Jantars are back :)

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

"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...

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 ;-)

Denis

C'mon, is that really true? How did he prove he was
still in the "aerodyne" when the barograph got its highest
altitude? Maybe he was just a big piece of hail.
My gosh, maybe he used the baro to tell his altitude
to make sure he didn't pull his chute too early...LOL

I think you misunderstood what I meant.
The IAS VNE at cruising altitude of 20000ft is 272kts
(assuming as I said before that IAS VNE is at cruising
altitude) . This equates to a TAS of 364kts. Which
means that VNE is 364kts TAS.
So in this aircraft at sea-level you could technically
go to 364kts IAS and still be below VNE.

again I'll re-iterate that VNE is influenced by TAS
(and Mach Number) NOT by IAS, which is merely an approximation
of TAS valid at sea level.

Your calculations were fine, it was just the assumption
that VNE would be based on sea level conditions rather
than cruise conditions that i think was wrong. I could
be wrong too, but it just seems logical that for an
aircraft that spends most of its time at 20000ft the
VNE should be based on IAS at this altitude to make
things simpler for the pilot.

Regards,
Jon.


p.s. Dont get any ideas about going above IAS VNE at
sea level in your glider - its VNE is normally based
on IAS at 5000ft leaving very little margin.

Jon Meyer wrote:
I think you misunderstood what I meant.
The IAS VNE at cruising altitude of 20000ft is 272kts
(assuming as I said before that IAS VNE is at cruising
altitude) . This equates to a TAS of 364kts. Which
means that VNE is 364kts TAS.
So in this aircraft at sea-level you could technically
go to 364kts IAS and still be below VNE.

Did you really mean "Vne", or just flutter related aspects of Vne?
Obviously, the potential aerodynamic loads will be about 80% greater at
364kts TAS at sea level.

again I'll re-iterate that VNE is influenced by TAS
(and Mach Number) NOT by IAS, which is merely an approximation
of TAS valid at sea level.

But isn't aerodynamic pressure an important factor (i.e, "influence") in
flutter? And that is what IAS measures?
--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Jon,

The only way to reach VNE is by diving, not by fling staight and level in
cruise.
And you can dive from 1000ft or from very high altitudes.
All the while the VNE is that radial line painted on you ASI, which reads
Indicated Airspeed and has to be respected as you see it (not in your mind
or in some calculator).
The exception for limits related to flutter in Gliders are done in the form
of a table so that you don't have to do mental math.

VNE is usually set at some % below whatever fenomenon determined it.
It might be different things for diffent aircraft, sometimes as simple as a
windshield that will not resist above a certain pressure, or even the
position of the glider (VNE for inverted flight is different from upright).
So, if you dive and your ASI pointer goes above that radial line that marks
VNE,
bad things will happen, regardless of altitude.

The ASI "underreads" at any altitude above Sea Level @ ISA conditions.
The aircraft surfaces "feel" the air the same way the ASI does, which means
most
aerodynamic reactions respond to the same Indicated Air Speed, regardless of
altitude.
That's why your Stalling Speed is at the bottom of the green arc, and it is
the same at 1000ft or at 10000ft.
Same holds true for gear extension/operation speed limits, flap speed
limits,
storm window speed limits and so forth.

The stuff that is REQUIRED by regulations to be painted on the ASI, are all
reactions that remain constant with Indicated Airspeed, that's why they are
painted on it.

The events that will occur at different IAS with different altitudes are NOT
painted on the ASI exactly because they vary.
They are related to Power (HP, SHP or LBS of Thrust), which always reduces
with altitude.
Examples are Vx and Vy for power airplanes, Vmc (for twins) and things like
that.

Not so with VNE witch is painted-on.
The reactions to flutter on gliders will however, require "new" VNEs at
higher altitudes, if you review all recent postings on these "tables of VNE
with altitude" it will become clear.

