Cessna 172L Weight and Balance

steviedeviant

steviedeviant

Pre-takeoff checklist
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StevieD
Hello all.

I just have a question to try and check my work on weight and balance. Normally just my wife and I fly around so W/B is never an issue. The Cessna is a four seater and tomorrow we are taking two other adults. I am showing after putting everything in that we are good on the weight and balance and so everything checks out fine.

The main reason I ask is that I thought many of you have posted how a four seater plane can't really hold four. The total weight between the four of us is about 650. Anyway, I guess just seeing that it would work wasn't "jiving" with many of the comments regarding four seaters.

So the question is, have many of you that fly the 172 had four adults before and how was the flight?

Any comments to share on W/B would be helpful. Thanks in advance.

S
 
really depends on the 172. Some do not have very good useful load. My 172n with the gross weight increase has a useful load of over 1,000 lbs so 4 average adults and full fuel will work just fine. What is your useful load?
 
Hopefully you're adding a buffer into your numbers to error on the conservative side.
 
Ha. Well, we are all under 200 pounds. Am allowing extra. I just wanted to run it by the group because again, I always hear it isn't really a four seater.

Thanks,
 
steviedeviant said:
38 gallons.
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So 38 gallons X 6lbs =228lbs

650 for the pax, that's 878lbs out of the 988 useful load you mentioned . Plot it in the W/B chart and what do you get?

Hard for anyone to give you any real answers when we don't have all of the specs. you're working with.
 
Maybe don't "allow extra" - 100 pounds over gross won't hurt nearly as much as being outside CG limits. Use real weights.
 
How do you know the weight data you have for your aircraft is correct? Old aircraft get fat, just like old pilots.
 
Hard to get a 172 out of CG, although it is possible with extreme loading scenarios and must be checked. Over gross is the real limiting factor.
 
Tom-D said:
How do you know the weight data you have for your aircraft is correct? Old aircraft get fat, just like old pilots.
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This is a rental plane and I have the recalculated weight and balance from the flight school. Here are the numbers on the sheet with the most current information:

Max take off weight 2300
Max gross weight 2300
New moment 48,681.26
New basic empty weight 1313.20
New moment arm 37.07
New useful load 986.80
 
steviedeviant said:
This is a rental plane and I have the recalculated weight and balance from the flight school. Here are the numbers on the sheet with the most current information:

Max take off weight 2300
Max gross weight 2300
New moment 48,681.26
New basic empty weight 1313.20
New moment arm 37.07
New useful load 986.80
Click to expand...
I've yet to see two facilities weigh an aircraft and come up with the same numbers.
How old are the numbers you used to get the 1313.20?
 
1313 empty is way too low. By 100 pounds, maybe. It would have to have no radios, no back seat, no paint, no wheelpants, no nothing, and would still weigh more than 1313. It would have to be a really old airplane to weigh so little, and then its gross would be 2200.

I have seen too many suspicious W&B amendments. Often the numbers have been added up wrong, resulting in an incorrect weight, and more often the moment and therefore CG is way off.
 
Tom-D said:
why should he be either?
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I don't know, why should he? I didn't advocate either. Just noted that a bit over gross is preferable to being a bit out of CG. And that using the true weights, as best you can determine, is preferable to "allowing extra" - calculate W&B (and maneuvering speed) using the real numbers, without adding fudge factors. You'll still probably be wrong, but just a little less so.
 
Hmm, they must have been lighter way back when. I just did a quick google and found a 1971 150HP 172L 'standard empty' listed as 1250 to 1300 pounds. The 160HP 172R I rent is 1690 empty. Cant fill that one up with fuel with 4 adults. Maybe his numbers aren't that far fetched.

This is the link I was looking at:
http://www.172guide.com/models/172L-71.htm
 
Many of the 172Ns I've flown had useful loads of 850 or so. If very lightly equipped, that might get a bit higher. 650 lb of people plus 240 lb of fuel is 890. Maybe. The older aircraft really are lighter, and sometimes the gross weight goes up with STCs.

There really is no substitute for running the real calculation with real numbers.
 
steviedeviant said:
This is a rental plane and I have the recalculated weight and balance from the flight school. Here are the numbers on the sheet with the most current information:

Max take off weight 2300
Max gross weight 2300
New moment 48,681.26
New basic empty weight 1313.20
New moment arm 37.07
New useful load 986.80
Click to expand...
Unless they weighed the airplane, "most current" and "accurate" aren't going to be the same...assuming they actually did the calculations correctly. ;)

I still wouldn't make random adjustments to my weights unless I had reason to believe that the weight or CG was actually in error.
 
exncsurfer said:
Hmm, they must have been lighter way back when. I just did a quick google and found a 1971 150HP 172L 'standard empty' listed as 1250 to 1300 pounds. The 160HP 172R I rent is 1690 empty. Cant fill that one up with fuel with 4 adults. Maybe his numbers aren't that far fetched.

