Victor gyroscope help needed

Sounds like a primary pitch potentiometer problem. The voltage between the wiper and an artificial centre tap drove a current (1mA fsd perhaps) through the moving coil pitch attitude pointer mechanism. Attached are a circuit that should help and a description of the ESU operation. I also have the ESU AP chapter if you need or want it (112C-0600-1B Section 4 Chapter 23A).

Hi Terry,

Thanks for your comprehensive replies! The gyros that are fitted in the tray beneath the Nav Radar desk work perfectly, the ones you see have just been slaved in using extra cables to the aircraft hence only one at a time is moving so the failure flag is appearing. It is one of the spare gyros that when slaved into the main system displays roll but no pitch. Without the dedicated test facilities this is the best we can do. Continuity and resistance checks on the spare gyro might tell us something!

The aircrafts MFS works as per spec with no failure flags or lights, we plugged the MFS test set in not too long ago and everything was in limits. Not bad for the ‘mystery’ flight system!

I guess your photo was taken without the “115V AC” switched on. (In the Vulcan this came from the 200V supply via transformers.) That would account for the MFS Power Failure Indicator being illuminated and the red “Attitude Failure Flag” showing in the Stbd Director Horizon. If the 115V power was on when the photo was taken then it’s a whole different scenario!

Did one or both (port and starboard) Director Horizons show any movement or attempt to oscillate and erect when the power was switched on?
Since the MFS Power Failure Indicator is illuminated and the red “Attitude Failure Flag” is showing then perhaps some of the fuses have failed (there were both aircraft fuses and fuses in the large MFS Junction Box) and this has been detected by the “Single Phase Supply Monitor” (a torque switch) which has then interrupted the DC and operated the light.

If the port (pilot’s) DH did erect then the co-pilot’s attitude failure flag could be on because there is, probably, a difference in the port and starboard DH roll and/or pitch indications, again perhaps due to a power supply failure to the starboard system.

However assuming the photo was taken “power off” but that you know that one or both of the attitude systems failed to run up when power was applied then I would guess that one or more of the time delays in the Erection Switching Unit has failed to switch at 20 seconds and thereby failed to remove the boosted supplies. This would probably result in damage to the gyro erection motors and/or the gyro motor itself since they were designed originally to run on lower voltages.

As sealed units, they are difficult to get into! And even if you could, then replacement of the motor windings is probably impractical and that even if you had replacement windings.

But continuity and resistance checks on the gyros themselves may give some clues! Especially if you have one reasonable gyro to compare readings against.
I do not have any spare gyros, Director Horizons or an Erection Switching Unit, though I may have a good Comparator Unit if you need it.

Some circuits I do have which I can email as attachments.

The two vertical gyros were fitted in a Mounting Tray which fitted into a Mounting Rack. However the tray also container the “Comparator Unit” which formed the backplate of the Tray and which connected to the Cannon plugs on the Rack. The Comparator unit acted as a junction box and also compared the roll and pitch output signals from the port and starboard gyros, and operated the failure warning flags.

Power supplies of 115V 400Hz 3 phase came from the aircraft’s electrical system into the comparator unit and then to the vertical gyros. However in order to provide faster run-up and erection of the gyros, an “Erection Switching Unit” (the box on the left in your photo) was inserted so that electrically it was between the comparator unit and the two gyros

The ESU ensures that the VGs are at full speed and erected within 30 sec of switch on. This is achieved by boosting the 115V supplies to 200V for 20 sec and after 5 sec switching the normal 20V erection motor supply to 115V for 15 sec or until erection is complete.

To achieve full operation in 30 seconds, at 5 seconds it boosted gyro rotor supply from 115V to 200V AC, provided automatic fast erection of gimbals with boosted erection motor supplies (from the normal 20V to 90V) and cut out the turn detector switch action which provided the “pitch/bank erection”.
Then at 20 seconds it switches the gyro rotor supply back to 115V and allows reversion of the erection motor supply to 20V if the gimbals erect.

Failure of the switching circuit can, and did often, result in damage to the gyros.

I have some more details such as some of the circuits involved but this may be heavy stuff for many forumites so feel free to PM me with an email address I can send them to.

I will try to write something to act as a bit more of a diagnostic aid for you, too,

Terry

Sure it’s not the vac system

They will spend a long time looking for any vacuum system associated with the Smiths MFS.

exmpa

Sure it’s not the vac system, if it’s low it won’t fully erect, if it’s the instruments, it sounds like a wee bit of corrosion on the bearings stopping it spinning up fully.

If you have no joy elsewhere you could try

http://www.aircraftinstrumentsltd.co.uk/about-us.html

Oohhhhh–rgr that Mike. Thanks.

Bill T.

Terry’s away on a long weekend celebrating his (?nth) wedding anniversary this weekend so don’t expect an answer until next week.

Anon.

Thanks a lot for that Bill.

Hello Sven,
The person who readily comes to mind on these would be forumite: Terry P. I’ll pass the word along to him.

Bill T.