Jantars are back :)

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.

Thank you Simon,

Exaclty like I said in a previous message :
The table below confirms it, It is NOT simply the VNE corrected as TAS.

Go ahead and check this table if you will :
100Kt IAS @ 26000ft is LEGAL, ALLOWED and SAFE as per the manual.
That's because table shows 111Kt IAS as being the limit at this altitude.

Now calculate your TAS for this condition (100Kt IAS @ 26000ft), with
various range of temperatures.
Here's what you will get as TAS for the various temperatures :
163Kt @ -45 Celsius (way below Standard),
167Kt @ -35 Celsius (aprox. std temperature for this altitude)
170Kt @ -25 Celsius (above Standard)

All of these TAS are higher than the original Low-altitude IAS VNE of
146Kt, painted on the ASI.
Which confirms what I said : the VNE is NOT simply to be corrected as a TAS
figure.

This limitation in IAS with Altitudes are "NEW" values for VNE, due to
flutter or whatever the reason with altitude.
But the resulting TAS at these conditions will be higher than the original
VNE.




"Simon Kahn" wrote in message
...
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.

Arnold Pieper wrote:

Thank you Simon,

Exaclty like I said in a previous message :
The table below confirms it, It is NOT simply the VNE corrected as TAS.

Go ahead and check this table if you will :
100Kt IAS @ 26000ft is LEGAL, ALLOWED and SAFE as per the manual.
That's because table shows 111Kt IAS as being the limit at this altitude.

Now calculate your TAS for this condition (100Kt IAS @ 26000ft), with
various range of temperatures.
Here's what you will get as TAS for the various temperatures :
163Kt @ -45 Celsius (way below Standard),
167Kt @ -35 Celsius (aprox. std temperature for this altitude)
170Kt @ -25 Celsius (above Standard)

All of these TAS are higher than the original Low-altitude IAS VNE of
146Kt, painted on the ASI.
Which confirms what I said : the VNE is NOT simply to be corrected as a TAS
figure.

This limitation in IAS with Altitudes are "NEW" values for VNE, due to
flutter or whatever the reason with altitude.
But the resulting TAS at these conditions will be higher than the original
VNE.

Perhaps you missed this post:

Quoting from the manual for my Schleicher ASH 26 E:

"4.5.8 High altitude flight

Flutter tests were carried out at about 2000 m msl. As the ASI
under-reads at increasing altitude, but since flutter limits for light
aircraft are determined by the true air speed, the following limitations
apply to high altitude flights:

[table of IAS at Vne for altitudes to 13000m follows]

If above airspeed limits given as IAS are regarded the true air speed
above 3000 m altitude will remain constant at 300 km/h = 162 knots."

So for this glider, the Vne in TAS does increase to 10,000', then
remains at a constant 162 knots TAS. They are quite explicit about the
Vne depending on TAS.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Eric,

Thanks, I see how explicit they are about it.
DG chose to not get into specifics, because the story is a bit more complex
than that.

The VNE of your glider is 146Kt (IAS), but above 10000' you should start
observing other IAS limits, that translate into 162Kt TAS due to flutter
considerations.

Therefore, simply using 146Kt as a TAS value is not correct, which is what
was being suggested earlier, and is what I had trouble with.

Nowhere in Aeronautic literature is VNE defined as a TAS value, it HAS to be
presented to the pilot as Indicated.

In high-performance aircraft where flutter is less of a consideration, there
is no such table for high altitude, VNE is always VNE, until MMo becomes a
factor.



"Eric Greenwell" wrote in message
...
Arnold Pieper wrote:

Thank you Simon,

Exaclty like I said in a previous message :
The table below confirms it, It is NOT simply the VNE corrected as TAS.

Go ahead and check this table if you will :
100Kt IAS @ 26000ft is LEGAL, ALLOWED and SAFE as per the manual.
That's because table shows 111Kt IAS as being the limit at this
altitude.

Now calculate your TAS for this condition (100Kt IAS @ 26000ft), with
various range of temperatures.
Here's what you will get as TAS for the various temperatures :
163Kt @ -45 Celsius (way below Standard),
167Kt @ -35 Celsius (aprox. std temperature for this altitude)
170Kt @ -25 Celsius (above Standard)

All of these TAS are higher than the original Low-altitude IAS VNE of
146Kt, painted on the ASI.
Which confirms what I said : the VNE is NOT simply to be corrected as a
TAS
figure.

This limitation in IAS with Altitudes are "NEW" values for VNE, due to
flutter or whatever the reason with altitude.
But the resulting TAS at these conditions will be higher than the
original
VNE.

Perhaps you missed this post:

Quoting from the manual for my Schleicher ASH 26 E:

"4.5.8 High altitude flight

Flutter tests were carried out at about 2000 m msl. As the ASI
under-reads at increasing altitude, but since flutter limits for light
aircraft are determined by the true air speed, the following limitations
apply to high altitude flights:

[table of IAS at Vne for altitudes to 13000m follows]

If above airspeed limits given as IAS are regarded the true air speed
above 3000 m altitude will remain constant at 300 km/h = 162 knots."

