Overweight takeoff / flight

|
| 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?

You would not necessarily feel heavier control forces if the airplane was
trimmed properly. Heavier control forces as you rotate would indicate a
forward cg, not over weight. You could be grossly over weight and have very
light control forces if the weight was mostly in the back. Most noticeable
is that the airplane does not accelerate as quickly as usual. If you are in
the habit of flying overvweight, you might not notice anything wrong at all.
Add in a hot day, short runway, and high altitude and suddenly you are going
to find yourself bitten by bad habits.

|
| 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?

Many airplanes take off from normal runways without flaps. A pilot can
easily forget to set flaps for short or soft field takeoffs. A lot of pilots
are also taught just 'plane' wrong. Consider the Cessna 172M, for example.
Most pilots are taught to set the flaps at 10 degrees for a short field
takeoff. Most aftermarket checklists tell you to do this, even the ones
designed for older Cessnas. Surecheck sells checklists that are supposedly
designed specifically for the 172M but they contain this error.

But read the manual. It tells you that if you set the flaps at 10 degrees
you will lift off the runway more quickly, but that you will climb more
slowly and you might not clear an obstacle at the end of the runway. The
manual says to use 10 degrees of flaps only when the runway is soft or is
short but there are no obstacles on climbout. But the idea that you use 10
degrees of flaps to do a short field takeoff is so pervasive that I have had
train my students in how to educate examiners on this issue.

Newer Cessna 172s use 10 degrees of flaps for all short field takeoffs, so
when transitioning from one model of Cessna 172 to another, be sure to read
the manual thoroughly.

CJ,

My C172SP POH states that for short/soft field takeoffs with a 50-ft
obstacle, flaps 10 should be used, as well as a climb speed of 56 kts
until obstacle is cleared. Flaps should be retracted after obstacles
are cleared after a safe flap retraction speed (what is that?) of 60
kts. is reached. Pitch for best angle of climb of 62 kts. after that
during the enroute climb, should obstructions again need to be
cleared.

I am guessing that the 56 kts speed is best angle of climb speed for
the flaps 10 configuration, even though that angle is probably less
than the normal 62-knot best angle of climb clean, due to the
parasitic drag induced by the flaps.

From my interpretation of the POH (and the latter doesn't make it
completely clear), if the runway was neither short nor soft, but with
obstacles at the end, I wouldn't use any flaps, lift-off at normal
speed, and pitch for the 62 kts. best angle of climb speed right away.

Thanks for replying,
Alex


"C J Campbell" wrote in message ...
|
| 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?

You would not necessarily feel heavier control forces if the airplane was
trimmed properly. Heavier control forces as you rotate would indicate a
forward cg, not over weight. You could be grossly over weight and have very
light control forces if the weight was mostly in the back. Most noticeable
is that the airplane does not accelerate as quickly as usual. If you are in
the habit of flying overvweight, you might not notice anything wrong at all.
Add in a hot day, short runway, and high altitude and suddenly you are going
to find yourself bitten by bad habits.

|
| 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?

Many airplanes take off from normal runways without flaps. A pilot can
easily forget to set flaps for short or soft field takeoffs. A lot of pilots
are also taught just 'plane' wrong. Consider the Cessna 172M, for example.
Most pilots are taught to set the flaps at 10 degrees for a short field
takeoff. Most aftermarket checklists tell you to do this, even the ones
designed for older Cessnas. Surecheck sells checklists that are supposedly
designed specifically for the 172M but they contain this error.

But read the manual. It tells you that if you set the flaps at 10 degrees
you will lift off the runway more quickly, but that you will climb more
slowly and you might not clear an obstacle at the end of the runway. The
manual says to use 10 degrees of flaps only when the runway is soft or is
short but there are no obstacles on climbout. But the idea that you use 10
degrees of flaps to do a short field takeoff is so pervasive that I have had
train my students in how to educate examiners on this issue.

Newer Cessna 172s use 10 degrees of flaps for all short field takeoffs, so
when transitioning from one model of Cessna 172 to another, be sure to read
the manual thoroughly.