This is the link I was looking at:
http://www.172guide.com/models/172L-71.htm
Click to expand...

Almost everything was an option back then. The weights added up in a hurry. The L and M models we had were all between 1420 and 1470 or so, actual W&B numbers. The 172SP, with the G1000, was well over 1700 empty. All those boxes and the standby battery come to 48 pounds or so. Gross 2550.
 
Dan Thomas said:
1313 empty is way too low. By 100 pounds, maybe. It would have to have no radios, no back seat, no paint, no wheelpants, no nothing, and would still weigh more than 1313. It would have to be a really old airplane to weigh so little, and then its gross would be 2200.

I have seen too many suspicious W&B amendments. Often the numbers have been added up wrong, resulting in an incorrect weight, and more often the moment and therefore CG is way off.
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I had numerous people (about a half dozen) tell me my Cherokee numbers were IMPOSSIBLE! "No cherokees are that light!" they said... Spent $150 for a new weight and balance to find out it was nearly dead on. It was 1.8 lbs heavier...which was counter acted by my wallet being lighter. I stopped listening to those people.
 
Do you calculate only for takeoff, or do you also calculate W&B at landing? When using fuel, isn't it possible CG moves forward, making it tail heavy?
 
You calculate W&B at takeoff, and with zero fuel. Landing really should be somewhere in between. :)

It's not usually a problem, but it could be in principle.

Planned landing weight is also necessary if the airplane has a max landing weight lower than its max takeoff weight, and you take off above max landing.

I imagine jumper dumpers, bombers, and fire tankers have more interesting problems.
 
MAKG1 said:
You calculate W&B at takeoff, and with zero fuel. Landing really should be somewhere in between. :)

It's not usually a problem, but it could be in principle.

Planned landing weight is also necessary if the airplane has a max landing weight lower than its max takeoff weight, and you take off above max landing.

I imagine jumper dumpers, bombers, and fire tankers have more interesting problems.
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Now I'm a little confused. Just a student, but from ground school and real flying experience I have learned to 1) include fuel and 2) also check expected W&B after expending the amount of fuel the trip will take.

I have been taught it isn't JUST the weight, but the CG and that even if under the max weight the CG can shift and depends on where the fuel tanks are located. Just read a pilots review of some newer type airplane where when fuel is expended and there are two up front, you pretty much need some "ballast" in the back to keep CG within limits. I think that means the CG moved back when significant fuel is used in that particular case.

I don't know, this is just what I'm being taught. Usually i find no issue when doing the calculations and CG Remains in limits when we use up fuel.
 
LongRoadBob said:
Now I'm a little confused. Just a student, but from ground school and real flying experience I have learned to 1) include fuel and 2) also check expected W&B after expending the amount of fuel the trip will take.

I have been taught it isn't JUST the weight, but the CG and that even if under the max weight the CG can shift and depends on where the fuel tanks are located. Just read a pilots review of some newer type airplane where when fuel is expended and there are two up front, you pretty much need some "ballast" in the back to keep CG within limits. I think that means the CG moved back when significant fuel is used in that particular case.

I don't know, this is just what I'm being taught. Usually i find no issue when doing the calculations and CG Remains in limits when we use up fuel.
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I think you have your cg thinking reversed. If the CG moves forward and you require weight in back, then you're fixing a nose heavy situation.
 
steviedeviant said:
This is a rental plane and I have the recalculated weight and balance from the flight school. Here are the numbers on the sheet with the most current information:

Max take off weight 2300
Max gross weight 2300
New moment 48,681.26
New basic empty weight 1313.20
New moment arm 37.07
New useful load 986.80
Click to expand...


Well, according to the sheet it was done three years ago and this is in they have at the school. Basically, I have been told flying four medium isn't much of and issue, but I was just wanting to complete a W&B for a real life situation rather than some test question. As it turned out, we didn't get to fly all together anyway, but this thread has still been very helpful.
 
Sundancer said:
Maybe don't "allow extra" - 100 pounds over gross won't hurt nearly as much as being outside CG limits. Use real weights.
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This. I wouldn't say "outside" though if you're a little over-gross. I would say "near" when a little over gross.

Yes, I know I'll get jumped on for this but I'll bet there isn't an experienced pilot on this board who hasn't been over gross at least once. "The plane flies much better a bit over gross than it does with empty tanks."
 
airdale said:
... I'll bet there isn't an experienced pilot on this board who hasn't been over gross at least once...."
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I've owned a Cessna 150...even though I'm average size and weight, and my girlfriend is average size/weight, I don't think there was a single time we didn't fly over gross. Ever.
 
steviedeviant said:
...how was the flight?

Any comments to share on W/B would be helpful. Thanks in advance.

S
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Keep in mind that the nose will be higher than what you are used to in all phases of flight. As an example, when you enter downwind and pull the power back, the nose will rise more than it usually does, and you may be tempted to push forward to achieve the same sight picture as you would usually have.
 
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