So for this glider, the Vne in TAS does increase to 10,000', then
remains at a constant 162 knots TAS. They are quite explicit about the
Vne depending on TAS.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

"Arnold Pieper" wrote in
message
om...
| Eric,
|
| Thanks, I see how explicit they are about it.
| DG chose to not get into specifics, because the story is a
bit more complex
| than that.
|
| The VNE of your glider is 146Kt (IAS), but above 10000'
you should start
| observing other IAS limits, that translate into 162Kt TAS
due to flutter
| considerations.
|
| Therefore, simply using 146Kt as a TAS value is not
correct, which is what
| was being suggested earlier, and is what I had trouble
with.
|
| Nowhere in Aeronautic literature is VNE defined as a TAS
value, it HAS to be
| presented to the pilot as Indicated.
|
| In high-performance aircraft where flutter is less of a
consideration, there
| is no such table for high altitude, VNE is always VNE,
until MMo becomes a
| factor.

I think the statement that you should use TAS as the limit
for Vne rather than IAS, comes from earlier times, when less
was known about instabilities such as flutter. I have heard
it said that something between IAS and TAS is what affects
flutter, but the percentage will change from one aircraft to
another, so it is safe to use TAS as a Vne limit. No one
said it was an exact statement, but it is known to be
*safe*.
TAS is calculated by power pilots as a matter of course for
flight planning, so the conversion is well known and easily
available on the various flight computers ("prayer wheels"
and such)
It is sometimes mandated by local Authorities that a table
based on manufacturer's data or TAS is provided.
The Gliding Federation of Australia has such a stipulation,
tied to the installation of oxygen in a glider. Part of the
installation is a placard to be fixed in the cockpit which
shows the table of Indicated Vne versus altitude, derived
either from the manufacturer's table or calculated using TAS
conversion for a standard atmosphere (pressure and
temperature with height)
Whether either table is "right" is immaterial, as long as
the table gives the pilot *safe* information.
Cheers, John G.

Arnold Pieper wrote:

Eric,

Thanks, I see how explicit they are about it.
DG chose to not get into specifics, because the story is a bit more complex
than that.

Even though they are explicit about it, I'm not sure if the reason is
regulatory or physical. An aeronautics fellow told me flutter doesn't
strictly follow TAS, but is somewhat higher, but testing at high
altitudes is needed to confirm exactly where it is.

The VNE of your glider is 146Kt (IAS), but above 10000' you should start
observing other IAS limits, that translate into 162Kt TAS due to flutter
considerations.

Again, I'm not sure where the 10,000' comes from: possibly below that,
Vne is restricted to IAS for reasons other than flutter, but above that,
flutter becomes the critical factor.

Therefore, simply using 146Kt as a TAS value is not correct, which is what
was being suggested earlier, and is what I had trouble with.

Nowhere in Aeronautic literature is VNE defined as a TAS value, it HAS to be
presented to the pilot as Indicated.

My glider manual does require a placard giving that information.

In high-performance aircraft where flutter is less of a consideration, there
is no such table for high altitude, VNE is always VNE, until MMo becomes a
factor.

It would be interesting to know why there is a difference, but I suspect
it might the regulatory requirements for different categories.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Sorry,

Misprint, The Groundspeed at altitude will be equal
to TAS and therefore much higher than the IAS (not
TAS as I earlier stated). That is why your groundspeed
will be higher than IAS.
This was simply meant in answer to the confusion of
how someone could achieve an average speed of 250+kph
at 20000ft nwithout exceeding VNE at altitude.

I am not confused about the issues concerning flutter.
Flutter is dependant on TAS. IAS is an arbitrary value
based on sea level air density. I still believe that
the reason you are confused is that the VNE of the
'high performance' aircraft you describe is specified
as IAS at cruising altitude - not at sea level. Therefore
your calculation of TAS being higher than VNE is flawed
because you have taken the wrong air density as your
datum.




At 20:12 09 December 2003, Jon Meyer wrote:
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.

Jon Meyer wrote:
Sorry,

I am not confused about the issues concerning flutter.
Flutter is dependant on TAS. IAS is an arbitrary value
based on sea level air density. I still believe that
the reason you are confused is that the VNE of the
'high performance' aircraft you describe is specified
as IAS at cruising altitude - not at sea level. Therefore
your calculation of TAS being higher than VNE is flawed
because you have taken the wrong air density as your
datum.


So Vne of power planes is a figure which
describes Vne at the highest cruising altitude? So
this means that actual Vne at a lower altitude may
be faster? Hmmm...this seems to make sense for power
planes...

