Carf-Models Ultra Flash, Instruction Manual

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Exhaust Duct/Thrust tube
The thrust tube consists of a lightweight aluminium outer
tube and a 0.25mm thick stainless steel inner tube,
spotwelded together. It is designed to work with a wide
range of turbines and it is, therefore, a compromise - but has
already been used very successfully with several different
turbines with thrust ranges from 8kgs (18Lbs) up to the max-
imum allowed of 12 kgs (28 Lbs).
Drill a 3mm diameter hole centrally in each of the 2 small
stainless steel angle brackets that are pop-rivetted to the
sides of the aluminium tube. With the fibreglass exhaust
nozzle fixed in place, slide the outer tube into the fuselage
from the wing opening until the angle brackets touch the
front face of the bulkhead F7. The back end of the outer
thrust tube should be flush with the back of the exhaust noz-
zle, or maximum 1mm in front of it (see photo P3). Bend the
angle brackets if needed to set this length. Rotate the thrust
tube so that the brackets are at about the 3 o’clock and 9
o’clock positions. Using a long Ø 2mm drill bit, make two
pilot holes into the bulkhead F7 and secure the tube with the
Ø2.9 x 10mm sheetmetal screws.
Bend the 6 metal tabs spot-welded onto the back of the
inner tube into a shallow ‘V’ shape as shown, to centre the
inner tube in the outer tube (photo right). The inner tube
must be secured inside the carbonfibre bellmouth (entry
cone). You can either use the 4 small (2.2 x 10mm) sheet-
metal screws provided, or 4 small pop-rivets. Both methods
work fine. Push the tube into the carbon bellmouth about
10mm (it is a tight fit and you may need to sand the carbon
a little), and insert into the fuselage so that the front face of
the carbon is exactly flush with the front of bulkhead F6.
Check that the back of the inner thrust tube is 6 - 8mm inside
the outer thrust tube (see photo P3). Adjust the position of
the tube in the carbon bellmouth to set this length. When the
length is correct, drill the 4 pilot holes through the carbon
and thrust tube for either screws or rivets (photo P4). Hold a
strip of plywood inside the thrust tube to prevent the drill bit
bending the tube (photo right), and use a sharp drill bit.
Fix the 2 small angle brackets (included) to the outside
edges of the carbon bellmouth as shown, using either the
small sheetmetal screws, or pop-rivets. Make sure that the
brackets align with the slots milled in the rear engine bulk-
head (F6) as shown. Adjust the size of slots to match brack-
ets if necessary. Drill 2mm Ø pilot holes and secure the bell-
mouth centrally in F6 with two Ø2.9 x 10mm screws.
We advise that you cut 2 small ‘NACA-style’ auxiliary air
intakes in the bottom of the fuselage either side of the ven-
11
(above) Drill Ø 3mm hole in
brackets on outer tube.
(below) Bend the 6 tabs at back
of inner tube into ‘V’ shape.
(above) Fix carbon bellmouth to
inner tube with rivets or screws.
(below) Fix 2 small angle brackets
to the bellmouth as shown here.
(bottom) Bellmouth brackets
secured to F6 with small screws.