SECTION 10
ENGINE MOUNT, WHEELS, BRAKES AND FAIRINGS
RV-8/8A
10-5
8-s10r9 7/11/11
Use your “sharpie” pen to make four ink “dots” on U-807 where each of the four fasteners will ideally be located.
Sand away the white gel-coat from the areas where the fairing touches the bracket so the bracket and the ink dots
can be seen through the translucent fiberglass.
Re-measure to verify that the fairing did not move during drilling. If desired, the airplane may now be removed from
the jacks/supports that were holding it off the floor. Enlarge all holes to final size and remove the wheel fairing.
Install nut plates to U-807. Rivet U-808 to the aft half of the fairing using AN426AD4-6 Rivets. Remove all blocks,
spacers, shims, etc. and install the wheel fairing to the airplane. Make sure that there is 5/8” clearence all around
the tire.
WOOD GEAR LEG STIFFENERS ON THE RV-8A MAIN GEAR (OPTIONAL)
With a rod gear leg, the wheels can move fore and aft, so, with no scrubbing action on the tire, there is no damping
resistance, and a fore-and-aft shimmy can result. This is most prevalent at low speeds (10-15 mph) and on paved
surfaces. Turf surfaces have sufficient rolling resistance to provide a dampening action. Out of balance wheels and
higher than necessary tire pressures also promote wheel shimmy (lower pressure in the tires increases rolling
resistance, and thus provides dampening). Generally such shimmy occurs on landing roll out or while taxiing, and
can be stopped with light brake application. Un-checked shimmy can transmit vibrations into the landing gear
mount and eventually cause cracking. However, wheel shimmy is a rather nebulous thing; it occurs on some
airplanes and not others, and with varying degrees of severity. The cause, or combination of causes, of shimmy is
very difficult to detect and define. Fly the plane first to determine if you need the stiffeners.
Wheel shimmy tendencies can be minimized by using the lowest practical tire pressures, having well balanced
wheels and tires, and brake discs which run true and don’t drag at one point of rotation.
Bonding a wooden block to the spring steel rod gear leg will alter its vibration characteristics and decrease the
tendency to shimmy. This is shown on DWG C3. The wood used in this illustration is a standard window molding
available from most building supply stores. The shape of this molding provides a good place to start. Sawing two
pieces of this molding lengthwise and bonding them together as shown will provide a tapered piece which attaches
easily to either the front or rear of the gear leg. The resulting assembly is attached with putty of epoxy and
thickening agent or even a “Bondo” type body filler.
Once this has cured, sand or file the excess bonding agent smooth, and wrap the whole assembly with 2 or 3 layers
of 9 ounce fiberglass cloth. Fiberglass tape, 2-3” wide wrapped around the gear leg works well because it is easier
to keep taut than a large sheet of fiberglass cloth. These wrappings of fiberglass tape are saturated with polyester
resin (or epoxy if you prefer) as they are applied.
The wood stiffener blocks may also be attached temporarily by spiral wrapping them with fiberglass filament re-
inforced packaging tape. This should be viewed as a short term installation, because the filament tape will
deteriorate and may not last for more than one or two years; much less if directly exposed to sunlight for long
periods of time.
INSTALLING THE FIBERGLASS RV-8A MAIN GEAR LEG FAIRINGS
Gear leg fairings are very important for drag reduction. While one might feel that a fairing on the large wheel and
tire would add more speed than a fairing on the small, round gear legs, just the opposite is true. Wheel fairings add
about 3-4 mph but the gear leg fairings add at least 8 mph. The combined wheel and gear leg fairings add around
12 mph to the top speed. Looking at it another way – it would take an additional 27 horsepower from the engine to
achieve the 12 mph contributed by the fairings. Obviously, a good fairing installation is necessary if high speeds
are to be obtained from your RV.
Proper alignment of the gear leg fairings is also important for purposes. Since the gear legs are located forward of
the aerodynamic center of the aircraft, they have a de-stabilizing effect on directional trim. Any misalignment will
have the same effect as a rudder input, but in the opposite direction and of much greater magnitude. For instance,
it was found that just a 1/4 inch misalignment of the lower trailing edge of one gear leg fairing produced a half-range
deflection of the skid ball. A very noticeable opposite rudder input was required to re-center the ball.
Main gear leg fairing installation is shown on DWG C3. Place the fairing, leading edge down, on a table or other flat
surface and use a square at one end to position the trailing edge exactly above the leading edge. Make sure that
the other end of the fairing also has the trailing edge exactly above the leading edge. This will verify that the fairing
was molded without twist. With the fairing in the “no-twist” position, place two or three spring clamps on the trailing
edge. Wrap a piece of tape around the trailing edge and then use a razor blade to split it at the trailing edge or
make a thin pen mark across the trailing edge. If the fairing becomes twisted, the tape edges or pen mark will not
line up.
