will prevent a shutdown during the first
Kerosene is drained through the UAT
to remove the trapped air in the paper
or cloth membrane. It’s easy to do with
the higher flow of a fuel filler pump. On
a new installation, one starts the turbine,
and then at a higher throttle setting
shakes the UAT until the trapped air in
the membrane is released with the air
bubbles flowing to the turbine pump.
If an air bubble is large enough, it can
result in a turbine flameout.
The method you choose to ensure
that all of the air is out of the UAT
membrane is not important, but make
sure you do it before attempting the first
takeoff. I have aborted more than one
takeoff because of a loss of power that
was caused by excess air bubbles in the
Landing Gear Systems
Pneumatic braking systems have
been around for decades and are well
developed. Set the brake proportional
valve by applying the desired brake
travel, and then pull the model on the
ground, making sure the tires still rotate.
If they are locked up, you have too much
brake power. The tires will lock when
brakes are applied, flat-spotting your
tires and reducing your travel volume.
If you have one of the electronic
valves that bleeds air off for proportional
braking, set the maximum air pressure
to pump up the brake system based on
this test. Full air pressure will still allow
the tires to rotate when they are pulled.
Many of today’s jet models are
equipped with electric brakes, so take
your time setting them up, read the
instruction manual, and follow the
directions, because each system has
nuances particular to that manufacturer.
Electric brakes are improving with
increased reliability and control of the
braking action. I am sure this trend
will continue. Remember that they are
typically set up for a specific battery
voltage. Varying from this voltage will
affect the braking efficiency.
You’re almost ready for the test flight,
but let’s get back to the basics with the
landing gear retract system. First on my
priority list is to check the operation
before installation for full freedom of
movement. I still get retracts that are
machined so tightly that they do not
lock in either the up or down position.
My preference is to have enough
clearance in the lock system to not jam
when the inevitable dust and dirt get
into the retract unit. A little touchup
and deburring with a file can ensure a
reliable landing gear system.
Check for loose screws in the retracts.
It’s amazing how many retract gears I
have seen with some side-plate screws
tight and others loose. A good rule of
thumb is that if any loose screws are
found, pull them and reinstall them with
a dab of Loctite Threadlocker Blue to
ensure that they do not loosen with use.
Make sure that all of the axles have
flat spots for the setscrews to dig into.
Not many strut manufacturers take
the time and effort on this small, but
Jet Pilots’ Organization
106 Model Aviation MAY 2016