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Weighing Scale In The Landing Gear?  
User currently offlineAlessandro From , joined Dec 1969, posts, RR:
Posted (5 years 6 months 1 week 6 days 8 hours ago) and read 5943 times:

To avoid planes taking off with too little fuel (like the ATR-72 Turinter and Gimli-glider)
and also have the right balance (central gravity) on the plane and notice overloading of aircrafts, would it make sense to have
wieghing scales on all landing gear. I read in a book about UN operations in Congo-Kinshasa where pilots on a aircraft would put their fist inbetween a place in the landinggear if you could
do that the plane wasn´t overload if not it was.

36 replies: All unread, showing first 25:
 
User currently offlineMetroliner From United Kingdom, joined Jan 2007, 1067 posts, RR: 1
Reply 1, posted (5 years 6 months 1 week 6 days 8 hours ago) and read 5940 times:

Normally, if there's any doubt about the readings from the tanks, you can work out the fuel remaining in them by using the logbook, or by checking with fuellers.

Aircraft do have pressure sensors in the gear to ascertain whether the plane is on the ground or not - for things like thrust reverser and ground spoiler operation.

I also heard something about piezoelectric weight sensors on the gear - but very vague, and I'm not sure if it would be accurate enough to measure fuel load by.

Quoting Alessandro (Thread starter):
UN operations in Congo-Kinshasa

That doesn't sound like standard operating procedure for many airlines!  Smile



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User currently offlineAlessandro From , joined Dec 1969, posts, RR:
Reply 2, posted (5 years 6 months 1 week 6 days 8 hours ago) and read 5938 times:

Metroliner, the 1960ies UN operations in Congo-Kinshasa was cowboy flying.
So how did Gimbli glider and Turinter crash happen? Firstly if the pilot had an indication that
the weight was too low, he/she could notice the take off, was it normal or shorter than a
take-off should be for this amount of weight?


User currently offlineMetroliner From United Kingdom, joined Jan 2007, 1067 posts, RR: 1
Reply 3, posted (5 years 6 months 1 week 6 days 8 hours ago) and read 5932 times:



Quoting Alessandro (Reply 2):
Firstly if the pilot had an indication that
the weight was too low, he/she could notice the take off, was it normal or shorter than a
take-off should be for this amount of weight

My knowledge is still that of the enthusiastic amateur, so I can only give you partial answers.  Smile

For what it's worth, noticing the load on take-off by feel alone is a pretty difficult thing to do - since all take-offs are different. Also, in the case of the Gimli Glider, the pilots made an error in computing the onboard fuel and then drew the rest of their calculations from it. The Tuninter case is less familiar to me, but I'd suspect the same thing happened.

What is unclear to me is why nobody seemed to check the fuel gauges on either plane before take-off - or perhaps they did, and assumed they were reading kilograms instead of pounds or some such error.

Quoting Alessandro (Reply 2):
cowboy flying

Well, the 'gouge' they used to check the loading is probably based on years of experience, so it has its use too  Smile



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User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 4, posted (5 years 6 months 1 week 6 days 8 hours ago) and read 5939 times:



Quoting Metroliner (Reply 1):
Aircraft do have pressure sensors in the gear to ascertain whether the plane is on the ground or not - for things like thrust reverser and ground spoiler operation.

Most aircraft use magnetic (squat) switches or speed sensors on the wheels, for ground sense (thrust reverse/auto ground spoilers).


User currently offlineMetroliner From United Kingdom, joined Jan 2007, 1067 posts, RR: 1
Reply 5, posted (5 years 6 months 1 week 6 days 8 hours ago) and read 5935 times:



Quoting 474218 (Reply 4):
Most aircraft use magnetic (squat) switches or speed sensors on the wheels, for ground sense (thrust reverse/auto ground spoilers).

Ahh, cheers  Smile I wasn't sure exactly how they worked.

But there is no system in place to measure their exact weight?



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User currently offlineZANL188 From United States of America, joined exactly 8 years ago today! , 3546 posts, RR: 0
Reply 6, posted (5 years 6 months 1 week 6 days 6 hours ago) and read 5927 times:
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Quoting Metroliner (Reply 3):
What is unclear to me is why nobody seemed to check the fuel gauges on either plane before take-off - or perhaps they did, and assumed they were reading kilograms instead of pounds or some such error.

Fuel quantity indicating system on the AC 767 was inop. This was the first item in the accident chain.



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User currently offlineOly720man From United Kingdom, joined May 2004, 6808 posts, RR: 11
Reply 7, posted (5 years 6 months 1 week 6 days 6 hours ago) and read 5917 times:



Quoting Metroliner (Reply 5):
But there is no system in place to measure their exact weight?

