
M with the skills to tackle this problem reside in this newsgroup

Hmm, quite interesting and it should indeed be very feasible,
especially a trike. Glue some strain gages on each landing gear and
connect to the appropriate measurement device and A2D converter. Have
a cheap microprocessor convert the digital signal to weight on each
gear leg and display; calibrate once with a scale at a few different
weights (empty, gross, nose heavy, tail heavy). Quite the fun and
practical project.

--
It is a government of the people by the people for the people no
longer; it is a government of corporations by corporations for
corporations.
~ Rutherford B. Hayes

Michael wrote:
The question was asked in another forum: why doesn't the aircraft have
sensors in the landing gear so that it knows it's exact weight? It
would also be able to calculate it's centre of gravity if such sensors
were installed.

Honeywell has such a system for big aircraft:

http://www.honeywell.com/sites/aero/...431B6C7F21.htm

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

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.

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

"Michael" wrote in message
...
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".

AFAIK, an integral weighing system was also supplied on the Lockheed L-1011.

I don't know how it worked, nor whether it was integrated with any other
systems. However, in the very probable case that the systems are not fully
integrated, the propability of occasional data entry errors would remain.

Just my $0.02
Peter

On 14 May, 11:37, Michael wrote:
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.
This was discussed somewhere where quite a few active
airline pilots hang out and they were most unimpressed by
the concept. One issue raised was they they did not really
want to know what the all up weight actually was. Or at least the
management didn't want to have to own up. That's what they
said anyway.

The technology is for sure used in aviation - engine torque
sensor for example will use strain gauge I would think.

I've made a toy one and it is all quite easy but a certifiable one
is clearly another matter altogether.

bod43 wrote:
On 14 May, 11:37, Michael wrote:
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.
This was discussed somewhere where quite a few active
airline pilots hang out and they were most unimpressed by
the concept. One issue raised was they they did not really
want to know what the all up weight actually was. Or at least the
management didn't want to have to own up. That's what they
said anyway.

The technology is for sure used in aviation - engine torque
sensor for example will use strain gauge I would think.

I've made a toy one and it is all quite easy but a certifiable one
is clearly another matter altogether.


I can't speak for all aircraft but some use oil pressure for
measuring torque. For the life of me I can't recall how it's done, I
just remember changing a torque transmitter on a T-29 in 1975. There was
a port on the front of the crank case near the shaft. A capillary tube
lead from there to the transmitter a few feet back.

Dan, U.S. Air Force, retired

On 14 May 2009 10:37:08 GMT, Michael
wrote:



"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."


I've heard a discussion of this and the point made was that the wings
are still flying while parked on the ground. in still air the system
would work but with a breeze, or worse in gusts, the system may never
sense the actual aircraft weight.

the other problem was calibrating the weighing (certifying the thing)
and finding really horizontal ground all the time.

on most light private aircraft just how critical is the weight anyway?
do you think it might be a solution in search of a problem?
Stealth Pilot

"Stealth Pilot" wrote in message
...
On 14 May 2009 10:37:08 GMT, Michael
wrote:



"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."


I've heard a discussion of this and the point made was that the wings
are still flying while parked on the ground. in still air the system
would work but with a breeze, or worse in gusts, the system may never
sense the actual aircraft weight.

the other problem was calibrating the weighing (certifying the thing)
and finding really horizontal ground all the time.

on most light private aircraft just how critical is the weight anyway?
do you think it might be a solution in search of a problem?
Stealth Pilot

Thanks for remindig me, because those are two of the three reasons why such
a system can never give an accurate weight and balance.

The thrid, which is closely related, is hysteresis in the system--especially
if the brakes are applied and/or hydraulic and/or pneumatic pressure is
measured.

As an asside--I was amazed to witness how little air movement it takes to
totally disrupt the weighing of a light aircraft. You really couldn't feel
any breeze, but we still had to close the hangar doors to get usefull
results!

Peter

Stealth Pilot wrote:
On 14 May 2009 10:37:08 GMT, Michael
wrote:


"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."


I've heard a discussion of this and the point made was that the wings
are still flying while parked on the ground. in still air the system
would work but with a breeze, or worse in gusts, the system may never
sense the actual aircraft weight.

the other problem was calibrating the weighing (certifying the thing)
and finding really horizontal ground all the time.

on most light private aircraft just how critical is the weight anyway?
do you think it might be a solution in search of a problem?
Stealth Pilot
While I'd agree with that last pair of rhetorical questions if all
pilots exercised some semblance of good judgment, perusal of accident
records will quickly reveal how critical excess weight can be.

Charlie