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9th Dec 2010, 21:12

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Does anyone out there have a sample MD-82 loadsheet ? I'm designing a combination load and trim sheet and would like to look at what is out there.

I have a sample from Transmeridian. They use the Adjusted Weight method along with tables for each combination of pax, fuel, cargo. I plan on designing a computerized version that plots the ZFW,TOW, and LDW within the envelope using a y-axis of weight in lbs and an x-axis of index units, and including % MAC lines.

While at it does anyone know the formula to calculate the Adjusted Weight using % MAC. Confirm the basic weight is rounded up to the nearest 100, and the % MAC is added to this figure.

e.g.

Basic weight: 82251, % MAC: 34.9
Basic weight rounded up: 82300
Adjusted weight = 82300 + 34.9
= 82334.9
The last two digits represent the % MAC = 4.9.

Does this sound right ?

Thanks
9th Dec 2010, 21:59
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Methinks you are embarked on a course of disaster at the moment ...

Does anyone out there have a sample MD-82 loadsheet ?

Be VERY careful pinching other loading systems or trying to use them for design work if you don't have a really detailed knowledge and understanding of how loading systems are designed and what limitations are inherent in the various methodologies. Each is tailored to a specific Type, model, and configuration and, indeed, one can generate 10 quite different trim sheets (or other loading systems) for the same aircraft .. all looking quite different and using quite different numbers .. but all giving accurate and acceptable results.

.. do please be wary of traps for young players unless you know what you are about with design of trimsheets.

I have a sample from Transmeridian.

Consider posting an image and we have something concrete for discussion.

They use the Adjusted Weight method

what, pray tell, is that ?

along with tables for each combination of pax, fuel, cargo.

one would ask why ? For this class of aircraft a conventional trimsheet wins out over load tables every time.

I plan on designing a computerized version that plots the ZFW,TOW, and LDW within the envelope using a y-axis of weight in lbs and an x-axis of index units, and including % MAC lines.

ie a computerised version of a trimsheet. Generally a waste of time as the graphical bits are not necessary with the computer's number crunching power. Be very wary when drawing pictures that you understand which lines are straight and which lines are curves.

While at it does anyone know the formula to calculate the Adjusted Weight using % MAC.

Again, tell us what Adjusted Weight might be and we might have some chance of leading you along the road

Adjusted weight = 82300 + 34.9 = 82334.9

First, why would one round up the BW in such a fashion ? Second, this non-equation constitutes adding apples and oranges to end up with garbage. First requirement for any equation is that the units make sense. This purports to add weight and a non-dimensional number to get something undefinable.

Does this sound right ?

Afraid not ...
10th Dec 2010, 09:03

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Hello John,

Thanks for responding. I figured only you would understand what I was talking about.

Adjusted Weight calculations are used mostly in America in designing loadsheets with tables.

Rounded Wt. + [Actual Wt. x (B.A.-Datum)]/(Moment Constant)
+ Datum Constant.

What results is a combination figure of mathematical weight and mathematical moment. Pretty neat. eg for an Adj Wt figure of 82334.9 The 4.9 at the end would represent the trim units in % MAC (in this case).

Anyway,what I'm working on is the simpler AHM 560 type loadmessage with a trimsheet graph included (see personal messages). This is straightforward. All information derived from the TCDS, weight and balance manual, weighing report, LOPAs, etc. There are no curved portions of the envelope since all the variations are straight-line. Curtailments are built in as necessary. There are plots for TOW/MAC, ZFW/MAC, LDW/MAC.

Contrary to what you may think, I'm not exactly a beginner when it comes to loadsheets. I've studied them for years.

E.
10th Dec 2010, 12:21
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Rounded Wt. + [Actual Wt. x (B.A.-Datum)]/(Moment Constant) + Datum Constant.

.. if this is one side of an equation, the units are inconsistent - something's wrong.

There are no curved portions of the envelope since all the variations are straight-line.

The only WT/IU envelopes with straight lines are the simplest seen with very small aircraft. Otherwise, generally, all have curved portions. Then again, you may be using tabular data to input only the final WT/CG in which case the envelope will present as straight lines for most aircraft

Need to see what you are playing with to offer further comment.
10th Dec 2010, 19:10

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PDF file

Hello John,

Would it be possible to get an e-mail contact where I can send you the PDF file ?

Ev.
12th Dec 2010, 23:06
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[email protected] is a useful spot for email attachments.
13th Dec 2010, 05:38

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I've sent you the excel file as a pdf.

