SECTION 12:
FITTING THE COWL, SPINNER & COOLING BAFFLES
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The cutout in the spinner cone should match the contour of the prop blade closely. A sliding pin “copycat”
contouring tool, widely available at hardware stores, can make the job easy. If you do not have such a tool, use a
sheet of single ply (shoebox type) cardboard to make a hole template for the prop. Using the cardboard to simulate
the spinner, align the edge of the cardboard with the rear edge of the rear mount and cut out an opening just large
enough to clear the prop blade. If this piece is carefully cut and removed, it may be used later to fill in behind the
prop. If not, the gap behind the prop must be filled with a separate aluminum plate riveted to the back plate. It may
require a couple of tries to achieve the desired shape.
On the spinner, mark two points at the rear edge exactly opposite each other, 180
q
opposed. Mark one point and
then measure the circumference of the opening. Divide the circumference by two to determine the location of the
opposing mark. Then lay the cardboard template on the spinner aligned with one of the marks, and mark the cut
out. Repeat for the opposing cut out.
The fiberglass can be cut with a tin snips or a cutting disc on a die grinder or Dremel tool. Because the tin snips
crush the fiberglass, cut about 1/16'' inside the marked line and then use coarse sandpaper to enlarge the opening.
Fit the spinner onto the prop. Chances are that the opening will not be quite large enough. Progressively enlarge
the openings as needed until they have approximately 1/16 to 1/8'' clearance from the prop blade. You do not want
a contact fit because there is enough movement between spinner and prop during operation to cause the edge of
the spinner to cut into the prop.
If the prop is thinner than the spinner plates were designed for, it may be necessary to build up the inside of the
spinner to mate with the flange of the front plate.
A fiberglass build up can be molded in place. Mark a ring around the inside of the spinner where it contacts the
front plate flange. Then lay up a ring of fiberglass mat 3/4'' wide around this ring. Wax the spinner flange so it will
not bond to the spinner. Slip the spinner with the wet lay-up into place and hold with clecos. When it is cured, the
spinner can be removed and any roughness in the reinforcement fiberglass can be sanded smooth. Remember
that anything added to the spinner should be evenly distributed around the circumference to help maintain balance.
The spinner should be aligned with the axis of the crankshaft so it does not “wobble” as it spins. This requires that
the prop and spinner be mounted on the engine. First, align the spinner as closely as possible and tape it to the
bulkhead. Then, mark a point in the exact center of the nose of the spinner. Stand a step ladder up in front of the
spinner with a pencil clamped to it and place the pencil point near at the mark on the spinner nose. Remove a
spark plug from each cylinder so that the prop can be rotated easily and safely. If the spinner is in perfect
alignment, its tip will remain in position with the pencil point through full 360 degree rotation. If not, reposition prior
to drilling.
While the spinner is still in place, cut out the gap filler plate to be used on the back side of the prop. Make this plate
of aluminum between 0.040” and 0.063'' thick, or use the fiberglass piece removed when the spinner was first fitted.
DWG C4 shows the fabrication and installation of this gap filler. It is riveted to the back plate and stays in place as
the spinner is installed and removed. The flange shown riveted to the long edge of the gap filler is essential and
should not be overlooked. The primary forces acting on the spinner are centrifugal, and without this flange which
ties the gap fairing to the spinner, it would bend outward and tear off.
Drill and cleco all holes in the rear mount plate; then progress forward to the front plate. While the spinner screws
are #8 size and require a #19 drilled hole, we suggest drilling the holes to 1/8'' (#30) initially. A 1/8'' cleco can then
be used to hold the K1000-08 nutplate in place while it is being drilled and riveted. Cleco the nutplate to the outside
of the mount plate flange and use it as a drill guide. Remove the nutplate, machine countersink the holes for
AN426AD3-3.5 rivets, drill out the screw hole to #19, and rivet the nutplate on.
The spinner is one of the most critical of the non-structural parts on an airplane. While it doesn't support any
productive loads, it is subject to considerable internal forces. Any weight imbalance can cause high loads on the
spinner mounts. In addition, the reversing, pulsating, loads caused by the intermittent combustion of the engine
come to bear on the spinner installation. Therefore, it is necessary to mount the spinner firm and true; to prevent it
from destroying itself. Use 14 equally spaced #8 screws in the rear mount plate and 6 in the front plate. Place
screws holes 5/8” from the edge of the prop hub cut-out, and then equally spaced around the circumference. Rivet
K1000-08 nutplates to the inside of the spinner mount flanges. The front plate should fit snugly in the spinner.
If you wish to use countersunk screws (many builders are satisfied with roundhead) the holes in the spinner may be
machine countersunk for AN509-8R8 screws and countersunk washers. If you do not have a #19 piloted machine
countersink, the spinner holes can be countersunk while they are still 1/8'' diameter.
SECTION 12:
FITTING THE COWL, SPINNER & COOLING BAFFLES
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ENGINE BAFFLE INSTALLATION
Cutting and bending the many sheet metal components of a complete baffle system is a tedious task. Almost all RV
builders choose to buy the optional baffle plans or the complete baffling sets available in Van's Accessories
Catalog. These include installation drawings and instructions.
