Ex. of W&B w/wo rear seat in C172

Leo O'Farrell

Leo O'Farrell

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Leo O'Farrell
Hi,

I'm looking for an example of a Weight and Balance document with and without the rear seat of a C172. I'm interested in trying to fly my 1959 C172 as a utility aircraft, using some type of strap to hold down the typical behind and on the rear seat cargo (sleeping bag, tools, oil, first aid kit, water, flight bag, folding bicycle, fire extinguisher, etc. I rarely carry passengers, if I do it's usually one person.

Having an actual example of how's it's done would help my A&P/IA do this with the numbers from my bird.

Also would be interested to know if anyone has ever slept (while tied down on the ground) in the back of their Cessna.

I've slept in my Jeep and other cars overnight and know that I'd like to stretch out more that I usually can. Thinking my Cessna could offer a place to rest or sleep in a pinch.

Curiously enough, my best car for a good nights sleep was a two seat 280Z. There was a flat area under the louvered hatchback for my upper torso and my legs seemed to do fine between the seats. Considering that I'm 6'3" it might seem odd, but I spent a comfortable night in a down bag in the backstreets of Reno.

Thanks.

Leo
 
Can't you just throw the seat on a scale and subtract that weight from the station it is at?
 
Gucci Pilot said:
Can't you just throw the seat on a scale and subtract that weight from the station it is at?
Click to expand...

This makes sense. Or if you want to make an A&P really happy, ask them to re-weight the plane with the seat out.
 
I've slept in the backseat of a 182... the seats reclined and while fairly roomy it was far from comfortable.
 
Get the TCDS, it should have details for the airplane in utility category, possibly without the back seats.
 
The equipment list in section 6 of my 172R manual list the weight of the backseat and the arm. It should be simple to make the changes to the W&B.

seat, rear, one piece back cushion cloth. 43.3. 79.5
Seat, rear, one piece back cushion, leather. 44.7 79.5
Seat, rear, one piece back cushion, leather/vinyl 44.3 79.5
 
Wheels said:
The equipment list in section 6 of my 172R manual list the weight of the backseat and the arm. It should be simple to make the changes to the W&B.

seat, rear, one piece back cushion cloth. 43.3. 79.5
Seat, rear, one piece back cushion, leather. 44.7 79.5
Seat, rear, one piece back cushion, leather/vinyl 44.3 79.5
Click to expand...

They've gotten heavier! The rear seat in my '58 C182A is only 30#.

This same topic was discussed quite recently and I posted this article and FAA interpretation on it:

Flying with the rear seat removed
 
Gucci Pilot said:
Can't you just throw the seat on a scale and subtract that weight from the station it is at?
Click to expand...
No, but you can get the weight and arm or moment from the equipment list for the plane and then run the numbers from there. Note that the arm of the seat assembly is usually not te same as the arm for the person sitting in it because a person's legs stick out forward of the seat moving the person's cg forward of the center of the seat bottom while the vertical seat back makes the cg of the seat more aftward.

And I see someone's posted the arms above. Since the earlier seats were lighter, if you don't have the data from the equipment list for that submodel 172, I'd weigh the seat and use the arm provided above.
 
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Why can't you weigh it? It likely doesn't weigh the same as what it did on the original equipment list anyway if you've had interior work done.

My plane plane had a new W&B produced after a renovation was completed in 2002. This was accomplished by physically weighing it. We then physically weighed the back seat a few years later when I needed to start flying without it and decided to follow the advice of the article that I attached a few posts ago.

I don't know what the weight of the backseat is in the original equipment list produced in 1958 but it was 30# in 2004 or 05.
 
timwinters said:
Why can't you weigh it? It likely doesn't weigh the same as what it did on the original equipment list anyway if you've had interior work done.

My plane plane had a new W&B produced after a renovation was completed in 2002. This was accomplished by physically weighing it. We then physically weighed the back seat a few years later when I needed to start flying without it and decided to follow the advice of the article that I attached a few posts ago.

I don't know what the weight of the backseat is in the original equipment list produced in 1958 but it was 30# in 2004 or 05.
Click to expand...

