Engine RPM's vs. manifold pressure

tgrayson said:
For what it's worth, Deakin, et al, think this recommendation is way too conservative.
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True, but even if it is conservative, I think it is a good starting point. Start with 50 degrees per minute and build a pilots knowledge from there.
 
Shock cooling isn't a myth, I personally know people who have pulled the power back to idle when it 25 below zero and had it crack a jug. However, 95% of the time, it should be no factor whatsoever.
 
ppragman said:
Shock cooling isn't a myth, I personally know people who have pulled the power back to idle when it 25 below zero and had it crack a jug. However, 95% of the time, it should be no factor whatsoever.
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Yeah, but you are also in Alaska!:D:D
 
ppragman said:
Oversquare is a myth too. Although running the motor at 27" x 2100RPM might not be the best thing to do.
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What's wrong with 27"/2100???

Oh...

Wait...

Were we talking radials or flat engines??:D



Used to open up the Commander to full throttle and leave it until we pulled the power back for either a low cruise (below 8000) or descent.
 
A myth that just won't die... in spite of one of the best teaching otherwise.
"Charles Lindbergh was given permission by Colonel Robert Morrissey to travel to Nadzah, New Guinea, and become familiar with the P-38. On the 15th of June, 1944 Lindbergh arrived and was soon spending time behind a P-38. He flew on combat missions as an observer, and quickly calculated that the combat radius could be extended by 30%. A standard technique at the time was cruising at 2200 - 2400 rpm's in auto-rich at low manifold pressure. Lindbergh called for only 1600 rpm in an auto-lean mixture with a high manifold pressure. This reduced fuel consumption to 70 U.S. gallons (265 liters) per hour, and resulted in a cruising speed of 185 mph (298 km/h). By comparison in July 1944, P-38s would fly a five-hour mission and come back on fumes, but after taking Lindbergh's advice they completed long missions with fuel to spare."​
 
tgrayson said:
I don't think he said "shock cooling" is a myth, it's just not as big a deal as many people think. You really have to work to damage the engine in this way. Even an iconoclast like Deakin doesn't think shock cooling is a total myth.
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For every person that says they damaged their engine from shock cooling there is another person that, according to person 1, abuses their engine and nothing bad happens.

I'm not saying you should take your turbocharged continental and run it at full throttle for an hour and then realize you waited too long to descend and pull it back to idle and then pull up to your parking spot and shut down, because that actually is engine abuse, but I know people who stick to the 1" per minute rule like glue... which presumably means they can't make flights shorter than 20 minutes ;)

Oh yeah, and they still have cylinder problems because Continentals suck ;)
 
trafficinsight said:
For every person that says they damaged their engine from shock cooling there is another person that, according to person 1, abuses their engine and nothing bad happens.
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Yes, anecdotal evidence isn't that useful. It's sorta like when people don't want to wear seatbelts, they tell you stories of someone who was thrown clear of an exploding car and survived due to not wearing a seatbelt.

More than likely "abusing" your engine, whatever that means, increases the likelihood of engine damage, but never makes it certain, because it depends on other unknown variables as well.

We just don't have enough statistically significant data on the subject to draw firm conclusions.
 
tgrayson said:
Yes, anecdotal evidence isn't that useful. It's sorta like when people don't want to wear seatbelts, they tell you stories of someone who was thrown clear of an exploding car and survived due to not wearing a seatbelt.

More than likely "abusing" your engine, whatever that means, increases the likelihood of engine damage, but never makes it certain, because it depends on other unknown variables as well.

We just don't have enough statistically significant data on the subject to draw firm conclusions.
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I disagree, lycoming and continental have been doing studies for years, if only we could get a hold of their information.
 
I think a much better question is why there aren't more modern powerplants (outside of the turbine world) powering modern GA aircraft.
 
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