Question - rudder flutter ?

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.

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.

Cheers

On Dec 26, 5:44 am, Bertie the Bunyip wrote:

Anthony also probably knows it just backwards

Does his sim show flutter beyond Vne? I wonder how that effect is
conveyed to the 'pilot' .

Cheers

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.
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

WingFlaps wrote in news:a27e082e-83e1-4df1-a634-
:

On Dec 26, 5:44 am, Bertie the Bunyip wrote:

Anthony also probably knows it just backwards

Does his sim show flutter beyond Vne? I wonder how that effect is
conveyed to the 'pilot' .

You could program it as a learning tool, but all it would be.is a lesson,
not an experience.


Sims are programmed to do all sorts of things like that, but it might as
well be a balloon that opens up and says "You're fluttering" as anything
else.


Bertie

to support this cycle. The other way you can stem it is to make the stab
fin or wing very rigid and this is why biplanes can have as high a
redline as , say a Mooney might though the bipe might have no balance
area at all and the Mooney would. All the surfaces are too rigid to
allow the cycle to start.
You would think that a greater load on the surface, i.e, "G". would tend
to dampen the action, but the opposite is the case.
Flutter will appear at a lower speed if the surface has an aerodynamic
load on it.


So at a practical level, is it reasonable to say that avoiding a red-
lining of airspeed is sufficient to avoid flutter in small GA
airplanes? Or are there other things to watch out for in normal flight
to avoid flutter? I didn't quite follow the part about flutter at
lower speeds but thanks for the informative post,

On Dec 25, 10:44*am, Bertie the Bunyip wrote:
wrote in news:d6ec528a-01a1-4a71-a603-
:

The other way you can stem it is to make the stab
fin or wing very rigid and this is why biplanes can have as high a
redline as , say a Mooney might though the bipe might have no balance
area at all and the Mooney would.

Is this because of the welded 4130 tube structure?

No, the rigging. The wings on a bipe won't budge at all because of the
flying wires. Same for the stab. 4130 will flex really easily by itself.
You can bend it by hand!
But even the tail surfaces on those airplanes are braced at about half span
so they don't flex significantly. A cantilever aluminum or even a wood
structure will flex quite a lot so that must be taken into consideration if
you want any kind of reasonable redline.
That kind of exhausts my knowledge of the subject, but there are some guys
over in rec.aviation.homebuilt, amongst other places, that know this stuff
backwards and forwards.
Anthony also probably knows it just backwards

Bertie

Ah, bracing. So the vertical stabilizer of a 4130 is internally braced
by cable?

Well, I figure I'm going to order the plans for the AcroSport II, even
if I don't wind up building it as a first aircraft (or ever). $125
ain't exactly expensive. I spend more on wines for dinner every couple
of weeks.

I'll still probably go STOL first, it'll take a lot less time to
build.

The links to the wing flutter and failure were VERY edumacational. Vne
-- respect it with your life.

On Dec 26, 6:36 am, WingFlaps wrote:
On Dec 26, 5:44 am, Bertie the Bunyip wrote:

Anthony also probably knows it just backwards

Does his sim show flutter beyond Vne? I wonder how that effect is
conveyed to the 'pilot' .

His Vne is when the monitor falls off the desk

wrote in news:2615a64e-b660-42a1-a2a2-e09e08ff5b94
@i12g2000prf.googlegroups.com:


to support this cycle. The other way you can stem it is to make the stab
fin or wing very rigid and this is why biplanes can have as high a
redline as , say a Mooney might though the bipe might have no balance
area at all and the Mooney would. All the surfaces are too rigid to
allow the cycle to start.
You would think that a greater load on the surface, i.e, "G". would tend
to dampen the action, but the opposite is the case.
Flutter will appear at a lower speed if the surface has an aerodynamic
load on it.


So at a practical level, is it reasonable to say that avoiding a red-
lining of airspeed is sufficient to avoid flutter in small GA
airplanes?

Yeah. If the airplane itself is OK. I can't think of any other reason why
it would start.

Or are there other things to watch out for in normal flight
to avoid flutter? I didn't quite follow the part about flutter at
lower speeds but thanks for the informative post,


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.

Bertie

wrote in
:

On Dec 25, 10:44*am, Bertie the Bunyip wrote:
wrote in news:d6ec528a-01a1-4a71-a603-
:

The other way you can stem it is to make the stab
fin or wing very rigid and this is why biplanes can have as high a
redline as , say a Mooney might though the bipe might have no
balance area at all and the Mooney would.

Is this because of the welded 4130 tube structure?

No, the rigging. The wings on a bipe won't budge at all because of
the flying wires. Same for the stab. 4130 will flex really easily by
itself. You can bend it by hand!
But even the tail surfaces on those airplanes are braced at about
half spa
n
so they don't flex significantly. A cantilever aluminum or even a
wood structure will flex quite a lot so that must be taken into
consideration i
f
you want any kind of reasonable redline.
That kind of exhausts my knowledge of the subject, but there are some
guys

over in rec.aviation.homebuilt, amongst other places, that know this
stuff

backwards and forwards.
Anthony also probably knows it just backwards

Bertie

Ah, bracing. So the vertical stabilizer of a 4130 is internally braced
by cable?

No, I'm talking about airplanes like Cubs or homebuilt bipes with
externally wire braced tails. Having said that, I don't think the
Wittman Tailwind has externally braced tail surfaces and I'm pretty sure
the tail is 4130 tube and God knows it's fast, so I don't know how Steve
Wittman managed that.

Well, I figure I'm going to order the plans for the AcroSport II, even
if I don't wind up building it as a first aircraft (or ever). $125
ain't exactly expensive. I spend more on wines for dinner every couple
of weeks.

I'll still probably go STOL first, it'll take a lot less time to
build.

What, like a Kitfox?

Bertie

On Dec 25, 1:22*pm, george wrote:
On Dec 26, 6:36 am, WingFlaps wrote: On Dec 26, 5:44 am, Bertie the Bunyip wrote:

Anthony also probably knows it just backwards

Does his sim show flutter beyond Vne? I wonder how that effect is
conveyed to the 'pilot' .

His Vne is when the monitor falls off the desk

Heh, catastrophic failure.

I was goofing around with MSFT a couple of weeks ago. Downloaded a
182RG. It sucked, kinda, cause it was freeware.

Anyway I pushed past Vne. The plane started "shaking" --
uncontrollable oscillations which, I guess, might've led to it coming
apart. But I pulled out of the "dive" before that happened. I've had
the T-38 bust on me by "pulling up" too quickly at high simulated
speed.