Weighing with electronic bathroom scales?

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Marc Zeitlin

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I understood that, but my point was that with less arrogance and more conscientious attention to detail, the out of of cg issue would have been detected before flight. Scales didn't cause the crash; mental and attitude inadequacies did.
Well, yes. And if folks are going to go to the trouble of basically calibrating their cheap bathroom scales, then they can get accurate answers for the W&B. But since the vast majority of folks that I run into haven't got the faintest clue how to do a W&B (or calculate what they got after doing a weighing), simplifying and taking inaccuracy out of the process makes mistakes less likely.
 

Marc Zeitlin

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... With regard to your memory citing aircraft accidents caused by an out of CG condition (these were first flight, post build EAB kit planes right? That would be in the context of my post. Anything else would be disingenuous), show me the data. I just couldn’t find anything and I‘m partial to weighing risks (pun intended) based on data.
See below - not first flights, but in Phase I.
Can you post a link to the NTSB report or Kathryn’s Report or Aviation Safety Network or a Builders Forum? I just want to do the right thing.
So the Detroit Flying Car crash of December, 2018 comes to mind. Then there's this:


which wasn't a first flight, but was early in Phase I. Same with Pat Young's COZY MKIV crash in 1996, I believe - a miscalculated CG (along with other factors) caused a non-fatal deep stall. Then there's Zubair Khan's heavily modified COZY MKIV crash:


also a deep stall, caused by an out of CG condition. That one was fatal, although not due to the deep stall itself.

So my position is that however intelligent, stupid, careful, or careless the person doing the W&B is, having accurate data can only help. Now, as stated above, _IF_ someone is going to calibrate the scales they're using themselves (if they know how to do so), then a bucket with rocks could be used to weigh the plane. But while (as @rv7charlie points out) many homebuilts have been weighed with crappy scales, why make things less accurate than they could be, when safety is at stake? I've seen too many planes that after _I_ weighed them with my calibrated scales, the weight and CG were different enough from what the original builder had stated that safety was compromised.

But YYMV, and if you know how to ensure accuracy of the scales, and Dunniing-Kruger is not the cause of you knowing how to ensure accuracy of the scales, then by all means, use whatever scales (or bucket of rocks) you like. @karmarepair did not give the impression of knowing how to do this or that it would be done if he did, hence my reaction.
 

Richard Roller

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Here is one Eachon Time Warp Spitfire 9 crash in Florida (N355DE) | PlaneCrashMap.com

The “designer” / builder / pilot rejected constructive input on several occasions.


BJC
Reminds me of a Starduster Too builder that approached me 20+ years ago for weight and balance help. Massive eyeball mods. The a/c was within 100 lbs. of design gross weight, empty, and 4 or 5 inches out the aft c.g. with nothing in the plane. He wanted my opinion of hanging an O-540 on an extended mount to get the c.g. in bounds. I told him I thought he was nuts. Fortunately the a/c never flew. He passed and the family broke up the a/c.
 

Bill-Higdon

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Reminds me of a Starduster Too builder that approached me 20+ years ago for weight and balance help. Massive eyeball mods. The a/c was within 100 lbs. of design gross weight, empty, and 4 or 5 inches out the aft c.g. with nothing in the plane. He wanted my opinion of hanging an O-540 on an extended mount to get the c.g. in bounds. I told him I thought he was nuts. Fortunately the a/c never flew. He passed and the family broke up the a/c.
I've seen that more than once myself, also say 1 that scared the owner/pilot so much he cut the plane up & sadly 1 that killed the pilot
 

PiperCruisin

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So the fact that something is inconvenient (scales can be rented or borrowed, and they're easily moved) is not a reason not to do the right thing.

