kurtverbose
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Overweight or out of balance aircraft - isn't this automatically monitored?

Mon Sep 30, 2019 11:01 am

I was reading about this Dash 8 incident where the airline made an assumption about the weight of the passengers that turned out to be wrong and eventually aborted a takeoff. The aircraft was significantly heavier than assumed and out of C of G limits.

I realise this is a smaller and older aircraft, but there are quite a few incidents of aircraft being overweight or out of C of G limits, and even of aircraft being underweight and not carrying enough fuel.

Isn't this monitored passively - e.g. through the landing gear load? I'd have thought it would be relatively easy to monitor this and then red flag the pilot if it was significantly different from what was entered in the flight management computer.
 
GalaxyFlyer
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Mon Sep 30, 2019 1:17 pm

No, no accurate enough. Used to be manual, now computers. An old -8, manual.

GF
 
VSMUT
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Mon Sep 30, 2019 4:55 pm

In theory it sounds simple enough, but there are major issues. Rainwater, snow and deicing fluid on top of the wings, even wind blowing over the wing and elevators creating lift would change the result.

Additionally, those kinds of sensors are really, really fragile and a general nuisance to keep functional, and the landing gear is subject to lots of wind, water, rain, ice and dirt. They would break down like there was no tomorrow.
 
kurtverbose
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Mon Sep 30, 2019 7:06 pm

Thanks guys, makes sense.
 
spacecadet
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Tue Oct 01, 2019 12:16 am

Not to mention, that would give you a (potentially inaccurate) total weight, but you would never be able to properly calculate CG. You could write software that would be able to give a rough approximation based on the weight on the nosewheel vs. weight on the main gear vs. total weight, but this is definitely not a proper CG calculation, where you're calculating weights, moments and arms for all items inside the aircraft, meaning you know the center of mass of all of those items, wherever they actually are. That lets you move stuff around if you have to in order to keep the plane within its CG limits, which is impossible if you're just doing a rough guesstimate based on total weight at two or three points on the aircraft.

I don't know if you've ever been in a plane where they ask for 6 or 7 volunteers to move up from the back to the front of the cabin, or something like that. I've had this happen several times. That's to get the plane within its CG limits, but they'd only know to do that by doing a proper calculation rather than just measuring the weight on the wheels. It's entirely possible that measuring at the gear would show no change whatsoever to the weight on either the nose or main landing gear, even though just that number of people moving up a few rows could mean the difference between a plane being out or within its CG limit. The existing software that calculates based on average weights does know that.
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Max Q
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Tue Oct 01, 2019 12:18 am

Having said all that the freighter version of the 747 have had optional
‘self weighing’ systems installed for years
The best contribution to safety is a competent Pilot.


Guns and the love of them by a loud minority are a malignant and deadly cancer inflicted on American society
 
strfyr51
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Tue Oct 01, 2019 4:01 am

I saw this happen twice while I worked the terminal for United at SFO. Once the US Treasury wanted a gondola container Loaded in the most aft position on a DC8 The container weighed close to 5,000 Lbs and it was loaded in a 500Lb Position where the weight X Arm nearly tipped the Airplane on to it's tail. Then the ramp foreman and the Treasury agents argued that they Every right to Load it where it was, Well? The Captain settled that by refusing the airplane Until the container was removed and the load rebalanced, Whatever was in the container? Wound up being repacked in an LD11 and being loaded on a DC-10.
 
JayinKitsap
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Tue Oct 01, 2019 5:25 am

spacecadet wrote:
Not to mention, that would give you a (potentially inaccurate) total weight, but you would never be able to properly calculate CG. You could write software that would be able to give a rough approximation based on the weight on the nosewheel vs. weight on the main gear vs. total weight, but this is definitely not a proper CG calculation, where you're calculating weights, moments and arms for all items inside the aircraft, meaning you know the center of mass of all of those items, wherever they actually are. That lets you move stuff around if you have to in order to keep the plane within its CG limits, which is impossible if you're just doing a rough guesstimate based on total weight at two or three points on the aircraft.

I don't know if you've ever been in a plane where they ask for 6 or 7 volunteers to move up from the back to the front of the cabin, or something like that. I've had this happen several times. That's to get the plane within its CG limits, but they'd only know to do that by doing a proper calculation rather than just measuring the weight on the wheels. It's entirely possible that measuring at the gear would show no change whatsoever to the weight on either the nose or main landing gear, even though just that number of people moving up a few rows could mean the difference between a plane being out or within its CG limit. The existing software that calculates based on average weights does know that.


