“Just make sure you keep the manifold pressure less than the RPM”.
For most of us, when we transitioned to complex and/or high-performance aircraft, we got a thorough introduction on the mechanics of how constant speed propellers work.
But, when it came down to actually flying the airplane (myself included), being told to “square up the manifold pressure and RPM” and/or “make sure to keep the manifold pressure less than RPMs” was about as in-depth as it got.
Some instructors, instead, seem to place more emphasis on the mechanical operation of a constant speed propeller and almost treat the actual in-flight operation as an afterthought.
I often see the results of this approach to training when conducting aircraft checkouts on pilots who already have complex and/or high-performance time in their logbook.
They can usually explain how things work mechanically, but once we get in the airplane, operating the constant speed propeller is shall we say, sloppy.
I’ve even come across more than a few pilots who have never even looked at the power settings and performance data in the POH, which is not only dangerous, it’s just plain stupid!
The problem is that understanding the mechanical operation is only half of the equation – to get the most out of a constant speed propeller you also need to understand how to operate it.
And the best way to do that, in my opinion, is to break things down into operating segments.
So, let’s get at it.
During training, you were probably taught by your CFI to cycle the propeller three times during run-up.
In cold weather, and/or for the first flight of the day, the Piper Arrow POH recommends cycling the propeller at least three (3) times to ensure that warm engine oil has circulated through the system.
But if the airplane has been flying all day, or if you just flew it an hour ago, in most modern engines and propellers, cycling the prop just once to ensure the system works properly is all that’s really needed.
Of course, this doesn’t mean that you can’t cycle the prop three times before every flight, it just means that it may not be necessary to do so.
Either way, check your airplane’s POH and do what it recommends.
For takeoff in a typical, light general aviation airplane like a Piper Arrow or C-182, the propeller lever (or knobs depending on your aircraft) should be set full forward and the mixture set for best power – usually full forward (rich) when departing from airports below about 5,000 feet density altitude.
Once lined up on the runway, we apply full throttle and begin the process of throwing aluminum skyward just like we normally do in a fixed pitch propeller airplane.
After takeoff and during the initial climb phase, I generally don’t touch the throttle, propeller, or mixture levers until reaching a safe altitude.
Because if something breaks here, it could be because I just moved one of these levers.
How much altitude do I consider to be safe?
Well, it depends, but generally, somewhere between 500 to 1,000 ft.
Personally, I don’t want to complicate my life any more than necessary at this point, so I don’t touch anything, and that includes retracting the landing gear, until reaching an altitude of at least 500 ft. AGL – even if I’ve run out of usable runway to land on.
I’m too busy flying the airplane, watching airspeed, monitoring engine gauges, looking for a place to land should the engine(s) fail, avoiding birds, other aircraft, and communicating with ATC, etc.
Plus, if I have an engine failure below 500 feet, getting the gear back down and pushing levers forward are just more things that I’ll have to remember to do in an environment where my stress level just went from zero to insane in less than a second.
While I’ve never had an engine failure on takeoff in a single engine plane, I have lost an engine just after departure in a Piper Seneca.
If you’re going to lose an engine in a twin, losing the left engine (critical engine) at 400 feet AGL, while in a climbing left turn over a highly congested area is the worst possible time it could happen.
To say that I was a little busy would be an understatement – things happened so fast that I honestly don’t even remember declaring an emergency (I did, I just don’t remember doing it).
I was so busy just trying to keep the airplane above the trees and above Vmc (I was only able to maintain about 3kts above Vmc), that had I put the gear up before it happened, I can’t honestly say that I would have remembered to lower them again.
To give you an idea of how fast it all happened; from the moment I rotated the plane, to the moment I brought it all the way around the pattern and got it back on the ground lasted a grand total of less than two minutes.
The airport emergency fire/rescue crew had not even gotten out of their station bay by the time I landed.
So, for me, this is one of the reasons why I don’t touch any levers or anything else until reaching a safe altitude.
But, there may be other things you need to consider.
For example, if the plane you’re flying has a gear retraction speed (Vlr), you made need to get the gear up before you reach 500 AGL to avoid exceeding this speed.
In this case, I get the landing gear up before Vlr, but I still don’t mess with the power settings until reaching 500 ft. AGL.
