Avoiding Shock Cooling in Quick Descent

[O. Sami Saydjari]

My engine operating manual (for my Piper Turbo Arrow III) strongly
discourages pulling the power back and doing a quick descent -- it warns
of engine-killing shock cooling. Sounds reasonable to me...but it (and
my airplane manual) does not really seem to say how best to do a fast
descent when you have to.

I inferred that the right thing to do might be to lower the prop speed
to a minimum and ease back power as slowly as you can. Does that sound
about right? How quickly can one expect to pull the throttle back and
not risk shock cooling? If one must get down (say, for air traffic
control reasons, or perhaps because one is trying to take advantage of
favorable winds as long as possible), what is the best procedure. What
about slipping it down? Does that risk the engine or the airframe at
all? I've never done slips at cruise speeds (just on approach), so
please forgive me if this is a naive question.

-Sami
N2057M
Piper Turbo Arrow III

[Jeff]

I read an article that said that if you dont go below 20' MP pressure you
should be ok.
Personally, I reduce power enough where I can do a 500 fpm decent and stay
under the yellow, usually this puts me at about 140 kts IAS, but only if its
smooth air, if I need to stay below Va or if they are trying to slam dunk me
then I drop the landing gear, that and about 25' MP and 2300 rom will give
you around a 800 fpm decent, sometimes faster if you let it. But I try my
best to only do 500 fpm decents.

I was taught to pull power off at about 1' MP per minute.

BTW how is that new T-arrow of yours doing.

"O. Sami Saydjari" wrote:

> My engine operating manual (for my Piper Turbo Arrow III) strongly
> discourages pulling the power back and doing a quick descent -- it warns
> of engine-killing shock cooling. Sounds reasonable to me...but it (and
> my airplane manual) does not really seem to say how best to do a fast
> descent when you have to.
>
> I inferred that the right thing to do might be to lower the prop speed
> to a minimum and ease back power as slowly as you can. Does that sound
> about right? How quickly can one expect to pull the throttle back and
> not risk shock cooling? If one must get down (say, for air traffic
> control reasons, or perhaps because one is trying to take advantage of
> favorable winds as long as possible), what is the best procedure. What
> about slipping it down? Does that risk the engine or the airframe at
> all? I've never done slips at cruise speeds (just on approach), so
> please forgive me if this is a naive question.
>
> -Sami
> N2057M
> Piper Turbo Arrow III

[Dan Luke]

"O. Sami Saydjari" wrote:
> I inferred that the right thing to do might be to lower the prop speed
> to a minimum and ease back power as slowly as you can. Does that
sound
> about right? How quickly can one expect to pull the throttle back and
> not risk shock cooling? If one must get down (say, for air traffic
> control reasons, or perhaps because one is trying to take advantage of
> favorable winds as long as possible), what is the best procedure.
What
> about slipping it down? Does that risk the engine or the airframe at
> all? I've never done slips at cruise speeds (just on approach), so
> please forgive me if this is a naive question.

What is the V-le for your airplane? If it's high enough, drop the gear
and use them as speed brakes to get down while leaving some power on to
keep the engine warm. Slipping is fine.

There is considerable debate about the danger of shock cooling. Google
these groups or see http://www.avweb.com/news/columns/183094-1.html for
more discussion.
--
Dan
C172RG at BFM
(remove pants to reply by email)

[Thomas Borchert]

O.,

> it warns
> of engine-killing shock cooling. Sounds reasonable to me
>

it does? Hmm. How about shock heating on take-off?

Why not lean to max EGT on descents?

--
Thomas Borchert (EDDH)

[[email protected]]

O. Sami Saydjari > wrote:
: My engine operating manual (for my Piper Turbo Arrow III) strongly
: discourages pulling the power back and doing a quick descent -- it warns
: of engine-killing shock cooling. Sounds reasonable to me...but it (and
: my airplane manual) does not really seem to say how best to do a fast
: descent when you have to.

: I inferred that the right thing to do might be to lower the prop speed
: to a minimum and ease back power as slowly as you can. Does that sound
: about right? How quickly can one expect to pull the throttle back and
: not risk shock cooling?

