JonathanMilbank
Joined: 14 Apr 2012
Posts: 391
Location: Aberdeen area
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 Posted: Fri Mar 10, 2017 3:08 pm Post subject: Bemused by W & B results |
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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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