Expert: Paul Soderman - 7/24/2006

Question

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Followup To

Question -
while calculating the downwash correction factor for Agard-B model in low speed wind tunnel, the value of k=0.24, and "tail length/tunnel width" ratio=0.288. How would i find the value downwash correction fator against these values in the graph given in A.pope (Low Speed Wind Tunnel Testing) fig 10.28.

Also, what is the percentage variation between corrected and uncorrected data of CA, CN and Cm.

yours truly

Answer -
Sorry Farrukh - I have the second edition of Low-Speed Wind Tunnel Testing (Rae and Pope), and it does not have fig 10.28.  The information is in a different chapter.  So, I need more information about the graph you mention.  For example, what type of wind tunnel are you assuming ?  If rectangular, what is the ratio of tunnel height to width ?

Paul,

Thanks Paul for your being concern. In, your answer you've asked about the type of the tunnel and about the tunnel height to width ratio.
well, i m using a low speed closed return circuit type wind tunnel of rectangular testsection and its height to width ratio is 0.7

best regards.
waiting for your reply  

Answer
Farrukh

My understanding of the curves is that the downwash correction factor in your case, delta, is about 0.117.  This allows you to calculate the corrected lift and drag coefficients.  The pitching moment correction requires an estimate of the downwash correction at the tail location.  For that I got tau = 1.08.  I don't have time to work through all the equations, but I believe you now have all the information you need to solve the problem.

Paul