From all I've read on it, the shock-cooling thing is probably mostly a bunch
of crap. Unless you do radical configuration changes (e.g. 8000' climb at Vy then kill
the engine and glide back down), you probably won't exceed the Lycoming recommended CHT
change rate of 50 degrees per minute. EGT only affects CHT as a secondary effect....
most of the CHT results from the combination of power produced and cooling.
Something akin to (MP x RPM)/IAS.

I pretty much figure from a cruise, you can either point the nose down and
speed up, or reduce the engine power, but shouldn't do a lot of both. For a relatively
rapid cruise descent of 500 fpm, this seems to keep the CHT from moving more than 50
degrees per minute. Either pull 4-5" MP, nose over another 10-20 kt, or maybe a bit of
both (2-3" and 5-10 kt).

The big one (I believe) is keeping the mixture at cruise lean. Since the power
is reduced, you can't hurt the engine with it. Keep cruise lean until it coughs on the
way down, then fatten as necessary.

Now with my flame-suit properly donned, what does everyone else think? :)

-Cory

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

[Tom Sixkiller]

"O. Sami Saydjari" > wrote in message
...
> My engine operating manual (for my Piper Turbo Arrow III) strongly
> discourages pulling the power back and doing a quick descent -- it warns
> of engine-killing shock cooling. Sounds reasonable to me...but it (and
> my airplane manual) does not really seem to say how best to do a fast
> descent when you have to.
>
> I inferred that the right thing to do might be to lower the prop speed
> to a minimum and ease back power as slowly as you can. Does that sound
> about right? How quickly can one expect to pull the throttle back and
> not risk shock cooling? If one must get down (say, for air traffic
> control reasons, or perhaps because one is trying to take advantage of
> favorable winds as long as possible), what is the best procedure. What
> about slipping it down? Does that risk the engine or the airframe at
> all? I've never done slips at cruise speeds (just on approach), so
> please forgive me if this is a naive question.
>
> -Sami
> N2057M
> Piper Turbo Arrow III
>

Pretty much a myth or OWT: http://www.avweb.com/news/columns/182107-1.html

[Paul Tomblin]

In a previous article, said:
>of crap. Unless you do radical configuration changes (e.g. 8000' climb
>at Vy then kill
>the engine and glide back down), you probably won't exceed the Lycoming

Glider tows and jumper planes do that all day every day, and they don't
seem to get shortened TBO out of it.


--
"The magic of usenet has never been its technology; and, only in part, its
reach. Its magic -- its power -- is based on the very real human connections
that form 'round its threads of conversation... the relationships that are
kindled, flamed and, on occasion, extinguished and mourned." -deCadmus

[Jeff]

Dale
does your decent method work well for not shock cooling the engine?

Dale wrote:

> In article >,
>
> >
>
> I fly turbo-charged 206 hauling skydivers so I make lots of descents.
> The drill we use is to reach jump altitude at least a minute before the
> jumpers exit to give us time to ease the power back and start cooling
> the engine. We're at 13000 and pulling 30 inches with 2600RPM. I
> reduce MAP to 27 inches (about 1" every 20-30 seconds or so), then
> slowly reduce RPM (which will also cause a reduction in MP) until
> getting 2100 RPM set. Then it's a further throttle reduction to 17-18"
> MP where I lean for 6-8 GPH (setting up for the descent). If I timed it
> right it's time to open the door, reduce power to 10-11" MP and lets the
> folks out..as soon as they're gone close the door, power back up to 18"
> and maintain the 18" throughout the descent, monitoring fuel-flow to
> keep EGT up while maintaining top of the green or even into the yellow.
> This gives descent rates of 2500-3500fpm...sometimes a little more if
> you want to work at it.
>
> We've been flying the turbo 206 a couple of years now with no engine
> problems...our other 206 has been operated for about 6000 hours as a
> jump plane and the engine goes to TBO or beyond.
>
> Your idea of reducing RPM is the way to go if you need a rapid descent.
> It allows you to keep the engine working to maintain some heat. Your
> descents will be made from cruise flight and the engine will not be as
> hot as after just making a best rate climb to 13K so there will be less
> change in engine temp during the descent. For a cruise descent I'd just
> push the nose over for the descent needed and reduce power to maintain a
> safe airspeed. ALL power changes should be made smoothly.
>
> Thermal cycles are certainly stressful for an engine but frankly, IMO
> shock-cooling is BS. Much more damage is done by not allowing the
> engine to come up to temp before applying power.....thermal stress
> happens both ways. <G>
>
> --
> Dale L. Falk
>
> There is nothing - absolutely nothing - half so much worth doing
> as simply messing around with airplanes.
>
> http://home.gci.net/~sncdfalk/flying.html

[Dale]

In article >,
Jeff > wrote:

> Dale
> does your decent method work well for not shock cooling the engine?
>

<G> Uh, yeah. That's why we get TBO or better. Of course I guess it
depends on your definition of shock-cooling.

