Panavia Tornado Combined Indicator
This article is about the Panavia Tornado 'Combined Indicator'. The Combined Indicator is a cockpit instrument to indicate the position of the:
This instrument is used only for the Panavia Tornado. The Panavia Tornado is the only airplane that can change it's wing position between 25 and 67 degrees as also marked on the indicator panel. The angle of the wings in relation to the fuselage can be changed in flight by the pilot. (Some Tornado's are outfitted with an automatic wing-sweep system to reduce pilot workload.) When the wings are swept back, the exposed wing area is reduced and drag is significantly decreased, which is conducive to performing high-speed low-level flight.
The instrument I have is marked with the following information:
Name: Combined Indicator
Part No.: 1015
Manufacturer: Farem S.p.A.
Year of manufacturing: 1985
The instrument is painted gray. The color is almost identical to RAL7031.
I bought this instrument in original (sealed) working condition with documentation.
Source: Wing angle information: https://en.wikipedia.org/wiki/Panavia_Tornado
The Combined Indicator is located at the left hand side of the front cockpit. The indicator location is marked on the image below.
There's only one connector placed on the back of the instrument. There's a (common) 19 pin circular connector as shown below. The pinout map is also shown below.
reverse engineering and schematic
There's no documentation nor description found, so the information is an 'educated guess'. So if you want to repair your own Tornado, remind that the information here is mainly suitable for educational/hobby purposes. ;-)
I spent some time (non destructive) reverse engineering to document the electrical design of the instrument. The results are shown below.
There's an independent circuit for panel illumination. By applying 5 Volts to pins K and L, the instrument panel is illuminated. The total current drawn is 428 mA. Therefore probably four 500 mW lightbulbs are used.
The indication is done by four galvanometers. Each galvanometers has two series resistors to (probably) match the current with the desired meter deflection. Each galvanometer has it's 'own' printed circuit board for the two resistors.
There are two pins J and M connected to the chassis ground and EMI filter caps. The rest of the circuit is 'floating'.
There's a main printed circuit board that acts as an interconnection board for all the signals. On the board are a diode, two inductors and two capacitors placed. The diode is probably to protect reverse polarity of the power input and the inductors and capacitors are likely used to act as a low pass EMI (Electromagnetic Interference) filter. There's a power resistor and a zener diode placed on the rear panel that acts as a crude voltage regulator. Depending on the input voltage the output voltage is approximately 15,7 VDC. The higher the input voltage, the more power is dissipated in the power resistor. Therefore it's likely that the input voltage is a little higher than 16 VDC. The bias current is 170 mA at 28 VDC input. So that's almost 5 Watts of heat. Therefore I think the input voltage is probably not the 'regular' +28VDc input voltage... If an output (C, E, F, N and/or S) is short circuited, the current is therefore also limited to (28V/68R=) 412 mA to protect the wiring. Since there are four galvanometers, five power outputs and four 'return' pins (via resistors), it's likely that the power outputs are used to power the four position sensors that sends the indicator signal back to this instrument. This is a rather safe assumption of the field components, but remind that this is still an educated guess.
controlling the instrument
The instrument is rather simple. The main components are four galvanometers to indicate the four meter positions. By applying a certain DC voltage, the meter deflection is obtained. By applying a 5V (approximately 428mA) to pins L an K the panel is illuminated. The rest of the circuit can be ignored. The four galvanometers have one common connection connected to pin B. Each galvanometer can be controlled individually by applying a voltage (up to approximately 16VDC). Sometimes a small bias voltage is needed to set the needle at it's start position. The voltages I needed for the corresponding indication is shown below.
|Input D for flaps
|Input T for airbrake
|Input P for wings
|Input G for slats
| UP = +2,0 VDC
MVR = +5,5 VDC
MID = +13,3 VDC
DWN = +15,0 VDC
| IN = +5,5 VDC
MID = +11,0 VDC
OUT = +16,0 VDC
| 25Âº = +2,9 VDC
45Âº = +8,8 VDC
58Âº= +12,3 VDC
dot = +14,0 VDC
67Âº= +15,6 VDC
| UP = +2,2 VDC
MVR = +10,2 VDC
DWN = +15,1 VDC
This results that this instrument is rather easily controlled. The meter deflation can be created by a variable resistor that acts as a voltage divider but controlling the meters using a microcontroller (Arduino board?!) with an opamp (to amplify the voltage form 5V to 16V) is also rather easily done.
reverse engineering images