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Rob_Ainscough

Weight and Balances ... LEMAC, TEMAC, %MAC and CG and TCDS?

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First off, please bare with me for those "in the know" as I bumble my way thru this.

I'm trying to setup a Weights and Balances profile (Medium range) for the Dash-8 400 (MJC) in Foreflight.  Foreflight has "SmartOptions" for Cessna, Cirrus, Diamond, Mooney, and Piper ... GA aircraft.  The limitations on using the Weights and Balances feature are: 

  • Fixed-wing aircraft
  • Weight limits don't vary by CG
  • CG is in length units not %MAC
  • Takeoff and Landing CG limit envelopers are the same
  • 1 Fuel moment table (single variable-arm fuel station)

Since the Q-400 is a "transport-cateogry" aircraft it's expressed in %MAC.  So my Foreflight weights and balances will probably not work well for me in regards to the Q-400.

But, putting that aside, I'm still very interested on how to CG in terms of inches from datum (which I assume is the nose of the aircraft).  I've been reading here on how to calc CG and MAC ... so questions:

How can we get this data from the manufacturer?  As I understand it is provided in the TCDS (Type Certificate Data Sheets), apparently LEMAC (leading edge), TEMAC (trailing edge), MAC is all provided.

If the wing is tapered, how are LEMAC and TEMAC calculated?

MAC = TEMAC - LEMAC

So the "station" values are provided by the aircraft manufacturer or is there a formula I can use to determine?

Hmmm ... TCDS from Foreflight ... which brings me to FAA TCDS search ... so I downloaded the TCDS file ... it's actually an Access 2010 database with 7 Tables in it ... so I queried the tables and found the DHC-8-400 (many entries).  However the web site seems to be the better option as I can look at current models and was able to find the De Havilland and got to a PDF with lots of great information (Vref, weights etc.) but NOTHING regarding MAC, TEMAC, LEMAC?

Cheers, Rob.

 

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15 hours ago, Rob_Ainscough said:

....I'm still very interested on how to CG in terms of inches from datum (which I assume is the nose of the aircraft)...

Not necessarily, Rob if we're talking datum positions in REAL aeroplanes, not sim reference values.

The datum might be in another location entirely.

If you do get a value for the CG position I suppose you could make an educated guess as to if that value is measured from the nose of the aircraft, knowing the overall dimensions

For example, the datum for a Tornado was a small plate with a slot in in positioned in the main undercarriage bay from which we could dangle a plumb bob and then measure the moment arm from the nosewheel and the mainwheels (they were on individual weigh bridges).

Many years ago, I used to be a weight engineer at BAe Warton.. but have probably forgotten more than I know :blush:

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Mark Robinson

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Looks like I would need the POH or AFM for the Q400 to be able to get LEMAC and TEMAC to determine MAC and then go from there.

Cheers, Rob.

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Length of MAC = 2.4006 m

LEMAC = 9.5025 m from zero


Flight Dynamics at Milviz ( DHC-3T, PA-30, PC-6, KA-350i, and more... )

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