Preflight Cycling of Controllable-Pitch Prop?

D_C71

D_C71

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D_C
Have read different suggested procedures for testing/pre-charging controllable-pitch props during the preflight runup.

I was "typically" instructed to cycle the prop THREE times and to watch for RPM Drop, Oil-Pressure Drop, etc, with each pull.

Elsewhere I have read once is enough, or that cycling the prop too much could be harmful to engine/prop.:nono:

What is your knowledge/experience on the subject?
 
i usually pull it a couple times, until i get an immediate response. if its the first flight of the day this might take 3 times. if its after a quick turn, usually once.
 
D_C71 said:
Have read different suggested procedures for testing/pre-charging controllable-pitch props during the preflight runup.

I was "typically" instructed to cycle the prop THREE times and to watch for RPM Drop, Oil-Pressure Drop, etc, with each pull.

Elsewhere I have read once is enough, or that cycling the prop too much could be harmful to engine/prop.:nono:

What is your knowledge/experience on the subject?
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i was taught the same thing as you. 3x, once for RPM drop, once for Oil-pressure drop, once to look outside and see if oil is spraying from it.

Why would cycling the prop be harmful to it?
 
When the engine is cold, like the first flight of the day, I triple-cycle it to push warm oil up in there. After that, once is enough to check the connections and operation. And yeah, I've discovered a disconnected prop linkage on the second flight of the day.
 
Ron Levy said:
When the engine is cold, like the first flight of the day, I triple-cycle it to push warm oil up in there. After that, once is enough to check the connections and operation.
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Ditto -- 3x to be sure all the oil in the hub is out and replaced with warm oil.

After that, once -- maybe twice.

On the electric -35 Bonanza -- once, every time (only so many cycles in those old, expensive parts!)
 
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I do what the AFM tells me, and it does vary from plane to plane, and even with different engine/prop combinations. Some have said to cycle it once, others three times.
 
D_C71 said:
Have read different suggested procedures for testing/pre-charging controllable-pitch props during the preflight runup.

I was "typically" instructed to cycle the prop THREE times and to watch for RPM Drop, Oil-Pressure Drop, etc, with each pull.

Elsewhere I have read once is enough, or that cycling the prop too much could be harmful to engine/prop.:nono:

What is your knowledge/experience on the subject?
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I think this is one of those "it depends" issues with no one size fits all answers. In most single engine airplanes, engine oil pressure (boosted by the governor is used to force the prop into coarse pitch. In that case I wouldn't expect that there's enough cold oil in the prop hub to be concerned about. I'd say the only reason to cycle the prop in such a single at all is to confirm that the governor is functioning and connected to the prop control and once should be sufficient.

With a twin things are a bit different with the governor's output used to move the blades toward fine pitch. That means that the hub will be filled with oil at whatever temp the engine was started with. But since you shouldn't be starting the engine when the oil is so cold it won't flow in or out of the prop hub, I see little benefit in cycling beyond what's necessary to confirm that things are working.

My SOP with the twin I fly is to do a feather check (this removes all the oil pressure from the hub) at the recommended 1500 RPM on the first flight of the day and skip the high RPM cycling entirely. It would become pretty obvious while still on the takeoff roll if the governor wasn't working at all and I'd rather not suck up all the debris on the runnup pad nicking my props and boots. Have you ever noticed a significant difference in the response of the prop to the governor between the first and third cycles?
 
On cold mornings, I will cycle it a few times until I lose a lot of the 'delay' in its reaction (3rd time is the charm). On a warmer day, or one a multiple flight day, I'll only do it once to verify everything is working and make sure oil isn't blowing out of it.
 
I dunno how warm the "warm oil" is when all you've done is idle, taxi, and 30 seconds of run-up...but I do 3 quick pulls and the first one usually doesn't respond too well. My CFI also said to not leave the prop in low pitch for any time at all.
 
Thanks Much. Appreciate all the replies.

Also, like Mike just said, most all instructors I've had, admonish that I make each pull as brief as practical. That was the part about it being hard on engine/prop.

