Cycling the prop

[ArtVandelay]

that's why I do 3; I was taught to check for the same things.  I had a CFI tell me 107F for the oil, so I've always gone with that as a minimum.  

107? Should be 108.143256.
It's amazing our engines haven't all exploded because of shock cooling, etc, personally I think our engines are little less fragile than that. When I start my car, I wait for a 3 seconds before putting it in gear and driving off.

[jaylw314]

I think I read somewhere that radials and/or full-feathering prop hubs do have a huge internal volume of oil compared to normal prop hubs, and so they might require the full 3 cycles.  That may be where the routine came from.

[N6758N]

4 minutes ago, teejayevans said:

107? Should be 108.143256.
It's amazing our engines haven't all exploded because of shock cooling, etc, personally I think our engines are little less fragile than that. When I start my car, I wait for a 3 seconds before putting it in gear and driving off.

I sure hope you aren't doing that with your airplane...I see fouled plugs and crappy running engines all the time because pilots don't let the engine get up to temperature before taking off.

 

[Hank]

19 minutes ago, N6758N said:

I sure hope you aren't doing that with your airplane...I see fouled plugs and crappy running engines all the time because pilots don't let the engine get up to temperature before taking off.

 

You mean this is wrong???

[rbridges]

1 hour ago, teejayevans said:

107? Should be 108.143256.
It's amazing our engines haven't all exploded because of shock cooling, etc, personally I think our engines are little less fragile than that. When I start my car, I wait for a 3 seconds before putting it in gear and driving off.

Haha. I always thought that was a weirdly specific number, but it was in the green so I just went with it. 

[N201MKTurbo]

FWIW

You don't have to worry about getting oil circulating through the prop governor. it flows all the time. Oil from the governor goes to the front main bearing where it is channeled through the crank to the piston in the prop hub. The front main bearing lets the oil flow out the sides like all other main bearings. The governor supplies enough volume to maintain prop pressure in spite of the flow through the bearing. The oil in the prop hub is stagnant unless you cycle it which causes the oil to come out of the hub and be replaced with new oil.

[RLCarter]

Heard/read on shock cooling and from what I've gathered you would have to work at it to cause any damage, I think flying through rain would be worse due to rapid and uneven cooling. 

[jetdriven]

1 hour ago, rbridges said:

Haha. I always thought that was a weirdly specific number, but it was in the green so I just went with it. 

Lycoming used to say 75F for takeoff, and the white dot on the 1977 M20J is also 75F.  on later models that dot was deleted, and Lycoming got quiet about that too. Its still a good idea with single grade 50W oil, with multiviscosity oil, probably doesnt matter.  

I still wait for CHT of ~250f for the runup and like to see ~290ish for takeoff.  burning 1.3 GPH, its cheap to wait and let it warm up.

[peevee]

Iirc the rocket manual calls for 3 cycles, and it's full feathering. Why I do not know. Or care I guess.

[MooneyBob]

On my first take off ( I usually don't cycle the governor more than once and very little RPM drop) my RPM reach 2700. Oil is around 140d hot.

On my next take off the RPM is 2650 and oil is around 155d. On my third take off my RPM is 2630 and oil temp is around 185d. I know that because I just got the Savvy Analysis back today. So it looks like I need to adjust my governor to higher max RPM and be careful on the first take off with cooler oil not to overspeed or wait until oil is hotter and cycle it few more times to get it into the prop. Does it make sense? 

[Danb]

4 hours ago, N6758N said:

Hmmm, wasn't him, I called him to ask where he was and found out he was in Houston on a corporate trip!

Nice of him to give you a courtesy call 

[Guest]

21 hours ago, Cyril Gibb said:

I read somewhere that you should only cycle the prop with full flaps if you have an AOA indicator, otherwise you'll burn up the cylinders.

Only if you're using Cam Guard and have Garmin avionics.

Clarence

[Marauder]

As someone who had a prop governor fail, I do cycle the governor during runup just to make sure. 

[mike_elliott]

1 hour ago, M20Doc said:

Only if you're using Cam Guard and have Garmin avionics.

Clarence

Lycoming should give you a loaner engine if the RPM red X's out of your G1000

[M20F]

3 hours ago, Marauder said:

As someone who had a prop governor fail, I do cycle the governor during runup just to make sure. 

I was going to come add this in seriousness to the thread.  Cycling the oil isn't really that necessary compared to a radial (governor works backwards and a lot more oil) the main purpose is to see that it actually works.  

[Skates97]

I cycle it once. I slowly pull the prop knob out keeping an eye on the oil pressure. As the oil pressure starts to drop I can hear the change in the RPM's and a quick glance at the tach as I'm pushing it back in confirms that. That confirms to me that everything is operating as it should.

[Hank]

1 hour ago, M20F said:

I was going to come add this in seriousness to the thread.  Cycling the oil isn't really that necessary compared to a radial (governor works backwards and a lot more oil) the main purpose is to see that it actually works.  

I also cycle before every takeoff, unless I'm doing pattern work [then it's just once before the first one]. When I pull the lever all the way back and nothing happens for a couple of seconds, then I know to do it again, until I have an immediate response. I've had too many things work during preflight / departure and not work on landing . . . from the stupid landing light to vacuum pump to my entire electrical system. It's nice to make sure the prop governor is functioning while still on the ground.

