Ok, this is probably much simpler than I'm making it out to be, but since my first airplane with a cs prop didn't come with any instructions, I'm trying to figure it out on my own. Even a pedantic book like 'Stick and Rudder' doesn't address propeller management in any detail.

Up to this point every plane I flew had a fixed pitch prop, thus there was really only one power setting option...the throttle. Now with more knobs to fiddle with, I'm wondering just how bad I'm going to screw things up with the old trial and error...

In my "blue knobs for idiots" class (the parting words of advice before I flew my new plane home), I was told to keep the mp and rpm squared, and to always make sure the propeller pulls the airplane and don't let the airplane push the propeller and I'd not go wrong. Makes sense...don't lug the engine; don't over-rev the engine. But is there a limit to this? how about 12"mp and 1200 rpm? something about that seems like it should be wrong, but I don't know why.

Is there a situation where you want to keep the rpm considerably higher than the mp? Why? How about running over-squared...say 21"mp and 1900 rpm? It seems like there should be a situation where this would be more efficient than running squared.

In descents, I reduce mp, then I keep wanting to coarsen the prop pitch. It just seems more efficient, but it also seems like a lot of adjustment for a rather simple maneuver. Somewhere on downwind, or before I have to add throttle if I level out too far from the field, I begin putting the prop in. I'm flat pitched by the time I'm abeam the numbers.

Would the owners manual for another airplane that was manufactured with this engine/prop be an accurate reference for power settings...maybe a Maule?

Hammer wrote:In my "blue knobs for idiots" class (the parting words of advice before I flew my new plane home), I was told to keep the mp and rpm squared, and to always make sure the propeller pulls the airplane and don't let the airplane push the propeller and I'd not go wrong. Makes sense...don't lug the engine; don't over-rev the engine. But is there a limit to this? how about 12"mp and 1200 rpm? something about that seems like it should be wrong, but I don't know why.

Don't reduce the power so quickly or so much that the prop is driving the engine. This is especially important with a prop with a reduction gear connecting it to the engine.

There is nothing wrong with operating the engine in an oversquare condition. In the 182, 185, 206, etc. For climb, I leave the throttle full open and reduce RPM to 2500-2700 RPM (2850 is max) in the 185/206 and leave the 182R at 2400 RPM (max). This, all the while, leaning to 1250-1300 EGT during the climb (where it is just after takeoff). The airplane will climb faster and the engine will run cooler. The CHT's in my 185 will shoot past 400*F pretty quickly if I fly a square 25/2500 and Vy after takeoff. Leaving the throttle in and accelerating to 120-140 MPH results in CHT's around 330-360*F, depending on OAT. I do everything in my power to keep the CHT's below 380*F. The CHT limits published for Lycoming (500*F) and Continental (435*F) are for momentary excursions only, not for continuous operation. Cool is good.

For cruise, fly whatever RPM feels smoother. There is nothing carved in stone that says you can't fly 2325 or 2420 or 2386 RPM. The airplane will tell you which RPM it likes, if you pay attention to the smoothness. At cruise altitudes above 2,500-3,000' , I just leave Wide Open Throttle (WOT) and adjust the RPM to what minimizes vibration or feels smooth.

Is there a situation where you want to keep the rpm considerably higher than the mp? Why? How about running over-squared...say 21"mp and 1900 rpm? It seems like there should be a situation where this would be more efficient than running squared.

Except for cruise above 5,000' (when the MAP normally decreases) and during descent approach and landing...not really.

In descents, I reduce mp, then I keep wanting to coarsen the prop pitch. It just seems more efficient, but it also seems like a lot of adjustment for a rather simple maneuver. Somewhere on downwind, or before I have to add throttle if I level out too far from the field, I begin putting the prop in. I'm flat pitched by the time I'm abeam the numbers.

I recommend leaving the throttle in and reducing the RPM to the bottom of the placarded green arc during the descent until the IAS approaches the yellow arc. At this point reduce the MAP to keep the IAS below the yellow arc, while maintaining 500 FPM to level-off altitude.

Would the owners manual for another airplane that was manufactured with this engine/prop be an accurate reference for power settings...maybe a Maule?

Get a POH or manual for your airplane. Use it and the green arc's on the MAP gauge and Tach.

There's more OWT's on this than can be imagined. I was taught the wrong way, taught the wrong way when I was a full-time CFI years ago, and now that I have my own airplane, have the data and have done the research, I do what I described, above...and the engine likes it.

