Overweight takeoff / flight

Howdy again,

After reading NTSB reports that attribute the cause of the accident to
exceeding the airplane's maximum takeoff weight, I began wondering
about the effects of an overweight takeoff within C.G. limits.
Specifically, what would I have to do differently when flying an
airplane that's heavier than what the POH specifies. I am not
supporting the practice, of course, so let it be purely educational.

Corrections, additions, and comments welcome.

I would start by considering the increase in weight as comparable to
an increase in load factor. Hence, all your aoa-related speeds would
increase by the square root of the load factor. Vs, Vx, Vy, Vglide,
etc. would all increase. Va would also go up.

Now, by virtue of rotation speed being a function of stall speed, I
conjecture you'd have to liftoff at a faster airspeed which would
equate to a longer takeoff roll.

Then, after pitching for your faster Vy airspeed, you'd notice a
decrease in climb rate at full power due to the increased power
requirement. During cruise, you'd notice a reduced cruise speed and
an increase in stall speed. At approach to landing, should you bump
up your approach speed, you'll find yourself sinking faster when
chopping off the power even though your glideslope will remain the
same.

Since your stall speed is invariably higher, you'll eat up more runway
when landing.

So to sum up:

Takeoff: higher takeoff distance, higher rotation speed.

Climbout: lower climb rate at higher Vy speed, same angle of climb for
obstacle clearance at higher Vx speed. Should Vx not be flown faster,
a poorer angle of climb would result, making obstable clearance
doubtful. *I may be wrong here* I am not sure if the max. angle of
climb is constant regardless of weight...my calculations don't show
so...could someone clarify?

Cruise/Maneuvering: lower cruise speed, higher maneuvering speed,
higher clean stall speed.

Approach to maintain glideslope & descent profile: higher approach
speed, higher sink rate for a given power setting. Higher dirty stall
speed.

Landing: higher landing distance

Question (1 of 2): Seems to me that flying "overweight" is possible if
you're aware of the performance reductions. So why do you read so
many NTSB reports with probable causes listed as "overweight takeoff,
exceeded performance limitations"? As you slowly pull the yoke to
rotate, wouldn't a pilot *realize* through control forces, feel, gut
feeling that something is wrong?

Question (2 of 2): When considering accidents due to exceeding maximum
takeoff weight, do the majority occur during takeoff? If so, is it
typically due to not reaching proper liftoff airspeed for that
increased weight, stalling, and spinning to the ground? Would this
scenario be consistent with failure to set the flaps/slats to their
takeoff value?

Alex

On 2003-11-26 05:23:36 -0800, (Koopas Ly) said:

Now, by virtue of rotation speed being a function of stall speed, I
conjecture you'd have to liftoff at a faster airspeed which would
equate to a longer takeoff roll.

Since your stall speed is invariably higher, you'll eat up more runway
when landing.

In both cases, it's not just the higher speeds involved, but the increased weight
also means that acceleration for takeoff and deceleration on landing will be
lower. F=ma with a (more or less) constant F, and increased m means
decreased a.

--
Larry Fransson
Seattle, WA

In article , Koopas Ly
wrote:


Approach to maintain glideslope & descent profile: higher approach
speed, higher sink rate for a given power setting. Higher dirty stall
speed.

Landing: higher landing distance


Once you have burned sufficient fuel to bring the weight back down into
the max gross/useful load range, why should landing parameters be any
different from published?
Published numbers are for max gross weight.

Koopas Ly wrote:

Howdy again,

After reading NTSB reports that attribute the cause of the accident to
exceeding the airplane's maximum takeoff weight, I began wondering
about the effects of an overweight takeoff within C.G. limits.

Seems to me that you have listed most of the effects correctly. One thing you
should consider, however, is the fact that the balance envelope for most (if
not all) planes gets narrower at the top. In other words, the more weight you
put in an aircraft, the closer to the center of lift that weight has to be. At
some point, all of the weight will have to be in the front seat.

I have read of cross-Atlantic ferry flights in which the aircraft was loaded to
weigh about 1.6 times the normal MGW. In one account, a Bonanza loaded that way
took over 6,000' to get airborne.

George Patterson
A man who carries a cat by the tail learns something that can
be learned no other way.

"G.R. Patterson III" wrote in message
...
Seems to me that you have listed most of the effects correctly. One thing
you
should consider, however, is the fact that the balance envelope for most
(if
not all) planes gets narrower at the top.

