Formula for Aircraft Propeller Thrust

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Discussion Overview

The discussion revolves around the calculation of thrust produced by aircraft propellers, focusing on the relationship between propeller diameter, pitch angle, and thrust. Participants explore existing formulas and seek to understand how different parameters influence thrust in real-world applications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a formula for thrust that includes propeller diameter, incoming flow velocity, and fluid density, but notes the absence of pitch angle in the equation.
  • Another participant argues that pitch angle is indirectly accounted for through the additional velocity term (V1) in the original formula.
  • A different viewpoint suggests that any equation explicitly including pitch angle would also introduce unknown constants related to blade design, complicating the analysis.
  • A later reply introduces an alternative thrust equation that incorporates pitch angle, providing a different perspective on the relationship between thrust and propeller parameters.

Areas of Agreement / Disagreement

Participants express differing views on whether the original thrust equation adequately accounts for pitch angle. While some believe it does through the V1 term, others argue for the necessity of an explicit pitch angle component. The discussion remains unresolved regarding the adequacy of the original formula.

Contextual Notes

Participants mention the complexity of relating thrust to pitch angle and the potential for additional unknown constants in more comprehensive equations. There is also a reference to the derivation of an alternative equation based on Newton's laws, indicating a reliance on foundational physics principles.

Who May Find This Useful

Individuals interested in aerodynamics, aircraft design, and propeller mechanics may find the discussion relevant, particularly those looking to understand the factors influencing thrust generation in propellers.

tilopa
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I'm trying to understand thrust for a real world application. I found this formula:

T= pi / 4 x D(squared) x (v+V1/2) x p x V1

Where:

T thrust [N]
D propeller diameter [m]
v velocity of incoming flow [m/s]
V1 additional velocity, acceleration by propeller [m/s]
P density of fluid [kg/m³]
(air: = 1.225 kg/m³, water: = 1000 kg/m³)

I understand how increasing the propeller diameter would increase the "amount" of air and therefor increase thrust. But the equation does not account for the increased pitch angle of the propeller blades. Intuitively (and by Newton's Third Law of Motion) if you increase the angle of the blade against the air you will be pushing more air (greater "amount" of air), correct? So, does anyone have an equation for thrust that includes the propeller angle. Or an equation that I can use that includes pitch angle to replace the D2 value in this equation?

Thanks.
 
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the equation does not account for the increased pitch angle of the propeller blades.

I think it does. Changing pitch would change the V1 term.

I think if you find one that has pitch in it explicitly it will also have unknown constants that relate to the blade design. For example the torque won't be zero at zero pitch. It might not be a maximium at max pitch either.
 
Last edited:
Thanks, I'll check out those links.
 
tilopa, I know this thread is old, but I wanted to share with you an equation I came across recently for propeller thrust that *does* include pitch angle. Here is the simplified version of the equation:

F = 4.3924e-8*RPM*d^3.5/sqrt(pitch)*(4.23333e-4*RPM*pitch – Vac).

F is thrust in Newtons, RPM is rotations per minute, d is prop. diameter in inches, pitch is prop. pitch in inches, Vac is aircraft airspeed in m/s. The full derivation of the equation begins with Newton’s laws, and is shown here: http://electricrcaircraftguy.blogsp...tatic-dynamic-thrust-equation-background.html
 

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