RV-12 LSA

"ET" wrote

I wonder about the cg issues with the rear mounted
fuel tank though (although obviously I trust Van to work that out...)

Van's spiel said that the cockpit is well forward of his other designs, with
the seat being in front of the main spar, instead of on top of it. With the
fuel tank just behind the seats, that would put it only slightly behind the
CG, so any weight changes during fuel burn would be small, due to such a
short moment arm of the tank's contents. That is what it sounds like to me,
anyway.
--
Jim in NC

Morgans wrote:
"ET" wrote


I wonder about the cg issues with the rear mounted
fuel tank though (although obviously I trust Van to work that out...)


Van's spiel said that the cockpit is well forward of his other designs, with
the seat being in front of the main spar, instead of on top of it. With the
fuel tank just behind the seats, that would put it only slightly behind the
CG, so any weight changes during fuel burn would be small, due to such a
short moment arm of the tank's contents. That is what it sounds like to me,
anyway.

The Delta has the fuel tank in approximately the same configuration.
The downside is that pitch trim will drift somewhat as fuel is burned
off. This can be controlled somewhat by the fuel tank design...shaping
the tank so that it is larger in the rear than the front. The CG of the
tank moves aft as fuel is burned off. It's not a fix, only an
improvement over a square tank.

The upside is a greatly simplified fuel system. With only one tank, you
can throw out a handful of valves and fittings. And you'll never have
fuel starvation with a full tank on the other side.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."