Hand propping - licensed pilot at the controls?

On Fri, 14 Jul 2006 19:05:58 GMT, Don Tuite
wrote:

Start with lawnmowers and let 'em work their way up to P47s.

My lawner is a LOT harder to start than the Cub.

(Of course, they are maintained by different mechanics



-- all the best, Dan Ford

email: usenet AT danford DOT net

Warbird's Forum: www.warbirdforum.com
Piper Cub Forum: www.pipercubforum.com
In Search of Lost Time: www.readingproust.com

On Fri, 14 Jul 2006 14:22:45 -0500, "Jim Macklin"
wrote:

The engine needs to have functioning
impulse couplings or some other "safe" method to alter the
timing for starting.

Right; that's the term I was searching for.

What's an impulse coupling, and how does it work?

I hear it clicking when I turn the prop. What's it doing?


-- all the best, Dan Ford

email: usenet AT danford DOT net

Warbird's Forum: www.warbirdforum.com
Piper Cub Forum: www.pipercubforum.com
In Search of Lost Time: www.readingproust.com

On 15 Jul 2006 01:06:24 -0700, "cjcampbell"
wrote:

There is no FAA regulation requiring it, but a surprising number of
local laws require that a licensed pilot be at the controls. There was
a pilot at Boeing Field in Seattle who got ticketed for it a couple
years ago. Also, any airport can have its own rules regarding the
matter, just as they can have rules prohibiting the starting of engines
in hangars, minimum insurance requirements, etc.

The one I was taught (and which presumably is a requirement at the
field where I learned, and where I still fly) is that a licensed pilot
OR mechanic should be at the controls.

Obviously, that includes a student pilot, since only in the first few
flights does an instructor go find another instructor (whomever) to
prop the plane. Once he gets to know the student, the instructor props
while the student goes brakes/cracked/hot.

We had a girl instructor for a time, and she was more cautious: she
left the tail tied down until the engine was going.


-- all the best, Dan Ford

email: usenet AT danford DOT net

Warbird's Forum: www.warbirdforum.com
Piper Cub Forum: www.pipercubforum.com
In Search of Lost Time: www.readingproust.com

When the engine is not turning, mechanical pawls extend on
the shaft and engage a spring-loaded housing, this causes
the spring to compress and the shaft to become retarded. At
the proper time during rotation, the pawls are released and
the spring snaps the magneto up to a higher rpm, generating
a strong and retarded spark, above about 400 rpm the
centrifugal forces lock the pawls and the shaft turns at a
fixed part of the engine. The clicking you hear is the
releasing and snap of the impulse coupling. It is much
easier to see, ask an A&P to show you a mag and explain how
it works. Often there will be mag around the shop that
they can use to show you.

It is early in the morning, so my explanation is not
perfect, editorial improvements welcome.



--
James H. Macklin
ATP,CFI,A&P


"Cub Driver" usenet AT danford DOT net wrote in message
...
| On Fri, 14 Jul 2006 14:22:45 -0500, "Jim Macklin"
| wrote:
|
| The engine needs to have functioning
| impulse couplings or some other "safe" method to alter
the
| timing for starting.
|
| Right; that's the term I was searching for.
|
| What's an impulse coupling, and how does it work?
|
| I hear it clicking when I turn the prop. What's it doing?
|
|
| -- all the best, Dan Ford
|
| email: usenet AT danford DOT net
|
| Warbird's Forum: www.warbirdforum.com
| Piper Cub Forum: www.pipercubforum.com
| In Search of Lost Time: www.readingproust.com

In article ,
Cub Driver usenet AT danford DOT net wrote:

What's an impulse coupling, and how does it work?
I hear it clicking when I turn the prop. What's it doing?

Clicking sound? Isn't that the igniter?

"Jim Macklin" wrote in message
news:my0ug.71145$ZW3.28168@dukeread04...
I phrased my answer poorly. The impulse coupling makes hand
propping easier and safer. Impulse couplers cause a
retarded spark and the spring snaps the magneto to a
momentary higher speed increasing spark strength. Impulse
couplings are used as the method to get a retarded spark for
starting, whether used with or without a starter.

