Rough-Running Magnetos in Your Life
Christopher Pettus
these symptoms, I realized that I have no clear idea of what was going
on.
In particular, after each startup, during the run-up magneto check, one
mag (the right) would always run quite rough. The procedure I was
taught was to run the other magneto at a lean mixture for a bit, then
recheck. Sure enough, it would always clear up the trouble, but what's
really going on? Lead deposits being burned off? Heating up the
cylendar? Why would it be so predictable (always one particular
mag, all the time)?
--
Christopher Pettus - "Poetry you can actually read!" - Apple Computer, Inc.
MS 3-PK -- (408) 974-0004 -- c...@apple.com -- Link CHRISTOPHE
"I used to think that the brain was the most wonderful organ in the body.
Then I realized who was telling me this." -- Emo Phillips
Gregory R. TRAVIS
>Having recently flown about 10 hours in a Piper Archer that exhibited
>these symptoms, I realized that I have no clear idea of what was going
>on.
>In particular, after each startup, during the run-up magneto check, one
>mag (the right) would always run quite rough. The procedure I was
>taught was to run the other magneto at a lean mixture for a bit, then
>recheck. Sure enough, it would always clear up the trouble, but what's
>really going on? Lead deposits being burned off? Heating up the
>cylendar? Why would it be so predictable (always one particular
>mag, all the time)?
The FBO at our field had an Archer, 47601, that used to exhibit this exact
symptom. I don't have any configuration info handy, but I believe that
O-360 had its mags set up so that the right mag fired all the bottom
plugs while the left fired the top plugs. I always assumed that during
shutdown, gunk from inside the cylinders (oil/lead) would collect on the
bottom plugs making them misfire.
My procedure was almost exactly the same - except that I would turn on only
the right/bottom mag and lean. If that didn't do it (usually because one
of the plugs was so fouled that it wasn't firing at all) I would switch
to the top plugs and repeat. Leaning raises the combustion temperature; the
idea is to burn off and flush out whatever it is that's clogging the plugs.
gregory travis center for innovative computer applications
gr...@cica.cica.indiana.edu
Richard A Hyde rah@btr.com
|Having recently flown about 10 hours in a Piper Archer that exhibited
|these symptoms, I realized that I have no clear idea of what was going
|on.
|
|In particular, after each startup, during the run-up magneto check, one
|mag (the right) would always run quite rough. The procedure I was
|taught was to run the other magneto at a lean mixture for a bit, then
|recheck. Sure enough, it would always clear up the trouble, but what's
|really going on? Lead deposits being burned off? Heating up the
|cylendar? Why would it be so predictable (always one particular
|mag, all the time)?
I experience this "problem" not infrequently in my club's 152s. The "cure"
is almost the same except I run lean on *both* mags and at a higher RPM
(2000 instead of 1700).
The right mag is always the rough one. My instructors explanation was
that the right mag was the lower one in the cylinder and thus more
susceptible to lead fouling. The higher RPM and lean mixture raised the
temperature enough to vaporize the offending lead deposit.
In any event, it seems that one plug runs cooler than the other... I
don't know about it's being the "bottom" one making any difference.
Perhaps the moral is that we should lean the mixture while taxiing?
I really don't know either.... Perhaps the timing is slightly different
on each mag??.... net.gods? :-)
Rick
--
------------------------------------------------------------------------------
| Richard Hyde | R...@btr.com | This space intentionally left blank |
------------------------------------------------------------------------------
Lars-Henrik Eriksson
>In article <51...@apple.Apple.COM> c...@Apple.COM (Christopher Pettus) writes
>
>I experience this "problem" not infrequently in my club's 152s. The "cure"
>is almost the same except I run lean on *both* mags and at a higher RPM
>(2000 instead of 1700).
I have been taught to run the engine lean at full power for half a
minute or so if this happens. It seems like a somewhat brutal
approach, but it works. My instructors claim that during this short
period there is no risk of damaging the engine.
The spark plug fouling problem is especially great when you use 100LL
fuel in engines designed for unleaded AVGAS 80/87. Our club's tow
aircraft, a PA25-235 (Pawnee) run on 80/87. Once, the 80/87 tank on
the field ran dry and we had to use 100LL in the aircraft. During one
runup the engine ran so rough that I was certain that there was a bad
spark plug. I had even identified the offending (cold) plug, when a
more experienced tow pilot came along. He ran the engine lean at full
power for two minutes. After that everything was all right again. Ugh.