The problem with any sort of mechanism for weighing an aircraft, mounted on the aircraft, is that the mechanism itself becomes part of the load bearing structure of the aircraft, with all the design, safety and reliability issues that then become involved. It would be very difficult to integrate such a device into the undercarriage and I expect operators would not be favourable.



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User currently offlineJetstar From United States of America, joined May 2003, 1650 posts, RR: 10
Reply 8, posted (5 years 6 months 1 week 6 days 5 hours ago) and read 5896 times:
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I think it could be done very easily

I would do it with the main landing gear strut compression. As long as the strut pressure is set right, a remote pressure gauge could be used to verify strut pressure then a potentiometer measuring the angle between the upper and lower drag links or one drag link and the strut could be calibrated to convert angle to weight.

On the JetStar, I could rough guess about how much fuel the pilots landed with by just looking at the extension of the struts.

JetStar


User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 9, posted (5 years 6 months 1 week 6 days 5 hours ago) and read 5879 times:



Quoting Alessandro (Reply 2):
So how did Gimbli glider and Turinter crash happen?

People not paying attention....



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 10, posted (5 years 6 months 1 week 6 days 3 hours ago) and read 5831 times:



Quoting Alessandro (Thread starter):
To avoid planes taking off with too little fuel (like the ATR-72 Turinter and Gimli-glider)
and also have the right balance (central gravity) on the plane and notice overloading of aircrafts, would it make sense to have
wieghing scales on all landing gear.

It's present on some aircraft now, but it's very hard to do it accurately. You can do it well enough to make sure you've got the stabilizer set right for the CG, but I think that's about it.

Quoting Metroliner (Reply 1):
I also heard something about piezoelectric weight sensors on the gear - but very vague, and I'm not sure if it would be accurate enough to measure fuel load by.

I don't think it's accurate enough for measuring fuel load, but the 777 uses a piezo sensor on the main landing gear beam as an air-ground sensor, so the concept can certainly work.

Quoting Metroliner (Reply 5):
But there is no system in place to measure their exact weight?

The FQIS measures exact weight. It really all starts from there...if the gross weight you put in the computer doesn't match OEW+payload+fuel, you know you have a problem.

Tom.


User currently offlineTristarSteve From Sweden, joined Nov 2005, 4022 posts, RR: 33
Reply 11, posted (5 years 6 months 1 week 6 days 3 hours ago) and read 5829 times:

The B747 and B777 have a pressure sensor on the nose gear strut that measures oleo pressure. This used to drive the green band on the stab trim indicator. But only in sectors. It gives the crew a quick balance check on dep.

Many years ago STAN was fitted to the BEA Merchantmen and worked in much the same way, but was on all three gears and showed weight of aircraft. But it was not very accurate.

There is no reason not to fit these to aircraft, but the problem is getting them accurate. If you consider it a gross error check OK, but you can't weigh aircraft on strut pressure accurately on the ramp. Biggest problem is that the struts have a lot of stiction and don't slide smoothly during loading, they move in jerks.


User currently offlinePart147 From Ireland, joined Dec 2008, 510 posts, RR: 0
Reply 12, posted (5 years 6 months 1 week 6 days 2 hours ago) and read 5739 times:

Hmmm, nice idea, but maybe a better solution would be to park the aircraft on a number of scales set into the concrete at the gate (like a weight bridge for trucks) - and that will solve the 'extra weight in the aircraft' problem!

This would only be useful to verify the fuel uploaded at the gate though - IIRC the gimli glider lost it's fuel during the flight itself so that kind of problem wouldn't have 'shown up' on the ground anyway!



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User currently offlineAlessandro From , joined Dec 1969, posts, RR:
Reply 13, posted (5 years 6 months 1 week 6 days 2 hours ago) and read 5730 times:

Part147, I think the Azores flight did, Gimli was too light when it took off.
Got another answer that the flying tigers tried two different systems out, first on the DC8 and then the B742, none of them worked so they where scrapped.
See, still things to invent out there, I wonder about helicopters, would that be easier to measure?


User currently offlineAlessandro From , joined Dec 1969, posts, RR:
Reply 14, posted (5 years 6 months 1 week 6 days 1 hour ago) and read 5730 times:



Quoting Metroliner (Reply 3):
My knowledge is still that of the enthusiastic amateur, so I can only give you partial answers.

For what it's worth, noticing the load on take-off by feel alone is a pretty difficult thing to do - since all take-offs are different. Also, in the case of the Gimli Glider, the pilots made an error in computing the onboard fuel and then drew the rest of their calculations from it. The Tuninter case is less familiar to me, but I'd suspect the same thing happened.

