dean van winkle wrote:

To Paul and all

Reference my recent posts on John Slade's swap of a lighter 13B for the Lyc engine.

In my attempt to provide a simple example of moving a lighter engine away from the firewall to maintain balance, I mistakenly selected the firewall as the fixed datum point.  My only excuse is that I must have been experiencing a "senior moment" :-) .  The only CG point that doesn't move in an aircraft with the configuration frozen is the empty weight (EW) CG which should have been used as the datum for determining the arm to the Lyc engine CG.  My example, even if corrected, was only the first step in a more complicated process and was highly unlikely to position the 13B prop flange in the same position as the Lyc.

Assuming for a moment that the Lyc installation provides the optimum EW CG for overall aircraft operations, then ideally the summation of moments of all engine compartment components for the 13B installation would equal the summation of moments for the removed Lyc installation.  The Lyc installation EW CG would be used as the datum point to make such a comparison.  As pointed out in other posts, battery relocation often will help in reaching the desired result.

In any case, the builder should calculate the EW CG of the new 13B installation using the designated aircraft datum and then determine if the aircraft will remain within the designated fwd and aft CG envelope under all combinations of min/max fuel, passenger, and baggage loadings.

Dean
RV-9A

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