--
Lars-Henrik Eriksson Internet: l...@sics.se
Swedish Institute of Computer Science Phone (intn'l): +46 8 752 15 09
Box 1263 Telefon (nat'l): 08 - 752 15 09
S-164 28 KISTA, SWEDEN
USENET Administrator
From: ri...@crowbar.apple.com (Rick Auricchio)
Path: crowbar!rick
>that the right mag was the lower one in the cylinder and thus more
>susceptible to lead fouling. The higher RPM and lean mixture raised the
>temperature enough to vaporize the offending lead deposit.
True, but on some engines the mag/plug association is somewhat more
complex. On the Lycoming IO-540, for example, the right mag fires
the top plugs in half the cylinders, bottoms in the other half.
The left takes care of the other ones. Guess this prevents a mag
failure from leaving you with all lower plugs running or vice versa.
>In any event, it seems that one plug runs cooler than the other... I
>don't know about it's being the "bottom" one making any difference.
Usually is. Also the bottom picks up lead and oil.
>Perhaps the moral is that we should lean the mixture while taxiing?
Definitely. ALSO, a temp of less than 800F won't keep the lead
vaporized. Idling at 1000RPM generally keeps cylinder temps
high enough to avoid lead deposits. I rarely idle below, say,
800RPM, even though it will idle at 650.
--
Rick Auricchio ri...@apple.COM Mooney N894AR (408) 974-4227
Apple Computer Inc, A/UX Engineering,10300 Bubb Rd, MS 50-UX Cupertino CA 95014
Work is for people who don't know how to fly.
My opinion is my own. My employer? They use a windsock and a fire extinguisher.
Jim Schinnerer
would lean the engine and run both mags for about 30 seconds. This
always worked. My instructor said that we were burning off the carbon.
I don't know if that is actually what is happening, but the experience
is similar to the previous post.
In about 40 hours in my Mooney, I have not had any roughness in the mags.
Does this imply new plugs?
---------------------------------------------------------
Jim Schinnerer - PP-ASEL-IA | Hewlett Packard
Mooney - 350X - "Buster" | Cupertino, CA
Hang IV - Magic KISS |
email - schi...@hpihoah.HP.COM |
---------------------------------------------------------
Dennis Hurvitz
> always worked. My instructor said that we were burning off the carbon.
> I don't know if that is actually what is happening, but the experience
> is similar to the previous post.
>
> In about 40 hours in my Mooney, I have not had any roughness in the mags.
> Does this imply new plugs?
>
> ---------------------------------------------------------
> Jim Schinnerer - PP-ASEL-IA | Hewlett Packard
our feed is back up after a week...
you're not really clearing mags, but plugs. i highly doubt your burning
off carbon, but actually cleaning fouled plugs. they are typically
either fuel fouled, or, hopefully not, oil fouled. i'll bet you a
quarter, it'll be the bottom plugs, 99 times out of 100.
the fuel fouling is typically pilot induced. priming, and cycling the
throttle (activating the accelerator pump) dumps fuel in either the
intake manifold or possibly even the cylinder (some fuel injected
engines). something to be aware of during starting.
oil fouled plugs are a warning that the cylinder in question has some
health problem (perhaps valve guides). the first appearance may be a
fluke, however if this repeats a second and third time, it may be time
for a top overhaul on that piston. should this occur your mechanic may
opt to only rebuild the valve section, or pull the cylinder off, have it
bored and refinished (we've had great success with the cermichrome process).
the cyclinder shops will also machine/rebuild the top valve section to
factory tolerances. it's not unusual for a 2000 tbo engine to need a top
overhaul at 1500 hours. turbo engines may need them every 100 hours
depending on operation :)
running the typical o-235,o320,o360 at 2000 rpm, leaning to peak and
counting to 10 or 20 should clean the plugs of most fuel (oil is
tougher) foulings. some pilots like to cycle the props a couple times to
increase bmep. (brake mean effective pressure in the cylinder)
many of us recommend leaning the idle mixture immediately after engine
start. you will not damage the engine from overleaning during taxi.
there is not enough heat being generated by the over lean idle mixture to
damage the engine at these low fuel flow rates. you need to experiment a
little to see how lean you can set the mixture. the technique is more
effective with fuel injected engines.
the fact that your mooney is not fouling plugs suggests engine health,
and good pilot technique in starting.
dennis hurvitz
David Papworth
>>
>> In about 40 hours in my Mooney, I have not had any roughness in the mags.
>> Does this imply new plugs?
>
>and good pilot technique in starting.
>
>
>dennis hurvitz
I have to agree with Dennis. In 400 hours on my Archer, I've had
the rough-on-one-mag-during-runup problem just once, and that
only lasted for 3-4 seconds.
I've found the best starting technique for the O-360 is to
pump the throttle twice if it is cold, once if warm, prior to
cranking. I never touch the primer unless it is EXTREMELY cold.
