Weight and balance question

david0tey

david0tey

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Taking a trip tomorrow with a heavy passenger in the Beech Musketeer. Weight and balance sheet from most previous calculation shows the arm as 107.87. POH shows the arm as 110.1. I can't get the airplane within CG limits with the 107.87 arm. It works fine with the 110.1 arm. Is it safe to assume the POH arm is accurate?
 
Most recent rules. What is the # with the pax seat pushed all the way back?
 
david0tey said:
Where would I find that?
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Use an arm figure halfway between the front and back seat arms will be good enough for this. You always want to load toward aft CG limits when possible for speed/economy and easier handling on landing.

I often put big passengers in the back seat not only for this, but comfort for both of us as well.
 
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The OFFICIAL Weight and Balance sheet rules.

Can you add ballast in the baggage compartment to bring the balance in limits?
 
Stewartb said:
Put some stuff in the back. Balance it out. No need to embarrass your friend.
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It's never been embarrassing. "This plane has weight distribution and balance limitations, in order to make that work in this plane, I need you to ride in the back seat." Just matter of fact and they always look relieved because they really did not want to cram into that front seat with me. I say it professionally with a smile and no sense of value judgement and they just climb into the back. Big people know they are big and that there are things they need to do to accomodate that. Typically they are much more comfortable in the back, and if non pilots don't really care to be up front anyway. A 172 or 182 I can scoot them back far enough though that things work pretty well. "I need you to keep your seat back here for center of gravity reasons." Just tell them the facts.
 
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Just put the pax in the seat, adjust it as far back as possible, measure from the Datum line.

Not sure about the beech, most cessnas have a forward and rear figure for the sliding seats.

Now aside from the regs (which you should follow of course), would the plane fly at 108 vs 110, I'd wager it would be safe, probably need a little more muscle in the flare and on rotation, she'll be a little slower enroute, but I doubt it would be the end of the world, theoretically speaking, of course.

As others said, you can also just do the easy thing and have big boy sit in the back.
 
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FastEddieB said:
risk his and his passenger's life on a "probably".
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A little bit of a overstatement.

2" on the C of G, won't make a life threating situation on most 4 place aircraft. After getting some hours on a airframe you should have a feel for what the plane can take [of course this statement is for educational/theoretical purposes only, follow the FAR and your POH].
 
Doesn't the front seat have different arms for seat positions, did you try the aft most position?
 
No experience with the Musketeer, but I know in most Cessnas if you were loading someone that heavy that you'd go out of W&B *FORWARD* -- you'd be WAY WAY WAY over the seat itself's load capability.

Perhaps the seat is on the floor in the Beech... but just mentioning it... any limits on the seats in that thing? Loading a Cessna with someone that big is an almost guaranteed busted seat roller, another crack toward the AD in the seat track, or just a crap-ton of wear and tear on the whole seat attachment system when they decide to slide it forward/move it.

Can get expensive REAL fast.
 
david0tey said:
Is it safe to assume the POH arm is accurate?
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No. The POH may well be just the "standard" values rather than your airplane's actual values. Yes, it's entirely possible there is a big math error somewhere in your airplane's W&B history, and the actual cg is close to the "standard" cg, but since your assumption could lead to being a couple of inches outside the cg envelope if the W&B sheet to which you referred is right, you really need to find out. I suggest you go back through all the W&B data and maintenance records and check every 2+2 to see whether somewhere along the line they got 3 instead of 4. I've done that a few times over the years when the W&B data looked wrong, and every time it fixed the problem, but that's no assurance that it will for you.
 
Greg Bockelman said:
The OFFICIAL Weight and Balance sheet rules.

Can you add ballast in the baggage compartment to bring the balance in limits?
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If you do that, you're betting that the W&B data showing a cg 3 inches forward of the "standard" value is correct. If that isn't true, then you're liable to end up a couple of inches aft of the aft cg limit, and that would be a very bad place to be. Given the large difference, I think it behooves you to dig back in the records and check every post-alteration W&B computation to see if there's a math error somewhere. BTDT with a few planes, and I always found the error.
 
The Musketeer at my FBO has a similar problem. No way to get two people of any nornal size in the front seats without adding ballast. Nobody believes it, then they run the numbers, twice.
 
I'd be inclined to use the POH station unless there's a flight manual supplement that supersedes it. FWIW I pull the Musketeer up on my W&B app and the pilot/co-pilot station is 110".
 
Is this the arm for the front seat?

Does the seat adjust?

Does the arm account for the adjustment?

Did you account for the difference in the person's CG location if they have a big gut vs. a big ass?