You can weigh it, do the math and make the correction.
 
Ron Levy said:
...if you don't have the data from the equipment list for that submodel 172, I'd weigh the seat...
Click to expand...

Isn't that exactly what I said? :dunno: Since it is a 59 model I was assuming it didn't come with as detailed of documentation as newer models. If it does, then yeah, just look at the equipment list and pull the numbers from that. But since he and his mechanic are stumped, I was assuming he didn't have an equipment list.

Ron Levy said:
...use the arm provided above.
Click to expand...

The ones listed were for an R model that was made at least 37 years later, they may not be the same.

Ron Levy said:
Note that the arm of the seat assembly is usually not te same as the arm for the person sitting in it because a person's legs stick out forward of the seat moving the person's cg forward of the center of the seat bottom while the vertical seat back makes the cg of the seat more aftward
Click to expand...

Ok...But we are talking about an empty airplane W&B. What does this have to do with anything?
 
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Ron Levy said:
It's why you can't use the rear passenger arm from the W&B sheet instead of the actual arm of the seat itself from the equipment list.
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tcds
tcds
tcds
tcds
tcds

oh, bother.
 
Ron Levy said:
You need the arm from the equipment list. Measuring isn't an option.
Click to expand...

So I can't use the datum line and measure back from that? And I can't use the MM and go to the section that shows the datum line and indentifies the stations and use that number to compute a W&B?

Really? :rolleyes2:
 
RotorAndWing said:
So I can't use the datum line and measure back from that?
Click to expand...
You'd have to take that seat and balance it on a knife edge to find out where the cg of the seat itself is, and then measure that point back from the datum. That's a bit tricky, although I suppose you could do it.

And I can't use the MM and go to the section that shows the datum line and indentifies the stations and use that number to compute a W&B?
Click to expand...
If the Maintenance Manual includes the arm of the rear seat, you could certainly use that. I don't know if that's in the Cessna maintenance manuals, although I know it is not in the Grumman maintenance manuals (only the equipment list). However, if you have a 1978 or later 172, the rear seat weight and arm are in the equipment list in the POH/AFM or IM, so it's only an issue for an earlier plane for which the separate equipment list has disappeared.
 
The arm of the back seat is located at 70 inches, see page 3 of TCDS No 3A12.
http://rgl.faa.gov/Regulatory_and_G...754258e86257acc0077095f/$FILE/3A12_Rev_83.pdf


Weigh the seat

multiply seat weight by 70 inches to get seat moment.

Subtract seat moment from airplane empty moment.

Subtract seat weight from airplane empty weight

Divide new airplane empty moment by new empty weight to get new empty arm.

Have a nice day.
 
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Equipment Lists are generally full of errors. Components are repaired, relocated, installed, removed, re-upholstered, weights change and the Equipment List is forgotten about. I'd be shocked if the OP even knows where the one is for the aircraft in question.
 
Ron Levy said:
You'd have to take that seat and balance it on a knife edge to find out where the cg of the seat itself is, and then measure that point back from the datum. That's a bit tricky, although I suppose you could do it.
Click to expand...


Ron Levy said:
If the Maintenance Manual includes the arm of the rear seat, you could certainly use that. I don't know if that's in the Cessna maintenance manuals, although I know it is not in the Grumman maintenance manuals (only the equipment list). However, if you have a 1978 or later 172, the rear seat weight and arm are in the equipment list in the POH/AFM or IM, so it's only an issue for an earlier plane for which the separate equipment list has disappeared.
Click to expand...

This from the Cessna 100 Series MM, a tape measure and a weighing scale and I can do this.


c172_zpsed9aa7d0.jpg
 
Ron Levy said:
You'd have to take that seat and balance it on a knife edge to find out where the cg of the seat itself is, and then measure that point back from the datum. That's a bit tricky, although I suppose you could do it.
Click to expand...