I do nearly all of my flying at 75 percent power. Out here, most
of the MEAs are so high that the throttle goes to full power
at takeoff, stays there during climb, level-off, and cruise, and
only gets pulled back for approach and landing. I lean the mixture
to 25 degrees-rich-of-peak EGT above 5000 MSL on the climb and
during cruise. I don't bother to lean at idle because the mixture
control doesn't seem to affect the idle system on the Marvel carbs
(except for idle cut-off). In really high-density altitude
take-offs I'll lean the mixture a bit during runup and on the roll.
The carb heat only gets used to check it during runup and when
I suspect carb ice (I actually had carb icing only a couple of times).
David Papworth
Archer N3334Q
Dr. Daniel R. Masys
>When I was training on C152's and C172's, when we had a rough mag, we
>would lean the engine and run both mags for about 30 seconds. This
>always worked. My instructor said that we were burning off the carbon.
Might have been carbon fouling from over-rich running, a very common event
in the low altitude training environment. Though recent postings have
talked of "vaporizing lead deposits", as I understand it they cannot be
vaporized or combusted, only dislodged. Note that the generous cooling
of the C152 causes relatively low cylinder head temperatures and a marked
increase in lead deposition, due to insufficient heat to activate the
lead scavenging agent(s) in avgas. The C172 is somewhat better, but not
a lot. However...
>
>In about 40 hours in my Mooney, I have not had any roughness in the mags.
>Does this imply new plugs?
>
the tightly cowled O-360 in Mooneys (and the tightly cowled O-470 in 182's
made after 1970) causes substantially higher mean cylinder head temps,
and far less susceptibility to plug fouling.
New plugs can foul in less than an hour of over-rich, low temp operation,
so it's unlikely to be plug youth. Thank Al Mooney for the design, though
you may have different words for him when you try to change those plugs.
Dan Masys
ma...@mcs.nlm.nih.gov
Bill Standerfer
>In particular, after each startup, during the run-up magneto check, one
>mag (the right) would always run quite rough. The procedure I was
>taught was to run the other magneto at a lean mixture for a bit, then
>recheck. Sure enough, it would always clear up the trouble, but what's
>really going on? Lead deposits being burned off? Heating up the
>cylendar? Why would it be so predictable (always one particular
>mag, all the time)?
During a spark plug discussion at annual this week, our A&P described an
incident he had some time ago with a 150. They had to clean the plugs on one
cylinder about every 25 hours or so. This was somewhat unusual, but they
couldn't find anything wrong. The mag checks were as if there was lead
fouling. The engine finally told them what was wrong by blowing a hole in a
piston. The contamination had actually been aluminum particles from a
disintegrating piston. It took a while for the damage to get to the
catastrophic stage.
Bill
Bill Standerfer -- KF0DJ -- Baron N1746W
bi...@hpisla.hp.com or {...}!hplabs!hpisla!bills
Hewlett Packard Measurement Systems Operation
PO Box 301, Loveland, CO 80539 -- 303-679-2378
G. David Frye
>I've found the best starting technique for the O-360 is to
>pump the throttle twice if it is cold, once if warm, prior to
>cranking. I never touch the primer unless it is EXTREMELY cold.
Sigh. Our club 172 has the same "recommended procedure." I don't like it.
I never will. The problem with the primer is that it floods the engine too
easily. The problem with the throttle-pumping method is that, if it's a
normally aspirated engine, you're pumping fuel into the carburetor, not the
cylinders, and a backfire could result in a carb fire.
In all the time I've been using this throttle procedure, I've had much more
consistent results from starting the 172. The primer is much more cantan-
kerous. Still, I feel like I'm dancing with the devil.
Has anyone ever had a real carb fire? Every private pilot candidate knows
the correct recovery procedure -- keep cranking the starter while you lean
the mixture. But, how do you know there IS a fire? Get out and take a
look? Hope that someone is lurking around the T-hangars and will alert you?
Wait for the "engine fire" indicator to light so you can push the "extinguish
fire" button?
In both cases of priming and throttle-pumping, an important "trick" is to do
the operation JUST before you crank. I holler "clear", _then_ prime, then
crank. If you wait too long, the fuel you sprayed/pumped winds up down in
the air box where the only fire it can start is one you don't want.
One horse in this discussion that isn't quite dead enough to stop beating --
if your engine has this problem sometimes, it probably has it more often
than you think. The suggestion to "lean during runup if you have problems"
is a good one, I suppose, but the smart practice is to *always lean during
ground operations*. How much to lean can be a matter of practice -- in the
same beloved club 172, I "know" that the mixture control should be pulled
out about an inch. I just leave it there, except during start and runup.
