Flying Information
Ending Swashplate
Link Confusions
By Mark Fortune
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Make sure Left side and Right side
pushrods
from bellcrank to swashplate
are the same length. |
Well, the flying season is now in full swing.
I have attended 4 funflys in the last few
months and am leaving in a couple of days
for another. It’s always good to see what
everyone has been working on over the
winter months. This year started out really
exciting! Leaving the flying site on Saturday
of the Birmingham, AL FunFly, I was
nearly involved in a major accident. My
traveling buddy, Al Warfield, was not so
lucky and took a direct hit into the mobile
hobbyshop trailer he was towing. Al and I
are both OK, but I’m sorry to say that others
traveling on that same road that night
can’t say the same. Thanks to all who
stopped by and helped us
unload Al’s trailer and all
the RC goodies he had inside.
Even more thanks to
“X” who offered us his
home for an overnight stay
before we started home
early the next morning.
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Here is a tool that will allow you to check that
the swashplate is level and for interaction
between the collective and cyclic system. It
sit on top of the swashplate and is used to
check if the swashplate remains level while
is moving along the main shaft.
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The small electric heli’s
are very popular and growing
every day. I have seen
several of them flying, over
the past few years, but honestly,
they all looked like
they were struggling just
to hover. Some of the types
I saw fly would get airborne
only long enough for something
to fail and crash. After
a while, I just simply
stopped watching them flying.
However, that changed
during the Huntsville, AL
FunFly. I’d heard of the TRex
series of small heli’s,
but never really paid them
much attention to them.
Well, these little machines
had performance like a 90 powered machine!
Clearly, this design was far and above
the great unwashed masses of the electric
heli’s I’ve seen fly previously. Not only is the
performance there in the T-Rex, but parts
are amazingly cheap! You can check around
some of the heli shops for prices, but here
are a couple of examples: Main rotor blades
$34.00, Main gear (2 pcs.) $10.50, Feathering
shaft (4 pcs) $6.00, Flybar (2 pcs) $4.00.
This reminds me when Miniature Aircraft
introduced the X-cell series of helicopters
in the 80’s. There was a lot of performance,
unique combination of proven parts design,
and replacement parts were cheap, as compared
to what was already on the market
back then. I’m hoping I can get a T-Rex
450SE up and running for a review.
I met an interesting guy named Darrel
Sprayberry at the Huntsville, AL FunFly.
Some of you may know him as well. He recently
placed first at the Weak Signals
Show in Toledo, OH in the helicopter static
display. He has some interesting
thoughts on electric powered helis. All of
his models are electric powered. Now I’m
not still talking about T-Rex or even 30
sized machines. His models are 60-90 sized
machines. The cool part is that they’re not
electric models by design, but were converted from glow powered versions. He was telling me how he
uses electric motors and toothed drive belts to convert his models.
I’m hoping he will give us more info on his conversions in
the future.
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This is a tool I made to assist in checking
that flybar is level. It can beused for many other setup
and building steps too. |
Set Up continued ...
A couple issues back, I left
you with a model whose
control linkages from the
servo to the bell cranks
were all the same size and
parallel to each other. Now,
we have to connect the
swash plate and ultimately,
the rotor head to these linkages.
As an overview, here is
how everything should be
set: Servo end points set
as per the manual for
CCPM, or if using mechanical
collective control -
100%. All sub trim and radio
trim should be at zero or
neutral. All mixing should
also be OFF and collective
pitch curve should be a
straight line from -10 to
+10, and with end points
set to 100% for high pitch
and 0% for low pitch. Collective
stick position should be in the middle
or 50% position.
Ok, so where should the swash plate
go? Well, the swashplate and washout unit
should be considered as one “unit”. Since the
washout arm links are not adjustable, the
distance between the swashplate and the
washout unit remains fixed. With that in
mind, it’s best the swashplate and washout
remain joined when centering the swashplate/
washout unit for setup.
With the main rotor head installed in
it’s proper position on the main shaft, push
the swash plate/washout unit up until it bottoms
out against the main rotor head block
or in the case of mechanics, like the Hirobo
line, to the adjustable mixing base driver.
Now, using a small ruler, measure the distance
from the bottom of the swash plate
to the top of the main frame. Next, deflect
the swash plate full over, either left or
right, until it bumps against the mainshaft.
