Devices for avoiding VNE?

From: John Galloway
Date: 3/28/2004 4:53 PM Central Standard Time

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.
etc. etc.
Ok john here we go---get a JATO bottle and mount it backwards in the nose.
Secondary uses. Glider release fails---torch that tow rope! Also very short
roll outs for them off airport landouts.
Along your thoughts for a fuselage mounted air brake--how about two chutes
about two foot in diameter each that would, when inflated, rest a little foward
of the wing T.E. and along side the fuselage. Like a "pilot" chute sorta
thingy deal. They could be released after the, to fast dive, had been
recovered or flown on in to a landing were you close enough to the airport.
Being close to the center line would be a plus if one should fail to open. The
canopy of the chute could even be attached to the fuselage to keep the little
buggers from beating around. You could pop them out of an aft and outward
facing oval ended surface flush tube and leave the "oval cover plate" on the
fabric of the chute. Hmmm--- The lanyard and everything could pack in the
tube. Pop it out with a coil spring.
Ok-- everybody saw it here first. John send me a check for 15% of the
profit on each of these you sell in the future. Now if I'd just get busy and
try this out on that 16 foot span RC motorglider I have hanging in the
basement. mac--- inventor--thinker--under paid

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 fuselge 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

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

Thanks Bill.

You detail the historical background to the paradox
implicit in the 'Avoiding VNE' thread that a glider
can be, at one and the same time, both technically
within its operating limits, and also in an irrecoverable
situation - i.e. if it is flying in a fast, accelerating,
steep angle configuration (leaving those as vague terms
as the values will vary between types) - even assumming
a hypothetical empty airmass of infinite size and zero
turbulence.

This is a bit unfortunate for those who find themselves
in that situation and I think that it would be nice
if gliders that are within their limits had the capability
of not exceeding them if it is technically possible.

John Galloway


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

John Galloway wrote:
Thanks Bill.

You detail the historical background to the paradox
implicit in the 'Avoiding VNE' thread that a glider
can be, at one and the same time, both technically
within its operating limits, and also in an irrecoverable
situation - i.e. if it is flying in a fast, accelerating,
steep angle configuration (leaving those as vague terms
as the values will vary between types) - even assumming
a hypothetical empty airmass of infinite size and zero
turbulence.

This is a bit unfortunate for those who find themselves
in that situation and I think that it would be nice
if gliders that are within their limits had the capability
of not exceeding them if it is technically possible.

It would be nice, and it is technically possible, but perhaps not
economically viable, judging by the number of manufacturer that offer
them. "Speed-limiting" gliders are available; for example, the Ka-6E and
other gliders designed to the speed-limiting standards, and gliders with
trailing edge dive brakes.

Personally, I think other things are more likely to kill me, so I would
prefer money and research effort be spent on more crash-tolerant
cockpits, pilot rescue systems, spin resistance, spoilers and canopies
that won't open when left unlocked, and simpler, more reliable
self-launching systems.
--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Todd Pattist wrote:

The airbrakes are designed for this purpose.

Not in any modern glider I know of. Anywhere close to
vertical will exceed Vne with the brakes open.

The elevator is designed for that purpose (getting out of the vertical
cone where a glider will exceed VNE with airbrakes) ;-)

--
Denis

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

John Galloway wrote:

This is a bit unfortunate for those who find themselves
in that situation and I think that it would be nice
if gliders that are within their limits had the capability
of not exceeding them if it is technically possible.

You're right but it's the pilot task to think ahead and not to fall into
such a situation. You cannot achieve high performance in a pilot-proof
glider...

The same when you are flying above unlandable terrain, there is nothing
illegal in this but you are in a great risk. And you have to think ahead
and stay within reach of a landing field...


--
Denis

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

It


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

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.

Not in any modern glider I know of. Anywhere close to
vertical will exceed Vne with the brakes open.
Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

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.

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.

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.
Even if you lag behind the glider and airspeed gets close to VNE, just open
the airbrakes and do a gentle pull out.




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

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.

Not in any modern glider I know of. Anywhere close to
vertical will exceed Vne with the brakes open.
Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

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.)