Gross Weight

"Mike Granby" wrote in message
oups.com...

"once you go over the max weight,
you are essentially a test pilot".

That's putting it a bit strongly.

No, it's putting it quite accurately.

As long as the CG issues are OK, the
effects of being reasonably over-weight are quite predictable in terms
of stall speed, take-off requirements etc.

The effects of flight at any weight are quite predictable in terms of stall
speed, take-off requirements etc. And yet, during certification, the
airplane is required to be *tested* at in a variety of configurations by a
*test pilot* to demonstrate the actual performance.

Just because one can predict the performance, that doesn't change the fact
that a person flying an airplane in an untested (as far as they know)
configuration is a "test pilot".

The structural issues won't
come into it as many aircraft have their max gross determined by other
things (eg. stall speed low enough for Part 23, or the need to
go-around at max gross with full flaps)

Very few single-engined airplanes have a stall speed at the maximum allowed
value (noting, of course, that the "maximum allowed value" isn't really so
much a hard limit, but rather one that a manufacturer is required to meet in
order to avoid other things). It's true that max gross weight may be
affected by things other than structural issues, but there is no way to know
whether this is true without consulting the manufacturer (which I doubt the
theoretical over-gross pilot is going to do), and I can think of at least
one common airplane for which structural issues DO limit the maximum landing
weight (which is lower than the maximum takeoff weight for that airplane).

and in any case, there's a
large safety margin in there.

The reason for that safety margin is for normal, legal weight operations.
It's not so you can operate over the legal limits. Operate over the legal
weight, and you've just abandoned your "large safety margin".

The fact is that assuming you're not on
the edge re DA or runway length, 5% overweight is going to be safe. It
isn't legal, but it will be safe.

It *might* be safe. You are still a test pilot when flying over the legal
weight, which is the comment to which you replied.

As to the arguement that breaking one
rule leads to breaking another, with respect, that is nonsense. That's
like saying speeding leads to murder...

That's a matter of opinion, I guess. I personally believe that if we had
better enforcement of the little laws, we wouldn't have so many people
disregarding the more important ones. Looking the other way when it comes
to speeding (and similar) simply teaches people disregard for rules. Each
person winds up setting their own limits, rather than respecting the limits
society claims to have made. And yes, in some cases, those limits go way
beyond just speeding.

Obviously each individual who speeds doesn't wind up a murderer, but general
disregard for the rules does certainly lead to other negative behavior.

Pete

Actually, I don't believe flying at max gross is necessarily safe
either.

If you have ever flown slightly gross weight, then you have already
flown as a test pilot. First, the official weight and balance is
probably decades old, and your aircraft most likely weighs several
pounds more now. Second, people under-estimate their weight. Unless you
have a weighing scale as people board, you can never be sure of the
actual weight. Finally, the aircraft is far different from when it was
tested during manufacture. A dirty airframe will reduce performance,
and an old prop will not work as well as a brand new one. Most
importantly, your engine definitely will not perform like a brand new
engine. So, whether you like it or not, you have already been a test
pilot. For this reason, I never fly an aircraft near its max gross. I
have seen pilots diligently trying to unload weight until it is exactly
equal to the max gross weight.







"Peter Duniho" wrote in
:

"Mike Granby" wrote in message
oups.com...

"once you go over the max weight,
you are essentially a test pilot".

That's putting it a bit strongly.

No, it's putting it quite accurately.

As long as the CG issues are OK, the
effects of being reasonably over-weight are quite predictable in
terms of stall speed, take-off requirements etc.

The effects of flight at any weight are quite predictable in terms of
stall speed, take-off requirements etc. And yet, during
certification, the airplane is required to be *tested* at in a variety
of configurations by a *test pilot* to demonstrate the actual
performance.

Just because one can predict the performance, that doesn't change the
fact that a person flying an airplane in an untested (as far as they
know) configuration is a "test pilot".

The structural issues won't
come into it as many aircraft have their max gross determined by
other things (eg. stall speed low enough for Part 23, or the need to
go-around at max gross with full flaps)

Very few single-engined airplanes have a stall speed at the maximum
allowed value (noting, of course, that the "maximum allowed value"
isn't really so much a hard limit, but rather one that a manufacturer
is required to meet in order to avoid other things). It's true that
max gross weight may be affected by things other than structural
issues, but there is no way to know whether this is true without
consulting the manufacturer (which I doubt the theoretical over-gross
pilot is going to do), and I can think of at least one common airplane
for which structural issues DO limit the maximum landing weight (which
is lower than the maximum takeoff weight for that airplane).

and in any case, there's a
large safety margin in there.

