Jantars are back :)

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?
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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

Well, the relationship of flutter to IAS and TAS is certainly a
puzzle to me.

Somewhere I got the understanding that IAS, in a sense, indicates the
impact rate (pressure) of molecules on the aircraft, and thus in
thinner air an aircraft will "actually" (TAS) be flying faster to
receive the same air molecule impact rate (pressure).

TAS, on the other hand, indicates, in a sense, indicates the speed
at which the air molecules are moving past the aircraft - something
quite independent of just how MANY air molecules are passing by
the aircraft in a given amount of time.

Further, I have had the impression that flutter is a consequence of
the speed of the aircraft through the air (molecules) (TAS) rather
than the number of air molecules that happen to be impacting the
aircraft in a given amount of time (IAS).

So, I have always considered it prudent to view VNE due to FLUTTER
to be a TAS airspeed, not an IAS airspeed.

Have I been wrong about this?

"Jim" wrote in message
...
Well, the relationship of flutter to IAS and TAS is certainly a
puzzle to me.

Somewhere I got the understanding that IAS, in a sense, indicates the
impact rate (pressure) of molecules on the aircraft, and thus in
thinner air an aircraft will "actually" (TAS) be flying faster to
receive the same air molecule impact rate (pressure).

True AFAIK, and the effectiveness of controls responds to this pressure.
Control flutter limitations are a function of IAS. Some sailplanes have
been designed with and even retrofitted with dampers. Bear in mind that
age, wear, repair, compromised mass balances, and paint can impact this.
(Not mutually exclusive changes)

TAS, on the other hand, indicates, in a sense, indicates the speed
at which the air molecules are moving past the aircraft - something
quite independent of just how MANY air molecules are passing by
the aircraft in a given amount of time.

Yes, and the center of pressure that generates lift shifts as a result and
may twist (maybe better un-twist) the wing. IIRC, the FL500 Grob had an
extra lamination or two of glass in the wings so it could fly faster than
stall speed at extreme altitude. In my DG-100 at speeds 120kts under
3000m, the amount of downward deflection at the tips was really impressive
and a bit unnerving. I don't recall similar deflection at 8500m at similar
TAS, but, like most everyone else, I have little empirical evidence.

Further, I have had the impression that flutter is a consequence of
the speed of the aircraft through the air (molecules) (TAS) rather
than the number of air molecules that happen to be impacting the
aircraft in a given amount of time (IAS).

Flutter in an elastic mode and is dependent on wing design. As I understand
it, a Lear Jet's Vne is based on IAS with Mach limits. The wings are quite
short and stiff compared to a sailplane, and have greater torsional
resistence by design. The twist in glider wings is there to provide more
benign handling, however, as in the OSTIV paper I've referenced previously,
sailplane design is a compromise of performance and engineering. The
elastic mode may be the limiting factor and engineering a sailplane to
perform at altitude as a Lear Jet would increase both weight and cost
unacceptably (unless your name is Fossett maybe). Since the sailplane
spends 99% of it's service life 6000m and a Lear Jet spends 90% of its
service life 8000m, each is designed appropriately.


So, I have always considered it prudent to view VNE due to FLUTTER
to be a TAS airspeed, not an IAS airspeed.

Perfectly safe as a conservative view.

Have I been wrong about this?

The conjecture in the OSTIV paper was that (IAS+TAS)/2 was safe and that
this envelope might extend to 0.8 * TAS. However, there are a couple of
Nimbus 4 incidents that might suggest adoption of the prudent view. There
are also some 15m designs with little twist and stiff wings that might be
real rocket rides. I have a little time in a Jantar Std 2 and found it
nimble, a bit stiff, and honest in performance. I also found that things
like the aileron hinges wear a bit more quickly than some other gliders, so
pressure effects might be of interest. Too many factors and not enough
evidence to say who's right or wrong or taking unacceptable risks. The
third mode of flutter is pilot induced. Control inputs at high altitude and
speed could potentially induce either of the other two modes, I suppose.

Anyway, that's my take,

Frank Whiteley
Colorado

Jim wrote:

So, I have always considered it prudent to view VNE due to FLUTTER
to be a TAS airspeed, not an IAS airspeed.

Have I been wrong about this?

No, it is prudent, but as several have pointed out, it may be
unnecessarily conservative. That's because the flutter usually occurs
somewhere between IAS and TAS, and not strictly by TAS.

Personally, I'd use TAS on "older" (designed/certified 20+ years ago)
gliders, and the glider's handbook for "newer" (designed/certified
within the last 10 or so years, unless I knew specifically what the
older glider was designed and tested to. My reasoning is the older
certifications were not as stringent in this area as they are now.

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

Eric Greenwell
Washington State
USA

It is a TAS, this is the reason it occurs at a lower IAS as the altitude
increases. Without some sort of sophisticated computations it is very
difficult to determine TAS. IAS is easy to see and use.