Carf-Models Ultra Lightning Instruction Manual page 13

The bypass duct itself is designed as an integrated struc-
tural part of the plane, and is incredibly strong when prop-
erly installed, in effect giving a 'monocoque' construction
and providing extra torsional strength to the fuselage.
Note: The 'upper' bypass is the one that will be at the top
when the plane is the normal way up, but all the next sec-
tion is done with the plane upside down - working thru' the
hatch in the bottom of the fuselage. Please don't get con-
fused...
The carbon bypass duct is already trimmed at the factory.
The 3 back fixings (M4 bolts and aluminium angles) for the
upper bypass are already installed, and you only need to
install the two M4 x 20mm bolts that fix the front end. All 5
aluminium angles have slotted holes for bolting to the bulk-
heads, and you can use these to adjust the back 3 (if
needed) so that they fit tightly against the surface of the
bypass duct.
Glue the 2 shaped laminated plywood blocks on to the top
surface of the aluminium angles with 30 min. epoxy and
milled-fibre mix. Rough up the aluminium surface first and
clean with acetone/alcohol for a good bond. Adjust the
height of the angles, using the slots, until the ply blocks
are about 1mm from the bypass duct outer surface. Apply
plastic tape and/or wax to the outside of the bypass in this
area, and a thick mixture of 30 minute epoxy and micro-
balloons to the top of both plywood blocks. Refit the
bypass quickly, and tighten the back 3 mounting bolts,
and tape the front of the bypass firmly in position.
When the glue is hard you will have a perfect fit between
the blocks and the bypass (P9). Remove the bypass and
tidy up the edges of the glue on the blocks. Refit, and bolt
in place again with the back 3 bolts. Carefully mark the centrelines of the 2 front blocks on
tape on the inside of the bypass, and drill right through the ply blocks and the aluminium
angles at an angle of about 30 degrees with a 3.2mm drill (photo P10). Then thread these
holes M4, and fix the bypass using the two M4 x 20mm long bolts and washers (photo P11).
Drill and thread one hole first, and insert the bolt before drilling and tapping the 2nd one.
NB: We recommend that you carefully mark the positions of all 5 aluminium angles on the
bulkheads before finally installing the bypass, because if they are moved later it is difficult to
find the right position again ! (see photo above)
When the upper bypass is completed, check the fit of the white fibreglass central duct joiner,
and trim the back edge if needed so that it just projects inside the bypass by 9 - 10mm. This
duct joiner does not need any additional fixings, as the back edge has a glass or carbon roving
on it that prevents it moving backwards when the lower bypass cover is fitted in place (see
photos P14 and P15).
Trial fit the other half (lower part) of the bypass to check that everything lines up OK. At this
point you should temporarily install the exhaust ducting onto the bypass cone, and slide this
(above and below) Glue the
shaped plywood blocks to the
front angles with 30 minute epoxy
and milled-fibre mixture as shown.
(above) Mark the final position of
all 5 angles for later reference.
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