And I know (off the top of my head - might be able to come up with more with a bit of thought) of at least two fatal accidents and one non-fatal of very common aircraft that were caused by CG being out of range. Maybe for a Zenith, it's never happened. And maybe for a Sonex, it's never happened. But every plane is different - folks make modifications, changes, and do things that can cause weight/CG issues. I would not trust any W&B performed on bathroom scales.
Risk is everywhere. I see no reason why a relatively inexpensive bathroom scale, that has been verified to be sufficiently accurate and repeatable, could not work for experimental. As was pointed out, you could use beams and weights to create a balance. Me, I have a load cell and scale from Omega.

I had an IA use certified scales on my plane. By inspection the numbers he was getting were incorrect and I called BS. Turns out the rechargeable battery needed to be replaced.

So with anything, calibrated/certified/official title or not, look at everything with a critical eye.
 

rv7charlie

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And that is the most scary thing of all. It's unfortunate that 'pro' can sometimes simply mean that the work was done for money instead of for fun & education, yet we too often trust pros without verifying.
 

Pops

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Well, yes. And if folks are going to go to the trouble of basically calibrating their cheap bathroom scales, then they can get accurate answers for the W&B. But since the vast majority of folks that I run into haven't got the faintest clue how to do a W&B (or calculate what they got after doing a weighing), simplifying and taking inaccuracy out of the process makes mistakes less likely.
How can you get a pp license without knowing how to do a W&B ?
 

Marc Zeitlin

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How can you get a pp license without knowing how to do a W&B ?
I assume this is a rhetorical question...

Most pilots have no idea what makes aircraft fly. Many pilots will argue about aircraft stalling in "downwind turns", as if that's a thing.

W&B calculations involve math, and most folks are scared of math - they'll tell you themselves that they suck at it. I guarantee that if you handed 100 pilots 3 scales, a tape measure, a plumb bob and the POH for an aircraft, fewer than 50 of them would configure the plane correctly and get the right answer for the empty weight and CG. They understand how to use the W&B calculator in Foreflight to put in their weight and the fuel weight and the baggage weight, and see what Foreflight tells them, but that's about as far as it goes. The folks yakking on this forum are NOT representative of the pilot population as a whole.
 

Stolch

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Umm, well although every example provided had nothing to do with using thrift store scales instead of real aircraft scales, after reading your report on Mr. Khan’s crash (I won’t call it an accident), I understand your point that folks- especially us Dunning-Kruger types- should heed the advice from those who do have the expertise. So in that spirit I will heed your advice and plan a trip to an acquaintance‘s hangar, he recently acquired a set of aircraft scales, and I will weigh my aircraft using his scales. Don’t know when I can get there but after I do I’ll circle back here and let you know how it turned out.
Was Mr. Khan wearing a parachute when he attempted to egress the aircraft in flight?
 

agpilot24

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I assume this is a rhetorical question...

Most pilots have no idea what makes aircraft fly. Many pilots will argue about aircraft stalling in "downwind turns", as if that's a thing.

W&B calculations involve math, and most folks are scared of math - they'll tell you themselves that they suck at it. I guarantee that if you handed 100 pilots 3 scales, a tape measure, a plumb bob and the POH for an aircraft, fewer than 50 of them would configure the plane correctly and get the right answer for the empty weight and CG. They understand how to use the W&B calculator in Foreflight to put in their weight and the fuel weight and the baggage weight, and see what Foreflight tells them, but that's about as far as it goes. The folks yakking on this forum are NOT representative of the pilot population as a whole.
In my experience, you have hit the nail on the head. I don’t like the reality, but it is true.
Most pilots know at least one guy that races cars, those guys have scales. A quick favor borrows those scales for the weekend. I have done just that for the many airplanes I have weighed. In my case, the scales were calibrated/certified because the race car guy already
needed them to be.
A good set of scales is good also because they are easy to use, you have literally all day to pull the airplane up on them and level it correctly. Just do it right, it’s not that hard.
 

Fiberglassworker

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I live in eastern Tennessee and have a set of calibrated wheel weighers, these will take up to 1500 lbs. per platform, they have 4 platforms. and I have a jumper plug to enable weighing of 3 wheeled aircraft. they weigh in 1/2 lb. increments over 500 lbs. per wheel and 1oz increments under 500 lbs. If anybody is within 40 miles of Cleveland Tn post a reply on here.
 

