I am trying to teach myself to knife edge using an Aero-Works 540T
Edge. Good airplane. I know I am supposed to give it opposite rudder
from the aileron roll but I can't stop the roll. What am I doing wrong?
On Mon, 15 Oct 2007 09:09:12 -0700, Ted wrote in
You have to "take the roll out" by returning the aileron
Leave the rudder alone for a little while. Just practice
1/4 rolls: roll to knife edge, pause, roll inverted,
pause, roll to the other knife edge, pause, roll upright.
Working on getting the roll stopped at the right points.
The pause doesn't have to be long--just long enough for
you to see what it takes to stop the roll.
If you roll from upright to knife edge using right
aileron, left rudder will be on top.
If you roll from upright knife edge using left
aileron, right rudder will be on top.
OH! It's possible that you have some "coupling" with
the rudder, so that when you input it, it causes the
plane to roll as well as to yaw.
I'm not very good at mixing out rudder coupling myself.
It can involve a small percentage of aileron and/or
elevator mixed with the rudder as the master channel.
I've heard and read a lot about it, but haven't had
a lot of success taming my bad knife-edge planes
(especially a Hangar 9 Ultra Stick). I tend to
just fish around with the sticks until I reach some
equilibrium. It's pretty ugly. :o(
At any rate, you can test the response to rudder
from upright. Put in right or left rudder and
see how the plane reacts to just that input.
It may roll as well as yaw and it may dive
or climb, too. You may need to go past neutral
on the aileron stick to hold the plane in knife
You can also roll the plane to knife edge,
wait a half-second to make sure that it has stopped
rolling, then input the correct top rudder. If
it starts rolling at that point, then you know
you have coupling issues.
The rudder to roll coupling is pretty much the same in straight and
level and knife-edge
(nit-pickers will note that all the interactions are not linear, and
the above is approximate ... hence the "pretty much")
So if you mix it out in level flight, you're 95% of the way there to
mixing it out of knife edge. Mixing it out in straight and level is
much easier to do pilot workload wise though
So, fly your plane straight and level, at a medium or medium/fast
Take a couple runs across the field without touching the controls to
make sure the trims are perfect, since the accuracy of the rest
depends on a good baseline.
Then, just input pure rudder stick (full or medium deflection), don't
pull or push the elevator, and especially don't touch the ailerons.
The plane will make a skidding turn. It will also likely bank into or
out of the turn (most likely into it)
The bank is what you are trying to eliminate.
You do that by using a Rudder to aileron mix. It will likely be a
small negative number, but it may vary.
On the ground check that moving your rudder makes your ailerons move
SLIGHTLY to oppose the rolling motion that you were getting.
Fly it again and repeat the rudder stick activation. Hopefully it
will bank less.
adjust the amount of the mix until moving the rudder stick gives you a
pure skidding turn, with no change in bank angle.
It is wise to put this mix on a switch, so that you can enable it
during aerobatics, but turn it off for landing.
The other Marty