Why do it this way, instead of leaning during runup? Because the deposits
are building while you're taxiing back to the hangar! There they sit and
have to be burned off later, i.e. after you've had to start it with the
plugs gunked up. The down side of this method is that you'd darn well better
put "mixture rich" on your pre-takeoff checklist if it isn't there already.
G. David Frye
-----------------------------------------------------------------------------
INTERNET: fr...@cerl.uiuc.edu PLATO: frye / s / cerl PHONE: (217) 333-7439
-----------------------------------------------------------------------------
Geoff Peck
O'Shaughnessy) writes:
> This is a great thread. Here in Minnesota, I was trained to run the
> Cessna's (152/172) full rich unless above 3000 MSL. We frequently
> experience large magneto drops, which was atributed to fouling the plugs.
>
> So, if I'm reading things correctly, I should be leaning during ground ops,
> even at 1000 MSL, and be taxiing at > 800 rpm? [If safe]
OK, here's what I do.
(1) For ground operations, lean the mixture about halfway; if the
engine starts to falter, enrichen it a bit. Indeed, when I start
most airplanes, I'll immediately bring the mixture back to the
halfway point after the engine starts. This is particularly
critical at high-altitude airports where the engine can "drown" due
to too much fuel and not enough air.
(2) For takeoff in a normally-aspirated engine below 3000' density
altitude, full rich (except for one particular airplane which had its
full rich setting way too rich...); above 3000', do a full-power
lean before takeoff, setting EGT to 50 rich of peak or "by ear"
about 1/4" of mixture travel rich of peak.
(3) If climbing from a sea-level airport, leave mixture alone until
about 5000', then lean in climb to 50 rich of peak, etc.
(4) If levelling off, _always_ lean, _regardless_ of altitude;
enrichen before you increase power (for climb, for example), and
then lean again when you reduce power.
(5) On shutdown, bring the engine to ~1500RPM for ~3 seconds, then pull
the mixture without touching the throttle.
My last set of sparkplugs in the Arrow (Lycoming IO-360) lasted 800 hours
-- and they were "ordinary" Champion plugs, not the fine-wire variety.
Geoff
John M. O'Shaughnessy
Cessna's (152/172) full rich unless above 3000 MSL. We frequently
experience large magneto drops, which was atributed to fouling the plugs.
So, if I'm reading things correctly, I should be leaning during ground ops,
even at 1000 MSL, and be taxiing at > 800 rpm? [If safe]
John
--
John M. O'Shaughnessy o...@osa.com
Open Systems Architects, Inc. Minneapolis, MN
Sean Foderaro
I've always been an aggressive mixture leaner since I was trained in a 152.
I'd like to add one note of warning to the 'run the engine up and lean it
out just before shutdown' step. Be careful where you do this. Parking areas
aren't as free of little rocks as runways and runup areas, and if you've got a
big prop with little ground clearance, running up the engine is going to
pick up those rocks and nick the prop or your plane. This is speaking as
someone who has spent more money recently dressing my prop than myself.
-sean
n28348 - "The gasoline powered rock thrower"
p.s. I'm flying across the country in a few days (from Oakland, Ca (OAK) to
State College, Pa (UNV) with visits to many northeast airports
over the next few weeks. I'll be taking the I-80 route. If you
see a white/green/gold Grumman Tiger with a large N28348 on the side
stop by and say hi.
p.p.s The tiger just had its first annual under my ownership and I did
it the owner-assisted way. It was a lot of work but definitely worth
it in terms of what I learned about the plane's systems and
in terms of money saved. I did it all with a manual screwdriver
and I'll never do that again (my hand is still blistered).
I found that the elt, whose battery had been
changed at the last annual, was turned off! [for those who've never
seen an elt, it has a three position switch: on (for continuous
broadcasting, off (for never broadcast) and arm (for start broadcasting
when you think I've crashed).]
G. David Frye
writes:
>
> I've always been an aggressive mixture leaner since I was trained in a 152.
>I'd like to add one note of warning to the 'run the engine up and lean it
>out just before shutdown' step. Be careful where you do this. Parking areas
>aren't as free of little rocks as runways and runup areas, and if you've got a
>big prop with little ground clearance, running up the engine is going to
>pick up those rocks and nick the prop or your plane. This is speaking as
>someone who has spent more money recently dressing my prop than myself.
If you lean during all ground operations, as I mentioned in my earlier posting,
there is no need to do the "runup before shutdown" step. I think this is
better overall for the engine.
