Weight and balance isn’t that damn hard!

M

MauleSkinner

Touchdown! Greaser!
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Oct 25, 2005
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Display Name
MauleSkinner
Weight x Arm = Moment

Add up the weights

Add up the moments

Divide the total Moment by the total Weight to get CG

check the results against the loading envelope. Are you in the envelope? Are you going to stay in the envelope?

If the manufacturer provides the procedure for doing this in the AFM, read and understand it…it’s in English!

Come to your checkride prepared!

</rant>

This has been a public service announcement.
 
An hour of what should be an hour and a half oral for a flippin’ JET TYPE RATING and the guy couldn’t figure out how to come up with a CG. After I showed him the formulas in the AFM. After I pointed at specific AFM statements that showed what he was doing wrong. After I tried to get him to walk through the procedure step by step.

Far too many applicants suck at weight and balance, but usually I can drag them through it. But I shouldn’t have to work that hard to find competence, especially at this level. Fifth grade math applied at the same level as it takes to pass a Private Pilot checkride.

Apparently my expectations are set way too high for “professional” pilots.
 
W&B is simple for the C-207, which is affectionately called a sled.

1. Load up the plane until full. If the nose wheel stays on the ground, good to go. If the nose wheel is off the ground, go to step 2.

2. Have a lineman hold the tail off the ground until the engine starts. If the nose wheel stays on the ground, good to go. If the nose wheel is still off the ground, go to step 3.

3. Hold the brakes, add power. If the nose wheel stays on the ground, good to go. If the nose wheel is still off the ground, shut off engine, unload the plane. Go to step 1, this time loading heavier cargo in the nose compartment.

Remember, cargo is revenue so don't leave anything behind...
 
You didn’t allow him the option of just calling load control? Or have the dispatcher figure it out for him?

Tools, running and ducking!

Only slightly more seriously, us gray hairs grew up loading one wheel wheelbarrows… this stuff was intuitive. Not so much anymore, it’s just academic, although it sounds like you couldn’t coax out academic… but academic is WAY EASIER with intuition.
 
MauleSkinner said:
An hour of what should be an hour and a half oral for a flippin’ JET TYPE RATING and the guy couldn’t figure out how to come up with a CG. After I showed him the formulas in the AFM. After I pointed at specific AFM statements that showed what he was doing wrong. After I tried to get him to walk through the procedure step by step.

Far too many applicants suck at weight and balance, but usually I can drag them through it. But I shouldn’t have to work that hard to find competence, especially at this level. Fifth grade math applied at the same level as it takes to pass a Private Pilot checkride.

Apparently my expectations are set way too high for “professional” pilots.
Click to expand...
Please fail them for the sake of the rest of us.
 
MauleSkinner said:
An hour of what should be an hour and a half oral for a flippin’ JET TYPE RATING and the guy couldn’t figure out how to come up with a CG. After I showed him the formulas in the AFM. After I pointed at specific AFM statements that showed what he was doing wrong. After I tried to get him to walk through the procedure step by step.

Far too many applicants suck at weight and balance, but usually I can drag them through it. But I shouldn’t have to work that hard to find competence, especially at this level. Fifth grade math applied at the same level as it takes to pass a Private Pilot checkride.

Apparently my expectations are set way too high for “professional” pilots.
Click to expand...
Since you seem to be pulling teeth anyway, have you considered a career in dentistry?
 
Don't forget to do the W&B twice: once with full fuel, again with empty fuel (or whatever variation of this is appropriate to the aircraft). The moment arm of the fuel tanks is usually not at the CG, so it shifts during flight.
 
MRC01 said:
Don't forget to do the W&B twice: once with full fuel, again with empty fuel (or whatever variation of this is appropriate to the aircraft). The moment arm of the fuel tanks is usually not at the CG, so it shifts during flight.
Click to expand...

Why not do a W&B for fuel at takeoff and fuel at landing?
 
MRC01 said:
Don't forget to do the W&B twice: once with full fuel, again with empty fuel (or whatever variation of this is appropriate to the aircraft). The moment arm of the fuel tanks is usually not at the CG, so it shifts during flight.
Click to expand...
This one’s way easier. You can do a ZFW calculation and call it good.
 
Doc Holliday said:
Why not do a W&B for fuel at takeoff and fuel at landing?
Click to expand...
You could do that too. My airplane is simple so if I do it full and empty, all possible fuel configurations are in between so I'm covered even if I make an unplanned stop and take on extra fuel. Maybe not all airplanes are like that? Some have fuel tanks near the tail, etc.

