Hi John,
Stupid you may call the position of the zero datum but the reason is mostly
historical, very practical and it standardises critical numbers like CG
positions across our fleet of Classics, XS's & motor gliders.
Taken in order the history started with the Classic where zero datum was the
front of the engine cowl. It was at this time also considered logical for
the sake of non mathematicians to keep all figures positive and not confuse
the issue with negative numbers. You don't have to look very far to find
stupid errors in critical calculations caused by deliberately introducing
negative moments.
As the XS nose was extended slightly further forward it was sensible to
leave zero datum as was. Hence the 29 3/4" point on ALL marks of Europa is
where the front of the engine cowl would have been had it been a classic.
This means, and this is important, that the CG limits and fuel tank pilot
passenger and baggage load points for all marks are consistent. It all makes
for less risk of confusion and error.
Had the first type of Europa to be produced been an XS then zero datum would
probably have been a quite different location.
Pete J
PS There may be good reason to change the baggage station of 88 ins to a
more realistic figure in light of the fact that this figure is still the
same as was applicable prior to the extended baggage bay mod.
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of John Wighton
Sent: 06 April 2021 10:58
Subject: Europa-List: Re: Weight and Balance question
Gentlemen (and Ladies, if present),
All this discussion on CG moment arm made my weekend, an absolute hoot from
start to finish (is it finished yet?). This is not helped by the rather
cack-handed approach prescribed in the POH.
A reasonably common piece of data in this thread is the location of the
datum. But even that may vary depending on who/how weighed/measured the
aircraft - treat this as a variable across the fleet, but a constant for
your aeroplane. Any calculation of W&B needs to use the actual mass as
measured and the actual moment arm as measured.
Weigh the item (you, pax, the dog, grannies apple pie or your bag of
birdseed). Use that data in a spreadsheet.
Link:
http://www.lightaircraftassociation.co.uk/engineering/Weight%20and%20balance
/w_and_b_main.html
Skydemon also provides a very nice W&B calculator (it is legally necessary
to do this for EVERY flight), which makes it easy-peazy.
The moment arm I use for baggage is a measurement to the centre of the bay.
However, the Europa Aircraft method of establishing the FS 0.0 datum is a
comedy. A position 29.25" fwd of the "Rear of joggle for cowling in
fuselage moulding" needs to be marked.
This is totally unnecessary - the cowling to fuselage joint is as good a
datum as any. It requires all moment arms forward of it to be given a
negative sign (for the initial W&B calculation and any subsequent firewall
forward mods) and all those aft of it to be positive.
Just measure along the horizontal fuselage datum WL (level sill can be used
as per POH) to the FS of the item to be measured.
Attached is an extract from the POH (note the depicted Trigear also has a
secreted mainwheel protruding from the fuselage!).
--------
John Wighton
Europa XS trigear G-IPOD
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=501290#501290
Attachments:
http://forums.matronics.com//files/europa_wandb_303.jpg
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