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

[Dale]

In article >,
wrote:


> Unless you do radical configuration changes (e.g. 8000' climb at Vy
> then kill
> the engine and glide back down), you probably won't exceed the Lycoming
> recommended CHT
> change rate of 50 degrees per minute.

Not true. On my 182 I had an engine monitor that alerted for shock
cooling (50 degrees/minute). At the end of a climb to 10K I could get a
"shock cooling" warning by simply pushing the nose over to accelerate
from the 80IAS climb without making ANY power reduction.

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

[O. Sami Saydjari]

VLE is 129 KIAS...Cruise is around 140-150 KIAS. To avoid stess, I
would probably not drop gear until I was about 115 KIAS. Still, it is a
good suggestion once I slow to that speed. Thanks.

Sami

Dan Luke wrote:
> "O. Sami Saydjari" wrote:
>
>>I inferred that the right thing to do might be to lower the prop speed
>>to a minimum and ease back power as slowly as you can. Does that
>
> sound
>
>>about right? How quickly can one expect to pull the throttle back and
>>not risk shock cooling? If one must get down (say, for air traffic
>>control reasons, or perhaps because one is trying to take advantage of
>>favorable winds as long as possible), what is the best procedure.
>
> What
>
>>about slipping it down? Does that risk the engine or the airframe at
>>all? I've never done slips at cruise speeds (just on approach), so
>>please forgive me if this is a naive question.
>
>
> What is the V-le for your airplane? If it's high enough, drop the gear
> and use them as speed brakes to get down while leaving some power on to
> keep the engine warm. Slipping is fine.
>
> There is considerable debate about the danger of shock cooling. Google
> these groups or see http://www.avweb.com/news/columns/183094-1.html for
> more discussion.

[O. Sami Saydjari]

>
> BTW how is that new T-arrow of yours doing.
>

Still undergoing an avionics upgrade (Garmin 430, GDL 49 weather uplink,
and GTX 330 transponder with TIS....pretty cool). Will be ready Friday
(I can't wait!!!). Flying it home 12 January (Reno to Central
Wisconsin)...Wish for good weather! If I end up taking a southerly
route, I will wave as I pass overhead :)

-Sami
N2057M

[Jeff]

one other thing, dont lean the engine on take off or during climb.
Wait untill your at your cruise altitude to do any leaning.
and make sure you get the new power settings, the book settings no longer
apply since that intercooler was installed. If you fly it at book settings,
you will be running at a higher power setting and will burn up cylinders.


"O. Sami Saydjari" wrote:

> >
> > BTW how is that new T-arrow of yours doing.
> >
>
> Still undergoing an avionics upgrade (Garmin 430, GDL 49 weather uplink,
> and GTX 330 transponder with TIS....pretty cool). Will be ready Friday
> (I can't wait!!!). Flying it home 12 January (Reno to Central
> Wisconsin)...Wish for good weather! If I end up taking a southerly
> route, I will wave as I pass overhead :)
>
> -Sami
> N2057M

[Jeff]

if you wait till you slow down to 115 to drop the gear, you better start way
way the heck out, its hard to get it slowed down that much with the gear up.
Especially if your up high.

If your to fast, the gear wont come down, your red unsafe light will come on.

once I hit 129 kts I pop the gear .. then you turn into a rock.

