All Electric Gyros - a list server thread . . .
Terry Chapman, president of Advanced Industries and a valued friend of mine
died along with his two passengers after he experienced multiple failures
in a multiply redundant instrument flight system. Click here
for a copy of the accident report. A few weeks later,
the following list-server thread touched on some of the more important
considerations for development and operation of reliable IFR flight
systems. I've uploaded the thread here to share with the rest of my
flying friends. . .
>"The modifications Ron outlined would add mucho weight,
>complexity, and expense."
>>That might be true if one built a system as Ron described, with WAY more
>>redundancy than is actually needed for safety.
>>But with one battery and one alternator, I believe the system would be
>>lighter, safer, more reliable, and easier to maintain than the typical
Actually, adding a second battery and/or alternator need not be
heavier. We want to carry a certain ampere-hour of capacity
on board to cover our needs for alternator out operations.
Interestingly enough with dual alternators, the need for backup
battery capacity goes away . . . now we can select batteries for
their ability to crank the engine and serve as stabilization for
alternators . . . NOW the combined capacity of both batteries
can be as low as 6-10 a.h. for a BIG weight reduction.
>It would be more expensive only because of the higher purchase and overhaul
>cost of electric AIs and DGs. That higher cost is, I believe, largely
>because almost nobody uses electric AIs and DGs. If all aircraft eschewed
>suction, they would cost the same.
Cost of electric gyros has always been the reason for sticking
with air driven gyros . . . plus the fact that past examples
of electric gyros were probably lower in MTBF numbers than
their vacuum cousins. Nowadays, I'd judge it to be a toss up.
>Gregg continues, "I'd rather have two differens sources of gyro
>With one alternator and one battery, you ALREADY have two different power
>sources. If you add suction, you've added a third power source which is
>less reliable than the first two. Then you use that less reliable power
>source to drive the two instruments which are easiest to use in the clouds.
>That strikes me as a bit wrong-headed.
The poentential for very reliable alternators has been proven
with years of experience by B&C where their return rate for
wearout and failure has been zero for over seven years.
The problem with battery "reliability" is the fact that
for one to fly with confidence, the battery must be periodically
tested for capacity. Were I to STC a single battery, single
alternator system for full electric panel IFR flight, I'd have
to say the for continued airworthiness, the aircraft should not
be flown in IFR conditions if:
(1) the battery has not been tested for capacity in the last
(2) if the battery has been depleted, the battery shall be
immediately tested for adequate capacity before initiating
Now, with dual alternators, one need not depend on battery
capacity for flight reliability. The batteries can be downsized
for a big reduction in weight.
>>"You could buy a new vacuum pump every year for the cost of an all elec.
>I haven't seen Gregg's numbers, but I'm skeptical that this is true.
>Certainly if you buy and maintain extra alternators and batteries, it
>drives up the cost. That's why I suggest a system with one alternator, one
>well-maintained battery, a well-designed "essential bus" with proper
>failure annunciators and controls, and all-electric gyros.
I can guarantee that a B&C 8-10 amp alternator on the vacuum
pump pad is lighter, less expensive and will demonstrate an
operating life of 3-10 times that of a vacuum pump. The companion
battery is the only on-going repetative maintenance item. I think
the two year, rotating replacement cycle I recommend would serve
well . . .
> . . . . . . I believe that
>if a retrofit kit were developed and approved, the cost would be quite
>tolerable, given the added utility, simplicity, and safety it would
The major delta-dollars driver is gyros. For the remainder of
the system's components, cost and weight will go down.
>Okay, now let me remember the checklist for ozone or smoke in the cockpit.
>I think the thing starts with "master switch OFF" .....
>I have an air driven attitude indicator, an electric heading indicator (HSI)
>and an electric turn and bank (NOT a turn coordinator!!) and a 2" standby
>electric attitude indicator.
Hmmmm . . . you could make excellent use of a 2-alt/2-bat system.
Too bad the vacuum pump pad is already ocupied . . .
>Redundancy, ie, an extra source of supply, for the vacuum system
>is simple to install, has Historical Precedent ( so it is "legal" ),
>has NO moving parts, and doesn't cost as much as a pair of RG
>batteries. It does its job even when the prop is stopped and
>all the batteries are tossed overboard: a venturi.
