Aeronautical Engineering/T-Tail Fairing

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Question
I'm designing a hydrofoil sailboat and I'm curious as to if the interference drag would be high enough to require a fairing. This hydrofoil uses a NACA 0014 airfoil and 3 sections come together. One comes down just for structure and the other two meet at the bottom of it at about 22 degrees. You can see an image here: http://s32.postimg.org/gkbxjudad/Wing_Fairing_Test_2.png . This image includes my best guess at what the fairing should be shaped like. I used a lathed Naca 0028 airfoil for the fairing and stretched it to 2.5x the chord of the wing sections. I set it to where the fairing extends 1 chord in front of the wing sections and 0.5 chord behind them. When I first designed the wing, I didn't think interference drag would play a very high role, but now I'm not so sure. I know some aircraft have similar fairings on similar wing sections (T-Tails), but high performance gliders don't tend to have them. It seems only very fast aircraft have them and in slower ones interference drag isn't a big enough issue to require them. This hydrofoil only goes about 32 mph maximum and has a chord of 4.5 inches. Since it's water though and not air, it's like the wing is traveling at a much higher speed than it is. Do you think interference drag would play a large enough role to be of much use in the case of this hydrofoil? If so, do you think this fairing would work alright, or do you have any suggestions as to how to set a fairing like this?

Answer
Interference drag of intersecting struts can be substantial, and does not disappear with increased airspeed. S.F. Hoerner (Fluid-Dynamic Drag) shows that the drag from an unfaired strut junction can be 10 times that of a properly faired junction. Unlike your image, Hoerner shows that a proper fairing or fillet at the junction extends downstream of the junction as much as one chord aft, not upstream. I suggest looking at his book (chapter VIII). The book is a little pricey online, but may be available in an engineering library or as a pdf file. Search on Google.

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Paul Soderman

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Aeronautics, Aerodynamics, Fluid Mechanics, Aeroacoustics, Noise Control, Muffler Design, Wind Tunnel Research.... I know nothing about India - do not ask about schools, jobs, application requirements, career choices, etc. for India. Please, no text message verbiage; I prefer full words in full sentences. Thanks.

Experience

38 years as research engineer at NASA

Publications
AIAA, NASA

Education/Credentials
B.S. and M.S. Aeronautical Engineering - U. of Washington, Graduate work Standford U.

Awards and Honors
AIAA Associate Fellow (American Institute of Aeronautics and Astronautics)

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