"O. Sami Saydjari" wrote:

> VLE is 129 KIAS...Cruise is around 140-150 KIAS. To avoid stess, I
> would probably not drop gear until I was about 115 KIAS. Still, it is a
> good suggestion once I slow to that speed. Thanks.
>
> Sami
>
> Dan Luke wrote:
> > "O. Sami Saydjari" wrote:
> >
> >>I inferred that the right thing to do might be to lower the prop speed
> >>to a minimum and ease back power as slowly as you can. Does that
> >
> > sound
> >
> >>about right? How quickly can one expect to pull the throttle back and
> >>not risk shock cooling? If one must get down (say, for air traffic
> >>control reasons, or perhaps because one is trying to take advantage of
> >>favorable winds as long as possible), what is the best procedure.
> >
> > What
> >
> >>about slipping it down? Does that risk the engine or the airframe at
> >>all? I've never done slips at cruise speeds (just on approach), so
> >>please forgive me if this is a naive question.
> >
> >
> > What is the V-le for your airplane? If it's high enough, drop the gear
> > and use them as speed brakes to get down while leaving some power on to
> > keep the engine warm. Slipping is fine.
> >
> > There is considerable debate about the danger of shock cooling. Google
> > these groups or see http://www.avweb.com/news/columns/183094-1.html for
> > more discussion.

[Jeff]

Hey Sami
I dont know how your door seals are, but there are some new ones out that
people said are really good. I got them for my plane and its in the shop
today being installed. their website is
http://www.aircraftdoorseals.com/

If your interested in them.

[O. Sami Saydjari]

I read somewhere recently that making a habit of doing things like
dropping gear and flaps right at the edge of the allowed speed puts too
much stress on them...so I was trying to be conservative. Since this is
probably not a typical maneuver, I guess it makes sense to drop it right
at 129.

-Sami

Jeff wrote:
> if you wait till you slow down to 115 to drop the gear, you better start way
> way the heck out, its hard to get it slowed down that much with the gear up.
> Especially if your up high.
>
> If your to fast, the gear wont come down, your red unsafe light will come on.
>
> once I hit 129 kts I pop the gear .. then you turn into a rock.
>
> "O. Sami Saydjari" wrote:
>
>
>>VLE is 129 KIAS...Cruise is around 140-150 KIAS. To avoid stess, I
>>would probably not drop gear until I was about 115 KIAS. Still, it is a
>>good suggestion once I slow to that speed. Thanks.
>>
>>Sami
>>
>>Dan Luke wrote:
>>
>>>"O. Sami Saydjari" wrote:
>>>
>>>
>>>>I inferred that the right thing to do might be to lower the prop speed
>>>>to a minimum and ease back power as slowly as you can. Does that
>>>
>>>sound
>>>
>>>
>>>>about right? How quickly can one expect to pull the throttle back and
>>>>not risk shock cooling? If one must get down (say, for air traffic
>>>>control reasons, or perhaps because one is trying to take advantage of
>>>>favorable winds as long as possible), what is the best procedure.
>>>
>>>What
>>>
>>>
>>>>about slipping it down? Does that risk the engine or the airframe at
>>>>all? I've never done slips at cruise speeds (just on approach), so
>>>>please forgive me if this is a naive question.
>>>
>>>
>>>What is the V-le for your airplane? If it's high enough, drop the gear
>>>and use them as speed brakes to get down while leaving some power on to
>>>keep the engine warm. Slipping is fine.
>>>
>>>There is considerable debate about the danger of shock cooling. Google
>>>these groups or see http://www.avweb.com/news/columns/183094-1.html for
>>>more discussion.
>>
>

[Jeff]

once the gear comes down, your going to slow down in a few seconds. your also going
to start decending so you need to trim the airplane to how fast your wanting to
decend. If you have taken to much power off to slow down to gear speed then you
will need to be ready to add power once it comes down also.

You will get the hang of it after a few times.
BTW I also keep the auto extend off, most people I have talked to if theirs hasnt
been disabled, put it on manual so you can get the gear up at a slower speed on
take off and it dont fall out if you slow down to much. You will want to ask if
your auto extend has been disabled or if it still works, There is a service
bulletin on it I think.


