30
VMAR CHALLENGER 40ARF TRAINER
TM
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STEP 8.1 - BALANCE THE AIRCRAFT.
The Centre of Gravity is often referred to as the "CG"
and is the point at which an aircraft is balanced with as
much weight aft of the point as it has weight forward of
the point. For your Challenger the CG should be located
at 89 to 108mm (3-1/2 to 4-1/4 in.) back from the leading
edge of the wing when the wing has been attached to the
fuselage.
Ideally we recommend that the CG be located at
95mm (3-3/4 in) back from the leading edge of the
wing
The CG is measured with the engine, tank, radio gear
and all other components installed but WITH NO FUEL IN
THE TANK.
Set up the CG with the Challenger as it will be when you
fly it BUT WITH NO FUEL IN THE TANK.
It is VERY IMPORTANT to have the CG correct. Flying
your Challenger with the CG too far aft will likely lead to
loss of control and a crash.
If you discover that after you have assembled your
Challenger and installed your radio and engine that the
CG is incorrect you must bring the CG to the correct
location by doing the following BEFORE FLYING:
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Move the battery pack fore or aft, and/or
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Move other components fore or aft, and/or
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Change engines to a lighter or heavier model and/or
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Add weight to the nose or tail. If adding it to the
nose, try to make it useful by going to a heavier duty
engine or adding a spinner with a heavy metal
backing plate. As a last resort, add stick on "dead"
weight where appropriate.
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PHASE 8 - CHECK OUT
TM
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Moving the battery pack fore or aft is the first step you
should take to get the CG located correctly.
If your engine is a plain bushing or lighter weight sport
type engine, you may find that the Challenger is nose
heavy with the CG too far forward. To correct this, gently
remove the fuel tank and extract the battery pack from
where it was located earlier under the fuel tank. Reposition
the battery pack further aft into the radio compartment.
Pad the battery pack securely into place with chunks of
foam. Relocate the tank back into position and check the
CG again. Do this repeatedly with small movements of the
battery pack until you get the CG right. If you still cannot
get the CG correct by moving the battery pack, you will
need to consider some of the other alternatives outlined
above.
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STEP 8.2 - SEALING THE FUEL TANK
INTO POSITION.
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8.2.1
Gently remove the tank from the Challenger.
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8.2.2
Note carefully which silicone fuel tube is applied
to which external metal pipe.
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8.2.3
Remove the silicone fuel tubes.
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8.2.4
Re-install a 50 mm (2 in.) piece of protective fuel
tubing from one pipe to another. This will serve to protect
the pipes from becoming contaminated with dust or
sealant.
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8.2.5
Remove the black rubber ring from the tank.
Apply a bead of silicone based sealant to the front face of
the tank in a circle around the stopper and put the black
rubber ring back on the tank.
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8.2.6
Apply a second bead of sealant to the front face
of the black rubber ring. Seal all the way around the neck
and onto the face of the rubber ring but don't over do it.
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8.2.7
Slip the tank carefully back into the fuselage and
fuel tank compartment keeping the metal tubes pointing
upwards and gently push the tubing and neck through the
firewall and snake the tubing out between the engine
mounts.
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8.2.8
Push the tank firmly forward to squish the
sealant against the backside of the firewall and out into
the hole in the firewall.
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8.2.9
Remove the protective piece of silicone tubing
that you installed between the metal pipes.
After balancing your Challenger and possibly moving the
battery pack in order to get the CG right, you should seal
the fuel tank into position with silicone based sealant.