Utility Category - Cessna 172

[Alex3745]

@Alex3745 are you being serious or trolling?

If you are being serious you need to study up ... your understanding of w&b is way off... to the point of not understanding it at all.

There’s not much to understand you literally just follow step 1-10 on figure 6-3 (page 6-10)

But you don’t use that with graph figure 6-8

It’s to be used with graph figure 6-7.

It’s even stated in step 10 which graph to use.

But the aircrafts empty weight moment arm is not in aft of CG. It’s in aft of nose

Go 62.6 back from the nose on figure 6-1 and you will see it falls right in the CG location of the diagram.

 

[Tarheelpilot]

There’s not much to understand you literally just follow step 1-10 on figure 6-3 (page 6-10)

But you don’t use that with graph figure 6-8

It’s to be used with graph figure 6-7.

It’s even stated in step 10 which graph to use.

But the aircrafts empty weight moment arm is not in aft of CG. It’s in aft of nose

Go 62.6 back from the nose on figure 6-1 and you will see it falls right in the CG location of the diagram.

Sorry. I don’t understand what you are saying...
just so you know the weight and balance procedures are the same regardless of what type of avionics are installed. There is no requirement to adjust anything because it’s a g1000

 

[Alex3745]

Dude you really need to study... what in the holy hell are you talking about?

So run a WB calculation using the POH worksheet but use the WB for your actual tail number. See where it falls on the graph, it’s going to end up nose heavy no matter what you do if you use the aft of reference datum figure on the amended WB sheet from the A/P

Mines
1- 1700lbs empty , 41 moment
2- 312lbs , 16 moment
3- 340lbs, 11.5 moment (FS 34)
4- n/a
5- n/a
6- n/a
7- 2352lbs, 68.5 moment

Now match that into the CG moment envelope and somehow the CG is way too far forward and well outside the normal category. Even though it’s just a standard full tanks flight with 2 people.

Now run the numbers again

But do it the way it’s done in the POH, which it isn’t giving the empty aircrafts moment in inches aft of datum and everything balances the way it should.

2352lbs and 94.4 moment

Nothing else to it. Try it yourself with your aircrafts WB sheet.

 

[Tarheelpilot]

I’m out.

Fly safe.

 

[dmspilot]

It’s not really a magic number it’s in the POH on figure 6-1. It’s the area forward of the reference datum.

Nope, 25.9 is not "the area forward of the datum", it's the area between the datum and the leading edge of the mean aerodynamic chord (MAC). You're reading the graph wrong.



Which would be more clearly labeled like this:



But none of this even matters as MAC is not used in GA to calculate W&B and has no practical purpose for us.

When’s the last time you saw an updated W/B done by an A/P for a G1000 172s come in empty at 1642lbs 62.6” arm like the POH’s stock 172.

I pointed out once before already that 62.6 is the moment in thousands of pound-inches and is not an arm or CG.

The sample loading problem on page 6-10 figure 6-3 is not deducting the 25.9 from the moment arm to be in aft of datum.

No, that is not what it's not doing (for lack of a better sentence to say "you are incorrect").

But open up the logs of whatever g1000 you have on the flight line the updated WB will be between 37-41 for a relatively stock aircraft.

Yes, that is a typical CG range for a C172.

62.6 moment arm - 25.9” = 36.7 arm aft of datum

Hold it right there buddy, you can't start with moment, measured in thousands of pound-inches, subtract a number, and get CG in inches aft of the datum. 62.6 thousand pound-inches minus 25.9 inches is NOT 36.7 inches. They aren't even the same units. You can't do that any more than you can divide by zero.

62.6 thousand pound inches is the MOMENT. In order to get CENTER OF GRAVITY you must DIVIDE the MOMENT by WEIGHT.

You seriously need to just delete all of the knowledge about weight and balance you think you've accumulated and start over from scratch. Give it up. Are you a student pilot? Ask you CFI for a weight and balance lesson. Please for our sanity.

 

[Alex3745]

Nope, 25.9 is not "the area forward of the datum", it's the area between the datum and the leading edge of the mean aerodynamic chord (MAC). You're reading the graph wrong.

View attachment 73775

Which would be more clearly labeled like this:

View attachment 73774

But none of this even matters as MAC is not used in GA to calculate W&B and has no practical purpose for us.



I pointed out once before already that 62.6 is the moment in thousands of pound-inches and is not an arm or CG.



No, that is not what it's not doing (for lack of a better sentence to say "you are incorrect").



Yes, that is a typical CG range for a C172.



Hold it right there buddy, you can't start with moment, measured in thousands of pound-inches, subtract a number, and get CG in inches aft of the datum. 62.6 thousand pound-inches minus 25.9 inches is NOT 36.7 inches. They aren't even the same units. You can't do that any more than you can divide by zero.

62.6 thousand pound inches is the MOMENT. In order to get CENTER OF GRAVITY you must DIVIDE the MOMENT by WEIGHT.

You seriously need to just delete all of the knowledge about weight and balance you think you've accumulated and start over from scratch. Give it up. Are you a student pilot? Ask you CFI for a weight and balance lesson. Please for our sanity.

Not a student but new to the Cessna WB graphs. On Piper we just used the arm and made dots to connect lines to see where it fell. More like the figure 6-8 graph in the Cessna POH, not loaded airplane moment (which I guess wouldn’t be using arms lol)

So your saying the arm for the aircraft needs to be converted. So (1700X41)/1000 to use that graph first, then can use the graphs and follow the steps?

 

[dmspilot]

Not a student but new to the Cessna WB graphs. On Piper we just used the arm and made dots to connect lines to see where it fell. More like the figure 6-8 graph in the Cessna POH, not loaded airplane moment (which I guess wouldn’t be using arms lol)

So your saying the arm for the aircraft needs to be converted. So (1700X41)/1000 to use that graph first, then can use the graphs and follow the steps?

So you're already a pilot? Or a mechanic? Or a flight simmer or what?

Did you not learn Weight x Arm = Moment? Weight/Moment = CG?

 

[Alex3745]

So you're already a pilot? Or a mechanic? Or a flight simmer or what?

Did you not learn Weight x Arm = Moment? Weight/Moment = CG?

Yeah learnt it, and know the formula don’t often actually use it though. In Piper was always more focused on the arm since on the plotter you move the CG around with the arms and the graph was also a lbs/arm graph. Similar to the figure 6-8 graph by Cessna, but shaped differently so it works with a plotter and you make dots and draw lines. The aircrafts empty weight/CG also a dot on the graph being the point you start from. So really you never need to calculate the aircrafts empty CG after doing it the first time. Then you just dot/photocopy the rest of the graphs with the starting point already done. The rest is just using the plotter. Only time you need to change it is when switching aircraft or after major service/paint.

Cessna seems to have more graphs one being similar to the pipers (weight/CG), and one that looks similar but in is not (weight/moment). Was getting the moments off the other graph so didn’t really need to think about what the numbers actually were, just figured they were moving the CG arm like the other WB graphs do not actually cueing into the word “moment” and subconsciously going “moment arm” lol

The second you cued me into needing to convert the empty W/B into moment, and realizing the provided loading graph (fig 6-4) also did the same I realized I was screwing up.

The Cessna way is good too though, get a loading graph which works very easily with the moment envelope graph. Just need to use it correct Much better then using fig 6-8 and needing to calculate the loads to figure out where the CG is all the time.