Flight Ops

Engine Power Settings For Climb and
The Myth of Climbing At Reduced Power

Bob Kromer
MAPA Executive
Director & Former Engineering Test Pilot

Editor's Note The first ten years of my career in general aviation was flying as an engineering test pilot for first Cessna and then Mooney Aircraft Corporations. I was fortunate enough to work on several developmental and certification flight test programs during this period. I was part of the flight test team that did the original Cessna P210 test program, the T210N and normally aspirated 210N, M2OJ and M2OK (231) model year changes, the M2OL Porsche initiative flight testing and the complete development and Certification program for the M2OK (252). This much flight testing on piston powered airplanes full of instrumentation gives one a good feel for what a piston engine will and won't do. It also brings one into contact with some of the best engineering talent and experience that Lycoming and TCM have (or had) available.

From this flight testing experience, I would like to share some of my opinions and feelings concerning the operation of our airplanes from an engineering point of view. I know that my opinions may differ from yours. I certainly don't want anyone to get the idea that I am a "know it all". Quite the contrary - I am still learning every day, even after 4500 hours in the cockpit. If you have different opinions or better ideas, I am always receptive to them. That is the reason for the "Letters" section of this magazine - to share your opinions and ideas with 5,000 of your fellow Mooney pilots.

With that said, my first article concerns some ideas on how to best climb our airplanes and the idea (or myth) of the engine power reduction after takeoff. Here are some suggestions I have on these subjects and the procedures I use in my everyday flying. They have served me faithfully for lots and lots of hours, but if you have some thoughts or other ideas, we look forward to hearing from you.

Lately we've been receiving lots of calls from pilots who have just bought a Mooney (old or new) with questions on how to most efficiently operate their airplanes. Seems they've flown Cessnas and Pipers, but nothing with the performance and complexity of the Mooney. They want to fly as efficiently as possible, but want maximum performance from their airplane. After all, that's why they decided on the Mooney.

In the course of these discussions, one of the primary areas we talk about is power settings for climb. The other is power settings for cruise. Concerning climb procedures, I am asked about what procedures to use for maximum climb efficiency and where the reduction to 'climb power' should be made. My answers surprise many.

From the hours I have flown installed power and cooling climb tests for FAA certification purposes, I would like to share with you my opinions on the best power settings to use when climbing a normally aspirated or turbocharged engine in a Mooney and how to obtain the best efficiency while climbing to altitude.

Normally Aspirated (Non-Turbocharged) Power Settings for Climb
For a normally aspirated (non-turbo) engine, full throttle, maximum rated RPM and aggressive leaning to 100 degrees rich of peak are the general rules I find most efficient. Additionally, Mooneys like to climb at airspeeds higher than Vy as long as terrain and ATC permits the slightly reduced rate of climb that results. An old test pilot at Mooney once told me the wing on a Mooney works most efficiently at around 120 mph. I think that is still true today, although with the higher weights we fly today it's probably closer to 120 knots than mph.

There are all kinds of advantages to climbing at higher airspeeds. Better engine cooling results, as does the ability to cover the ground faster during the climb. You can see better over the nose and you can trail the cowl flaps to 1/2 open if you wish to reduce some drag.

With that said, here is my general list of guidelines for climbing a normally aspirated Mooney the most efficiently to altitude:

Full throttle. Keep the power tip. The induction system is tuned for full throttle settings--the cylinders get a more even distribution of induction air with the throttle full open. Unless specifically required by the manufacturer in the POH (and the Mooneys we fly are not), forget that old practice of reducing the throttle after take-oil to "save the engine". Forget the old "25 squared" idea. There is no reason on a normally aspirated engine to reduce the throttle for climbs. Why sacrifice climb performance for nothing?

Maximum rated RPM. Static thrust (the thrust the propeller produces with the airplane standing still) increases with RPM. Static thrust is also stronger at climb airspeeds with higher RPM. The engines we fly are rated for continuous operation at max RPM (redline). So why not climb there? Your thrust will be better and your climb to altitude will be quicker. The only area where reducing RPM for climb might be a consideration is over noise sensitive areas in the departure path of the airport. But Mooneys don't put out a horrible exterior noise profile like a Cessna 185 cranking away at 2800 rpm. And the idea of reducing the RPM in climb to "make the engine last longer" is simply wrong. You can reach TBO operating at 2700 rpm while climbing just as easily as climbing at 2500 rpm.

Mixture leaned to 100 degrees rich of peak EGT (exhaust gas temperature).
You can leave the in mixture control at fill rich until you reach a density altitude of 3000 feet or so, but after 3000 feet of density altitude, get on that mixture control. Lean to peak, then enrichen to 100 degrees rich of peak. That's approximately best power mixture. Here, the fuel/air ratio is set to produce the most horsepower. That's exactly what you need for climb--horsepower. Certainly, you need to monitor the cylinder head temps and the oil temps with the mixture leaned in the climb, but I think you will find that they will be satisfactory, especially if you are climbing at an airspeed higher then Vy (see item 4). Most normally aspirated engines have good cooling margins in climb. Take advantage of this with a mixture setting reduced from lull rich. I have actually seen Mooneys climbing with black smoke coming from the exhaust. The mixture is so rich that the engine is flooding. I'm amazed these airplanes have enough horsepower with mixture settings this rich to even climb. The mixture setting to climb with: 100 degrees rich of peak.

