L-1011 Avionics Bending: Collins ADI Power On Test (Video)

The video above shows the Collins ADI used on the Lockheed L-1011 during my first power-on test. According to the tear-down tags that came with the unit these ADIs had not been powered ever since 1998. The power-on test is a gradual test where I power on the device and run one or two functions. I study the power consumption and look for obvious problems with the power supplies. In later avionics bending posts you will see the devices progressively integrated with the flight simulation environment.

The power-on tests are important to the project because the show me what does and what does not work. So far I have had a pretty good success rate and I would say that about 75% of the instruments that I have bought over the years out of surplus have powered up.

In the video above you see the Glideslope function active in both normal as well as Flight Director, or Gate, mode. In gate mode the pilot would receive the Localizer/Glideslope information superimposed on the ADI as a round gate. The pilot would simply fly the aircraft down the gate or the Autoland system would follow the Gate.

The ADI is powered by a 115VAC 400Hz power source and the ADI and LOC deviations are driven by a National Instrument 6024E card over a range of -3VDC to 3VDC. 

L-1011 Flight Controls: DLC and Glide Slope (27-41/44)

The image above shows the aircraft on approach path. DLC spoilers 1, 2, 3 and 4L and 4R are up to null position of approximately 10º up. The spoilers will operate up to 20º or close to 0º from the null position with session of Pilot or Autopilot pitch inputs. 

Once panels have moved to a position from the 10º null position they drift back to the null position ready for the next excursion.

If the aircraft moves above the glide slope, DLC commands spoilers 1, 2, 3 and 4 open to 20º reducing approximately 10% of lift. 400,000 lb. of weight results in a -40,000 lb. of lift reduction. The airplane returns to approach path with only a minor pitch change. This provides increased passenger comfort. 

If the aircraft has drifted below the glide slope, pitch input causes the close the increasing lift and the aircraft flies back into approach path with only minor pitch changes. DLC serves one additional important function: its use reduces the size of the landing touchdown zone scatter. Thereby improving category III autoland precision.

The image above shows the Surface Position Indicator with DLC spoilers 4 and right 2 indices traveling also the speed brake lever traveling in the DLC range in response to pilot commanded stabilizer movements.

DLC automatically disengages under any one or all of the following conditions:

1. Stall Warning 
2. Go-Around Switch Activated
3. Any two Throttles Advanced 
4. Flaps Retracted less than 30º
5. Pilot-mnaual Override of Speed Brake Lever
6. Pilot Assist Disable Switch Pressed
7. System Failures

L-1011 Autoflight: Glideslope Capture and Track (22-31)

Glideslope capture cannot be initiated until after localizer capture is initiated, but localizer track status is not a pre-capture requirement. Nearly simultaneous capture of localizer and glideslope is poossible. The glideslope is normally captured from below the beam, but it can also be captured from above using vertical speed as pitch pre-capture guidance. When glideslope capture starts, the GS ARM annunciation changes to GS, and the pre-capture pitch mode is released, removing its annunciation on the AFCS MODES panel. A glideslope capture timer also start with initiation of glideslope capture.

When 25 seconds have elapsed on the glideslope capture timer and the glideslope deviation is 1/6 dot or less, the status changes from glideslope capture to glideslope track. This change in status it not annunciated. When these conditions have been satisfied, a glideslope gain change takes place reducing sensitivity of the autopilot/flight director system by 75 percent. This gain change is to partially compensate for glideslope beam convergence as the airplane approaches the transmitter.

Direct Lift Control (DLC) becomes active when the flap handle is moved through the 30 degree position.