Shock *Heating*?

: Given that cylinders are 1k each, I'll keep the temps up on decent when
: possible. I mean how hard is it to pull back to 2,000 RPM instead of
: idle??? Yeah, it's probably a waste of gas but I'm burning the cheap
: stuff
: anyway.

: That about sums up my feelings, too.

: We can't prove that it exists, but the very threat of a cracked cylinder
: head due to shock cooling is enough to make us fear it, and fly like it's
: real.

Don't forget another pilot-induced mechanism to lead to rapid cylinder
head cooling: pushing the mxture full rich at the top of descent, while
simultaneously reducing the throttle a modest amount. At this point, the
pilot could probably lean the mixture more, or leave it leaned for cruise,
until time to add power to level out.

--
Aaron Coolidge (N9376J)

For descents, I just pull back my MP about 4" for 500 fpm. Don't touch the
mixture until leveling back off, don't touch the throttle, don't touch the
trim. Most times, this won't register as shock cooling on my JPI, and the
times it does it just over the 50 deg/min alarm limit. This technique keeps
your airspeed constant, and makes for a minimum pilot load, and cools the
cylinders gently. PIC taught me the technique in one of my instrument
refreshers.

Aaron Coolidge wrote:

: Given that cylinders are 1k each, I'll keep the temps up on decent when
: possible. I mean how hard is it to pull back to 2,000 RPM instead of
: idle??? Yeah, it's probably a waste of gas but I'm burning the cheap
: stuff
: anyway.

: That about sums up my feelings, too.

: We can't prove that it exists, but the very threat of a cracked cylinder
: head due to shock cooling is enough to make us fear it, and fly like it's
: real.

Don't forget another pilot-induced mechanism to lead to rapid cylinder
head cooling: pushing the mxture full rich at the top of descent, while
simultaneously reducing the throttle a modest amount. At this point, the
pilot could probably lean the mixture more, or leave it leaned for cruise,
until time to add power to level out.

--
Aaron Coolidge (N9376J)

--
--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

(Malcolm Teas) wrote in message . com...
"Jay Honeck" wrote in message news:QdQZb.376650$na.567800@attbi_s04...
In another thread (about cold starting) it was mentioned that Alaskan bush
pilots routinely drain their oil, take it inside, and heat it on the stove
before starting in the morning.

Getting back to the subject, one might surmise that by
far the worst temperature shock happens to the engine
when the key is turned on.

One should avoid this action.

Bill Hale

On mine, all turning the key does is unground the p-leads on the mags (I need to push the starter button to
get the prop to turn). How does turning the key on induce 'the worst temperature shock'? ;-)

Bill Hale wrote:

(Malcolm Teas) wrote in message . com...
"Jay Honeck" wrote in message news:QdQZb.376650$na.567800@attbi_s04...
In another thread (about cold starting) it was mentioned that Alaskan bush
pilots routinely drain their oil, take it inside, and heat it on the stove
before starting in the morning.

Getting back to the subject, one might surmise that by
far the worst temperature shock happens to the engine
when the key is turned on.

One should avoid this action.

Bill Hale

--
--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

If you don't have a slippery plane why pull the power at all for
descents? In my 182 I close the cowl flaps if they aren't already and
simply roll in two swipes of nose down trim. Leave power as is, which
for me is almost always top if the green throttle and prop or the max it
will give me. Bingo, 500 fpm down. Don't even get into the yellow.



Ray Andraka wrote:
For descents, I just pull back my MP about 4" for 500 fpm. Don't touch the
mixture until leveling back off, don't touch the throttle, don't touch the
trim. Most times, this won't register as shock cooling on my JPI, and the
times it does it just over the 50 deg/min alarm limit. This technique keeps
your airspeed constant, and makes for a minimum pilot load, and cools the
cylinders gently. PIC taught me the technique in one of my instrument
refreshers.

Aaron Coolidge wrote:


: Given that cylinders are 1k each, I'll keep the temps up on decent when
: possible. I mean how hard is it to pull back to 2,000 RPM instead of
: idle??? Yeah, it's probably a waste of gas but I'm burning the cheap
: stuff
: anyway.

: That about sums up my feelings, too.

: We can't prove that it exists, but the very threat of a cracked cylinder
: head due to shock cooling is enough to make us fear it, and fly like it's
: real.

