TheSonntag
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Accuracy Of Older Planes Avionics/gauges

Thu Aug 30, 2007 9:40 pm

A lot of old DC-3 airplanes are still flying around, as are old Ju-52s and other old planes.

This leads to my question: How precise were old gauges compared to new ones. For example, were altitude and speed gauges in the 1940s as precise as newer ones which were installed in the 1960s and today?

Certainly modern planes have more capabilities than the older ones, but what about the instruments themselves, how good are the old ones?

Michael
 
FredT
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RE: Accuracy Of Older Planes Avionics/gauges

Fri Aug 31, 2007 3:22 am

As with everything else, there are variations in quality in aircraft instruments. You can buy cheap ones with less precision and you can buy expensive ones with more precision. Technology advances, meaning instruments get cheaper for the same precision or more precise at the same cost. Instruments age and wear, and as they do they become less precise.

Was that the answer to your question?

If you want to quantify this, you have to specify which instruments you want to compare. The instruments in a state-of-the-art 1930's airliner differed a lot from the instruments in a 1930's surplus WWI warbird barnstormer. I frankly would not bother looking it up, even if I had any idea about where to find the data, as the exact figures won't really do much to further the progress of mankind.

For an example of how to measure instrument performance, I suggest googling at the requirements for RVSM certification.

Cheers,
/Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
SlamClick
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RE: Accuracy Of Older Planes Avionics/gauges

Fri Aug 31, 2007 3:29 am

Accurate enough for the speed and performance in question. A Fokker trimotor can just barely turn fast enough to keep up with gyroscopic precession.  

Seriously, if reliability is not in question, the accuracy of these gauges will permit you to hand-fly ILS approaches to 200' and a half mile any old rainy night.

ADF approaches were fun, in a Revolutionary War re-enacting sort of way. Like blacksmithing or flint-knapping, it is cool to master a skill of another time.

edit: Kay for tea

[Edited 2007-08-30 20:30:17]
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Jetlagged
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RE: Accuracy Of Older Planes Avionics/gauges

Fri Aug 31, 2007 10:12 am

Quoting TheSonntag (Thread starter):
A lot of old DC-3 airplanes are still flying around, as are old Ju-52s and other old planes.

This leads to my question: How precise were old gauges compared to new ones. For example, were altitude and speed gauges in the 1940s as precise as newer ones which were installed in the 1960s and today?

If you are comparing pitot-static gauges, then there is no reason why not, because the technology involved is exactly the same. Since the 1960's, Air Data Computers have allowed correction for position errors, etc. EFIS has removed the instrument errors, but ultimately the altitude and airspeed displays still rely on the same pitot-static sources. It's only comparatively recently that accuracy has been increased significantly to cater for RVSM, etc.

I should imagine that the design and construction standards of original Ju-52 gauges would be hard to beat even today.
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KELPkid
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RE: Accuracy Of Older Planes Avionics/gauges

Fri Aug 31, 2007 10:26 am

Quoting SlamClick (Reply 2):
ADF approaches were fun, in a Revolutionary War re-enacting sort of way. Like blacksmithing or flint-knapping, it is cool to master a skill of another time.

How about following a course on an old four-course radio range?  eyebrow 

Okay, back to my Ernie Gann books...  Wink
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SlamClick
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RE: Accuracy Of Older Planes Avionics/gauges

Fri Aug 31, 2007 11:14 am

Quoting KELPkid (Reply 4):
How about following a course on an old four-course radio range?

Never flew one of them but I did mess around with a similar technology.
Adcock range used the morse code A or N (.- or -.) for orientation.
The Army used FM homers that converted a signal received by dipole antennas to a D or a U (-.. or ..-) They overlap in precisely the same manner as A and N. So the memory gouge to stay on the beam was either "step on the dash" or "U-turn right"
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saintsman
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RE: Accuracy Of Older Planes Avionics/gauges

Fri Aug 31, 2007 3:52 pm

Not exactly ancient but still old, the compass system on the VC-10 was (is) set up to an accuracy of 0.2 of a degree. That was more accurate than the pilots can read on their instruments.

