Utility Category - Cessna 172

HPNPilot1200

HPNPilot1200

En-Route
Joined
Jul 6, 2005
Messages
2,662
Location
Huntington Beach, CA
Display Name
Display name:
Jason
Quick question...I was working on a new weight and balance spreadsheet for the flight school and came the conclusion that the newer Cessna 172's we have are not able to fly in the utility category that is documented in the POH. The BEW and CG puts the aircraft outside of the utility category at all times. Adding pilot + co-pilot and 10 gallons of gas still puts it way aft of the utility category aft CG limit (aprox. 40.5 inches).

If my theory is correct, why would Cessna continue to certify and document aircraft in the utility category?

Best,
 
HPNPilot1200 said:
Quick question...I was working on a new weight and balance spreadsheet for the flight school and came the conclusion that the newer Cessna 172's we have are not able to fly in the utility category that is documented in the POH. The BEW and CG puts the aircraft outside of the utility category at all times. Adding pilot + co-pilot and 10 gallons of gas still puts it way aft of the utility category aft CG limit (aprox. 40.5 inches).

If my theory is correct, why would Cessna continue to certify and document aircraft in the utility category?
Click to expand...

That doesn't seem right -- are you sure your numbers are accurate?
 
dmccormack said:
OK, and in that configuration is outside the utility category?

Is there any combination of fuel/people/baggage which is w/n Utility category?
Click to expand...

Correct, this is what it looks like graphed (first image).

If you theoretically put 433 lbs. in the front (pilot) and don't fuel it up (IOW, 0 fuel), you're still aft of the utility category and at the max takeoff weight of 2200 lbs. The second image is how that looks.
 

Attachments

  • new172weightbalance.JPG
    new172weightbalance.JPG
    92.7 KB · Views: 68
  • new172weightbalance_2.JPG
    new172weightbalance_2.JPG
    96.3 KB · Views: 56
HPNPilot1200 said:
Correct, this is what it looks like graphed (first image).

If you theoretically put 433 lbs. in the front (pilot) and don't fuel it up (IOW, 0 fuel), you're still aft of the utility category and at the max takeoff weight of 2200 lbs. The second image is how that looks.
Click to expand...

A 433 lb pilot in a 172?

Maybe a Pilatus is more suitable....

Anyway...

I don't have that a/c's W&B in front of me, but it may be that that airplane cannot be flown utility category in its current configuration.

Most (if not all) 172s need attention to fuel load and no anvils in the back to remain utility -- this is the first I've encountered that can't ever be utility...
 
Last edited:
Has anything been added or taken away from the factory equipment list? Most mechanics (not the ones on this forum) have a difficult time with basic math.
 
dmccormack said:
A 433 lb pilot in a 172?

Maybe a Pilatus is more suitable....

Anyway...

I don't have that a/c's W&B in front of me, but it may be that that airplane cannot be flown utility category in its current configuration.

Most (if not all) 172s need attention to fuel load and no anvils in the back to remain utility -- this is the first I've encountered that can't ever be utility...
Click to expand...

I put 433 lbs. in the pilot seat theoretically to show that even at max gross takeoff weight for the utility category, it's aft of the CG limit for that category. The empty design weight according to Cessna stats is 1,721 lbs for the newest of new 172s with the integrated GFC700. This 172 is equipped with the KAP140 which probably contributes slightly to the extra weight.

kgruber said:
Has anything been added or taken away from the factory equipment list? Most mechanics (not the ones on this forum) have a difficult time with basic math.
Click to expand...

Don't believe so, it's a stock C172SP G1000 w/ KAP140. See above.
 
Jason,

I don't know about those new planes and I confess I haven't look in detail at you numbers.

In my C172S, with an empty weight of 1738 lb., pilot and co-pilot each weighing 180 lb. and 18 gal. of fuel, I'm within limits in the utility category. The numbers are takeoff weight 2,198 lb, arm 40.9 and moment 89.9.

1,760 is heavy. Remove the rear seat, aprox. 50 lb.

Take care,
 
Last edited:
Well the G1000s do have a lot of avionics in the back, so it's possible that your airplane as equipped can't be operated in the utility category. Still, I'd be sure (and please take no offense if you've already done this) to:

Get the W&B info from the AFM, and check it yourself to be sure the math is correct.
Grab the envelope data from the AFM (not a reprint)

Just to be sure you're working with correct numbers.
 
