1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Lets talk Turbines

  1. Apr 17, 2005 #1
    Last edited: Apr 17, 2005
  2. jcsd
  3. Apr 18, 2005 #2

    FredGarvin

    User Avatar
    Science Advisor

    Jet engines have a thrust horsepower calculation, but I don't think it could be held applicable in this case. The rule is at 375 mph, 1 Lbf of thrust is equal to 1 HP.
     
  4. Apr 19, 2005 #3
    These Wren turbines are just under three inches in diameter..
    very cool stuff..
     
  5. Apr 19, 2005 #4

    Q_Goest

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Hey Fred, that works out, because if you say an aircraft is flying at 375 mph and that aircraft requires 1 lbf of thrust to keep it going at that speed, the power (force times distance per unit time) works out to 1 hp. But that's an arbitrary velocity. If the aircraft has more resistance, and can only fly at 100 mph with the same engine, then the equation results in a power output of 0.2667 hp. And if it's zipping along at 1000 mph, the power output becomes 2.667 hp.

    So there doesn't seem to be a correlation between hp and thrust. But there should be since the power actually equates to energy in (ie: energy burned in the engine).

    I always wondered about this one, how can you equate thrust to hp? Perhaps because it's "static thrust" one must be able to get a "thrust curve" which is analogous to a pressure curve on a centrifugal pump, along with an efficiency.

    There has to be more to it than simply thrust at 375 mph equates to a given hp.
     
  6. Apr 20, 2005 #5

    FredGarvin

    User Avatar
    Science Advisor

    You do bring up good points. Personally I have NEVER expressed a thrust producing engine in terms of horsepower. It is always in thrust. For some (unknown to me) reason there is a small need to express HP in this fashion. The relationship [tex] THP = \frac{F_n * MPH}{375}[/tex] is actually from a Pratt and Whitney reference I have. It is the only reference I have that even states it. What it's method of derivation is I really do not know.
     
  7. Sep 21, 2005 #6
    Oops my mistake..
    please disregard..
     
  8. Sep 23, 2005 #7

    Danger

    User Avatar
    Gold Member

    As I understand it, hp:thrust ratio depends on not only speed, but also altitude. I assume that it has something to do with factoring in air resistance.
    It always bugs me that a full-throttle jet bolted to a test stand produces zero horesepower.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Lets talk Turbines
  1. Turbine blades (Replies: 20)

  2. Wind turbine (Replies: 4)

  3. Wind turbine (Replies: 4)

  4. Wind turbine (Replies: 2)

Loading...