You are right, it should match the performance. There are a couple of
reasons why it doesn't.

The flight test data is taken on a perfectly rigged airplane.

In addition to a new engine, the airplane had a new prop.

Airplanes tend to get heavier over time. I have seen three airplanes
weighed and every one was 30 to 100lbs heavier than the W&B indicated.

People and their stuff is probably heavier than they admit.

Most of the performance data is calculated from a limited number of test
points. The airplane wasn't really flown at every point on the performance
chart.

Mike
MU-2


"Mark" wrote in message
om...
Nathan Young wrote in message
. ..
Glad to hear you made it safely. Probably the best lesson learned is
that the real world performance of a 30 year old plane rarely matches
the numbers in the POH, and that when operating near the edge of the
envelope - there is little margin for error (or Mother Nature).


I'm Curious about something. Everyone says that a 30-year-old
airplane will not perform like when it was a new airplane. However I
never heard anyone explain WHY this is so.

Assuming that a airplane (either a new factory aircraft or 30 year old
trainer) has had it's annual done and engine is up to par (compression
ect..) than why would these values change? An engine close to TBO
will still deliver fuel and power values very close to the POH. The
only source of diminished performance I can think of would be from the
rigging and/or airframe that could be a little out of alignment,
however any large deviations would have to be fixed.

If the performance value of a 30-year-old airplane does not match the
values in the POH for that make/model of aircraft (i.e., performance
values change over time), then I suggest that the FAA needs to address
this issue.