"Peter Duniho" wrote in message
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"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.


Both the Warrior and the C172 c of g moves forward with fuel burn but so
does the allowable limit, at the same or greater rate, which is why it is
not possible to go outside the envelope under any loading conditions.

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.

this is basically why I do the analysis, to break it down to simple rules
that will not require me to have to do the c of g calcs each time.
conclusion with the C172N is that, with the weight restrictions satisfied
1. it is impossible to get c of g too far forward.
2. the only way to have c of g too far back is with more weight in back seat
than front. ( most unlikely situation for me)
3. it is impossible to go outside by burning fuel.
So my simple rule becomes stay within the wt constraints and do a c of g
check only if I want more wt in the back seat than the front. - which is
likely to be never.

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).

I certainly wouldnt assume that without doing the same analysis on the
particular aircraft. It seems to me that the aircraft I have referred to (
warrior and C172N) are probably designed so that fuel burning will not cause
an adverse c of g . I would also be curious to know if other models of C172
or the higher performacne C177, C182 C206, C210 follow the rules I outlined
above.
Excuse my ignorance but I hadn't heard of a Lake Renegade, but I did do a
google and note that it is a beautiful looking amphibious aircraft whch
obviously has some specific design characeristics for its intended
application, namely an engine above and behind the cabin, which makes it a
little different from the aircraft I am likely to fly, but I take your point
that fuel burning may be an issue in some small planes.
terry
PPL downunder