Green arc- tachometer and manifold

[Cardiff Kook]

I have been working on slow flight recently in preparation for some canyon flying.

In the 185 to slow down to 70 knots and maintain altitude requires about 13 mp. Green arc low end is 15. Is there an issue with running here for say 20 or 30 minutes? What does the normal operating range indicate?

Same question for fixed pitch cub re: rpm. I cant recall lower bound or green arc for cub at the moment (2000?) but I think to get down to 60 mph which is a good slow speed I am at maybe 1800 rpm? Is there an issue being here for or 30 min?

I dont really get the lower bounds for power settings. High end makes sense.

Input appreciated.

 

[mvivion]

The “Normal Operating Range” is precisely what it says…..that’s where we typically operate, under “Normal” situations. I’ve spent a lot of hours at flaps 20 and power way back, in both 185 and Cubs.

In the 185, you have additional options, due to the constant speed prop. Reduce prop rpm, and you can run a little higher MP.

Unless there are specific operating LIMITATIONS marked on the tach or in the flight manual, use the power setting that makes sense for conditions. An example of limitations is on the O-360 A1A engine, max power-2700 rpm is limited to 5 minutes, and that engine equipped with certain constant speed props has a “no continuous operation between xxx and yyy rpm” placard. You get to decide what “continuous operation” means.

MTV

 

[hotrod180]

Kook, read this:

Minimum Cruise RPM (tcmlink.com)

 

[frequent_flyer]

Minimum Cruise RPM (tcmlink.com)

It was interesting to me that this CSB makes no mention of cruise manifold pressure. Also wondering if TCM ever gathered enough data to confirm the association between low cruise rpm and shedding of counter weights. Wasn't there a much more recent SB that suggested shedding of counter weights may be caused by incorrect installation of the weight retaining circlips?

 

[stewartb]

I’m having a hard time imagining maintaining level flight at 13” MP. My slow flight is done on the back side of the power curve and requires considerable power regardless of flap setting. But in truth I’ve never paid attention to MP.

 

[Cardiff Kook]

I’m having a hard time imagining maintaining level flight at 13” MP. My slow flight is done on the back side of the power curve and requires considerable power regardless of flap setting. But in truth I’ve never paid attention to MP.

20 degress of flaps.

 

[BC12D-4-85]

Here's some things to consider in extended low power ops. Check your oil dipstick for any changes like increased carbon, fuel, and water buildup...look and give it a sniff after. Cold air can make it worse. Look at your exhaust pipe outlet. Does it look the same as after normal cruise flight, or does it change the color of any deposits? Fueling and air/fuel mixtures aren't perfect, so see if it tends to run rich (dark exhaust deposits) or lean (real light deposits) in slow flight. Also, the oil breather tube may exhaust more oil and moisture...keep track of that.

Like MTV I did lots of 15" slow flight in a C-185 but tried to keep the prop specs at the bottom of the green to put a load on the engine. In a Cub with that flat prop there's not much engine load available, so the piston rings may bypass combustion products more. And feel for engine roughness. Try to keep it smooth by adjusting rpm and MP if available.

Carb heat may not be as available at low power ops. Check it more often to confirm it's there if needed.

Gary

 

[hotrod180]

..... Wasn't there a much more recent SB that suggested shedding of counter weights may be caused by incorrect installation of the weight retaining circlips?

Mandatory Service Bulletin Released for Crankshaft Counterweights (continental.aero)

turned into an AD:

Federal Register :: Airworthiness Directives; Continental Aerospace Technologies, Inc. Reciprocating Engines

article about this SB & AD:

Crankshaft Counterweights and the Potential for Catastrophic Failure - FLYING Magazine

 

[frequent_flyer]

Mandatory Service Bulletin Released for Crankshaft Counterweights (continental.aero)

turned into an AD:

Federal Register :: Airworthiness Directives; Continental Aerospace Technologies, Inc. Reciprocating Engines

article about this SB & AD:

Crankshaft Counterweights and the Potential for Catastrophic Failure - FLYING Magazine

Thanks for the references. I am left wondering if TCM still believes low cruise RPM ever contributed to the loss of counterweights.