Welcome Guest. Sign in or Signup

3 Answers

Propeller pitch

Asked by: 7470 views Aerodynamics, Aircraft Systems, General Aviation, Student Pilot

hey everone

i am a bit confused about propeller pitch. propeller pitch is the forward distance which the propeller blades cover in one rotation.now in respect of a piston engine aircraft having constant speed HARTZEL propeller the manufacturer has defined different RPM for take off, cruising flight and landing. My question is why it is recommended to Take off with high Rpm and cruise at lower RPM?

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

3 Answers

  1. Jim Foley on Sep 15, 2012

    Propeller pitch is the angle of attack which the airfoil (prop blade) meets the oncoming air; just like a wing. A constant speed/variable pitch prop can be though of similar to the gears on a car. Assuming the same RPM, a lower pitch will provide more power. On takeoff, you want maximum engine power (RPM), you set the prop to the lowest pitch. In cruise, you slow the engine down (reduce RPM) and increase blade pitch. The prop is taking a bigger “bite” out of the air, thus more speed. As I said, you can equate this to shifting to a higher gear in a car. Read http://www.free-online-private-pilot-ground-school.com/propeller-aerodynamics.html for more info.

    0 Votes Thumb up 2 Votes Thumb down 2 Votes

  2. Brian on Sep 15, 2012

    Brake horse power is directly proportional to engine RPM. The higher the RPM the greater your BHP. This explains the desire for high RPM on takeoff.

    In flight the propeller is just like your wing, an airfoil. Each airfoil has an L/D max, just like your wing. Recall this corresponds to best glide, or a point of maximum efficiency for the airfoil; occurring at a specific AOA.

    With a propeller, if pitch is kept constant, as forward speed is increased there is a decrease in the propellers AOA. By altering the propellers pitch we keep the propeller’s AOA at or closer to it’s L/D max angle. Thus improving it’s efficiency in both cruise and climb applications.

    I really dislike the ‘takes a bigger bite out of the air’ phrase because in reality the propeller AOA is not changing as this statement implies. Instead we alter the blade pitch in an attempt to keep the AOA relatively constant as forward speed is increased; that is, at L/D max. Think of how the two relative winds, forward speed and propeller speed, interact when trying to grasp this concept.

    +5 Votes Thumb up 5 Votes Thumb down 0 Votes

  3. H. Odell on Sep 16, 2012

    When transitioning to cruise from low pitch climb position and full power, you reduce the rpm to cruise speed and then increase the pitch to a predetermined manifold pressure as per the manual. At 10 to 14 thousand feet, you will not be able to have too much manifold pressure as the engine, having been leaned out carburator wise to the best mixture willl not be producing as much horsepower as it does at low altitudes.
    These propellers are called constanst speed as the RPM might otherwise increase in a decent, the propeller increases pitch thus keeping the RPM the same.
    Always reduce pitch before reducing rpm to keep from exceeding max. manifold press.
    I have often thought that this would be good for an auto automatic transmission. ie. control the manifold pressure for max power.
    BTW most engine manuf. have a min. manifold pressure, maybe 15 lbs.

    -3 Votes Thumb up 0 Votes Thumb down 3 Votes

The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.