Do whatever is appropriate to the aircraft - the point is to do it more than once with different fuel setups because the CG usually shifts.
 
MauleSkinner said:
An hour of what should be an hour and a half oral for a flippin’ JET TYPE RATING and the guy couldn’t figure out how to come up with a CG. After I showed him the formulas in the AFM. After I pointed at specific AFM statements that showed what he was doing wrong. After I tried to get him to walk through the procedure step by step.

Far too many applicants suck at weight and balance, but usually I can drag them through it. But I shouldn’t have to work that hard to find competence, especially at this level. Fifth grade math applied at the same level as it takes to pass a Private Pilot checkride.

Apparently my expectations are set way too high for “professional” pilots.
Click to expand...


It’s taught poorly. Five minutes of balancing a few fishing sinkers along a yardstick will drive home the concept far better than an hour of doing paperwork. Get the idea across, then the math will make sense and become easy.
 
As my late father would have said “the darn schools have educated all the common sense out of people these days”. Weight and balance, very basic leverage calculations, should be something a 9 year old should be able to fully grasp the concept of and execute. It is not advanced math.
 
Flatiowa said:
As my late father would have said “the darn schools have educated all the common sense out of people these days”. Weight and balance, very basic leverage calculations, should be something a 9 year old should be able to fully grasp the concept of and execute. It is not advanced math.
Click to expand...
Or younger - most kids use a teeter-totter before reaching age 9, and get the idea pretty quick especially when their Dad is on the other side. :)
 
Flatiowa said:
Weight and balance, very basic leverage calculations, should be something a 9 year old should be able to fully grasp the concept of and execute. It is not advanced math.
Click to expand...

True, to a point.

But I remember questions like "How much weight would have to be moved from Station 125 to Station 130 to move the CG to within the MAC limits shown on the chart and loadings in the sample shown below?"

I did not find these questions easy. In fact, I doubt I could answer them today without some - or a lot of - refreshing.
 
FastEddieB said:
True, to a point.

But I remember questions like "How much weight would have to be moved from Station 125 to Station 130 to move the CG to within the MAC limits shown on the chart and loadings in the sample shown below?"

I did not find these questions easy. In fact, I doubt I could answer them today without some - or a lot of - refreshing.
Click to expand...
Touche, but I believe if the underlying concept of the principles are understood then it is not unrealistic to expect somebody entrusted with the lives of their passengers to have the mental capacity to work out the answer from logic (not memorized formulas). I believe the questions are intentionally confusing to weed out the memorizers and ensure that the scope of concept is understood (I could be wrong and have been many times before).
 
Half Fast said:
It’s taught poorly. Five minutes of balancing a few fishing sinkers along a yardstick will drive home the concept far better than an hour of doing paperwork. Get the idea across, then the math will make sense and become easy.
Click to expand...
More accurately, some instructor probably committed primacy and told them it was hard.
 
FastEddieB said:
But I remember questions like "How much weight would have to be moved from Station 125 to Station 130 to move the CG to within the MAC limits shown on the chart and loadings in the sample shown below?"
Click to expand...

That points to one of the foolish things about a multiple-choice written test. They give you four or five choices, one of which is the right answer, so you can just run each of the choices through the calculation and see which one works. You don't really have to solve the problem; just check the answers they provide.
 
Is fltplan.com W&B cheating?
 
FORANE said:
Is fltplan.com W&B cheating?
Click to expand...

Cheating? No. I use APG for performance and W&B.

However the OP was administering a test for a type rating. Every type rating program I have attended requires doing a long form (AFM) weight and balance, and being able to discuss it during the oral.
 
Doc Holliday said:
Cheating? No. I use APG for performance and W&B.

However the OP was administering a test for a type rating. Every type rating program I have attended requires doing a long form (AFM) weight and balance, and being able to discuss it during the oral.
Click to expand...
He could actually have used APG if he’d had it, per the company. But since he didn’t have it, he probably should’ve paid more attention when it was taught from the AFM.
 
Never did a single one at delta…

Did it EVERY LEG MANUALLY at Eagle.
 
I was disappointed not to get a single weight and balance question on my private exam. At least from my memory. Maybe they snuck one in and didn't realize it was.
 
Weight shift problems are easy if you know the equation. If you need it in your operation you'll know it, or have it readily accessible. If you don't, you won't.
 
