On Aug 10, 2011, at 5:01 AM, Lancair Mailing List wrote:
Lancair Mailing
List Digest #3478
1) Re: Kind of frustrated because of my AC..
by Brent Regan <brent@regandesigns.com>
2) Re: Fw: Re: Re-doing my panel - carefully thinking through failures
by Colyn Case <colyncase@earthlink.net>
3) Re: Re-doing my panel - carefully thinking through failures
by GT Phantom <gt_phantom@hotmail.com>
4) Re: Trans-Pacific in a 360
by rwolf99@aol.com
5) TSOs and equipment failure
by rwolf99@aol.com
6) Re: Re-doing my panel - carefully thinking through failures
by GT Phantom <gt_phantom@hotmail.com>
7) Re: Trans Pacific in a Lancair 360
by GT Phantom <gt_phantom@hotmail.com>
8) Re: Fw: Re: Re-doing my panel - carefully thinking through failures
by Hamid Wasti <hwasti@lm50.com>
9) Re: Fw: Re: Re-doing my panel - carefully thinking through failures
by "Michael Newman" <mnewman@dragonnorth.com>
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Date:
August
9, 2011 6:55:38 AM CDT
Subject:
Re: Kind of frustrated because of my AC..
Ronald laments:<<<
my AC breaker (50AMPS) trips as soon as I get airborne, taxing is not a
problem, run up is ok too.
>>>
I suspect that my friend Dr. Katz is correct that there is insufficient cooling
for the condenser causing higher overall system pressure leading to a higher
pressure ratio and higher compressor current, tripping the breaker.
Other possibilities include:
Excessive freon charge, leading to a high system pressure.
Defective expansion valve.
Defective breaker.
Poor voltage regulation from the electrical system. High sustained RPM causes
higher voltage leading to higher compressor current.
Undersized wiring causing a large voltage drop resulting in compressor stall.
Poor connection at the breaker leading to resistance heating and tripping at
lower than rated current.
Low buss voltage caused by gear hydraulic pump (HPU) and AC compressor running
simultaneously.
Or it could be something else...
Regards
Brent Regan
Date:
August
9, 2011 6:55:38 AM CDT
Subject:
Re: [LML] Re: Fw: Re: Re-doing my panel - carefully thinking through failures
Hamid,
that is very helpful. I can see lots of ways that the e bus would lose
power.
The particular scenario I was worried about was an event on the A bus reaching
the B bus. This would require probably that both diodes that feed
the e bus fail closed with little or no reverse current protection remaining on
the B leg.
Colyn
On Aug 8, 2011, at 9:40 PM, Hamid Wasti wrote:
Colyn Case wrote:
At the risk of topic drift.....I put in those big fat diodes
to my essential bus also.
Since them I'm wondering if there's a failure mode on one
bus that crosses the diodes and takes out the other bus.
A diode can fail open, shorted or "out of spec"
meaning that one or more parameters (voltage drop, reverse current, series
resistance etc) is very high. According to various documents on Failure
Mode Distribution, about 50% of the failure modes in power diodes result in a
shorted diode, about 30% in open diode and about 20% in out of spec failure.
Different sources use different numbers and they vary for different components,
but that is a ball park to get a sense of things.
A shorted diode is basically a direct connection, tying the
two busses together and essentially making them one. An open diode prevents
power from going through the diode to the destination buss, leaving it
permanently isolated from one of its sources. Parameter change is an
unsustainable state. It may allow the diode to function briefly, but with use
under load, it will invariably fail either open or shorted.
Diodes can fail for many reasons, among them: Over-heating,
Over-voltage, Over-current. If you have under-sized the diode or not properly
heat sunk it, it will die after some time in "normal" use.
Heat is generated in a diode's die and is a function of the
current and the diode's voltage drop (voltage in volts multiplied by current in
amps = power in watts). That heat needs to be conducted to the outside of the
case, then through some mechanical interface to the heat sink and then to the
ambient air. If the case to heat sink interface is not properly designed and
properly implemented, the die can be considerably hotter than the heat sink. If
the heat sink is not receiving cooling air, it can be considerably hotter than
the ambient air around it. If the air is circulating in a closed environment it
may be a lot warmer than the outside. If the air happens to be low on air
molecules (flying at FL280) it may not be taking away as much heat as you had
tested at sea level. All of this can conspire to over-heat the die and lead to
failure.
