The challenge to a aircraft antenna designer is to achieve reasonable RF performance across the VHF 18 MHZ bandwidth, minimize the drag, and have a robustness that will standup to hurricane force winds.
The bent element VHF antenna is a compromised design, not capable of the VSWR?s of a straight element VHF antenna in broadband conditions. Bending the element back near parallel to the ground plane, the element proximity to the ground surface and metal objects in the near field, all add to poor VSWR?s results.
Automatic antenna tuners do offer the antenna designer options of optimizing antenna performance over a very wide band but they add complexity, cost and little realized enhancement to the communication process in line of sight operation.
With that said, the key to 1/4 wave aircraft antenna performance is good grounding, most if not all, VHF antennas ground thru the mounting screws. Many use star type washers under the nuts to insure good contact from the mounting screws to the aircraft fuselage.
Sealing the antenna base to the fuselage can keep moisture out and minimize the effects of corrosion. The EAA has a good video linked below describing methods to seal the antenna.
In addition to the info in the video, I suggest masking the antenna base and fuselage so the sealant forms a neat 1/8? wide bead when the tape is removed.
http://www.eaavideo.org/video.aspx?v=1136841468001