Lower the swash plate/washout unit until
it either touches the side frame or the
washout unit is within 3mm of disconnecting
from the drive pins. Being careful
not to change the position of the swashplate/
washout unit on the mainshaft, level
the swashplate and measure the distance from the bottom of
the swash plate to the top of the main frames. Subtract the distance of the lowered swashplate position from
the raised swashplate position. Example:
swashplate/washout unit raised=63mm.
Swashplate/washout unit lowered=18mm.
63-18=45. This means there is 45mm of usable
travel for the swashplate/washout unit.
Since we are interested in centering the
swash plate for equal travel, we will need
to divide the 45mm of usable travel in half.
45/2=22.5. Now, raise the swash plate until
there is 22.5mm between the bottom of
the swash plate to the top of the main
frames.
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Evening at IRCHA 2006 |
Measure the distance between the link
ball on the swashplate and the link ball on
the bell crank, center to center. Make a
pushrod this exact same length and install.
Repeat for each bell crank that attaches to
the swash plate. This is the same method
used when the bell crank is eliminated and
the pushrod connects directly to the servo.
This is also tremendously useful for checking
ARF helicopter’s linkages to be sure
they are what they should be, as well as a
method for double checking the manual’s
dimensions of a kit heli.
Next, with the swashplate/washout unit
centered along it’s travel on the main shaft,
measure the distance between the swashplate
ball and the fly bar control horn. Make
two pushrods this same length. Make sure
the flybar is correctly installed at this time.
This means that the flybar is centered in
the main rotor head and secured in that position.
Also, the flybar control horns are parallel
and “in-plane” to each other and are
also secured. Don’t worry about the paddles
for now. We’ll take a look at them later.
After you’ve double checked you
pushrod lengths, install the pushrods on the
swashplate and flybar control horn balls.
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Now, there are only two pushrods left,
but they are certainly two of the most important.
These are the pushrods from the
swashplate to the bell-mixer to each blade
grip and from the bell mixer to the fly bar.
It’s important the relationship between these
two pushrods is established from the beginning.
It is possible to get the correct pitch
readings at one location, but the relationship
between the pushrods is all wrong. Ok, here’s
how to get them in the right position. You
can make some rough measurements between
the swashplate ball and the bellmixer
ball, and the flybar and the bell-mixer
ball. Once this is complete, make two
pushrods each for these two lengths. Install
one each of these pushrods. Don’t worry
about the other blade until after you get one
side right. Transferring measurements over
is a whole lot easier than trying to remember
what side you were just working with.
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Once you have the first
pushrod to the proper length, duplicate this length
for the
other pushrod going to the swashplate.
Be sure to record this length for future
reference. |
Next, with the servos, bellcranks, swashplate/
washout unit still centered, lock the
flybar perpendicular (90 deg.) to the main
shaft. Some manufacturers sell flybar locks
for just this purpose. I made a tool for just this
reason. It will allow you to see when the fly
bar is perfectly level. Hint: use a small piece
of Saran Wrap between the bell-mixer ball and
the ball link. This will provide just enough interference
fit to hold the flybar in position.
With both pushrods connected to the bell-mixer,
check the bell-mixer to see if it’s level and
adjust it if necessary. This is made easier by
placing a small bubble level on the bell mixer.
Place a small amount of grease on the
bell-mixer to aid in holding the bubble level
in place. Next, install the rotor blade in the
main rotor grip. Be sure blade is parallel to
the feathering shaft while in the blade grip.
An easy way to get this right is to disconnect
both bell-mixer pushrods from the swashplate
and flybar. Rotate the blade back or
forth within the grip until the blade will no
longer flop around by itself when released.
When the blade grip will stay put, carefully
tighten the blade grip bolt to keep it there.
I’ll stop here for now. The very next
part of this setup process will be determined
by your flying style.There are some
digestible bits that you should go back and
re-read anyway. Next time I’ll tell you how
to set your pitch according to your style.
So until then ... go attend a funfly somewhere!
If you don’t know the answer to
something, a funfly is a great place to find
it. Look for sponsored pilots. They are
there to help you ... that’s why the manufacturers
send them there!
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