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#1
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Avoiding Shock Cooling in Quick Descent
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 |
#2
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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 |
#3
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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 |
#4
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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 |
#5
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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 |
#6
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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 |
#7
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"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) |
#8
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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. |
#9
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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. |
#10
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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. |
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