monitoring pusher props

Jim, you're always looking for simple DIY projects for your kitplane
articles, aren't you?

Some guys on the flyrotary list have be batting around ideas on how to
determine if the prop on a pusher is windmilling. Would a piece of
reflective tape and an optical pickup suffice?

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Ernest Christley wrote:
Jim, you're always looking for simple DIY projects for your kitplane
articles, aren't you?

Some guys on the flyrotary list have be batting around ideas on how to
determine if the prop on a pusher is windmilling. Would a piece of
reflective tape and an optical pickup suffice?

What I'd do is to use two magnets securely affixed to the shaft, and a
hall sensor, to read them.
Optics get dirty IME.
I assume the prop is connected to the crankshaft in some manner that
means if one turns the other does.
You may already have suitable crank sensors.

Ernest Christley asks:

Some guys on the flyrotary list have be batting around ideas on how to
determine if the prop on a pusher is windmilling.

On my COZY MKIV, I look at my tachometer. I've had the engine quit on
me in a test, but it was still spinning, and the tach was registering.
Assuming the prop bolts haven't come off, the prop will be spinning if
the tach is indicating RPM.

Everybody's got a tach, right? Is that not sufficient?

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006

Marc J. Zeitlin wrote:


Everybody's got a tach, right? Is that not sufficient?


Believe it or not, NO...

If you get your tach signal from your Engine Controller, and your engine
fails because the electrical system or the engine controller goes kaput,
then it is very likely you will not have a tach signal. (this was the
scenario explicitly discussed in the flyrotary listserv)

How does the traditional a/c engine do it... hall effect on the
flywheel? Direct drive tach cable?

Some kicked around the idea of a rear view mirror someplace.. or an
optical tach of sorts..

Dave

Dave S asks:

If you get your tach signal from your Engine Controller, and your
engine fails because the electrical system or the engine controller
goes kaput, then it is very likely you will not have a tach signal.
(this was the scenario explicitly discussed in the flyrotary listserv)

OK - I guess then you're SOL using the tach :-).

How does the traditional a/c engine do it... hall effect on the
flywheel? Direct drive tach cable?

My Lyc. has two choices - either a mechanical cable (which I've capped
off), or a tap off the magneto P-lead (that's what I use). I guess if
that one mag died, I'd lose tach signal, too.

I guess I was thinking that the engine died from fuel exhaustion, or
throwing a rod or something. If the electrical thing that supplies the
tach signal croaks, then yeah, that's toast.

Some kicked around the idea of a rear view mirror someplace.. or an
optical tach of sorts..

I keep a small pocket mirror in the map pocket to look at my fuel gauges
in the back seat - I think I could see the prop with it.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006

"Ernest Christley" wrote in message
...
Jim, you're always looking for simple DIY projects for your kitplane
articles, aren't you?

Some guys on the flyrotary list have be batting around ideas on how to
determine if the prop on a pusher is windmilling. Would a piece of
reflective tape and an optical pickup suffice?

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Just out of curiosity, what usefull information would this give you that
isn't known from the tach?

I realize that some drive systems allow the prop to freewheel if the engine
stops; but no control is provided, so the benefit to be derived from the
added knowledge is not obvious...

Peter

"Dave S" wrote in message
nk.net...
Marc J. Zeitlin wrote:


Everybody's got a tach, right? Is that not sufficient?


Believe it or not, NO...

If you get your tach signal from your Engine Controller, and your engine
fails because the electrical system or the engine controller goes kaput,
then it is very likely you will not have a tach signal. (this was the
scenario explicitly discussed in the flyrotary listserv)

How does the traditional a/c engine do it... hall effect on the flywheel?
Direct drive tach cable?

Some kicked around the idea of a rear view mirror someplace.. or an
optical tach of sorts..

Dave

The traditional aircraft engine has a drive on the accessory case, usually
from the oil pump drive gear or some such, that connects to what is
basically a "speedometer" cable that connects to the tach. The tachometer
is basically a "speedometer" calibrated in RPM. It is a small aluminum cup
with a needle on it and a hairspring to keep it from rotating. The cable
connects to a small armature inside the cup with a refrigerator magnet glued
to it. When the magnet turns, the eddy currents induced in the cup cause it
to try to follow the rotation of the magnet. There isn't very much torque
available, although the torque does increase as the speed difference between
the magnet and the cup increases because the magnet induces more current in
the cup if it moves relatively faster. The hairspring essentially works as
a "brake dynamometer" to measure the torque by displaceing the needle. We
lable the needle positions with numbers and calibrate the numbers to
approximate the rpm of the little magnet. Hence a tachometer.

Same meter with numbers and we label and calibrate the numbers to
approximate the mph or kph of a road vehicle by measureing the rpm of some
object in the drive train and call it a speedometer.

I you have the guts to trust one computer with everything and then want to
know something that trivial when it quits working you can buy a simple
optical hand held Tachometer that is powered with a nine volt battery that
reads prop RPM from the reflections from the blades. They are very accurate
since the count blade passages for some unit time and then do the math
digitally to get the prop RPM. They cost about $40 and we use them to check
those cheesy mechanical tachometers when we annual an airplane.

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

R. A. H Flyin at Pinckneyville is this weekend. May 19, 20, and 21. The
weather looks good.

Peter Dohm wrote:


Just out of curiosity, what usefull information would this give you that
isn't known from the tach?

I realize that some drive systems allow the prop to freewheel if the engine
stops; but no control is provided, so the benefit to be derived from the
added knowledge is not obvious...

Peter

If your engine tach is inop because the electrical device that displays
it is FUBAR, then you dont HAVE a tach per se to refer to.

What would it tell you?
One item would be wether or not you need to engage the starter in an
air-restart situation. If the prop is windmilling, then you already have
compression/airflow. Just need to add fuel and spark. Engaging the
starter is not likely to help. If its stopped, then engaging the starter
would be a "really good idea (TM)"

Just one of the quirks of pushers without a bubble canopy.. hard to tell
if you are on fire.. hard to tell if you are streaming anything... and
hard to tell if the prop is turning.

Dave

"Dave S" wrote in message
nk.net...
Peter Dohm wrote:


Just out of curiosity, what usefull information would this give you that
isn't known from the tach?

I realize that some drive systems allow the prop to freewheel if the
engine
stops; but no control is provided, so the benefit to be derived from the
added knowledge is not obvious...

Peter

If your engine tach is inop because the electrical device that displays
it is FUBAR, then you dont HAVE a tach per se to refer to.

What would it tell you?
One item would be wether or not you need to engage the starter in an
air-restart situation. If the prop is windmilling, then you already have
compression/airflow. Just need to add fuel and spark. Engaging the
starter is not likely to help. If its stopped, then engaging the starter
would be a "really good idea (TM)"

Just one of the quirks of pushers without a bubble canopy.. hard to tell
if you are on fire.. hard to tell if you are streaming anything... and
hard to tell if the prop is turning.

Dave

You've really only served to emphasise the correctness of the point that
Highflyer made in two posts during the hour preceeding your post above.

However, I'll play along for one more inning: Please elaborate on the chain
of events that would result in the loss of both engine power and engine
instruments. Please also justify the presumed deviation from the standard
practice of making the engine essentially self sustaining, and at least some
of the engine instruments self powered as well.

Sorry to play the prig,
Peter

("Dave S" wrote)
Just one of the quirks of pushers without a bubble canopy.. hard to tell
if you are on fire.. hard to tell if you are streaming anything... and
hard to tell if the prop is turning.


Speaking of cams ....how 'bout a nanny-cam?


Montblack