Online Community of Zenith Builders and Flyers
Dr. Andy Elliott (the Dr part is in Aerospace Engineering, he knows a bit about drag and stuff) built and flew a 601XL taildragger that was a pretty good performer. I expect you could find some of his old posts here in the archives that detail some of his mods I think the current owner of the plane is in this forum so maybe he can send some pictures. The only picture I can find in my computer is not very high quality but it shows the three things I'm about to discuss.
Dr Andy made a composit fairing for the tail feather intersection area - a one piece fairing that smooths in the front base of the vertical fin and the front intersection of the horizontal stabilizers. The part that smooths the horizontal stab to the fuselage also comes forward to form a strake to clean up the airflow in that area. He also fabricated fairings to cover the main gear mounting brackets and bolts and stuff. He also used small main gear tires, 5.00 by 5 I think, and enclosed them in very snug fairings that also surrounded and faired in the brakes. I think the wheel fairings are from Van's but I'm not sure. He claimed to have gained quite a bit of speed from those three things but I don't recall how much.
Dr Andy did not make a fairing for the wing root area. Others have but I recall him stating that he did not think it would particularly help the 601XL. That is an old memory and might not be accurate so don't take it as gospel.
The picture is not great but it gives you the idea. I'm sure you can find more details with some searching.
You will find some information, I believe the wing root fairing does increase airspeed ; as well as keeping cooling drag low, and having an aerodynamic cowling including spinner. Some aerodynamicist's see little benefits in fairing the landing gear attach area ( at least in tri-gear setup) Good prop helps as well
I gained about 5 mph by raising the flaps about 1.5 degrees above neutral . I loosened the jam nut on the flap motor to adjust the flaps above neutral and re-tightened the jam nut.. I don't remember if it shortened or lengthened the threaded rod. . Simple fix to increase the cruise speed . Doesn't cost anything and no permanent mods. I can't take credit for the idea as other aircraft (Maule) did it first. My cruise speed went from 115 mph to 120 mph.... Cont. 0200 engine. Whirlwind 2 blade (GA200CN) ground adj. prop 72" 12.7 pitch I added a 4" spacer block to the front tire to raise the front up a little to compensate for the prop length.