Posted Monday, February 2, 2009
This past
weekend, I got some more work done on the plane. So, here's the latest.
First up was to rework
the retract control linkage between the air valve and the servo that drives it. My original linkage used 2 Dubro ball swivel
links, but the completed part interfered with the stabilator linkages which I installed after the I made it.
In keeping with my personal rule not to use EZ
connectors, I made up the retract valve actuator linkage this past weekend, installed and tested it. Computer radios make
setting travel volumes (control throws) so easy. Here are a couple photos of the completed setup.
Viewed from the right side of the plane, the linkage
for the retract valve appears as though it's hitting the right side stabilator linkage. It's close, but it clears
fine.
The linkage as viewed from the rear. The servo is in
the "wheels up" position and the control arm moves clockwise to operate the valve to the "wheels down"
position. Very little movement is required, so use of the digital ATV settings was necessary.
Rudder Servo Installation
The rudder servo for this plane had to be a micro type. I used the HS-85MG; an
analog, metal geared ball bearing unit from HiTec. It cost about $35 and has a torque rating of 40 oz/inches. There is no
connecting linkage for the nose-wheel; it's operated with a separate servo I mentioned in a previous section.
HiTec HS-85MG Servo for Rudder
Construction Note - IMPORTANT
Here's
something I learned when I installed this servo. The rudder and nose-wheel steering servos operate opposite of each other
when using a standard Y harness. That means when the rudder goes right, the nose-wheel... you guessed it... goes left. There
are two ways to fix this. First, you can buy a Y harness with a servo reverser. Second, you can
mix the rudder channel with an unused channel on your radio.
Since the former requires yet another device at a cost of $20, I packed up the transmitter and headed to my local
hobby shop and had someone help me with the mixing function on the Spektrum DX7. In a few minutes, I had the basics down and
headed home to make it all work. I ended up using the AUX2 channel and mixed the two until I achieved the desired result.
Great. $20 saved.
The assembly manual does
not address the use of a reversing Y harness, only the need for a standard Y and an extension, so you'll
need to use one or mix it down as described here.
As
you can see from the photo, Cermark pre-cuts the servo hole, but you'll need to drill the pilot holes in the the fuse.
There is a ply block under the fuse, so the screws have plenty to bite into.
The servo clearance hole in the fin required some enlargement
as the length was short by about 1/8" and 1/32" on the width. After trial fitting a couple times, the fin slid down
over the servo. You have to install the control arm onto the servo, then manually align it lengthwise with the servo so the
fin can clear it. When you turn the radio on, the control arm pops out perpendicular to the fuse.
I used a Dubro #181 ball link for the servo control arm. It was right
about this time I had to get ready for my biz trip, so I slipped the fin over the servo and secured it using the 3mm x 15mm
machine screw, turned on the radio and verified the servo arm would clear the slot on the fin. Done for now.
The Dubro #181 Ball Link. I've used
these for years.
Vertical Fin and hinged rudder in place
with servo arm ready for the ball link.
Done for now. More assembly work yet to
come.
Page 6 is in development. Stay
tuned.
