Feathering Single Engine
- Thread starter JC150
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I don't know if it stretched my glide but the other reason to go to high pitch (low rpm) on engine failure is if that thing is rattling you to death like mine was, slowing it down helps a lot.
Sac Arrow
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Snorting his way across the USA
There has been a similar discussion a while back. In any case, if you are able to stop the prop, there is less drag than there would be with a windmilling prop.
RV10flyer
Pattern Altitude
The prop driving the engine at low rpm/low mp is okay.
What you do not want is high rpm/low mp, as in a steep descent using your prop drag to reduce speed.
Another thing you can do in an actual emergency engine-out once finished all troubleshooting with no restart, is to open thethrottle. Of course fuel and ignition will be off. Now your pistons are not pulling as much of a vacuum on the intake stroke.
MauleSkinner
Touchdown! Greaser!
Engines quit on good airplanes, too...Id say 5 of mine weren't in "iffy" airplanes.
RV10flyer
Pattern Altitude
I have to slow to nearly full flaps stall speed 54 kias to stop the prop, 95 kias to get it going again. In an emergency engine out from very high altitude, I may do that. Down low, I will leave it windmilling, as I sink like a rock behind the power curve.
James331
Ejection Handle Pulled
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James331
You're taking turbine.
A piston will go full flat pitch when it looses its oil pressure.
But yeah, if you can, it will make a difference.
Here's a bit of a primer on props and governors.
http://www.mccauley.textron.com/pga_governors.html
http://www.mccauley.textron.com/pga_governors.html
I've always practiced emergency descents with high rpm and low mp. Why isn't this good? I always thought the MP should be lower than the RPM.
RV10flyer
Pattern Altitude
Yes. Drag is less for the two blades stopped in fine pitch, than it is with them turning in coarse or fine pitch.
Ring flutter, broken rings. With the throttle closed and the piston moving swiftly up and down, the cylinder pressure goes negative on the intake stroke.
Fearless Tower
Touchdown! Greaser!
It isn't so much the spring as much as the fact that because the prop will never fully feather, it will start to windmill again as soon as you lower the nose and pick up speed.
brcase
En-Route
This is a myth in every plane I have tried it in. It turns out pulling the power back to idle in most small single engine airplane does a very good job of simulating a windmilling propeller.
Also if the engine is windmilling and there are no other mechanical problems to cause loss of oil pressure you will have enough pressure to actuate the prop. In fact some planes (Bellanca Viking) recommend pulling the prop back as part of the engine out procedure, and it helps reduce the descent rate a lot.
Brian CFIIG/ASEL
So, what is the safest way to practice emergency descents or simulated engine failures? Idle MP and low rpm? Wouldn't the high rpm help you get down quicker for the emergency descent?
S Joslin
Pre-takeoff checklist
Maybe...he's the perfect person to take advice from since he's been thru seven engine failures and is here to talk about it. Just sayin'...
roncachamp
Final Approach
Only if he's to be held up as a bad example.
RV10flyer
Pattern Altitude
During practice or simulated, take care of the engine...Idle/low rpm.
If I had an engine fire, then I would use high rpm and get on the ground as quickly as possible.
Thanks for that! Learned something new. I will do that from now on. For some reason I thought using a low rpm with the engine idling was bad for it.
Out of curiosity, this is unrelated but you seem to know a lot about engines, if you had the option of cruising at 2100 RPM and 26" or 21" and 2500RPM, which would you pick? Both are 65% horsepower at the same altitude. I've been using lower MP because i was taught never to use a higher MP than RPM setting, but i've been taught a lot of wrong things it seems.
This is for a Lycoming IO-360 for an Arrow.
Is the general rule that you should always use a lower MP than RPM another one of those myths I was taught? I should make a giant list of them
RV10flyer
Pattern Altitude
I typically run 2,100 rpm and 45-55% power for better fuel economy, less wear, lower noise levels down low/short trips. On long xc flights between 8.5-12.5K, I usually run 2,100-2,400 rpm and never above 65% power. I try to run WOT in cruise as your engine breathes better and use rpm to keep the power where I want it. I follow the charts in the Lycoming Engine manual and low rpm/high mp are not recommended. At 2,100 rpm, 27.5" mp is the book limit for my engine. I try not to operate near the limits. I try to keep cht under 400F at all times. Takeoff and climb at 2700 rpm.
I just looked up the POH and you're correct. It also says to go to full throttle after cutting fuel to the engine to "reduce engine back pressure"
That's the first I've heard about that.
3393RP
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3393RP
About ten years ago Peter Garrison explored this issue in a very well written article in Flying.
He used his own aircraft as the test article and experimented with most of the scenarios posters have mentioned above.
I can't recall any of the specifics of the outcomes, but if anyone is interested in finding the article some good Google-fu might locate it.
He used his own aircraft as the test article and experimented with most of the scenarios posters have mentioned above.
I can't recall any of the specifics of the outcomes, but if anyone is interested in finding the article some good Google-fu might locate it.
denverpilot
Tied Down
I personally know two people with four each and one 20,000+ hour instructor who's had exactly zero. It's a scatter plot.
