Jantars are back :)

Arnold Pieper wrote:
Certain models of sailplanes have limitations in IAS with altitude for
various reasons,
(Flutter is not the only factor in determining VNE).
When a sailplane does have this limitation, it will be expressed so in their
manuals, and there will be a table of limiting IAS x Altitude.

So what are these reasons? Can someone explain this a bit better?
At 25,000 feet with a 90 knot headwind I'd like to know if
pushing the nose down to redline is maybe a bad idea...
and I'm not so sure I'd be confident doing it just
because there are blank pages in the manual...

No.

The BGA have produced a book published 2002 by A & C Black, London titled
"Gliding - The British Gliding Association Manual", ISBN 0-7136-5947-5
(not to be confused with the book "Gliding" by Derek Piggott published in
about 1958 and now I think in its 6th edition).

This book covers the technical knowledge which the BGA thinks glider pilots
should have, and is required reading for BGA rated instructors. The main
author is Steve Longland, and he had input from many others.

In chapter 5 "The placard, structure and flight limitations" there is a
section starting on p.155 "The effects of changes in air density".
In this section an explanation is given as to why the Vne is related to True
Air Speed and not to Indicated Air Speed. I do not claim to fully
understand it myself, but I certainly intend always to obey.
The conclusion is:
"Avoiding flutter.
"The practical rule of thumb is that you should reduce the glider's Vne by
"1.5% for every 1,000ft above sea level. If your glider's Vne is 128kt,
"then at 20,000ft the ASI reading corresponding to TAS of 128kt is 90kt,
"and at 30,000ft it will be 70kt. ....."

If you read the earlier section in the same chapter about test flying, you
will see that the glider is not tested to Vd (Design dive speed) but only to
Vdf (Demonstration design speed) which is 95% of Vd and that the placard
speed Vne is 90% of Vd.
To quote from the book: "If the glider's Vne is 130kt, it has only ever been
6.5kt faster, once, when it was new, in ideal conditions, and flown by a
specially trained test pilot."

If anyone thinks this is wrong, could we please have a reasoned argument and
not just abuse.

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


"Arnold Pieper" wrote in message
om...

Gents,

As far as the pilot is concerned, VNE is always read directly as an IAS
limit, that's why it's painted on the ASI as a radial line.
I've never seen any remarks about VNE as "VNE is XXX at Sea Level at ISA".
There is no such thing.

VNE is always good as an Indicated figure, except at altitudes and
airspeeds where compressibility comes into play, in which case MMO
(Maximum Mach Operating speed) becomes the limiting factor, usually well
above our speeds. That happens at a certain altitude, up to which the
pilot uses the Indicated VNE as a limit, then after that the MMO.


Exception :
Certain models of sailplanes have limitations in IAS with altitude for
various reasons, (Flutter is not the only factor in determining VNE).
When a sailplane does have this limitation, it will be expressed so in
their manuals, and there will be a table of limiting IAS x Altitude.

The Jantar Std 2 is not one of these, so, VNE is good as an IAS as high as
it will go.

The bottom-line is that it dependent on each design, but VNE is not a TAS
figure, whoever told you so, doesn't know what he/she is talking about.

AP

Mark James Boyd wrote:

Arnold Pieper wrote:

Certain models of sailplanes have limitations in IAS with altitude for
various reasons,
(Flutter is not the only factor in determining VNE).
When a sailplane does have this limitation, it will be expressed so in their
manuals, and there will be a table of limiting IAS x Altitude.


So what are these reasons? Can someone explain this a bit better?
At 25,000 feet with a 90 knot headwind I'd like to know if
pushing the nose down to redline is maybe a bad idea...
and I'm not so sure I'd be confident doing it just
because there are blank pages in the manual...

Old (guessing: "certified before the early '80s") sailplanes may not
have the limitation in the manual because of the regulations in effect
at the time. A lot has been learned since then, leading to more
stringent testing and more conservative ratings. If I were flying an
older glider, I'd go by the TAS unless I knew for a fact it had been
designed and tested at Vne (indicated) at high altitudes (meaning the
altitudes I'd be flying it at).
--
-----
Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

Maybe it would be prudent to keep one's parachute straps tight and an
emergency O2 bottle attached -- then pray for luck, The Gods do get
angry now and then.

W.J. (Bill) Dean (U.K.). wrote:
No.