But an engine without a starter has the prop indexed so that
hand propping is safer.

Yep, yep, yep.


"Dave Stadt" wrote in message
.net...
|
| "Jim Macklin" wrote
in message
| news:zSVtg.68471$ZW3.23809@dukeread04...
| They used different magnetos at different times, I just
| remember SN E-22 [an early BE 36, before the A] had
Shower
| of Sparks and a pilot tried to prop it. He didn't get
hurt,
| but it didn't start either.
|
| I general, airplanes with starters are not setup to be
hand
| propped, the prop is indexed differently on the crank
and
| the magnetos have the impulse coupling.
|
| Jim
|
| Engines with mags with impulse couplings hand prop just
fine. In fact those
| without impulse couplings can be a pain to hand prop.
|
|
| "RST Engineering" wrote in
message
| ...
| | As I vaguely remember, the older E-series engines on
the
| bo used impulse
| | mags, but I could be wrong. I don't do retracts, so
this
| is from ancient
| | memory.
| |
| | Jim
| |
| |
| |
| | "Jim Macklin"
wrote
| in message
| | news:qaStg.67773$ZW3.2136@dukeread04...
| | Some engines just are not safe to hand prop. The IO
520
| on
| | the Beech Bonanza uses the Shower of Sparks ignition
to
| get
| | a retarded timing and it uses battery power through
a
| coil
| | and vibrating points to get the shower of sparks.
| |
| |
|
|
|
|

"Jim Macklin" wrote in message
news:IU5ug.76203$ZW3.72851@dukeread04...
When the engine is not turning, mechanical pawls extend on
the shaft and engage a spring-loaded housing, this causes
the spring to compress and the shaft to become retarded. At
the proper time during rotation, the pawls are released and
the spring snaps the magneto up to a higher rpm, generating
a strong and retarded spark, above about 400 rpm the
centrifugal forces lock the pawls and the shaft turns at a
fixed part of the engine. The clicking you hear is the
releasing and snap of the impulse coupling. It is much
easier to see, ask an A&P to show you a mag and explain how
it works. Often there will be mag around the shop that
they can use to show you.

It is early in the morning, so my explanation is not
perfect, editorial improvements welcome.



--
James H. Macklin
ATP,CFI,A&P

Good explanation James. An impulse coupling retards the spark from 25 to 30
degrees before top dead center (whatever your engine is timed to) to within
a couple of degrees either side of top dead center below 300 to 400 rpm.
That's why you hear the couplings click the last second or so on start up
and shut down. Makes them easier to start and reduces the possibility of
kick back to nearly zip. Regarding hand propping..........you can imagine
the fun of an engine kicking back just as you start to pull it through
before even reaching the top of the compression stroke. Gives a whole new
meaning to YEE HAA and is the reason you don't ever wrap fingers around the
prop. It's a good thing to check at annual as at least Slicks will get out
of adjustment.

"john smith" wrote in message
...
In article ,
Cub Driver usenet AT danford DOT net wrote:

What's an impulse coupling, and how does it work?
I hear it clicking when I turn the prop. What's it doing?

Clicking sound? Isn't that the igniter?

I thought jet engines, stoves and furnaces had igniters. Never heard of one
in a recip.

"john smith" wrote

Clicking sound? Isn't that the igniter?

I have an old Wisconsin engine that has a Fairbanks Morse magneto that
functions much the same as an aircraft magneto. It is a separate bolt on
construction, turned off of the camshaft.

It has to be taken apart and cleaned, once in a while. When turning it by
hand, very slowly even, it winds up the spring at the correct place on the
rotation, then releases the spring-making the loud click that they are
talking about. When it releases at that slow hand turned RPM, it spins the
innards very rapidly and you had better not have your hand across the spark
plug lead. If you do, you are about to have a very shocking experience.

Such it is with such a beast, that makes turning a prop with the switch not
turned to off, or if it has a bad grounding wire. It makes such a hot spark
timed after top dead center, even with barely moving the prop, that if there
is a fuel mixture in the cylinder, that the engine may start.
--
Jim in NC