Is it reasonable to think that one knows the actual arm for a random seated human being to within one or two inches?

How much difference does it make in the computed aircraft CG?
 
OK, I've reread the thread, and get the idea that you're asking about the correct arm for the pilot/co-pilot seats rather than the correct arm for the empty cg. Is that correct? If so, I'd ask what the source of that W&B worksheet is. If you really can't determine the provenance of that worksheet, I'd say use the POH number for two reasons:
1. The POH is FAA-approved.
2. If the POH one is wrong and the worksheet is right, your actual cg will be further forward than you thought, and that's a lot safer than actual cg being further aft than you thought.
 
Wait.

If we are in fact talking about the arm of the seat, all you need is to know the reference datum and go grab a tape measure.

I thought we were talking about the empty weight CG. That's the only thing that would change over time from the POH "Sample Airplane" data, or the original empty weight CG, with the addition and subtraction of equipment.

Which is it?
 
FastEddieB said:
If we are in fact talking about the arm of the seat, all you need is to know the reference datum and go grab a tape measure.
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It's not quite that easy. You'd have to determine where the center of mass of the combined seat and occupant is, and that's a bit tricky. Remember that legs extend out in front of the seat's forward edge.
 
Ron Levy said:
It's not quite that easy. You'd have to determine where the center of mass of the combined seat and occupant is, and that's a bit tricky. Remember that legs extend out in front of the seat's forward edge.
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Is that allowed for? I never thought it was. A quick perusal of the FAA Weight and Balance does not seem to mention it, and their diagrams are consistent with just measuring to the center of the seat.

As an example, from the below diagram would you not assume they simply give the station as shown - the center of the seat?

16480300968_9c770cd27b.jpg
 
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Greg Bockelman said:
Can you add ballast in the baggage compartment to bring the balance in limits?
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david0tey said:
Even doing this will be a forward CG.
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That's the major problem with Musketeers. Way too nose heavy and a front gear that can't take the pounding. I remember Beech adding lead weights in the tail of later models. A lightweight starter helps.

With max weight in the baggage does playing with the fuel help? Maybe a little weight in the back seat too? Helium in the front tire?
 
FastEddieB said:
Wait.

If we are in fact talking about the arm of the seat, all you need is to know the reference datum and go grab a tape measure.

I thought we were talking about the empty weight CG. That's the only thing that would change over time from the POH "Sample Airplane" data, or the original empty weight CG, with the addition and subtraction of equipment.

Which is it?
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See post 11 :redface:
 
Ron Levy said:
No. The POH may well be just the "standard" values rather than your airplane's actual values. Yes, it's entirely possible there is a big math error somewhere in your airplane's W&B history, and the actual cg is close to the "standard" cg, but since your assumption could lead to being a couple of inches outside the cg envelope if the W&B sheet to which you referred is right, you really need to find out. I suggest you go back through all the W&B data and maintenance records and check every 2+2 to see whether somewhere along the line they got 3 instead of 4. I've done that a few times over the years when the W&B data looked wrong, and every time it fixed the problem, but that's no assurance that it will for you.
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On the Arm? The arm is just measurement off the datum line, I would expect that to be correct and accurate on the type certificate, and unless the datum is changed or fuselage stretched, the arm of the referenced locations will not change.

As for 2" forward, I hate being forward, it makes for nose heavy landings that have a greater propensity for bending metal on a bad landing while making a bad landing more likely. Toss them in the back seat, enjoy the extra 5-10kts and cabin space.
 
I'll go back through the weight and balance sheets from maintenance calculations tomorrow . Every time I do this calculation with the 110.1 empty aircraft arm (as stated in the POH), I can get the CG just perfect. However, with a 280 lb passenger in the front seat (fully back position with an arm of 112) and the calculated empty arm of 107.87, I couldn't get it within CG limits even if I added 80 lbs in the back seat and took ZERO fuel! Doesn't seem right to me.
 
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david0tey said:
Every time I do this calculation with the 110.1 empty aircraft arm (as stated in the POH), I can get the CG just perfect. However, with a 280 lb passenger in the front seat (fully back position with an arm of 112) and the calculated empty arm of 107.87, I couldn't get it within CG limits even if I added 80 lbs in the back seat and took ZERO fuel! Doesn't seem right to me.
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It appears my initial impression was correct.

David is talking about the arm of the empty weight CG.

David, hate to say it but there's been much confusion in this thread due to the very imprecise language you're using. It's made different forum members have to guess as to your issue.

A 3 or 4 inch discrepancy in the arm of the empty weight CG is kinda huge. You MUST sort this out.

