Question - rudder flutter ?

What, like a Kitfox?


CH701.

There's a guy has his own grass strip just east of Burnet (shows up as
Deiterich on the San Anton sectional), he's got a 701 and I hope to go
out and take a look at it pretty soon. Just need to find the time.

It is very small but it looks quite fun for STOL operations.

Only thing about it is that, even though you only need a short space
to land in, if you do loose your engine there better be a field within
a couple of miles -- glide ratio little better than a piano ...

wrote in news:b417bb1d-52bc-4423-8300-
:

What, like a Kitfox?


CH701.

There's a guy has his own grass strip just east of Burnet (shows up as
Deiterich on the San Anton sectional), he's got a 701 and I hope to go
out and take a look at it pretty soon. Just need to find the time.

It is very small but it looks quite fun for STOL operations.

Only thing about it is that, even though you only need a short space
to land in, if you do loose your engine there better be a field within
a couple of miles -- glide ratio little better than a piano ...


You'll get one of those thngs out of anywhere, but if the field is, say,
400 yards or more, you'll get an acrosport in and out of it easily. Even
shorter if ou're sharp.

Bertie

You'll get one of those thngs out of anywhere, but if the field is, say,
400 yards or more, you'll get an acrosport in and out of it easily. Even
shorter if ou're sharp.


Suffice to say I'm pretty excited about the AcroSport, it's
performance, and how you can fly it. Plus, it's a fabric covered
biplane. How kick azz is that? Well, very.

It's a longer term project though.

I wonder if you could use a Mazda 13B -- should fit in the weight / hp
range. Not many moving parts to break, either. Hmm. Don't know if
anybody's done aerobatics with a 13B though.

I want to give a shot at plans building the 701. There's a nice set of
videos that show quite a bit of the 701 construction sequence from
those Canadian guys at Can Zac. I might buy some of it as a kit to
save some time though.

I suppose these thoughts are way off topic. To bring it back: I know
of only one Zenith STOL that had structural failure probably due to
flutter as a result of exceeding Vne: somebody dived an 801 at the
ground and apprently ripped the wings off on the way down. NTSB report
says both pilot and passenger had a good bit of THC in their blood ...
only fatalities I know of in the STOL series from Zenith and clearly
pilot caused.

On Dec 26, 6:45 am, Bertie the Bunyip wrote:
WingFlaps wrote in news:7896a421-7658-44d1-
:





On Dec 26, 5:31 am, Bertie the Bunyip wrote:

It's done all the time, but it doesn;t have to be at one end and it
doesn't have to be a horn. It also doesn't have to be a 100% balance
if
the performance doesn't neccesitate it or if the stab or wing is
rigid
enough for flutter not to be an issue within the speed envelope.
But for anythng that goes very fast, you have to have 100% balancing,
which means it's statically balanced at the hinge line.

Even more than 100% is needed in some common planes (e.g. the
Bonanza). In this case a wing roll will be dampened automatically (I
think) -I'd guess it makes the plane feel more docile, but perhaps
you know this plane and can comment. But I disagree with you about one
point, the center of lift of the control surface is still important. I
think this is because the control linkages aren't stiff enough to stop
a control surface flutter. (I am keeping to the question of control
surface flutter and trying to avoid the coupling in of the flying
surface the control is attached to.)
I think you would agree that if the Cl of the surface were ahead of
it's COG control surface flutter would be guaranteed (no linkages
would be stiff enough to control it)? I believe that this mode may be
excited by the disturbed air flowing through the gap between control
surface and wing which slightly reduces the surface lift on one side
which then couples into the potential for the flutter. It would be
felt as a vibration in the stick whereas a wing flutter _might_ not be
felt through the stick at all (esp. if the control surface is 100%
balanced!!)

Nice to have a bit of flying/tech discussion instead of troll lures.

Anthony must be out begging. I was bored.



Cheers

leads to . I'll agree that normally the Cl will be behind the COG for
a typical triangular section control surface but if a dynamically
balanced design is sought, the Cl moves much closer to the hinge line
and then the COG may not be far enough forward. I'd suspect this might
have been a big problem with some early WW1 type rudders that looked
to be highly balanced.

Don;t think what you're saying about the Cl and the GG realationship of
the surface is correct, but I don't know for sure. The way most control
surfaces are constructed would pretty much gauruntee that that is the
case ( skinny at the back) but it's the wing or stab that is th emore
important ingredient there anyway.

