Message text written by "Fergus Kyle"
> I see some discussion of Altitude Hold phase of Flight control
management. While I am in no position to question builders/fliers on their
experience, I feel it imcumbent to mention it if those unaccustomed to
auto-control are contemplating its installation.
The one phase of 'altitude hold' deserves careful
consideration.
In modern transport aircraft, this phase by itself is inherently unsafe,
unless Airspeed Control is also imposed. While it's obvious that we don't
want to hold altititude 'til the airspeed loss induces a cruise wing stall
-
it's happened - it IS possible that in this phase other distractions can
make it happen.<
Whilst I understand and agree with Fergus' point with jet transports these
aspects are less critical with prop aircraft because prop aircraft tend to
have a steeper drag curve. We had a relatively crude altitude hold on the
C130 with no auto throttle. This was never a problem due to the speed
stability in the cruise however it is still reasonable to expect a certain
amount of monitoring by the pilot. The Europa has a flairly flat curve for
a prop aircraft due to its slippery shape but unless it is flown close to
minimum drag speed there is little risk of it falling behind the drag curve
in the cruise. On the basis that altitude hold in this application would be
only used in VFR conditions in the cruise, I think that an altitude hold
feature without auto throttle would be quite acceptable for the Europa.
However you might ask if this is truely necessary in the first place. In
smooth conditions the pitch stability is good enough to be hands off for
several minutes at a time with no altitude deviations and when VFR a couple
of hundred feet of error is hardly critical anyway. In rough conditions it
is probably better to fly manually holding an attitude rather than chasing
a nominal cruise altitude.
Just a thought.
Nigel Charles
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