CG shift question

Captain

Captain

Final Approach
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First Officer
Whats the formula to shift / add weight?

I know W x A = M, but that's about all I remember....
 
Umm, dM = W x dA for shift, dM = dW x A for weight addition/removal.

Not sure what you're getting at.

Unless you really want the CG (it's easier to deal with the moment).

CG' = (CG * GW + dM) / (GW + dW)

Or if the weight is small compared to GW, dCG = dM/GW
 
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Let's start basic. I have a weight, CG, and. Moment of a plane. I also can find all the stations with their arm.

How do you:

A: add weight to a station,
B: subtract weight from a station, and
C: move weight from one station to another.

As the weights go I know the item weights and station arms. I need to end up with a new CG for the plane.
 
They teach all this in part 61.
 
Captain said:
Let's start basic. I have a weight, CG, and. Moment of a plane. I also can find all the stations with their arm.

How do you:

A: add weight to a station,
B: subtract weight from a station, and
C: move weight from one station to another.

As the weights go I know the item weights and station arms. I need to end up with a new CG for the plane.
Click to expand...

Easy.... get a FAT person.... load them up in your SL and have them move around...:yikes:
 
MAKG1 said:
Shorthand for change in M, change in CG. It's helpful when deriving these things.
Click to expand...

Ah, thanks. I think I can make that work now.

For any curious, on the line I use an app for W&B. We don't do it manually. Even before apps we used CG Whiz Wheels to spin on and off pax and bags. Never used the math and I've found if I don't use it I lose it.

Well now I'm on an office tour and we're redoing our stock on the plane. Figuring out a new operating weight for the fleet aircraft and it's back to old school.

Thanks MAKG1 for the refresher....
 
Captain said:
Let's start basic. I have a weight, CG, and. Moment of a plane. I also can find all the stations with their arm.

How do you:

A: add weight to a station,
B: subtract weight from a station, and
C: move weight from one station to another.

As the weights go I know the item weights and station arms. I need to end up with a new CG for the plane.
Click to expand...

There's shortcut formulas in the PHAK but you can do it easily enough without them. Just do it the normal way.

Code: 
Aircraft   1500 lb.  40 in.   60,000 lb-in.
Fuel        200 lb.  50 in.   10,000 lb-in.
Pilot       170 lb.  30 in.    5,100 lb-in.
TOTAL      1870 lb.  40.2 in. 75,100 lb-in.
Need to add or subtract weight, just start where you left off. For example, adding 50 lbs of baggage:

Code: 
Old Total 1870 lb.  40.2 in. 75,100 lb-in.
Baggage     50 lb.  80 in.    4,000 lb-in.
TOTAL     1920 lb.  41.2 in. 79,100 lb-in.
Turning the aircraft into a drone:

Code: 
Old Total     1920 lb. 41.2 in. 79,100 lb-in.
Remove pilot: -170 lb. 30 in.   -5,100 lb-in.
TOTAL         1750 lb. 42.3 in. 74,000 lb-in.
 
Everything you'd ever want to know about aircraft weight and balance is in this free handbook from the good 'ol FAA

FAA-H-8083-1A
 
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Silvaire said:
Everything you'd ever want to know about aircraft weight and balance is in this free handbook from the good 'ol FAA

FAA-H-8083-1A
Click to expand...

Yeah, I have access to the 'pubs'. Being lazy like I am I thought I'd use PoA as a shortcut. I'm working with my Chief Pilot on this and was sort of showing off how fast an answer would show up. Aside from Ed's little antics y'all did great.
 
Captain said:
Yeah, I have access to the 'pubs'. Being lazy like I am I thought I'd use PoA as a shortcut. I'm working with my Chief Pilot on this and was sort of showing off how fast an answer would show up. Aside from Ed's little antics y'all did great.
Click to expand...
The only think you really need to know (besides W*A=M) is that moments can be added regardless of the reference station. That's the reason we use moments when combining weights at various locations.
 
Tomorrow I hit the books with this stuff. Maybe I'll post an actual problem and see if my work is right.

