Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Fri, 24 May 2002 18:34:06 -0400
Message-ID: <redirect-1247318@logan.com>
From: Sky2high@aol.com
Subject: Re: [LML] Vacuum v. all electric
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There are several problems with "old Technology" systems, some not inherent 
in the system but in the implementation.  GA aircraft built to 1940's FAA 
(CAA) standards are, frankly, ridiculous in today's environment.  My 1973 
Skymaster had two vacuum pumps, but ultimately shared the single 
instrumentation system.  The worst part was that the vacuum gauge was placed 
down by my left knee - not part of the instrument "scan".  The lack of 
instant failure warnings have led many to first recognize the problem only 
after entering an unusual attitude, just before the wings come off.

Vacuum systems, by themselves, are cumbersome, capable of many single point 
failures, subject to wear and age deterioration and are relatively cheap 
because of widespread use.

Electric gyros frequently have failure flags displayed in the instrument 
itself, but are subject to the same wear and age deterioration as vacuum 
gyros.  Again, GA implementation of such instrumentation  has been poor, 
frequently ignoring the use of essential bus logic, backup batteries and 
secondary alternators.  Usually the electric system was installed simply as a 
backup to the vacuum - better, but still not completely designed to deal with 
certain multiple-failure situations.  These electric gyros are also much more 
expensive than vacuum ones.  Note, I did add an electric attitude gyro to the 
Skymaster after the vacuum gyro slowly died one VMC day and was no longer 
matching the real horizon.  BTW, the autopilot was managed by the attitude 
indicator, therefore was not a backup to a vacuum failure, more likely to 
take down to the garden path.

Currently, my 320 has vacuum AI and DG with the gauge directly above the AI.  
The backup is the electric turn coordinator but, more exactly, the S-TEC 50 
autopilot.  The electric system failures are "managed" by an essential bus 
system, but still only one alternator and one battery.  There are panel space 
limits, engine compartment limits and weight limits.  Besides, "hard" IFR is 
avoided, I don't have to be anywhere at anytime anymore.  As noted in my 
story, one unexpected failure (AP) left me with only my unreliable self as 
the backup, ergo I landed ASAP and had that problem repaired. And, also 
changed my operating procedure so I am better prepared for that "unexpected" 
type of failure.  My system was designed in 1990, using then available 
avionics (including Loran and ADF) .

Let's look at more modern possibilities - all of which depend more on 
electricity. So, the most important part of the early design is to make sure 
that the electrical system  itself is redundant, reliable and capable of 
delivering electrons to critical circuits under a variety of failure 
scenarios.  This should include consideration of circuit isolation, multiple 
alternators (requires the engine to continue operating, just like vacuum), 
split buses, multiple batteries, lightning protection, cross connection 
switches, etc.  

Consider Gyros, not Greek and not electric spinning ones, but electronic 3-D 
(laser ring, magnetic, accelerometer, GPS carrier, etc) ones have the 
greatest future if multiple ones are used.   Unfortunately, very expensive at 
this time.  One benefit is that they can be remotely mounted rather than 
consuming scarce panel (and back-panel) space and have a low current draw.  

Consider display functions, for example the DG, as we know it,  is one 
instrument that can disappear.  Its major function was to provide a 
consistent frame of reference for track control.  Frankly, it didn't have to 
be precisely set to match the magnetic heading - other instruments (VOR, ILS, 
12th century compass, etc) set the direction, the DG helped to hold the 
lateral path.  Today, GPS track, whether digitally or pictorally presented, 
is the frame of reference for track control.  Sometimes, when ATC asks for a 
heading, I will ask what track they would like me to fly.  If you will 
utilize a TruTrak AP,  then such a request is almost required.

If modern computer-like displays are to be used, you must have more than one 
and you must be able to swap the display function for backup purposes.

Now, if we could only get rid of turbulence.

Anyway, no matter what systems you choose, first design and build a robust 
electrical system - your future depends on it.