The BGA have produced a book published 2002 by A & C Black, London titled
"Gliding - The British Gliding Association Manual", ISBN 0-7136-5947-5
(not to be confused with the book "Gliding" by Derek Piggott published in
about 1958 and now I think in its 6th edition).

This book covers the technical knowledge which the BGA thinks glider pilots
should have, and is required reading for BGA rated instructors. The main
author is Steve Longland, and he had input from many others.

In chapter 5 "The placard, structure and flight limitations" there is a
section starting on p.155 "The effects of changes in air density".
In this section an explanation is given as to why the Vne is related to True
Air Speed and not to Indicated Air Speed. I do not claim to fully
understand it myself, but I certainly intend always to obey.
The conclusion is:
"Avoiding flutter.
"The practical rule of thumb is that you should reduce the glider's Vne by
"1.5% for every 1,000ft above sea level. If your glider's Vne is 128kt,
"then at 20,000ft the ASI reading corresponding to TAS of 128kt is 90kt,
"and at 30,000ft it will be 70kt. ....."

If you read the earlier section in the same chapter about test flying, you
will see that the glider is not tested to Vd (Design dive speed) but only to
Vdf (Demonstration design speed) which is 95% of Vd and that the placard
speed Vne is 90% of Vd.
To quote from the book: "If the glider's Vne is 130kt, it has only ever been
6.5kt faster, once, when it was new, in ideal conditions, and flown by a
specially trained test pilot."

If anyone thinks this is wrong, could we please have a reasoned argument and
not just abuse.

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


"Arnold Pieper" wrote in message
.com...

Gents,

As far as the pilot is concerned, VNE is always read directly as an IAS
limit, that's why it's painted on the ASI as a radial line.
I've never seen any remarks about VNE as "VNE is XXX at Sea Level at ISA".
There is no such thing.

VNE is always good as an Indicated figure, except at altitudes and
airspeeds where compressibility comes into play, in which case MMO
(Maximum Mach Operating speed) becomes the limiting factor, usually well
above our speeds. That happens at a certain altitude, up to which the
pilot uses the Indicated VNE as a limit, then after that the MMO.


Exception :
Certain models of sailplanes have limitations in IAS with altitude for
various reasons, (Flutter is not the only factor in determining VNE).
When a sailplane does have this limitation, it will be expressed so in
their manuals, and there will be a table of limiting IAS x Altitude.

The Jantar Std 2 is not one of these, so, VNE is good as an IAS as high as
it will go.

The bottom-line is that it dependent on each design, but VNE is not a TAS
figure, whoever told you so, doesn't know what he/she is talking about.

AP

Mark James Boyd wrote:

But I must say I don't entirely understand WHY flutter
is based on TAS.

it's not. It is only because the IAS at which flutter happens is likely
to vary with altitude (it may be lower or higher !) that some
manufacturers and/or authorities limit the VNE at a constant TAS above
2000 or 3000 m (i.e. the altitude where tests have been conducted)


I also don't know if the IGC cares
if Vne is exceeded during a world record.

IGC don't care of exceeding any limit, with the exception of legal
day/night flight rules.

I think there is still a provision that the record may only be validated
if the glider lands back in one piece (that rule was set after some
altitude gains in CuNimbs where the pilot had jumped with the barogramm
after his glider broke ;-)

Only in championships you must have a valid permit-to-fly and respect
the limitations of your glider (weight, etc.)


--
Denis
Private replies: remove "moncourrielest" from my e-mail address
Pour me répondre utiliser l'adresse courriel figurant après
moncourrielest" dans mon adresse courriel...

W.J. (Bill) Dean (U.K.). wrote:

No.

No to what ???


The BGA have produced a book

Oh, I see... it written in a book ! So it is certainly true ;-)


--
Denis
Private replies: remove "moncourrielest" from my e-mail address
Pour me répondre utiliser l'adresse courriel figurant après
moncourrielest" dans mon adresse courriel...

This seems to me to be some arbitrary way of staying conservative.
High altitude research is NOT an early 80s affair, I don't even know about
any such research during the 80s.

The Sierra Wave project was done during the 50s in the Owens Valley of Ca
with very old gliders that have been flown to 45000ft, altitudes at which,
according to this calculation, they would barely be able to fly.
However, curiously enough none of them flutter themselves to pieces.

To make a long story short :
-Look at the ASI on any turboprop or even some turbocharged aircraft, and
you will see that they fly at TAS much faster than the VNE painted on their
ASI.

