L-1011 Trainer Installation: Fuel Indication - Power-On Tests

L-1011 Trainer - Fuel Indication System

Getting the instrumentation online is quite exciting because suddenly the Lockheed L-1011 simulator/trainer gradually starts to come alive. Today I powered up the Fuel Indication system. It consists of 4 tank gauges and a fuel totalizer. The four fuel gauges feed signals to the Fuel Totalizer who then displays the total fuel load and allows for the Gross Weight of the aircraft to be entered prior to takeoff.

I have previously quite extensively blogged about the Fuel Level indicators, and you can find the more detailed blog posting on the Fuel Level indicator and the Fuel Totalizer by clicking on the link.

Below is a video that shows the #2L and the #1 fuel level gauges active and feeding data into the totalizer on the left hand side. For the test the indicators are instructed do point to roughly 1/2 tank full by supplying 5VDC to the instruments.

We are missing a Deutsch 15-S7 connector ... until then we are not able to power up the #3 tank gauge. If you have one ... let me know.

L-1011 Avionics Bending: Fuel Quantity Indicator Test (Video)

The youtube video above shows the Lockheed L-1011 Fuel Quantity indicator powered up using a 115V 400Hz power source and driven by a National Instruments 6024E card. You can find the pinout for the Fuel Quantity Instrument here. The device uses about 26mA during operation and roughly 15mA at rest. The simulated transducer signal for the fuel level in the tank ranges from 0VDC to +10VDC. In the test the instrument is driven from 0VDC to +5VDC. 

Avionics Bending: Total Fuel Quantity Indicator - Pinout

The Total Fuel Quantity Indicator is used to display the aggregate data from all individual Tank Fuel gauges. The instrument has two digital drum displays showing the total gross weight and the total fuel weight. The gross weight can be manually adjusted to give the total weight.

Just as the the individual Tank Fuel indicators, the Total Fuel Quantity Indicator is made by Simmonds Precision in Vergennes, Vermont. The one used on the L-1011 has a manufacturer serial number of 393081-105.

The Total Fuel Quantity Indicator consists of a several components:

1. DC comparator for each input channel

2. Polarity detector to determine if the instruments counts up or down

3. The stepper motor Controller

Each of the Tank Fuel Gauges has a DC voltage output on Pin 7. The DC voltage corresponds to the tank fluid level. The total fuel quantity indicator takes the four tank input signals and combines them into a single value. Below is the Pin-out for the Simmonds Precision 393081 Total Fuel Quantity Indicator:

Pin 1: Instrument Lighting 5VAC (Hi)

Pin 2: Instrument Lighting 5VAC (Lo)

Pin 3: Not Used

Pin 4: Not Used

Pin 5: Not Used

Pin 6: GND

Pin 7: 115VAC 400Hz Power Input

Pin 8: Not Used

Pin 9: Not Used

Pin 10: Tank Signal Ground

Pin 11: GND

Pin 12: Tank No 1 Input

Pin 13: Tank No. 2R Input

Pin 14: Tank No. 3 Input

Pin 14: Not Used

Pin 15: Tank No. 2L Input

Avionics Bending: Fuel Quantity Indicator - Pinout

There are four Fuel Quantity Indicators and one Fuel Totalizer on the L-1011 Fuel System panel. The four Fuel Quantity indicators have identical pinouts, however they have different scales. The Fuel Totalizer pinout will be discussed in another blog posting.

The instrument is a combination of pointer and digital display as seen below. The one I use in the example here shows the scale in Kilogram [kg] as would have been used on, let's say, a British Airways L-1011.

The instrument was made by Simmonds Precision in Vergennes, Vermont. The particular one used here in the blog posting has a MFR Part Number of 393090-115 and a Serial Number of 129E.

The arm and the digital display in the instrument are driven by a stepper motor. The tank level would have been sent to the indicator from a Tank Signal Conditioning unit located close to the actual tank. The main component pieces of the instrument are:

1. A DC Comparator analyzing the Tank Quantity as a DC value above GND.

2. A Polarity Detector to see if the counter should count UP or DOWN.

3. The Stepper Motor logic.

So all in all a rather simple instrument. Here is the pin-out for a Simmonds Precision Primary Fuel Quantity Indicator Model 393090:

Pin 1: Instrument Lighting 5VAC (Hi) or 5VDC

Pin 2: Instrument Lighting 5VAC (Lo) or GND

Pin 3: Not Used

Pin 4: Not Used

Pin 5: Tank Quantity GROUND

Pin 6: Tank Quantity as DC Voltage - Input

Pin 7: Tank Quantity as DC Voltage to Fuel Totalizer - Output

Pin 8: Not Used

Pin 9: Not Used

Pin 10: Not Used

Pin 11: Not Used

Pin 12: 115V 400Hz Power (Hi)

Pin 13: Power Ground

Pin 14: Not Used