Fei Bao MiG-21 Fishbed Instruction Manual - page 18
Fei Bao MiG-21 Fishbed Instruction Manual (Draft Rev 0)
Page 18 of 24
route through this area. Ensure that the air lines and servo wires are routed such that they are
not chaffed by the main wheels when the landing gear is retracted.
Bypass and Turbine Installation
The builder may opt to install a full bypass, or no bypass with a bell mouth to smooth airflow into
the exhaust duct. Many modelers forgo a full bypass in the interests of simplicity. A lower
bypass installation (as pictured below) has the advantage of providing some FOD protection,
blending the airflow into the exhaust duct, yet allows for easy access to the turbine without the
need to remove the top cover. The bypass installation is simplified if you perform it prior to
bolting on the rear fuselage.
Install a 1” wide x 3/8" thick piece of plywood to the top of the turbine mounting rails to center
the bypass in the fuselage. An additional 3/8” plywood spacer over the bypass flange is
required to center a JetCat P-120 turbine in the bypass since the flanges on JetCat mounting
straps are above the turbine centerline. Mount the turbine using screws or bolts and blind nuts.
Fuselage Joining/Exhaust Duct Installation
Remove the turbine and lower bypass and join the front and rear fuselage using the provided
bolts/washers. Test fit the double walled exhaust duct in the rear fuselage. The outer diameter
tapers slightly and the pipe should be installed such that the rear of the duct is approximately
5/8” forward of the fiberglass tailpipe to preserve the scale look of the plane. Use a Dremel tool
with a sanding drum to adjust the size of the duct cutout in the fuselage former as required.
Reinstall the lower bypass.
The forward end of the exhaust duct should extend approximately 3/8” inside the bypass. Mark
and cutoff the inner duct as required. Cut off the forward end of the outer duct approximately ½”
aft of the inner duct (not shown in photo below). This will allow cooling air from within the
fuselage to be drawn into the exhaust duct and then out of the model. Use high temperature
RTV silicon to fill any gap between the cutout in the bypass and the inner exhaust duct.
Two exhaust duct mounts are spot-welded to near the front of the exterior duct. Mark the
location where they intersect the fuselage bulkhead and bend each mount 90 degrees. Cut off