Redundant systems in aircraft have been around for decades
and have never been "illegal" . . . the problem is, has been
and will continue to be employees of big brother who take
refuge in tradition rather than join the industry in moving
forward technologically . . . I see it at all levels of
aviation where I'm involved . . . except for amateur built
>Sadly, a suitable _valve_ for switching between the engine-driven
>pump and the passive venturi is less apparent and available, but
>one is surely "out there".
A venturi that will produce 5" of vacuum at Vy in sufficient
volume to keep two gyros spun up is more than you want hanging
of the skin of your airplane. The other problem is that it
takes about 2-3 times the watts of heat to de-ice the venturi.
A venturi would require 20-30 amps of 14v power just to de-ice
the thing. A B&C 8A+ alternator doesn't need de-icing and
puts out enough energy to run everything you need for comfortable
en route IFR navigation. A 40A alternator will carry all goodies
needed for en route IFR plus pitot heat. All-in-all, a much
better use of horsepower.
>Such a valve is included in the Safe Flight system ( ? mfg ? )
>which provides a tap into the intake manifold for suction a-la
>our automobiles. That "optional source" kit sells for $350,
>a bit pricey for a valve and hose fitting, but the outrageous
>extra-cost of electric gyros makes even this seem a bargain.
System vacuum with a manifold tap is equal to the number
of inches BELOW local atmospheric pressure that your engine
is running. One of the times you need engine power the most
is during missed approach go-around where the common action
is to apply full throttle . . . vacuum goes to zero and gyros
start to spin down. Available power from the engine becomes
a trade off between keeping gyros spun up by closing the throttle
and increasing throttle to stay airborne . . .
>There is also a hybrid vacuum system, using an electric motor
>to drive a "normal" vacuum pump. "...STC'd for most Bonanza's...",
>the ad says, and it is only $1,500.
I helped design an electrically driven vacuum pump while
in the employ of Electro-Mech about 20 years ago. Nowadays,
I think one would be better off taking out the engine
driven vacuum system and saving the $1,500 for a standby
system to buy gyros and but in some cheap . . . very
A friend of mine had such a two-pump system in his C-210
along with a 2" electric attitude indicator and turn
coordinator when things began to go south over the mountains
of New Mexico a year ago. He had so many instruments
showing so much conflicting information that he lost the
airplane anyhow . . . I'm going to miss him.
Backups on top of backups equate to more weight, complexity,
and a HIGHER likelihood that SOME part of the system is going
to break. Combine that with the problem of sorting out all
the readings when nothing seems to be telling us the
right story and we may find that more is actually less.
All that redundancy may only serve to make NTSB's task
more complicated when they're trying to figure out what
happend . . . .
I'll take two, sources of attitude info combined with a
simple arbitration device (turn coordinator) over any
other combination of goodies . . . provided we can keep
'em powered up. And that, my friends, is very simple
>1. I would have a LONG talk with FSDO reps before I started a project of
Aside from getting their commitment to look at your data, failure
mode analysis and POH mods, there's nothing to "talk about". With
few exceptions, they're unlikely to understand what you want to
do and how it will work. YOU will have to teach THEM about building
reliable aircraft systems. . .
>2. I would STILL like to find an owner of a PRODUCTION aircraft who has an
>all-electric gyro panel . . . with over 500 operating hours (the time by
>which I would have expected at least ONE vacuum pump failure), to hear about
>their track record.
What would this tell you? My friend in the C-210 had LOTS of hours
on his multi-indicator, mulit-power source system. If he'd talked
to you before his trip, you might have found his testimony
comforting. Now, I'll suggest there's little to learn from whatever
he might have told you.
>3. I would like to find out how many (or how few) owners have ever had an
>in-flight BATTERY failure which preceded an ALTERNATOR failure.
HUNDREDS of flights are initiated in this country every day
with a "failed" battery. I.e. the airplane was started with a ground
power cart for the umpteenth time or the battery was 4 years old
and down to 25% capacity and the pilot launched into the gray
anyhow . ..
>4. I think there is merit to the "redundant delivery system" discussed for
>the all-electric gyro panel (ie, dual alternators and/or dual batteries). I
>would install at least one redundant battery or alternator (with dedicated
>delivery system to the critical electrical flight equipment).
