Windmilling propellers
Joined: Aug 1998
Aviation Qualifications: ATPL
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From: Ex-pat Aussie in the UK
Originally Posted by johns7022
How about a raise of hands...everyone in here with an MEI that has actually taken up a student, shut down an engine on a muti-engine turbocharged aircraft, feathered a prop, then started it back up....
(my hand is up)
Joined: Nov 2007
Posts: 36
Likes: 2
From: RH base 36R
It shouldn't come as a big surprise that we are not the first to contemplate this matter.
This text, "Gauge Indications on a Failed Engine", Warbird Notes #6 was written by Mr. Randy Sohn in 1994.
I have no way of knowing whether Mr. Sohn is correct in everything he writes, but he does appear to carry a lot more credibility than most if not all of us here: Randy Sohn .
An index to all of his "Warbird Notes" can be found here Warbird Notes INDEX . Highly recommended!
This text, "Gauge Indications on a Failed Engine", Warbird Notes #6 was written by Mr. Randy Sohn in 1994.
I have no way of knowing whether Mr. Sohn is correct in everything he writes, but he does appear to carry a lot more credibility than most if not all of us here: Randy Sohn .
An index to all of his "Warbird Notes" can be found here Warbird Notes INDEX . Highly recommended!
Joined: Apr 2008
Aviation Qualifications: ATPL
Posts: 836
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From: uk
Thank you Moody Blue. At last a reference, as opposed to someone telling us what he thinks will happen.
"Cut a mixture and just leave the throttle alone where it was set at cruise, lets say, for example in this case, 27". If you can visualize a big air pump, that is exactly what the engine is, with the throttle located at the intake. After seeing for yourself that the MP stays unmoving at 27" ....."
"The engine keeps turning and as long as it does the oil pump keeps pumping, right? So the oil pressure stays up and doesn't give you a clue about which one failed. Over the short period we're discussing here the temperature stays up too."
"When we cut the mixture at cruise airspeed the RPM sagged about a hundred and then went right back to where it had been. Let's analyze that for a minute. The engine is still turning so the oil pump is still putting out normal pressure. Where does the prop governor get its supply? That's right, from engine oil pressure. So it keeps doing its thing according to your request through the prop control. You had the control set to cruise RPM so (after a second or two of decrease followed by an immediate increase as the blades assume a new angle) that's what it delivers. It will as long as it has oil pressure and, with this proviso, that the cruise speed stays high enough so that the blades don't reach the pitch stops while trying to maintain the requested RPM."
This all exactly what virgo wanted confirmed, and exactly what a few of us who have actually flown supercharged (NOT turbocharged) multi's have been saying
"Cut a mixture and just leave the throttle alone where it was set at cruise, lets say, for example in this case, 27". If you can visualize a big air pump, that is exactly what the engine is, with the throttle located at the intake. After seeing for yourself that the MP stays unmoving at 27" ....."
"The engine keeps turning and as long as it does the oil pump keeps pumping, right? So the oil pressure stays up and doesn't give you a clue about which one failed. Over the short period we're discussing here the temperature stays up too."
"When we cut the mixture at cruise airspeed the RPM sagged about a hundred and then went right back to where it had been. Let's analyze that for a minute. The engine is still turning so the oil pump is still putting out normal pressure. Where does the prop governor get its supply? That's right, from engine oil pressure. So it keeps doing its thing according to your request through the prop control. You had the control set to cruise RPM so (after a second or two of decrease followed by an immediate increase as the blades assume a new angle) that's what it delivers. It will as long as it has oil pressure and, with this proviso, that the cruise speed stays high enough so that the blades don't reach the pitch stops while trying to maintain the requested RPM."
This all exactly what virgo wanted confirmed, and exactly what a few of us who have actually flown supercharged (NOT turbocharged) multi's have been saying
Joined: Mar 2000
Posts: 8,571
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From: Arizona USA
but he does appear to carry a lot more credibility than most if not all of us here: Randy Sohn .
Perhaps Sohn hasn't flown these types..IE, only concerned himself with 'warbird' types...
Joined: Nov 2007
Posts: 36
Likes: 2
From: RH base 36R
Quote:
but he does appear to carry a lot more credibility than most if not all of us here: Randy Sohn .
but he does appear to carry a lot more credibility than most if not all of us here: Randy Sohn .
I only know the R4360 and R3350 from museums, they certainly are different beasts than the R-1830 (the one radial I know a bit about) so I wouldn't have a clue as to who's "right" here. It could indeed very well be that there's a difference in behaviour between these types of engines, and you are both right... now wouldn't that be nice...
Looks to me like we're not going to get the definitive answer - but the good thing is that we did get to learn something maybe (I sure did)
