*
In any other instance, if there is significant additional obstruction to the air
flow, then it may be necessary to provide externally forced/cooled air to the
amplifier.
3.3.2
Ducting Considerations
The amplifier is provided as standard with an air inlet cowl, the normal orientation of
which is pointing towards the base of the amplifier (see section 3.1). Additional cowls
are available from e2v technologies and can be fitted to the air outlet, in a similar
orientation to that of the inlet cowl. The cowls can be turned through 90
8
for an
alternative amplifier mounting configuration.
These cowls are designed to avoid driving rain entering the unit if a secondary cover
is not utilised. The cowls can be removed and replaced with circular duct adaptors,
which utilise the same fixing holes. These circular duct adaptors are available from
e2v technologies and are designed to accept 8.9 cm (3.5 inch) diameter ducting.
Any ducting connected to the inlet or exhaust will create additional back pressure,
reduce the airflow and increase the internal temperature of the amplifier. Each
amplifier is designed to handle some additional back pressure, but this must be
minimised. When designing ducting systems:
*
Keep ducting lengths to a minimum; check the amplifier maximum operating
temperature derating for the length of duct required.
*
Route ducting directly; avoid sharp bends and ensure that the minimum bend
radius is three times the ducting diameter.
*
Use the largest cross sectional area of ducting possible.
*
Use smooth walled ducting; avoid corrugated ducting as it is more restrictive to
airflow.
*
Transitions in ducting sizes should be smooth; avoid step changes.
*
Do not use ducting adaptors that reduce the internal cross sectional area of the
ducting.
If the installation dictates restrictive duct systems, install additional external fans to
provide adequate airflow and counteract the effects of ducting. Additional fans
should be installed on the air input to the amplifier, where the air is at its coolest.
3.3.3
Equipment Housings
All equipment housings, including basic flight cases, roof mount enclosures, cabins
and air conditioned rooms, have common cooling system design requirements:
*
Maintain an adequate supply of air to the inlet; a 58 cm
2
(9 inch
2
) unimpeded
aperture should be provided into any enclosure for each Stellar amplifier.
*
The local source and destination of cooling air should ideally be common, to
avoid back pressure caused by differential pressure effects.
*
Housings that are exposed to environmental wind effects should use a common
face for inlet and exhaust vents, to avoid back pressure caused by differential
wind effects.
*
Terminations of inlet and exhaust vents should be of a design that prevents
direct environmental wind effects, whilst avoiding creating additional restriction
to airflow.
*
If a sealed cooling system, with recirculating air conditioners, is used, an over
temperature alarm should be fitted to the cabin to detect air conditioner failures.
HBN63xx-1, Issue 8, Page 12
