You don't have to exceed VNE to see a high enough true airspeed that could
cause flutter.

VNE is indicated airspeed, not true airspeed. As you go higher and the

air
gets thinner, your IAS can remain the same -- and well within the green arc
-- while your true airspeed goes higher.

With flutter, it is the true speed of the air passing over the airframe that
is critical -- because it has to do with the frequency of the

vibrations.

Just like an engine has certain critical frequencies, it will be susceptible
at certain engine speeds.

If you're flying at 12,000 feet and you encounter a gust, you should be okay
in terms of structural integrity as long as you are in the green arc. That's
because even though your true airspeed is higher, the dynamic pressure

your
airframe is seeing is the same as it would be at a lower speed and

higher

air pressure. So the increased angle of attack caused by the gust will

not
break your airplane, as long as you are in the green arc.

However, this does not protect you against flutter. If you encounter

that

same gust while going at the same speed, well within the green, it will not
break your airplane, but it could set your tail vibrating. And because

you
are going at a higher true airspeed, the frequencies may not damp out

as

they would at lower true airspeed.

Have a look at that Van's article; it has a first-hand report from an

RV4

pilot who was going high to climb over some clouds. With his IAS well in the
green, he got a scary shaking in his tail as he executed a 360 to

avoid

towering cumulus. And this guy should be a pretty good stick -- his day job
is driving an F-16.

So even if you stay well within VNE you could still get flutter if your true
airspeed is high enough.


Regards,

Gordon.

So what you are saying is one cannot relie on the markings of
one's airspeed indicator. Does the FAA know about that?
Perhaps he built the airplane himself and he did not balance
things properly. Either that the RV4 has insufficient margin
of safety in the tail flutter which I find hard to believe
given all the people flying them and the total absence of
flutter induced crashes. Another possibility is the tail was
painted by somebody that did not rebalance the surfaces.

Paul Lamar ...No rotor no motor.

My take on Vans published Vne limits was that it was only partially
related to flutter- the real limiting factors involved structural
strength margins given industry standard parameters of planning for
~50ft/min downdraft/up drafts in turbulent air at the various
airspeeds.  The 9series RV's have longer, more efficient Roncz-style
wings designed to withstand 4.6 Gs; they perform very well with less HP
but structural limits cap the top speed.  The choice of the 160HP-max
engine pretty much limits performance below Vne at higher altitudes,
unless they are turbocharged.  FWIW, I have a friend who was flying off
his initial hours in a new 9A that popped all of the rivets on the
elevator trailing edge in a 230 (dont know kt or mph) indicated airspeed
dive from 9000 ft altitude- I assume flutter was the reason.  He had no
warning as the plane was flying beautifully before he felt the sudden
vibration.

The short wide wings on the RV 7and 8's have a higher 6G rating and are
therefore rated for larger engines and higher top speeds.  I believe the
RV8 has a top speed/Vne around 230, although the cruise speed specs are
only a few mph higher than the 9's.

Mike Parker

These are all cruise and top speed issues. You don't have to open the
throttle
all the way if you don't want to. However the HP is there when you need
it.
Namely getting off the ground under all conditions expeditiously and
climbing
over clouds and mountains. It is analogous to a car with a lot of power.
Who
drives at 150 MPH? But you need the HP margin at 60 MPH to pass a truck
quickly on
a two lane road.

Paul Lamar


So you're the guy that passes like a bat outta hell on a two lane
highway! :)
Rick Irwin

Yep! The less time I spend in the left lane the better :)