After the initial climb-out and completion of the departure checklist, and having found that everything is operating like it’s supposed to; next up is the cruise climb phase.
Now it’s time to get busy moving things:
ADJUST THE THROTTLE (MP) FIRST
Start by moving the throttle lever back until the manifold pressure gauge reads the proper value. In the case of flying a PA-28R-200, we’re looking for 25 inches.
ADJUST THE PROPELLER (RPM) SECOND
Then we’ll slowly move the propeller lever back to 2,500 RPM. This is the cruise climb setting for a Piper Arrow - PA28R-200, and what is often meant by “squaring up” the power settings.
Once we’ve reached our cruising altitude, we have more options for throttle/MP settings, so, having the POH within reach to reference may not be a bad idea.
Ultimately, the power settings you choose will depend on the objective(s) of your flight.
Are you just going out to the local training area where you may not be too concerned about fuel burn, or is it a long cross-country flight where fuel burn may be more of an issue?
Either way, this is where we’ll reference the POH to find the best MP/RPM setting.
Looking at the POH for a PA28R-200, we can choose throttle settings between 15 and 23 inches MP and prop settings between 2,100 and 2,400 rpm.
At 5,000 feet and standard temperature, pulling the throttle back to 21.7 inches MP with a prop setting of 2,100 RPM, would give us 55 % power, a fuel burn of around 8.2 Gallons per hour, and a TAS of 138 MPH.
At 5,000 feet and standard temperature, pulling the throttle back to 21.7 inches MP with a prop setting of 2,400 rpm, would give us 65 % power, a fuel burn rate around 9.2 gallons an hour, and a TAS of 151 MPH.
MAXIMUM PERFORMANCE CRUISE
At 5,000 feet and standard temperature, operating at full throttle with the prop set to 2,400 rpm, would give us 75% power, a fuel burn rate of around 10.2 gallons per hour, and a TAS of 162 MPH.
Now, if you’re just flying out to the local area, you may not bother with, or even care about the power settings for cruise flight.
I’m not messing with it when I’m only flying 15 or 20 miles from my home airport.
I just make sure to keep the power setting within limits.
But if I’m flying a cross-country of any real significant distance where fuel burn matters to me, I take a good look at the different power settings (in the POH) and use what works the best for the situation.
MAKING ALTITUDE CHANGES
Since no flight ever goes exactly as planned, we may find the need to change altitude after we’ve established cruise flight.
If we’re flying at 5,000 feet and decide we want to climb to 7,000 feet, we start by moving the blue prop lever forward, increasing the rpm to 2,400, and then moving the throttle forward to increase mp to 24 inches.
After leveling off at 7,000 feet, we can pull the throttle back to 21.2 inches mp and then pull the prop back to 2,100 rpm to achieve 55% power (economy cruise), or 21.3 mp and 2400 rpm for normal cruise at 65% power.
Descending is the easy part.
If we’re flying at 7,000 feet and want to descend to 5,000 feet, we simply pull the throttle back to the desired setting and let the nose drop to descend until we begin to level off.
After reaching our intended altitude, it’s only a matter of increasing the throttle back to our cruise power setting.
Nothing to it, right?
This is the last important step in flying an airplane with a constant speed propeller.
All that’s left to do now is to hit the traffic pattern and land.
Just before, or upon entering the traffic pattern, we need to slowly move the propeller lever to the full forward position.
This is so that if we need to go-around we’ll have the maximum climb performance available.
I’ve seen pilots push the prop full forward while still ten miles from the airport.
While there isn’t necessarily anything wrong with doing this, unless the POH or your company’s operating procedures call for it, under normal conditions I see no reason to push the prop to the full forward position so far out from the airport.
If anything, it will annoy the hell out of you if you still have the power up.
TRAFFIC PATTERN & LANDING
Once we’ve entered the traffic pattern, we simply move the throttle forward (remember, the prop is already full forward) or back just like we do in an aircraft with a fixed pitch propeller.
And lastly, after turning final, make one last check just to make sure the prop is still full forward in case you need to go around.
I’ve seen pilots accidentally pull the prop lever instead of the throttle while trying to make last minute power adjustments on final.
So, a quick glance down to verify that your hand is actually on the throttle and that the propeller is full forward may not be a bad idea.
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