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