Had a tough time with a Twin Comanche last month. My instructor told me to bring the left engine to Full-Feather during our runup.

The engine/prop got "Stuck" (in "Full Feather,") then the engine died and we couldn't get a clean restart. We had to taxi it over to maintenance to have them get it restarted, and it still didn't want to get "un-Stuck."

I know, there are different means and mechanisms depending on type, that act to un-feather the prop, but it certainly was disturbing at the time.

DC
 
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D_C71 said:
Also, had a tough time with a Twin Comanche last month. My instructor told me to bring the left engine to Full-Feather during our runup. It got "Stuck" (in "Full Feather") and we had to taxi it over to maintenance to have them get it "un-Stuck."

I know, there are different means and mechanisms depending on type, that act to un-feather the prop, but it certainly was disturbing at the time.

DC
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Bummer. You missed out on the chance to do a real single engine (or at least real only one generating thrust) approch (assuming that was the engine used for a simulated engine failure).
 
Yes, it DID happen at runup. Didn't do much for my confidence in that aircraft.

If I did need to do an in-flight feather (to practice engine-out, critical engine at that,) or (in a "True" engine out,) say I was able to troubleshoot the problem, and restart the engine, would I still be without thrust or not??? :nonod:

I have survived a "real" landing-gear power-pack failure (had to pump the gear down,) but at least that worked.:blueplane:

No fun.

DC
 
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What Lance said. There is no point whatsoever in doing it three times, so why do it 3 times? 1 time is usually plenty to confirm operation. This is one of those things that's thought by many CFIs without any support.

smigaldi said:
Why would cycling the prop be harmful to it?
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Because most people do the check at "runup RPM", and since they usually chose an RPM that's unnecessarily high, staying there long enough to cycle the prop 3x while the a/c is stationary will get little stones in the prop.

-Felix
 
My 1958 Cessna 182 POH says "Once", for either Hartzell or McCauley prop.

A local old-timer mechanic agrees, as did my Dad, a professional pilot (30,000+ hours), and an A&P. He would keep all ground run-ups as short as possible to protect the engine and prop, from DC-3's to Piper J-3's.

So read your engine and prop manuals for the answers.

Burt
Marfa
 
Marfa Gliders said:
My 1958 Cessna 182 POH says "Once", for either Hartzell or McCauley prop.

A local old-timer mechanic agrees, as did my Dad, a professional pilot (30,000+ hours), and an A&P. He would keep all ground run-ups as short as possible to protect the engine and prop, from DC-3's to Piper J-3's.

So read your engine and prop manuals for the answers.

Burt
Marfa
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Not all POH's specify.

Short run-ups make sense, though. Too often I'm stuck on the taxiway behind some guy that wants to do a second preflight while the engine roars along.....
 
sba55 said:
What Lance said. There is no point whatsoever in doing it three times, so why do it 3 times? 1 time is usually plenty to confirm operation. This is one of those things that's thought by many CFIs without any support.
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Once is enough to check operation - But you can double-check that your tach, MP, and oil pressure gauges are functioning properly as well. If they're all sufficiently close together that you can do that with one pull, great. I need at least two.
 
flyingcheesehead said:
Once is enough to check operation - But you can double-check that your tach, MP, and oil pressure gauges are functioning properly as well. If they're all sufficiently close together that you can do that with one pull, great. I need at least two.
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Well, that makes you an idiot Kent.
 
flyingcheesehead said:
Once is enough to check operation - But you can double-check that your tach, MP, and oil pressure gauges are functioning properly as well. If they're all sufficiently close together that you can do that with one pull, great. I need at least two.
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I can tell if my MP, tach, and oil pressure gauges are working right after starting the plane (probably a good idea o check them before starting too, gotta add that to my prestart flow). I don't see any point in increasing the time spent above idle to further confirm the operation of those gauges.
 
D_C71 said:
Have read different suggested procedures for testing/pre-charging controllable-pitch props during the preflight runup.

I was "typically" instructed to cycle the prop THREE times and to watch for RPM Drop, Oil-Pressure Drop, etc, with each pull.

