Bathroom scales for W&B

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justin.schoeman
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Bathroom scales for W&B

Postby justin.schoeman » Thu May 24, 2012 8:14 pm

One of the few outstanding tasks on my Raven build is the final W&B. I have been hunting a set of mobile scales for the last 3 weeks, as there are none at Rhino Park. I finally do have a lead on a set, but in the process of phoning around, I received a suggestion from a prominent AMO that I buy a set of digital bathroom scales, and use those.

Apparently, in the weight range of LSA aircraft (<150kg per wheel), these scales are very accurate, and more than sufficient for a W&B.

Does anybody have any actual experience with this? Logically, it seems like a good idea, and the measurements are easily verifiable: Just add 20L of fuel to the tanks, and make sure the sum of all the scales goes up by 14.4kg. If it does, it means that all the scales are still linear under the aircraft's weight. I can also weigh myself on all three scales, and confirm that they agree with each other, and are within a kg, or two of a ''known' weight.

What are your thoughts?
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Re: Bathroom scales for W&B

Postby Duck Rogers » Thu May 24, 2012 8:34 pm

Nothing wrong with bathroom scales Justin. I've used them many times. Like you rightly pointed out, just make sure they read the same.
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Re: Bathroom scales for W&B

Postby Dobbs » Sat Jun 02, 2012 12:02 pm

Not legal as far as I know -

Was told by a local AP that they can only be done on calibrated scales which have to have a calibration certificate confirming calibration within the past 12 months

For practical purposes, if your AP is happy, bathroom scales are sufficient, although mine have been set to start at -10 kg's vhpy
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Re: Bathroom scales for W&B

Postby KFA » Sun Jun 03, 2012 6:12 pm

Scales have to be calibrated by a SANAS approved lab and the certificates must be valid. They are normally only valid for 12 months. If it is just for yourself then the bathroom scales are Ok but your AP is actually not allowed to use uncalibrated scales.
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Re: Bathroom scales for W&B

Postby janjacobs66 » Sun Jun 03, 2012 6:54 pm

I frown upon the issue that bathroom scales are no good for W&B,
but let me tell you, I took my Philips Electronic (bathroom) scale and checked it with
known weights & then compared it with a pal's "regulation / calibrated" scale used for his gas filling station
.. my scale was spot on to the digit

as long as you ensure that the "spacer" used on the other 2 wheels are accurate with relation to your scale in use,
I don't see a problem .... then again, I'm no expert, there might be other factors that I'm not aware of

I assume that if you use 3 scales at once the readings would be spot on ?

would a few 100 grams make that much of a difference ?
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Re: Bathroom scales for W&B

Postby KFA » Sun Jun 03, 2012 7:31 pm

The argument about the scales is not how you see it, it's the same as the argument in law that no justice was done. There is a big difference between justice and the law. In this case it has to do with what the law requires. Your bathroom scales might and probably are quite accurate but how do you prove that. The only acceptable proof is a calibration certificate from an approved facility.
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justin.schoeman
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Re: Bathroom scales for W&B

Postby justin.schoeman » Sun Jun 03, 2012 7:52 pm

KFA wrote:The argument about the scales is not how you see it, it's the same as the argument in law that no justice was done. There is a big difference between justice and the law. In this case it has to do with what the law requires. Your bathroom scales might and probably are quite accurate but how do you prove that. The only acceptable proof is a calibration certificate from an approved facility.

In the end, I did both. I managed to find a set of calibrated scales to rent, and I bought some bathroom scales, and measured on both.

The total weight always agreed between the two sets of scales, but the calculated arm differed quite a bit, as the extra precision of the bathroom scales allowed for a more accurate measure - especially on the fairly close coupled fuel arm. The calibrated scales resulted in an arm near the side of the tank, while the bathroom scales agreed with the plans, and put the arm just slightly over centre.

In the end, the difference is about 1kg on the nose to make the CG range from the calibrated scale match that of the bathroom scale...
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Re: Bathroom scales for W&B

Postby janjacobs66 » Sun Jun 03, 2012 10:05 pm

I rest my case ... ## ##


but KFA, yes, point taken - you are absolutely correct with that statement :wink:
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Re: Bathroom scales for W&B

Postby Maathai Wangari » Mon Mar 11, 2013 10:24 am

I am confident from the measurements of bathroom scales. Variety of bathroom scale is available in digital bathroom scales and electronic scales which can be buy from online stores such as Ebay. You can choose to best bathroom scales from this list such as: Glass Digital, Electronic Body Health, electronin, Ultra slim bathrooms etc.
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Re: Bathroom scales for W&B

Postby benharry » Tue May 09, 2017 9:26 am

Is there any information about the kitchen scales as i want to know something about it.
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Re: Bathroom scales for W&B

Postby nicow » Tue May 09, 2017 3:06 pm

benharry wrote:Is there any information about the kitchen scales as i want to know something about it.
???
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