"Jim" wrote in message
news
On Wed, 09 Mar 2005 21:52:58 GMT, "Mike Rapoport"
wrote:


"T o d d P a t t i s t" wrote in message
. ..
"Mike Rapoport" wrote:

I've never heard of Vne being related to TAS, only IAS. It makes no
sense
to me. Could you provide a reference?

Vne is a fixed mark on the airspeed indicator and,
as such, doesn't move.

Despite the Vne mark on the altimeter, it definitely is not
a fixed IAS (or CAS) number. Nor is it always a fixed TAS
number. It is the number defined by the manufacturer that
is usually found in the flight manual. My sailplane has a
Vne that drops with altitude, and while it's closer to a
fixed TAS than IAS, it's not exactly either.

A fixed TAS makes sense because it is often flutter that
sets the Vne limit, and flutter is a timing related issue
that relates to TAS more closely than IAS.

"It is possible to fly without motors, but not without knowledge and
skill."
Wilbur Wright

So what is the mark on the airspeed indicator supposed to mean then? I
have
never seen anything in any of the flight manuals that I have (four)
referring to Vne going down with altitude. I am not disputing that it
does
but I am mystified as to why it isn't better explained in flight manuals.
Similiarly, Vmo is given as a single IAS number. In the MU-2 Vmo is
250kts
IAS at any altitude up to about 22,000' where the Mach limit takes over.
This is a large range of TAS. Is it perhaps actually related to Mmo
rather
than Vne as gliders don't have airspeed indicators with barber poles? Can
you give some examples wth real numbers and altitudes?

Mike
MU-2


Here is the information from the Flight Manual for the DG-500 glider.

Section 4.5.9 Flight at high altitude and at low temperatures:

...

2. Attention must be paid to the fact that at higher
altitudes the true airspeed is greater than the
indicated airspeed.
The max. speed Vne is reduced. See the
following table:

...

Altitude in ft. 0-6600 10000 13000 16000 20000
Vne IAS kts. 146 138 131 124
117

Hope this helps.



Thanks, it does. The question of what the red mark on powered airplanes
means remains. Is it Vne at the aircraft's ceiling? If it is Vne at sea
level then there should be some language in the flight manual warning of
this.

The reference to low temperatures is also interesting. Is the strength of
the glider's resin reduced at low temperatures?

Mike
MU-2