WPvsMW
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Posts: 1990
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Onboard W&B check system

Wed Mar 13, 2019 8:07 pm

IMO, the ET302 crash could be a C/G problem (control problems started immediately)... but even if there was a different cause, it spurred the thought: why not add some sensors and logic to an a/c to report a W&B-related C/G problem before leaving the gate?

There could be both a static and a dynamic test. Static test based on sensors at the NLG and MLG. Dynamic test based on those sensors and tail sensors; dynamic test performed with a percussion applied to the tail skid or other hard point, or maybe with a calibrated pull by the tug.
 
Max Q
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Re: Onboard W&B check system

Thu Mar 14, 2019 2:24 am

I believe there is an optional built in weight and balance system on the 744 and 748 freighters
The best contribution to safety is a competent Pilot.
 
747Whale
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Re: Onboard W&B check system

Thu Mar 14, 2019 5:21 am

We've had this discussion before.

Weight and balance is a bit too important to leave to dirty worn uncalibrated sensors on the gear. Various aircraft have had them, or have them; weight and balance is derived based on calculations and measurements beyond a simple weighting on the gear; the number is also variable and must be calculated separately: zero fuel weight, and the center of gravity as it's impacted by fuel burn or shifting, etc.
 
WPvsMW
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Re: Onboard W&B check system

Thu Mar 14, 2019 6:13 am

Whale, your point is well taken re: static data from gear only, which is why I suggest adding a dynamic test, which would be far more accurate. The static data would provide weight, and a first approximation of balance.

Imagine a hundred accelerometers (like in your smart phone) distributed throughout a frame. That could give you the C/G to a micrometer. The alleys could have a "test bump" to trigger the dynamic sensor readout. Stripes on the alley for motion sensors to read to calculate ground speed.

Boeing and others have IP on strut-based systems ... but they are not dynamic.
https://patents.google.com/patent/US20080119967A1/en

https://patents.google.com/?q=~patent%2fUS20080119967A1
 
stratclub
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Re: Onboard W&B check system

Fri Mar 15, 2019 6:55 am

If you know the weights on the main gear and nose gear, MAC and CG can be easily calculated. There is no need to make something very simple complicated. Adding a bunch of tech can sometimes make a problem worse.

To the Ethiopians the concept of MAC and CG probably are concepts that escape them. Third world countries flying aircraft can be a scary proposition.
 
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747classic
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Re: Onboard W&B check system

Fri Mar 15, 2019 12:43 pm

KLM has since 1975 a calibrated W&B computer at their 742, 743 and 744 fleet (all pax, combi and full freighter).
All gear loads are measured via the axles (strain gauges) and are indicated by actual aircraft weight and MAC position (CG).
At the start of the operation in the seventies we had some reliability issues, but later the operation went very smooth.
On the 742 and 743 fleet : with a difference exceeding 7000 kgs (MTOW 377.000 kgs) or 3% CG, compared to the loadsheet data, we had to re-check the loadsheet and/or the actual loading.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
ChrisKen
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Re: Onboard W&B check system

Fri Mar 15, 2019 1:00 pm

stratclub wrote:
To the Ethiopians the concept of MAC and CG probably are concepts that escape them. Third world countries flying aircraft can be a scary proposition.

What a blinkered, nonsensical and frankly disgusting point of view. All Ethiopians (3rd worlders) are retards? Grow the fark up, Eithiopian aviation has the same professionals within it as any other dam country.
 
stratclub
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Re: Onboard W&B check system

Fri Mar 15, 2019 8:14 pm

ChrisKen wrote:
stratclub wrote:
To the Ethiopians the concept of MAC and CG probably are concepts that escape them. Third world countries flying aircraft can be a scary proposition.

What a blinkered, nonsensical and frankly disgusting point of view. All Ethiopians (3rd worlders) are retards? Grow the fark up, Eithiopian aviation has the same professionals within it as any other dam country.


I have talked to field service folks that have first hand seen operations in 3rd world countries such as many countries in Africa and true not all operators are deficient in maintenance and procedures, but without a doubt some operators have room for improvement.

I will con-seed that my comment is just an opinion about African carriers in general, more so than fact about Ethiopian Airlines safety record. Ethiopian's safety record actually is good compared to other African airlines. https://en.wikipedia.org/wiki/Ethiopian ... _incidents

I do appreciate you wanting me to expand on my comment. I do not appreciate you assuming things about my comment I did not say. I don't believe Jerry Springer is a MOD on this forum...........
 
Max Q
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Re: Onboard W&B check system

Fri Mar 15, 2019 10:41 pm

747classic wrote:
KLM has since 1975 a calibrated W&B computer at their 742, 743 and 744 fleet (all pax, combi and full freighter).
All gear loads are measured via the axles (strain gauges) and are indicated by actual aircraft weight and MAC position (CG).
At the start of the operation in the seventies we had some reliability issues, but later the operation went very smooth.
On the 742 and 743 fleet : with a difference exceeding 7000 kgs (MTOW 377.000 kgs) or 3% CG, compared to the loadsheet data, we had to re-check the loadsheet and/or the actual loading.



