10
model aircraft are equipped with Walbro carburetors and most of
these engines have the carburetor mounted to the side of the
cylinder head, at non-linear angles.
The ball-link throttle arm
connection solves this problem. Note: If the throttle arm on your
engine is spring loaded, either remove the spring or cut it from the
throttle arm with wire cutters.
❑
20) Choose a location on the throttle arm that will best provide
fore and aft linear movement from the servo. This is the location
to mount the ball link fitting. Drill the throttle arm to accept the ball
link and mount it in place. In the case of the FPE 3.2 engine, the
hole in the throttle arm is already present, just mount the provided
ball link stud to the throttle arm with the 2-56 threaded nut. Note
that some throttle arm locations and shapes may require an
extension that must first be attached to the primary carburetor
throttle arm. If this is the case with your engine, make and attach
the extension with the ball link fitting in place.
Note: With the variety of gasoline engines that are available today,
it was not practical to pre-cut the holes in the fuselage formers for
the nylon pushrod housing. Each manufacturer of R/C gasoline
engines has the carburetor mounted in a different position and/or
orientation. The following instructions show how we installed the
FPE 3.2 engine in the Sun Dancer, but these instructions should
be similar for other engines as well.
Use a pencil to mark the firewall at the point where the throttle
pushrod will be placed. Remove the engine from the firewall and
use a 13/64" dia. drill bit to make a hole through the firewall at that
mark. Once the nylon pushrod housing is permanently installed, it
will have a slight arc or bend in it from the firewall to the servo
output arm.
Next, drill a hole in the right side of the next fuselage former (F-2)
that is on the same vertical plane, but 3/4" higher, than the hole in
the firewall. Perform this operation from inside the fuselage by
reaching through the wing opening in the bottom of the fuselage.
Insert the nylon pushrod housing through the hole in the firewall,
former F-2, and into the fuselage interior. Using your fingers, hold
the nylon pushrod housing until it is the same height as the output
arm as the servo. Mark the location where the housing passes
next to the third fuselage former (F-3) with a pencil.
Cut a
1/4" x 1/4" notch in the fuselage former at the marked location.
Make a pushrod guide from a 1/8" piece of scrap plywood and drill
a 13/64" hole through it. Slide the guide over the pushrod and
epoxy it to the backside of fuselage former (F-3) as shown in the
previous photo. Adjust the position of the pushrod housing so that
the end of the housing is 1/2" past the fuselage former. Glue the
pushrod housing in place. Trim off the excess pushrod housing
leaving 1" of the pushrod housing protruding from the firewall.
After the outer pushrod housing tube is in place, remount the
engine permanently in place to the firewall. Be sure to use thread
lock compound on the bolt threads. Attach the wiring leads to the
engine.
❑
21) The inner nylon throttle pushrod is now prepared. Thread
one of the provided 2-56 threaded studs halfway onto one end of
the inner nylon pushrod. Next, thread onto the stud one of the
nylon ball-link connectors. Working from the servo end, insert the
inner nylon pushrod into the outer nylon housing and snap the
nylon ball-link onto the metal ball that was previously installed on
the output arm. Place the throttle servo in the neutral position so
that the output arm is 90
O
to the servo. Position the throttle lever
of the carburetor so it is in the middle of its range of travel. Thread
the remaining 2-56 threaded stud into the nylon ball-link fitting and
press ball link fitting onto the metal ball link on the carburetor
throttle arm. Place a mark on the nylon pushrod that is 1/4" from
the end of the nylon ball-link fitting and cut off the excess nylon
pushrod tubing. Remove the nylon ball-link and treaded stud from
the carburetor and thread into the end of the nylon pushrod until
you have about 1/4" gap between the end of the nylon pushrod
and the end of the nylon ball-link. This should allow for more than
enough adjustment to set up the throttle properly.
❑
22) The Sun Dancer is a large model so make it easy on
yourself by installing a fueling valve in his airplane. For gasoline
engines, Du-Bro makes a very good fueling valve, Du-Bro #335.
This valve is easy to use and we have provided an aluminum
bracket in your kit that will allow you to mount the valve directly to
the firewall. We mounted this valve behind the engine on the left
side of the firewall as shown in the photo. In addition, make a
bracket to hold the overflow fuel line from a piece of scrap 1/8"
plywood. Drill a 1/4" hole in the plywood bracket and epoxy it to
the firewall. Pass the fuel vent line through the plywood bracket
and trim off the excess tubing leaving 3/4" protruding through the
plywood bracket. Connect the fuel pick-up line from the fuel tank
to the angled nipple fitting of the filling valve. Attach a piece of
tubing to the straight nipple on the fueling valve and to the fuel inlet
on the carburetor.
MODELER’S TIP: Once you have flown the Sun Dancer, it is a
good idea to plug the fuel vent line after every flying session.
Harmful and dangerous gasoline vapors can vent from the tank
while traveling to and from the flying field. Du-Bro sells an
assortment of fuel line plugs that work quite well. Simply select
the proper size plug and insert it into the end of the fuel vent
line.