The forward limit is there for a reason. That reason, IIRC, is usually the elevator's ability to lift the nose. Hence, a CG forward of the forward limit may result in...

An aircraft unable to rotate, or,

An aircraft that runs out of elevator authority in the flare.

Neither is a good thing, nor is the decreased performance that accompanies a forward CG.

Is there any way to scan/photograph the two documents that are giving you the conflicting data and oust them here?
 
I don't know what he meant by a "previous calculation" or by POH information.

There is W&B info for the particular plane which is likely NEITHER a "previous calculation" or the generic stuff in the POH. That's where you need to go.

The answer to forward CG is to either move stuff back or lower the weight (most envelopes have a "foldover" where above a certain gross weight the forward CG limit goes aft with further increase in weight.
 
david0tey said:
I'll go back through the weight and balance sheets from maintenance calculations tomorrow . Every time I do this calculation with the 110.1 empty aircraft arm (as stated in the POH), I can get the CG just perfect. However, with a 280 lb passenger in the front seat (fully back position with an arm of 112) and the calculated empty arm of 107.87, I couldn't get it within CG limits even if I added 80 lbs in the back seat and took ZERO fuel! Doesn't seem right to me.
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That's a horse of a different color.

The empty weight arm in your POH may be a "typical" value, but the arm in the latest weight and balance should typically be different because it has been adjusted for equipment changes - radios, starters, propellers, batteries, and whatever else has been done over the years. Moving the CG of the empty aircraft is significant.

Your options are to use the CG found on the W&B, review all of the changes made over the years to find if there is an error in a calculation somewhere, or have the airplane weighed to find out where the empty arm really is.
 
david0tey said:
I'll go back through the weight and balance sheets from maintenance calculations tomorrow . Every time I do this calculation with the 110.1 empty aircraft arm (as stated in the POH), I can get the CG just perfect. However, with a 280 lb passenger in the front seat (fully back position with an arm of 112) and the calculated empty arm of 107.87, I couldn't get it within CG limits even if I added 80 lbs in the back seat and took ZERO fuel! Doesn't seem right to me.
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I gather then that I was right the first time -- you're talking about the empty cg, not the arm of the front seats on the loading worksheet. You most certainly cannot use the "standard" empty cg in the sample loading problem in the POH (which I gather is 110.1) as the empty cg arm for your plane -- you must use the actual (weighed, or calculated based on last weighing plus computations for alterations) empty cg, which I gather your paperwork says is 107.87.

If you think that number is wrong, you'll have to go back to the last weighing, and then first check the math which turned the three wheel weights (nose and both mains) into an empty cg (I've found errors there which carried forward for a couple of decades), then check the math on every alteration W&B update from there to today (I once found a Comanche where a bad computation on an avionics change in the 60's carried forward into the 21st century).
 
Henning said:
Yep, 107 is your empty weight arm that you start with, unless you reweigh the plane and come up with something new, that is your base line.

Can you show your entire calculation set so we can see if you are making a mistake in your calculation to derive your final CG?
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You're talking about a lot of pages of data, including every W&B update since the last weighing plus the source information from the aircraft logbooks. You probably also need the weighing/cg computation instructions from the POH or maintenance manual.
 
Ron Levy said:
You're talking about a lot of pages of data, including every W&B update since the last weighing plus the source information from the aircraft logbooks. You probably also need the weighing/cg computation instructions from the POH or maintenance manual.
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No, I just want to see his flight plan W&B calculations using the given datums. If he thinks he should be able to do this and that he is getting an incorrect result, the only way to answer that is to check his work. Maybe he is missing something, but I doubt it, I think he needs to put them in the back seat or use a 172/182 so the front seat slides back far enough. All depends on the purpose is f the flight, to introduce them to aviation, or provide transportation.
 
You may want to do a new weight and balance for a couple of reasons. The weight of most planes do change over time. Collection of dirt is a big reason, equipment changes are another. Your W&B was done 14 years ago and recalculated 3 year later not reweighed. As it stands 107 is your number. As for seat position I think the arm goes from 104 to 112 for the front seats
 
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Here's what I have:

Weight Arm Moment

Empty. 1448 107.87 156173


Fuel (25 gal) 150.5 117 17608


Pilot 185 110 20350


Passenger 190 110 20900


Rear seats(ballast) 100 142 14200






Total. 2073 lbs (under max gross). Moment 229.22


This is still forward of allowable CG.
I like this plane but if you can't make those parameters within CG, that's pretty ridiculous. I should also add: it's not like this thing is decked out with avionics that would make the CG that far forward. Design flaw IMO.
 
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