Devices for avoiding VNE?

Arnold Pieper wrote:

The CG is ahead of the Aerodynamic Center of the wing

No ;-)

Although this is one of the most common misconception it's not true.
Except at very forward CG position, the glider CG is *behind* the
aerodynamic center of the wing.

If you don't believe me, check the CG range on your flight manual. And
compare with the mean aerodynamic chord (the aerodynamic center in all
common profiles is at 25% of the chord)

Frankly, that must have come from someone who hadn't finished
reading the whole aerodynamic book yet, and started jumping to conclusions.

You perhaps read the whole book, but unfortunately many books are wrong
(especially those destined to student pilots), in an effort to explain
the stability issue simplier, pretending that the CG must be ahead of
the wing AC...

Anyway we are well out of the subject of this thread ;-)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Paul Repacholi wrote:

Concorde, when it was acelaring through transonic speeds had to do a
large fuel xfer to the aft tanks to conpensate for the strong nose
down trim shift.

It was rumoured to be certified

Surprisingly... but I'm confident that, had the soaring price of oil in
the 70's not succeeded in killing commercially this beautiful bird, the
FAA would not have been so kind to let it fly over the USA with such a
dangerous feature ;-)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis,

Since you're not helping move things in the right direction, I'll explain it
in a bit more detail.

I referred to the Aerodynamic Center, which applies to the isolated wing
analysis, because people were referring to the Center of Pressure, that also
applies to the isolated wing analysis.
The AC does not move, the CP does, however, is the AC that is used for
stability analysis, not the CP.

Anyway :
When you consider the glider as a whole, as opposed to the isolated wing,
there is something called the "Neutral Point", which is the point where the
Lift vector acts considering all aerodynamic forces acting on the glider,
and it too does not move with AOA.
The CG must be always ahead of this Neutral Point, and the Horizontal
Stabilizer/elevator is what keeps them balanced.


"Denis" wrote in message
...
Arnold Pieper wrote:

The CG is ahead of the Aerodynamic Center of the wing

No ;-)

Although this is one of the most common misconception it's not true.
Except at very forward CG position, the glider CG is *behind* the
aerodynamic center of the wing.

If you don't believe me, check the CG range on your flight manual. And
compare with the mean aerodynamic chord (the aerodynamic center in all
common profiles is at 25% of the chord)

Frankly, that must have come from someone who hadn't finished
reading the whole aerodynamic book yet, and started jumping to
conclusions.

You perhaps read the whole book, but unfortunately many books are wrong
(especially those destined to student pilots), in an effort to explain
the stability issue simplier, pretending that the CG must be ahead of
the wing AC...

Anyway we are well out of the subject of this thread ;-)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Arnold Pieper wrote:

When you consider the glider as a whole, as opposed to the isolated wing,
there is something called the "Neutral Point", which is the point where the
Lift vector acts considering all aerodynamic forces acting on the glider,
and it too does not move with AOA.
The CG must be always ahead of this Neutral Point, and the Horizontal
Stabilizer/elevator is what keeps them balanced.

Yes. Now I better agree ;-)

The CG must be always ahead of this Neutral Point (the whole glider
Aerodynamic Center) - although the CG may be *behind* the Aerodynamic
Center of the wing (and is actually behind, except in far forward CG
position - or in tailless designs)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

http://www.jaa.nl/section1/jars/445499.pdf

JAR 22.73 Descent, high speed
It must be shown that the sailplane with the
airbrakes extended, will not exceed VNE in a
dive at an angle to the horizon of:
(a) 45° when the sailplane is approved for
cloud flying and/or aerobatics when certificated
in the Aerobatic or Utility Category;
(b) [in other cases
(i) 30°
(ii) less than 30° when a rate of
descent of more than 30 m/s can be achieved].

Don't know how many sailplanes may be built to para b. Guess I assumed all
JAR22 aircraft were designed to para a standards.