Example : Twin Commander, VNE=255Kt (it's on it's ASI), Cruise TAS = 280Kt
to 300Kt.

The same holds true for all airplanes that fly up to the 20s and higher,
which aviation has been doing since WWII.


Look at the manual of some gliders, that do have the limitation on IAS with
Altitude.
You will see that the table of IAS is not correcting the VNE as a TAS value.

Nowhere in aviation VNE is considered a TAS value.


"W.J. (Bill) Dean (U.K.)." wrote in message
...
No.

The BGA have produced a book published 2002 by A & C Black, London titled
"Gliding - The British Gliding Association Manual", ISBN 0-7136-5947-5
(not to be confused with the book "Gliding" by Derek Piggott published in
about 1958 and now I think in its 6th edition).

This book covers the technical knowledge which the BGA thinks glider
pilots
should have, and is required reading for BGA rated instructors. The main
author is Steve Longland, and he had input from many others.

In chapter 5 "The placard, structure and flight limitations" there is a
section starting on p.155 "The effects of changes in air density".
In this section an explanation is given as to why the Vne is related to
True
Air Speed and not to Indicated Air Speed. I do not claim to fully
understand it myself, but I certainly intend always to obey.
The conclusion is:
"Avoiding flutter.
"The practical rule of thumb is that you should reduce the glider's Vne by
"1.5% for every 1,000ft above sea level. If your glider's Vne is 128kt,
"then at 20,000ft the ASI reading corresponding to TAS of 128kt is 90kt,
"and at 30,000ft it will be 70kt. ....."

If you read the earlier section in the same chapter about test flying, you
will see that the glider is not tested to Vd (Design dive speed) but only
to
Vdf (Demonstration design speed) which is 95% of Vd and that the placard
speed Vne is 90% of Vd.
To quote from the book: "If the glider's Vne is 130kt, it has only ever
been
6.5kt faster, once, when it was new, in ideal conditions, and flown by a
specially trained test pilot."

If anyone thinks this is wrong, could we please have a reasoned argument
and
not just abuse.

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


"Arnold Pieper" wrote in message
om...

Gents,

As far as the pilot is concerned, VNE is always read directly as an IAS
limit, that's why it's painted on the ASI as a radial line.
I've never seen any remarks about VNE as "VNE is XXX at Sea Level at
ISA".
There is no such thing.

VNE is always good as an Indicated figure, except at altitudes and
airspeeds where compressibility comes into play, in which case MMO
(Maximum Mach Operating speed) becomes the limiting factor, usually well
above our speeds. That happens at a certain altitude, up to which the
pilot uses the Indicated VNE as a limit, then after that the MMO.


Exception :
Certain models of sailplanes have limitations in IAS with altitude for
various reasons, (Flutter is not the only factor in determining VNE).
When a sailplane does have this limitation, it will be expressed so in
their manuals, and there will be a table of limiting IAS x Altitude.

The Jantar Std 2 is not one of these, so, VNE is good as an IAS as high
as
it will go.

The bottom-line is that it dependent on each design, but VNE is not a
TAS
figure, whoever told you so, doesn't know what he/she is talking about.

AP

Ok,

Firstly VNE is very much limited by TAS not IAS. If
you understand the maths behind how an ASI works then
you will know that the ASI indicates a TAS based on
an assumed air density equivalent to sea level. TAS
is the speed that affects flutter, IAS is simply a
gash estimate of TAS which is reasonable at low altitudes.
Hence the rules of thumb for safe flight at altitude.

Secondly, ground speed at altitude is much higher than
TAS due to lower air density and can be greatly affected
by very high velocity winds at altitude. This is how
high average speeds can be achieved without exceeding
TAS VNE. Try looking at your GPS groundspeed when at
high altitude, it should be much higher than your IAS
even when the wind effect is removed.

I suspect that the VNE of these aircraft will be calculated
based on IAS at cruising altitude, That is why TAS
is not mentioned. Sailplanes normally operate at a
low cruising altitude so VNE is calculated based on
IAS at (i think) 5000ft. That is why a factor has to
be applied for higher altitudes. (read Fundamentals
of Sailplane Design if you want to check)


At 19:54 09 December 2003, Arnold Pieper wrote:
This seems to me to be some arbitrary way of staying
conservative.
High altitude research is NOT an early 80s affair,
I don't even know about
any such research during the 80s.