In the absence of wind (that could mess things up big time) having accurate strain gauges on the gear would give very accurate weight and CG calculations, plus with the MLG in a line + nose wheel it is structurally determinant. However, a calculated CG based on the payload where it is located and the fuel where it is located gives much better results. That is because the fuel gets used up in flight, but hopefully nothing else. Using just the gear there is no way to know accurately where the fuel is at the beginning. It would need to have a weight and balance done using gear reactions with it at zero fuel weight.
 
buzzard302
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Tue Oct 01, 2019 2:29 pm

Although it might be considered intrusive and slow down the process, airlines could implement a scale each passenger steps on as they scan their tickets. The computer could then map the weight associated with each seat position and automate total weight and CG calculations. I assume something like this has never been done because there are simpler methods that help calculate total weight. If I recall correctly, they make a general weight assumption for each male and female passenger on board, and the averages are usually close enough?
 
kurtverbose
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Tue Oct 01, 2019 7:26 pm

I guess the more pasengers boarded the closer to the average they will be.

A 15 seat plane carrying a rugby team would be way off though.
 
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Faro
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Fri Oct 04, 2019 6:14 pm

Best solution would be to have weight-sensing pads under the areas where the MLG and nose gear would rest...but that would probably come with its own set of issues, including cost...


Faro
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Armadillo1
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Fri Oct 04, 2019 8:39 pm

may be this topic more suited for this link:
http://avherald.com/h?article=4cd54844&opt=0
An Air Greenland de Havilland Dash 8-200, registration OY-GRJ performing flight GL-548 from Nuuk to Kangerlussuaq (Greenland) with 29 passengers and 3 crew, was accelerating for takeoff from Nuuk's runway 05 when the crew rejected takeoff above Vr due to the aircraft not rotating despite full back pressure on the yoke. The aircraft slowed safely and stopped about 50 meters short of the end of the runway.

...



The mass and balance calculations, based on standard masses, prepared by the flight crew before the flight and subsequently by the AIB resulted in a CG within aircraft CG limitations.

The mass and balance calculation, based on actual masses (an increase of masses compared to standard masses of approximately 13% on crew, wardrobe, passengers and carry-on hand baggage), prepared by the AIB resulted in a CG 2.4 inches forward of and outside aircraft operational CG limitations.

To the AIB, actual masses above standard masses resulted in the CG being forward of and outside aircraft operational CG limitations and was the root cause to reduced aircraft rotation ability.
 
VSMUT
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Fri Oct 04, 2019 9:19 pm

Faro wrote:
Best solution would be to have weight-sensing pads under the areas where the MLG and nose gear would rest...but that would probably come with its own set of issues, including cost...


Faro


No, that would be just as useless. Rain, ice, snow and wind would still affect the balance.
Weighing of aircraft is done in a windless and dry hangar for a reason.
 
WPvsMW
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Fri Oct 04, 2019 9:48 pm

The only accurate automated solution would be sensors embedded in flex circuits along all stringers and frames. Thousands of sensors. Baseline from dry, windless hangar measurements. In use, processor has met inputs (wind, precip, etc.) to eliminate the inputs not related to C/G calc. With the rapid adoption of processors embedded in flex circuits, it's certainly doable, and would produce results more accurate than manual calc.
 
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Starlionblue
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Sat Oct 05, 2019 7:14 am

VSMUT wrote:
Faro wrote:
Best solution would be to have weight-sensing pads under the areas where the MLG and nose gear would rest...but that would probably come with its own set of issues, including cost...


Faro


No, that would be just as useless. Rain, ice, snow and wind would still affect the balance.
Weighing of aircraft is done in a windless and dry hangar for a reason.


Indeed. Closed doors are mandatory.
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kurtverbose
Topic Author
Posts: 552
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Re: Overweight or out of balance aircraft - isn't this automatically monitored?

Sun Oct 06, 2019 8:03 am

Armadillo1 wrote:
may be this topic more suited for this link:
http://avherald.com/h?article=4cd54844&opt=0
An Air Greenland de Havilland Dash 8-200, registration OY-GRJ performing flight GL-548 from Nuuk to Kangerlussuaq (Greenland) with 29 passengers and 3 crew, was accelerating for takeoff from Nuuk's runway 05 when the crew rejected takeoff above Vr due to the aircraft not rotating despite full back pressure on the yoke. The aircraft slowed safely and stopped about 50 meters short of the end of the runway.

...



The mass and balance calculations, based on standard masses, prepared by the flight crew before the flight and subsequently by the AIB resulted in a CG within aircraft CG limitations.

The mass and balance calculation, based on actual masses (an increase of masses compared to standard masses of approximately 13% on crew, wardrobe, passengers and carry-on hand baggage), prepared by the AIB resulted in a CG 2.4 inches forward of and outside aircraft operational CG limitations.

To the AIB, actual masses above standard masses resulted in the CG being forward of and outside aircraft operational CG limitations and was the root cause to reduced aircraft rotation ability.


I can tell you've carefully read the thread before posting.
 
DashTrash
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Overweight or out of balance aircraft - isn't this automatically monitored?

Sun Oct 06, 2019 3:11 pm

Hard for me to imagine a -200 that far out of CG to where it wouldn’t rotate. I’d be interested to see if something was off with the spring tabs.

I’m not going to say it’s not possible, but I bet there’s more to the story.


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