Desert,

The point he made was that his airplane wasn't BORN with this engine. In fact, his airplane wasn't born with a C/S prop. So a POH won't do him any good in this case, though that's good advice for an airplane with original equipment.

Hammer,

If your airplane didn't come with one, contact Lycoming, and order an operator's manual for your engine. That won't give you a LOT of information, but it will tell you what Lycoming says is approved for that engine. It will also offer POWER CHARTS.

Before reading all sorts of operating procedures for a Continental engine, and trying to apply them to your Lycoming engine, do some reading on Lycoming's web site: http://www.lycoming.textron.com/

Specifically, look at the Key Reprints publication, available on the web site here: http://www.lycoming.com/support/tips-ad ... /index.jsp

Look in the Operations section of this for good information on operating your engine, for example:

TO INCREASE POWER — first, enrich mixture, increase RPM, then follow with throttle.
TO DECREASE POWER — first, reduce throttle, reduce RPM, and then adjust mixture.
INCREASING POWER — enrich mixture first to ensure protecting
the engine against damage from higher power when previously leaned out for a lower power setting.
Next, increase RPM because in some models the engine and propeller would have undesirable pressure and stresses with a high manifold pressure and lower RPM.
Then, follow with the appropriate manifold pressure, now that the mixture and RPM have been correctly set to accommodate the increased throttle.
DECREASING POWER — Most models of our engines require the basic procedure for decrease of power by retarding throttle, followed by RPM. However, we do have an exception
in several older models of our geared normally aspirated power plants, such as the GO-480 and GO-435 series. In the climb configuration, we recommended full throttle throughout the climb for internal fuel cooling with RPM reductions initially
to 3000 RPM and then 2750 RPM for prolonged climb.
Turbocharged and supercharged engines require careful application
of the basic power sequences as outlined in the beginning. It is also possible to create an overboost condition on these engines by going to takeoff manifold pressure at cruise RPM, such as might take place in an unexpected go-around. The stresses and pressures on prop and engine would create a threat to both.
A letter received here at the factory asked a question we have heard quite often:
“Is it a fact, or is it fiction, that engines with constant speed props should not use power settings where inches of mercury
exceed RPM in hundreds? I am referring, of course, to
non-turbocharged engines in general .”
The answer to this question is easily found in cruise power charts of the airframe Pilot’s Operating Handbook. Whatever the combinations of RPM and MP listed in the charts — they have been flight tested and approved by the airframe and
power plant engineers. Therefore, if there are power settings such as 2100 RPM and 24" MP in the power chart, they are approved for use.
The confusion over so-called “squared” power settings
(i.e., 2400 x 24" MP), appears to have been a carry-over from some models of the old radial engines which were vulnerable to excessive bearing wear where an MP higher than “squared” was used. More pressure on the bearings with the higher than “squared” MP was the cause of their problem. However, changes in design, metals and lubricants permit changes in operation in the more modern flat-opposed power plants.
Let’s look at the power charts in a couple of the Pilot’s Operating Handbooks of two different aircraft manufacturers, but where both are using the four-cylinder 200 HP Lycoming engine.
Cessna’s Model 177 RG, using the Lycoming IO-360-A1B6D, in the cruise range at 6,000 feet, lists a cruise power-setting range at that altitude of anywhere from 2100 RPM to 2500 RPM with variations all the way from 18" MP to 24" MP. They list a recommended
power-setting for 66% power at 2100 RPM at 24" MP."

In my opinion, you should set power in cruise based on two factors: Desired percentage of rated power desired, and fuel economy desired, which will dictate whether you use best economy or best power procedures. These procedures are also described in Key Reprints Operations section.

The percent power settings for your engine will be given in the handbook for your engine.

As to managing prop rpm as you descend toward an airport for landing:

My procedure is simple: Leave the prop at the cruise rpm setting as you descend. The 170 isn't going to go supersonic in a descent, so you won't have to reduce throttle much either. Don't worry about the airplane "pushing" the prop--that isn't going to be a factor in that airplane.

I then enter downwind at the airport, and at the point where I have to reduce power below the governing range of the engine for a descent, generally when I reduce power abeam the landing spot, I push the prop up to max rpm for a possible go around.

You can make the use of a C/S prop so complex that it'll make you crazy. It need not be so, and in fact there is NO legitimate reason to adjust the prop control more than a couple times on your airplane for any given leg, unless you are changing altitudes a lot.

