I think positive static stability means that this doesn't
happen. The only certified aircraft I'm aware of that
tucks in pitch is the Learjet 20/30/50 series, but
this happens at transonic speeds as the center of lift
moves aft. The aircraft is certified with a stick puller
to ensure you never get there.

In most aircraft the phugoid mode is pretty lightly
damped and has a period on the order of tens of seconds,
so the speed can build up a bit before the nose comes
up. Are you sure that's not what you're experiencing?
The only other thing I can think of is a c.g. out
of limits, so it might be worth double checking your
weight and balance if your aircraft behaves this way.


At 06:18 01 April 2004, Eric Greenwell wrote:
Mark Navarre wrote:

As speed increases, the nose will come up (away from
vertical) even if you
don't want it to, and even with full forward trim,
it would still require an
honest push on the stick to maintain that attitude.


Not true with all gliders. Several modern racing
ships will, when trimmed
within CG limits for best climb performance, 'tuck'
or pitch down with
increasing airspeed, resulting in a large outside
loop or exceeding VNE without
pilot input. The crossover speed for this in my own
ship is about 115 kts,
above which slight back pressure is needed to maintain
speed.

Which glider is that? I thought a pitch-up tendency
with increasing
speed was a certification requirement? And what is
the CG position for
this to happen? Is this 'feature' mentioned in the
flight manaul? Sounds
kind of scary.

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Eric Greenwell
Washington State
USA