Interesting idea. I can second that on the big 182 prop it's a significant difference if you can get I to course pitch.
Others covered this, but slowing way up below best glide will usually get it to stop windmilling, but you really need spare altitude to mess with it and in doing so you're burning altitude you might need to get a marginal glide performance increase after you go back to best glide. Not worth it.
But there's YouTube videos of people braver or stupider than truly necessary who like creating possible emergencies when they don't have to, who've stopped both fixed pitch and constant speed props at altitude and then the compression and what not counteracting getting it windmilling again seems to work on lighter/slower aircraft. Heavier/faster aircraft exert enough force that the prop will start rotating again.
See above. There used to be some YT examples. I think a number of them have been removed by their posters though, deciding that advertising that one creates unnecessary emergencies in flight, on a public video forum, is probably not a great idea.
I'd heard this long ago and forgotten it. Thanks for the reminder.
Have also heard this but many manufacturers do demand this sort of operation for an emergency descent and many many schools and instructors and examiners and what not, want this procedure done even in training, by the book. Will be an interesting discussion in person with some mechanics and instructors at the airport however. Interesting point.
Yeah that's the gist of my comment above.
And I understand what you're saying here, too. I think if we really want to get to the bottom of this we'd have to talk this through with mechanics on specific powerplants. Some may behave far better than others in this regime.
Heh. Just a side note. Boy you gotta love turbochargers! Heh. You can regularly see takeoff power way up above 34" on the Turbo Seminole turning just over 2500 RPM. Wheee.
What was really amazing today was seeing it was possible to poke an engine into overboost above 11,000 MSL because it was cold as all get out up there here today. -18C measured. Normally up there for various demos you can truly go to full throttle on those engines but not today! Brrrrrr.
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Do you have a good resource that talks more about high rpm/low mp? I'd like to learn more about why low MP and high RPM is bad. Thanks
MAKG1
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MAKG
I would as well.
The cylinder pressure ALWAYS goes negative compared to ambient during the intake stroke, or the mixture doesn't enter the cylinder. It never goes negative in absolute pressure because that's not possible. So, what do you mean by that?
Fearless Tower
Touchdown! Greaser!
Keep in mind that most of those radials have geared props and blowers, so the RPM is naturally going to be lower than the MP.
General rule of thumb for cruising in a radial is 1-10" of MP for 100 rpm. So if you are cruising at 1800 RPM, MP can be 18-28".
denverpilot
Tied Down
I really need to take a big bird feather along the next time we have the cowl off of the 182 for a photo for this thread. I love to feather my single engine, the big dumb O-470 turns out, is into being a little kinky during oil changes.
RV10flyer
Pattern Altitude
Sorry about the "vacuum" confusion. I meant the higher rpm's pull a deeper vacuum. This is where I learned about it a few years back. Good reading. Below is from the Service Instruction 1427B that I received with my IO-540...
"AVOID LOW-MANIFOLD PRESSURE DURING HIGH ENGINE SPEEDS (UNDER 15”
HG.) AND RAPID CHANGES IN ENGINE SPEEDS WITH ENGINES THAT HAVE
DYNAMIC COUNTERWEIGHT ASSEMBLIES. THESE CONDITIONS CAN DAMAGE
THE COUNTERWEIGHTS, ROLLERS OR BUSHINGS, THEREBY CAUSING
DETUNING.
6. Descend at low cruise power while closely monitoring the engine instruments. Avoid long
descents at low manifold pressure. Do not reduce altitude too rapidly or the engine temperature
may drop too quickly.
CAUTION
AVOID ANY CLOSED THROTTLE DESCENTS. CLOSED THROTTLE OPERATION
DURING DESCENTS WILL CAUSE RING FLUTTER CAUSING DAMAGE TO THE
CYLINDERS AND RINGS."
Here are some links...
http://www.avweb.com/news/pelican/186778-1.html
http://www.highpowermedia.com/RET-Monitor/3762/piston-ring-flutter
http://www.motorstate.com/TheGreatPistonRingControversy.htm
"AVOID LOW-MANIFOLD PRESSURE DURING HIGH ENGINE SPEEDS (UNDER 15”
HG.) AND RAPID CHANGES IN ENGINE SPEEDS WITH ENGINES THAT HAVE
DYNAMIC COUNTERWEIGHT ASSEMBLIES. THESE CONDITIONS CAN DAMAGE
THE COUNTERWEIGHTS, ROLLERS OR BUSHINGS, THEREBY CAUSING
DETUNING.
6. Descend at low cruise power while closely monitoring the engine instruments. Avoid long
descents at low manifold pressure. Do not reduce altitude too rapidly or the engine temperature
may drop too quickly.
CAUTION
AVOID ANY CLOSED THROTTLE DESCENTS. CLOSED THROTTLE OPERATION
DURING DESCENTS WILL CAUSE RING FLUTTER CAUSING DAMAGE TO THE
CYLINDERS AND RINGS."
Here are some links...
http://www.avweb.com/news/pelican/186778-1.html
http://www.highpowermedia.com/RET-Monitor/3762/piston-ring-flutter
http://www.motorstate.com/TheGreatPistonRingControversy.htm