AP


"Jon Meyer" wrote in message
...
I think you misunderstood what I meant.
The IAS VNE at cruising altitude of 20000ft is 272kts
(assuming as I said before that IAS VNE is at cruising
altitude) . This equates to a TAS of 364kts. Which
means that VNE is 364kts TAS.
(.....................)

At 00:36 12 December 2003, Arnold Pieper wrote:
Jon,

The only way to reach VNE is by diving, not by fling
staight and level in
cruise.

Hope you dont mean that literally Arnold! I had a go
in a microlight once that had a cruise speed only 10kts
below its VNE!!- very easy to exceed vne in straight
& level. Plus in a glider if the wave/ridge is strong
enough you can get to VNE can't you?

Apart from that I think you explained the whole altitude/
density/ flutter /vne faff quite well.

Some people around here have incredibly complicated
ways of explaining things! With that in mind, for
the next debate can I suggest an explanation of :

Transition level, transition altitude, transition layer
and altimeter settings!? QFE QNH SPS....

AAARHGH NO! on second thoughts spare us!! :-) :-)



And you can dive from 1000ft or from very high altitudes.
All the while the VNE is that radial line painted on
you ASI, which reads
Indicated Airspeed and has to be respected as you see
it (not in your mind
or in some calculator).
The exception for limits related to flutter in Gliders
are done in the form
of a table so that you don't have to do mental math.

VNE is usually set at some % below whatever fenomenon
determined it.
It might be different things for diffent aircraft,
sometimes as simple as a
windshield that will not resist above a certain pressure,
or even the
position of the glider (VNE for inverted flight is
different from upright).
So, if you dive and your ASI pointer goes above that
radial line that marks
VNE,
bad things will happen, regardless of altitude.

The ASI 'underreads' at any altitude above Sea Level
@ ISA conditions.
The aircraft surfaces 'feel' the air the same way the
ASI does, which means
most
aerodynamic reactions respond to the same Indicated
Air Speed, regardless of
altitude.
That's why your Stalling Speed is at the bottom of
the green arc, and it is
the same at 1000ft or at 10000ft.
Same holds true for gear extension/operation speed
limits, flap speed
limits,
storm window speed limits and so forth.

The stuff that is REQUIRED by regulations to be painted
on the ASI, are all
reactions that remain constant with Indicated Airspeed,
that's why they are
painted on it.

The events that will occur at different IAS with different
altitudes are NOT
painted on the ASI exactly because they vary.
They are related to Power (HP, SHP or LBS of Thrust),
which always reduces
with altitude.
Examples are Vx and Vy for power airplanes, Vmc (for
twins) and things like
that.

Not so with VNE witch is painted-on.
The reactions to flutter on gliders will however, require
'new' VNEs at
higher altitudes, if you review all recent postings
on these 'tables of VNE
with altitude' it will become clear.

AP


'Jon Meyer' wrote in message
...
I think you misunderstood what I meant.
The IAS VNE at cruising altitude of 20000ft is 272kts
(assuming as I said before that IAS VNE is at cruising
altitude) . This equates to a TAS of 364kts. Which
means that VNE is 364kts TAS.
(.....................)

In article ,
Mark Parker wrote:

Plus in a glider if the wave/ridge is strong
enough you can get to VNE can't you?

Yery easily. Most gliders have descent rates less than 1000 feet per
minute at Vne, and the better ones are more like 500 fpm. That's 5 - 10
knots down, which means that a 10 - 20 knot wind hitting a reasonably
steep hill (30 degrees, sin = 0.5) is enough to keep a glider at Vne in
level flight. And if the hill is 45 or 60 degrees...

-- Bruce

Mark James Boyd wrote:


C'mon, is that really true? How did he prove he was
still in the "aerodyne" when the barograph got its highest
altitude? Maybe he was just a big piece of hail.
My gosh, maybe he used the baro to tell his altitude
to make sure he didn't pull his chute too early...LOL

Well, the record may have been validated as a free fall altitude loss by
the International Parajumping Commission ;-)

--
Denis
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