A true generalization as far as I know, but I'm sure there are a number of
exceptions and in many cases, the shape of the W&B envelope has as much to
do with what test parameters the manufacturer chose to look at, as it does
any real structural or aerodynamic issues.

The main thing is to make sure one is paying attention to the W&B envelope.
When flying overweight (with FAA approval, of course) one can make an
educated guess by extrapolating the existing graph, but the bottom line is
you don't really know what the shape of the W&B envelope is over gross,
unless the manufacturer has been kind enough to publish it (and they usually
aren't).

In other words, the more weight you
put in an aircraft, the closer to the center of lift that weight has to
be.

Not really. In some aircraft, the envelope is sloped on the aft portion too
as weight goes up. For rearward CG configurations, additional weight needs
to be put farther from the center of lift, not closer. All you can say
without seeing the actual W&B envelope is that usually you have a narrower
range at higher weights. You can't say which direction that range trends,
and even that generalization has exceptions.

[...] At some point, all of the weight will have to be in the front seat.

Even if the previous statement were true, not all airplanes have their
center of lift aligned with the front seat.

I have read of cross-Atlantic ferry flights in which the aircraft was
loaded to
weigh about 1.6 times the normal MGW. In one account, a Bonanza loaded
that way
took over 6,000' to get airborne.

How much runway did Voyager take? I'll bet it was a LOT.

Pete

On Wed, 26 Nov 2003 10:18:14 -0500, "G.R. Patterson III"
wrote:


Seems to me that you have listed most of the effects correctly. One thing you
should consider, however, is the fact that the balance envelope for most (if
not all) planes gets narrower at the top. In other words, the more weight you
put in an aircraft, the closer to the center of lift that weight has to be. At
some point, all of the weight will have to be in the front seat.


Not really. You can put 50 pounds 3 feet in front of the zero cg
datum and 50 pounds 3 feet behind the datum and it is the same as
adding 100 pounds at the datum (front seats I guess).

I have read of cross-Atlantic ferry flights in which the aircraft was loaded to
weigh about 1.6 times the normal MGW. In one account, a Bonanza loaded that way
took over 6,000' to get airborne.

I let students take off at 2000 rpm in a 172. You roll a long way
(very sensitive to temperature) and the climb performance is down
right scary.

George Patterson

Mike Weller

Mike Weller wrote:

Not really. You can put 50 pounds 3 feet in front of the zero cg
datum and 50 pounds 3 feet behind the datum and it is the same as
adding 100 pounds at the datum (front seats I guess).

That would be true enough, except that you can't put 50 pounds 3 feet in front
of the zero cg point in most light singles. That would be where the engine is
in my plane.

George Patterson
Some people think they hear a call to the priesthood when what they really
hear is a tiny voice whispering "It's indoor work with no heavy lifting".

An old pilot once told me, when I was a young pilot, "...sumbitch flies a
hell of a lot better overweight than it does outta gas..."

JG

"John Gaquin" wrote in message
...
An old pilot once told me, when I was a young pilot, "...sumbitch flies a
hell of a lot better overweight than it does outta gas..."

JG

I've got an old Flying Magazine (circa 1970 or so) where one of the editors
makes the comment that it is better to take off overloaded (with fuel) than
it is to try a launch with marginal fuel in order to stay under gross. The
comment was the same... It'll fly better over gross than outta gas.

I bet the magazine's lawyers wouldn't let them print that now...

KB

I've got an old Flying Magazine (circa 1970 or so) where one of the editors
makes the comment that it is better to take off overloaded (with fuel) than
it is to try a launch with marginal fuel in order to stay under gross. The
comment was the same... It'll fly better over gross than outta gas.

I bet the magazine's lawyers wouldn't let them print that now...

Don't tell anyone... but I did that almost routinely training for my
PPL. We were flying an old, tired C-150 in a Georgia summer (which
automatically means density altitudes are incredibly high). I weighed
about 180 at the time; my instructor was about 240. We were usually
over gross by about 40-50 lbs, and when flying dual we were lucky to
get 250fpm out of it.

My examiner was even bigger... I had to check the fuel levels and set
it up so that I'd burn enough on the way over to his airport that we'd
be right at gross for the checkride... which meant coming back home
afterwards was cutting it close (but then, it's only an 11 mile
flight).