Thanks.

E.
14th Dec 2010, 01:03
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Thanks for the loadsheet - appears to be fairly typical of that genre. Suggest you post it as a graphic for discussion.

Where does the "adjusted weight" comes into play ?
14th Dec 2010, 02:00

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How do I do that ?

Hello John,

I don't know how to post a PDF file as a graphic. Can you assist ? Will it have to be in JPEG format ?

Thanks.

Ev
14th Dec 2010, 02:12

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Adjusted weight or the mathematical combination of weight and moment into one figure is used with a different type of loadsheet system.

Each item of pax, cargo, or fuel has its weight adjusted by a formula that gives a new number. The sum of the APS adjusted weight, pax, cargo, and fuel(adjusted weights) gives a takeoff adjusted weight whose last three digits represent balance units (usually %MAC units).

I have the formula for adjusted weight using index units but the one %MAC, I can't get to grips with.

Ev.
14th Dec 2010, 04:22
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Posting graphics to PPRuNe guidance.

I have the formula for adjusted weight using index units but the one %MAC, I can't get to grips with.

I think that we need you to type out your formulae so that we can offer comment - all sounds a bit strange to me - I'm sure we can sort it out once we can see the details
14th Dec 2010, 11:17

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Here is the excel loadsheet for the MD-82. I will post the formulas for adjusted weight.
14th Dec 2010, 12:24

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15th Dec 2010, 06:29
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Ah .. progress.

The index equation (#3) makes it clear what is going on as it concatenates the weight with the standard IU calculation.

In a conventional manual tabulation style of calculation one would total weight and IU values taken from tabulated data sheets. The resulting totals would then be plotted on an envelope to test for correct loading.

What the adjusted weight technique does is concatenate the two columns by rounding off the weight entries to make room for the IU values. Innovative but, in my view, not a great deal of value in the field ?

My concerns are -

(a) the technique introduces an increased level of error via round off considerations for both weights and IU.

(b) the technique is so un-intuitive and not amenable to commonsense (sanity) checks by the person running the sums that I would expect an increased level of arithmetic errors and, in all likelihood, some occasional significant error events.

(c) design considerations would need to be constraining to avoid ill-conditioned results and a nonsensical IU total.

(d) error considerations dictate that it not be used for small aircraft

(e) doing the same calculation set via a load and trimsheet for a larger aircraft would provide both better accuracy and quicker results. Indeed, using a load sheet tabulation for weights and a prayer wheel trimsheet for the IU calculations would win hands down every time for speed and accuracy over the adjusted weight technique.

It needs to be kept in mind that a well designed trimsheet is as accurate as a longhand calculation to all practical intents and purposes .. assuming a modest endeavour to execute the working with a little care.

That is to say, the adjusted weight technique is workable ... but why would anyone want to use it ? I just don't see any rational advantage to be gained.

However, I stand by for those who have used such systems routinely to offer contrary comment .. it may well be that my concerns are unduly conservative due to unfamiliarity with using the technique in the field.

I will have to play with #1 and #2 to see what is going on there as the relationships don't offer any immediate understanding.

Perhaps you might define what is meant by

(a) reference weight

(b) BA/trim unit

(c) datum trim unit

(d) BA/%MAC

(e) datum%MAC

15th Dec 2010, 08:32

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Definitions

John,

My sentiments exactly. However thats what they want.

Anyway, let me try and decipher some of your queries.

Formulas for the MD-80 series:

Index = ((Wt*(Arm-922)/1000)) + 5000. 922 is the Datum.This formula is not for individual items. For individual items remove the 5000.

% MAC = ((Arm-885.547)/158.512)*100. LEMAC = 885.547, MAC = 158.512

Forget the Stab Trim Equation for the moment please. Regarding the % MAC Equation:

Reference Weight: I have no idea what that is.

Balance Arm / %MAC: Each 1 % MAC change corresponds to a certain amount of inches of arm movement, in this case 1.6 inches.

Datum %MAC: This the Datum in inches converted to %MAC. In this case 23%.

Boeing guys help us out here please.

I think this information is available with access to My Boeing Fleet.

Ev.
15th Dec 2010, 21:04
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That's cleared up several points.

Boeing guys help us out here please

Are you seriously suggesting that Boeing developed this method of doing things worse than the conventional way ?
15th Dec 2010, 21:48

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Original Problem

Here is the original problem:

For the fuel weights below, how did they arrive with the adjusted weight units shown?

Fuel Weight-lbs. Arm-in. Adjusted Weight Units.