Elsewhere I have read once is enough, or that cycling the prop too much could be harmful to engine/prop.:nono:

What is your knowledge/experience on the subject?
Click to expand...

If someone tells me that, I'm not flying their plane. The prop and mechanism is dirt simple, and if I can't cycle it all I want, it's not airworthy, end of story. Can someone find me a cycle reference on props from manufacturers? The dam thing cycles on a moment by moment basis while in flight. Every time you change pitch, the prop will change pitch. The wisdom of morons never ceases to astound me. "Don't pull the plane by the prop" is another of my favorites... Oh yeah, what do you think those 300hp are pulling the plane by?
 
Henning said:
If someone tells me that, I'm not flying their plane. The prop and mechanism is dirt simple, and if I can't cycle it all I want, it's not airworthy, end of story. Can someone find me a cycle reference on props from manufacturers? The dam thing cycles on a moment by moment basis while in flight. Every time you change pitch, the prop will change pitch. The wisdom of morons never ceases to astound me. "Don't pull the plane by the prop" is another of my favorites... Oh yeah, what do you think those 300hp are pulling the plane by?
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Actually, the Bonanza A36 POH specifically warns against using the prop for ground handling.

I'll have to dig up the POH, but that's one that doesn't have an explanation. It wasn't my plane, so I didn't push on the prop.
 
gismo said:
I can tell if my MP, tach, and oil pressure gauges are working right after starting the plane (probably a good idea o check them before starting too, gotta add that to my prestart flow). I don't see any point in increasing the time spent above idle to further confirm the operation of those gauges.
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Hey, I was going to say that. You stole my line!!! :nono:
 
sba55 said:
Hey, I was going to say that. You stole my line!!! :nono:
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I'd be willing to sell it back for half of what you paid originally. You can still collect the insurance and we'll both be ahead.
 
Henning said:
If someone tells me that, I'm not flying their plane. The prop and mechanism is dirt simple, and if I can't cycle it all I want, it's not airworthy, end of story. Can someone find me a cycle reference on props from manufacturers? The dam thing cycles on a moment by moment basis while in flight. Every time you change pitch, the prop will change pitch.
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I agree that cycling the prop on the ground isn't going to do anything bad to the engine or prop directly, but IME it can generate nicks in the prop (and the boots on a twin) and that's the reason I avoid it as much as I can.
The wisdom of morons never ceases to astound me. "Don't pull the plane by the prop" is another of my favorites... Oh yeah, what do you think those 300hp are pulling the plane by?
Click to expand...
That one isn't as obvious as it seems, there is some potential for damage as the many tons of "centrifugal" force that loads the pitch change bearings when the prop is "pulling" the plane is missing when you tug on the non-moving blade(s). So it is theoretically possible that pulling a plane by it's prop could create a load on those bearings they weren't designed to take. That said I've never seen any data or pictures of such damage and don't really believe that it's possible to damage the props this way on the planes we fly. Whenever I need help pulling my airplane I have the help pull on the props. I did have a threaded hub crack once though but the prop shop that inspected it didn't suggest it was the result of pulling on the blades. Personally I think the original reason behind the recommendation to avoid pulling on the blades is to reduce the slight safety risk of starting the engine if you happen to turn the prop in the process and you're having a bad day.
 
gismo said:
I agree that cycling the prop on the ground isn't going to do anything bad to the engine or prop directly, but IME it can generate nicks in the prop (and the boots on a twin) and that's the reason I avoid it as much as I can.

That one isn't as obvious as it seems, there is some potential for damage as the many tons of "centrifugal" force that loads the pitch change bearings when the prop is "pulling" the plane is missing when you tug on the non-moving blade(s). So it is theoretically possible that pulling a plane by it's prop could create a load on those bearings they weren't designed to take. That said I've never seen any data or pictures of such damage and don't really believe that it's possible to damage the props this way on the planes we fly. Whenever I need help pulling my airplane I have the help pull on the props. I did have a threaded hub crack once though but the prop shop that inspected it didn't suggest it was the result of pulling on the blades. Personally I think the original reason behind the recommendation to avoid pulling on the blades is to reduce the slight safety risk of starting the engine if you happen to turn the prop in the process and you're having a bad day.
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I've had props open and apart in front of me and saw all the parts. I can generate a maximum force of about 180lbs on the propeller. There is not a part I saw in there that I could possibly damage by pulling on it. Now if we're talking "Dont put slings around the blades and hook em to your truck to pull the plane out of the mud", yeah, ok, I can agree. For me to pull the plane out of its parking spot to keep from prop blasting someone on the ramp, sorry, I'm not gonna hurt a damned thing.
 
