Weight question came up today while weighing my plane

[ArtVandelay]

Probably a bunch of little things like cowl flap motors, split rear seats with headrests, articulated front seats, overhead wemacs, a tone generator and second overhead speaker for gear and stall warnings instead of sonalerts. But, my gross weight is 2900 so I still have 1000 lb. useful load.
I’m pretty sure my 1978 J was a few knots faster, too. 
Skip

Good summary, a couple of other changes:
They also beefed up the steel roll cage, there was some discussion here why 2900 lb increase only applies to certain serial numbers.
And replacing the roof door air inlet with NACA inlet ducts in the tail and all the extra ductwork to go with it.
No free lunch.
If anyone wants to lighten the plane, total avionics upgrade can probably drop your weight by ~75lbs, figuring $75000 cost or 1 AMU per pound. :-)

[Pinecone]

13 hours ago, MikeOH said:

No - You read it how you want it to read.

Except I, and it seems many people here, read it the way he does.  You seem to be the only one to read it differently.

If the floor is tilted, the scale will be tilted, unless an effort is made to level them

[MikeOH]

12 minutes ago, Pinecone said:

Except I, and it seems many people here, read it the way he does.  You seem to be the only one to read it differently.

If the floor is tilted, the scale will be tilted, unless an effort is made to level them

Yes, if the floor is tilted the scale is tilted that was wombat's point.  NOT that the reading was off because the plane was tilted which is what 1980Mooney was criticizing him for.  Wombat NEVER claimed the error was a function of the plane's angle. Merely that the plane was ALSO tilted.

[T. Peterson]

14 hours ago, EricJ said:

No, the tilted scale reads too low.    You can maybe see how if you imagine the extreme, with one scale on its side and one flat the way it is supposed to be.   The scale on its side may read zero, even if you have half of your weight on it, which would be supported in an axis other than what the load sensor can measure accurately.

This is why it is important to have scales on a level surface, especially if you are measuring something, like an airplane, with multiple scales and adding them up.   As mentioned previously, small deviations from level will not have much consequence, often within the error tolerance of the scales, but as any tilt increases it can become problematic if the angle starts to get significant.

This makes intuitive sense to me. I would think that a very slight slope ( say a quarter bubble on a level) would make no significant difference on weighing a Mooney, but full deflection of a bubble may affect the weight. Specifically could the OP’s 60 pounds be accounted for by a sloping hangar floor? Of course I understand all the other concerns such as fuel in the tank of the heavy side etc.

 I am just trying to get this straight in my head in layman terms.

[1980Mooney]

1 hour ago, ArtVandelay said:

Good summary, a couple of other changes:
They also beefed up the steel roll cage, there was some discussion here why 2900 lb increase only applies to certain serial numbers.
And replacing the roof door air inlet with NACA inlet ducts in the tail and all the extra ductwork to go with it.
No free lunch.
If anyone wants to lighten the plane, total avionics upgrade can probably drop your weight by ~75lbs, figuring $75000 cost or 1 AMU per pound. :-)

In the 2,900 lb GW modification, Mooney only changed 2 tubulars less than 2 ft. long - from 0.035 to 0.049 wall thickness.  part - 340155-135 (L&R).  That can't make much change in weight. - less than 1 lb?

[T. Peterson]

14 hours ago, 1980Mooney said:

He didn’t say “tilted scale”. He just said “lower”. 

Ahh, I can see a difference in perception. And of course it leads me to a follow-on question. But first, in my question I assumed the scale under each wheel would be tilted at the same angle as the floor. Now if the scales themselves had shims on their respective low sides so that the scales were absolutely level even though the floor and therefore the airplane were tilted, would this eliminate a false reading?

[EricJ]

2 minutes ago, T. Peterson said:

Ahh, I can see a difference in perception. And of course it leads me to a follow-on question. But first, in my question I assumed the scale under each wheel would be tilted at the same angle as the floor. Now if the scales themselves had shims on their respective low sides so that the scales were absolutely level even though the floor and therefore the airplane were tilted, would this eliminate a false reading?

It would eliminate any error due to the scale tilt, so the total weights measured by the scales would be correct.   If the airplane is not level in pitch, though, the tilt in the airplane may move more weight onto or off the nosewheel (which would be compensated on the main gear weights), and the CG computation could be off.   Likewise a lateral (roll) tilt could put more weight on one main gear than another, but the total weight would still be correct.

[MikeOH]

32 minutes ago, T. Peterson said:

This makes intuitive sense to me. I would think that a very slight slope ( say a quarter bubble on a level) would make no significant difference on weighing a Mooney, but full deflection of a bubble may affect the weight. Specifically could the OP’s 60 pounds be accounted for by a sloping hangar floor? Of course I understand all the other concerns such as fuel in the tank of the heavy side etc.

 I am just trying to get this straight in my head in layman terms.