The Sierra Wave project was done during the 50s in
the Owens Valley of Ca
with very old gliders that have been flown to 45000ft,
altitudes at which,
according to this calculation, they would barely be
able to fly.
However, curiously enough none of them flutter themselves
to pieces.

To make a long story short :
-Look at the ASI on any turboprop or even some turbocharged
aircraft, and
you will see that they fly at TAS much faster than
the VNE painted on their
ASI.

Example : Twin Commander, VNE=255Kt (it's on it's ASI),
Cruise TAS = 280Kt
to 300Kt.

The same holds true for all airplanes that fly up to
the 20s and higher,
which aviation has been doing since WWII.


Look at the manual of some gliders, that do have the
limitation on IAS with
Altitude.
You will see that the table of IAS is not correcting
the VNE as a TAS value.

Nowhere in aviation VNE is considered a TAS value.


'W.J. (Bill) Dean (U.K.).' wrote in message
...
No.

The BGA have produced a book published 2002 by A &
C Black, London titled
'Gliding - The British Gliding Association Manual',
ISBN 0-7136-5947-5
(not to be confused with the book 'Gliding' by Derek
Piggott published in
about 1958 and now I think in its 6th edition).

This book covers the technical knowledge which the
BGA thinks glider
pilots
should have, and is required reading for BGA rated
instructors. The main
author is Steve Longland, and he had input from many
others.

In chapter 5 'The placard, structure and flight limitations'
there is a
section starting on p.155 'The effects of changes
in air density'.
In this section an explanation is given as to why
the Vne is related to
True
Air Speed and not to Indicated Air Speed. I do not
claim to fully
understand it myself, but I certainly intend always
to obey.
The conclusion is:
'Avoiding flutter.
'The practical rule of thumb is that you should reduce
the glider's Vne by
'1.5% for every 1,000ft above sea level. If your
glider's Vne is 128kt,
'then at 20,000ft the ASI reading corresponding to
TAS of 128kt is 90kt,
'and at 30,000ft it will be 70kt. .....'

If you read the earlier section in the same chapter
about test flying, you
will see that the glider is not tested to Vd (Design
dive speed) but only
to
Vdf (Demonstration design speed) which is 95% of Vd
and that the placard
speed Vne is 90% of Vd.
To quote from the book: 'If the glider's Vne is 130kt,
it has only ever
been
6.5kt faster, once, when it was new, in ideal conditions,
and flown by a
specially trained test pilot.'

If anyone thinks this is wrong, could we please have
a reasoned argument
and
not just abuse.

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


'Arnold Pieper' wrote in message
om...

Gents,

As far as the pilot is concerned, VNE is always read
directly as an IAS
limit, that's why it's painted on the ASI as a radial
line.
I've never seen any remarks about VNE as 'VNE is
XXX at Sea Level at
ISA'.
There is no such thing.

VNE is always good as an Indicated figure, except
at altitudes and
airspeeds where compressibility comes into play,
in which case MMO
(Maximum Mach Operating speed) becomes the limiting
factor, usually well
above our speeds. That happens at a certain altitude,
up to which the
pilot uses the Indicated VNE as a limit, then after
that the MMO.


Exception :
Certain models of sailplanes have limitations in
IAS with altitude for
various reasons, (Flutter is not the only factor
in determining VNE).
When a sailplane does have this limitation, it will
be expressed so in
their manuals, and there will be a table of limiting
IAS x Altitude.

The Jantar Std 2 is not one of these, so, VNE is
good as an IAS as high
as
it will go.

The bottom-line is that it dependent on each design,
but VNE is not a
TAS
figure, whoever told you so, doesn't know what he/she
is talking about.

AP

From DG website DG1000 flight manual:

http://www.dg-flugzeugbau.de/index-e.html
==========
Warning: At higher altitudes the true airspeed is higher
than the indicated airspeed, so VNE is reduced with
altitude according to the table below, see also section
4.5.5.

Altitude in [m] 0-3000 4000 5000 6000 7000
8000
VNE indicated km/h 270 256 243 230 217
205

Altitude in [ft] 0-10000 13000 16000 20000
23000 26000
VNE indicated kts. 146 138 131
124 117 111

-------
Simon.

19:54 09 December 2003, Arnold Pieper wrote:
This seems to me to be some arbitrary way of staying
conservative.
Look at the manual of some gliders, that do have the
limitation on IAS with Altitude.
You will see that the table of IAS is not correcting
the VNE as a TAS value.

Nowhere in aviation VNE is considered a TAS value.