Order an engine operating book from Lyc, pick some power settings, experiment with them, and use those.

For takeoff, I use max rpm, full throttle. At 500 agl, I reduce to 2500 and 25 inches (for no reason other than that I don't generally need max everything for climb) for climb. When I arrive at my cruise altitude, I use one of several rpm/mp settings, depending on what I want to do. I may cruise at 2350/21, or 2300/20, 1900/21, etc. I generally use very low power settings, simply because in these airplanes, 80 % power won't make you go THAT much faster than 65%.

Operating oversquare (ie: 1900/21) is approved for these engines, by Lyc. As Desert noted, some engines operate smoother at certain rpm than at others. Pick the rpm that your engine/prop is smoothest at. Some of these engines just don't run smooth oversquare, and I wouldn't run them that way if so.

If your airplane has the standard Hartzell propeller, it should have a restricted operating range marked on the tach, or placarded. Don't operate continuously in that range, regardless of what other pilots tell you. My airplane has a long prop and harmonic damper, which eliminates the restricted operating range.

Finally, if the engine/prop haven't been dynamically balanced, GET THAT DONE. It will smooth out the rotating assembly significantly, be MUCH easier on the airframe as well as the occupants, and is well worth the cost.

Most of all, have fun, but READ the Lyc Key Reprints. If you are at any of the major events where Lycoming exhibits, they'll give you a free paper copy. It's a great resource.

MTV

Excellent explanation. Thank you.

When I saw "the blue knob" title, I thought of the "polishing your spinner" thread and the comment there that this isn't one of those kind of websites.

When I saw "the blue knob" title, I thought of the "polishing your spinner" thread and the comment there that this isn't one of those kind of websites.

Zero1victor...I'm no doctor or nothing, but you might have a circulatory problem...

MTV and 185,
Thanks all for the great advice! I printed out all the Lycoming flyers and will study them as time permits. My biggest concern is to treat the engine and propeller kindly...we tend to fly a lot of places where an engine out would be so much more than just expensive. I'm also guilty of over-thinking otherwise simple procedures...a habit that probably does little to make me more efficient.

Speaking of which, those of you with experience in more types of aircraft...if you have the same engine and propeller in two dramatically different airframes (say a Mooney and a Maule, or some such thing), will you see much difference in the recommended power settings?

Our propeller has a dynamic balancer which the builder states eliminates the prohibition of flying in the 2000~2250 rpm zone. And maybe it does, but I'm not keen on just taking his word for it. Until I know more I'm just avoiding those rpm's.

Hammer,

No worries on the restricted operating range. The Harmonic damper takes care of that.

Two identical engines on two different airframes will have the same settings for same percent power. Point is, though, that there are a LOT of different O-360's out there, for example, so be sure you are in fact dealing with the same Model of engine, ie: O-360 A-1A.

MTV

I fly a 182 Cessna with a O470 cont. and a CS Prop. I don't fly with the MP and RPM squared. On take off I start with every thing in, that is full throttle and high RPM on the blue knob. as soon as possible I change throttle slowly back to 23 inches of MP. and 2450 RPMs. I keep adding throttle on climb. If I don't climb to high, I cruise at 21 MP and 2300 RPM. Of course if I go up high enough I would have the throttle all the way in.
On landing I reduce throttle to 1700 and the RPM stays on 2300 rpm sitting until I am on long final. Then I push the blue knob in, I also push in the carb heat. I do this so if I have to do a go around all I have to do is push in the throttle and milk away the flaps, after I have a positive rate of climb. Bob

Hammer wrote:MTV and 185,
Thanks all for the great advice! I printed out all the Lycoming flyers and will study them as time permits. My biggest concern is to treat the engine and propeller kindly...we tend to fly a lot of places where an engine out would be so much more than just expensive. I'm also guilty of over-thinking otherwise simple procedures...a habit that probably does little to make me more efficient.

I fly to AUN occasionally. We could meet for lunch and airplane talk. Do you know Earl Allen?

Hammer wrote:

When I saw "the blue knob" title, I thought of the "polishing your spinner" thread and the comment there that this isn't one of those kind of websites.

Zero1victor...I'm no doctor or nothing, but you might have a circulatory problem... ..................

Q: What's the difference between pink & purple?

A: Your grip!

(sorry, couldn't resist!)

Ok I just fell outtta my chair