Been contemplating the transponder/ADS-B antenna...  Monopole or blade?  Seems like most people are going for the monopole, but I was told by someone at TAF USA to go with a blade because it won't break as easily as a monopole.

Also, my own research shows that the monopole does not actually meet the Garmin antenna requirements for the GTX 45R.  See thread here: http://www.vansairforce.com/community/showthread.php?t=93785

But, if you read down the comments on that thread you'll see that while a monopole doesn't meet the requirements, it's probably good enough.

The blade, despite it's much larger size, has much lower drag than a monopole.  I'm not surprised by that since a circular cross section has terrible drag (my fluid dynamics class in college was one of my favorite classes!  To demonstrate a shock wave the prof exploded an M80 in class. :-})

Of course a monopole is easier to install...  Decisions decisions!

Decision: I'm going to go ahead and fabricate a backing plate and see how that comes out.  My two considerations are that it's firmly attached to the two adjoining ribs and that the mounting holes line up the blade perfectly with the airflow.  I think fab the plate without the holes, install it, then drill the holes to perfectly line up.