TeenDoc said:
Jason,

I don't know about those new planes and I confess I haven't look in detail at you numbers.

In my C172S, with an empty weight of 1738 lb., pilot and co-pilot each weighing 180 lb. and 18 gal. of fuel, I'm within limits in the utility category. The numbers are takeoff weight 2,198 lb, arm 40.9 and moment 89.9.

Take care,
Click to expand...

The POH I had has the aft CG limit as 40.5 inches. At an arm of 40.9, you're still fore of that aft limit? Or is the limit different on your 2002 172?
 
TMetzinger said:
Well the G1000s do have a lot of avionics in the back, so it's possible that your airplane as equipped can't be operated in the utility category. Still, I'd be sure (and please take no offense if you've already done this) to:

Get the W&B info from the AFM, and check it yourself to be sure the math is correct.
Grab the envelope data from the AFM (not a reprint)

Just to be sure you're working with correct numbers.
Click to expand...

That's what I'm planning to do in the morning. I received the W&B info from the director of flight training who has it in a spreadsheet, but I'll double check it with the AFM.

I'll also grab the envelope data just to compare.

Best,
 
TMetzinger said:
Well the G1000s do have a lot of avionics in the back, so it's possible that your airplane as equipped can't be operated in the utility category. Still, I'd be sure (and please take no offense if you've already done this) to:

Get the W&B info from the AFM, and check it yourself to be sure the math is correct.
Grab the envelope data from the AFM (not a reprint)

Just to be sure you're working with correct numbers.
Click to expand...

:yes::yes:
 
Remember that the basic 172 design dates from 1955 or so, and Cessna has added hundreds of pounds of changes since then. The basic design may have worked in Untility in 1955, but when you add it all up with today's equipment, it's 10 pounds of stuff in a 5 pound bag. In every system's design modification history, there comes a time when, if you want the original capability, you have start over with a clean sheet design.
 
yea, i know, necro thread, anyway:

I'm trying this exercise 172L and I'm still not able to get in the utility CG, can anyone do this? Is the category a myth? Seems like you'd have to stuff some bowling balls in the engine compartment to make this work.

0 fuel, front pax totaling 330lbs gets me on the line

take the pax to 500lbs (you each carry a 100 lb weight in your lap) and you can add 15 gallons of fuel to get to the cg line.

it doesn't seem realistic (therefore kind of silly to even document in the POH)

maybe there is some model with a super heavy engine that can do this and they just carry the graphs over to all the models which can't possibly utilize the utility category.

does anyone have one of these unicorns that can be loaded within the utility cg range and have enough fuel to operate for an hour with reserves?
 
It's not uncommon to be very hard to keep a plane in the utility cateogry. Just because your particular airframe may be heavy (or on the cg limits) doesn't mean the entire type is.

To get the Navion into the utility category, I'm going to have to be solo and with less than full mains.

The main point of the utility category is to allow certain manoeuvres that you probably don't want to be doing at gross and with full tanks anyhow.
 
flyingron said:
It's not uncommon to be very hard to keep a plane in the utility cateogry. Just because your particular airframe may be heavy (or on the cg limits) doesn't mean the entire type is.

To get the Navion into the utility category, I'm going to have to be solo and with less than full mains.

The main point of the utility category is to allow certain manoeuvres that you probably don't want to be doing at gross and with full tanks anyhow.
Click to expand...
I get what you're saying, but out of a 1998 172S, a 2002 172R, a 1971 172L, none seem to be able to do it at any usable configuration. I'm just wondering if anyone on this forum has a 172 that can be used in Utility category.
 
Just ran it with my 172N with Air Plains O-360 conversion ...

With just myself aboard and full (40 gal.) fuel, it's within the Utility Category limit -- 1973 lb and moment 76.1 lb-in/1000, well within the aft limit of Utility. Still good with half fuel and a 140 lb passenger.

I have a 2010 172S POH, so I ran the numbers assuming the "Sample Airplane" in that book. Again, just myself and 40 gallons (not full fuel in that model), it's well within the Utility envelope (2082 lb, 81.7 lb-in/1000). Even full fuel (56 gal.) works.
 
