L-1011 Procedure: APU and Air Conditioning Startup

When the simulator is powered up and the EXT POWER switch located on the simulator power control panel is in the ON position the simulator emulates the behavior of the aircraft sitting on the ground with external power connected to it.

The next step will be to start the APU. The APU will be started by the Flight Engineer with the following procedure:

If external power is not in use, but the green AVAIL light is illuminated, actuate the external power switch. This will provide AC and DC power to the simulator systems.

Note: If external power does not turned on in the simulator, turn the battery switch ON . This will provide power to the simulated Ground Control Unit (GCU) and the DC standby bus. Once external power is on the simulator, it will be able to power the GCU through the DC standby bus.

Prior to starting the APU, check the fire detection system for the APU and engines.

1.  Detector loop selectors ....... BOTH

2.  Detector loop lights .. EXTINGUISHED

3.  Press A & B Test buttons simultaneously and check:

• Waring bell is on (press cutout to silence)
• A and B loop lights illuminated 
• Master fire warning lights on glare shield illuminated 
• Fire Pull handles illuminated 
• FIRE DET LOOP annunciator light on Caution and Warning Panel

APU START PROCEDURE

From Lockheed L-1011 Flight Training Manual

1. Select DC meter to BAT and AC meter to APU. Check that the BATTERY CONDITION light on the APU panel is not illuminated.

2. Position the APU master power switch to ON. (OBSERVE: Primary emergency shutoff fuel valve opens. AUTO FIRE SHUTDOWN ARMED light on APU panel illuminates.

3. IF external AC power is available, turn on #2 fuel tank pump.

4. Position the Bleed Air Mode switch on the APU Panel to MIN MODE.

5. APU Bleed Air S/O switch unlatched and OPEN light extinguishes.

6. Press the Start switch until the DOORS IN TRANSIT light illuminates. (OBSERVE: DOORS IN TRANSIT light cycle as the engine inlet and APU compartment ejector doors open).

After pressing Start, monitor the following:

• DONT LOAD light and APU GEN OIL PRESS light (on the electrical panel) illuminated after DOORS IN TRANSIT light extinguished. 
• While the APU RPM and APU TGT are increasing, check the Battery volts and amps. If either is low the simulator is presenting you with an abnormal APU start. 
• When APU RPM and APU TGT have stabilized in the green range, with the DONT LOAD light extinguished, check that the APU generator field flow bar is illuminated, generator oil PRESS light extinguished, and generator volts and frequency are normal 

      Voltage = 117 +/-2, Frequency = 401 +/-2Hz

• Check APU generator KW load. 81KW max, but normal around 40-50KW with system on.
• DC ammeter indicates normal battery charging. 

Preparing for APU Air

From Lockheed L-1011 Flight Training Manual

1. Aft fuselage ISLN and both crossbreed valves are latched in.

2. Pack Flow Control valve switches unlatched (closed). When Pack Flow Control valve switches 2 and 3 are unlatched, their hot air valves should be unlatched at the same time. 

3. Pack Auto/MNL switches latched in --> AUTO illuminated 

4. Ground control switch latched in and legend not illuminated. 

5. Aircraft zone air trim switches latched in and not illuminated. 

6. Zone temperature control to 12 o'clock position. 

Accepting APU Bleed Air

From Lockheed L-1011 Flight Training Manual

1. Latch in APU Bleed Air S/O switch and observe the OPEN legend illumination.

2. Observe bleed air pressure on the engine duct pressure indicators.

3. Latch int he No. 2 pack flow control valve and its hot wire valves.

4. Turn the APU Mode Selector to Normal.

Simulator Integration Planning: ATA 21 - Air Conditioning and Pressurization (Label Assignments - Part 3)

L-1011 Air Cycle Machine Temperature Ranges

In order to program the AC behavior of the L-1011 correctly we will have to go a bit deep on the various parameters in the system. First, lets take a look at the normal temperature ranges we should observe on the ECS Monitor in cruise flight. The numbers in the table below correspond to the numbers in the image above:

• [1] Pack Inlet Bleed Air Temperature ... 160º-200ºC in cruise
• [2] Compressor Discharge Temperature ... 60º-80ºC in cruise (depending on Turbine bypass valve setting)
• [3] Turbine Inlet Temperature ... 15º-20ºC in cruise (will vary with RAM air setting)
• [4] ACM Discharge Temperature ... 15º-20ºC in cruise. The lowest possible ACM discharge temperature is 2ºC
• [5] Hot Air Manifold Output Temperature .... 110ºC

The normal Pack Flow outflow for Pack #2 and #3 is between 2000 and 2500 CFM (#1 has 300-400 less). The spring loaded valves for the Pack Flow Control and the Hot Air Manifold will not open if the duct pressure is below 15 PSI.

Warning Indicators

• Pack Flow Control Switch OVHT light illuminates when the Compressor Discharge Temperature [2] exceeds 200ºC or when the ACM Discharge [4] temperature exceeds 96ºC.
• DUCT OVHT ... illuminates when the Hot Air Manifold Duct temperature has reached 145ºC. This causes both Hot Air Isolation Valves to close until the temperature falls below 120ºC.
• Hot Air Isolation Switch OVHT ... illuminates when the respective valve has reached 135ºC

Valve Position Values

There are a number of default valve position values that the system simulator needs to take into account.

