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1 Answers

Re-setting power on takeoff

Asked by: 1198 views Student Pilot

My new instructor has me resetting MP to 25 (from full) and RPM to 2500 (from 2700) on takeoff (typically around 200 AGL)... chatted with my first instructor and he suggested against messing with MP on takeoff..  any thoughts? Thanks, Jeff

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1 Answers

  1. John D Collins on Jan 01, 2016

    Unless the engine has a limitation declared in the POH, I use full power until I have climbed to a safe altitude and then only reduce the RPM.

    The engine will run hotter if you pull the throttle back because at the full throttle position, it is set to run an over rich mixture. Have you ever noticed that a substantial pull of the throttle does not affect the performance in any material way and it takes some significant movement of the throttle before the MP begins to drop. This is because all you are really doing on the initial retarding of the throttle is leaning the mixture, which makes the engine run hotter in the climb. Eventually, the MP will begin to drop. So at sea level, assuming you are getting 28.5 inches of MP at full throttle, bringing it back to 25 inches will reduce your climb performance, make the engine run hotter, while giving you more pilot work to do. If your airplane is typical, it will probably average 700+ FPM in the climb, so by the time you climb to 3500 feet, the throttle will be back up at full power if you maintain 25 inches adjusting it up as you go to maintain the 25 inches.

    With most engines being rated for continuous usage at full throttle and full RPM, it makes very little sense to reduce and continuously adjust the MP just to climb at a reduced power for less than 5 minutes. In the old days, instructors taught to bring the throttle back and the RPM back at 200 feet. This is not the current thinking. Today, most instructors will teach to leave the throttle at the stop, and climb to altitude before adjusting the throttle. They also teach to reduce the RPM to reduce noise and be a good neighbor.

    I routinely climb my Bonanza at full throttle and full RPM to at least 1000 feet AGL and then reduce the RPM for a cruise climb. There is nothing wrong with climbing to altitude will full throttle and RPM, you will hurt nothing and get to altitude quicker.

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