After many incremental improvements (as well as a few missteps), I finally landed on a solution that offers me near silence and a calm bubble of air in the cockpit of my Multistrada.
Like many of you, I followed the various threads here on "hiss flaps." And also like many of you, I have Barkbusters installed over my handguards. I tried fashioning folding hiss flaps (not unlike gabeschine's hinged hiss flaps
), but I finally just settled on a simpler solution that mounts the flaps onto the windscreen itself.
I cut the flaps out of a sheet of ABS plastic and heat-formed them with a hot-air gun. I call them "roar flaps" because the turbulent air hitting the bottom of my helmet sounds more like a roar to me and less like hiss. These roar flaps significantly reduce that turbulence.
The F.Fabbri screen
is slightly taller than the stock screen and not much wider. But crucially, it has little "winglets" that I was able to heat-form into mounting “platforms” for my homemade roar flaps.
I actually started with these spacers and the stock screen. Yes there was improvement in terms of reduced noise, but there was also improvement in terms of ergonomics. With the spacers, I have more room behind the screen to lean forward during spiriting riding.
When I switched to the taller F.Fabbri screen, the spacers were a necessity -- without them, I would hit my helmet against the lip of the screen, especially while mounting or dismounting.
Importantly, the Aztec spacers combined with the F.Fabbri screen allowed me to mount my roar flaps out of the way of my Barkbusters, even at full steering lock.
StolSpeed vortex generators
With the roar flaps, F.Fabbri screen, and Aztec spacers, the silence was golden. Unfortunately, that bubble of calm air was not very wide. If I moved my head just a couple inches left or right, once again my helmet would be thrashed with turbulent air and my ears would be tortured with the deafening roar. And if I happened to be passing a large SUV or truck, the bubble of calm air would mostly disappear.
To better understand where the turbulence was being generated, I covered my windscreen with homemade telltales (pieces of yarn taped down so that they show the flow of the air) and rode around at various speeds. I realized that a significant source of the turbulence was from the screen pushing the air diagonally upwards to the left and right -- at the correct angle to hit the bottom of my helmet when I leaned slightly left or right.
So I mounted StolSpeed vortex generators
with 30 mm spacing at 15 degree angles to the streamlines indicated by the telltales. Wow, what an unbelievable difference!
I can now move my head almost a foot in either direction and stay in smooth air. Who knew a handful of tiny plastic vortex generators could widen the sweet spot by so much?!?!
(BTW, I purchased my StolSeed vortex generators from Aircraft Spruce
, who shipped them out the same day. I received them two days after I ordered them.)