Just as an EXAMPLE, let's say the plane's actual weight is 1800 pounds; 750 on each main, and 300 on the nose.  So, a 2% error (the outside line on a spirit level) on ONE main would be 15 pounds.  It would take about an 11 degree scale angle to introduce a 2% error.

Does that help?

[jkgyr52]

Repainted airplanes often gain weight. I was told by one paint shop that clear coat can add ~ 50# of weight.

[1980Mooney]

15 minutes ago, MikeOH said:

Just as an EXAMPLE,.. So, a 2% error (the outside line on a spirit level) on ONE main would be 15 pounds.  It would take about an 11 degree scale angle to introduce a 2% error.

The Tower of Pisa leans at 5.5 degrees. So you will have us imagine our plane is in a maintenance hangar that leans twice as much … Really? 

[MikeOH]

1 minute ago, 1980Mooney said:

The Tower of Pisa leans at 5.5 degrees. So you will have us imagine our plane is in a maintenance hangar that leans twice as much … Really? 

And, I even bolded the word EXAMPLE.

T. Peterson referenced a bubble level and full deflection.  So, I worded my post in that context.  Sorry, that is so difficult for you to comprehend.  To spell it out for you: the scale has to be off level by quite a bit to introduce a significant error.

Again, you seem more motivated to criticize people than to provide helpful responses. But, whatever makes you feel superior, I guess.

[wombat]

My first message on this thread said "If the individual scales are not level, they might be measuring wrong.  "   I didn't put any thought into how much they would need to be individually unlevel to have a meaningful impact, but also made no reference to the relative elevation difference between individual scales.

After that, my next post was agreeing with @EricJ's statement about the normal force on the scale not being aligned with the measuring axis of the load cell causing error.   Including his statement that the error was small for small angle changes.

Next I agreed with @Hank and gave an example where the aircraft was level but the scales were not, which would result in error.    Again, I didn't address the relative quantity of error in relation to the angle of the scales.

@1980MooneyUnless someone deleted or edited their posts, the only times the word 'lower' has been used in this thread before page 3 is when you said it, and then when you said "He didn't say tilted scale, he just said lower", or when you talked about the right wing being lower than the left side.  Or when others were quoting you.

 

So in summary, we all agree on the following things

• If the individual scales are level, even if the aircraft isn't, the total weight measured will be accurate.
• If the individual scales are not level, even if the aircraft is, the total weight measured will be lower than actual.
• If the aircraft is level and the scales are level, the weight and the balance will be accurate. (Please, nobody bring up if the scales are calibrated!!!)
• If the aircraft is not level, the balance measurements will be wrong, regardless of if the scales are measuring correctly or if the total weight is correct.
• The amount that the individual scales would need to be tilted by in order to have a meaningful impact on their measurements is unreasonably large to be a factor in real-life aircraft measurements.

 

Edited April 22, 2023 by wombat

[1980Mooney]

48 minutes ago, wombat said:

@1980MooneyUnless someone deleted or edited their posts, the only times the word 'lower' has been used in this thread before page 3 is when you said it, and then when you said "He didn't say tilted scale, he just said lower", or when you talked about the right wing being lower than the left side.  Or when others were quoting you.

@T. Peterson said:

"This is my question: If your hangar floor had a six inch drop left to right or right to left, even though the whole airplane weighed the same as though level, would the low wheel weigh more than the high wheel?

and 

"What if you did the same test with two scales, one under each foot. Do you think the total would add up accurately assuming the high scale would show less than the low scale?"

In each case he is talking about one wheel or one scale which is at a "low" elevation (i.e. "lower") vs. the other wheel or one scale that is a "high" elevation (i.e. "higher).  He is not referring to "tilt" of the scale or scales.  And in the first case, if you are assuming that the entire floor is tilted and hence both scales are tilted, then both scales are equally in error percentagewise - He is asking if the wheel at the "low" (lower) elevation would weigh more than the wheel at the higher elevation.

 

[Ragsf15e]

I was reading to escape my 7 year olds for a few minutes.  I’m going back to them.

[T. Peterson]

3 hours ago, MikeOH said:

Just as an EXAMPLE, let's say the plane's actual weight is 1800 pounds; 750 on each main, and 300 on the nose.  So, a 2% error (the outside line on a spirit level) on ONE main would be 15 pounds.  It would take about an 11 degree scale angle to introduce a 2% error.

Does that help?

Absolutely. Thanks 

[gmonnig]

Nice! Glad your plane is getting out of the shop. I was getting mad for you! Every time I walked in there I would shake my head and feel my blood pressure rise. Hope it was worth the wait. 

[1980Mooney]

18 hours ago, Ragsf15e said:

I was reading to escape my 7 year olds for a few minutes.  I’m going back to them.

Enjoy your time with them while you can.  Your kids will grow up depending upon personalized ChatGTP bots and other AI to get all their information and answer all their questions - and probably use it to communicate with all their friends personalized AI Chatbots. 

