Aerobatics in semi acrobatic certified sailplanes

"I have amassed quite a bit of info on the subject now, some
interesting technical stuff that suggests that you cannot overstress a well
designed sailplane at Va no matter what you do."

Then you still have some reading to do!!!!

http://www.flyingmag.com/myth-maneuvering-speed

http://uras.gliderpilot.net/?op=s2&id=39082&vt=





At 12:02 04 October 2012, jams wrote:

Thanks for all the input.

I have found out a fair bit more info on aerobatics since I posted this
question. I think a better way of asking the question would have been:
What aerobatic manoeuvres can a 'semi-aerobatic' sailplane perform!?

I have amassed quite a bit of info on the subject now, some interesting
technical stuff that suggests that you cannot overstress a well designed
sailplane at Va no matter what you do. I will have a read up on it all
and post something here with my findings.

Kirk,

Your sentence: 'Glider acro (unless in a Swift/Fox, etc) is a relaxed,
gentle form of the art. It's not about pulling a lot of G, it's about
energy management, and not exceeding VNE.' Sums up exactly what I'm
interested in. I dont want a pure acro aircraft, because I dont want to
do anything to mad but would like to be able to explore more than just
loops and chandelle during flights.

Also having found what G forces are generated in the figures i'm
interested in (in the PIK aerobatics supplement), and your comment about
not much neg G occurring, suggests that most sailplanes could handle
what the PIK was doing in the video anyway.

Regards

James




--
jams

On Thursday, October 4, 2012 8:02:37 AM UTC-4, jams wrote:

I have amassed quite a bit of info on the subject now, some interesting

technical stuff that suggests that you cannot overstress a well designed

sailplane at Va no matter what you do.


This is a common misconception, and was cited as contributing to the American Airlines flight 587 crash of an A300. I know there will be differences between the transport category vs. glider and US vs. European standards. However, be aware that Va may only give you protection for one full deflection of a control surface on one axis. If you make alternating applications on one axis or apply large deflections on more than one axis simultaneously, you can defeat the structure even at a speed below Va. Here is the FAA summary written after AAL587.

SUMMARY: The Federal Aviation Administration amends the airworthiness standards applicable to transport category airplanes to clarify that flying at or below the design maneuvering speed does not allow a pilot to make multiple large control inputs in one airplane axis or single full control inputs in more than one airplane axis at a time without endangering the airplane's structure. The FAA is issuing this final rule to prevent pilots from misunderstanding the meaning of an airplane's maneuvering speed, which could cause or contribute to a future accident.

http://en.wikipedia.org/wiki/America...nes_Flight_587

http://www.ntsb.gov/doclib/reports/2004/AAR0404.pdf

http://en.wikipedia.org/wiki/Maneuvering_speed


Glenn Fisher

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?

On Saturday, October 6, 2012 12:59:58 PM UTC-5, 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?

Not sure about gliders, but a B-52 lost it's vertical tail in CAT (may have been rotor?).

http://www.usread.com/flight587/Prev_Tail_Sep.html

Interesting read on how the crew, with the help of Boeing engineers on ground, reconfigured their crippled bomber inflight and got it home safely.

As Winston Churchill said: "Never, never, never give up!"


Kirk
66

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 10/6/2012 11:59 AM, 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?


Happened a long time ago, but to a superbly maintained, "reasonably new"
Pratt-Read descending through rotor in the Jet Stream Project...estimated 20G
rotor-induced gust encountered (as I recall without verifying) "well below"
maneuvering speed...arguable whether the wings or wing carry-through structure
failed first.

Details can be found in old "Soaring" mags (article by the project-pilot/pilot
Larry Edgar), or the book "Exploring the Monster".

Regards,
Bob W.

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 |