why is Vne a TAS?

The limiting airspeed, Vne is the speed where the airplane structure still
meets the certification requirements. For light aircraft it is normally set
at 90% of Vd (demonstrated dive speed) The limit could be where the
maximium design gust equals the structural limit of the airplane or it could
be the highest speed where a reasonable flutter margin is present. As
others have said, it could be related to critical Mach number although this
is unlikely to be the limiting factor for slow, light airplanes. If the
limit is for gust loading, then it is based on CAS. If it is based on
flutter or Mach limit, it is based on TAS. Even if it is based on TAS, it
is given in IAS in airplanes without a Mach meter. or barber pole. The IAS
limit is based on the ceiling of the aircraft.. The same thing can be
accomplished by placards (reduce Vmo (or Vne) by x knots for every thousand
feet above xx,xxx' altitude.

The "coffin corner" is where stall and Mmo (not Vne) come together. I don't
think that there is an aiplane that can reach the coffin corner that even
has a Vne.

There is some discussion of this topic in one of Barry Schiff's books.

Mike

"private" wrote in message
news:6FOUe.465897$s54.126911@pd7tw2no...
Hello Todd,

In a recent thread on R.A..S.(interesting question about stall and
airspeed)
that morphed into a discussion about coffin corner, Todd explained,

"Flutter limits high true airspeed operations, and it is possible to get
to
the coffin corner where stall speed and Vne approach each other."

and Jim suggested we "consider Vne as a TAS".

Can I have the groups wisdom and further explanation of the reasons for
this
and of how Vne changes with altitude.

Should we be doing preflight calculations of Vne IAS reductions when
planning aerobatics at 9000 ft. or soaring or high speed flight at
15-18,000
ft?

Thanks in advance

Mike Rapoport wrote:

I don't think that there is an aiplane that can reach the coffin
corner that even has a Vne.

Airplanes probably not. Aircraft, yes.

Stefan

Which ones?

Mike
MU-2


"Stefan" wrote in message
...
Mike Rapoport wrote:

I don't think that there is an aiplane that can reach the coffin corner
that even has a Vne.

Airplanes probably not. Aircraft, yes.

Stefan

Mike Rapoport wrote:

Which ones?

I had thought of some older gliders which have pretty low Vne. After I
had hit the send button, it dawned to me that they also have a pretty
low stall speed, though...

Stefan

"Stefan" wrote in message
...
Mike Rapoport wrote:

Which ones?

I had thought of some older gliders which have pretty low Vne. After I had
hit the send button, it dawned to me that they also have a pretty low
stall speed, though...

Stefan

I was thinking of sailplanes too. Hard to imagine a sailplane with a
critical Mach number equating to a IAS of 45kts or so even at FL500.

The key to this issue (IMHO) of Vne is that it may be based on any one of a
number of limiting factors, some of which are related to CAS and some to
TAS. The airplanes where Mach number is an issue (that I am familiar with)
have a Vmo and Mmo but don't use a Vne.

Mike
MU-2