Description: From the outset of my Europa-build, I've felt that the standard XS wing root fairing fell short of an optimum fuselage-wing intersection and did not adequately address the issue of interference drag. Here are some photos which describe the fabrication of a modified wingroot fairing designed to replace the portion of the standard fairing which is aft of the spar.
I've not discovered any specific formulas on fuselage/wing fairing/fillets, nor do I have any training in aerodynamics, but I have studied examples like the Hughes H-1, the Spit, P-40, and the more modern Cirrus and Lancair. I've benefitted from email exchanges w/ several knowledgeable people, limited discussion of the topic on the forum, and Mike Arnold's videos of his very efficient design which squeezed 213 mph out of 65 hp. Somewhere along the way, I've been told that forward of the center of lift, a nominal radius at the intersection does the job. It appears to me that the general principal is to prevent the low pressure airflow over the wing aft of the center of lift from getting sucked into a tight radius intersection between wing and fuselage which then becomes turbulent and draggy. I am particularly indebted to Justin Kennedy and the work he has done in this area on G-ZTED; I thank him for his encouragement and thoughtful comments.
One of the design goals was to ensure that the new fairing would allow for transport on the standard Europa (mono) trailer; consequently, a portion of the fairing is bonded to the wing, a portion gets bonded to the flap, and the rearmost portion is bonded and fairs into the side of the fuselage.
Another goal was to not increase the frontal area, and by all practical means ensure that the port and starboard fairings were as near to being perfectly symmetrical as possible.
Its my understanding that interference drag between fuselage and wing does not build up forward of the center of lift, consequently I saw no reason to change the 1" radius of the standard XS fairing forward of the spar. However, I have increased the radius at the intersection as a function of the angle of incidence and the thinning of the airfoil as one moves towards the trailing edge. I established a waterline 1" above the top surface of the wing; moving aft, the distance between the wing surface and waterline generated an increasing radius which was recorded at station points every 2.25".
I have taken molds which are stabilised with armatures so the wingroot fairings can be replicated; contact me off-list if anyone would like to buy a set.
