The core tenant of the paper is that roughness reduces drag IN the transition zone. A very small region of the total flow. Thats the region between laminar and turbulent flow. Laminar flow is typically 5x less drag than turbulent, and will be encountered about a Reynolds number of 500K-1M (ratio of inertial flow to viscous flow). Surfboards will have a Reynolds number of 10^7 which is entirely turbulent. A Cessna air…
Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…
Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…
We’ve known about this for a while I feel from dimples on a golf ball.
> Surfboards will have a Reynolds number of 10^7 which is entirely turbulent. A fin, foil or daggerboard below the board/boat is operating well within the range of Reynolds' numbers where laminar flow is relevant.
The vertical stabilizing surface of these elements is really insignificant to the entire surface of a board. Combining drag coefficients is done with the wetted surface area. In truth there's some contamination from the upstream flow. Stabilizing elements are behind the center of pressure, so they will see the most "diry flow"
You are thinking about a slow boat in displacement mode, or a wave-surf board with very small fins.
But I can tell you that the wetted surface area of my wing-foil board is exactly zero after takeoff, and all wet surfaces of the foil are, for a significant percentage, in laminar flow. Same for a windsurf board planing: just the last 50cm of the board is touching the water and the fin is extremely significant for drag.
A key difference is that war planes occasionally want to be able to rapidly change their trajectories. With sufficient thrust you can fly around in a cube.
Would you a have a link that would show case something like that? It feels like only a T-1000 would be able to make any rapid coherent decisions under such load. Thank you.
Instability just means that they don't naturally return to stable flight. Fighter jets benefit from this because when you want to make a maneuver, you're not fighting the plane's natural inclination to stay where it's pointing. You don't need particularly powerful hardware to do this kind of control, quadcopters are an even more obviously inherently unstable example, because any thrust imbalance will immediately make it roll. Quadcopter control loops only need to run at a few hundred hertz to achieve stability.
Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…
So you’re telling me I should sand my carbon fiber wing foil mast and wing with 1000-1500 grid sand paper for better gliding results?
I’m fairly new to the sport and never heard of this yet.
A key difference is that war planes occasionally want to be able to rapidly change their trajectories. With sufficient thrust you can fly around in a cube.
Would you a have a link that would show case something like that? It feels like only a T-1000 would be able to make any rapid coherent decisions under such load. Thank you.
Enter drone piloting, enter autonomous AI... We are maybe approaching that stage, not necessarily with shiny exoskeletons, but not-human nevertheless.
Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…
as usual these things are presented as new and revolutionary but aren't actually. the specific process and implemention however are usually newer or slightly different from before. this is our sensationalistic based society - any iterative progress, or sometimes even copy, is explained as a revolution. now show me a 737 using 40% less fuel - guess what - that wont happen - however, perhaps we'll get a slightly better…
"... this flying wing will burn 50% less fuel than today's jets..."[1]
The vertical stabilizing surface of these elements is really insignificant to the entire surface of a board. Combining drag coefficients is done with the wetted surface area. In truth there's some contamination from the upstream flow. Stabilizing elements are behind the center of pressure, so they will see the most "diry flow"
You are thinking about a slow boat in displacement mode, or a wave-surf board with very small fins. But I can tell you that the wetted surface area of my wing-foil board is exactly zero after takeoff, and all wet surfaces of the foil are, for a significant percentage, in laminar flow. Same for a windsurf board planing: just the last 50cm of the board is touching the water and the fin is extremely significant for drag…
I have 2 foil drives for wake thieving and a SUP for downwinding and I’m just excited that someone on HN is talking about foiling. Such an underrated sport.