Last edited:
Pilawt said:
Just ran it with my 172N with Air Plains O-360 conversion ...

With just myself aboard and full (40 gal.) fuel, it's within the Utility Category limit -- 1973 lb and moment 76.1 lb-in/1000, well within the aft limit of Utility. Still good with half fuel and a 140 lb passenger.
Click to expand...
You win!
 
Pilawt said:
Just ran it with my 172N with Air Plains O-360 conversion ...

With just myself aboard and full (40 gal.) fuel, it's within the Utility Category limit -- 1973 lb and moment 76.1 lb-in/1000, well within the aft limit of Utility. Still good with half fuel and a 140 lb passenger.
Click to expand...
What is your empty weight and moment(or arm)?
 
exncsurfer said:
I get what you're saying, but out of a 1998 172S, a 2002 172R, a 1971 172L, none seem to be able to do it at any usable configuration. I'm just wondering if anyone on this forum has a 172 that can be used in Utility category.
Click to expand...

Sure, 1975(ish) M model, 200lb pilot, 150lb front seat passenger, 10lbs of junk in the baggage area, 3 hours of fuel and still well within utility.

Tim
 
Pilawt said:
EW 1533 lb, moment 57.1
Click to expand...
you're so much more nose heavy on the empty weight comparatively, i'm at 1387lb, moment 57324, edge of the utility arm is 40.5, i'm at 41.3 empty, front pax bring it down barely at station 37 but the fuel brings it up very quickly at station 48.

your empty arm is 37.2 which makes more sense and must be what the design had intended, somewhere along the way it got heavy in back(or light up front, firewall forward).
 
exncsurfer said:
somewhere along the way it got heavy in back(or light up front, firewall forward).
Click to expand...
You may be right. When new, with the original O-320-H2AD engine, my 172N's empty weight was 1476 and arm was 38.8 inches. Now it has an O-360-A4M and Power-Flow exhaust. Empty weight now is 57 pounds heavier and arm is an inch and a half further forward (37.2").

In its original configuration my airplane would still be within the Utility envelope with myself solo and full fuel, but just barely. Your 172L is considerably lighter.

There's something fishy here. I'm looking at a 1972 172L owners manual. The "Sample Airplane" is 1364 lb empty and moment of 51.7 (arm 37.9"). Yours is only 23 pounds heavier, but the arm is almost three and a half inches further aft. Whats up with that??! If your CG was anywhere near the "Sample Airplane" you'd be golden.
Has it been weighed recently?
 
I did spin training in a C172SP. Two adult males up front and just about everything else cleared out of the plane. Only 18 gallons of fuel when we started the manuevers. Our CG was 39 point something.
 
Pilawt said:
You may be right. When new, with the original O-320-H2AD engine, my 172N's empty weight was 1476 and arm was 38.8 inches. Now it has an O-360-A4M and Power-Flow exhaust. Empty weight now is 57 pounds heavier and arm is an inch and a half further forward (37.2").

In its original configuration my airplane would still be within the Utility envelope with myself solo and full fuel, but just barely. Your 172L is considerably lighter.

There's something fishy here. I'm looking at a 1972 172L owners manual. The "Sample Airplane" is 1364 lb empty and moment of 51.7 (arm 37.9"). Yours is only 23 pounds heavier, but the arm is almost three and a half inches further aft. Whats up with that??! If your CG was anywhere near the "Sample Airplane" you'd be golden.
Has it been weighed recently?
Click to expand...
It's a rental so could be fishy. I'll have to check the date. Maybe there is a bowling ball mounted in the tail.
 
arnoha said:
Just tried it with my plane. There's no practical way to get my 172S into Utility category. This isn't uncommon for the restart Cessna.

http://tools.wvfc.org/WeightAndBalance.php?org=&mk=Cessna&md=172SP&t=N194SP&ppg=&env=1500,35.0,47.25,1950,35.0,47.25,2550,41.0,47.25&uenv=1500,35.0,40.5,1950,35.0,40.5,2200,37.5,40.5&aenv=&base=1712.1,41.19,2550,2558,2550&wma=Front+Seats,340,0,37.0,Rear+Seats,170,0,73.0,Fuel:35,210,318,48.0,Baggage+1,50,120,95.0,Baggage+2,0,50,123.0&w1=400&w2=0&w3=120&w4=0&w5=0&cmd=Calculate
Click to expand...

