There was one plane, I believe it was an experimental, that had some
questions about its flight characteristics at aft CG. It was, IIRC, A
4-place plane. The designer took a garage door opener screw mechanism,
with a trolley attached and hooked a weight of ~125 pounds to it. The
motor for the mechanism powering the screw was battery powered, and the
weight could be moved fore or aft with a simple switch that regulated
the movement and direction of the screw, hence the direction of the
weight. Before taking off, the W&B was done for different positions of
the weight, and the position of the trolley marked accordingly.
The plane was flown at different CG locations, and the results reported.
IIRC, that took place at least 15 years ago. Someone else probably can
find the article about it.
On 7/11/2022 11:24 PM, Dr. Feng Hsu via KRnet wrote:
Since CG location is such a critical and sensitive element on aircraft
safety, why there hasn't anyone in the experimental world tried to
resolve this issue by design?!
Considering the troublesome CG issue whenever we fly with luggage
loading concerns, I kept thinking why can't someone design an easy
"inflight adjustable CG" mechanism, which could manually or even
automatically adjusting the CG balance with a push of an electric switch?
For example, to add on a CG auto balance subsystem based on sensors
attached to a slidable or moveable weight? This can't be too
complicated of a flexible CG mechanism to design and add on to small
and CG sensitive aircraft, especially for the experimental crow,
perhaps? I believe it could save lives if done correctly...!
Any thoughts on this?
Dr. Hsu
On Mon, Jul 11, 2022, 10:15 PM Flesner via KRnet
<krnet@list.krnet.org> wrote:
On 7/11/2022 8:34 PM, MS wrote:
but if it's a conventional gear KR, filling up the header and
lifting the tail will tell you how tail heavy the plane is. In
my experience with two of them this lifetime, the KR has a wide
CG range that, if exceeded, can be easily compensated for with
extra speed if necessary. Both my KR's have let me get away
with murder, but both KR's were built by engineers who were
precise with their work. Assuming a KR has been built with
finesse, my impression is they are very forgiving.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
I'm amazed that someone with your experience takes such a cavalier
attitude to weight and balance of an aircraft. Tail light or heavy
tells you nothing about the CG location but rather the location of
the landing gear in relation to the CG. An aircraft with
uncontrollable aft CG might have a light tail if the gear is close
to the CG location and a very nose heavy aircraft could have a
heavy tail if the gear is mounted well forward. The actual CG
must be determined with scales, measurements, and math. An
engineer / designer will try to place the main gear on a
conventional gear aircraft as close to the CG as possible for the
best possible ground handling. In the case of the C140 they went a
bit too far and made the airplane extremely tail light and pilots
were putting the airplane on the nose with excessive braking. The
fix was to modify the gear and place the wheels about 4 inches
further forward. Lifting the tail before and after the mod would
not give you the location of the CG but only the relative location
of the gear to the CG. The CG location never changed only the
tail weight. Was the CG location correct? Only scales,
measurements, and math can determine that.
As far as the KR letting you get away with murder, I'm thinking
the design more likely kept you from committing suicide. CG should
not be taken lightly............
Larry Flesner
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