Surely the easiest thing in the world is to make sure that
you use a diode with a higher current rating than the highest possible current
in your system. Right? Actually, no! The important part is to use the
correct current rating, which is not always obvious. The headline current
rating is valid at a certain temperature, which is often (but not always) 25C
die temperature. In real life, the die is going to be a lot warmer than that,
maybe as much as 100C warmer. Buried in the datasheet is a graph indicating the
maximum current at higher temperatures, or a footnote along the lines of
"Maximum current decreases by .....A per degree C for higher
temperatures" To know if the diode is going to work for you, you
need to figure out the maximum power dissipation, figure out the temperature
increase due to that much power, add that to the maximum heat sink temperature
and then make sure that it can handle the current at that die temperature. The
resulting current limit is invariably going to be a lot lower than the headline
number and if you are exceeding that, your diode is under-sized.
If you have battery disconnection on one buss, the
alternator can generate a voltage spike of several 10's of volts. DO-160 calls
for 28V certified systems to be able to survive up to a 100mS wide 80V spike,
followed by 48V for 1 second. If there is an 80V spike on the A Buss, while the
B Buss stays at 28V, the diode between the essential buss and the B Buss will
see a voltage of close to 50V. Is it rated for that? If you B Buss happens to
be off due to a failure, the diode is going to see almost the full 80V. Will it
survive that? If it fails shorted, you just lost your essential buss. Unlike
over-current, there is no transient specification for over-voltage. Even a
momentary over-voltage can damage a diode.
Turning off switches and hot-unplugging a high current load
can cause a flyback voltage due to the inductance of the power wire. Unless
this is anticipated and protected against, it can kill an isolation diode. An
intermittent power connection in a tray is the same as repeatedly
hot-plugging/hot-unplugging.
Finally, a word about the worst kind of failure: The
out-of-spec failure. Lets say due to one of the aforementioned events, you have
an out-of-spec failure where the diode's internal resistance increases an order
of magnitude or more from the original value of a few mili-ohms. Lets say you
have a system where the "A Buss" and "B Buss" feed an
essential buss and the diode on the A Buss side has failed with high
resistance. If you do a system check at every startup where you sequentially
shut down both busses and make sure that the essential buss can run from the
remaining one, you are likely to find that the essential buss works. The failed
diode will be able to operate the load for a little bit while it over-heats.
During normal operation, the diode on the A Buss will take all the load. But if
you have a failure of the A Buss and all the current starts going through this
high resistance diode, it is quickly going to fail and as Murphy's Law states,
there is 100% likelihood that this will be one of the 30% of times where it
fails open.
I am sure I can think of a few more scenarios where a
failure can go undetected by typical checks. The bottom line is that unless you
are willing and able to get into it a lot deeper, a "simple and
reliable" system may only be half so.
Regards,
Hamid
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Date:
August
9, 2011 6:55:38 AM CDT
Subject:
Re: Re: Re-doing my panel - carefully thinking through failures
Brent,
I suppose I should have been more specific - I assume that pilots of
experimental aircraft will exercise sufficient judgment not be flying into
thunderstorms, and thus the likelihood of in-flight lightning strike is nearly
nil. Not absolutely nil, naturally, but approaching or below the
likelihood of vacuum failure, which is fairly common. Of course, perhaps
I should not make such an assumption given that a very famous pilot died just
last year flying his Bonanza into thunderstorms.
Absent thunderstorms, we will simply have to agree to disagree. Vacuum
pumps and vacuum-operated artificial horizons are notoriously fallible, and a
poor vacuum can give insidious symptoms causing catastrophic results.
While there have been some experimental EFIS units (notably one you
mention, also the original pioneer Blue Mountain) which had early individual
failure rates much higher than vacuum equipment, still the likelihood of two or
more going down simultaneously is rather rare. In my personal experience
my TSO Garmins failed just as often as my experimental equipment - anecdotal
evidence, to be sure, but 3 TSO failures in 600 hrs not counting vacuum pump
failure and attitude indicator partial failure ("lazy" attitude,
"sort of" working).
None of this absolves individuals contemplating use of experimental equipment
from the burden of research to draw their own conclusions about reliability.