Unfortunately gliders don't have an altitude limited by
power. So this is much stickier. I noticed the PW-5
initially had a 15,000 foot altitude limitation (1998?)
and there were some vigorous complaints. Then
apparently the limitation was removed (don't know
exactly why). Perhaps test pilots determined the
"flutter" was caused by gaps in the elevator connection
and not actual "flutter."

But what this seems to suggest is that a manual which
does not specifically address Vne and altitude should
be viewed with skepticism. A grob 102 at 49,000 feet
pushed to Vne makes you a test pilot...

Excellent discussion! Fantastic fountain of (sometimes
varied) opinions and advice. It's also nice to
see the thoughts converging, and I can visualize
a lot of readers shuffling through arcane texts
asking "is that really true?" Thanks for your posts...

"Mark James Boyd" wrote in message
news:3fd75f4f$1@darkstar...
Jon Meyer wrote:
Sorry,

I am not confused about the issues concerning flutter.
Flutter is dependant on TAS. IAS is an arbitrary value
based on sea level air density. I still believe that
the reason you are confused is that the VNE of the
'high performance' aircraft you describe is specified
as IAS at cruising altitude - not at sea level. Therefore
your calculation of TAS being higher than VNE is flawed
because you have taken the wrong air density as your
datum.


So Vne of power planes is a figure which
describes Vne at the highest cruising altitude? So
this means that actual Vne at a lower altitude may
be faster? Hmmm...this seems to make sense for power
planes...

Unfortunately gliders don't have an altitude limited by
power. So this is much stickier. I noticed the PW-5
initially had a 15,000 foot altitude limitation (1998?)
and there were some vigorous complaints. Then
apparently the limitation was removed (don't know
exactly why). Perhaps test pilots determined the
"flutter" was caused by gaps in the elevator connection
and not actual "flutter."

But what this seems to suggest is that a manual which
does not specifically address Vne and altitude should
be viewed with skepticism. A grob 102 at 49,000 feet
pushed to Vne makes you a test pilot...

Excellent discussion! Fantastic fountain of (sometimes
varied) opinions and advice. It's also nice to
see the thoughts converging, and I can visualize
a lot of readers shuffling through arcane texts
asking "is that really true?" Thanks for your posts...
From my 2000 post on this topic.
quote
There was an interesting article in Technical Soaring a few years ago about
much of this. In gliders there is also an elastic flutter mode WRT the
center of pressure and location of the wing spar in modern composites and
the resultant bad twisting things when the threshold was reached. This is
separate from control and PIO induced flutter modes.

IIRC, this results from design/weight considerations, airbrake and ballast
tank placements, and optimization of designs [spar placement where
applicable] for operating 6000m most of
the time [like 99%]. The proposal of the article was for consideration of a
high
altitude VNe (with an adequate margin of safety) somewhat higher that TAS
VNe. I believe the formula was (VNe (TAS) + VNe (IAS)) / 2. I don't know
if this proposal has since been discredited or tested. The authors
postulated the actual safe zone extended up to something like 0.8 *
VNe(IAS).

AFAIK, no testing of gliders above 6000m is done by or required of
manufacturers. Thus, if you are heading really high, you're a test pilot.

I keep waiting for Technical Soaring archives to appear on CD-ROM. BTW
Larry, if you're lurking, what's the current status of this (IMVHO long
overdue) project?

[ADDED WRT to the above para: OSTIV is supposed to be working CD-ROM
distribution of old articles
according to my last contact about a year ago.]

Frank Whiteley
Colorado
/unquote

Jon,

My "calculation" of TAS being higher then VNE is flawed ???

It's simple. Real life scenario :
ASI has the VNE (painted on) at 255 kt.
Cruise IAS at 25000ft is 185Kt (well below the VNE).
OAT shows -25 celsius at this altitude.

The TAS calculation using any E6B computer shows TAS at this condition to be
272Kt.
I'll say again, TAS at this altitude is therefore 272kt.

If you were to reach VNE at this altitude, your TAS would be 364kt.
So you are IN FACT below VNE. Of course. That's the whole point.

The VNE painted on the ASI says 255Kt, but that is INDICATED, and someone
thought that was to be taken as TAS, which is wrong.




"Mark James Boyd" wrote in message
news:3fd75f4f$1@darkstar...
Jon Meyer wrote:
Sorry,

I am not confused about the issues concerning flutter.
Flutter is dependant on TAS. IAS is an arbitrary value
based on sea level air density. I still believe that
the reason you are confused is that the VNE of the
'high performance' aircraft you describe is specified
as IAS at cruising altitude - not at sea level. Therefore
your calculation of TAS being higher than VNE is flawed
because you have taken the wrong air density as your
datum.


So Vne of power planes is a figure which
describes Vne at the highest cruising altitude? So
this means that actual Vne at a lower altitude may
be faster? Hmmm...this seems to make sense for power
planes...