10000 937.1 10001.4
15000 944.8 15002.7
20000 946.5 20003.7

The bold figures are the balance units (%MAC) concatenated with the weight.

Any ideas?
16th Dec 2010, 14:40

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Guys,

I have followed your discussions with interest and I would say that in my experience I would not recommend the use of adjusted weight index system over other methods (tabular or dropline) as I personally feel that any benifits are out weighed by the negatives.

The essence of the Adjusted Weight Index Loading System (AWIS) is that balance units (expressed to one decimal place), are added to each element of weight on the Load Manifest, to give adjusted weights.

When these adjusted weights are summated, they provide both an aircraft weight, indicated by the digits to the left of the decimal point, and the Centre of Gravity (C.G.) value, indicated by the right hand digits.

Balance Units are increments of moment about a reference datum, and at take-off they correspond closely to Mean Aerodynamic Chord (M.A.C.).

The datum must be selected and is normally a typical take-off weight with a lever arm located at the aircraft Centre of Gravity datum.

An example Datum for a B767-200 would be :-

320000.0 lb. 24.0 % M.A.C.

Balance units will correspond exactly to % M.A.C. at the above datum weight.

HOWEVER, At other take-off weights the degree of accuracy decreases the further away the actual take-off weight is from the datum take-off weight.

[FONT=LotusLineDraw][FONT=Arial][COLOR=#000000]If you need any further assistance with this or other W&B problems, please feel free to contact me by PM.
17th Dec 2010, 14:01

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Enlightening.

Thanks,

You have shone a light in a dark corner. I did not realize that the reference weight was an average takeoff weight.

Makes a lot more sense now. I can see the errors with a large variation from the average.

I will send you the PDF of the other version of the loadsheet. The nor I'd rather use.

Ev.
18th Dec 2010, 10:41
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This thread is starting to confuse me mightily. It may be that folk are being a little lax in the use of terminology .. and, I note, I am regularly guilty of the same .. However, the subject material is pretty important to flight safety so it is worth gnawing at the bone until we get it sorted out ..

The bold figures are the balance units (%MAC) concatenated with the weight

I suggest not.

%MAC is just another way of writing CG.

One cannot add CGs of loads to end up with a final figure with any sense. The addition has to be one of either moment or IU.

The bold figures, presuming they are IU, can be derived easily if one has, as the IU equation, a trim datum of 905 and a IU constant of 225000. This equation may not be precise as we only have three examples to play with, With a few more example combinations. it could be refined quite easily.

When these adjusted weights are summated, they provide both an aircraft weight, indicated by the digits to the left of the decimal point, and the Centre of Gravity (C.G.) value, indicated by the right hand digits

So far, searches of the net and this thread have given nothing concrete as to the derivation of the method (other than for the index equation which is quite conventional). Probably, I am going to have spend some time trying to make sense of the two other "equations" cited in the earlier post ...

Unless someone can present a rational derivation, it is my present contention that you cannot add CG values to get any sensible result ....

The essence of the Adjusted Weight Index Loading System (AWIS) is that balance units (expressed to one decimal place), are added to each element of weight on the Load Manifest, to give adjusted weights.

When these adjusted weights are summated, they provide both an aircraft weight, indicated by the digits to the left of the decimal point, and the Centre of Gravity (C.G.) value, indicated by the right hand digits.

Balance Units are increments of moment about a reference datum

(My bolding)

You can't have it both ways .. what are balance units ? CG or moment values ?

Balance Units are increments of moment about a reference datum, and at take-off they correspond closely to Mean Aerodynamic Chord (M.A.C.).

At the risk of offending, I suggest that the second part of your statement is nonsensical. The MAC is a fixed length so, if your statement were to be corrent, balance units would be invariant and pretty meaningless ? If you mean %MAC, then how does one relate a moment to a CG .. other than to the extent that, as the moment increases in number line magnitude (ie to the right), the CG moves aft ?

The datum must be selected and is normally a typical take-off weight with a lever arm located at the aircraft Centre of Gravity datum

Again, this appears to be nonsense. Datum is a position on the fuse station line .. ie a distance from somewhere else but, now, you are suggesting it is a weight ?

An example Datum for a B767-200 would be :-
320000.0 lb. 24.0 % M.A.C.
Balance units will correspond exactly to % M.A.C. at the above datum weight

The datum might well be 24%MAC but has naught to do with 320000lb. Can you provide the balance units value for your example and that might lift the veil of confusion somewhat ?

yours in confusion .... JT