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