Question - rudder flutter ?

"F. Baum" wrote in news:8149eb30-36fe-4721-8858-
:

On Dec 25, 10:45*am, Bertie the Bunyip wrote:

Big flexible surfaces can flutter all by themselves *as shown in that
clip of the A6 I posted and that might be what you mean about the Cl CG
relationship. In fact that's one of the reasons that a wing mounted
engine is a good idea and why the pods on jet airliners (which have the
structural rigidity of Jel-lo) are mounted out in front. The change in
CG helps dampen the flutter in the same way as mass balance on an
aileron would.

Bertie, What are you trying to do here? Do you realize that your
respectful aviation related post will ruin this list for guys like Jay
and his petty abusive OT posts ?

God, I hope he told my IP tha! I clearly need to be stopped.


Bertie

On Dec 26, 11:55 am, Bertie the Bunyip wrote:


Control surface flutter is caused by a lack of rigidity in the wing.
Control surface flutter probably won't fail the surface itself, it wll
fail the surface it's attatched to. Your elevators prolly won't fall
off, but your stab will probsbly fail, or even the fuselage, long before
th ehinge lets go.


Here's a case to think about:
http://www.flyingmag.com/article.asp...print_pag e=y

"It's hard to understand how a coat of paint can add three-quarters of
a pound to a surface area of only around 15 square feet, but the
National Transportation Safety Board's (NTSB) report on the accident
passes over this oddity without comment. Apparently, however,
investigators hypothesized that the other control surfaces, including
the mostly vanished rudder, might have been similarly overweight and
underbalanced, and Grob's analysts affirmed that rudder flutter was
possible under these conditions. The probable cause of the accident,
the NTSB concluded, was "failure of maintenance personnel to rebalance
the flight controls after the airplane had been repainted, which
resulted in rudder flutter and inflight breakup of the airplane."

The hinge allowed the rudder to drop off first followed by other bits.

Cheers

Yipes.. *The only thing I don;t like about those Zenairs is they are
very light indeed. That 6061 is beer can stuff really, but the airplanes
have a good record, so...
You might not need the STOL performance unless you're flying out of your
own driveway, though. they're pretty slow....

Yup, slow. Check this out. If you could have a "favorite" NTSB
accident report, then this would be my favorite:

"As the pilot approached the vicinity of the destination airport, he
noted that the winds were about 35 to 40 miles per hour (mph). In
order to land into the wind he opted to perform a landing on a ramp
area of the airport. The airplane touched down on the ramp's surface
with a forward groundspeed of about 3 mph. A side load was placed on
the left main landing gear, and the tire subsequently deflated. The
airplane veered to the left and pitched forward, resulting in damage
to the firewall. A weather reporting station in the area reported
winds at 24 mph, gusting to 28 mph."

There's a lot of these flying and they have been around since
something like 1985 or so. Not many NTSB reports and no fatals.

Anyway it just looks like good plain fun.

It's more common than you think. A lot of WX accidents, for instance, where
there is loss of control due to disorientation in cloud *often ended up in
an inflight breakup precipitated by a spiral dive or other stressful flight
condition. Next time you see an airplane scattered across several fields,
you can be relatively certain that flutter did at least some of the damage
on the way down.

And it even happens to people like Scott Crossfield.

"It's hard to understand how a coat of paint can add three-quarters of
a pound to a surface area of only around 15 square feet, but the
National Transportation Safety Board's (NTSB) report on the accident
passes over this oddity without comment. Apparently, however,
investigators hypothesized that the other control surfaces, including
the mostly vanished rudder, might have been similarly overweight and
underbalanced, and Grob's analysts affirmed that rudder flutter was
possible under these conditions."

Hell.

Why paint?

Here's a case to think about:http://www.flyingmag.com/article.asp...cle_id=112&pri...

From this same article:

Flutter is usually associated with high speed, but low-speed aircraft
can also flutter if they are sufficiently flexible. In 1991 a
homebuilt amphibian crashed during an early test flight after one of
its external-airfoil flaperons fluttered, causing the left wing to
separate from the airplane. The builder-pilot was wearing a parachute,
but he bailed out at such a low altitude that there was insufficient
time for it to open. In this case, the builder had elected not to
install the "strongly recommended" balance weights on the flaperons
because they would make the airplane heavier, and he "felt that they
were not needed."

This makes me remember something I read in William Wynne's Corvair
conversion manual: "It's not the probability of being right, it's the
cost of being wrong."

I think I'll stick to the plans and have it checked by a third party.

"Stefan" wrote in message
...
Bravo Two Zero schrieb:

What is rudder flutter ?