Pops

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In my experience, you have hit the nail on the head. I don’t like the reality, but it is true.
Most pilots know at least one guy that races cars, those guys have scales. A quick favor borrows those scales for the weekend. I have done just that for the many airplanes I have weighed. In my case, the scales were calibrated/certified because the race car guy already
needed them to be.
A good set of scales is good also because they are easy to use, you have literally all day to pull the airplane up on them and level it correctly. Just do it right, it’s not that hard.
Sorry to say, from what I see I think that you and Marc are correct.
 

Marc Zeitlin

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Was Mr. Khan wearing a parachute when he attempted to egress the aircraft in flight?
Yes. He was apparently an experienced acrobatic pilot, so was wearing a chute. What he wasn't (however nice a guy he was, and he was) was good at listening to advice.

My point was not that cheap scales killed anyone - it was that having an accurate W&B is important for safety. Whatever leads to an accurate W&B (and an understanding of it) is good, and anything that jeopardizes having an accurate understanding of an aircraft's CG range and actual W&B is bad. Bathroom scales CAN be good, but it's far more likely that they're not, given the capabilities (and inclinations) of most folks in obtaining and calibrating them.
 

thompsonbb

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In this discussion, we've tossed around the terms of both calibrated and certified scales. As far as my reading of AC 43.13-1B, section 10-15(e) goes, it looks like the regs clearly specify that the scale is calibrated (unless you want to debate the legal implications of the word "should"). And, unless it's specified somewhere else, there doesn't appear to be a requirement for certified scales to do a weight and balance. Do I have that right?
 

Toobuilder

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First off, lets remember that AC 43.13 isn't a regulation, its a "best practices" manual. Second, it is the A&P or the builder/manufacturer that "certifies" the W&B process. It is up to that certifying entity to determine the appropriate equipment to use. With that background, I'd opine that use of the term "calibrated" or "certified" WRT scale equipment means "reads accurately within the range used".

So I'd agree with Marc that any weighing scheme can provide good source data for a W&B calculation IF THE REACTION WEIGHT IS ACCURATE.

I'll also agree that yes, pilots are required to demonstrate the ability to calculate CG for every flight, but that is a different animal than the weighing process and arriving at an accurate baseline for the airplane. Same math, but requires a level of comprehension that is clearly lacking in much of the pilot population.
 

Pops

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If all you can do is use the W&B grafts in the POH, you really do not have an understanding of what you are doing and a good chance of why. Sort of like a flight instructor I know. Can quote all the regs at the snap of a finger but has zero understanding of what he is saying and how to apply them. Crashed 2 airplane and run out of fuel 4 times.
 

PiperCruisin

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My point was not that cheap scales killed anyone - it was that having an accurate W&B is important for safety. Whatever leads to an accurate W&B (and an understanding of it) is good, and anything that jeopardizes having an accurate understanding of an aircraft's CG range and actual W&B is bad. Bathroom scales CAN be good, but it's far more likely that they're not, given the capabilities (and inclinations) of most folks in obtaining and calibrating them.

Why? The accuracy I mean. How accurate does it have to be? Sorry, not trying to be a jerk.

Three reasons for the weight and balance:
1. Forward c.g. and elevator effectiveness.
2. Rear c.g. and stability.
3. Total weight for performance (TO, climb, stall) and structural loading.

#1 is relatively easy to figure out. #3 has a lot of parts, but not sure weight accuracy to 6 digits is necessary here. #2 is the tough one, to me anyways. I've read a lot about it and quizzed a number of AEs I know and they were more clueless about it than I was. Example: one of the key data calculations is knowing your neutral point which is impacted by a number of things, one of which is the fuselage which most ignore. I use the method that Roncz has in his spreadsheet. Anyways, which there was a better explanation those of us that are not too bright.
 