Bill Standerfer
> altitude, full rich (except for one particular airplane which had its
> full rich setting way too rich...); above 3000', do a full-power
> lean before takeoff, setting EGT to 50 rich of peak or "by ear"
> about 1/4" of mixture travel rich of peak.
>
A respected American Bonanza Society proficiency instructor (and A&P and AI
and...) recommends leaning to only 200 degrees rich of peak. He is concerned
about the engine running too hot on takeoff and initial climb. My personal
technique is to lean agressively when taxiing, then, as I roll out onto the
runway, mixture to full rich, throttles full forward, then lean until I see a
slight increase in RPM. This technique will usually bring the EGTs to about
100 degrees below peak. We have a digital fuel flow meter and can see 4 to 8
GPH reductions in fuel flow when doing this. Of course, if you are flying a
turbocharged airplane, follow the POH strictly.
> (3) If climbing from a sea-level airport, leave mixture alone until
> about 5000', then lean in climb to 50 rich of peak, etc.
>
Well, some airplanes are different. Our POH, for example, says 3000'. Use the
manual as a guideline. Use 5000' if it has no guideline. BTW, when you pass
through our part of the country, if it is 85 degrees (a nice, normal summer day
in eastern Colorado), the density altitude is about 8500' *on the ramp*. Learn
how to lean properly!
> (5) On shutdown, bring the engine to ~1500RPM for ~3 seconds, then pull
> the mixture without touching the throttle.
Some folks subscribe to a full power runup, leaning for several seconds, then
shutting down. Do this around my airplane and I'll feed you to the prop!
Geoff's recommendation is preferred by most of "the literature". Some of the
excessively high runups do more damage to the airplane and its surroundings
than can be justified.
Geoff Peck
Standerfer) comments on my leaning procedures from <51...@apple.Apple.COM>.
On takeoff, I suggested setting EGT to 50 rich of peak in a full-power lean
before takeoff. In my experience, that results in a mixture of ~100
degrees rich of peak on initial climbout. (Maybe my airplane is wierd.)
In any case, I would suggest glancing at the EGT gauge frequently during
climb, and never let it get hotter than 50-rich -- probably best around
100-rich.
Bill in several cases recommends following the POH (Pilot's Operating
Handbook). I agree. Different airplanes suggest different altitudes for
leaning during climb, initial leaning at high density altitude airports
(particularly turbocharged aircraft), etc. However, POHs may not always be
"the last word". You might also want to check the _engine_ operating
handbook and, Light Plane Maintenance's Light Aircraft Engine Operating
Handbook. From my perspective, the POH usually has priority, but if there is
broad concurrence on a different procedure from a varitety of sources
(usually including my mechanic), then I may modify the POH procedures.
The Piper Malibu (the original, with the "exciting" Continental engine) has
particularly unique leaning instructions in the POH -- one typically leans
it 50 degrees _lean_ of peak for cruise, as I recall.
GP> (5) On shutdown, bring the engine to ~1500RPM for ~3 seconds, then pull
GP> the mixture without touching the throttle.
BS> Some folks subscribe to a full power runup, leaning for several seconds,
BS> then shutting down. Do this around my airplane and I'll feed you to the
BS> prop! Geoff's recommendation is preferred by most of "the literature".
BS> Some of the excessively high runups do more damage to the airplane and
BS> its surroundings than can be justified.
Clearly, being aware of one's surroundings is critical when performing this
maneuver. If the surroundings are inappropriate (you're about to blow gravel
at someone else's airplane), then don't do it! Also, one should be careful
to not bring the power up higher than about 1500 RPM, and one should be quick
about pulling the mixture. In reality, I suppose the sequence is really
more like "throttle up -- pull mixture" -- there's no 3-second delay.
Geoff
David E Allen
> The problem with the primer is that it floods the engine too easily.
> The problem with the throttle-pumping method is that, if it's a
> normally aspirated engine, you're pumping fuel into the carburetor, not the
> cylinders, and a backfire could result in a carb fire.
There's another way to use the primer that might help. Pump it once or so
just to fill the lines, then just leave it open. The engine will suck in
what it needs and perhaps not flood as much. I would always do this with
the Luscombe for very cold starts. Be sure to close it securely before
taxiing or anything else.
dave allen - Fly because you love it.
Steven Philipson
(G. David Frye) writes;
> Has anyone ever had a real carb fire? [...]
> But, how do you know there IS a fire? Get out and take a
> look? Hope that someone is lurking around the T-hangars and will alert you?
I've seen one and read about others. Usually you can see smoke;
fuel-rich fires generate smoke and soot. Engine compartment hoses do
too. Another sign is noise -- you can sometimes hear the fire burning.
