ASX-1 Operating Manual
Page 10
11 Installation
Connect the static port to a suitable static air pressure line. If you have a slow aircraft or an aircraft were the internal cabin
pressure does not change during flight and is equivalent to the outside air pressure you may find that it is not required to
connect a static port. For installations in typical ultralight aircraft pods, be aware of possible pressure changes inside the
pod during flight caused by ram air or suction effects. This may lead to a false indication of altitude and/or airspeed. Often
these effects are dependent on the current angle of attack of the airflow around your pod. You will need to install a
suitable static port in these cases. Connect your pitot tube to the “pressure port”. Pitot tubes are found in a large variety at
your aircraft parts shop, in mail order catalogs or you can make your own. Contrary to popular belief, pitot tubes are not
carefully designed and calibrated, but are simple orifices or tubes that get pointed in the direction that you are flying. The
forward movement of the aircraft causes air to dam inside the pitot tube. This increases the pressure inside the tube. Most
small aircraft such as ultralights or microlights do not require a connection to a static port. In these cases, simply leave the
static port open. Ensure however that the static port does not receive pressurized air due to the forward movement of the
aircraft. Be especially critical of your pod or panel if you do not use a static port. Any build up of a pressure differential due
to ram air or suction can lead to large errors of the indicated airspeed. Static ports are usually mounted at a strategic
position on the rear side of the aircraft fuselage for faster, pressurized aircraft. Suitable pitot tubes can be made from a
short piece of hollow aluminium or copper piping. Length and diameter are not important. Ensure that the front of the pitot
tube has a suitable chamfer if you use thick walled tubing or you may introduce a speed reading error if you have a faster
aircraft.
Example cross-section of thick walled pitot tube.
Suitable connection hose for both pitot tube and static port can be obtained from a hardware store or even a pet shop.
Good quality tubing is often used for fish tanks and it has just the right diameter. Please note that this kind of tubing is not
advised for pressurized aircraft. In this case you would need to obtain aircraft grade tubing of suitable diameter. You
would also have to use hose clamps to fasten the hose onto the ASX-1 pitot and static ports. The ASX-1 allows you to
calibrate the airspeed reading. This is done in the “Calibrate” menu item. The main reason for this is to be able to remove
errors introduced due to the airflow around your aircraft which may have an effect of your pitot tube pressure.
11.1 ASX-1 DB9 Cable connections
DB 9 Pin
Color
Function
1
Black
Ground
4
RCA
(Inner
cable)
Airtalk communication
Used for firmware upgrading and
interfacing to the FF-1/SP-X (Airtalk speed
message) or the CNV-AT (Airtalk to
parallel Gillham code output encoder)
6
Red
8-30Vdc power
9
White
Alarm Output
