21B Environmental/Air Conditioning
|
TTP |
B1-L3 |
ATA21B |
|
Beech 90 Series |
B2-L3 |
Pressurization |
21 Environmental/Air Conditioning
00
General
10
Compression
20
Distribution
30
Pressurization Control
40
Heating
50
Cooling
60
Temperature Control
70
Moisture/Air Contaminant Control
INTRODUCTION
The environmental system
consists of the bleed-air
pressurization, heating, and cooling systems and the associated controls.
LJ-1
through LJ-501 consists of an 80,000 BTU combustion
heater and a 16,000 BTU refrig- erative air
cooler working through a cabin temperature control box maintain cabin comfort. Pressurization for the cabin is provided by either a hydraulic driven (King Air 90), or mechani- cally driven (King
Air A90/B90) Roots type supercharger. The King
Air B90 had an optional auxiliary pressurization system which
utilized engine bleed air from the right engine to provide additional or alternate pressurization.
In
the following configurations; LJ-502 and after, LW-1 and after, and LA-1 and after,
the cabin heat and pressurization are provided
by engine bleed air supplied by
each engine. Cabin heat may be supplemented by electric
heat. The air conditioner unit is electrically driven, has a capac-
ity of 16,000 BTU and uses a refrigerant
gas.
GENERAL
Air
for pressurizing the cabin, heating the cabin and cockpit, and operating the aircraft
pneumatic system is obtained by bleeding P3 compressor air from each engine (refer to the MSM). This engine
bleed air is ducted from the engine to the flow control unit on the lower engine mount trusses. A pressure supply line, to
operate the pneumatic system, tees off
the bleed-air line just aft of the first
fire seal forward of the firewall. The
bleed air from either flow control
unit provides adequate air for pressurization, heating, and the pneumatic system should
the opposite engine fail.
The
bleed air and ambient air from
the cowling intake are mixed
together by the flow control units to produce a total airflow
of 14
pounds per minute from both the right and left engine
units. Bleed air comprises as much as 10 pounds
of the total airflow
on cold days and as little as six pounds
on hot days. The air from each flow con-
trol unit is ducted aft through the firewall along the inboard side of each nacelle, inboard through the center section forward
of the main spar, and into the fuselage. The heat in the air may either be
retained for cabin heating or somewhat cooled down
as the air passes through the center section to the fuselage.
To
cool the bleed air, it is routed through an air-to-air
heat exchanger where heat is transferred
from the bleed air to outside ambient ram air. The ram air enters a duct on the wing leading edge and is dumped overboard
through a vent on the bottom of the wing. A variable bypass valve, adjacent to each heat exchanger, allows the hot
air to be ducted through, or around, the heat exchanger controlling the amount of heat sent into the cabin air ducts.
The
right and left bleed-air
lines meet at a tee on
the right side of the fuselage under
the cabin floor.
Two flapper valves prevent the loss of pressure
should either engine fail. The bleed-air line from
the tee is routed forward along
the right side of
the fuselage through a muffler to a mixing plenum underneath the copilot rudder pedals.
A venturi has been plumbed into the bleed-air line immediately forward of the muffler. Two test lines, tapped off from the high- and low-pressure areas of the venturi, are routed to immediatelyaft and below the static system drains beside the copilot. A manometer can be connected to the end fittings of the two lines to measure bleed air flow.
The
bleed-air lines from the engine compartment to the plenum are wrapped with insulation and aluminum tape to reduce heat loss. Air
from the top of the plenum is routed through ducts behind the instrument panel to
outlets on each side of the cockpit
and to the defroster outlets for the wind- shield. Valves to each outlet and the defroster duct control the flow
of heated air into the cockpit.
These valves are regulated by
push–pull controls on the subpanels. A low-pressure duct from the aft side of the plenum extends aft under
the right- hand seat deck of
the cabin and distributes the heated
air through the floor
outlets on each side and aft of the cabin.
The
heating/cooling system consists of engine bleed air supplemented by an electrical
heater or a
16,000 BTU vapor-cycle air conditioner
to maintain cabin comfort.
The systems may be operated in automatic mode, manual heat mode, or manual cool mode. The
hourly output of the bleed-air
heating system is 45,000 BTU.
During extremely low temperature or low power settings, additional heating
is available from
an electrical heater containing eight heating elements
rated at
1,000 watts each. The
maximum output of the electrical heater is 27,300 BTU during ground operation with all eight heater
elements operating. Only four elements
are available during flight
for a total output of 13,650 BTU. The aircraft
electri- cal system is
protected against an
overload
by a
lockout circuit that prevents
use of the electrical heater during operation
of the propeller deicers or windshield deicers.
|
PTP Beech 90 Series |
B1 |
LOC |
FOT |
|
MEL |
TS |
|
|
B2 |
LOC |
FOT |
|
MEL |
TS |
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