And yes, sometimes you don't know for sure until you get out and look,
or until someone starts jumping up and down in front of the airplane,
or the tower asks that innocuous little question... "Barnburner 321,
are you experiencing difficulty?" I *hate* it when they ask that. :-)
The April issue of Sport Aviation has a few lines about a carb
fire in the Weddel-Williams replica. The carb box itself was on
fire -- it was made of magnesium. The other interesting point was
that the dry chemical fire extinguisher did almost as much damage as
did the flames. We put a Halon extinguisher in our plane. 'Course,
carb fire's aren't much of a concern for a fuel injected Arrow.
Steve
(the certified flying fanatic)
ste...@decwrl.dec.com
Rick Koril
>In article <1991Apr15.0...@ux1.cso.uiuc.edu>, fr...@cerl.uiuc.edu
> (G. David Frye) writes;
>
>> Has anyone ever had a real carb fire? [...]
>> But, how do you know there IS a fire? Get out and take a
>> look? Hope that someone is lurking around the T-hangars and will alert you?
>
> I've seen one and read about others. Usually you can see smoke;
>fuel-rich fires generate smoke and soot. Engine compartment hoses do
>too. Another sign is noise -- you can sometimes hear the fire burning.
>And yes, sometimes you don't know for sure until you get out and look,
>or until someone starts jumping up and down in front of the airplane,
>or the tower asks that innocuous little question... "Barnburner 321,
>are you experiencing difficulty?" I *hate* it when they ask that. :-)
>
A couple winters ago I had the misfortune of one from pumping the
throttle in my 182. The battery was dead and we ended up jumping
the plane from the car (one advantage to 14v electrical system).
A pilot friend who I sometimes fly with was handling the start
while I handled the battery hookup and my car. The plane backfired
and flames shot from the open cowl flaps. I shut the car off,
hollered at my friend, and we dumped snow down the cowl. I'm not
sure this was the best thing, but the fire quickly went out. The
fire extinguisher remained in the plane throughout this entire
episode. Needless to say, our departure was well delayed while
we had the engine compartment checked out - no damage other than
my pride for not following starting procedures to a "T".
BTW, one of our local mechanics suggested using the primer for
cold weather starts to avoid this exact scenario. Set the throttle
appropriately, prime as usual (but leave the primer all the way
out), and while you engage the starter, push the primer in (and
repeat, if necessary). This has to do with the fact that the
primer shoots fuel directly in the cylinders (but not necessarily
all of them), while the throttle send it thru the carburator.
I find it works well for me, but as always, your mileage may vary.
Rick Koril
Ed Falk
>
>A couple winters ago I had the misfortune of one from pumping the
>throttle in my 182. The battery was dead and we ended up jumping
>The fire extinguisher remained in the plane throughout this entire
>episode.
Whenever I jump-start my plane; I always pull out the fire extinguisher
first and keep it in my back pocket. Thanx for verifying to me that
this is a Good Idea.
Also, 14v electrical systems *are* nice. Why did the industry
switch? I don't know how I'd get by without a plane I couldn't
jump with ordinary jumper cables if I had to.
-ed falk, sun microsystems
sun!falk, fa...@sun.com
In the future, somebody will quote Andy Warhol every 15 minutes.
Geoff Peck
> pumping the throttle in my 182. [...]
> BTW, one of our local mechanics suggested using the primer for
> cold weather starts to avoid this exact scenario.
Hmmm. Well, I'm definitely not mechanically inclined, but I've been told
the following from enough reliable sources that I tend to believe:
- Carbureted Cherokees, such as Warriors and Archers, have a "throttle
pump" which works in a manner somewhat similar to the primer. The
primer provides better fuel distribution, so it should be used in
preference to the throttle pump, but one can still pump the throttle
to get additional fuel into the engine _safely_.
- The throttle-pump procedure should _not_ be used on Cessnas, either
because of the high-wing gravity-feed fuel system or because of the
design of the carburetor.
- In general, one should utilize the primer _only_ when not cranking
the engine with the starter. If the engine doesn't start, then stop
cranking, re-prime it, and try starting it again. In carbureted
Cherokees, however, a couple of full strokes of the throttle are OK
during cranking.
Note that the procedural differences between the Warrior and the Cessna 172
are most striking, because in many model years they share the same basic
powerplant -- the Lycoming O-320. They do utilize different variants of the
engine.
Would someone on the net who has honest-to-goodness experience tearing
apart both types of airplanes care to comment? Let's not just keep
speculating...
Geoff
Dr. Daniel R. Masys
>throttle in my 182.
