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Why don’t airports have scales?

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Pilot-34

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Weight and balance seems like such an important issue I don’t understand why airports don’t have scales.

It wouldn’t really be any big deal to have a two section scale that would weigh the front and rear and display the weight for each.
Better yet a projected laser line Could display the exact location on the plane.
None of this is particularly expensive or technicallogically challenging.
 

Tiger Tim

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It’s a clever idea and at one time I was thinking of something similar except on board the plane. I figured you could run a pressure line off the gas/oil gear legs to either a gauge or pressure transducers to do the work electronically. The display could be in the cockpit.

My way would be one extra thing to pay to check at annual, yours would probably be a nightmare of certification to keep proving it’s accurate.

Unfortunately, all it takes is a couple knots of wind for the figures generated by either of our methods to be worthless.
 

Pilot-34

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Trucks have a scale similar to what you propose it runs off air suspension usually but there are those that have loads Cells under springs.
Truck scales at truck stops in other places are certified regularly it’s no different than any other measurement being tested .
you know like the fuel pump
 

Riggerrob

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large military transports (e.g. Lockheed C-5A Galaxy) have scales built into their landing gear. Sclaes measure air pressure in tires of hydraulic pressure in shock absorbers. These scales duplicate calculations made by load-masters and ground schedulers. Weight and balance is so important that it has to be approved by two or three different people before the airplane is allowed to taxi.
 

BJC

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Weight and balance seems like such an important issue I don’t understand why airports don’t have scales.
For the same reason that neither rest areas on the Interstate nor parking lots have automobile engine chip readers.


BJC
 
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Dan Thomas

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Unfortunately, all it takes is a couple knots of wind for the figures generated by either of our methods to be worthless.
That there. W&B has to be done in a closed hangar. Any air movement shift the weight around. And the W&B is measured with the airplane in level flying attitude, an attitude that almost no airplane achieves in taxiing attitude. Just getting a 172 levelled as per the manual has the tail way high. It always amazes the uninititated folks who see it. A taildragger like the 185 will have its tail high enough to walk under.

Trucks on scales aren't made to fly at 60 MPH. Airplanes are.

1589215411673.png
 

Pilot-34

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That there. W&B has to be done in a closed hangar. Any air movement shift the weight around. And the W&B is measured with the airplane in level flying attitude, an attitude that almost no airplane achieves in taxiing attitude. Just getting a 172 levelled as per the manual has the tail way high. It always amazes the uninititated folks who see it. A taildragger like the 185 will have its tail high enough to walk under.

Trucks on scales aren't made to fly at 60 MPH. Airplanes are.

View attachment 96555
So what ?
You don’t think that’s the ONLY way to weigh a plane do you ?
It’s just a simple way for the manufacturers to standardize.

In any case the gross weight would be valid.
 

Toobuilder

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No. That's pretty much the "only"way the airplane can be weighed if you are looking for the CG. It's a geometry problem, not raw weight.
 

Dana

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So what ?
You don’t think that’s the ONLY way to weigh a plane do you ?
It’s just a simple way for the manufacturers to standardize.

In any case the gross weight would be valid.
No, even the weight reading would change if the wings are providing any lift. And you have to do it in the level flight attitude, because it's the level flight horizontal position of the CG that matters and the position will be different in different attitudes.
 

Pilot-34

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No, even the weight reading would change if the wings are providing any lift. And you have to do it in the level flight attitude, because it's the level flight horizontal position of the CG that matters and the position will be different in different attitudes.
That doesn’t make any sense at all to me. I fly at lots of different attitudes. In fact it would seem like the center of gravity would be most important at extreme angles of up and down pitch.
 

ScaleBirdsScott

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Well what's the actual goal of the proposed project? Is it to provide per-flight W&B data? Or is it to have at each airport a system local pilots can setup as needed to make sure their plane is still within the balance point it used to be?

Is the target use case the large passenger craft that will have a constantly shifting payload for each flight, but also have large weights and footprints? Or is it a smaller rig for the GA pilots who have often pretty consistent loading but may time to time want to check that a full flight is not out of bounds?

In any case I'm assuming the aircraft designer (or builder community) would probably have to work out what the "as read by the scale system" CG point should be using this method. OR these scales would need to come with an adjustable cradle system that can lift small taildraggers and the rest at a specific reference angle (level or otherwise) Or some combination of both.
 

Wanttaja

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You guys are funny. Seeking perfection you give up a great improvement
Just hate seeing our airports spending our hangar-lease money on improvements of doubtful utility. How many airplane owners are going to take advantage of it? Probably few. Bad CG is a surer killer than overweight, and as several posters have said, a casual set of scales are not going give an accurate reading.

The scales will not only have to measure the weight on the nosewheel, tailwheel, and mains, but would have to establish the EXACT physical point that the weight is resting. Truck-stop scales have platforms multiple feet long, and the wheel's position on it is immaterial since it's only measuring weight. If you're going to compute CG, you need to know EXACTLY the point that the wheel is resting, so you can't just repurpose existing commercial scales.

Finally, of course, the airport would have to be nuts to assume legal liability for the weight/CG location determined.

Ron Wanttaja
 

jedi

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Airlines have tried that (on board calculations) and decided it would not work. Said it was not accurate enough. I suspect the problem was it came up with too much weight. Passengers don't weigh 170# and 120# with light weight bags. I expect the average passenger and baggage is at least 10% over the "standard" and the fueler knows not to short the fuel sheet.

I recall one trip where we were over max landing weight so we diverted to the alternate, refueled and returned to the same runway with the same payload (cargo and people) and more fuel but a "corrected, i.e. recalculated" weight and balance sheet.
 

Dan Thomas

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That doesn’t make any sense at all to me. I fly at lots of different attitudes. In fact it would seem like the center of gravity would be most important at extreme angles of up and down pitch.
If the airplane isn't levelled during the weighing, the CG calculations are way off. Nose-up increases the weight on the mains in a trike, and decreases it in a taildragger. So with a CG position that's off, all your calculations are garbage and you could end up nose or tail heavy in flight, with commensurate control difficulties.
 

Pilot-34

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Calculating the exact horizontal point of the center of gravity is not difficult at all .
good grief pilots do it every day guessing at the amount of weight in each particular location and that’s considered to be good enough
Yet every year multiple planes crash from either overweight or out of the envelope center of gravity’s
 

Vigilant1

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For the same reason that neither rest areas on the Interstate nor parking lots have automobile engine chip readers.

BJV
What would that be ?
My take: because there is neither a regulatory requirement nor a monetary inducement to provide them. And that's (IMO) the way it should be.

My little muni airport won't put in unleaded mogas. The folks who run it believe it won't payvoff. If yhey have an extra $20k, I'd much rather have that than have high-tech permanent scales.
 
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