Don't forget another pilot-induced mechanism to lead to rapid cylinder
head cooling: pushing the mxture full rich at the top of descent, while
simultaneously reducing the throttle a modest amount. At this point, the
pilot could probably lean the mixture more, or leave it leaned for cruise,
until time to add power to level out.

--
Aaron Coolidge (N9376J)


--
--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

That is how i used to do it, but the pulling 4" off turns out to be less of a
workload, which makes a difference in IFR conditions especially in the terminal
environment.

The difference is that using power to control the descent, you get a primary
instrument to maintain the descent (MP/RPM), where controlling it with trim you
have to rely on secondary instruments (VSI). Using power to control it, you set
the power to the target setting, wait for the descent to become established, cross
check the rate on the VSI, and then if necessary tweak the power a fraction of an
inch. On mine a 4" reduction gets me a 500 fpm descent regardless of the
configuration (flaps, trim). Once established, maintaining a constant rate
descent is just a matter of moving the throttle to keep the MP pegged (it will
creep up as you descend into denser air). As long as the MP is constant, the rate
of descent is too. Note that the trim sets the airspeed, and in this case you
maintain a constant airspeed throughout the maneuver. Since the power is reduced,
there is no harm in leaving the mixture at the leaned for cruise setting until you
increase power at the end of the descent (in fact it helps to keep the engine
warm). I have only one lever to move throughout my descent, one mixture
adjustment as I level off, and one gauge to look at to immediately see the result
of my moving that lever.

If you use the trim to control your descent, you have no indicator to directly
show the control setting, instead you have to rely on the VSI and the AI for
secondary info. Additionally, you need to adjust the trim as you pick up speed in
the descent to keep the descent rate up. You'll pick up speed both because of the
change in the trim, as well as from the gradual increase in power as you descend
into denser air. Since there is no primary instrument to use in maintaining the
trim, you have to rely on the secondary instruments to adjust the trim based on
the end result. This is a feedback loop and is prone to getting you into a
chasing the needle situation. This method also requires you to monitor and
continuously adjust the mixture because at full power you will need mixture
enrichment as you descend into lower altitudes to keep from running in an
overleaned high power configuration, which is bad for the engine. Also, the
amount of trim required to achieve a given descent rate varies considerably with
airspeed, so you have multiple settings to memorize to fit all the flight
configurations you use. You also need to keep close tabs on the airspeed unless
your airplane is a brick. I have a Cherokee Six, which is by no means a slippery
airplane. Using your technique will put me into the yellow arc in a descent from
cruise, which can be a problem if the air down there is bumpy as it often is.

Newps wrote:

If you don't have a slippery plane why pull the power at all for
descents? In my 182 I close the cowl flaps if they aren't already and
simply roll in two swipes of nose down trim. Leave power as is, which
for me is almost always top if the green throttle and prop or the max it
will give me. Bingo, 500 fpm down. Don't even get into the yellow.

--
--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

"Bill Hale" wrote in message
om...
(Malcolm Teas) wrote in message
. com...
"Jay Honeck" wrote in message
news:QdQZb.376650$na.567800@attbi_s04...
In another thread (about cold starting) it was mentioned that Alaskan
bush
pilots routinely drain their oil, take it inside, and heat it on the
stove
before starting in the morning.

Getting back to the subject, one might surmise that by
far the worst temperature shock happens to the engine
when the key is turned on.

One should avoid this action.

Bill Hale

So if my plane does not have a key the engine will last forever?

Bill Hale wrote:

Getting back to the subject, one might surmise that by
far the worst temperature shock happens to the engine
when the key is turned on.

One should avoid this action.

Wilco. I'm gonna start leaving the ignition on all the time and propping it.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way that
you look forward to the trip.

"Bushy" blathered...

Boyfriend not putting out?

;)

"Ben Jackson" wrote in message
news:Nwt_b.45072$Xp.200197@attbi_s54...
In article eTn_b.385903$na.592869@attbi_s04,
Jay Honeck wrote:

So, I treat my engine like it's made out of glass.

Oh great, now there will be a big flamewar over whether after 100 years
of sitting your glass engine would be thicker on the bottom...

--
Ben Jackson

http://www.ben.com/