Your statement that TSO is required for legal flight is simply untrue. If
you wish to dispute this, please feel free to point out the section of the FARs
that you believe says otherwise (it does not exist, but knock yourself
out). I don't expect to convince you of that; it seems that there are
some folks who have made up their minds and aren't interested in anyone else's
opinion. That's fine, you are entitled to yours. I, like many, have
reviewed the pertinent FARs along with (among others) my mechanic who was a
chief avionics safety inspector for a major airline. For the type of
flying for which Experimental aircraft are authorized there is no such rule
stating that each piece of equipment must be certified to pass TSO. The
altimeter must, or pass the test for equivalent accuracy (performed during the
annual pitot-static check). Doesn't mean it's a bad thing, only
unnecessary for legal flight. Just as you admonish people who are not
engineers (I too was a software engineer by trade) to form unwarranted opinions
about avionics, you too should not consider yourself an expert on FARs simply
because you build avionics. Glass houses, etc.
Blocked pitot or static tubes are no longer a killer for correct attitude
indication on any of the three leading experimental EFIS units (GRT, Dynon,
MGL). May also not be on others, haven't kept up. Of course, you
will not get accurate airspeed with either blocked and will not get accurate
barometric altitude with static blocked, but that would happen irrespective of
the type of avionics you use. However, you will still have accurate
horizon, and GPS can provide altitude and ground speed which, combined with a
pilot's knowledge of their aircraft power settings, etc. should enable you to
fly safely to landing.
At the end of the day, you are putting your own life on the line. If you
feel more comfortable with spinning gyros, by all means load up. However,
if you feel you have done your research and would rather replace that vacuum
pump for a second alternator to prevent power-out and ditch the gyro for a
small self-contained backup EFIS, then your odds of total failure will
ultimately be about the same - just different causes.
Fly safe!
Bill
On 01/-10/-28163 02:59 PM, Brent Regan wrote:
Bill speculates:
<<Given that two EFIS units with battery backup are more reliable than a
single vacuum pump, your argument that people must have
"TSO'd" equipment is logically ridiculous - especially if they also
have as part of their panel an independent 2-axis autopilot.>>
The primary assumption here is false. It is not "given" that
"two EFIS units with battery backup are more reliable than a single vacuum
pump". Analysis and data show the opposite is true.
Having designed several Certified EFIS systems and sensors (AHRS, Air Data,
Magnetometer, OAT etc.) over the last 15 years and shepherded those systems
through DO160 certification testing I can say with the confidence of having
empirical data (Remember that one test is worth a thousand expert
opinions) that I would NOT fly behind a panel that had ONLY electronic gauges,
regardless of their certification level or lack thereof. Even the Starship,
with a million dollar 17 tube Pro Line 21 integrated avionics suite, STILL has
a mechanical Airspeed, Altimeter and AH.
Regan Designs was the first company to design equipment that passed the DO160
Lightning Induced Transient Susceptibility (section 22) and Lightning Direct
Effects (section 23) requirements introduced in 2004. Hamid engineered
several test articles that he then subjected to simulated lightning strikes in
a certified laboratory. Based on those tests I can say with a high level
of confidence that most GA certified EFIS and likely all experimental EFIS
systems will not survive a proximal lightning strike, let alone a direct
strike. Same goes for experimental autopilots. And that is considering just 2
of 26 sections. There is also Shock, Vibration, Temperature, Magnet
Effect, Voltage Spike, Operational Voltage, RF Susceptibility, ESD, etc.
etc. etc.
One transient event can take out most of the digital electronics wired into the
aircraft. A battery back up won't do any good if your EFIS is fried.
Here are some additional reasons for a spinning mass backup to an EFIS.
1) Compelling disaster. If your EFIS starts to roll (e.g. due to a long
climbing departure turn), you feel compelled to follow it to your doom. Having
a familiar AH in you scan will help you keep you wings level.
2) Different physics. Spinning mass and MEMS gyroscopes work on different
principals and physics. The set of events that will kill both is small and most
of those involve the pilot not surviving either.
3) Old faithful. Most of us learned to fly with an AH. The response to and AH
display is nearly reflexive and may save you life during a helmet fire.
Some words on TSOs. TSOs are the Technical Standards that equipment must meet
to to be considered as equipment on aircraft. Therefore, in order to have an
"altimeter" in your aircraft you must have an instrument that meets
the TSOs for an "Altimeter". You can either let the instrument
manufacturer do the testing or, as an aircraft manufacturer, you can do the
testing, and document same. Why? Imagine you took a rock and printed
"8,250 feet" on it. You then "install" it in your aircraft
and claim it is an altimeter as it will tell you your altitude during certain
conditions of flight. One of those conditions must be that you are actually
flying at 8,250 feet MSL. To prevent this type of thing the FAA has established
standards that a device must meet in ordered to be qualified to function as a
required device. See FAR 21.601.b.1.