Marc Zeitlin

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Why? The accuracy I mean. How accurate does it have to be? Sorry, not trying to be a jerk.

Three reasons for the weight and balance:
1. Forward c.g. and elevator effectiveness.
2. Rear c.g. and stability.
3. Total weight for performance (TO, climb, stall) and structural loading.

#1 is relatively easy to figure out. #3 has a lot of parts, but not sure weight accuracy to 6 digits is necessary here. #2 is the tough one, to me anyways. I've read a lot about it and quizzed a number of AEs I know and they were more clueless about it than I was. Example: one of the key data calculations is knowing your neutral point which is impacted by a number of things, one of which is the fuselage which most ignore. I use the method that Roncz has in his spreadsheet. Anyways, which there was a better explanation those of us that are not too bright.
So "How accurate does it have to be" is like asking "how long is a piece of string". "Enough", is the right answer. I've seen W&B calculations that were an inch or two off in empty CG position - in an airplane where the whole CG range is 4.5", that's a HUGE error. On the other hand, a 0.5" error in a plane with a 15" CG range is fairly unimportant. I've seen planes where the recorded empty weight was 100 lb. off of the actual empty weight - in a plane with a MGW of 4500 lb., that's fairly meaningless, but in a plane with a 1200 lb. MGW, it can be critical to takeoff performance.

You're correct on the three reasons for caring, but "how accurate" will be dependent on the particulars of the plane in question. If you've got a tailwheel plane, with a long moment arm from the CG to the tailwheel, and your tailwheel should have, say, 75 lb on it when empty and level, but your scale tells you that you've got 85 lb on it, that's a substantial moment difference that will give an error in empty CG, and you'll end up loading your aircraft incorrectly with a too forward CG, with a possible rotation and takeoff speed issue. Conversely, if it tells you 65 lb., you may end up with an aft CG issue, with possible stability and stall issues.

Most aircraft/racing scales are accurate and repeatable to something like 0.5 - 1 lb. When I do datum/fuselage station measurements with a plumb bob and the aircraft level, I try to get the stations (moment arms) accurate to within 0.1".
 

karmarepair

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But YYMV, and if you know how to ensure accuracy of the scales, and Dunniing-Kruger is not the cause of you knowing how to ensure accuracy of the scales, then by all means, use whatever scales (or bucket of rocks) you like. @karmarepair did not give the impression of knowing how to do this or that it would be done if he did, hence my reaction.
I can see where I gave that impression, but I have written directives and specifications in my work life with the phrase "traceable to National Bureau of Standards".

You can't always get that though and my query was part of my decision making process; what tools can I get, what process can I manage, do I Buy or Do, what is the required Goodness, what's an acceptable level of risk. Marc, this is not the first time your tight, tart shares have improved my thinking, and I'm grateful. Pat Panzera, of blessed memory, was another useful reviewer of my thinking, and if anything, even blunter.

And in DMs, people have relayed to me at least two other fatals due to inaccurate W& B determination.

I especially appreciate your sharing of your own standards; really helpful.
 

Riggerrob

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I can see where I gave that impression, but I have written directives and specifications in my work life with the phrase "traceable to National Bureau of Standards".

You can't always get that though and my query was part of my decision making process; what tools can I get, what process can I manage, do I Buy or Do, what is the required Goodness, what's an acceptable level of risk. Marc, this is not the first time your tight, tart shares have improved my thinking, and I'm grateful. Pat Panzera, of blessed memory, was another useful reviewer of my thinking, and if anything, even blunter.

And in DMs, people have relayed to me at least two other fatals due to inaccurate W& B determination.

I especially appreciate your sharing of your own standards; really helpful.
A simple way to verify scales is to take your kettle balls to the Post Office and weigh them on a gov't certified scale. With Post Office stickers on your kettle balls, you can confirm the accuracy of your bathroom scales.
We used this method at one of the parachute factories where I worked and the FAA Inspector accepted that method as "traceable to National Bureau of Standards."
 
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