I believe this resulted from the supposedly demonstrated difficulty in
maintaining a vertical descent, even in cloud, as a result of some empirical
testing about 40 years ago. At least that's what I recall from
conversations in the '70s.

If you want vertical limiting airbrakes, I know where you can buy a
Schweizer 1-34;^)

Frank Whiteley

"Arnold Pieper" wrote in message
om...
The glider won't stay at 90 degrees nose down like I said. As it
accelerate
it will bring the nose up.
That in itself is no guarantee you won't reach VNE before long, of course,
so you have to control the recovery.
Avoid reaching VNE by deploying the airbrakes if you see the speed
increasing too fast, as I said, controlling the dive.
That is always better than trying to bend the wings by pulling too many
Gs.
Your attitude will be at 45 degrees or less in a matter of seconds, and at
that attitude, the airbrakes will prevent the overspeed or at least
minimize
the condition (if they were deployed too late).

You can go over VNE if you don't deploy the airbrakes and just try to
"G-load" your way out of such a high-speed dive,and that's the condition
in
which you overstress the structure, produce internal cracks, bend or
damage
some of the hardware in the control system.
That's the reason you should watch the airspeed and deploy the airbrakes
in
time (before reaching VNE).

Don't be affraid to open the airbrakes at high speed, believe me, the
manufacturer is just a little smarter than that.
You have to be careful at high speed just because they tend to jump out
more
easily, so, have a firm hand on it.

Real aerobatic training (as opposed to some occasional loops) will clarify
a
lot of this.


"Todd Pattist" wrote in message
...
"Arnold Pieper" wrote:

Maybe true if "near vertical", however, staying at a near vertical dive
is
something that requires a conscient effort.
The glider won't just stay there on its own.
To remain in a 90 degree vertical dive requires a significant amount of
forward stick force and concentration.
As speed increases, the nose will come up (away from vertical) even if
you
don't want it to, and even with full forward trim, it would still
require
an
honest push on the stick to maintain that attitude.

All of this is true, but it's not relevant to whether the
airbrakes of a modern glider are speed limiting. They
aren't. There are lots of initial conditions that will
exceed Vne with the brakes out.

If you're recovering from an unusual attitude that puts you in a near
vertical dive, just don't sweat it.
Open the airbrakes and slowly pull out of the dive. There is no need to
overstress.

There is also no guarantee that you will not exceed Vne or
that your final speed will be lower than someone who applies
a higher AOA with it's higher G-load and reduces the descent
angle more quickly.

If you want to feel safer, go for aerobatic training.
You will see that you can actually dive 90 degrees down and recover
without
exceeding VNE, without using the airbrakes and not getting even close
to
G
limits.

I do loops often. Slow and vertical is far different from
fast and vertical.


Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

The Type Certificate is Glider Utility Category for the Duo Discus, which
would seem to be inappropriate given the 45degree requirement of
JAR22.73(a), unless this was subject to some caveat during certification.
Never having seen a Duo POH, what does it say? Perhaps that's enough to
satisfy the certification requirement.

Frank Whiteley

"Chris Rollings" wrote in message
...
Nimbus 3 and 4 and Duo Discus brakes do not meet the
'speed limiting in a 45 degree dive' requirement, but
do achieve that in a 30 degree dive. That's why they
are non-aerobatic.

At 15:18 31 March 2004, W.J. \bill\ Dean \u.K.\. wrote:
NO. This is thoroughly misleading.

HISTORICAL.

When the first gliders with good (for the day) performance
were built,
it was found that the good performance made them difficult
to land.

So they were fitted with spoilers as a landing aid.

Then pilots started to cloud fly, and some lost control
in cloud
and overspeeded and overstressed their gliders, which
broke up.

This was countered by developing and fitting speed-limiting
airbrakes
(DFS, e.g. Weihe and Slingsby Sky, and Schempp-Hirth).
These were intended
to be speed limiting in a true vertical dive.