Items such as altimeters were set up in the workshop bays using manometers and correction tables issued. The limits were pretty strict.

People think that just because things are modern they must be better. For example digital radios. In order for them to be digital they clip the top of the frequencies to make a square wave. A high end analogue radio will therefore produce a better sound because you get all of the frequency. Modern probably means more reliable though.
 
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Jetlagged
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RE: Accuracy Of Older Planes Avionics/gauges

Fri Aug 31, 2007 8:46 pm

Quoting Saintsman (Reply 6):
For example digital radios. In order for them to be digital they clip the top of the frequencies to make a square wave. A high end analogue radio will therefore produce a better sound because you get all of the frequency.

Digital radio means that amplitude information is sent in digital form, analogous to a CD. Nothing to do with clipping waveforms. Fidelity is preserved as long as the bit rate is high enough.

On the modern versus less modern theme, most people listen to music on MP3 download these days without realising this is a significant loss of quality compared to CD. You pay the same amount for poorer quality, assuming legal downloads of course.  Confused
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sprout5199
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RE: Accuracy Of Older Planes Avionics/gauges

Fri Aug 31, 2007 9:12 pm

Quoting Saintsman (Reply 6):
For example digital radios. In order for them to be digital they clip the top of the frequencies to make a square wave. A high end analogue radio will therefore produce a better sound because you get all of the frequency.

Actually, what you describe is sort of what happens in a FM radio. You can amplify a FM signal many times without losing any of the quality, but with AM when you amplify it you also amplify all the noise with it I.E. lighting stikes and such. The digital radios that I work on are a 4 level modulation using a IMBE Vocoder(APCO project 25). when looking at it with a Oscope, it sort of looks like a sine wave depending of the what tone you using to modulate it.

Dan in Jupiter
 
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Starlionblue
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RE: Accuracy Of Older Planes Avionics/gauges

Fri Aug 31, 2007 10:32 pm

I am currently reading the Hornblower books by Forester. Interesting to see how navigation was carried out in the Age of Sail. Chronometers, sextants, soundings, logs (the original wooden kind), estimates of currents. Even counting of oar strokes in the fog. It amazes me the kind of precision they actually managed given the technology. It required a lot of the navigators to get it just right.

Quoting Jetlagged (Reply 3):
I should imagine that the design and construction standards of original Ju-52 gauges would be hard to beat even today.

Those Germans always know what they are doing.

Quoting Saintsman (Reply 6):
Modern probably means more reliable though.

Don't forget smaller and cheaper, probably the two main advantages of modern electronics.

Quoting Jetlagged (Reply 7):
On the modern versus less modern theme, most people listen to music on MP3 download these days without realising this is a significant loss of quality compared to CD. You pay the same amount for poorer quality, assuming legal downloads of course.

You're assuming ripping at a lower bitrate. Digital rips do not inherently have lower quality than a CD. While MP3 always has some compression (and thus some loss), it is possible to record at full bitrate (320kbps if memory serves) and get pretty much CD quality. Or you can just use AAC or some similar lossless format.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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Jetlagged
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RE: Accuracy Of Older Planes Avionics/gauges

Sat Sep 01, 2007 4:00 am

Quoting Starlionblue (Reply 9):
You're assuming ripping at a lower bitrate.

Well I was only thinking about the extra compression, comparing a download to a CD, rather than a ripped MP3 to the original CD. However I see your point, because my experience of reduced MP3 quality is from ripped CDs, rather than downloads (my son's area of expertise).

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Starlionblue
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RE: Accuracy Of Older Planes Avionics/gauges

Sat Sep 01, 2007 12:19 pm

Quoting Jetlagged (Reply 10):
Well I was only thinking about the extra compression, comparing a download to a CD, rather than a ripped MP3 to the original CD. However I see your point, because my experience of reduced MP3 quality is from ripped CDs, rather than downloads (my son's area of expertise).

Well, you and I know about loss. Most people don't. Most people use a lower bitrate for MP3 ripping. If nothing else, programs like Windows Media Player rip at a lower bit rate by default (192kbps if memory serves).
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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