Yes, I agree that the wing or stab is important -but control surface
flutter (maybe more common in models with loose linkages) is bad too.
Loss of the elevator is probably a terminal failure.

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.

Yes that's what I'm thinking about.

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.

A good point, I hadn't thought about engine pylons serving that
function.

Cheers

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.

Relative to where it would start unloaded. IOW if you were overspeeding as
a result of an unusual attitude recovery and you were pulling like hell at
the same time, the flutter would appear at a lower airspeed than it would
if you were just in a dive with the wing loaded at 1 G. Both of these
speeds should still be over red-line.

Ah, I see, that makes it more clear. Interesting how flutter sounds so
benign (like a butterfly!) but is actually more like a quick trip to
the graveyard. However it must be a rare phenomenon because I never
came across the term in my PPL training and I don't remember even
seeing this topic discussed in any AOPA article in the last 2 years.

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 ?
FB

wrote in news:b98d38db-fc5c-4cc8-9272-
:

You'll get one of those thngs out of anywhere, but if the field is,
say,
400 yards or more, you'll get an acrosport in and out of it easily.
Even
shorter if ou're sharp.


Suffice to say I'm pretty excited about the AcroSport, it's
performance, and how you can fly it. Plus, it's a fabric covered
biplane. How kick azz is that? Well, very.

It's a longer term project though.

I wonder if you could use a Mazda 13B -- should fit in the weight / hp
range. Not many moving parts to break, either. Hmm. Don't know if
anybody's done aerobatics with a 13B though.


You could, but It's easier and cheaper to use an airplane engine at the
end of the day. Unless it's your "thing" to mess with things like that.
If you're just looking to save money, forget it.

I want to give a shot at plans building the 701. There's a nice set of
videos that show quite a bit of the 701 construction sequence from
those Canadian guys at Can Zac. I might buy some of it as a kit to
save some time though.

Yeah, someone in my group built one fairly quickly. I haven't flown it
but I've eyed them up over the years. Not very fast, though.
You could prolly get an acrosport cheap enough partly finished or one
needing a recover.

I suppose these thoughts are way off topic. To bring it back: I know
of only one Zenith STOL that had structural failure probably due to
flutter as a result of exceeding Vne: somebody dived an 801 at the
ground and apprently ripped the wings off on the way down. NTSB report
says both pilot and passenger had a good bit of THC in their blood ...
only fatalities I know of in the STOL series from Zenith and clearly
pilot caused.


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....


Bertie

WingFlaps wrote in news:b113861f-e022-4153-b0e5-
:


Don;t think what you're saying about the Cl and the GG realationship
of
the surface is correct, but I don't know for sure. The way most
control
surfaces are constructed would pretty much gauruntee that that is the
case ( skinny at the back) but it's the wing or stab that is th emore
important ingredient there anyway.

Yes, I agree that the wing or stab is important -but control surface
flutter (maybe more common in models with loose linkages) is bad too.
Loss of the elevator is probably a terminal failure.


You're misunderstanding what I'm saying.

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.

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.

Yes that's what I'm thinking about.

Those are unlikely in light planes.

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.

A good point, I hadn't thought about engine pylons serving that
function.



Bertie

wrote in
:



Relative to where it would start unloaded. IOW if you were
overspeeding as a result of an unusual attitude recovery and you were
pulling like hell at the same time, the flutter would appear at a
lower airspeed than it would if you were just in a dive with the wing
loaded at 1 G. Both of these speeds should still be over red-line.

Ah, I see, that makes it more clear. Interesting how flutter sounds so
benign (like a butterfly!) but is actually more like a quick trip to
the graveyard.

It is. I know someone who died doing aerobatics which induced flutter. It
was a Sonerai. Aileron flutter. It snapped the spar and the wing warapped
around the top of the canopy precluding his exit. He rode it in trying to
get it to roll to et the wing off and securing the airplane for impact at
the end. He was using this little VW powered airplane to try and compete in
competition aerobatics.It wasn't up to the task. I think there was a bit of
re-design of the aircraft after that.

However it must be a rare phenomenon because I never
came across the term in my PPL training and I don't remember even
seeing this topic discussed in any AOPA article in the last 2 years.

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.



Bertie