If the weight and dollars were commensurate with alt/bat/pump
installation, why not go for the whole enchallada?
>5. I MIGHT be persuaded to drop the redundant power supply if the new
>installation (installed in conjunction with overhaul of the engine) made it
>to TBO along with the engine.
A philosophy waiting to bite you badly. TBO, MTBF, service life, etc.
have absolutely nothing to do with system reliability. System
reliability comes from system design that shows no single failure
having the ability to put the pilot into an uncomfortable situation.
This failure might happend every two weeks and three times in
January and you might still have a very reliable SYSTEM.
>Absolutely correct. But the probability of a battery failure is so remote
>that I'm comfortable relying on a single battery. If you want even more
>redundancy, then lightweight RG batteries are available that can power a
>well-designed essential bus longer than the fuel will hold out.
Agreed . . . to a point. Before we hung two electric gyros on the
bus, a well trimmed E-bus could be kept on the order of 3-4 amps
which means a 24 a.h. battery half used up will keep the goodies
running for duration of fuel. Two gyros now means that we ought
to check the battery for about 75-80% of capacity for replacement
purposes. The really NICE thing about redundant alternators is that
they are not energy limited . . . as long as the engine is running,
you can use ALL of their capability without draining battery(ies).
As I mentioned above - two alternators need not weigh or cost more
than an alternator/pump installation - and the need to test batteries
of ANY capacity simply evaporates.
>Based on what you have said, If this was a court case, and I was on the
>jury, I'd still be inclinded towards the present system.
How come? Given recent judgments from the legal system in this
country combined with government's 1950's mentality for the
sheparding of systems design, I'll suggest that both legal
and regulatory considerations are irrelevant.
>But what if I had my druthers. Well one thing I'd consider is a drive
>adapter that would allow two vacuum pumps to be hung off the same
>mount. It would have some sort of selector to mechanically select
>between Pump 1 and Pump 2. The same linkage would switch a
>diverter valve between the respective pumps.
Twice weight, three times the cost and most airplanes don't
have room between engine and firewall to accomodate the bulk.
Mooney's used to have a dual pad options with a special drive
gear assembly . . . IMNSHO a really scary piece of trash.
>Another approach would be to get rid of the mechanical gyros
>entirely using magnetometers to show heading, pitch, and roll
>information on some sort of glass display. That would leave you
>an electric system only, but with the extremely low power these
>things require each could have a built in rechargable that could
>keep it up for hours in the event on an electrical system failure.
ALL of the technology to do just that has been driving around
in automobiles for years. The prices are falling like a stone,
accuracy and longevity are going up.
>These pumps, alternators and batteries we are all still
>using date back 30 to 50 years. There have been some
>developments over that period. Maybe it's time to look at
>more advance options.
Long past time . . . but with so much "help" from government,
don't look fu or any sane business person to do it soon. I'll have
some products for amateur built airplanes and soon-to-be-decertified
Canadian singles but I don't look for any sales amongst you guys
for some time to come.
>I would bet that it would be less expensive to install an S-Tek A/P
>than it would to install an all electric DG and AI, and you get and
>autopilot in the deal....
An astute observation. Years ago, Mooney's came stock with a
Britain wing leveler. The whole system was vacuum powered
and active 100% of the time. The pilot could disable the feature
with push-button on the yolk but it wasn't necesary. With
the tomato-juice can actuators you couldn't wear them out,
warm them up or break 'em by simply steering where you wanted
to go and turning loose of the wheel when the new heading
An electric encarnation of this system could be totally
independent of the gyros yet provide magnetic heading hold,
and digital compass display. My guess is that present
technologies would produce a system that would weigh less
than 4 pounds and consume about 3 amps in maximum effort
with less than 0.5 amps cruise.
The saddest thing about this idea is that I had been talking
with Terry Chapman about having his company participate in the development.
I'd hoped to have him produce it for sale under our lable. I figured
after I'd sold a few hundred systems in Canada and to the amateur
builders, government MIGHT consider making it easier to sell
it to certified aviation. Now, if Terry only had such a system installed
in his C-210 he might have missed that appointment with a
New Mexico mountain . . .
Comments and alternative views welcomed . . .