Dave has about 250 HP
  when  he is   running about 45 inches of Hg. With a p-port my guess
  that would go   to about 300 HP. Dave has done nothing on drag
  reduction so far.   I can get to 300 HP NA if I go up to a 3.17:1
  and turn 8000 to 9000   RPM with a p-port. The red line on the RX8
  engine is 9000 RPM.

  Both Dave, I and others. RV tail flutter. We all agree on this. To go
  faster than 230 MPH we need to fix the tail first.

  We spoke to an expert on this RV4 RV6 problem at Reno.


  Consequently I am in the process of redesigning the vertical and rudder
    in carbon fiber to make it stronger and stiffer without adding any
    weight.
    I spoke to the people in Oxnard today that built the Kis and a
    lot of other aircraft like early Lancairs. They have an oven and
  vac bag   facilities. They agreed to do it. For some strange reason
  you do not  hear   about flutter on composite airplanes. At least I
  have no heard about it.
  I also consulted with my carbon fiber expert Alex Kozlof this morning.
    Alex and his son won the Little America cup race in a carbon cat Alex
    designed.
    Alex is also a distributor of uni carbon and a pilot. More on this
   later.
  Paul Lamar


  "For some strange reason you do not  hear   about flutter on composite
  airplanes"

  Mmm, maybe.  It depends on what types you look at.  There are a number
  of plastic sailplanes that have suffered flutter.  As well, (and I
  hate to even mention it), a couple of Rutan canard type airplanes have
  experienced flutter.  In the case of the Rutan airplanes, I believe
  the common cause was overweight (and/or under balanced) control
  surfaces (improper build).

  One thing that plastic airplanes have going for them is that the skins
  are usually thicker than they would be for a comparable metal
  structure (I believe).  This helps from a column/buckling/compression
  rigidity standpoint (even if the material itself may be less rigid).
  As well, in the case of the Rutan designs, the airfoil structures are
  built on foam cores which means that oil canning is reduced compared
  to metal.

  All that said, both types of structures can be designed to avoid
  flutter over a reasonable speed range.  It's obviously critical that
  they be built properly.  And I don't think either has a significant
  edge in terms of weight, at least not using materials and methods
  available to the home builder.


  Matt-


  Well put Matt.

  Vacuum bag is not all that hard to do. Here is a .032 carbon layup
  that has significant advantages over .032 aluminum. Uni carbon
  spar caps are a decided advantage.

  There is a lot of evidence out there that the unbalanced aluminum
vertical
  tails on the RV4 and RV6 are marginal. I was considering redesigning them
  in vacuum bagged carbon with balance weights. In the mean time I will
  stick with going less than what Dave did at Reno. Namely 229 MPH.
  Either that or I will buy a parachute :)

  -------------------------------------------------------

  I need to put these carbon numbers from the jpg in context.

  .032 aluminum weighs about .1 pound per cubic inch.
  A foot square sheet of .032" is 4.6 cubic inches.
  That computes to .46 pound per square foot of .032 sheet aluminum.
  From the jpg 4 layers of carbon would be .032 and weigh
  .24 pounds per square foot.  The skin weight is by far the largest
  contributor to the weight of an aircraft structure. In theory
  then the tail would weigh half as much. Of course to balance
  the rudder one would have to add it's weight in lead.

  The stiffness of vacuum bagged carbon laminate is 1.5 times that
  of the same thickness in aluminum.

  Unidirectional carbon tensile and compressive strength  as used in
  the spar caps would be 150,000 psi.

  2024 T351 Aluminum starts to take a permanent bend at 41,000 psi.

  Perhaps the biggest advantage of composites are it's lack of crack
  propagation.

  www.ornl.gov/~webworks/cpr/v823/rpt/106099.pdf

  All this is why Airbus and Boeing spent so much R&D money building
  airliners and the 787.

  As for the future large improvements may be possible.
  It might be possible to sew several layers of carbon cloth
  together before impregnating it with the resin infusion method to make
  it even stronger as far as de-lamination is concerned.

  Paul Lamar



 Do rudders need to be mass balanced as well as aerodynamically
 balanced?  I always thought elevators and ailerons are mass balanced
 because if the force of gravity pulling the surface down causes a
 deflection of the surface (as on an unbalanced elevator), it could set
 up sympathetic vibration at certain speeds..  I guess you have to
 worry about the slip/skid forces while banked - knife-edge flight.
 When wings level or coordinated flight, I suspect the mass balance of
 a rudder doesn't matter.



 Regards,

 Matt-

 The consensus on that seems to be yes.
 I think the reason is lateral accelerations of the tail cause
 rudder deflections which can result in oscillation.

 Lets say the tail goes to the right side causing the aircraft
 to yaw left. When it is stopped by
 the vertical fin the inertia of the rudder deflects it outward
 causes the aircraft yaw right.... accelerating the tail towards
 the left side. When it gets to the left side limit it starts all
 over again.

 I noticed in Daves RV6 when flying with the auto pilot
 on and maybe with it off the tail would wag from side
 to side. If you put your feet on the pedals and held
 the rudder fixed the oscillations went away.

 My C182 does not do that.

 Paul Lamar



Your point about reaction mass is a good one.  That makes sense -
hadn't thought of it that way.  Although I believe the real flutter
issue isn't about yawing the airplane, but about flexing the fin in a
springy way.

I don't think the 182 has a mass balanced rudder..  Could be wrong..
Maybe the newer ones (like yours) does, and the old ones (like mine)
doesn't.

The aerodynamic balance on a rudder reduces pedal forces.

In my opinion, the size of the fin on an RV, with respect to the
length of the moment arm (fuselage length), is too small.  I've ridden
a few hours in an RV-6 and noticed the same thing.  Lots of low wing
airplanes are like that, and I'm not sure why..  Maybe it's
interaction with the amount of dihedral they have.  Maybe Cessna just
put larger/longer fins on their airplanes.

Piper Tomahawks are terrible in this regard.  It's called the
"Bonanza-Boogie"..  Because V-Tail Bonanza's also do this.

My first long solo cross country for my private involved taking a
Tomahawk across the desert from Pocatello, ID to Boise, in the middle
of a June afternoon - lots of convective turbulence.  The Tomahawk
sets up a rhythmic swinging, which after more than an hour kinda gets
into your brain.  When I went home after the flight and took a shower,
with my eyes closed, my ears were telling my brain that I was still
swinging.  It took a few hours for that to go away.

Locking the pedals effectively adds the rudder to the overall fin
area.  A longer fuselage, moving the CG forward, a larger fin, a
thicker fin airfoil, or locking the rudder, all improve yaw stability.
 Or a yaw damper.  But, they all add weight and/or drag.

The RV4 flown solo looks like it should be better in this regard..
With someone in the back seat, I'll bet the RV4 and RV6 are about the
same.

Maule and Stinson go the other way - big fixed fins..  Which makes
them run out of rudder in much of a cross wind - these airplanes
strongly weathervane..



Matt-



Paul,
Interesting to note that the RV-10 rudder IS balanced and they still have
had an AD on it.
Bill Jepson