On Jan 6, 10:49*am, bildan wrote:
On Jan 5, 4:44*pm, wrote:





Here's a reference to complement the DG video and also a discussion of
changes in certification requirements w.r.t. flutter. An interesting
read.

http://www.dg-flugzeugbau.de/dg1000-flattern-e.html

Some of the wording is a bit ambiguous, but the way I read it there
are two conclusions that are relevant to this discussion:

1) Holding on to the stick tends to damp out one mode of wing flutter
(and perhaps other controls too). It is a mode that is exacerbated by
the fact that when the wing flexes up an unbalanced aileron will tend
to deflect downward and vice versa.

2) Adding water ballast can decrease the flutter speed. If I read it
right the DG-300 had it's Vne reduced due to the test depicted in the
video.

9B

I'm reaching way back here but I remember flight test aircraft
equipped with dampers in the control system, similar to small shock
absorbers. *The dampers would stiffen up if a control surface started
to flutter. *The idea was to let the test pilot note the airspeed at
onset of flutter without letting it become destructive. *The controls
felt like they were in molasses but the aircraft was still flyable for
the purposes of the test.

That might still be a workable strategy for those pushing the envelope.- Hide quoted text -

- Show quoted text -

Another question about high altitude gliding - My understanding is
that the potential energy available to the sailplane is height times
weight. The potential energy would not vary with altitude. The drag,
however, would be less because of the thin air. Therefore would the
sailplane travel farther for a given amount of potential energy
used?? I have very limited time in the cockpit of jets, but it
appeared to me that the fuel flow was much less at altitude while the
true airspeed stayed high. More miles for a given amount of energy.

Also any comments on the post reporting different indicated air speeds
(at different altitudes) (in the flight manual) to achieve best L to D
in a jet. I would haved guessed that the best L to D would always
occur at the same indicated air speed.

On a dual wave flight at 25,000 feet I was warned about the danger of
high true air speed at altitude. We were cruising at a about 60 knots
IAS. I calculated that was a TAS of about 90 knots. I ask the
instructor if he thought our sink rate was what you would expect for a
Grob going 90 knots? He said no.

6W