ANN's Daily Aero-Tips (02.23.06): The Horsepower Curve | Aero-News Network
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Thu, Feb 23, 2006

ANN's Daily Aero-Tips (02.23.06): The Horsepower Curve

Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.") It's part of what makes aviation so exciting for all of us... just when you think you've seen it all, along comes a scenario you've never imagined.

Aero-News has called upon the expertise of Thomas P. Turner, master CFI and all-around-good-guy, to bring our readers -- and us -- daily tips to improve our skills as aviators, and as representatives of the flying community. Some of them, you may have heard before... but for each of us, there will also be something we might never have considered before, or something that didn't "stick" the way it should have the first time we memorized it for the practical test.

It is our unabashed goal that "Aero-Tips" will help our readers become better, safer pilots -- as well as introducing our ground-bound readers to the concepts and principles that keep those strange aluminum-and-composite contraptions in the air... and allow them to soar magnificently through it.

Look for our daily Aero-Tips segments, coming each day to you through the Aero-News Network. Suggestions for future Aero-Tips are always welcome, as are additions or discussion of each day's tips. Remember... when it comes to being good pilots, we're all in this together.

Aero-Tips 02.23.06

In Aero-Tips 1/8/06 we learned that the peak, or highest Exhaust Gas Temperature (EGT) is the benchmark for all mixture leaning. But how can we use this information?

Peak Horsepower

Engine horsepower follows a predictable curve in relation to EGT. Maximum, or peak horsepower occurs at about 80°F rich of peak EGT. That is to say:

  1. Carefully lean the mixture until you arrive at peak EGT
  2. Note the exhaust gas temperature at this point (Note: the precise temperature of EGT isn’t important; you’re looking for a temperature difference relative to peak)
  3. Carefully enrichen the mixture (add fuel) until the EGT drops about 80°F below that indicated at peak (Note: most standard EGT gauges are marked in 25°F increments... the horsepower curve is fairly flat at this point, so three lines, or 75°F rich of peak EGT, is very close)

No EGT gauge? You can approximate the same mixture setting in smooth flight by leaning for maximum rpm (with a fixed-pitch propeller) or maximum indicated airspeed (with either fixed-pitch or adjustable propellers). These methods, of course, are less precise.

You’re now at the mixture setting that provides the greatest horsepower for the manifold pressure and/or rpm you have selected. This is the mixture setting to select for maximum airspeed so long as it meets engine limitations, provides adequate cylinder cooling, and results in an acceptable rate of fuel burn for a specific flight.  Many sources call this the “Best Power” mixture setting, but it is “best” only if it meets the criteria I just listed.

For more information see www.advancedpilot.com.

Aero-tip of the day: Know what’s meant by a “peak horsepower” mixture setting, how to achieve it in the airplane you fly, and when it makes sense for you.

FMI: Aero-Tips

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