Jantars are back :)

"Jon Meyer" wrote in
message ...
| 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 am confused !
How can the ground speed exceed TAS when measured in still
air ?
TAS means TRUE Air Speed. i.e. the actual speed of the
aircraft through the particular parcel of air around the
aircraft. If this parcel of air is stationary with respect
to the ground, the ground speed of the aircraft must equal
the TAS.
Cheers, John G.

Arnold Pieper wrote:

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.

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]

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Eric Greenwell
Washington State
USA

Jon,

I don't like to come accross as arrogant, I'm sorry if I do, but you seem to
be confusing the issue.

IAS is what you see in your ASI.
TAS is the speed at which the aircraft is is moving trough the air (nothing
to do with groundspeed).

To obtain you TAS at any time during flight, you look at what your ASI is
indicating, then apply a correction based on altitude and oustide air
temperature. You can do that with an E-6B type computer.
If you don't have an OAT reading, you're out of luck, but the well-known 2%
per 1000ft will give you an approximation.

Groundspeed, on the other hand is the speed at which you move in relation to
the ground.
The Groundspeed is the result of your TAS plus (or minus) the wind
component.

When I say most Turboprops and Turbocharged airplanes fly at faster TAS than
their IAS VNEs,
that's exactly what I mean :
At altitudes of 20k plus, their TAS will be higher than their indicated VNE,
regardless of what the Groundspeed is.

The Twin commander will be reading Groundspeeds of 350Kt when eastbound
(tailwind) and it may read as little as 230Kt westbound.
But in both cases, with the same power setting, it will be doing 290Kt TAS,
which is more than the 255Kt VNE.

Meanwhile, their ASI will be showing 180Kt to 190Kt, depending on altitude
and powersetting, well below the VNE of 255Kt.

Same thing holds true for all these airplanes. Other examples :
TBM-700, cruises at 290Kt TAS (not groundspeed), while the VNE is 265Kt.
King Air 350, cruises at 300Kt TAS, VNE is 265Kt.





"Jon Meyer" wrote in message
...
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.

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.

--
-----
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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.

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:

Secondly, ground speed at altitude is much higher than
TAS due to lower air density
^^^^^ ^^^ ^^^^^^^

Are you joking ?


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

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...