"O. Sami Saydjari" wrote:

> I read somewhere recently that making a habit of doing things like
> dropping gear and flaps right at the edge of the allowed speed puts too
> much stress on them...so I was trying to be conservative. Since this is
> probably not a typical maneuver, I guess it makes sense to drop it right
> at 129.
>
> -Sami
>
> Jeff wrote:
> > if you wait till you slow down to 115 to drop the gear, you better start way
> > way the heck out, its hard to get it slowed down that much with the gear up.
> > Especially if your up high.
> >
> > If your to fast, the gear wont come down, your red unsafe light will come on.
> >
> > once I hit 129 kts I pop the gear .. then you turn into a rock.
> >
> > "O. Sami Saydjari" wrote:
> >
> >
> >>VLE is 129 KIAS...Cruise is around 140-150 KIAS. To avoid stess, I
> >>would probably not drop gear until I was about 115 KIAS. Still, it is a
> >>good suggestion once I slow to that speed. Thanks.
> >>
> >>Sami
> >>
> >>Dan Luke wrote:
> >>
> >>>"O. Sami Saydjari" wrote:
> >>>
> >>>
> >>>>I inferred that the right thing to do might be to lower the prop speed
> >>>>to a minimum and ease back power as slowly as you can. Does that
> >>>
> >>>sound
> >>>
> >>>
> >>>>about right? How quickly can one expect to pull the throttle back and
> >>>>not risk shock cooling? If one must get down (say, for air traffic
> >>>>control reasons, or perhaps because one is trying to take advantage of
> >>>>favorable winds as long as possible), what is the best procedure.
> >>>
> >>>What
> >>>
> >>>
> >>>>about slipping it down? Does that risk the engine or the airframe at
> >>>>all? I've never done slips at cruise speeds (just on approach), so
> >>>>please forgive me if this is a naive question.
> >>>
> >>>
> >>>What is the V-le for your airplane? If it's high enough, drop the gear
> >>>and use them as speed brakes to get down while leaving some power on to
> >>>keep the engine warm. Slipping is fine.
> >>>
> >>>There is considerable debate about the danger of shock cooling. Google
> >>>these groups or see http://www.avweb.com/news/columns/183094-1.html for
> >>>more discussion.
> >>
> >

[Mike Rapoport]

Is it at Aviation Classics?

Mike
MU-2


"O. Sami Saydjari" > wrote in message
...
>
>
> >
> > BTW how is that new T-arrow of yours doing.
> >
>
> Still undergoing an avionics upgrade (Garmin 430, GDL 49 weather uplink,
> and GTX 330 transponder with TIS....pretty cool). Will be ready Friday
> (I can't wait!!!). Flying it home 12 January (Reno to Central
> Wisconsin)...Wish for good weather! If I end up taking a southerly
> route, I will wave as I pass overhead :)
>
> -Sami
> N2057M
>

[O. Sami Saydjari]

Yes, as a matter of fact it is. Do you want to stop by and check on it
for me? :) Just don't bug them...its a big job and they are trying to
get it done by Thursday night so they can do a certifying flight on
Friday :)

-Sami

Mike Rapoport wrote:
> Is it at Aviation Classics?
>
> Mike
> MU-2
>
>
> "O. Sami Saydjari" > wrote in message
> ...
>
>>
>>>BTW how is that new T-arrow of yours doing.
>>>
>>
>>Still undergoing an avionics upgrade (Garmin 430, GDL 49 weather uplink,
>>and GTX 330 transponder with TIS....pretty cool). Will be ready Friday
>>(I can't wait!!!). Flying it home 12 January (Reno to Central
>>Wisconsin)...Wish for good weather! If I end up taking a southerly
>>route, I will wave as I pass overhead :)
>>
>>-Sami
>>N2057M
>>
>
>
>

[O. Sami Saydjari]

Dan, Thanks for the pointer. Even more appropriate, since we are
talking about a Turbo aircraft, is the AVWeb article.
http://www.avweb.com/cgi-bin/udt/im.display.printable?client.id=avweb&story.id=182107

Very interesting article. One interesting thing about it is that the
guy actually presents hard data to back up his claims (at least for his
aircraft).

