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Bob, I like your idea of looking at a different system than one that says,
"Hey, you, pilot. Look at this lite and listen to the warning tone your are
getting. Your engine is detonating and about to self-destruct."
The first obvious alternative that comes to mind, which would seem to be
more useful, would be a Fuel/Air Ratio gage. Ed Anderson has built one with
some LEDs in a "bar graph" kind of display (sorry Ed if I'm not exactly
remembering). Point being, that my previous reply indicates that my main
worry about detonation is "detonation caused by incorrect F/A ratio".
- So, Bob, you properly challenge us to look for something more useful
than "hey, you are detonating".
Maybe the F/A output could be shaped so that these modern engine instrument
systems, with all the preset limits, could give us a warning of a F/A ratio
that is not close enough to where it ought to be, e.g., , "Hey, your F/A
ratio is shifting from (or you have manually changed it from) (or your
descent from high thin air to lower denser air has caused F/A ratio to shift
from) "X" to "Y" and maybe you should tend to your mixture control vs F/A
ratio BEFORE you get detonation."
The next step up would be: Make the warning be dependent on two sensors:
Manifold pressure (limit of 75% of sea level) which, if over 75%, would
"activate" the system to look at and warn of "Fuel/Air Ratio limit(s)".
- Conventional certified aircraft piston engine design "wisdom" is that
detonation is not a worry at 75% power and below - can lean to anything you
want and you will NOT get detonation.
- So, as already said above, for really good warning, you could have a
manifold pressure sensor "limit" that would bring in the F/A ratio sensor's
output with a preset limit of "leanness" that would trigger a warning BEFORE
you could get detonation.
Is that closer to a more rational and useful and informative design
philosopy to deal with "detonation"?
F/A ratio gages and LED displays are easy enough for us home builders. We
might have to work on the nature of the output (pure optical LED readouts
would not be suitable for input to an engine monitor system) to get a
digital or analog output that could be set in the engine inst sys black box.
David
----- Original Message ----- From: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
To: <aeroelectric-list@matronics.com>
Sent: Tuesday, August 05, 2003 12:33 PM
Subject: Re: AeroElectric-List: Re: Knock Sensors
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<bob.nuckolls@cox.net>
At 09:24 PM 8/4/2003 -0500, you wrote:
>--> AeroElectric-List message posted by: "David Carter"
><dcarter@datarecall.net>
>
>Bob,
>
>This is one of those areas of discussion where "hundreds of others don't
>have this problem" is not a logical or proper method of addressing the
basic
>question/issue. Not that the "macro" statistical overview isn't without
>merit, in some cases. But the "micro" (1 of a kind or 1 out of a
thousand)
>event, when catastrophic, is not to be dismissed so lightly.
>
> <snip>
>Electronically controlled fuel injected engines make the injectors spray
for
>a calculated amount of time to get the desired F/A ratio, which SHOULD
(is
>supposed to) preclude pinging/detonation.
> - BUT, all you have to do is gum up 1 or more injectors and get
less
>fuel than the engineer/programmer "assumed" would flow in a given bit of
>time, and you wind up with a leaner than "assumed/engineered" mixture,
which
>tends toward the threshhold of detonation. There are other things that
can
>be different from "engineered/assumed" that do the same.
> - That is why I will have a knock sensor on my (aircraft)
>auto-conversion engine.
Understand . . . and your machine is indeed an "experimental"
airplane . . . it might even be considered a "research"
tool. Allow me to offer some background to which my
antennas are tuned . . .
In a time when the latest buzzword is "FADEC" we're moving
forward with clumsy but effective evolution of aircraft power
management that reduces pilot workload and potential for
pilot error.
You've identified a real hazard associated with the operation
of your chosen powerplant. I recall a couple of decades ago,
we identified another system generated hazard to aircraft: It
seems that Ni-Cad batteries in turbine engine aircraft had
a bad habit of catching fire. Rather than mandate redesign
of ship's voltage regulators to automatically mitigate the
risk, we (the FAA . . . and industry dutifully followed
in lockstep) decided to put a battery temperature readout
on the panel with companion warning lights and a page
of new information in the POH telling pilots how to
deal PERSONALLY with this new risk.
My question for you is, "are you moving in a positive
direction?" What combination of features offered by
this powerplant transcend a perceived need to personally
intervene to forestall disaster?
If you are DEPENDING on a panel readout as warning of
impending failure, what mechanisms are or will be in
place to make sure the warning system is accurate and
reliable? If it fails, how will you know it failed and
what options are available to you for comfortable
completion of flight with engine and skin intact?
Suppose I were standing in front of my compatriots at RAC
trying to sell your system onto a production (not
experimental, not research) aircraft. They're going
to beat me soundly about the head and shoulders until
I convince them and the FAA that the proposed system
BENEFITS far outweigh the costs, risks, and increases
in pilot responsibility and workload.
Are there other options with favorable track records
that are more pilot-friendly than the configuration
currently under consideration? Are there ways to
reliably control and/or monitor the effects and
automatically reduce the risk? Keep sight of a need
for a monitor/control system that is MUCH more
reliable than the system prone to hazard?
Of course, the way you plan to use the airplane should
influence your decisions. If research is your interest
and joy, by all means drive ahead. But how much
"researching" do you want to do while you and
the wife are on your way to Santa Fe?
Bob . . .
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