Aerobatics in semi acrobatic certified sailplanes

On Sat, 06 Oct 2012 10:59:58 -0700, son_of_flubber wrote:

What are the G forces in unintentional aerobatic maneuvers... say flying
through extreme rotor?

Have there been cases of gliders losing their wings in rotor on their
way to mountain wave?

A Nimbus 4 broke up in severe turbulence during practice for the 1995
World Champs at Omarama, NZ:
http://aviation-safety.net/wikibase/wiki.php?id=29823


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

I have been flying acro in gliders for many years. I own and fly an
LS-8/SZD-59/Fox and have flown acro in other gliders and powered
aircraft. It is true that most modern sailplanes are built to a
JAR-22 standard and have +/- G limits that are well within the forces
expected in WELL EXECUTED acro maneuvers. The problems develop in
learning maneuvers and how to recover from BLOWN maneuvers. In a
modern sailplane with a T-tail the speeds build very quickly in blown
maneuvers and the chances for overstressing really increase rapidly.
THe other thing to remember is that most truely aerobatic gliders do
not have T-tails...they have standard configurations with a low
horizontal stabilizer. Why?????? Because a T-tail can't take much
twisting forces.

I think loops are good in virtually any sailplane. But, once you add
rotations about the longitudinal axis you are in danger of
overstressing the tail. Remember, the G limits are for purely non-
rotational loads. Tailslides are another complete subject. Most acro
gliders have control surface limits built into the control surfaces at
the interface between the control surface and the wing structure.
Most regular gliders have the control surface limits built into the
control linkage system, usually at the connections to the stick. In
a tail slide you run the risk of bending/breaking the control linkage
system in a regular sailplane.

Anyway, after years of tickling the dragon's tail in many different
aircraft with many different pilots...don't learn acro in a regular
sailplane. Learn acro in a rated aircraft with a competent pilot and
then make your own decisions. I think you will find that the more you
learn about acro maneuvers...especially failed maneuvers...the less
likely you are to be adventurous in your PIK-20 or Discus.

Guy "DDS"

On Sunday, 7 October 2012 07:38:04 UTC+13, Martin Gregorie wrote:
On Sat, 06 Oct 2012 10:59:58 -0700, son_of_flubber wrote:

What are the G forces in unintentional aerobatic maneuvers... say flying
through extreme rotor?

Have there been cases of gliders losing their wings in rotor on their
way to mountain wave?

A Nimbus 4 broke up in severe turbulence during practice for the 1995
World Champs at Omarama, NZ:

http://aviation-safety.net/wikibase/wiki.php?id=29823

That glider was overspeed and in cloud, so not really a case of G induced failure.

I fly in the wave a lot, and used to fly a DG1000 with a G meter. The most I saw in rotor was around 4G positive and maybe 1.5G negative.

I do remember a ridge crossing that was particularly rough that got 5G positive and 2.5G negative once. That was very unpleasant.

--
Phil Plane

On Sat, 06 Oct 2012 13:31:44 -0700, philplane36 wrote:

On Sunday, 7 October 2012 07:38:04 UTC+13, Martin Gregorie wrote:
On Sat, 06 Oct 2012 10:59:58 -0700, son_of_flubber wrote:

What are the G forces in unintentional aerobatic maneuvers... say
flying through extreme rotor?

Have there been cases of gliders losing their wings in rotor on their
way to mountain wave?

A Nimbus 4 broke up in severe turbulence during practice for the 1995
World Champs at Omarama, NZ:

http://aviation-safety.net/wikibase/wiki.php?id=29823

That glider was overspeed and in cloud, so not really a case of G
induced failure.

I fly in the wave a lot, and used to fly a DG1000 with a G meter. The
most I saw in rotor was around 4G positive and maybe 1.5G negative.

I was responding to the 'loosing wings in rotor' comment, not the
'aerobatic G' one. I thought I'd heard it was an overspeed in rotor
situation but the report I dug up didn't mention that so neither did I,
in order to avoid speculating.

I do remember a ridge crossing that was particularly rough that got 5G
positive and 2.5G negative once. That was very unpleasant.

Sounds nasty.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |