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W&B envelope problem


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Hello,
I always get a 'overloaded' or 'outside the centre of gravitiy' with this data (weight in kg):

EmptyWeight="509.300000" EmptyArmLon="0.44" EmptyArmLat="0.00" Envelope="238.00,558.000000,320.00,750.000000,392.00,750.000000,292.00,558.000000">
    <FuelLoadingPoint Name="Fuel" LeverArm="0.33" LeverArmLat="0.00" DefaultValue="109.60" Capacity="120.00" />
    <LoadingPoint Name="Pilot" LeverArm="0.58" LeverArmLat="0.00" DefaultValue="80.00" />
    <LoadingPoint Name="Front Passenger" LeverArm="0.58" LeverArmLat="0.00" DefaultValue="0.00" />
    <LoadingPoint Name="Baggage" LeverArm="1.30" LeverArmLat="0.00" DefaultValue="10.00" />

But the numbers should be correct - could anybody help please?






George Reid
George Reid
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Hi there.

I think that the data you are using for the W&B envelope is incorrect.  The data are meant to be in paired sets of Lever arm, Weight.

Your data appear to be in the form Moment, Weight   (Where Moment = Lever Arm multiplied by weight).  Thus to correct your envelope data you need to divide each of the moment figures by the corresponding weight.

Your data for the envelope will then be:  0.427,558.0,0.427, 750.0,0.523, 750.0, 0.523,558.0

George E A Reid

Ipad Mini 2,  IOS 12.4,  SD 3.12.8.190
PC(Win 10, Version 1809)  SD 3.12.8
PilotAware 20190621
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Hi George,
Thanks for your answer, but with your data I didn't see a graph.

I just took the data from the manual - and with this numbers the envelope looks like the picture in the manual:




George Reid
George Reid
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In the graph that you have shown the horizontal axis has the units KgMetres, ie it is a a MOMENT.  Sky Demon Weight and balance graphs show weight against lever arm.  The units of the horizontal axis should be be metres or cm or mm, whatever you prefer.

The values that I sent you were in metres.  try inputting them in mm:

Eg  427.0,558.0 ,427.0, 750.0 ,523.0,750.0 ,523.0,558.0

However all other lengths used must then also be converted to mm for consistency.




George E A Reid

Ipad Mini 2,  IOS 12.4,  SD 3.12.8.190
PC(Win 10, Version 1809)  SD 3.12.8
PilotAware 20190621
George Reid
George Reid
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Hi there,

I've taken the Weight and balance figures you have provided and created an aircraft profile for you (Test Aircraft).  Store this profile
in the SkyDemon\Aircraft folder.  Then you will be able you will be able to select it for use.  I have only entered data in the Weight and Balance section.  All the data in the other sections will be meaningless for your aircraft.  You will need to edit these sections.

The Weight and balance envelope that is produced is not the same as the chart you attached to your last post.  That is because the chart you showed is a Weight MOMENT envelope.  Sky Demon charts the Weight LEVER-ARM envelope.  For Safe flight the Weight must be within the graph bounds and the centre of gravity must be within the LEVER ARM bounds.

Hope this helps



George E A Reid

Ipad Mini 2,  IOS 12.4,  SD 3.12.8.190
PC(Win 10, Version 1809)  SD 3.12.8
PilotAware 20190621
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Test.aircraft (350 views, 1.00 KB)
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George,

Honestly I still don't understand it correctly and have to think about it.
However, I'm sure your example will help me to get it...    Wink

Thanks a lot for your help!


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