Tail Extension for the DFXL

I’ve seen old photos on the internet of some custom modifications on Daniel Fenn’s DF. These mods were never made available for sale. One that looked interesting was the tail extension shown below.

A friend of mine, Doug from Riverside, recently was able to talk Daniel into selling him a couple of copies. Doug then surprised me by sending me one. I know that the extension probably wouldn’t make any speed difference for me at the speeds that I travel, but I wondered if it might improve stability in cross winds.

I’ve been working with Peter Borenstadt on a few aero pieces for his upcoming Battle Mountain run in his DF (see the “aero” hood in an earlier post). Peter had a home made tail extension so I asked him if he’d like to borrow the real thing. Of course he said yes. Before shipping it off to him, I decided to make a quick mold and copy just in case anything happened to the original. Making the mold wasn’t difficult. But it was tricky laying up the part because of its very thin trailing edge.

Here’s the original extension with temporary flanges and the resulting 2-piece mold.

To lay up the trailing edge of the part, I chopped up some carbon fiber material into short strands. I shaped a piece of wood with a skinny rounded tip that fit into the radius of the trailing edge. After applying the gel coat and letting it partially cure, I put the chopped carbon fiber along the trailing edge and up the walls a bit then tapped it into position with the stick. Then I just wet laid up 2 layers of cloth in the rest of the mold and overlapped the chop. The part turned out pretty nice with no voids but a bit heavier than the original. The original was just a single layer with no gel coat.

Here’s my copy of the tail extension, painted to match

I tried it out for the first time yesterday on a nice ride with my friend Gregory (who rode my WAW). I couldn’t feel any changes in stability nor speed. At least my red electrical tape mounting system worked as the tail didn’t fly off during the ride.