You could do it with 440lbs in the front seats and 8 gallons of fuel. Launch it from Courchevel Altiport and land it at a lower elevation. :)

But from an area with more reasonable terrain, the fact that your empty arm is aft of the 40.5" utility limit is a pretty good telltale that it isn't practical.
 
First, I have encountered numerous weight and balance reports that are out to lunch. It's easy to make a mistake when amending a W&B especially if the positive/negative arms aren't kept sorted out. An older 172 that can't meet utility numbers with the backseat empty and no baggage will have some defect with the W&B paperwork. They need actual weighing to get things sorted out.

Now, the newer models, particularly the G1000 versions, won't meet utility without removing the back seat. All the seats in all the 172R/S airplanes were upgraded to revised FAR 23 requirements that demanded 19G strength for the back seats and 23 for the fronts, and so they weigh at least three times what they used to. The G1000 has a whole rack of avionics boxes behind the baggage compartment, plus elevator and trim servos behind that, and the CG moves way aft of where it was in old airplanes.
 
I know this thread is old but it has some incorrect information about calculating CG in a Cessna. I’ll try and describe it as best I can where this calculation went wrong.

The problem you were having is you are using the incorrect CG graph. The one you want to be using is Figure 6-7 (center of gravity moment envelope) as specified in step 10 on the sample loading problem.

For the graph you are using it’s using inches aft of datum. To use that on a g1000 you need to take the aircrafts empty CG moment and subtract 25.9 from it to convert into inches forward datum.

On our g1000s the empty arm is 40.9 on the updated WB sheet. So with half tanks and 320lbs of pilot up front they have the opposite issue and the CG is too far forward for a 2200lb loading. The utility limit is 82-89 for the loaded airplane moment @ 2200lbs. Only way I could find to balance it is 40lbs in baggage area B.

Same issue occurs when converting to inches aft of datum for the CG and adding the moment arms to it.

Odd thing is for dual instruction flights the CG seems to fall too far forward even in normal loadings.

If you are curious where the 25.90 comes from to convert CG arm of the airplane to CG aft of datum you can find it on the airplane weighing form. It’s in the formula to locate percent mac. Where the 25.9 comes from is the measurement from the nose to FS 0.0. Since the datum in a Cessna is at flight station zero you need to have the aircraft in CG aft of datum to use that graph you posted.

Additionally can see on figure 6-1 (airplane diagram) the “stock” empty CG. The POH states it’s arm is 62.6 so if you subtract 25.9 so the CG should be at FS 36.7 (pilot/copilot position) which is exactly where it falls.
 
Alex3745 said:
If you are curious where the 25.90 comes from to convert CG arm of the airplane to CG aft of datum you can find it on the airplane weighing form.
Click to expand...

You have to convert CG arm of the airplane to CG aft of the datum? Wtf are you talking about?

Alex3745 said:
It’s in the formula to locate percent mac.
Click to expand...
MAC isn't used in W&B calculations in single-engine piston GA aircraft.

Alex3745 said:
Since the datum in a Cessna is at flight station zero you need to have the aircraft in CG aft of datum to use that graph you posted.
Click to expand...
Every datum is at station zero by definition because that's what a datum is. The reference or "zero" point for measuring arms and CG.

Methinks you are very, very confused. And if a CFI taught you what you posted, you need a new one.
 
dmspilot said:
You have to convert CG arm of the airplane to CG aft of the datum? Wtf are you talking about?


MAC isn't used in W&B calculations in single-engine piston GA aircraft.


Every datum is at station zero by definition because that's what a datum is. The reference or "zero" point for measuring arms and CG.

Methinks you are very, very confused. Too confused to fix on an internet discussion board. And if a CFI taught you what you know, you need a new one.
Click to expand...

There are 2 different WB charts to use in the Cessna POH. One uses the aircrafts CG moment envelope, and the other uses CG location inches aft of datum.

So depending which one is being used you might need to correct for FS0.0.

Take the same loading problem on page 6-10 in the G1000 172s POH. Empty weight of 1642 and moment arm 62.6 for the stock aircraft.

