"d&tm" wrote in message
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[...]
Are there any single engine airplanes out there that really can go outside
the envelope by burning fuel?

Sure. Any airplane in which the CG moves as fuel is burned has that
potential, depending on what other aspects of loading exist.

I haven't looked at the 172 case recently. Possibly due to weight
restrictions for baggage or seats you can't load it close enough to the
critical end of the CG range with full fuel for the CG to move outside the
range by using up fuel? I don't know off the top of my head.

What I do know is that I own a single-engine airplane (Lake Renegade) that
can wind up with the CG out of range after fuel has burned. I also know
from my friends who own Bonanzas that at least some models of Bonanza have a
similar issue. I am sure there are a number of smaller single-engine
airplanes that have the same requirement to pay close attention to weight &
balance.

Of course, there's a difference between the potential for problems
generally, and the potential for problems with specific loadings. Generally
speaking, I've found that the issue of CG moving out of range with fuel burn
still only happens in specific loading configurations. For example, in my
airplane the issue is most pronounced when the airplane is heavily loaded to
start with, and when that weight is mostly up front. Even at higher
weights, there are loading configurations that are generally assured to not
wind up outside the CG range as fuel burns.

As long as you've done enough W&B calculations to check the various
configurations and be very familiar with how the CG moves according to
loading and fuel, then to some extent it's not necessary to do a full W&B
calculation for every flight, assuming you've otherwise ensured you're not
overweight and have a loading configuration for which fuel burn isn't an
issue.

But, it's certainly not safe to say that one need not worry about fuel burn
for single-engine airplanes, even if you limit that statement to the smaller
ones (two- and four-seat).

Pete