[carusoam]

PV,

The things to know about Missile and Rocket prop governors...

Good: When the engine fails, the governor doesn't produce any oil pressure, the prop goes to full feather... land straight ahead.

Worth knowing: when the governor's pump fails or that shaft plug falls out, the engine is still running, but the prop goes full feather anyway... land straight ahead...

If not familiar, check the details...

PP thoughts only, not a mechanic...

Best regards,

-a-

[cliffy]

The school house is open. You can see that double acting props have a huge amount of oil compared to our single acting props. Cycling was a way of warming the oil "in the dome" and making sure the system worked. Usually it was 3 cycles as standard for run-up.  On our props its also to get the oil moving but we don't have the volume so one should suffice. Hydromatic Propellers

Basic Operation Principles : The pitch changing mechanism of hydromatic propeller is a mechanical-hydraulic system in which hydraulic forces acting upon a piston are transformed into mechanical forces acting upon the blades.

Piston movement causes rotation of cam which incorporates a bevel gear (Hamilton Standard Propeller) . The oil forces which act upon the piston are controled by the governor

Single Acting Propeller: The governor directs its pump output against the inboard side of piston only, A single acting propeller uses a single acting governor. This type of propeller makes use of three forces during constant speed operation , the blades centrifugal twisting moment and this force tends at all times to move the blades toward low pitch , oil at engine pressure applied against the outboard side of the propeller piston and this force to supplement the centrifugal twisting moment toward the low pitch during constant speed operation., and oil from governor pressure applied against the inboard side of the piston . The oil pressure from governor was boosted from the engine oil supply by governor pump and the force is controlled by metering the high pressure oil to or draining it from the inboard side of the propeller piston which balances centrifugal twisting moment and oil at the engine pressure.

Double Acting Propeller: The governor directs its output either side of the piston as the operating condition required. Double acting propeller uses double acting governor. This type of propeller , the governor pump output oil is directed by the governor to either side of the propeller piston.

Principle Operation of Double Acting :           Overspeed Condition : When the engine speed increases above the r.p.m. for which the governor is set . Oil supply is boosted in pressure by thr engine driven propeller governor , is directed against the inboard side of the propeller piston. The piston and the attached rollers move outboard. As the piston moves outboard , cam and rollers move the propeller blades toward a higher angle , which inturn, decreases the engine r.p.m.           Underspeed Condition : When the engine speed drops below the r.p.m. for which the governor is set. Force at flyweight is decrease and permit speeder spring to lower pilot valve, thereby open the oil passage allow the oil from inboard side of piston to drain through the governor. As the oil from inboard side is drained , engine oil from engine flows through the propeller shaft into the outboard piston end. With the aid of blade centrifugal twisting moment, The engine oil from outboard moves the piston inboard. The piston motion is transmitted through the cam and rollers . Thus, the blades move to lower angle

[cliffy]

I should have added that unlike that pictured above on single acting propellers our small stuff , for the most part, instead of having oil opposing oil in the dome , we have governor oil pressure being opposed by springs, air pressure and centrifugal twisting forces, depending on the design of the particular prop.

I hope this clarifies the issue a little better. 

[jlunseth]

Same as cnoe, I cycle it once.  Living in the cold though, if I have had to plug in the engine heater or am otherwise in cold start conditions, I will give it two or three cycles.  In my mind, I am moving cold gooey oil through the prop and replacing it with warm, but that is just my belief, what is actually going on in the prop may be different.

I do notice that the RPMs take some time to fall on the first cycle, I think that is from moving the slow oil through, when its cold I am more attuned to that - when do the RPMs start to respond quickly, then that's enough cycling.

Edited July 7, 2017 by jlunseth

[peevee]

1 hour ago, jlunseth said:

Same as cnoe, I cycle it once.  Living in the cold though, if I have had to plug in the engine heater or am otherwise in cold start conditions, I will give it two or three cycles.  In my mind, I am moving cold gooey oil through the prop and replacing it with warm, but that is just my belief, what is actually going on in the prop may be different.

I do notice that the RPMs take some time to fall on the first cycle, I think that is from moving the slow oil through, when its cold I am more attuned to that - when do the RPMs start to respond quickly, then that's enough cycling.

I dunno which heater you have, but our prop gets pretty warm from ours. I haven't checked but I bet (hope) the hub does too.

[INA201]

One cycle based on advice from two of my high time commercial pilot buddies who were taught by other high time pilot buddies of theirs.  No issues by doing it this way.

"I heard it from a friend who....heard it from a friend who.....heard it from a friend....................cycle the prop once"?

Is that how the song goes?

[jlunseth]

On ‎7‎/‎7‎/‎2017 at 0:53 PM, peevee said:

I dunno which heater you have, but our prop gets pretty warm from ours. I haven't checked but I bet (hope) the hub does too.

And I don't remember which one it is either, but I do remember it is a tank heater, it sits in the bottom of the oil sump, it is not the cylinder band type.  So the oil in the sump gets warm, but not the oil in the prop unless you make that oil move.  At least that is what I think.  What I actually do is cycle it however many times it takes to get a good response in the RPMs.  In the cold, it is usually slow to respond the first time, better the second.