In the U.K. it was a requirement that the glider was
test flown to prove
that at max. all up weight in a vertical dive Vne was
not exceeded,
I understand that the Slingsby Skylark series all passed
this test.

Note that max. manoeuvring and rough air speeds WOULD
be exceeded.

Later, it was found that with higher wing loadings,
thinner wing sections
and higher aspect ratios it became practically impossible
to fit true speed
limiting brakes (in the sense that Vne would not be
exceeded in a true
vertical dive at max. a.u.w.). The first U.K. built
gliders for which this
applied were, I believe, some at least of the Slingsby
Dart series.

Also, if the rules were relaxed life would become a
lot easier for the
designer, because it would save weight and cost.
So the rules were
relaxed, and 'Speed limiting' came to mean 'In a dive
at X degrees', usually
I understand of 45 degrees.

TODAY

Most gliders today, including I believe all those built
in Europe, are
designed to JAR 22.

See:
Joint Aviation Authorities, Europe. http://www.jaa.nl/
,
JARs - Section 1 - JAR-22 http://www.jaa.nl/section1/jars/445499.
pdf .

The relevant clause is:

'JAR 22.73 Descent, high speed

'It must be shown that the sailplane with the airbrakes
extended, will not
exceed VNE in a dive at an angle to the horizon of:

'(a) 45° when the sailplane is approved for cloud flying
and/or aerobatics
when certificated in the Aerobatic or Utility Category;

'(b) 30° in other cases.

'[Ch. 5, 28.10.95]'

Some modern gliders, including some being built today,
probably still have
true speed limiting brakes by the strict old definition
given above; my
guess is that these would all be gliders with trailing
edge brakes or
braking flaps such as the early Pik 20; but this would
not necessarily be
true for all gliders with such brakes.

Some gliders were built with tailchutes, either in
an attempt to comply with
the old strict requirement, or because it was necessary
if they were to
comply with the relaxed rule. I have always understood
that the Janus was
fitted with a tailchute to be speed limiting in a 45
degree dive at max.
a.u.w. with full water ballast.

At what dive angle would a Duo-Discus with full brakes
go through Vne?
I would be astonished if this is more than 45 degrees,
it may very well be
30 degrees.

So if in a spin recovery, or for any other reason,
you are diving at a very
steep angle your air-brakes are unlikely to save you
from exceeding Vne.
I am sure they won't in the Nimbus 3/4 series; it was
not a requirement for
certification.

W.J. (Bill) Dean (U.K.).
Remove 'ic' to reply.


'Arnold Pieper' wrote in message
. com...

John,

The airbrakes were designed not only to be used for
approach and landing,
but also to avoid reaching VNE.

Look at your glider's POH and check what is the maximum
speed to deploy
the airbrakes, and what becomes the VNE with them
deployed.

In most modern design gliders, the airbrakes can be
deployed up to VNE,
and they will prevent the glider from reaching VNE
when fully opened.

The airbrakes are designed for this purpose.

Once the airbrakes are opened and will prevent you
from going over VNE,
there's no need to pull at anything even close to
the design limit G.

Spin training therefore, is the best way to ease this
fear and learn how
to pull without overstressing the airframe.

AP


'John Galloway' wrote in message
...

Through the contributions to the avoiding VNE thread
runs the theme of the difficulty of avoiding overspeeding
and/or overstressing some modern designs in accidental
spin recovery. This is made more difficult than
in
older composite gliders because they had a little
more
drag and a little more (fortuitous) margin in the
g
limits.

Is it not blindingly obvious that there is a need
for
an emergency drag device that does not reduce the
G
limits of gliders? Clearly if we all handled the
recovery
from inadvertent spins etc perfectly all would be
well
but equally clearly that does not always happen and
it is a shame to lose pilots in this situation.

