My first in-flight mechanical failure

Michelle P wrote:

If you have a Constant Speed prop you will not see the RPM drop as long
as you are within the authority of the governor.

Well, when I bought my Maule, I couldn't scrape up the extra $15k for the version
with the CS prop. :-)

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

Marco Leon wrote:
I'm with you on that one Peter. I didn't get the impression that you were
hesitant to declare an emergency for any other reason than you didn't really
think it was an emgergency.

having failed magnetos is definitely an emergency. Can the other fail
too? Sure. The first died so it would be a good assumption to say the
2nd are stressed an equal amount and possibly now even more. Is a dead
stick landing an emergency? Well as long as you don't stall it in.....
I don't think I need to go any futher. What it comes down to is the
airplane, it's airworthiness is compromised. Get on the ground at
completely your descretion. Declare an emergency.

You received the same results (i.e. service from ATC) and that's what counts.

in this case yes but when in ANY doubt, declare it. Would it be
unreasonable for ATC to say "you are #2 for landing" rather than
"everyone get the hell out of the way for the aircraft that declared
an emergency." If there is ANY doubt, declare it. It can only help.

Gerald Sylvester

Andrew Gideon wrote

So that would only occur if the capacitor failed "closed"?

No!
Just can't win, can you Andrew.....:-)

Bob Moore

On 27 Sep 2004 13:34:51 -0700,
(Michael) wrote:

Peter R. wrote
I just received a call from my trusted mechanic early this morning.
He discovered that a capacitor failed in-flight, which in turn grounded
the mag.

This is a bit beyond my limited knowledge of aircraft mechanics and I
cannot correctly explain what a capacitor does, but the good news is
that it is much cheaper to replace a capacitor than a mag.

When I was an auto mechanic, we still had points type ignition
systems. Each set of points included a condenser, which is another
name for a capacitor.

The points provided the make and break component that caused the coil
to build voltage and discharge it creating the spark that is sent to
the distributer where it was distributed to the spark plugs.

The points sometimes saw as much as 12 volts but most had a ballast
resistor to reduce the amount of voltage the points had to deal with.

Electrons have inertia, once they are in motion, they like to keep on
moving. That's why when you unplug a light, or fan or something that
is drawing current, you see a spark from the plug. The moving
electricity wants to keep moving and attempts to keep the connection
as you pull the plug out.

The same thing happens at the points. When they are bumped open by
the cam that opens and closes the points inside the distributer, the
electricity tries to continue to flow through the points. Without the
capacitor/condensor, they'd arc every time and burn out quickly, or
build up a cap of burned metal, or literally weld themselves together.

The capacitor provides a momentary alternative (but dead end) path for
the electricity when the points open. The capacitors I'm familiar
with consist of thin aluminum foil insulated on both sides by a thin
paper, wrapped up in a roll and encased in a metal cylinder. The
cylinder is usually capped with some ceramic or plastic cover out of
which extends a wire.

Here is an "official" and more complete explanation of a capacitor I
found on the web: "Capacitor (Condenser) - The capacitor performs
several functions. It prevents the points from arcing and prevents
coil insulation breakdown by limiting the rate of voltage rise at the
points. It's primary function is to provide for a rapid decay of the
primary coil current. The capacitor also "third-harmonic" tunes the
coil, raising the peak output voltage and increasing the secondary
voltage rise time. This increases the efficiency and the amount of
energy transferred to the spark plugs. If the coil secondary voltage
rises too quickly, excessive high frequency energy is produced. This
energy is then lost into the air-waves by electro-magnetic radiation
from the ignition wiring instead of going to the spark plugs where we
would like it to go. Voltage rise time should be more than 10
microseconds; a 50-microsecond rise time is OK. Conventional systems
have a typical rise time of about 100 microseconds."

The capacitor is tested by checking to see if the wire is grounded to
the body of the capacitor. If it is, the capacitor has failed. If it
is not, the capacitor is theoretically ok.

The capacitor provides the afore mentioned dead end path for the
electricity when the points open. Remember, the electrons WANT to
keep on moving. They want to keep flowing through the points and can
and will arc to attempt to do this. But the when the points open, the
electrons see the path into the capacitor and jump inside and circle
all the way to the end of the foil, finds it's a dead end and races
all the way back out to the points. But they are open too far now for
the electricity to arc across them so they race back to the end of the
capacitor then back out again in ever diminshing cycles as it looses
energy.

You can see this on the oscilloscope, it's the up and down oscillating
lines that continue in diminishing amplitude after the spark fires.

The person who invented the capacitor was pretty smart. Magnetos
still use points, so they need to have capacitors or the points would
fail quickly. If the capacitor shorts to ground, it grounds out the
the points, which of course fails the magneto.

Corky Scott

In article , Peter R.
writes:

at least the
controller gave you what you needed to have a successful outcome,
regardless of the side they chose in the bet.

Only after we disregarded his "instructions" and told him what we were going to
do.

John

Corky Scott ) wrote:

snip
The person who invented the capacitor was pretty smart. Magnetos
still use points, so they need to have capacitors or the points would
fail quickly. If the capacitor shorts to ground, it grounds out the
the points, which of course fails the magneto.

Thank you for taking the time to expand on the explanation. It is now
coming together for me.

--
Peter

Peter Duniho wrote:

The capacitor is in the circuit in parallel with the normal path of the
current. If it fails in the closed circuit state, this provides an
alternate route for the current coming from the magneto, shorting it out
and
preventing a spark from being generated. But when it fails in the open
state, there is still the normal path of the current available for
shorting out the magneto when the ignition switch is in the off position.

Make sense?


Yes, thanks.

- Andrew

Bob Moore wrote:

Andrew Gideon wrote

So that would only occur if the capacitor failed "closed"?

No!
Just can't win, can you Andrew.....:-)

So that would only occur if the capacitor failed sideways?

- Andrew

My experience with failed mags is fortunately limited to Fouled plugs
on the runup. However I am aware of 2 interesting incidents involving
Mag's.

1. My flight Instructor was flying departing in a 414. Upon starting
one engine he could just barely get it run it was coughing, sputtering
backfiring, etc. He shut down and brought the Mechanic who determined
that the timing on one of the Mags had slipped. It was firing but at
the wrong time. Sorry I am not a Mechanic so I don't know what would
have happed to cause that. However had my instuctor done a mag check
he would have found that the engine ran fine on one mag and not at all
on the other. lesson Learned if an engine start running rough or badly
in flight a mag check is a worth while check.

2. A local Cropduster pilot had just finished up and was taking his
Ag-Cat back to the home base about 5 miles away. On his Runup he
discovered that one mag had died completely. He opted to fly it back
to base to get it fixed. Upon landing at his home base he 1st took it
to the fuel pump and fueled it. After Fueling he could not get it to
start. The 2nd Mag had failed!

So far my worse experience with a Mechanical Fail has been the nut on
one of the intake valves worked loose in our Tomahawk and the engine
began running rough and lost a couple hundred RPM. We simply informed
ATC that the engine was running rough and we were diverting to the
nearest airport.

Brian
CFIIG/ASEL

Brian Case wrote:

After Fueling he could not get it to
start. The 2nd Mag had failed!

While possible, it's much more likely that the dead mag was the one with the impulse
coupling. The impulse coupling retards the spark and increases the magneto output to
get the engine started. There is usually only one, and it's usually on the left
magneto.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.