Retractable landing gear are mechanical and pneumatic contraptions
that require proper installation, some periodic maintenance and preflight
inspection if we are to expect reliable operation.
BVM kit instructions cover the installation of the units, struts and
wheels. We would like to emphasize here that when using retract units with up
locks, the struts and wheels should not touch or rub against any structure when
in the gear up position.
interference when the gear is trying to reach the "up lock" position requires
extra force from the air cylinder. If that force is available and it does get
to the up and locked position, there is a good chance that the gear will not
unlock and extend because each cycle reduces the available air
If your model experiences
a hard landing or hits a bad bump or hole in the runway such that the strut is
bent even slightly, it may cause the above situation to occur.
Prior to the first flight of the day,
cycle the landing gear system and watch the air pressure gauge on your
pump or the mini gauge in your model to
observe how much pressure drop occurs to retract the gear. Observe the gauge to
be sure that it does not continue to drop while the gear is up. Sometimes it
takes a few cycles for the cylinder "O"-rings to seal, especially on a cold
thin lube will usually help a lazy
cylinder to reseal.
Sourcing an Air Leak
If you hear a hissing sound coming from the air selector valve,
there is a good chance that the valve is not at fault, but rather a cylinder
"O"-ring is not sealing and the air is bypassing and thus exiting at the
Unless an air leak is
very obvious, i.e. a disconnected tube, use a pair of forceps to pinch off
sections of the system, starting at the air selector valve until you isolate
The solid color (verses translucent) air line tubing that BVM switched to in 2001
appears to be good for at least 3 years of use in a model and we sometimes
pressurize the systems to 120psi.
High Flow Rate Selector Valve
All graphics and photos
Copyright 2010 BVM, Inc.
Use of graphics or photos without written permission from