Cut out the paper trim template (for YOUR airplane) found on DWG C3. Position the trim template over the fairing
RV-8/8A
SECTION 10
ENGINE MOUNT, WHEELS, BRAKES AND FAIRINGS
10-6
8-s10r9 7/11/11
using the molded-in scribe lines and the leading edge parting line as reference points. Smooth the template over
the outside of the fairing and use spring clamps to hold it in place. Trace the root end, trailing edge, and tip end trim
lines onto the fairing. Make small “tick-marks” on the tip and root at the gear leg centerline. Extend the gear leg
centerline marks approximately ¼” to the center of the part after removing the template. The marks will be helpful
later when positioning the fairings to the gear legs. Trim the root and tip ends of the fairing, but not trim the trailing
edge. After trimming, file or saw notches approximately 1/16” deep in the edges of the fairing at the gear leg
centerline marks.
Trim the hinge material to 2 inches longer than the length on the drawing. Do not trim the hinge pins yet. The hinge
material is left 2 inches long so there will be a 1” excess on each end to help clamp the hinge to the fairing. Mark
(but do not drill) fastener locations and final trim locations on each of the hinge segments.. When drilling the hinge
to the fairing, the fastener location marks will be visible through the translucent fairing.
Place the trimmed gear leg fairing on the gear leg and clamp the trailing edge closed with two or three spring
clamps. Use the tape or pen marks to be sure that the fairing is not twisted. Adjust the position of the fairing to align
the gear leg centerline marks with the gear leg centerline. The trim as defined by the pattern was conservative, and
the fairing may be slightly too large. Trim the lower end of the fairing as required for proper fit.
Note: Each hinge half must be drilled, clecoed, de-burred, countersunk, and riveted before moving to the next hinge
half because the fairing section is too thin at the tip to allow installation of clecos in both sides without interference.
Position the marked hinge inside the trailing edge of the fairing and clamp the ends of one hinge half in place. With
the hinge ends clamped in position, begin at one end and drill #40 through the fairing and hinge using the fastener
locations marked on the hinge to position the holes. Use light pressure and high drill speed, and allow the bit to cut
through without distorting the hinge. Work from one end of the fairing to the other, clecoing each hole before drilling
the next.
Un-cleco the hinge from the fairing and clean out any metal chips. De-burr holes and trim the 1” excess hinge from
each end. Remove and countersink the fairing for AN426AD3 rivets. Because the fairing is quite thin, it is
recommended to that you keep the hinge clecoed to the fairing while countersinking. The holes in the hinge will
guide the countersink cutter and keep it from elongating the holes in the fairing. Rivet the hinge to the fairing, using
a hand squeezer. Don’t fully set the rivets as you would in a metal structure. This would cause the thin composite
fairing to crack around the holes.
Remove the fairing from the aircraft and insert the hinge pin to join the trailing edge. Use a long sanding block to
remove any excess “tail” on the fairing and even the sides of the trailing edge.
Remove the pin and the lower 1” to 90º. Grind the upper end to a chisel tip. This shape helps guide the pin through
the eyes of the hinge. Drill a #40 hole in the upper surface of the lower end of the fairing. A piece of safety wire can
be looped to hold the hinge pin in place.
Wrap the gear leg with wear resistant plastic adhesive tape at two or three locations to prevent chafing and hold the
brake line in place. Slip the fairings over the gear legs and insert the hinge pin from the bottom. The hinge pin is
thin enough to curve as it is inserted without taking excessive permanent bend.
Roughly align the fairing to the airflow, and align the gear leg centerline marks with the gear leg centerline. At the
top end of the fairing, install a hose clamp around the gear leg capturing the ¾ inch wide fingers of the fairing to
help hold it in place. When installing the hose clamp for the first time, use a heat gun to soften the fingers so they
conform to the surface of the gear leg as the hose clamp is slowly tightened. When the hose clamp is fully
tightened, leave the fairing in place and allow it to cool.
You can also, as an option, add one or two layers of fiberglass cloth under the fingers. The purpose is twofold: to
strengthen the finger and to contour the inner surface of the finger to the landing gear leg. Cut one or two
laminations of 9 ounce fiberglass cloth so they fan out and anchor to a larger surface area of the gear leg fairing.
See the dashed lines on the full scale trim templates.
Before laying up the fiberglass, prepare the surface of the gear leg by locally coating it with wax, mold release
agent, or thin cellophane packaging tape. Cut out the glass cloth doubler patches and attach them to the inside
surface of the fairing with a liberal application of epoxy resin. Before the resin cures, install the fairing to the gear leg
using the hinge pin to close the trailing edge. Lightly clamp the lower end of the fairing if necessary to hold the
fairing in place. After cure, remove the fairing and trim any rough edges around the doubler patches. The exterior
surface of the finger can be filed or sanded to provide a smoother contact surface for the hose clamp.
The alignment of the fairings is important and can substantially affect the way the airplane flies. While a very careful
“eyeball” alignment job might come close, this is difficult because of visual illusions created by the sweepback of the
gear legs.
The gear leg fairing must be aligned with
no load on the wheels
, simulating the in-flight condition of the gear legs.