Airspeed at some value above Vy
How much airspeed above Vy will vary, but generally you will find 15 to 20 knots works the best. FAA certification flight tests must demonstrate the engine will cool during a sustained climb at Vy. Any airspeed above that is a bonus for cooling. Why not lower the nose a little bit and accelerate to Vy+15 or Vy+20? As long as either terrain or ATC will allow a slightly less climb rate, the advantages of a higher airspeed climb are better engine cooling, better over the nose visibility and more horizontal distance traveled over the ground during the trip up to cruising altitude.

For normally aspirated Mooneys, try climbing at full throttle, max rated RPM, mixture 100 degrees rich of peak EGT, airspeed at Vy + 10 or 20.

Cowl flaps modulated between full and 1/2 open, depending on CHT and/or Oil Temp.
Lots of pilots think those cowl flaps have to be full open during the climb, but they don't. Use them as necessary keep the CHT and Oil Temp below the top 1/8 of the green are. The advantage of trailed cowl flaps is less aerodynamic drag and better climb performance. Trail them to 1/2 open if you can.

So there you have it- my suggestions and opinions for climbing normally aspirated Mooneys in the most efficient manner. Your techniques and opinions may vary from mine, and that's great - whatever works for you. But when I'm flying a normally aspirated Mooney, you'll find me using the above techniques for getting to altitude in the most efficient manner.

Turbocharged Power Settings for Climb
Now, lets talk about an entirely different animal - the turbocharged Mooney Here things change. Turbocharged engines are massive heat producers. Turbochargers are great devices for boosting power at higher altitudes, but the penalty we pay for this boost is heat.

As pilots flying turbocharged engines we have to manage this heat carefully. In a normally aspirated engine, there are generally all kinds of cooling margins, giving us the ability to aggressively lean. In a turbocharged engine, those margins are much slimmer. We have to he careful, we can actually do some serious damage to a turbo engine if we don't keep it cool in the climb. Keeping this in mind, here is my checklist for climbing a turbocharged Mooney to altitude:

Manifold pressure at redline or somewhere within three inches of redline.
Again, the turbocharged engines we fly in our Mooneys are all rated for continuous operation at maximum rated power. That's redlining manifold pressure and RPM. But you've got to be careful. Remember, our cooling margins with a turbocharged engine are much less than our normally aspirated friends, especially in climb. But the advantages of climbing with the manifold pressure at maximum are significant--better climb performance and more even induction air being delivered to all the cylinders But be careful - if CHAT or Oil Temps approach 20 degrees or so of redline be ready to back off the manifold pressure If the temps start getting high, back off the manifold pressure a little bit. On a really hot day, that reduction might be as much as 5 inches or so. But for most conditions try to climb at maximum or near maximum manifold pressure.

RPM at maximum continuous. Keep the RPM up for the same reasons as a normally aspirated engine. Static thrust is better at maximum RPM, so take advantage of this and climb at redline (maximum continuous) RPM. And with a turbo engine, you really don't want to heat a condition of low RPM and high manifold pressure. This is hard on a turbocharged engine. The turbocharger is being forced to work really hard (spin fast) to produce high manifold pressure at low engine RPM. Try to avoid this condition in the climb. Keep the RPM up.

Mixture leaned to 125 degrees rich of peak TIT (turbine inlet temperature). Again, the idea is best power mixture for maximum horsepower. But be careful. It's unfortunate, but full rich fuel flows are sometimes set by the manufacturer to cool the engine with fuel. That's terribly inefficient, but is a fact of development and certification flight testing. As long as the temps are in the green, it's okay to lean to 125 degrees rich of peak TIT. But if the oil and the cylinders start getting hot, better enrichen a little more - say to 150 to 200 degrees rich of peak.

Airspeed at some value above Vy, terrain and ATC permitting. Airspeed above Vy is our number one ally in the climb to keep turbocharged engine temps in check. Remember, FAA certification testing requires satisfactory engine cooling in a sustained climb at Vy at maximum rated power. So anything we can do airspeed-wise above Vy is a bonus. Since there is usually an excess of engine power in a turbo engine, I love to climb a profile in a turbocharged Mooney at Vy +20, 30 or even 40 knots. And the engine loves me for doing this.

For turbocharged Mooneys, try climbing at maximum manifold pressure, max rated RPM, mixture 100-150 degrees rich of peak TIT, airspeed at Vy + 20 or 30.

Cowl flaps modulated between full open or 1/2 open, depending on CHT and/or Oil Temps. At lower airspeeds, the cowl flaps should be full open. At the higher climb airspeeds. 1/2 open works better. Again, we have lesser margins to work with in a turbocharged engine, but there is nothing to say you can't trail the cowl flaps in climb as long as the engine temps allow it. Cowl flaps trailed to 1/2 open reduce the aerodynamic drag on the airplane significantly and will result in better climb rates (as much as 50 fpm).

So there you have it: my recommendations, suggestions and opinions concerning engine power management during climbs. These ideas and suggestions I have developed after flying engineering flight tests for many years early in my career and have served me well in flying Mooneys for 3000 of my 4500 hours. Except for the combination of a hot day and a turbocharged engine, notice that there is not one mention of reducing power for the climb. The old "25 squared" idea is nowhere to he found.

The bottom line is try keeping the power up, the mixture leaned and the airspeed above Vy. If you fly a normally aspirated Mooney, these suggestions are bulletproof. If you fly a turbocharged Mooney, be aware that you are flying an engine that is a big heat producer, so be a little more conservative with your engine in the climb. But overall, I think you will find these suggestions and opinions will work for you just like they do me.

Next month we'll look at some ideas concerning engine operation and leaning techniques in level cruise flight. Until then, keep that power and airspeed up in the climb!