At the risk of inciting a religious war, I found site backing up my
previous claim that VNE is dependent on TAS not IAS nor CAS:
http://www.auf.asn.au/groundschool/flutter.html<http://www.auf.asn.au/gro
undschool/flutter.html>
13.2 Standard airspeed limitations<>
If Vne is expressed in terms of true airspeed then its value remains the
same no matter what the [density] altitude. However though indicated
airspeed reflects dynamic pressure it understates the true airspeed so
if the structural limitations which define Vne for an aircraft type are
particularly associated with the distribution of forces associated with
flow velocity then the specified Vne as an indicated airspeed has to be
decreased as altitude is increased - to adjust it to the true airspeed,
which latter is about 1.5% greater than IAS/CAS for every 1000 feet of
altitude, see rule of thumb
#2<http://www.auf.asn.au/groundschool/umodule2.html#cas_tas>.
For most light aircraft it is reasonable that only one Vne is specified
in the Pilot's Operating Handbook or Flight Manual and that value may
have been calculated for a 'normal' cruising altitude, say 5000 feet,
rather than ISA mean sea level.
If uncertain about a particular aircraft multiply the (density)
altitude, in 1000s of feet, by a factor of 1.5 to get the percentage
DECREASE to apply to the specified Vne for a corrected Vne appropriate
to the altitude. For example if altitude is 8000 feet and specified Vne
is 100 knots then 8[000] =D7 1.5 = 12%. Corrected Vne = 88% of 100
= 88 knots IAS/CAS.
Table 1 is a normal calculation of corrected Vne, you can see that the
difference between the 140 knots specified and the corrected Vne is
significant and that it appears quite possible for turbocharged low drag
aircraft to exceed corrected Vne in level flight at higher altitudes.
Vne as a maximum airspeed applies only for smooth atmospheric conditions
and for gentle control movements; even vertical gusts associated with
mild turbulence or control movements greater than say 25% travel will
lead to some nasty surprises, if operating close to but below Vne. At
such high speed the controls are very effective with a high possibility
for over-control applying extreme loads to the structures and some
aircraft control systems provide an inadequate feedback of the load
being exerted i.e. a high load can be applied with a relatively low
stick force..
Be aware: deliberately exceeding Vne is the realm of the test pilot -
who always wears a parachute!
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