I want to analyse NACA airfoils using BEMT. I have only yet done it for basic symmetric airfoils. I would like to know what all assumptions remain same in NACA airfoil analysis and to what degree it is accurate. Like for starters, will accounting for Cl-alpha change and geometrical changes in angle of attack be enough to analyse NACA airfoils?

  • $\begingroup$ To clarify: I usually hear of BEMT to analyze rotors or propellers, given particular airfoil sections. Are you trying to analyze a variety of NACA airfoils so that you have an expanded set of airfoil tables to reference in a BEMT analysis? $\endgroup$
    – Marius
    Dec 5, 2020 at 1:00
  • $\begingroup$ It is for analysing rotors. I cant think of any difference to BEMT analysis except for the airfoil table changes when NACA airfoils are considered. I feel like the accuracy is going to be way off if that's just it $\endgroup$ Dec 7, 2020 at 15:44
  • $\begingroup$ Technically, symmetrical airfoils are just NACA00xx airfoils, and I think that frames the problem better. If you do not use the right airfoil data -- particularly when moving from symmetrical to asymmetrical airfoils -- you are going to see significant errors in the results for sections that are pre-stall. But that's it if you are doing a traditional BEMT analysis...the described change in airfoils won't effect compressibility effects since neither are supercritical airfoils, and that's the only other change that comes to mind outside of the airfoil tables. $\endgroup$
    – Marius
    Dec 8, 2020 at 3:14

1 Answer 1


The only difference would be the lift and drag coefficients used. You'd need those to be specific to the airfoil(s) you choose. Momentum theory is otherwise not sensitive to the airfoil shape.

Given the same lift and drag, momentum theory will give you the same induced velocity.


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