The reason for that safety margin is for normal, legal weight
operations. It's not so you can operate over the legal limits.
Operate over the legal weight, and you've just abandoned your "large
safety margin".

The fact is that assuming you're not on
the edge re DA or runway length, 5% overweight is going to be safe.
It isn't legal, but it will be safe.

It *might* be safe. You are still a test pilot when flying over the
legal weight, which is the comment to which you replied.

As to the arguement that breaking one
rule leads to breaking another, with respect, that is nonsense.
That's like saying speeding leads to murder...

That's a matter of opinion, I guess. I personally believe that if we
had better enforcement of the little laws, we wouldn't have so many
people disregarding the more important ones. Looking the other way
when it comes to speeding (and similar) simply teaches people
disregard for rules. Each person winds up setting their own limits,
rather than respecting the limits society claims to have made. And
yes, in some cases, those limits go way beyond just speeding.

Obviously each individual who speeds doesn't wind up a murderer, but
general disregard for the rules does certainly lead to other negative
behavior.

Pete

"Andrew Sarangan" wrote in message
1...

Actually, I don't believe flying at max gross is necessarily safe
either.

I can certainly agree with that. There's safe, and there's legal. Safe is
not always legal, and legal is not always safe.

As a pilot, it is our duty (in my opinion) to take the more conservative of
either limitation, except under duress (in which case it could still be
argued the chosen action is still the most conservative action available at
the moment).

Pete

At the same time, if an airplane can fly safely at MGW with an
underpowered engine and a dirty airframe, what prevents an airplane
maintained to a higher standard from flying slightly above MGW? I am
not suggesting that people try this, but except from a regulatory point
of view, what is the real difference between these two scenarios?

At the same time, if an airplane can fly safely at MGW with an
underpowered engine and a dirty airframe, what prevents an airplane
maintained to a higher standard from flying slightly above MGW? I am
not suggesting that people try this, but except from a regulatory point
of view, what is the real difference between these two scenarios?

It depends on what the actual limiting factor is. If there is a
structural member that is the limiting factor, more engine power and a
cleaner airframe won't make a difference.

What I can see more easily is, for situations where (say) takeoff
aerodynamics is the first limiting factor, a graph of MGW vs density
altitude.

Jose
--
Nothing takes longer than a shortcut.
for Email, make the obvious change in the address.

"Andrew Sarangan" wrote in message
oups.com...
At the same time, if an airplane can fly safely at MGW with an
underpowered engine and a dirty airframe, what prevents an airplane
maintained to a higher standard from flying slightly above MGW? I am
not suggesting that people try this, but except from a regulatory point
of view, what is the real difference between these two scenarios?

I guess that depends on whom you ask. I already stated that I didn't feel
the 2% overage example given in the original post was likely to cause
problems for most pilots. I think it ought to be obvious to the most casual
observer that in reality, flying a pound or so over max gross is, for all
intents and purposes, the same thing as flying right at max gross.

Performance suffers in a continuously gradual way as weight increases.
There's nothing magical about the certificated max gross weight that changes
a safe plane into an unsafe plane at the moment you cross that line. But
there IS a limit to how safe the plane is as you increase its weight. There
IS a weight above which you should not be flying the plane, even from a
safety standpoint. The manufacturer and the FAA have drawn a very clear
line for the pilot to mark that maximum weight, and it is the pilot's
responsibility to respect that line.

A pilot's personal judgment may place that line somewhere else. But they do
not have the legal ability to put that line at a higher weight than the
manufacturer and FAA have put it. While piloting is in many respects all
about making individual judgment calls in order to establish the safety of
the flight, that is not ALL that it is about. Not today, and it hasn't been
for a long time. Pilots have a responsibility to ensure that the flight
remain safe AND legal.

The maximum certificated weight of the airplane is a somewhat arbitrary
line. Yes, it could have been set a little lower or a little higher, with
very little practical effect on airplane performance. But for better or for
worse, it is set where it is set. A responsible pilot will respect that.

Pete