So, Bill's statement that "...(the) argument that people must have
"TSO'd" equipment is logically ridiculous..." is false. You MUST
have at least one of each of the required instruments and they MUST meet the
TSO. You can call it ridiculous, but it does not change the fact that it is the
law.
Bill also postulates that " Experimental EFIS units work acceptably with either
good pitot-static input or GPS input, removing the single point of
failure in steam gages.". This statement is non sequitur. The most common
Pitot Static problems are blocked ports (insects or ice), leaks or water in the
lines, any of which will produce a similarly wrong reading in either the steam
or electronic display. Redundant sensors are fine ONLY if you have a method for
differentiating good data from bad data.
FWIW, Being a good pilot, as I am sure Bill is, does not make you a good engine
mechanic or good at failure analysis. You can take or ignore the advice of
those with experience. Fred has put a lot of thought into his system and has
reduced the likelihood of a catastrophic electrical failure. Now if you could
only do the same for rocker arms.......
Regards
Brent Regan
Date:
August
9, 2011 6:55:38 AM CDT
Subject:
Re: Trans-Pacific in a 360
When I have some real numbers I'll switch to graph paper. I
don't even know what my empty weight is yet -- I was guessing (perhaps
optimistically) 1100 pounds. I also don't know the actual fuel
requirement as a function of airspeed and gross weight. I also only had
rough measurements of a ferry tank capacity. I was mostly trying to determine
whether it was possible at all and whether it had been done before.
From what I have been able to determine, it may be doable but is
definitely marginal. Certainly it may be fun to see if I can do it --
even if I demonstrate it to myself by flying from California to
Massachusetts.
I had been toying with the idea several years ago, but gave up the
idea since I didn't want to leave my wife without a husband for something that
was really not that important. The risk/benefit just wasn't there.
Now that this is no longer an issue I have been thinking of it again. You
guys have given me some good ideas to consider, and some data points to gather
in my initial flight test program.
Date:
August
9, 2011 6:55:38 AM CDT
Subject:
TSOs and equipment failure
<<What you are saying is that in a system with multiple
alternator/batteries and isolated/redundant busses, a TSO's system and a
non-TSO's system can equally survive an adverse event like a lightning induced
power surge or an alternator caused voltage surge. I would strongly disagree
with your conclusion.>>
Actually I agree completely with Hamid. Environmental
effects such as the indirect effects of lightning are precisely where the TSO'd
units have an advantage. With my electrical power example I was trying to
say that there are other failure modes (loss of electrical power for a variety
of reasons) where the TSO'd unit goes dark just like the non-TSOd unit.
I did envision electrical power surges due to failures in the
electrical system causing the non-TSOd unit to fail which the TSOd unit might
survive. In this case, Hamid is right -- the TSOd unit has an advantage
here as well. The lesson is that problems with the fairly mundane portion
of our avionics systems (electrical power generation and distribution) can also
cause failures of our whiz-bang EFISs and glass panel displays. It
doesn't take a lightning strike.
Steam gauges in my airplane!
Date:
August
9, 2011 6:55:38 AM CDT
Subject:
Re: Re: Re-doing my panel - carefully thinking through failures
I don't doubt that, taken in aggregate, experimental
avionics experience failure more often than TSO equipment.
My point was that people who make blanket statements suggesting people should
not use experimental equipment at all are drawing the wrong conclusion (and
thus giving others bad advice). That conclusion is using the same gross
generalization behaviors as a small child that once burns themselves on the
stove and then draws the (incorrect) generalization that "all stoves are
bad." In reality it's not that stoves are bad; simply that you must
be careful in their use.
All avionics can be compared to light bulbs. Cheap ones tend to burn out
quicker than expensive ones, but there are always counter-examples (expensive
ones going out sooner, cheap ones lasting longer). The key is, if you
have lots of bulbs you won't be in the dark when one fails.
Cheers,
Bill
On 01/-10/-28163 02:59 PM, rwolf99@aol.com
wrote:
<<Modern electronic EFIS systems properly installed with
backup batteries and internal automatic isolation circuitry are about as
fail-proof as a single piece of electronic equipment can get.>>
This is not Brent's statement. Rather, this relates to a
suggestion that non-TSOd units should be considered equally reliable as TSOd
units, which is something that Brent disagrees with.
I think Brent is saying that a device that has successfully passes
environmental qualification testing (a TSOd unit) is way less likely
to fail than a unit which has not. His first-hand experience taking an
experimental system through this process (Sieera Flight Systems, now Chelton)
bears this out. Such units are most likely more resilient to power
fluctuation, temperature extremes, shock and vibration, and even exposure to
water. In this sense, the TSOd unit is more reliable.