As the Phoebus pilot pointed out a tail chute is
ideal
for this - providing that it can be made to actuate
and jettison reliably. (I found the design used
on
the Kestrel particularly good and I never once had
a failure for landing use.) On the other hand they
are expensive and inconvenient to replace and there
are several ways that they can fail.

So can anyone think of a better idea than a chute?
The best I can come up with is some sort of flush
fitted rectangular-with the-long-edge-horizontal
rear
hinged airbrakes (like old fashioned automobile suicide
doors) located on the fuselage sides somewhere in
the
region below or below/behind the wings. If they
opened
to about 45 degrees with a spring actuator (and limited
by sliding metal stays that hinge/attach to the front
of the panel and whose inner ends slid along in runners)
then they would provide a lot of drag without any
deep
internal mechanism (such as wing airbrakes have).
Once they have done their job the rear end of the
brakes
could be released by a spring loaded mechanism similar
to the front end so that the brakes would then instantly
spring to as position set out from and parallel to
the fuselage so that there would be very little drag
- only that provided by the stays at both ends and
the brake panels edge on to the wind. That configuration
would be good enough to fly home with. It would
only
be possible to reset these brakes on the ground and
they would not replace conventional wing airbrakes
for approach control - although they could have a
secondary
use for emergency approach control.

I am envisaging something the could be included in
new designs although there does not seem to be any
obvious reason why such a device could not be retrofitted
as a fairly major modification. The contours of
the
brake panels would be specific to the individual
fuselage
type but the mechanism could be generic. The assembly
would be fairly shallow and complete within itself
apart from e.g. a cable release attachment.

I am not advocating a technical solution to this
problem
in place of spin recovery practice but I do think
that
there must be something that the combined intellects
of the gliding community can come up with other than
observing that if we get into that particular overspeeding/steep

attitude condition we are stuffed.

Anyone got any simpler or better ideas? I am definitely
not an engineer.

John Galloway

F.L. Whiteley wrote:

The Type Certificate is Glider Utility Category for the Duo Discus, which
would seem to be inappropriate given the 45degree requirement of
JAR22.73(a),

You need to read carefully:

a) 45° when the sailplane is
*approved for cloud flying and/or aerobatics*
when certificated in the Aerobatic or Utility Category

Stefan

"Stefan" wrote in message
...
F.L. Whiteley wrote:

The Type Certificate is Glider Utility Category for the Duo Discus,
which
would seem to be inappropriate given the 45degree requirement of
JAR22.73(a),

You need to read carefully:

a) 45° when the sailplane is
*approved for cloud flying and/or aerobatics*
when certificated in the Aerobatic or Utility Category

Stefan

Ah yes, good point.

Frank

Denis, I hope you're just trying to make fun of the limited views some
people express here.

If you refer to the need to transfer fuel to stay in balance, the Concorde
was neither the first, nor the last airplane with that need. Fuel management
is an issue with most large airplanes, weather of not they are Delta wings
or even Supersonic.

Boing was working on a similar design (although a few years behind) at the
time the Concorde was launched, and it too would have the exact same
challenge to stay in balance, as a large delta-wing supersonic aircraft.

Or is it just that most people could never overcome the fact that the
europeans beat everyone else into the SST commercial world, and 40 years
later nobody could repeat that ?




Denis" wrote in message
...
Paul Repacholi wrote:

Concorde, when it was acelaring through transonic speeds had to do a
large fuel xfer to the aft tanks to conpensate for the strong nose
down trim shift.

It was rumoured to be certified

Surprisingly... but I'm confident that, had the soaring price of oil in
the 70's not succeeded in killing commercially this beautiful bird, the
FAA would not have been so kind to let it fly over the USA with such a
dangerous feature ;-)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Or is it just that most people could never overcome the fact that the
europeans beat everyone else into the SST commercial world, and 40 years
later nobody could repeat that ?


It more like nobody is stupid enough to do it...

They predicted they would sell several hundred of em....they built about 12 and
sold none....

Yep, anothe Euro victory......

With victories like that who needs failures?

blll