Try finding a place for that on the Center of gravity limits on page 6-16 graph 6-8. Or loading that aircraft in any legal way on this graph.

It needs to be done on graph 6-7.
 
Alex3745 said:
There are 2 different WB charts to use in the Cessna POH.
Click to expand...

That's the only thing you wrote that I agree with.

Alex3745 said:
One uses the aircrafts CG moment envelope, and the other uses CG location inches aft of datum.
Click to expand...

One shows a range of allowable moments and one shows a range of allowable CG locations.

Alex3745 said:
So depending which one is being used you might need to correct for FS0.0.
Click to expand...

There is no need to "correct" anything other than choose the correct graph. And I have no idea what that sentence above even means.

Alex3745 said:
Take the same loading problem on page 6-10 in the G1000 172s POH. Empty weight of 1642 and moment arm 62.6 for the stock aircraft.
Click to expand...

You keep using the term moment arm incorrectly. 62.6 is the moment in thousands of pound-inches. It's not an arm or a moment-arm, whatever that means.

Alex3745 said:
Try finding a place for that on the Center of gravity limits on page 6-16 graph 6-8. Or loading that aircraft in any legal way on this graph.

It needs to be done on graph 6-7.
Click to expand...

62.6 is not the center of gravity. It's the moment. Total moment divided by total weight equals center of gravity.

You definitely aren't going to be able to convert moment to CG by adding or subtracting anything :eek2:

Are you a student pilot? :confused2: Have you been taught how to do CG calculations? :confused2:
 
I’d get the TCDS for the specific model and use that as the starting point to work along with the POH.
 
dmspilot said:
That's the only thing you wrote that I agree with.



One shows a range of allowable moments and one shows a range of allowable CG locations.



There is no need to "correct" anything other than choose the correct graph. And I have no idea what that sentence above even means.



You keep using the term moment arm incorrectly. 62.6 is the moment in thousands of pound-inches. It's not an arm or a moment-arm, whatever that means.



62.6 is not the center of gravity. It's the moment. Total moment divided by total weight equals center of gravity.

Are you a student pilot? :confused2: Have you been taught how to do CG calculations? :confused2:
Click to expand...


6-7 is the center of gravity moment envelope so the CG is there but it’s not displayed in terms of aft of Datum. It’s displayed in aft the nose aka the nose being the datum. They technically display they exact same thing if you covert between graphs but you need to take into account the 25.9” forward of FS0.0 to get to the results on the CG- inches forward of datum graph
 
Alex3745 said:
6-7 is the center of gravity moment envelope so the CG is there but it’s not displayed in terms of aft of Datum. It’s displayed in aft the nose aka the nose being the datum. They technically display they exact same thing if you covert between graphs but you need to take into account the 25.9” forward of FS0.0 to get to the results on the CG- inches forward of datum graph
Click to expand...

You are speaking in tongues buddy. You have no idea what you're talking about.

The difference in the two charts is one shows moment vs. weight and the other CG vs. weight. They have nothing to do with the location of the datum in relation to the nose or this magic 25.9" number you came up with.

Please sign up for a weight and balance lesson with a CFI.
 
dmspilot said:
You are speaking in tongues buddy. You have no idea what you're talking about.

The difference in the two charts is one shows moment vs. weight and the other CG vs. weight. They have nothing to do with the location of the datum in relation to the nose or this magic 25.9" number you came up with.

Please sign up for a weight and balance lesson with a CFI.
Click to expand...

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.

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 would guess never.

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.

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.

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

Now that aft of datum CG is the one used for the empty weight in figure 6-8’s graph

I guarantee whenever g1000 you find a weight and balence sheet for will have 1700lb range empty weight and an arm listed in the high 30s or low 40s. Not an arm anywhere near the 62.5 range for an empty aircraft.
 
Alex3745 said:
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.

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 would guess never.

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.

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.

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

Now that aft of datum CG is the one used for the empty weight in figure 6-8’s graph

I guarantee whenever g1000 you find a weight and balence sheet for will have 1700lb range empty weight and an arm listed in the high 30s or low 40s. Not an arm anywhere near the 62.5 range for an empty aircraft.
Click to expand...
Dude you really need to study... what in the holy hell are you talking about?
 
You must log in or register to reply here.
Back
Top