"Aircraft
setup is a constant process really. Every time something
is changed, there is the chance it will affect something
else. Take your time, and work through it, you'll
find yourself fighting the airplane less during
a sequence, and that makes it much easier to score
well."
Sitting
at a recent IMAC contest, Mike Caglia (well known
FAI Pattern and 2000 Tournament of Champions Invitational
competitor) and I were discussing aircraft setup and
both of us came to the conclusion that few people
were really setting up their airplanes well. I think
much of this is simply due to not knowing how. Much
of this article deals with setup before flying the
airplane. After basic setup, it will take anywhere
from 30 - 50 flights to really dial in an airplane.
This seems like a lot but read on, and you'll see
why. While this article is based upon the JR PCM-10X
radio and it's programming references, the information
really is applicable to any modern computer radio.
The setup described here is for a precision setup
(not 3D or freestyle) but again the same theory can
be applied.
Start
With the Right Tools:
Probably
the most critical item needed to setup an airplane
properly is a control surface throw gauge. I use CRC
Throw Meters. You need to accurately determine how
much your surface moves. While it's possible to use
a ruler or protractor, throw meters make the job much
easier.
Throughout this process, you'll be making several
flights, and then changing and adjusting. It's important
that you change only one thing at a time and then
completely retest the airplane each time.
Step
1 - Setup the Airplane First:
The
setup of the airplane really starts during the building
process. The following is a minimal checklist to start
with. You may think of other things you want to add.
- Hinges:
Hinge lines should be straight and centered on
the surface.
- Pivot
Point of Control Horns: Control horns should
be setup such that the pivot point of the horn
is exactly on the hinge line to avoid building
in a differential.
- Servo
Arms: The arm on the servo should be exactly
parallel to the hinge line. Servo arms should
be switched around until you get the spline alignment
correct. Always try to avoid using the radio to
center the servos whenever possible.
- Seal
Hinge Lines: Hinge lines should be sealed
so no air can pass through. It doesn't matter
how tight you think it is, seal it on the bottom
with some covering. You want to minimize pushrod
slop as much as possible.
- Ball
Link Attachments: Use high quality ball link
attachments and machined aluminum servo arms for
the best setup.
- Proper
Weight and Balance: The model should also
be balanced properly before any of the flight
trimming starts. Try to find out about other people's
experience with your airplane to get the best
balance point. The aircraft should also be balanced
laterally if possible. Add small amounts of weight
to a light wingtip to correct it.
Step
2 - The Radio:
Start
With Fresh Memory:
First
off, let's start with a fresh model memory (or reset
the current memory) to ensure there isn't anything
left over in the airplane. Now setup the reversing
switches such that the controls move in the correct
direction. The amount they move isn't important right
now.
Now you have a fresh, very basic setup. What you
want to do now is ensure you're getting the maximum
resolution out of your servos. You should have your
high rate selected since this is a fresh memory
location. Select ATV (code 12) and set all used
channels up to 150% in both directions. Don't forget
the flap and aux channels if your using multiple
aileron or elevator servo setups.
This step allows for the maximum travel out of your
servos and therefore maximum servo resolution. Most
modern computer radios are 1024 radios, meaning
there are 1024 steps of servo resolution for it's
full range of travel. By running your ATV up to
maximum, you utilize all 1024 steps to command the
servos.
Aileron
Setup:
Mechanically
adjust your linkages so that your ailerons are perfectly
centered and get the maximum throw recommended by
the manufacturer. You'll probably have to move higher
up on the control horn, and closer to the center of
the servo arm. Here is where the CRC Throw Meters
come in. If all your initial building was straight
and true, you should have exactly the same throw in
either direction. If they're not exactly equal, mechanically
setup the lower of the two to be the correct deflection
and reduce the higher direction in the ATV setup screen
(code 12) so they're EXACTLY the same. Do this for
both ailerons independently of each other. Don't worry
about differential just yet.
Elevator
Setup:
The
procedure for elevator setup is the same as the ailerons.
Pay close attention to the center and throw. I setup
the maximum throw for precision flying (not 3D or
freestyle). Again this is probably going to require
long control horns, and short servo arms. Make sure
elevator throw is exactly equal in both directions.
Rudder
Setup:
Initially
setup the rudder to use its maximum available throw.
It's important to setup the rudder with the best mechanical
advantage possible to ensure good resolution and power.
You might adjust the throw later on, but for now get
as much as you can.
Initial
Flights:
First
flights are sometimes nerve-wracking experiences.
Just get the airplane up to some reasonably high altitude
and get it trimmed for level flight. Get a feel for
the aircraft's control throws. You'll want to adjust
these mechanically once you land. Initial trim on
the rudder should also be performed now. Fly directly
up wind, and straight away from you if possible. With
wings level, pull the nose up to the vertical. Note
if there is any loss of heading or roll to the airplane.
You MUST be wings level to properly evaluate rudder
trim. If there are no major heading changes, continue
the pitch-up into a series of loops. Do NOT correct
them but take note of which direction they fall off
center. Add a click or two of rudder trim to correct
and try it again. Repeat this several times until
you're sure you've got the rudder trimmed as well
as possible. Now land.
Ground
Trim:
Once
you've flown the airplane and got it basically in
trim, you need to go back and get everything mechanically
neutral again. Write down the trim offset for each
control. Now get out your CRC Throw Meters and measure
the offset of each surface in degrees. What you want
to do now is adjust the linkages such that you have
this offset in the surface with the trims centered.
Aileron and rudder trim are really limited in what
can be done to solve a problem other than linkage
adjustments, lateral balance changes, or SLIGHT thrust
adjustments.
For elevator though, we have much more available.
