×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Propeller efficiency versus efficiency losses.

Propeller efficiency versus efficiency losses.

Propeller efficiency versus efficiency losses.

(OP)

When you say that a propeller has an efficiency of 51%, does it then mean that the efficiency losses with respect to the ideal propeller are 49%?
My answer would be NO!
Why? Because the ideal propeller will have an efficiency lower than 100%! Therefore the losses with respect to the ideal propeller will be less than 49%.

Right?

RE: Propeller efficiency versus efficiency losses.

ONEMORECHANCE:   An ideal propeller has an efficiency of 100%.  The efficiency of a propeller is the same as other mechanical devices.  PowerOut / PowerIn.  If there is an actual propeller absorbing 100 hp from an engine then the propeller will generate less that 100 hp worth of thrust.  The propeller loses include, but not limited to: drag, compressibility, tip losses, etc.

Regards
Dave

RE: Propeller efficiency versus efficiency losses.

(OP)
Yes, it only depends on how you define it.
If defined as follows:
Overall Propeller Efficiency = Useful Power / PowerIn = (Useful Power / PowerOut)* (PowerOut / PowerIn)

Then an ideal propeller has efficiency < 100%, because Useful Power < PowerOut.
(Useful power is the Thrust * Airspeed)

RE: Propeller efficiency versus efficiency losses.

What effect does diameter have on speed... say from 78 to 84 inches but in the same blade shape... What effect does altitude have on all this?  Horsepower remains the same nad rpm remains the same

RE: Propeller efficiency versus efficiency losses.

the larger diameter creates a larger disc (D^2) and so produces more thrust (as you've described it ... same section, same rpm)  since you've specified same Hp then the power will be absorbed (by the propeller disc) at a lower velocity (P = T*V).  the caution is that as you increase the D and maintain the rpm, then you're increasing the tip speed (rpm*(2pi/60)*D/2) which could go supersonic and in any case may invalidate the assumption that the propellor is creating the same Ct.  

altitude affects things in a really complicated manner (write that in your answer and see how far you get !).  altitude typically reduces the power output of the engine (as you reduce the amount of O2 in the charge air volume).  supercharging helps maintain sealevel performance at altitude.  the V in the power equation above is true airspeed; the Thrust generated by the propeller (T = Ct*q*A) is, i think, relatively independent of altitude.

RE: Propeller efficiency versus efficiency losses.

Eighty two inch diameter Hartzell Super Scimitar prop turning 2500 rpm  and six and eight thousand feet  280 HP on a 3800 lb plane

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources