Run up for plug clearing

The answer to questions such as this can be found in the POH from the
manufacturer who supposedly knows more than the average flight instructor or
public thought about what is right.

For the Cessna Model 152 Section 4 Normal Procedures under "Takeoff" "Power
Check" says
"It is important to check full-throttle engine operation early in the
takeoff run. Any sign of rough engine operation or sluggish engine
acceleration is good cause for discontinuing the takeoff. IF THIS OCCURS,
YOU ARE JUSTIFIED IN MAKING A THOROUGH FULL-THROTTLE STATIC RUNUP BEFORE
ANOTHER TAKEOFF IS ATTEMPTED. The engine should run smoothly and turn
approximately 2280 to 2380 RPM with carburetor heat off and mixture leaned
to maximum RPM."
(Emphasis added.)

You will not harm the engine therefore if you use 2000 RPM and lean to clean
the plugs.

I suggest if you are serious about this you discuss the matter with a
mechanic.

On Sat, 09 Oct 2004 10:54:44 GMT, "Roger Long"
wrote in ::

Any thoughts?
http://www.sacskyranch.com/faq_spark_plug/index.html
http://www.sacskyranch.com/faq_spark_plug/FAQ00007.htm

"Roger Long" wrote

I can't remember where I "learned" it but I always thought 1800 RPM was the
limit for ground running leaned to clear plugs. I had a really bad one
yesterday with 250 RPM drop. I taxied back to the shop and they said to try
full throttle before pulling the plugs.

It worked but running the engine full power (near sea level) while leaned
for best power and peak EGT with minimum airflow for the minute it took
seems pretty abusive to me. Maybe you can get away with it because the
CHT's have not yet risen to max.

Any thoughts? What were you taught?

I was tought the full-power tactic. But what I found out empirically
was that leaning like crazy for all ground ops (to the point the
engine will barely run) has so far prevented the mag drop problem from
occurring again. I posted about this within the past few months and
found that others use similar procedures.

Jim Rosinski

For the engine, the higher the RPM the better. However, 1800 is used
because its a high RPM but doesn't suck as many rocks into the prop as
full RPM. If you run up to full RPM everytime you'll send up replacing
your prop every annual.

-Robert



"Roger Long" wrote in message ...
I can't remember where I "learned" it but I always thought 1800 RPM was the
limit for ground running leaned to clear plugs. I had a really bad one
yesterday with 250 RPM drop. I taxied back to the shop and they said to try
full throttle before pulling the plugs.

It worked but running the engine full power (near sea level) while leaned
for best power and peak EGT with minimum airflow for the minute it took
seems pretty abusive to me. Maybe you can get away with it because the
CHT's have not yet risen to max.

Any thoughts? What were you taught?

(Robert M. Gary) wrote in message . com...
For the engine, the higher the RPM the better. However, 1800 is used
because its a high RPM but doesn't suck as many rocks into the prop as
full RPM. If you run up to full RPM everytime you'll send up replacing
your prop every annual.

-Robert

1800 (or 1700 or even 1600 in other installations) is selected
because that's where cylinder pressures are highest for the static
condition. Lower RPMs give lower pressures because the throttle is
closed too much, and higher revs will give slightly lower pressures
because the volumetric efficiency of the engine is beginning to drop
off (there's too much friction in the intake and exhaust systems). At
highest cylinder pressures weak mags or sparkplugs are most likely to
cut out, which is what we're checking for.

Dan



"Roger Long" wrote in message ...
I can't remember where I "learned" it but I always thought 1800 RPM was the
limit for ground running leaned to clear plugs. I had a really bad one
yesterday with 250 RPM drop. I taxied back to the shop and they said to try
full throttle before pulling the plugs.

It worked but running the engine full power (near sea level) while leaned
for best power and peak EGT with minimum airflow for the minute it took
seems pretty abusive to me. Maybe you can get away with it because the
CHT's have not yet risen to max.

Any thoughts? What were you taught?

