How do I find the three factors $c_{h0}$, $c_{h\alpha}$ and $c_{h\eta}$?

  • 1
    $\begingroup$ Use eta ($\eta$) for deflection. Use XFOIL to determine the coefficients. $\endgroup$ Oct 15, 2016 at 7:48
  • $\begingroup$ i apologize, may i have the tutorial XFOIL for calculate coefficient moment? actually i never use XFOIL. thank sir. $\endgroup$ Oct 18, 2016 at 18:50

1 Answer 1


First download and install xfoil from this site http://web.mit.edu/drela/Public/web/xfoil/
if you use ubuntu - sudo apt-get install xfoil

user manual and typical session inputs are also there. please refer to them as you haven't used it before.

And there are many video tutorials in youtube.
[Link removed I cant put more than 2 links here- Just search xfoil tutorial in youtube]

For this specific case;

  1. open your airfoil in xfoil
    xfoil name.dat
  2. Set the flap as you want enter GDES and FLAP and follow the prompts.
  3. Type these commands in sequence
  4. Enter OPER menu and set the RE number
    visc 1e6 (1 million Re for this case)
  5. type these commands in sequence
    hinc (hinge moment togle enabled)
    pacc (accumilate polar - give a file name)
    aseq 0 10 0.5 ( sequence of alfa to run - here from 0 to 10 in 0.5 increase)

  6. Open the resulting file. which has two coloums along with other parameters to show alfa and hinge moment. (first and sixth) enter image description here

plot it or linearize it or whatever you like to do to find the above parameters.

PS: Another suggestion is XFLR5. It is same as XFOIL but with GUI. you may find it easier.


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