Aircraft weight distributions

Michael M

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Hi All.
I have been asked to put together a spreadsheet that calculates load distribution in aircraft.
The user wants the result to appear in a graphical form.
There are a significant no of formulae involved to create the graph and rather than re-invent the wheel would like to know if any one has already done this OR where I might be able to access the template.
Any assistance would be appreciated, otherwise it's many hours on the drawing board

Regards
 

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andshep

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Try asking this lot on the computers and internet forum. There are some pretty clever excel people there that know a lot about aviation

www.pprune.org
 

Michael M

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Aircraft Loading

Thanks to all those that replied.
However, in the most part the sites weren't what I was after.
It looks like sitting down with the user and giving 'em what they want from first principles

Thanks again
Michael
 

Brian from Maui

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Re: Aircraft Loading

Michael M said:
Thanks to all those that replied.
However, in the most part the sites weren't what I was after.
It looks like sitting down with the user and giving 'em what they want from first principles

Thanks again
Michael

I have a spreadsheet that calculates CG, but not in a graph.
 

Michael M

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Thanks Brian
What is CG.........You can tell I'm an expert!!
I might be OK with Excel, but keep me away from planes .

Regards
Michael
 

liam.gartside

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CG stands for Centre of Gravity and along with total weight are two things you'll need to calculate before take off to verify both are within range.

The aircraft being overweight is a pretty obvious problem, but consider if you have something small but very heavy like a suitcase full of gold bars. Putting it at the very front of the airplane might mean that whilst still light enough to fly the distribution of the weight witin the aircraft is such that you could never lift the nose off the ground to start flying.

Generally, the aircraft is divided into sections (or stations). A light aircraft might have front seat, rear seat, baggage area, plus fuel and oil. A cargo aircraft will generally have sections like nose compartment, Zone A, Zone B, Zone C, wing lockers fuel oil etc. Plus each individual aircraft has a unique empty weight and CG position.

Your task is to calculate the effect of all these variables, fuel, oil, crew, pax, and cargo distribution to verify that the CG remains within limits, or whether some cargo needs offloading, or (preferably) moving to a different location within the aircraft. Not only that, but make sure that each individual section remains under gross - for instance the floor loading in Zone A might limit you to 500 lbs at that station.


Oh and when you go to pprune, forget the computers and internet forum, come and visit JetBlast. :eek:k:
 

Michael M

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Thanks Liam
I appreciate your input.
I can see there is a fair bit involved here, so will be visiting as many sites as possible.
Also, thanks for the tip about pprune.
Regards
Michael
 

liam.gartside

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How much info do you want?

Each aircraft has a Datum Point which is an arbitrary point along the Longditudinal axis which is used as a basis for all the calculations.

The Longditudinal axis is a line from the front to the rear of the aircraft (the other two axes are the Vertical and the Lateral, this way, three dimensional motion and control input can be referenced to an axis)

Generally in Single Engined Cessna aircraft, the Datum point is the very front of the aircraft. Other manufacturers use other points, the fiewall, wherever, it really makes no difference.

Each station has what's called an Arm which is the distance between the "centre" of the station and the datum.

Any cargo, fuel or pax at each station creates a force relative to the Datum in proportion to its weights and to its Arm. This force is called the Moment. Remember a seesaw (teetertotter in the US) where the fat kid sitting closer to the fulcrum balanced the skinny kid all the way at the end?)

Any station forward of the Datum Point will have a negative Moment, those aft of the DP will have a positive Moment.

So all you have to do is to multiply out the different weights by their arms to create a series of moments, add the moments up and divide by the total weight to find the CG of the aircraft (relative to the Datum of course)


Consider this example:
Code:
Item      Weight(lbs)       Arm(ft)     Moment(ft/lbs)
Empty wt        3000            0.5      1500
Pilot            170            2         340
Fuel             200            1         200
Baggage           50            4         200
               -----        ------     ------
                3420                     2240


the CG of the aircraft can be seen to be at 2240 / 3420 = 0.65

If the aircraft has CG range of say 0.62 to 0.66, This calculation shows it to be within range for CG.


There are formulas for what happens if you take some cargo out of one section and place it in another, but that's all just simple trignometry.



Generally a person is considered to be 170 lbs, though I think they just increased that. Fuel is 6lb a gallon, but I'm not sure about jet fuel. Jets typically quote their fuel in pounds not gallons anyway.


HTH

Liam
 

Michael M

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Thanks Liam
The example you supplied has enlightened me.
now I can see the forest.
Since you are fairly knowledgeable on this subject, has anybody done this type of calc in Excel before ??

Regards
Michael
 

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