If you required some up trim, you can move the CG
back, change the incidence in the stab, or just
adjust the linkages. For now, stick with either
balance or linkage adjustments, as we'll be working
on incidence and thrust changes later.
Now that you have the trims centered again. It's
time to fly and verify your changes. Again, follow
the same procedure and note if any trim changes
are needed. If all went well you should have an
airplane that is nicely trimmed for straight and
level, upright flight with the trims centered.
Before we get too far into flight trimming, I want
to emphasize one thing. As you make trim changes,
or other adjustments, it is important that you change
only one thing at a time, and then fly again and
retest. Each change can affect other properties,
and multiple changes can only confuse the issue
you're trying to fix.
Balance
Setup:
Roll
the airplane inverted and see how it feels. Did the
nose drop dramatically during the roll? Pushing too
much elevator to hold level? I use balance to adjust
this generally to get the feel I want. Move the CG
forward or back and retest. This should be done in
SMALL increments, retesting the aircraft after each
adjustment. Once you're happy with the way the airplane
feels in both upright and inverted level flight, move
on to the next phase.
Thrust
and Incidence:
You'll
hear a lot of different ideas on this, but simply
put, thrust controls the vertical up lines. Flying
directly into the wind, wings level, smoothly pull
to the vertical and let it go. Does it pull to the
belly or canopy? Does the nose pull left or right?
If it pulls to the canopy, land and add a slight amount
of down thrust. You could also move the CG back slightly
as well. If the nose pulls right or left, add side
thrust to counteract this tendency.
Note: Left or right thrust requirements can change
depending on the prop used. If you change props,
you may have to readjust side thrust. This is especially
noticeable when changing from a 2 blade to 3 blade
prop, which generally require more right thrust
due to the increased spiral slipstream.
Once you're getting consistently good, straight
up lines, move onto the down lines. Climb the airplane
up to 500 feet or so and get into a vertical down
line and let go. Does it pull out or tuck under?
I generally like to correct slight down line issues
with SMALL balance adjustments. If the airplane
pulls out of a long down line, move the CG back
slightly. This part of setup is a big juggling act,
as each change affects something else. It takes
awhile, but eventually you'll narrow it down.
Roll
Differential Setup:
Any
time you roll an airplane, the downward moving aileron
generates more drag than the upward moving aileron
due to the induced drag caused by the down aileron
lifting that wing panel. With modern aerobatic airplanes
using fully symmetrical airfoils, this is usually
a very small force. When you roll most airplanes,
the drag on the down aileron actually pulls the nose
offline. So even though you're rolling right, the
nose is going left.
From level flight, pull the nose up to 45 degrees
and put in full right aileron. Does the nose go
offline? Differential can help this. Select Wing
Type (code 22) and adjust the differential to about
4% to start with so that the down aileron travels
less than the up aileron. Now fly it again and retest.
This should also be tested on a vertical up line
and down line to make sure the airplane rolls axially.
Knife-Edge
Coupling Setup:
Almost
all aircraft exhibit some coupling between yaw, pitch,
and roll. Basically, we're going to mix for moderate
to high-speed flight. Slow speed knife-edge generally
isn't encountered in precision aerobatics. The airplane
must be properly balanced to get anything useful out
of this part of setup. Airplanes like the Cap232,
Extra 300S and so forth will generally pitch towards
the belly of the airplane with application of rudder,
while some mid-wing airplanes like the Extra 260,
or Edge 540 may actually pitch to the canopy. You
may or may not get some roll coupling as well.
At full throttle, level flight, roll to knife-edge
and hold altitude with the rudder. Try to keep the
airplane flying straight. Do you have to hold much
elevator to keep it straight? What about aileron?
Make a mental note of how much input is required.
Keep in mind these are for small to moderate rudder
inputs. Exaggerated rudder inputs will have to be
mixed out differently.
Select the dedicated Rudder - Aileron, Rudder -
Elevator mixer (code 64) and deflect the rudder
hard over. Now add about 5% up elevator mixing (or
down if needed) and re-fly. Does it need more or
less? Work on one axis, and one direction at a time.
Once you have one rudder direction fixed, move on
to the other. We still haven't fixed any roll coupling.
Just fly the correction for now, once the airplane
will hold a straight knife-edge on either side for
the entire length of the field. Work on the roll
coupling in the same manner. Start out with a correction
of only 2-3% though as aileron isn't usually needed
as much as rudder. I leave this mixing on as it's
needed in all rudder inputs.
Throttle
Setup:
Yep,
you read right. Throttle setup is just as important
to a smooth flight as anything else. I use the throttle
curves (code 18) to make the throttle response as
linear as possible. I want to hear an rpm change with
every click on the stick. Most gas engines seem to
deliver most of the power in the initial 50% of the
carb movement, so this requires an initially flat
curve, which then climbs sharply.
It takes some playing to really get it perfect,
but when done it makes it SO much easier to get
a smooth, constant speed flight. Those of you without
dedicated throttle curves can use a programmable
point mixer and mix throttle to throttle to get
the same effect.
Other
Tricks You Can Try:
These
are just some slight modifications to the setup that
I use as a personal preference. First off, I don't
like to push as hard to get good outside performance,
so I generally run about 5% more down elevator than
up elevator. I also run about 5% less expo on down
elevator as well. For most maneuvers, I run the normal
aileron rates, but for rolling circles, I knock that
down to about 30-40%. Yes, I'm giving up resolution
but this lets me move the stick more making it easier
to control the roll rate.
Aircraft setup is a constant process really. Every
time something is changed, there is the chance it
will affect something else. Take your time, and
work through it, you'll find yourself fighting the
airplane less during a sequence, and that makes
it much easier to score well.
If you have any questions or need help, feel free
to e-mail me.
. C4@san.rr.com
or douglas_cronkhite@intuit.com
10's..
Doug
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