-Sami

Dan Luke wrote:
> "O. Sami Saydjari" wrote:
>
>>I inferred that the right thing to do might be to lower the prop speed
>>to a minimum and ease back power as slowly as you can. Does that
>
> sound
>
>>about right? How quickly can one expect to pull the throttle back and
>>not risk shock cooling? If one must get down (say, for air traffic
>>control reasons, or perhaps because one is trying to take advantage of
>>favorable winds as long as possible), what is the best procedure.
>
> What
>
>>about slipping it down? Does that risk the engine or the airframe at
>>all? I've never done slips at cruise speeds (just on approach), so
>>please forgive me if this is a naive question.
>
>
> What is the V-le for your airplane? If it's high enough, drop the gear
> and use them as speed brakes to get down while leaving some power on to
> keep the engine warm. Slipping is fine.
>
> There is considerable debate about the danger of shock cooling. Google
> these groups or see http://www.avweb.com/news/columns/183094-1.html for
> more discussion.

[Thomas Borchert]

O.,

all the engine management columns by John Deakin are a must read. There
are many more at Avweb.

--
Thomas Borchert (EDDH)

[O. Sami Saydjari]

Thomas,

Thanks for the pointers. The articles are indeed quite good, but there
is something I do not understand. It seems the whole theory on LOP
operation is conditioned on having GAMI injectors, because the article
implies that you can not do LOP operations on "normal" engines because
of uneven fuel distribution causes roughness due to different cylinders
outputing different powers when you start leaning past peak. Am I
missing something here? What percentage of planes actually have GAMI
injectors?

-Sami

Thomas Borchert wrote:
> O.,
>
> all the engine management columns by John Deakin are a must read. There
> are many more at Avweb.
>

[john smith]

"O. Sami Saydjari" wrote:
> Thanks for the pointers. The articles are indeed quite good, but there
> is something I do not understand. It seems the whole theory on LOP
> operation is conditioned on having GAMI injectors, because the article
> implies that you can not do LOP operations on "normal" engines because
> of uneven fuel distribution causes roughness due to different cylinders
> outputing different powers when you start leaning past peak. Am I
> missing something here? What percentage of planes actually have GAMI
> injectors?

The 1997 Cessna 182S that is new to the club I am in flies LOP quite
easily. To the best of my knowledge, this is a stock engine (not GAMI
equipped). It is only advantagous to fly this way if you are flying LONG
legs. The corresponding drop in cruise airspeed is not suited to short,
fast trips.

[Tom Sixkiller]

"O. Sami Saydjari" > wrote in message
...
> Thomas,
>
> Thanks for the pointers. The articles are indeed quite good, but there
> is something I do not understand. It seems the whole theory on LOP
> operation is conditioned on having GAMI injectors, because the article
> implies that you can not do LOP operations on "normal" engines because
> of uneven fuel distribution causes roughness due to different cylinders
> outputing different powers when you start leaning past peak. Am I
> missing something here?

No, you're not. You're seeing a good example of just how sloppy the typical
FI systems are.

> What percentage of planes actually have GAMI
> injectors?

GAMI has sold about 7,000 sets of their GAMIjectors, so figure that against
the entire fleet of FI engines; probably 5%. They cost less than $1000 a
set, but most pilots will spend much more for other toys, never realizing
the fuel cost savings they're missing and the damage they do to their
engines (note how many planes need a top overhaul well before TBO).

http://www.gami.com/gamijectors_order_form.html

I'll be buying an F33A in the next few weeks, and damn sure it will have
GAMI's installed before it goes anywhere.

http://www.gami.com/gamibrochure.html

(Also, I'm itching for a PRISM ignition system.)

http://www.gami.com/prism.html

HTH!!

[Victor J. Osborne, Jr.]

I agree. I had GAMI's on N100DA (IO-520-B) and now TCM's (so-called)
equivalents on an IO-550 and the CHT's are way out of line.

I'm looking at getting GAMI's when the time is right.

--

Thx, {|;-)

Victor J. (Jim) Osborne, Jr.



take off my shoes to reply

[Ray Andraka]

Yeah, too bad they can't do something similar for carbureted engines....

"Victor J. Osborne, Jr." wrote:

> I agree. I had GAMI's on N100DA (IO-520-B) and now TCM's (so-called)
> equivalents on an IO-550 and the CHT's are way out of line.
>
> I'm looking at getting GAMI's when the time is right.
>
> --
>
> Thx, {|;-)
>
> Victor J. (Jim) Osborne, Jr.
>
>
>
> take off my shoes to reply

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759

[Tom Sixkiller]

"Victor J. Osborne, Jr." > wrote in message
...
> I agree. I had GAMI's on N100DA (IO-520-B) and now TCM's (so-called)
> equivalents on an IO-550 and the CHT's are way out of line.
>
> I'm looking at getting GAMI's when the time is right.
>

What time would that be?

