UNDERCARRIAGE SELECTOR SWITCH

LEADING PARTICULARS

Stores Ref. No.:5CW/7836
Manufacturer:Dowty
Manufacturer Part No.:DN.1076Z Mk.4
Connection:6 BA screw terminals
Attachment:28DU/9419600 | A113/5B | Bolt, No. 6 UNC mushroom head

DESCRIPTION

This selector controls the undercarriage of the aircraft. It contains a 4 pole double throw switch (4PDT), and an interlocking solenoid.

The lever includes an integral spring loaded collar which requires lifting to unlock the lever from either the "UP" or "DOWN" positions, to avoid unintentional operation.

It contains an electro-mechanical interlock solenoid, which in the Lightning is controlled by a pitot pressure operated speed switch. This solenoid physically prevents the selector being moved to the "UP" position if the air speed is lower than 165 knots, which avoids accidental undercarriage retraction whilst on the ground. This solenoid can be manually overridden by turning the red knob clockwise in an emergency situation, or for maintenance when cycling the undercarriage with the aircraft supported on jacks. The selector can be moved to "DOWN", lowering the undercarriage at any speed.

These selectors were initially made by Dowty, but later by Ultra (UEL). The selector in use for this project is hand marked "BIN.7" signifying R.A.F. Binbrook, a home of Lightnings, and is a Dowty produced version.

MYTH BUSTING

Not only used on the Lightning, but they were also fitted to other aircraft. This is important to note, as often eBay sellers will falsely declare these to be exclusively TSR-2 parts, with the intention of driving the price up. This selector switch is also used on the following aircraft types (and likely more), the numbers are to indicate this parts actual "rarity":

So just on these numbers alone (not including other aircraft types to use this selector, still to be discovered), there is at most a 1 in 209 probability of one of these selectors having been used on a TSR-2 aircraft! Don't believe the eBay ads!

I have seen eBay sellers falsely declare the angle of the override red knob to signify TSR-2 - again this is complete BS; see my original research in the videos below which explain the knob angle, backed up by the literature in the references given.

REPAIR

The solenoid interlock of this selector was found to work intermittently, occasionally allowing UP to be selected with the solenoid de-energised.

Exploring the action of the internal interlock solenoid:

Adjustment made to the solenoid armature:

Unit re-built and tested:

SIMULATION

This selector can be easily interfaced to, as it contains just switch contacts and a solenoid.

The Lightning model for Flightgear already has the 165 knot pitot speed switch and relevant circuitry configured, so operating the solenoid will be straightforward.

REFERENCES

Dowty literature:
DE/80/2/500/R/JC, 1076 series Undercarriage Lever Switch - Source: Dowty Heritage ↗
DE/80/1A Norman Brothers Ltd. January 1971, 1076 series Undercarriage Lever Switch - (Note price in pencil)
DE/23/3/AD/762/JC, Type DN.1076.Z series Undercarriage Lever Switch

T Mk. 5 electrical "Vol. 1":
AP101B-1005-1B, Section 6, Chapter 5, A.L.54, June 1973, Alighting Gear and Brake Parachute - Paragraphs 2 to 5

T Mk. 5 wiring diagrams:
AP101B-1005-10, Sheet 20, A.L.5, Dec. 1984, Alighting Gear