I had a look at both

What is the equation for calculating static thrust?


Is there any equation to bind velocity, thrust and power?

However, it does not mention how much would the thrust be affected by the amount of blades. e.g if it was a 20 blade propeller with a given RPM, how much would it affect the amount of thrust

Could you please kindly help me with this? Thank you

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    $\begingroup$ Hi and welcome to the site! The term you are missing, and why your searches are not yielding results, is solidity, and it indirectly represents the number of blades. $\endgroup$ Jun 26, 2019 at 11:13
  • $\begingroup$ Adding blades is actually bad for thrust. The only time you really need "more blades" is to reduce loading. Ideally you'd only have one blade on a propeller, but that has its own issues. The reason solidity is used in a formula is because it makes a reasonable approximation. The problem with blades is the interaction with them, so adding more creates aerodynamic issues (since blades operate in the wake of the proceeding one). A single formula doesn't scale that way. $\endgroup$
    – Ron Beyer
    Jun 26, 2019 at 11:58

1 Answer 1


The most simple propeller thrust equations replace the propeller with an abstract disk in which the flow is accelerated. How this disk is composed in detail does not matter. However, more elaborate codes which also model the helical wake of each blade will use blade count specific algorithms.

So the answer is yes, there are algorithms which account for the number of blades, but they are more complex than a single equation.

This answer shows how the number of blades of the propeller for the Supermarine Spitfire grew with engine performance, and this answer sheds light on the number of blades of helicopter rotors.

  • $\begingroup$ Hi Peter, thanks for the answer. Could you please point me into some reading about the more complex algorithms. And where would be the best place to find a list of propeller/turbine characteristic table? The propeller that I had in mind has more blades like a turbine engine without the compression&Combustion part (pretty much an 100%bypass turbofan if that makes sense). $\endgroup$
    – Scriptbaby
    Jun 28, 2019 at 16:28
  • $\begingroup$ @Scriptbaby: Something like this, maybe? For algorithms, I recommend Larabee, Liebeck or directly XROTOR by Mark Drela. Caution: It assumes lightly loaded propellers, and those with many small blades need more intricate codes. $\endgroup$ Jun 28, 2019 at 19:31
  • $\begingroup$ kaempf compared to the fantrainer, i want more blades. How about if we see it from a turbine engine design point of view? E.g Rolls, PW, GE. How would they, "roughly" calculate how many blades and what pitch are required for their fan? Sorry if this does not make sense $\endgroup$
    – Scriptbaby
    Jun 30, 2019 at 7:31
  • $\begingroup$ @Scriptbaby: It does make complete sense. Those fans are specific for very powerful engines which need to avoid large propeller (= fan) diameters, so they compensate with a high solidity. Make no mistake, they buy the capacity for a high thrust / mass flow ratio with a loss in efficiency. $\endgroup$ Jun 30, 2019 at 9:17

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