Artificial Feathers to Reduce Drag?

[theunchosen]

Originally Posted by Otto

Feathers, fur on otters and seals, etc. also act as compliant wall surfaces, helping to dampen the oscillation of turbulent flow at its source, thereby reducing drag. This per research by Denis Bushnell et al at NASA Langley in the 1980s, with whom I spoke briefly at the time.

Also, some homebuilt airplane guy in Alaska about that time tried an experiment where he says he put fur (coulda been polar bear fur, but I don't recall exactly) on his plane, and reported that it reduced the drag, presumably for the same reasons. He approached the Air Force with this idea, and they told him to take a hike. This per Sport Aviation article at the time.

Perhaps this phenomenon stems from the same concept as the Sinha deturbulator tape, which is claimed to counteract turbulent flow as it begins.

Comments?

I have never heard of this fellow, but what the site advocates is the same material that the US navy already deployed. As per my earlier post the technology was lifted off of Mako sharks(tests were prompted because the shark was able to achieve astounding power-weight ratio with normal drag).

That technology works by trapping a layer of fluid against the surface "permanently." It doesn't flow at all. The barrier allows for a semi-compressable membrane that can assume the most hydro-aerodynamic shape possible within the micro-meter thickness. The drag between the fluid air and the trapped air creates a lower drag. It would be like engineering panels on a car that could manipulate slightly to take advantage of instantaneous low or high pressure zones and then return to normal as they dissipate. Infinitely more efficient than actually using a mechanical system because the sensors would disrupt flow and the equipment would be bulky and too slow.

[Otto]

Google for "Sinha deturbulator tape." He's reportedly done work in conjunction with Mississippi State University, no slouch in the aero department. Doesn't answer emails, though. The soaring crowd was pretty stoked about this concept, and apparently did some comparative glide tests, and found the tape worthwhile due to significant gains in L/D.

Anyhow, I suspect there is more to it than maintaining zero flow at the skin surface, per shark skin. Denis Bushnell was ~27 years ago looking for a good shark to freeze and test in the NASA Langley wind tunnel, as part of his compliant wall surface study. The 3M riblet film used on America's Cup sailboats was based on the sharkskin concept, certainly good and an improvement, but perhaps not be the final word on optimum skin design.

Feathers evolved over millions of years to do several things, including streamlining, but also as insulation, chill factor being what it is at altitude and speed. Perhaps we should have a closer look at the Arctic Tern, which flies pretty much non-stop from pole to pole. Surely, this is one of nature's finest works, from which we might learn.

[theunchosen]

The airline industry already adopted a film of this nature as I also already mentioned. The designs are the same but the airline industry did it back in 2000.

The purported max on decreased drag was 10% though.

Lately, I've had my fill of "phenomenon" events that offer answers without any decipherable science behind them. Particularly ones that have already been explained but are not useful in vehicles.

It's not really about zero flow at the surface because my sheet metal doesn't flow at all. Its about a continuously, infinitely variable surface that can respond to oscillations in the fluid and either expand into low pressures and pull the surface(the trapped water which will provide a df of force on the sheet metal) or compress away from high pressures to avoid drag. Your sheet metal, FG, CF or whatever will just be pulled on creating a tiny force that increases drag instead of compressing or expanding(only microns) to "evade" that increased pressure.

Unless its quantum physics or something of the magnitude of 50% of the universe we can explain most events if not in words and elegant equations then in extremely complicated mathematical formulae.

A CVT takes advantage of the same idea. If your transmission is static you can't decide that the tractor trailer is providing a very friendly FE spot(yes its still FE friendly 2 seconds behind him) and gear appropriately for max efficiency at that speed. You are stuck. CVT slides its cone outward a little so your gearing gets you taller and taller until the engine is producing just enough power to maintain speed at the lowest possible rpm and you didn't have to leave the FE sweet spot behind the semi to get into that sweet spot rpm.

The fluid surface does this. Low pressure sure I'll expand into it to create larger surface area towards the low pressure and pull with a tiny amount of force. High pressure I'll compress and cause less force to be imparted into the sheet.

[jamesqf]

Originally Posted by Otto

Feathers evolved over millions of years to do several things, including streamlining, but also as insulation...

Don't forget waterproofing - consider ducks & seagulls, not to mention penguins. They also serve as a lightweight body armor - compare picking up a chicken vs a mammal of similar size - and can be put to work for advertising and/or camoflage...