(Robert M. Gary) wrote in message . com...
For the engine, the higher the RPM the better. However, 1800 is used
because its a high RPM but doesn't suck as many rocks into the prop as
full RPM. If you run up to full RPM everytime you'll send up replacing
your prop every annual.

-Robert

1800 (or 1700 or even 1600 in other installations) is selected
because that's where cylinder pressures are highest for the static
condition. Lower RPMs give lower pressures because the throttle is
closed too much, and higher revs will give slightly lower pressures
because the volumetric efficiency of the engine is beginning to drop
off (there's too much friction in the intake and exhaust systems). At
highest cylinder pressures weak mags or sparkplugs are most likely to
cut out, which is what we're checking for.

Dan



"Roger Long" wrote in message ...
I can't remember where I "learned" it but I always thought 1800 RPM was the
limit for ground running leaned to clear plugs. I had a really bad one
yesterday with 250 RPM drop. I taxied back to the shop and they said to try
full throttle before pulling the plugs.

It worked but running the engine full power (near sea level) while leaned
for best power and peak EGT with minimum airflow for the minute it took
seems pretty abusive to me. Maybe you can get away with it because the
CHT's have not yet risen to max.

Any thoughts? What were you taught?

On Sat, 09 Oct 2004 10:54:44 GMT, "Roger Long" wrote:

Any thoughts? What were you taught?

However you monitor engine temperature, oil temp or CHT, just avoid overheating
the engine. I was taught to try a lower RPM for a set period, and if that did
not work go to full power for a set period while closely tracking engine temp.

By set period, I was taught 30 or 60 seconds timed by a watch, not by feel or
guessimate.

Demonick

"Roger Long" wrote

I can't remember where I "learned" it but I always thought 1800 RPM was the
limit for ground running leaned to clear plugs. I had a really bad one
yesterday with 250 RPM drop. I taxied back to the shop and they said to try
full throttle before pulling the plugs.

It worked but running the engine full power (near sea level) while leaned
for best power and peak EGT with minimum airflow for the minute it took
seems pretty abusive to me. Maybe you can get away with it because the
CHT's have not yet risen to max.

Any thoughts? What were you taught?

I was tought the full-power tactic. But what I found out empirically
was that leaning like crazy for all ground ops (to the point the
engine will barely run) has so far prevented the mag drop problem from
occurring again. I posted about this within the past few months and
found that others use similar procedures.

Jim Rosinski

"Roger Long" wrote in message ...
I can't remember where I "learned" it but I always thought 1800 RPM was the
limit for ground running leaned to clear plugs. I had a really bad one
yesterday with 250 RPM drop. I taxied back to the shop and they said to try
full throttle before pulling the plugs.

It worked but running the engine full power (near sea level) while leaned
for best power and peak EGT with minimum airflow for the minute it took
seems pretty abusive to me. Maybe you can get away with it because the
CHT's have not yet risen to max.

Any thoughts? What were you taught?

The standard technique taught in many airplanes for the
short-field takeoff is brakes locked, full power, lean for best RPM,
and go. This can take some time for a student, and I try to get the
instructors to limit it to 15 seconds or so, no more. We use the same
technique to clear fouled plugs. If they don't clear in a few seconds
at full power, they aren't going to clear adequately for flight. If
it's just a bit of oil that's fouled the bottom plugs during an
extended idle, they'll clear. If it's lead fouling, they won't clear
well and need to come out and get serviced.

Dan

For the engine, the higher the RPM the better. However, 1800 is used
because its a high RPM but doesn't suck as many rocks into the prop as
full RPM. If you run up to full RPM everytime you'll send up replacing
your prop every annual.

-Robert



"Roger Long" wrote in message ...
I can't remember where I "learned" it but I always thought 1800 RPM was the
limit for ground running leaned to clear plugs. I had a really bad one
yesterday with 250 RPM drop. I taxied back to the shop and they said to try
full throttle before pulling the plugs.

It worked but running the engine full power (near sea level) while leaned
for best power and peak EGT with minimum airflow for the minute it took
seems pretty abusive to me. Maybe you can get away with it because the
CHT's have not yet risen to max.

Any thoughts? What were you taught?