FUSELAGE ASSEMBLY, PART III: Cowling and Spinner
For the following steps you will need these parts:
•
The fuselage assembly
•
1 - Fiberglass Cowling
•
5 - M2.6 x 8mm PWA Screws
•
1 - 2-1/4" Plastic Spinner Assembly
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1) Try fitting the Fiberglass Cowling over your engine and back
onto the fuselage.
If you have a typical MAYHEM engine
installation (meaning a single-cylinder engine mounted inverted)
you will need to make an opening in the bottom of the cowling for
the engine cylinder to stick through. Watch carefully to see where
the head of the engine first hits the inside of the cowling and mark
that location with a pencil or felt tip marker. Remove the cowl, and
use a Dremel
®
Tool to make a small opening in the cowl at the point
of contact. Refit the cowl, checking the hole location and size,
adjust as needed and again use the Dremel
®
Tool to make the
opening bigger. Keep refitting, remarking and readjusting the hole
until the cowling can be slipped over the engine into correct
position on the fuselage. As a general rule, you should end up with
at least 3/16" clearance between the cowling and any engine part.
❑
2) Once the cowling is in place without any part of the engine
contacting it, mount your spinner backplate and propeller on the
engine prop shaft. Tighten the prop assembly sufficiently to bring
the spinner backplate firmly in contact against the engine's prop
mounting flange. Now check to see that you have at least a 1/16"
gap between the back of the spinner backplate and the front of the
cowling (1/16" to 1/8" is OK).
Adjust the final location of the
cowling, making sure that the spinner backplate is centered on the
front and that the back edges are tight against the fuselage. Use
masking tape to temporarily hold the cowling in correct position on
the fuselage.
❑
3) With the cowling securely taped in place, use a 3/64" (or #56)
dia. drill bit to drill pilot holes in the fuselage, centered in each of
the four pre-drilled mounting holes in the cowl. Mount the cowl to
the fuselage with the four M2.6 x 8mm PWA Screws provided.
❑
4) Determine what size and shape opening you will need in the
cowling to accomodate your engine's muffler.
Then cut the
opening in the cowling, starting small and gradually opening it up
to the final size.
Note: As you can see in the next photo, the cutout for the YS-63
muffler in our photo model was a fairly simple 5/8" wide slot cut
straight forward from the back edge of the cowl.
The slot is
approximately 2-1/4" long. We used an additional M2.6 x 8mm
PWA Screw (provided) to hold down the corner of the cowling just
above the slot. Depending upon your exact engine ocnfiguration,
you may do something similar for your Mayhem.
❑
5) Determine the location of the hole required in the cowling for
access to your engine's needle valve. Start with the engine and
cowling on the airplane and "eyeball" the approximate location of
where the needle valve will exit the cowling. Take your best guess
and mark that location on the cowl. Now make a small 1/16" dia.
hole at the marked location. Chances are that you are close to the
correct spot. Stick a piece of music wire into the hole, down to the
needle valve.
Carefully observe if the hole needs to be
repositioned to straighten up the wire, as if it were the needle
valve. Make another mark on the cowl and open the hole just a
little towards the corrected position.
In this manner, continue
checking and adjusting the exit hole until it aligns perfectly with the
carburetor/needle valve position. Then enlarge the hole enough to
insert and install the needle valve in the carb. Be sure the hole has
at least 3/32" clearance around the needle valve to avoid contact.
Tip: A handy tool to assit with cutting holes in the cowling is a
small penlight.
The penlight can be used from the inside or
outside of the cowl to highlight and spot the required hole location.
❑
6) Figure out how you are going to light your glow plug and
whether that will require an additional opening in your cowling.
Note: For the YS-63, we did not need an additional opening - the
glow plug is accessible through the opening we made in the
bottom of the cowling.
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