jesse said:
Well, that makes you an idiot Kent.
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Uh, okay. :eek:

gismo said:
I can tell if my MP, tach, and oil pressure gauges are working right after starting the plane (probably a good idea o check them before starting too, gotta add that to my prestart flow). I don't see any point in increasing the time spent above idle to further confirm the operation of those gauges.
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Well, I'm not looking at 'em when I start. After start, I can see where they are. I like to make sure they move and aren't doing an on-off type of thing. Meh... Habits.
 
Henning said:
The wisdom of morons never ceases to astound me. "Don't pull the plane by the prop" is another of my favorites... Oh yeah, what do you think those 300hp are pulling the plane by?
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Tell it to Sensenich, who has that instruction in their literature. When it comes to props, I doubt they're morons.
 
jmaynard said:
Tell it to Sensenich, who has that instruction in their literature. When it comes to props, I doubt they're morons.
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I wonder how much of the justification for that language is the fact that some people try to pull from the tips or far away from the hub. By simply saying "Don't pull from the prop, ever" they don't have to try to explain how far away from the hub is ok to pull from.
 
jmaynard said:
Tell it to Sensenich, who has that instruction in their literature. When it comes to props, I doubt they're morons.
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Doesn't Sensenich only maufacture fixed-pitch props?

I have a hard time seeing how applying enough force to a FP prop to roll a lightweight plane could possibly do anything.


Trapper John
 
Trapper John said:
Doesn't Sensenich only maufacture fixed-pitch props?
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[/quote]I have a hard time seeing how applying enough force to a FP prop to roll a lightweight plane could possibly do anything.[/QUOTE]
Good question. It's probably, as Chris said, because people pulling on the tips cause problems. Nevertheless, if they say it, I'm going to follow it.

Besides, I spent $100 on that nice Bogert tow bar, so I'm going to damned well use it.
 
Trapper John said:
I have a hard time seeing how applying enough force to a FP prop to roll a lightweight plane could possibly do anything.


Trapper John
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There are a bunch of new FlightDesign CTs on the ramp at KLNS.

One day I walked over and took a look around.

The prop looked so tiny.. I touched it on the blade as I would checking for nicks (I know -- so sue me).

It moved under my very light touch of the edge.

Yeah, yeah -- I know carbon fiber is strong.

But -- sheese.
 
I guess I had limited my thinking to aluminum props.

Now I'm curious to check out a composite prop, I know nothing about them. How would you file out a nick on a composite prop, for instance?


Trapper John
 
composite props i've seen usually have a titanium leading edge. helps protect against damage, and keeps water (rain) from delaminating it.
 
Trapper John said:
I guess I had limited my thinking to aluminum props.

Now I'm curious to check out a composite prop, I know nothing about them. How would you file out a nick on a composite prop, for instance?


Trapper John
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You can't, and you have no idea how far the microfractures have spread (and they will continue to grow until...) or when it will turn to catastrophic explosive failure. The Brazilias had a few planes lose blades a while back.
 
jmaynard said:
Good question, and I don't know the answer...and when I get to that point, I'll have to ask Sensenich and find out. (My prop is a wood core composite.)
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You don't, and the wood core will save you.
 
Henning said:
You can't, and you have no idea how far the microfractures have spread (and they will continue to grow until...) or when it will turn to catastrophic explosive failure. The Brazilias had a few planes lose blades a while back.
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So how do you check for fractures with composite props? Is there some zyglow equivalent, or is it ultrasonic or something else?

These composite props have to go through the same certification tests as aluminum ones, birdstrike, lightning, overspeed, etc., right?


Trapper John
 
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