What is unclear to me is why nobody seemed to check the fuel gauges on either plane before take-off - or perhaps they did, and assumed they were reading kilograms instead of pounds or some such error.

Tuninter was a faulty fuelgauge, an ATR-42 gauge instead of an ATR-72 installed on the plane.


User currently offlineOldtimer From United Kingdom, joined Aug 2006, 191 posts, RR: 1
Reply 15, posted (5 years 6 months 1 week 5 days 22 hours ago) and read 5674 times:

The Gimi glider had both fuel gauges u/s. Fuel loading was carried by using the dripsticks in the tanks, unfortuneately, the crew thought the readings were in kg but they were in lbs so basically they had less than half the fuel they thought they had.

Can't remember now but either the L1011 or DC10 had a gross weight indicator, haven't worked on either since early eighties, but the F/E's said thay never used them as they were not certified for use so used load sheets for gross weight.



Oldtimer, I should have known better!
User currently offlineOkie From United States of America, joined Jul 2003, 3100 posts, RR: 3
Reply 16, posted (5 years 6 months 1 week 5 days 19 hours ago) and read 5610 times:



Quoting Oldtimer (Reply 15):
Can't remember now but either the L1011 or DC10 had a gross weight indicator, haven't worked on either since early eighties, but the F/E's said thay never used them as they were not certified for use so used load sheets for gross weight.

Gross weight indication was an "advertised option" on the 741 during its public introduction.
Most operators did not buy the option and from what I can remember that there were either reliability issues involved with the system or inacuracies and was abondoned quickly.
Whether the reasons were engineering in nature or too few units to sustain factory/manufacturing support or both I do not know.

There were a lot of items on aircraft from that era that do not exist anymore. 1,000 round dial gauges, and a F/E for starters.

Okie


User currently offlineDocLightning From United States of America, joined Nov 2005, 19927 posts, RR: 59
Reply 17, posted (5 years 6 months 1 week 5 days 15 hours ago) and read 5543 times:



Quoting Oly720man (Reply 7):

The problem with any sort of mechanism for weighing an aircraft, mounted on the aircraft, is that the mechanism itself becomes part of the load bearing structure of the aircraft, with all the design, safety and reliability issues that then become involved. It would be very difficult to integrate such a device into the undercarriage and I expect operators would not be favourable.

Not really. It merely needs to measure how compressed a spring of known compressibility is. The landing gear have shock absorbers, which are springs of known compressibility. All you need is the measurement device, which is neither integral nor load-bearing.


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 18, posted (5 years 6 months 1 week 5 days 15 hours ago) and read 5529 times:



Quoting TristarSteve (Reply 11):
Many years ago STAN was fitted to the BEA Merchantmen and worked in much the same way, but was on all three gears and showed weight of aircraft. But it was not very accurate.

Many Boeing 707 freighters had the STAN (Sum Total and Nose) system fitted, and it proved to be very accurate, IF properly maintained.


User currently offlineTristarSteve From Sweden, joined Nov 2005, 4022 posts, RR: 33
Reply 19, posted (5 years 6 months 1 week 5 days 14 hours ago) and read 5527 times:



Quoting Metroliner (Reply 1):
Aircraft do have pressure sensors in the gear to ascertain whether the plane is on the ground or not

The B777 uses strain gauges on the landing gear support beam to provide a Weight on Wheels signal.
I wonder if a more sophisticated version could provide weight output?


User currently offlineZappbrannigan From Australia, joined Oct 2008, 247 posts, RR: 0
Reply 20, posted (5 years 6 months 1 week 5 days 10 hours ago) and read 5468 times:

Without being an engineer, I think strut-based weighing devices wouldn't be able to calculate ramp weight accurately enough to make them a replacement for the current methods of determining ramp/TOW. I can imagine them requiring excessive levels of frequent calibration to produce a legally usable TOW with aircraft that weigh in excess of 400 tonne in many cases - which would immediately fail the all-important $$$ test.

However I can definitely see a system that can detect obvious errors in weight calculation - e.g. the EK A340 that departed here a few weeks ago with an apparently massive error in the FMS weight input - closest Australia's ever been to a catastrophic air disaster - a good 300m of tail-drag off the end of a 3600m/11,000' runway - very large discrepancy in calculated vs. required V-speeds. When the input vs. calculated ramp/TOW/ZFW is out by tens of thousands of kilos, then perhaps this is a case where such a system would save the day.