>and flames shot from the open cowl flaps. I shut the car off,
>hollered at my friend, and we dumped snow down the cowl. I'm not
>sure this was the best thing, but the fire quickly went out. The
>fire extinguisher remained in the plane throughout this entire
>episode. Needless to say, our departure was well delayed while
>we had the engine compartment checked out - no damage other than
>my pride for not following starting procedures to a "T".
>
remove the air filter element and look for signs of damage. The standard
Cessna paper filter "usually" gets charred by a carb fire, and then
goes on (some 1-100 hours later) to fall apart and dump paper
chucks into the induction system. A few 182's have experienced
engine failures due to ingestion of the paper air filter, apparently
precipitated by a prior carb fire.
I had an inapparent carb fire (all I heard was a "backfire" sound) during
a cold weather start. The way I knew something had happened is that
my carb ice detector probe was incinerated instantly, and the carb ice
indicator came on permanently. Another incidental benefit(?) of a carb
ice detector (well, the ARP folks rebuilt it for $35 plus shipping; not
too bad all things considered).
A cure for the paper filter risk is to install the Brackett foam air filter.
Dan Masys
ma...@mcs.nlm.nih.gov
Fred Black
leaving it out while cranking. As a pilot trained (and still flying) in the
'great white north' I have a few comments to offer.
In really cold weather (-20 C or around 0 F,) starting SOP for the Cessnas that
I have flown (150, 172) is to prime the engine (3-5 shots,) leave the primer out
and if necessary keep the engine running by pumping the primer. I have had to
keep the engine running by pumping the primer for as much as 30 seconds in really
cold weather. (yes I use preheat when I can). Once the engine is running, the
primer can be pushed in SLOWLY with no adverse consequences.
The above technique should only be necessary in really cold weather. At this
time of the year, 2 strokes of the primer, lock the primer and turn the key
works fine.
I have only been in Pipers as a passenger, so I can't comment on starting them.
--
Fred G. Black E-mail: cr...@bnr.ca Bell-Northern Research
PPSEL,G P.O. Box 3511 StationC
My opinions only. Ottawa, Ontario
Canada K1Y 4H7
Claude Goldsmith
>In article <1991Apr27....@informix.com> rko...@informix.com (Rick Koril) writes:
>> A couple [of] winters ago I had the misfortune of [an engine fire] from
>> pumping the throttle in my 182. [...]
>> BTW, one of our local mechanics suggested using the primer for
>> cold weather starts to avoid this exact scenario.
>
>Hmmm. Well, I'm definitely not mechanically inclined, but I've been told
>the following from enough reliable sources that I tend to believe:
>
> - Carbureted Cherokees, such as Warriors and Archers, have a "throttle
> pump" which works in a manner somewhat similar to the primer. The
> primer provides better fuel distribution, so it should be used in
> preference to the throttle pump, but one can still pump the throttle
> to get additional fuel into the engine _safely_.
Several years ago I had the carburetor off during an annual. Being the curious
sort, I couldnt refrain from moving all the parts to see what they
did. Unfortunately I was looking right down the barrel when I moved
the throttle arm. I was rewarded for my effort with a face full of
avgas. :-( It seems that we (I) had neglected to empty the gas bowl after
removing the carburetor.
Now, speaking as an expert, those carburetors equiped with an "accelerator"
(throttle) pump will shoot a **powerful** stream of gasoline up into the
intake manifold any time the throttle is advanced (pushed in) from it's present
setting. The problem, which can lead to the carburetor fires, is that when the
engine is not running a lot of that gasoline will fall straight down
again. Some of that gas will pass right through the venturi and end
up as a puddle in the plenum where heated air from the muffler shroud
mixes with filtered outside air.
The plenum usually has a drain whose main purpose is to get rid of
water "ingested" while flying through rain. Much of the gas which
has fallen back down will drain out onto the ground. However enough
remains to creat a significant fire hazard in the event of a backfire
from the engine. Also, the drain from the carburetor probably doesnt
have a hose on it to carry any liquid out of the cowling. Therefore,
the gas which drains from the carburetor may pool in the cowling
before overflowing onto the ground; creating an additional fire
hazard within the cowling.
For the record, my Mooney has a Lycomming O-360-A1D engine with a
Marvel-Shebler (sp?) MA4-5 carburetor.
Claude Goldsmith, CFI-IA <cla...@leadsv.UUCP>
twisted-pair (408) 742-7514 | Opinions expressed are not
on the air - WB6UOO | necessarily those of my
through the air - Mooney N6416U | employer.
Tony Verhulst
>> But, how do you know there IS a fire? Get out and take a
>> look? Hope that someone is lurking around the T-hangars and will alert you?