Scott Krueger
N92EX

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<HTML><FONT FACE=arial,helvetica><FONT  SIZE=2>There are several problems with "old Technology" systems, some not inherent in the system but in the implementation.&nbsp; GA aircraft built to 1940's FAA (CAA) standards are, frankly, ridiculous in today's environment.&nbsp; My 1973 Skymaster had two vacuum pumps, but ultimately shared the single instrumentation system.&nbsp; The worst part was that the vacuum gauge was placed down by my left knee - not part of the instrument "scan".&nbsp; The lack of instant failure warnings have led many to first recognize the problem only after entering an unusual attitude, just before the wings come off.<BR>
<BR>
Vacuum systems, by themselves, are cumbersome, capable of many single point failures, subject to wear and age deterioration and are relatively cheap because of widespread use.<BR>
<BR>
Electric gyros frequently have failure flags displayed in the instrument itself, but are subject to the same wear and age deterioration as vacuum gyros.&nbsp; Again, GA implementation of such instrumentation&nbsp; has been poor, frequently ignoring the use of essential bus logic, backup batteries and secondary alternators.&nbsp; Usually the electric system was installed simply as a backup to the vacuum - better, but still not completely designed to deal with certain multiple-failure situations.&nbsp; These electric gyros are also much more expensive than vacuum ones.&nbsp; Note, I did add an electric attitude gyro to the Skymaster after the vacuum gyro slowly died one VMC day and was no longer matching the real horizon.&nbsp; BTW, the autopilot was managed by the attitude indicator, therefore was not a backup to a vacuum failure, more likely to take <U>down</U> to the garden path.<BR>
<BR>
Currently, my 320 has vacuum AI and DG with the gauge directly above the AI.&nbsp; The backup is the electric turn coordinator but, more exactly, the S-TEC 50 autopilot.&nbsp; The electric system failures are "managed" by an essential bus system, but still only one alternator and one battery.&nbsp; There are panel space limits, engine compartment limits and weight limits.&nbsp; Besides, "hard" IFR is avoided, I don't have to be anywhere at anytime anymore.&nbsp; As noted in my story, one unexpected failure (AP) left me with only my unreliable self as the backup, ergo I landed ASAP and had that problem repaired. And, also changed my operating procedure so I am better prepared for that "unexpected" type of failure.&nbsp; My system was designed in 1990, using then available avionics (including Loran and ADF) .<BR>
<BR>
Let's look at more modern possibilities - all of which depend more on electricity. So, the most important part of the early design is to make sure that the electrical system&nbsp; itself is redundant, reliable and capable of delivering electrons to critical circuits under a variety of failure scenarios.&nbsp; This should include consideration of circuit isolation, multiple alternators (requires the engine to continue operating, just like vacuum), split buses, multiple batteries, lightning protection, cross connection switches, etc.&nbsp; <BR>
<BR>
Consider Gyros, not Greek and not electric spinning ones, but electronic 3-D (laser ring, magnetic, accelerometer, GPS carrier, etc) ones have the greatest future if multiple ones are used.&nbsp;&nbsp; Unfortunately, very expensive at this time.&nbsp; One benefit is that they can be remotely mounted rather than consuming scarce panel (and back-panel) space and have a low current draw.&nbsp; <BR>
<BR>
Consider display functions, for example the DG, as we know it,&nbsp; is one instrument that can disappear.&nbsp; Its major function was to provide a consistent frame of reference for track control.&nbsp; Frankly, it didn't have to be precisely set to match the magnetic heading - other instruments (VOR, ILS, 12th century compass, etc) set the direction, the DG helped to hold the lateral path.&nbsp; Today, GPS track, whether digitally or pictorally presented, is the frame of reference for track control.&nbsp; Sometimes, when ATC asks for a heading, I will ask what track they would like me to fly.&nbsp; If you will utilize a TruTrak AP,&nbsp; then such a request is almost required.<BR>
<BR>
If modern computer-like displays are to be used, you must have more than one and you must be able to swap the display function for backup purposes.<BR>
<BR>
Now, if we could only get rid of turbulence.<BR>
<BR>
Anyway, no matter what systems you choose, first design and build a robust electrical system - your future depends on it.<BR>
<BR>
Scott Krueger<BR>
N92EX<BR>
</FONT></HTML>
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