Turbine Bypass Indicator - The turbine bypass value is positioned full warm until the RAM AIR louvers have reached the full cool position as indicated on the RAM AIR indicator (9 o'clock  on the ground or 1 o'clock position in flight). Once this status has been reached, the turbine bypass valve will now be positioned to hold the required temperature. With the pack turned off, the turbine bypass valve will be set to the 11 o'clock position by default.

RAM Air Indicator - With the Pack turned off the the louvers are automatically set to the 9 o'clock position on the ground and the 1 o'clock position in flight.

Turbine and RAM Positions on Ground.

Turbine and RAM Positions in Flight.

In part 4 of this series we are going to start developing a model that will allow us to compute the approximate temperatures and cabin zone temperatures base on the relationships established in normal cruise flight. Again, the idea is the create a systems simulation of the L-1011 air conditioning and pressurization system that is as real-world as feasible for this project. 

Simulator Integration Planning: ATA 21 - Air Conditioning and Pressurization (Label Assignments - Part 2)

L-1011 AC Pack

Simulating the L-1011 Air Conditioning and Pressurization for the simulator will be a lot of fun. As you saw in part one of this posting, the basics of the pressurization system for the aircraft is realized in the Laminar Research x-plane simulator. However, the Air Conditioning system is not implemented at all. To make the simulation complete these systems need to be simulated in software as well

The image above shows a single AC PACK for the L-1011, there are 3 of them in the system. Each of them has a number of switch controllers. For simplicity of this blog posting I will only talk through one of the packs (pack 2) but the others work exactly the same way.

So we start from top to bottom:

1. Pack Flow Control Switch

Pack Flow control is a switch light that shows either a FLOW BAR or  OVHT (Overheat). Here are the two elements on the actual panel and in the schematic:

The schematic shows a small [S] next to the valve. This indicates that this valve is spring loaded to shut.  In other words, when pressure is coming from the bleed air system the valve will be pushed open by the pressure and the flow bar will illuminate. When the valve gets too hot (bleed air too hot) the OVHT warning illuminates. So why is it a switch if all it takes to illuminate the bar is pressure on the valve. When the switch is "latched" (in) the valve is in normal operation and does exactly what I just describe. When the switch is unlatched (out), however, the valve is permanently closed and will never open, even with bleed air pressure.

2. Hot Air Switch 

The hot air switch allows for bleed air to be directly fed to the hot air planum. The valve is spring loaded [S] and opens automatically with pressure from the bleed air. When the valve is pushed open, the flow bar will illuminate on the switch. This is the normal operation when the switch is latched. When the switch is unlatched the valve will remain closed even with bleed air pressure. When the switch is unlatched the OFF legend illuminates.

3. Temperature Control 

Bleed air from the pack flow control valve (1) is cooled through a primary and a secondary heat exchanger. The cooling provided by the heat exchangers is controlled by the position of the RAM AIR exhaust doors which determine the flow of ambient outside air across the heat exchangers. This is the primary way of cooling air. Additional cooling is provided as needed by the Air Cycle Machine (ACM).  The ACM is a combination compressor and turbine powered by the bleed air flowing through the pack. When the ACM is working primary air from the primary heat exchanger passes through it and is heated by compression, cooled again by the secondary heat exchanger and the rapidly expanded by the turning for additional cooling.

The amount of cooling provided by the ACM is controlled by the Turbine Bypass Valve.

The system either operates in an automatic or manual mode as selected by the switch-light. Latched (in) the mode is automatic and ram air outlet and turbine bypass are controlled by the planum temperature demand. When unlatched (out) the system is in manual mode and the WARM and COOL momentary switches drive the position logic for TURB BYP and RAM AIR.

4. System Monitoring

There are a number of controls and gauges that allow the monitoring of temperatures in the system. All monitoring happens on the the ECS Monitoring panel:

There are a total of 5 temperature parameters that can be monitored for each AC Pack (controlled by the PACK SELECT switch on the ECS Monitor panel). They are:

1. Pack Inlet Temperature taken right before the Pack Flow Control Valve
2. Compressor Discharge Temperature measured before air from the ACM enters the secondary heat exchanger.
3. Turbine Inlet Temperature measured after the secondary heat exchanger and prior to air entering the turbine 
4. Air Cycle Machine (ACM) Discharge Temperature is measured after the air leaves the pack and water separator and prior to it being mixed into the Cold Planum. 
5. Hot Manifold Temperature is taken prior to hot air entering the Hot Air Manifold. 

Lastly, the air flow in Cubic Feet per Minute is displayed on the PACK FLOW meter also on the ECS Monitor Panel.

Software Considerations

All in all the system seem pretty complicated, however, from a software perspective it should not be too bad to model a somewhat lifelike system. Each PACK will be an object with attributes and parameters. The code will not attempt to compute actual air flow or heat exchange but will simply roughly approximate what the system would do under certain ambient air and airspeed conditions.

Ambient outside air at altitude and airspeed we can both get from x-plane as a dataref:

sim/weather/temperature_ambient_c
sim/cockpit2/gauges/indicators/airspeed_kts_pilot

With these two I should be able to develop an approximation of cooling efficiency of the air at altitude and simulate the automatic or manual operation of the ACM systems. As mentioned earlier, many of the spring loaded valves open automatically with bleed air pressure in the system. For bleed air there are also a number of datarefs that will come in handy:

sim/cockpit2/annunciators/bleed_air_off ... for each engine
sim/cockpit/warnings/annunciators/bleed_air_fail ... for each engine