Interesting, where was the readout for these weights and CG position on the Classic, on the FE panel ?
The best contribution to safety is a competent Pilot.
 
WPvsMW
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Re: Onboard W&B check system

Fri Mar 15, 2019 11:04 pm

stratclub wrote:
If you know the weights on the main gear and nose gear, MAC and CG can be easily calculated. There is no need to make something very simple complicated. Adding a bunch of tech can sometimes make a problem worse.
.


By MAC, do you mean mean aerodynamic chord, or do you mean the aerodynamic center of the MAC?
https://en.wikipedia.org/wiki/Aerodynamic_center

The dynamic test would be more accurate, and also a double check on the static test. The strut based systems do work (viz., KL jumbos), but the ones I know of lack redundancy.

747classic wrote:
KLM has since 1975 a calibrated W&B computer at their 742, 743 and 744 fleet (all pax, combi and full freighter).


747classic, do you recall the supplier of the W&B computer system?
 
stratclub
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Re: Onboard W&B check system

Fri Mar 15, 2019 11:47 pm

WPvsMW wrote:
stratclub wrote:
If you know the weights on the main gear and nose gear, MAC and CG can be easily calculated. There is no need to make something very simple complicated. Adding a bunch of tech can sometimes make a problem worse.
.


By MAC, do you mean mean aerodynamic chord, or do you mean the aerodynamic center of the MAC?
https://en.wikipedia.org/wiki/Aerodynamic_center

The dynamic test would be more accurate, and also a double check on the static test. The strut based systems do work (viz., KL jumbos), but the ones I know of lack redundancy.

747classic wrote:
KLM has since 1975 a calibrated W&B computer at their 742, 743 and 744 fleet (all pax, combi and full freighter).


747classic, do you recall the supplier of the W&B computer system?

Mean Aerodynamic Chord. I meant those W & B calculations I learned in AMT school and soon forgot after I took the test. CG and MAC are calculated from static weight measurements IIRC. Center of pressure has a direct correlation to the fwd and aft MAC range allowed which is calculated by engineering.

For weight and balance purposes you would use the MAC range as provided by the appropriate document as your target for aircraft loading. Center of pressure is used by engineering as part of defining MAC limits and IIRC would not be referenced in the Weight and Balance manual.

I have no clue about what dynamic weight and balance is.
 
WPvsMW
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Re: Onboard W&B check system

Sat Mar 16, 2019 12:38 am

For operations, having the C/G within the MAC range is the rule of thumb. Aligning the aerodynamic center of the MAC (center of lift aka center of pressure) with the fore/aft center of load is the "engineer's optimum". The center of pressure is usually about a quarter of the chord behind the leading edge. The more fore or aft of that center the load center is, the weirder the handling becomes. More refinement is starboard/port centering plus fore/aft centering.
https://en.wikipedia.org/wiki/Center_of ... _mechanics)
https://en.wikipedia.org/wiki/Chord_(aeronautics)#Mean_aerodynamic_chord

Dynamic tests are more accurate than static... like tire balancing at a tire shop.
 
747Whale
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Re: Onboard W&B check system

Sat Mar 16, 2019 3:56 am

A final weight with a center of gravity is only part of the picture. It's also important to know the empty weight and CG, and the influence of fuel , and of the zero fuel weight and center of gravity. All have import. All are necessary to know.
 
WPvsMW
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Posts: 1990
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Re: Onboard W&B check system

Sat Mar 16, 2019 5:46 am

The EW, EW C/G, ZFW, and and ZFW C/G don't change, correct? They can be stored uniquely for each frame.

General remark: A dynamic W&B has the additional advantage of indicating how stressed the frame is in turbulence, hard landing, etc., things a static system can't do. If all the gear isn't bearing all the aircraft weight, a strut-based system isn't accurate.
 
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747classic
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Re: Onboard W&B check system

Sat Mar 16, 2019 1:34 pm

For the 747 classics the W&B computer (optional) was installed at the F/E panel, individual gears could be calibrated in flight with the gears up. I will try to find the OEM.

For the 744 (and also the 748) the digital W&B system was (still is) delivered by Honeywell, see : https://www.flightglobal.com/FlightPDFA ... 202060.PDF
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
kalvado
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Re: Onboard W&B check system

Sat Mar 16, 2019 2:11 pm

my strong impression is that the existing situation allows airlines legally dispatch overweight flights, and nobody wants to give up that opportunity.
Ever been to a regional flight where they ask people to collect gate check bags and put them in a cabin, as otherwise plane is too heavy to fly?

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