This is rudder flutter. (Actually, it's aileron flutter, but the principle
is the same.)

http://www.youtube.com/watch?v=kQI3AWpTWhM

I should add that this was a test flight done by the factory test pilot
and the wings were reinforced for this test. Standard wings would have
fallen off pretty quickly, as you can see in related videos.


Thanks Guys espec. Bertie the Bunyip.

So the next question would be, if you experience rudder flutter in flight,
what would you do ( apart from prey !!!)

On Dec 26, 7:38 pm, "Bravo Two Zero" wrote:
"Stefan" wrote in message

...

Bravo Two Zero schrieb:

What is rudder flutter ?

This is rudder flutter. (Actually, it's aileron flutter, but the principle
is the same.)

http://www.youtube.com/watch?v=kQI3AWpTWhM

I should add that this was a test flight done by the factory test pilot
and the wings were reinforced for this test. Standard wings would have
fallen off pretty quickly, as you can see in related videos.

Thanks Guys espec. Bertie the Bunyip.

So the next question would be, if you experience rudder flutter in flight,
what would you do ( apart from prey !!!)

Reduce speed ASAP

Cheers

WingFlaps wrote in
:

On Dec 26, 11:55 am, Bertie the Bunyip wrote:


Control surface flutter is caused by a lack of rigidity in the wing.
Control surface flutter probably won't fail the surface itself, it
wll fail the surface it's attatched to. Your elevators prolly won't
fall off, but your stab will probsbly fail, or even the fuselage,
long before th ehinge lets go.


Here's a case to think about:
http://www.flyingmag.com/article.asp...article_id=112
&print
_page=y

"It's hard to understand how a coat of paint can add three-quarters of
a pound to a surface area of only around 15 square feet,



Pick up a can of paint sometime!


This is a relatively common problem, believe it or not. There have been
lots of accidents over the years on repainted aicraft. When Bonanazas
started to come apart in numbers large enough to catch the NTSB's
attention, at least a few of them were down to repaints without correct
balancing done afterwards.


but the
National Transportation Safety Board's (NTSB) report on the accident
passes over this oddity without comment. Apparently, however,
investigators hypothesized that the other control surfaces, including
the mostly vanished rudder, might have been similarly overweight and
underbalanced, and Grob's analysts affirmed that rudder flutter was
possible under these conditions. The probable cause of the accident,
the NTSB concluded, was "failure of maintenance personnel to rebalance
the flight controls after the airplane had been repainted, which
resulted in rudder flutter and inflight breakup of the airplane."

The hinge allowed the rudder to drop off first followed by other bits.


Yeah, but it probably fractured the fuselage just before it departed the
aircraft.. I remember reading the report on a lass glider that got
flutter momentarily in the elevator. The pilot managed to land it to
find the aft half of the fuselage was almost completely gone, the tail
held on only by threads.
I had a low freq tye of flutter once. I was flying a Twin Beech on a
sched pax service and after airborne on the second sector a hinged
inspection panel on the outboard section of the top wing opened (the
airplane had been on an inspection) and the panel, probably about
10"X6" flapped up and down and caused a sympathetic motion in the
aileron, probably a couple of Hz or so. There's a name for this kind of
flutter, but I can't remember it. We slowed down and the freq decreasd,
but I don't think it ever went away. It was more than a bit disturbing,
but fortunately the flight was relatively short.


Bertie

wrote in
:

Here's a case to think
about:http://www.flyingmag.com/article.asp...&article_id=11
2&pri...

From this same article:

Flutter is usually associated with high speed, but low-speed aircraft
can also flutter if they are sufficiently flexible. In 1991 a
homebuilt amphibian crashed during an early test flight after one of
its external-airfoil flaperons fluttered, causing the left wing to
separate from the airplane. The builder-pilot was wearing a parachute,
but he bailed out at such a low altitude that there was insufficient
time for it to open. In this case, the builder had elected not to
install the "strongly recommended" balance weights on the flaperons
because they would make the airplane heavier, and he "felt that they
were not needed."

This makes me remember something I read in William Wynne's Corvair
conversion manual: "It's not the probability of being right, it's the
cost of being wrong."

I think I'll stick to the plans and have it checked by a third party.

Good plan. You'll find that the Acrosport probably doesn't have balance
weights on it because it's so rigid, but the 701 more than likely will have
quite large ones. IIRC all the control surfaces have very large aerodynamic
balance areas anyway, so it's very simple to add stips of lead in the
leading edge to bring them to the specified balance.
What you usually do is get a postage scale and put it under the trailing
edge after painting and add lead untio it gets to the specified weight.


Bertie