Re: Buffalo DASH crash.

On Jun 5, 1:10 am, eunome...@xxxxxxxxxxxx wrote:
On May 22, 4:39 am, "Ken S. Tucker" <dynam...@xxxxxxxxxxxx> wrote:
[snip]

Euno, are you a pilot? (asked sincerely).

A bit in sailplanes.

As to your essay...What if the battery cable is loose?
A pilot friend had a piece of his prop fly off his Cessna
150, and due to vibration, his battery got disconnected,
but he nursed the a/c to the airport safely, using old
tried and true magneto's and cables to flight flaps.

Fly By Wire Systems need to be duplicated or even triplicated and that
means power buses as well.

The reason is that electrical (and optical) connections are more like
to fail suddenly rather than progressively as in mechanical systems.

No because components drift unexpectedly.

The good news is that duplication, triplication is actually so easy to
achieve in electrical systems the FBW system can be made MORE
redundant and therefore safer and lighter.

I also don't think that the electrical system on that cessna 150 was
well designed, placing the battery so close to the engine is not a
good idea.

Keeps the starter cable short.

I can throw alot of "what if's" at FBW, because I'm a pro
technician/electronics designer.

So am I, electrical engineer.

One fine integrated system I designed worked great
until it was struck by lightning.

Dealing with lightning and electromagnetic interference is very well
understood. Methods include
1 Faraday cage like shielding,
2 Isolated power supplies, transformers for each sud device
3 RLC filteriing
4 varistors,, transorbs, zeners
5 screened and shielded cables
6 optical links

Yes, the power grid and automobiles are fairly immune
to lightning.

Other systems I fixed had an "intermittent faults, you
should really know what they are, a jumper was missed
in the factory, for a CMOS circuit, leaving an open gate
input fluctuating, obviously depending on the weather.
I can provide a lot of examples.

Jumpers wouldn't be allowed. Jumpers = no certification.

Intermittant faults are caused by well known phenomena: dry solder
joints, faulty IC sealing. All can be managed by a proper quality
control system.

Most noteworthy however is that proper duplication and redundancy will
detect and isolate the fault.

You know how capable modern electronics is. (I deal with fail safe
safety systems quite a lot)

You've heard of a PICAXE microcontroller? An 8 pin chip, programable
in BASIC via a single pin seriel port and equiped with on board
intputs and outputs including an analog input. It can be delivered in
packages with 0.5mm pin spaceing. Its been around for a long time.

You've proably heard of the I2C bus, which has been around for 20
years. With this two pins on a chip (like a PICAXE) can communicate
with dozens of peripheral chips such as analog to digital converters,
seriel ports, external memmory chips etc.

So tiny chips with minimal pin counts can be used to put together
complicated systems.

So now immagine a side stick controller. How would we build this so
that it is totally reliable? Imagine we are using variable resistors
to measure side stick roll and pitch. I know in real life an RVDT or
optical disk encoder is likely to be used but the Variable resistor is
easy to understand.

The controller would be equiped with 6 potentiometers, 3 for roll and
3 for pitch.

I built a controller with a rudder on the stick.

For each potentiomenter we must have excitation say 10V
excitation and we must measure the pickoff voltage. To do this we
have a 10V source, we have analog to digital coinverters to measure
confirm the source voltage and we have two A to D to measure the
pickoff. Readings are read back into the microcontroller via the I2C
bus. Here the two A to D converters are compared and that the
correct excitation is being used is also confirmed.

In other words each pot has its own micro contoller with suffiecient
independant and isolated A to D conveters to do self diaganostics.
We also allow the 10V source to be modulated so that errors (short to
ground or supply) can be tested periodically.

Each microcontroller will have 3 seriel ports so that it can send data
to the other controller via optocouplers. Should one one unit be
partially out of order it will produce a different result and the
microcontroller can exclude that data whether they fault be in the
electronics or in the potentiometer

The three microcontrollers would thus be able to compare notes and
exclude faulty data but each would still send data over its own cable
route to a central controller.

Three pairs of shielded wires or optical fibres would transmit the
side stick controllers positional data to a central computer, itself
composed of three CPU's all talking to each other.

It sounds complicated but it isn't: the side stick controllers
microcontroller boards would be three circuit board about 3 cm by 6 cm
with maybe 5-6 chips with each one handling one roll and one pitch
potentiometer.

Not also the system isn't only redundant but self diagnosing.

Quality would be high, isolated A to D intputs, three independant
power supplies.

3 pairs of cables with a pair of wires in each is not onerous.

That electronics is redundant to a mechanical system,
which in light planes rarely fails and everybody knows it,
it's ultra reliable, economical and easy to maintain.

Pushing FBW, beyond it's place, to try to make something
idiot proof penalizes the 90% who aren't idiots.

The ingenuity of idiots outpaces the intelligence of engineers.
Bus seriously people make mistakes.
I personally would desire a light plane or a sailpane with Fly by Wire
and the same protections against stall, spin etc that airbus have.

And if your sailplane battery is flat?
Ken
.

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