Having just converted my Classic installation to Nev Eyre's improved version of
the XS firewall forward and retaining the same 912ULS engine, I was nevertheless
expecting a little weight increase and a noticeable forward movement of C
of G. However my expectations were wrong (again) on both counts.
Exactly the same set of scales were used as for the previous weighing and as
before
the scales were accurately calibrated with weights made for the purpose.
Also as before the fuselage was levelled by reference to the left door sill. The
outcome is that the weight hasn't changed at all and the aircraft empty C of
G has moved forward by only .03". Very strange!
How to account for this? These are the significant factors to my simple mind:
1) The cowls are about the same weight as before and Nev's extended and
simplified
engine bearer frame is not much heavier than the Classic's.
2) The longer starter motor which I have installed is certainly a couple of
pounds
heavier.
3) The new spinner and its backing plate are somewhat lighter.
4) No longer are the radiators and oil cooler with their fluids hanging at the
front of the cowl, but are now beneath the engine and closer to the firewall.
5) Although I never weighed them, the Classic exhaust system was quite a lot
heavier
than the XS system.
6) The new 8.33 KHz radio is a little lighter FWIW.
7) No longer is there an air box plenum attached to the carburettors.
Having spelled out all of the above, I would really have expected the aircraft
empty C of G to have moved forward by maybe 0.5". But I'm not complaining; just
putting my observations out there for interest.
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