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#41
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: 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) |
#42
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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 http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759 |
#43
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#44
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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 http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759 |
#45
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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 http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759 |
#46
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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 http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759 |
#47
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"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? |
#48
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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. |
#49
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"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/ |
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