Not only is the fuel use better, but there is virtually NO vibration since
the engine runs much more smoothly.

[James M. Knox]

"O. Sami Saydjari" > wrote in news:100jq2b8dks3j44
@corp.supernews.com:

> Thanks for the pointers. The articles are indeed quite good, but there
> is something I do not understand. It seems the whole theory on LOP
> operation is conditioned on having GAMI injectors, because the article
> implies that you can not do LOP operations on "normal" engines because
> of uneven fuel distribution causes roughness due to different cylinders
> outputing different powers when you start leaning past peak. Am I
> missing something here?

Not a lot. The article is not restricted to planes with GAMIjectors, but
it *is* relevant to engines that can operate with acceptable smoothness
LOP. That rules out most every carb'd engine (although sometimes you get
lucky), and most every big-bore TCM engine. Smaller engines and Lycoming
engines are a "sometimes can and sometimes can't" proposition.

Try it at 65% power and see what happens, especially if you have all-cyl.
monitoring. [I did once have an O-320 engine that would run absolutely
smooth all the way to idle-cutoff. Just a fluke.]



-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

[[email protected]]

James M. Knox > wrote:
: Not a lot. The article is not restricted to planes with GAMIjectors, but
: it *is* relevant to engines that can operate with acceptable smoothness
: LOP. That rules out most every carb'd engine (although sometimes you get
: lucky), and most every big-bore TCM engine. Smaller engines and Lycoming
: engines are a "sometimes can and sometimes can't" proposition.

: Try it at 65% power and see what happens, especially if you have all-cyl.
: monitoring. [I did once have an O-320 engine that would run absolutely
: smooth all the way to idle-cutoff. Just a fluke.]


I pretty much run my Lycoming O-360 as lean as I can get it with
at most just a slight hint of roughness. This typically amounts to
slightly lean of peak for a couple cylinders, and at peak for others.
Since Lycoming calls that "economy mode" and is acceptable for 75% power
cruise or less, I cruise at 65% max power for a margin. Watching CHT
on the hottest (#3), the spark plug probe stays at 400 or less, which is
actually more like 340 or less (on a bayonet probe). I figure that's
probably as aggressive as you can get with a normal carb'd engine. The
big thing I came away with from all the reading is if you lean
agressively, you need to know what power you're running at. Basically,
you can do anything you want with the red knob at 65% or below, provided
the CHT's are acceptable.

FWIW
-Cory

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

[Victor J. Osborne, Jr.]

I fly a lot and with a vacation in May for a few weeks. That's the right
time.

Thx, {|;-)

Victor J. (Jim) Osborne, Jr.

[Tom Sixkiller]

"Victor J. Osborne, Jr." > wrote in message
...
> I fly a lot and with a vacation in May for a few weeks. That's the right
> time.
>
> Thx, {|;-)
>
> Victor J. (Jim) Osborne, Jr.
Just be aware that GAMI's are not really something you can just stick on
the engine and go; it'll take a while to "re-learn" the leaning process and
to determine the power curves for _your_ engine.

[J]

On Mon, 19 Jan 2004 10:39:29 -0700, Tom Sixkiller wrote:

>
> "Victor J. Osborne, Jr." > wrote in message
> ...
>> I fly a lot and with a vacation in May for a few weeks. That's the right
>> time.
>>
>> Thx, {|;-)
>>
>> Victor J. (Jim) Osborne, Jr.
> Just be aware that GAMI's are not really something you can just stick on
> the engine and go; it'll take a while to "re-learn" the leaning process and
> to determine the power curves for _your_ engine.

Also, you want to have an engine analyzer. If you do you can do the lean
test described on the GAMI site. Then send the results to GAMI. They
will use the data to tweak the injectors for your particular engine. I did
this 3 times and the spread between peaks is now very small.

jerry

[Victor J. Osborne, Jr.]

I'm aware of the flying and analyzer requirements as I had GAMI's on another
plane. I have the JPI analyzer with data record.

--

Thx, {|;-)

Victor J. (Jim) Osborne, Jr.



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