Why are gyros driven by vacuum and not high pressure air?
Join Date: Jan 2014
Location: Ontario
Age: 81
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
I believe the first gyros, for turn indicators, were venturi operated. It was soon found, the hard way, that venturis were prone to icing (a dim memory says that an iced-up venturi was involved in Knut Rockne's (famous football coach) death in a Fokker). But (I think) the same instruments could be used with engine source vacuum. Electrical systems came along for navigation light and cockpit lighting, and then artificial horizons which if operated electrically gave redundancy, anyways the vacuum was more reliable and the turn indicator gyro didn't topple.
Some may have read of a certain Convair 240 (?) which took off from Boston circa 1950 +- a year or two in IFR conditions at night, with all gyros operated electrically, and suffered a total electrical failure. Luckily the captain was able to manage in a rough way with the magnetic compass and staggered along to the New York area where visibility improved and they found a lighted airport. I think this reinforced the idea of vacuum plus electrics.
Now of course electrical systems in aircraft are almost perfectly reliable.
Some may have read of a certain Convair 240 (?) which took off from Boston circa 1950 +- a year or two in IFR conditions at night, with all gyros operated electrically, and suffered a total electrical failure. Luckily the captain was able to manage in a rough way with the magnetic compass and staggered along to the New York area where visibility improved and they found a lighted airport. I think this reinforced the idea of vacuum plus electrics.
Now of course electrical systems in aircraft are almost perfectly reliable.
Psychophysiological entity
I hope so. Oddly, the other evening after posting on this thread, I found myself looking at some Pathe film that would never be shown to the public.
The British Eagle Viscount lost its electrics, and John Dawdy, probably following a cloud-break, snapped off the outer wings in a failed attempt to raise the nose. We were told then that the recorder wire was in 20,000 pieces.
I'd pictured the scene a thousand times, but the reality was quite different. Now I was looking at the FO's window and a bit of the roof. I'd spent many hours behind that glass. No punches were pulled in the photography the public were protected from. I suppose I must have taken a breath during the film but I felt as though time outside the scenes had stopped.
I'm mindful of the Egypt Air's hasty returns in the days leading up to the loss of the crash. The Eagle Viscount had a fault that no one could find - electrical intermittences are like that - but it had gone on a long time. One crew found themselves going into Malta at night not being able to see anything whatsoever, apart that is, from one bright red light telling them the electrics had failed. The captain (G Birch IIRC) told me he tried time and time again to reset the power, and suddenly it came on, I gather, just in time for the cloud break.
Different days, but even in our modern era electrical failures can be so subtle that they can lurk without revealing themselves for months. In those days, just one tiny physical fault, and now a fault and or a rouge digit lying fallow in seldom read code.
The British Eagle Viscount lost its electrics, and John Dawdy, probably following a cloud-break, snapped off the outer wings in a failed attempt to raise the nose. We were told then that the recorder wire was in 20,000 pieces.
I'd pictured the scene a thousand times, but the reality was quite different. Now I was looking at the FO's window and a bit of the roof. I'd spent many hours behind that glass. No punches were pulled in the photography the public were protected from. I suppose I must have taken a breath during the film but I felt as though time outside the scenes had stopped.
I'm mindful of the Egypt Air's hasty returns in the days leading up to the loss of the crash. The Eagle Viscount had a fault that no one could find - electrical intermittences are like that - but it had gone on a long time. One crew found themselves going into Malta at night not being able to see anything whatsoever, apart that is, from one bright red light telling them the electrics had failed. The captain (G Birch IIRC) told me he tried time and time again to reset the power, and suddenly it came on, I gather, just in time for the cloud break.
Different days, but even in our modern era electrical failures can be so subtle that they can lurk without revealing themselves for months. In those days, just one tiny physical fault, and now a fault and or a rouge digit lying fallow in seldom read code.
air pressure changes with altitude
Remember it's the pressure differential across the instrument that matters, so as ambient air pressure drops the amount of vacuum pressure difference also decreases.
What is important is the amount of air flow through the instruments. To create the required amount of flow you need a minimum pressure differential. Hence the need for pressure/vacuum regulators on the gyro air system.
Join Date: Aug 2013
Location: PA
Age: 59
Posts: 30
Likes: 0
Received 0 Likes
on
0 Posts
Soon, these types of gyros will be obsolete, as the new solid state gyros come into the market.
Like everything else, your MSFT game controller has a better gyro than your aircraft.
Like everything else, your MSFT game controller has a better gyro than your aircraft.