Sifting through mountains of information in seconds is something that ChatGTP and other AI tools shine at even in their evolving forms today.  Professionals in many areas have testimonials that tasks that used to be "a day and a half" online search are now done in minutes.

New MIT Research Shows Spectacular Increase In White Collar Productivity From ChatGPT – JOSH BERSIN

There will be no need to waste time in forums like this or reading blogs in order to sift out information.  Let's face it that forums like this can consume way too much of one's time.  There will be no more misunderstanding, incorrect assumptions, misreading, political rants, perceived negativity or BS.  In fact kids will be even less likely to go their parents for questions and answers because their personal ChatGTP bot won't give them a lecture.

And when your kids are in their teens, today's ChatGTP-4 will seem like a neanderthal clunker (like an iPhone3 today,...).  They will have a hard time relating to your stories of the past:

"When you were little, we used to use things called "Forums" for answers - like something called "Mooneyspace".  But they died not long after AI Chatbots became popular and took over.  Just like magazines and publications died when the "Forums" were popular.   There are a few old fossils that pass around old copies of aging, yellowing paper publications/magazines like something called MAPA - which ceased long ago......"

[Fly Boomer]

7 minutes ago, 1980Mooney said:

Sifting through mountains of information in seconds is something that ChatGTP and other AI tools shine at even in their evolving forms today.  Professionals in many areas have testimonials that tasks that used to be "a day and a half" online search are now done in minutes.

Recently read about someone who is holding down four full-time jobs, and paid taxes on a little over $500,000 last year (author of the article verified tax documents).  None of the four companies is aware of any of the others.  He uses multiple AI engines to write, communicate, develop code, and as many other tasks as possible.  Unemployment is going to increase again -- this time because of technology.  We already have an increasing population chasing a diminishing number of jobs, and it's only going to get worse.

[1980Mooney]

2 minutes ago, Fly Boomer said:

Recently read about someone who is holding down four full-time jobs, and paid taxes on a little over $500,000 last year (author of the article verified tax documents).  None of the four companies is aware of any of the others.  He uses multiple AI engines to write, communicate, develop code, and as many other tasks as possible.  Unemployment is going to increase again -- this time because of technology.  We already have an increasing population chasing a diminishing number of jobs, and it's only going to get worse.

It will be white collar jobs in danger this time.  No need for law firms to use jr. lawyers or interns to search through history of prior cases for precedent - financial analysts searching and analyzing trends, accountants - application of rules, tax - same, etc.  The "safe" jobs of the future will be - food service jobs, caregiving, roofing, landscaping, sanitation, construction, and airplane mechanics!

[Fly Boomer]

14 minutes ago, 1980Mooney said:

It will be white collar jobs in danger this time.  No need for law firms to use jr. lawyers or interns to search through history of prior cases for precedent - financial analysts searching and analyzing trends, accountants - application of rules, tax - same, etc.  The "safe" jobs of the future will be - food service jobs, caregiving, roofing, landscaping, sanitation, construction, and airplane mechanics!

Great point.  As I was writing my previous post, I was thinking medical profession should be safe -- for the foreseeable future, people will continue to get sick.  And airplane mechanics are already in short supply.  Expect prices to continue to go up.

[Echo]

8 hours ago, 1980Mooney said:

Enjoy your time with them while you can.  Your kids will grow up depending upon personalized ChatGTP bots and other AI to get all their information and answer all their questions - and probably use it to communicate with all their friends personalized AI Chatbots. 

Sifting through mountains of information in seconds is something that ChatGTP and other AI tools shine at even in their evolving forms today.  Professionals in many areas have testimonials that tasks that used to be "a day and a half" online search are now done in minutes.

New MIT Research Shows Spectacular Increase In White Collar Productivity From ChatGPT – JOSH BERSIN

There will be no need to waste time in forums like this or reading blogs in order to sift out information.  Let's face it that forums like this can consume way too much of one's time.  There will be no more misunderstanding, incorrect assumptions, misreading, political rants, perceived negativity or BS.  In fact kids will be even less likely to go their parents for questions and answers because their personal ChatGTP bot won't give them a lecture.

And when your kids are in their teens, today's ChatGTP-4 will seem like a neanderthal clunker (like an iPhone3 today,...).  They will have a hard time relating to your stories of the past:

"When you were little, we used to use things called "Forums" for answers - like something called "Mooneyspace".  But they died not long after AI Chatbots became popular and took over.  Just like magazines and publications died when the "Forums" were popular.   There are a few old fossils that pass around old copies of aging, yellowing paper publications/magazines like something called MAPA - which ceased long ago......"

Sadly I believe you are likely over the target regarding your prognostication.  I enjoy acerbic bantor.  Likely because my father participated in the act as his father did before him.  To you and Mike I say thank you as I learned something AND found you both entertaining (in a good way).  Buckle up, the future is now and it is gonna be a wild ride.