Having said that, no electronic unit will work without
power. Now you look at internal backup batteries, redundant power
sources, multiple generators/alternators, duplicate paths for power, no single
point failures, and perhaps other things which are totally separate from the
unit itself. In this sense, the non-TSOd unit and the TSOd unit are equally
reliable.
p.s. I'm using a vacuum pump and steam gauges. I don't need
no stinkin' electricity.... (But then, if the weather is really bad -- like
it's raining -- I stay on the ground. YMMV)
Date:
August
9, 2011 6:55:38 AM CDT
Subject:
Re: Trans Pacific in a Lancair 360
While it is certainly do-able, one has to question why you
would take the risk if you're not trying to break some record?
Take the wings off, carefully pack the entire airplane (and anything else you
will be wanting in Hawaii) in a shipping container, and ship it. Probably
won't cost much more than flying it, and with no risk to yourself.
Blue skies,
Bill
On 01/-10/-28163 02:59 PM, rwolf99@aol.com
wrote:
I'm running the numbers for a ferry tank to take my Lancair 360
from California (probably Watsonville) to Hawaii. My back-of-the-envelope
calculations suggest that I can do this with a GTOW of 2000 or 2100 pounds and
have the range for 2100 nmi with a 30 kt headwind (no reserves).
Has anyone made this trip before in a 320 or a 360? I know a
few IVs have done it.
Needless to say, the shakedown flights will be the other way --
California to Boston, or something like that.
Date:
August
9, 2011 6:55:38 AM CDT
Subject:
Re: [LML] Re: Fw: Re: Re-doing my panel - carefully thinking through failures
Correcting a typo in my previous e-mail. The changes in the new paragraph are
highlighted.
Hamid Wasti wrote:
Lets say you have a system where the "A Buss" and
"B Buss" feed an essential buss and the diode on the A Buss side has
failed with high resistance. If you do a system check at every startup where
you sequentially shut down both busses and make sure that the essential buss
can run from the remaining one, you are likely to find that the essential buss
works. The failed diode will be able to operate the load for a little bit while
it over-heats. During normal operation, the diode on the A Buss will take all
the load. But if you have a failure of the A Buss and all the current starts
going through this high resistance diode, it is quickly going to fail and as
Murphy's Law states, there is 100% likelihood that this will be one of the 30%
of times where it fails open.
Lets say you have a system where the "A Buss" and
"B Buss" feed an essential buss and the diode on the _*B Buss*_ side
has failed with high resistance. If you do a system check at every startup
where you sequentially shut down both busses and make sure that the essential
buss can run from the remaining one, you are likely to find that the essential
buss works. The failed diode will be able to operate the load for a little bit
while it over-heats. During normal operation, the _*good*_ diode on the A Buss
will take all the load. But if you have a failure of the A Buss and all the
current starts going through this high resistance diode _*from the B Buss*_, it
is quickly going to fail and as Murphy's Law states, there is 100% likelihood
that this will be one of the 30% of times where it fails open.
Regards,
Hamid
Date:
August
9, 2011 6:55:38 AM CDT
Subject:
RE: [LML] Re: Fw: Re: Re-doing my panel - carefully thinking through failures
You have a pretty good setup BUT…
I had an avionics master breaker (switch type) in my Bonanza
that failed. What happened was that the housing cracked behind the panel. The
switch failed open on an IFR flight when the housing was no longer able to hold
the contacts together. Your DPST switch can fail in the same way and will fail
open. Both sides will be open from this common mechanical cause.
My solution was to put in two separate breaker switches in
parallel. I turn only one on at a time. If one fails I can simply turn on the
other.
My avionics switch is a DPST switch. Basically two switches in
one. Each side controls the power feed from one electrical system. Sure, both
sides of the switch could fail at the same time but that would be unlikely. On
top of that I have a separate, isolated switch that feeds power only to the
GPS/Com so that even if both sides of the avionics switch should fail or both
electrical system 1 and 2 fail, I can power this unit from system 3. System 3
is an 8 amp B&C generator and an Odyssey 545 battery.
N6ZQ IV under construction
Fred,
Even with all the extra weight and redundancy, your avionics are
all reliant on a single switch. If that $7 switch goes, your plane is
blind, deaf, and dumb! The aeroelectric list does not recommend an
avionics buss. This is part of the reason for that.
Bill B