:rofl:

I've seen 135 op specs on a 510 that didn't even require W&B revision until the change was over 5 pounds. As long as we use common sense, we measure. How do you think these 40 years of calculations get done?
 
bnt83 said:
:rofl:

I've seen 135 op specs on a 510 that didn't even require W&B revision until the change was over 5 pounds. As long as we use common sense, we measure. How do you think these 40 years of calculations get done?
Click to expand...
The rules on a jet of that size are different for the rules on a light single. See AC 43.13-1B for details.
 
Ron Levy said:
The rules on a jet of that size are different for the rules on a light single. See AC 43.13-1B for details.
Click to expand...

So we have a seat and the OEM "balanced it on a knife" is it going to be the same after you re-upholster it? Clearly none of the arms on the Equipment Lists are valid after 40 years.
 
bnt83 said:
So we have a seat and the OEM "balanced it on a knife" is it going to be the same after you re-upholster it? Clearly none of the arms on the Equipment Lists are valid after 40 years.
Click to expand...
That just isn't true. And if the weight of the seat changes more than one pound with reupholstering, the mechanic signing off the return is supposed to determine both the new weight and cg of the modified seat and make appropriate changes to the W&B and equipment list documents. Again, see AC 43.13-1B.
 
RotorAndWing said:
The methods for W&B are all similar in computations.

You're reaching.
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Similar in procedures, perhaps, but not in the W&B changes considered "insignificant" and this which can be ignored.

At the end of the day, the question is whether you want to do this right or just make the paperwork look good even if it doesn't reflect the actuality. Your choice to make.

-30-
 
So, I guess by extrapolation...

When I fold the back of my rear seat down to haul long stuff, I should carry a third weight and balance and be remeasuring the arm to reflect that the back of the seat (a whopping 12# or so) is no longer the same distance from datum line?

This could go on infinitely.

;)
 
Ron Levy said:
That just isn't true. And if the weight of the seat changes more than one pound with reupholstering, the mechanic signing off the return is supposed to determine both the new weight and cg of the modified seat and make appropriate changes to the W&B and equipment list documents. Again, see AC 43.13-1B.
Click to expand...

The seat isn't relocated, but the weight of the seat will change. The CG of the empty seat will even change.The Equipment List won't be revised.
 
Ron Levy said:
Similar in procedures, perhaps, but not in the W&B changes considered "insignificant" and this which can be ignored.

At the end of the day, the question is whether you want to do this right or just make the paperwork look good even if it doesn't reflect the actuality. Your choice to make.

-30-
Click to expand...

I can "do this right" using the information and tools I have mentioned.

As far as the OP question, using the information and tools mentioned he can recompute a W&B for the removed seat. Easy.
 
Ron Levy said:
That just isn't true. And if the weight of the seat changes more than one pound with reupholstering, the mechanic signing off the return is supposed to determine both the new weight and cg of the modified seat and make appropriate changes to the W&B and equipment list documents. Again, see AC 43.13-1B.
Click to expand...

Or, I suppose the airplane could just be weighed after a complete interior/exterior renovation, like mine was, and none of information would be known?
 
timwinters said:
So, I guess by extrapolation...

When I fold the back of my rear seat down to haul long stuff, I should carry a third weight and balance and be remeasuring the arm to reflect that the back of the seat (a whopping 12# or so) is no longer the same distance from datum line?

This could go on infinitely.

;)
Click to expand...

bnt83 said:
The seat isn't relocated, but the weight of the seat will change. The CG of the empty seat will even change.The Equipment List won't be revised.
Click to expand...

Not to mention seats that are adjustable for an aft. Should we do a W&B for each stop hole in the rail? :rolleyes:
 
RotorAndWing said:
Not to mention seats that are adjustable for an aft. Should we do a W&B for each stop hole in the rail? :rolleyes:
Click to expand...

I think you should!

(I was going to mention that one too but thought it might be a wee bit over the top!) :goofy:
 
timwinters said:
Or, I suppose the airplane could just be weighed after a complete interior/exterior renovation, like mine was, and none of information would be known?
Click to expand...

I guarantee re-upholstering a seat will change its center of gravity and its total assembled weight. These CG changes are not reflected by changing the arm on the equipment list. It is so miniscule compared to the big picture it's a waste of time, even when calculating a new empty weight.
 
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