Sometimes I wonder if some pilots might benefit a bit from having some RC time. In this case, have them learn to fly a cheap foamy RC plane around setup normally. Then move the CG back a few inches, give them the controls and ask them to fly it around. Guessing that might change someone's perspective on W&B.
 
If they can't calc CG, just wait til you give them the multi-leg XC planning question where they have to manually compute the GS/fuel burn/ETE etc. I wouldn't hold my breath on them being able to do that.
 
I have a weight and balance App. Once you download, it takes about 30-45 min to program to match your airplane. It has slipped ders for the weight in various positions. It works pretty good too.
 
MauleSkinner said:
An hour of what should be an hour and a half oral for a flippin’ JET TYPE RATING and the guy couldn’t figure out how to come up with a CG. After I showed him the formulas in the AFM. After I pointed at specific AFM statements that showed what he was doing wrong. After I tried to get him to walk through the procedure step by step.

Far too many applicants suck at weight and balance, but usually I can drag them through it. But I shouldn’t have to work that hard to find competence, especially at this level. Fifth grade math applied at the same level as it takes to pass a Private Pilot checkride.

Apparently my expectations are set way too high for “professional” pilots.
Click to expand...
Give him the slip stick from the Co-Pilots B-52. Also have him compute how to manage the fuel burn by changing where the fuel flows as the plane gets lighter. Oh, and then add a 100,000# fuel onload somewhere mid-flight.
 
BillTIZ said:
Give him the slip stick from the Co-Pilots B-52. Also have him compute how to manage the fuel burn by changing where the fuel flows as the plane gets lighter. Oh, and then add a 100,000# fuel onload somewhere mid-flight.
Click to expand...
If this was an earlier version of the same airplane, I could ask how to manage fuel for maximum speed. :D
 
Albany Tom said:
Sometimes I wonder if some pilots might benefit a bit from having some RC time. In this case, have them learn to fly a cheap foamy RC plane around setup normally. Then move the CG back a few inches, give them the controls and ask them to fly it around. Guessing that might change someone's perspective on W&B.
Click to expand...
A few inches aft CG for most RC models would be totally unflyable - maybe an inch?
(In my training experience, introducing a full-scale pilot to RC flying is much more difficult than introducing a non-pilot. The full-scale guys apparently think they need to be moving the controls around constantly, for some reason.)
 
If one was so inclined, one could put together a simple W&B spreadsheet for calculating weight and CG, and even color-code it to flag exceeding limits. But that kind of skill seems to elude even my "computer-savvy" undergraduates in chemistry. "Computer-savvy" these days means knowing how to use social media. Excel or Google sheets? Pfft.
 
chemgeek said:
If one was so inclined, one could put together a simple W&B spreadsheet for calculating weight and CG, and even color-code it to flag exceeding limits. But that kind of skill seems to elude even my "computer-savvy" undergraduates in chemistry. "Computer-savvy" these days means knowing how to use social media. Excel or Google sheets? Pfft.
Click to expand...
Or, Matlab.
Spreadsheets suck. :)

Fun fact: Octave is a free alternative to Matlab that does a LOT of stuff and uses the same programming syntax as Matlab. I found I have to tweek one or two things - usually very minor. The only thing that I have found really missing (for me, so far) is creating video directly from a series of plots.
 
Albany Tom said:
Sometimes I wonder if some pilots might benefit a bit from having some RC time. In this case, have them learn to fly a cheap foamy RC plane around setup normally. Then move the CG back a few inches, give them the controls and ask them to fly it around. Guessing that might change someone's perspective on W&B.
Click to expand...
None of this teaches them how to calculate CG per the OP. It's one thing to know an aft CG is bad, it's another to be able to determine where your CG actually is. Knowing both is a requirement for even private pilot candidates.

Capt. Geoffrey Thorpe said:
Or, Matlab.
Spreadsheets suck.
Click to expand...
A spreadsheet for a single W&B calculation is overkill, but works great for repetitive calcs and can quickly be set up to look like Form F's or whatever weight and balance format you like. Matlab is an awesome tool but is waaaaay overkill for this simple calc. Might as well "fire up the Cray" to sum a few moments and divide by weight.

Nauga,
bearing arms and weights
 
Every major EFB out there has a W&B feature. Even if for some reason you forgot how to do it from your student pilot days, there’s tools to do it for you. No excuses.
 
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