Nice catch, btw on the barnstormers ad. Obviously I didn't follow it and just assumed it was 'as advertised' (pun intended).
 
Think of each weight/load as the pull on the handle of a torque wrench. The length of each torque wrench is the distance from that load to the reference point of that plane type. The foot lbs. of moment or torque or twisting force applied to the reference point by that load is the moment for that load. Every load, including the empty weight and moment, applies torque to the reference point. Add the torques/moments to find the total twisting force applied to the reference point. Divide that total twist by the total weight and you get the length (distance from the reference point) of one big torque wrench combining all of the individual torque wrenches and weights. That length is the distance of the total CG from the reference point. Positive values are behind the reference point. Negative values are ahead of it. If the reference point is the point of the spinner (Piper), there are no negative values. If the reference point is the firewall (Cessna?), anything ahead of the firewall is a negative value.
 
Weight X Arm = Moment...... It is a simple concept... The scary part is high time, commercial pilots cannot grasp it...:no::eek:
 
You know the funny thing is I used do stuff like that for a living (structural statics involving forces and moments) yet I sometimes have brain farts adjusting aircraft W&B problems, just like Captain, even though they're far more simple mathematically.
 
N801BH said:
Weight X Arm = Moment...... It is a simple concept... The scary part is high time, commercial pilots cannot grasp it...:no::eek:
Click to expand...

I may or may not be a jerk, but even I wouldn't fault someone for not remembering how to do something after 13 years of not doing it.
 
EdFred said:
They teach all this in part 61.
Click to expand...

N801BH said:
Weight X Arm = Moment...... It is a simple concept... The scary part is high time, commercial pilots cannot grasp it...:no::eek:
Click to expand...


You two did not help. To the rest, thank you. Ya'll do realize that when you climb on a B-777 the pilots are not doing a weight and balance like you do, right?

I know most of you do but from EdFred's and N801BH's comments you'd think all aviation in all forms is the same and everyone does what everyone else does. Tip: They don't. Some of us have dispatchers and programs to do the simple stuff for us. Lean on the 'programs' long enough and you forget how to do it long hand.

Nice job punching someone who is simply asking a question. Then we wonder why people are hesitant to ask questions around here. Seriously, if we want pilots to ask what they do not know then maybe we should stop kicking them when they ask.

Or we can all just march around pretending we know everything and see where that gets us.
 
Captain said:
You two did not help. To the rest, thank you. Ya'll do realize that when you climb on a B-777 the pilots are not doing a weight and balance like you do, right?

I know most of you do but from EdFred's and N801BH's comments you'd think all aviation in all forms is the same and everyone does what everyone else does. Tip: They don't. Some of us have dispatchers and programs to do the simple stuff for us. Lean on the 'programs' long enough and you forget how to do it long hand.

Nice job punching someone who is simply asking a question. Then we wonder why people are hesitant to ask questions around here. Seriously, if we want pilots to ask what they do not know then maybe we should stop kicking them when they ask.

Or we can all just march around pretending we know everything and see where that gets us.
Click to expand...

Take a chill pill sir......:yes::D
 
Captain said:
You two did not help. To the rest, thank you. Ya'll do realize that when you climb on a B-777 the pilots are not doing a weight and balance like you do, right?

I know most of you do but from EdFred's and N801BH's comments you'd think all aviation in all forms is the same and everyone does what everyone else does. Tip: They don't. Some of us have dispatchers and programs to do the simple stuff for us. Lean on the 'programs' long enough and you forget how to do it long hand.

Nice job punching someone who is simply asking a question. Then we wonder why people are hesitant to ask questions around here. Seriously, if we want pilots to ask what they do not know then maybe we should stop kicking them when they ask.

Or we can all just march around pretending we know everything and see where that gets us.
Click to expand...

Hypocrisy. It's what's for dinner. Maybe if you didn't act like a giant douche all the time people might actually help when you ask for it. You want to come into a room and take a dump, and then expect people to appreciate that you blessed us with your turd. Sorry pal, not likely.
 
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