>
> I've seen one and read about others. Usually you can see smoke;
>fuel-rich fires generate smoke and soot. Engine compartment hoses do
>too. Another sign is noise -- you can sometimes hear the fire burning.
>And yes, sometimes you don't know for sure until you get out and look,
>or until someone starts jumping up and down in front of the airplane,
>or the tower asks that innocuous little question... "Barnburner 321,
>are you experiencing difficulty?" I *hate* it when they ask that. :-)
I rent Warriors at the local FBO. Last January I showed up one chilly
morning at 8am with the thermometer hovering about 0F (-18C). After pre-
heating, the lineman (also a CFI) said "this plane is a pain to start when it's
cold. You handle the starter and I'll handle the prime and throttle". I
said "fine" and we commence to start the airplane. He gives it 8 or 9 primes,
pumps the throttle a few times (I've been told not to do this on down draft
carbs) and I hit the starter. No joy. He's sitting in the right seat with
door open and suddenly he says s**t, bolts out of the airplane and heads
for the hangar. I don't know what happened but it dawns on me that it might
be wise for me to unbuckle and depart the airplane in a similarly hasty
fashion - which I do. That's when I see the smoke. By the time I get the
cowl open, the CFI is back with a fire extinguisher and puts the fire out.
Damage was minimal.
Aircraft carbs have accelerator pumps and each time you move the throttle
forward, you squirt a little fuel into the carb. Squirt too much and the
fuel leaks out of the carb and then all it takes is one backfire.
Take care out there.
Tony V.
Tony Verhulst
>said "fine" and we commence to start the airplane. He gives it 8 or 9 primes,
>pumps the throttle a few times (I've been told not to do this on down draft
>carbs) and I hit the starter.
Oops! Dick Seymour sent me the following mail. I said down draft carbs
but should have said updraft carbs. Thanks for the correction, Dick.
-------------
just one nit to pick(le)
it's UPdraft carbs you shouldn't throttle-prime.
DOWNdraft carbs are on TOP of the engine, and the air passes thru heading
down into the engine. fuel introduced by the accellerator pump will
end up in the cylinders, where it belongs.
UPdraft carbsw (like Cessna 172's have...) are UNDER the engine, and the
air (normally) passes UP thru them into the engine.
but if you pump the throttle without the engine running, the gas squirts
up into the intake manifold, and then falls back down (backwards) thru
the carb into the plenum... or out into the cowl.
just waiting for a little backfire to touch it off...
Jay Maynard
My training here in Houston (where it's big news if the temperature gets below
20 F in the winter, and summer days with highs under 90 F are uncommon) was
to set up the various controls, stick the key in the ignition, pump the
throttle twice, open it the recommended amount, yell "clear prop!!", make sure
nobody's running, and crank it up. The whole procedure from throttle pumping
to cranking takes only a couple of seconds.
As it was explained to me, the accelerator pump does better than the primer
for this purpose in moderate temperatures because the fuel is better vaporized
and therefore easier to light off. The primer, I was told, was for really
recalcitrant cases in very cold weather, since it dumps a stream of raw fuel
straight into the cylinders. I seem to remember a discussion along these lines
in the _Light Plane Maintenance_ book on engine operation, as well.
Now comes this discussion about carburetor fires. Am I really inviting
trouble doing as I was taught? Should I use the primer instead?
--
Jay Maynard, EMT-P, K5ZC, PP-ASEL | Never ascribe to malice that which can
jmay...@thesis1.med.uth.tmc.edu | adequately be explained by stupidity.
"Reality is not binding on news admins." -- Cathy Foulston
Per Lindberg
writes about priming vs pumping the throttle in the hot Texas.
Here in the cold Sweden (close to the North Pole :-) you really must
be careful not to use the throttle (accelerator pump) for priming,
ESPECIALLY IN THE WINTER. Our club's chief mechanic, who is an old man
with lots of experience, has been flaming (pun intended) about this
for years and years. The fuel will not evaporate, but run downwards
out under the plane. You run a high risk getting a nice cozy fire.
Over-priming may also cause a fire in the exhaust system, but that's
another story.
--
Per Lindberg (p...@front.se) ! __!__
Front Capital Systems, Box 5727, ! _____(_)_____ Ceci n'est pas une Piper
11487 Stockholm, Sweden. 8-6611510 ! ! ! !
Steven Philipson
> Also, 14v electrical systems *are* nice. Why did the industry switch?
A given wire can carry more power at the higher voltage, or you can use
a thinner wire to carry the same power at the higher voltage. Either way,
it translates to the same thing -- you'll have to carry less weight in
wire. It's yet another tradeoff -- higher useful load versus higher cost.