David Staten wrote:
Would you mind providing the documentation that backs up that claim
of warranty denial? How would they KNOW if you ran rich (or lean)
of peak? Especially if from a scientificly proven standpoint that
Rich of Peak is actually hotter/harder on the engine?
Dave
I don't have it. It was told to me by a Lycoming rep at Reno.
Of course they would not know if it was something other than a
burned exhaust valve or melted cylinder head.
By definition "peak EGT" is the hottest EGT. How can anything be
hotter than the hottest? This is not opinion. This is fact.
Rich of peak EGT cools the engine and lean of peak EGT cools the
engine as well. There is no doubt what so ever that the hottest EGT
is harder on the exhaust valves and the aluminum cylinder heads.
This too is fact and not opinion.
Paul Lamar
Matt Prather wrote:
Hi Paul,
How are you doing these days??
I think John Deakin and George Braly demonstrate that the operating
mixture that Lycoming recommends (25-75 deg ROP) is hotter for the
engine than a 100deg LOP operating point which is possible on many
properly injected Lyc or Cont. If the mixture distribution in a Lyc
or Cont is good enough that all of the cyls reach Peak EGT at the same
mixture setting, operating LOP is a very viable alternative. Just
don't run it within that hottest window, beit ROP or LOP (like you
said).
Regards,
Matt-
VE N34RD, C150 N714BK
I am doing fine. Thanks for asking.
I think that is quite possible. I also think what Lycoming has in mind
is if you are at cruising altitude and you are leaned 100 degrees LOP
when you descend and forget to richen the mixture the engine will go to
Uh... Actually, the mixture will get even leaner as you descend. You have
to move the mixture control leaner and leaner the higher you go to keep
stoichiometry. That means, as you climb, the unadjusted mixture would get
richer with increased altitude, leaner as you descend. The risk is the
engine
might just up and quit as you descend. I've nearly had this happen in my
VariEze - lean agreesively at 10500 - the control is almost at the idle
cutoff,
start a descent and the engine starts to run very badly by the time I am down
to 8500. If you started a climb, the EGT would creep toward peak for the
altitude that you are at. If you are above 8500MSL, it's not really too
much of
a concern because you can't generate all that much heat below 75% power.
Most airplanes require nearly full rich to get to peak EGT at sea level.
If you
start a descent from 8500MSL when leaned to 100ROP, as you descend, the
mixture is going to get leaner, and the engine is going to make more power -
probably requiring a power setting reduction.
peak EGT and burn the valves or ruin the head. One must always think out
of the box and take every possible scenario into consideration. We as
engineers still screw up because there is always someone out there that
will do something you never expected them to do knowing what you know.
In other words the correct operations you take for granted.
Agreed..
If it is always on the rich side it will just get richer when you
descend. All you need do is screw up once and you are out a couple of
thousand dollars the next time the annual comes around more than making
up for the few gallons you saved by running LOP.
I agree here, though not with the descent condition.
Fortunately we don't have to worry about that. The rotary does not care
what the mixture is because it has no exhaust valves and the rotor
housing won't melt unless you are running an electric water pump :)
Yep.
BTW I was flying with a group of people in C172s around Australia. The
so-called leader (Lang Kidby I think) of the group was buying the gas.
He ragged me all the time about burning more gas than everyone else. I
was aware of Lycoming cautions and I do forget to check the mixture
when I descend every now and then. I was running rich of peak. I would
rather not have the engine drop a valve over the outback. That probably
makes me a bad pilot. Well I got even with him. I made an unscheduled
stop and put 10 gallons extra in the tank on my own nickel without
telling him. You should have seen his face the next time he filled up
the C172 I was flying :)
Hahaha!! That was probably pretty funny.. :) I haven't played that
trick on
anyone, but just the other day my buddy was telling about something very
similar. A friend of his had recently bought a new pickup and drove it to
work every day. My buddy started pouring a gallon of gas in the tank each
day without his friend's knowledge. After doing this for a month, my buddy
stopped the contributions. His friend took was very disappointed with the
change in fuel economy and finally took the truck back to the dealer to have
it 'fixed'.
Regards,
Matt-
VE N34RD, C150 N714BK
Scenario: Pilot forgets to change the mixture.
Start Operation. Power ...... Fuel Air...... Mixture .. EGT
---------------------------------------------------------------
LOP ..climb .... Reducing ....Same decreasing leaner lower
LOP ..descend .. Increasing ..Same increasing richer higher
ROP ..climb .... Reducing ....Same decreasing leaner maybe the same due to reduced power.
ROP ..descend .. increasing ..Same increasing Richer lower
The combination of increased power with richer mixture and higher EGT
while descending is the valve killer while operating lean of peak.
Paul Lamar
I am sorry for beating this dead horse further, but I must disagree.. Still.. The first line of your
chart shows decreasing air associated with climbing, leading to leaner mixture. By definition,
decreasing air means richer mixture. Right? Am I smoking crack?
Regards,
Matt-
You are right Matt. Sorry made a mistake.
This chart is still a work in progress.
Start Operation. Power ...... Fuel Air...... Mixture .. EGT
---------------------------------------------------------------
LOP ..climb .... full ........Same decreasing richer higher
LOP ..descend .. reduced .....Same increasing leaner lower load on engine decreasing
ROP ..climb .... full ... ....Same decreasing richer lower
ROP ..descend .. reduced .. ..Same increasing leaner higher load on engine decreasing
The combination of increased power with richer mixture and higher EGT
while climbing is the valve killer while operating lean of peak.
I would like to make a further point now that I am thinking about it again.
We are trained to richen the mixture when we climb. If you start LOP
and go to rich you may increase the EGT. As you can see starting
with LOP peak is opposite to what we are taught.
There are some secondary effects here.
Pull back the throttle when descending.
Keep the throttle the same.
Increase the prop pitch when descending.
Leave the prop pitch the same.
Decrease the prop pitch.
Perhaps a few others. My point is one must fly all these scenarios
to see what happens to the EGT. A computer controlling the mixture based
on the EGT is the answer.
We in the rotary world don't need.
Paul Lamar
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