Originally Posted by
supakva
I have no knowledge of compass workings, is this a major problem that will cost lots more money, or is it a simple fix.
For its day the Compass System on the Mark 2 was state of the art but in a modern context is actually quite simple.
There are really two areas where there may be problems, neither usually difficult to fix. One is the MFS with its instruments, gyros etc, the other is the one of magnetism.
An MFS problem might be one of amplifiers or gyros but I would hazard a guess that it is neither as these are testable items and not ones that would only present problems during calibration.
Magnetism, OTOH, might be more likely and the throwaway about magnetic rivets actually quite likely. We had a Phantom where many of the canopy arch rivets round the standby compass were magnetic. The rivets had become mixed in the shed and were otherwise indistinguishable from the alloy ones.
I had a problem with the first swing on the Lancaster where the P10 would just not fix until a young engineering officer (he was older than me at the time) suggested a Sperry swing. See below.
The Vulcan has been sat on one heading for many years, years longer than it has ever sat before. In that process it will have acquired magnetism and this will need greater corrections than normal. The problems might be with the E2B in the cockpit or the Sperry flux valves in the wing tips. The former had a pair of bar magnets to be adjusted. The flux valves can be coarse aligned by a few degrees. More than that becomes more difficult. A coarse error should have been identified even before the aircraft left Brunty. Our Phantom problem was identified while it was still in the hangar.
Back to Sperry.
The first correction is the deviation on E-W / 2. So if the deviation on East is -2 and on West is -1 then the total error correction is -2 --1 /2 or minus 0.5 deg. Easy. Or maybe it was -2 and + 1 which would be -3/2 or minus 1.5.
The problem starts to arise with gross errors as we had in the Lancaster where the East was about -60 and the West was about -50. The formula produces a correction of just 5 degrees and the errors are hardly altered. The cause is quite simple - the aircraft system is not NEAR east or west so the correction is wholly wrong.
The answer was the Sperry swing. First make the aircraft comass on an easterly heading read EAST. Then move the aircraft to west and make the heading read WEST. After I had been given guidance (pun) the rest was easy.
For the Lancaster we just used a Landing Compass. For the Vulcan we used a Watts Datum. As a bomber it needed an accuracy of 0.1 deg. As a display aircraft it would not need to be better than a degree or so. Swings just take time. A day is nothing.