Welcome Guest. Sign in or Signup

2 Answers

Constant Speed Propeller and relation to manifold pressure setting.

Asked by: 3639 views Aircraft Systems, Commercial Pilot, Flight Instructor, General Aviation

Hello everyone,

I am currently doing my CFIA course in Arrow and let us say when we set up our cruise power at 2400RPM for good, and I noticed something strange when playing with throttle.

RPM was constant through out various manifold pressure setting(throttle), and when I decrease the throttle, the airspeed started to bleed off. Conversely with throttle pushed forward, airspeed picks up.

I understand that constant speed prop does its job maintaining constant RPM but my question is why airspeed decreases and increases at different throttle setting?

Is this because there is a change in prop pitch?

Steve.

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.

2 Answers



  1. EAD on Jul 03, 2016

    Chapter 11 of the Airplane Flying Handbook should have the answer you seek

    -2 Votes Thumb up 0 Votes Thumb down 2 Votes



  2. Skyfox on Jul 07, 2016

    As you change the throttle, the constant speed prop will increase or decrease the blade pitch angle to maintain the set RPM. Increasing the throttle and therefore power will cause the prop to react by increasing the blade pitch, taking a larger bite out of the air and increasing airspeed without increasing RPM. Likewise, decreasing throttle will result in the prop decreasing to a shallower pitch angle, taking a thinner bite out of the air which doesn’t generate as much thrust and reducing airspeed. And of course, if the throttle is brought back far enough the prop won’t be able to get any shallower and RPM will decrease along with airspeed.

    +2 Votes Thumb up 3 Votes Thumb down 1 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.