Jantars are back :)

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...