User currently offlineZappbrannigan From Australia, joined Oct 2008, 247 posts, RR: 0
Reply 21, posted (5 years 6 months 1 week 5 days 10 hours ago) and read 5464 times:



Quoting Alessandro (Reply 2):
So how did Gimbli glider and Turinter crash happen? Firstly if the pilot had an indication that
the weight was too low, he/she could notice the take off, was it normal or shorter than a
take-off should be for this amount of weight?

I read in the official Flight Safety magazine in this country on the 20th anniversary a couple of years ago that the Gimli takeoff was conducted at higher thrust than normal for the calculated weight (let alone the actual weight), and due to this the crew may not have noticed any unusual performance increase.

Quoting Metroliner (Reply 3):
What is unclear to me is why nobody seemed to check the fuel gauges on either plane before take-off - or perhaps they did, and assumed they were reading kilograms instead of pounds or some such error.

I'm sure it's been mentioned heaps in this thread - the Gimli Glider's problems began with inop fuel gauges (which were properly MEL'ed), coupled with errors in litres to pounds vs. kilos calculations by ground crew.


User currently offlineDavid L From United Kingdom, joined May 1999, 9524 posts, RR: 42
Reply 22, posted (5 years 6 months 1 week 5 days 8 hours ago) and read 5435 times:



Quoting Alessandro (Reply 14):
Tuninter was a faulty fuelgauge, an ATR-42 gauge instead of an ATR-72 installed on the plane.

Yes, so they did check a gauge that appeared to indicate that they had enough fuel. It was the fact that it showed the wrong quantity that was the problem. This was compounded by the assumption that the overnight change in the indication was due to refuelling, with no check of the corresponding paperwork.

If you add another system to indicate the aircraft's weight (using the same safeguards) you could still fit the wrong part and get an incorrect weight indication. It might just be simpler to prevent the wrong fuel gauge from being fitted, as was the case with the ATR fuel gauges after the Tuninter accident... and to check the paperwork before departing.  Smile


User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 23, posted (5 years 6 months 1 week 5 days 3 hours ago) and read 5367 times:



Quoting Alessandro (Reply 14):
Tuninter was a faulty fuelgauge

The fuel gauge was not faulty... it worked just fine. The issues was it was not for the type of aircraft it was installed in.



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineRedFlyer From United States of America, joined Feb 2005, 4354 posts, RR: 28
Reply 24, posted (5 years 6 months 1 week 5 days 3 hours ago) and read 5361 times:



Quoting TristarSteve (Reply 11):
If you consider it a gross error check OK, but you can't weigh aircraft on strut pressure accurately on the ramp.

IMO, wouldn't a gross-error check make it worthwhile? The thread on the A345 tailstrike in MEL last month is reporting that the pilots entered the planes T/O weight incorrectly and it was off by around 100t. If the system could measure the weight to, say, 10% of actual it could act as a general "catch-all" safety check. Not something to be used for T/O performance calculations, but simply as a "Are you sure your numbers are correct?" warning.



My other home is a Piper Cherokee 180C
25 Ceph : Oh man... I was beaten to this... I was thinking of making something like this for my Aeronautical Engineering diploma Final Year Project. Had that id
26 Tdscanuck : The problem is that there isn't an obvious candidate for the "spring". Oleo displacement is a horrible choice because, as noted, their spring constan
27 Wingscrubber : The accuracy of a weight measuring 'strain gauge' would depend on consistent gas strut pressure, shocks leak air just like tyres, so deflection can be
28 Tdscanuck : How do you back out friction in the strut seals? Tom.
29 A342 : Well, many excavators and forklifts have integrated weighing equipment, and they also work with hydraulics. Somehow this should be applicable to aircr
30 Tdscanuck : Interesting...what's the accuracy requirement? Also, construction equipment has effectively no weight constraint, so that might be why it's practical
31 A342 : I have no clue. Trucks do. Earth, gravel etc is weighed by the excavator before being put in a dumptruck. IIRC these systems add the weights of multi
32 Okie : I think the big issue is not what the accuracy of the total weight of the airframe but where the weight is in relation to the MAC of the aircraft. Ex
33 Rwessel : If the scale on each gear leg is reasonably accurate, then determining the CG is trivial. It's exactly the same calculation as the normal weight-and-
34 Okie : Thanks for the explanation Rwessel. That works great as a redundant check. You still need to know the correct weights before loading to have your CG
35 ScrubbsYWG : what kind of strain gauges are used in service like this? My only experience with strain gauges was during my thesis and they were fairly delicate an
36 Tdscanuck : Piezoelectric. Very durable. Tom.
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