DDW.mov
Why Physics Stack Exchange recommends it
Physics Stack Exchange answerers and commenters point people to it as a real demonstration of the 'dead downwind faster than the wind' vehicle when explaining how such a cart can outrun the wind.
Recommended by 1 people across 1 different months, 2021 to 2021.
What it is
A short 2010 clip from the windjetproject channel showing a propeller-driven cart built to travel dead downwind faster than the wind itself. The uploader says it reached about 50 mph in roughly 20 mph of wind, and presents it as something he saw first hand.
What people said
Recommends Ravindra HV · 2021-07 · Physics Stack Exchange · on “How does down-wind faster than the wind (over-land) really work?”
There has recently been posts on youtube where in a land based propeller/fan driven tricycle (blackbird) has been shown to roll faster than the wind that is behind it. The youtube channel veritasium covered it recently and the topic has apparently been around for a while. Although veritasium does provide an answer in terms of formulae and additionally explains based on the power in the wheels (which is counter-intuitive to me as noted in the points able), I have an understanding to cross-validate on this (and hence the question) and wanted a confirmation if it was correct. However if it is incorrect, then am at least looking for an explanation in the same sort of layman's terms that I am try
Cites Carl Witthoft · 2021-02 · Physics Stack Exchange · on “Why does the car move faster?”
In fact, you have just discovered the physics behind the oft-debated DDWFTTW [this video] (Dead downwind faster than the wind) vehicle. The increased back-pressure at the propellor forces the vehicle forward in response. (There are related videos that will show up at that youtube page)
Cites ThinAirDesigns · 2021-08 · Physics Stack Exchange · on “Is the steady-state velocity same as wind speed?”
The answer to #1 depends greatly on the direction the craft is traveling. If it is traveling directly downwind, the steady state speed will never reach that of the wind because of real world frictional losses in bearings, tires, etc. If however it is being sailed on a broad reach at the proper angle to the wind, both its speed across the ground and its downwind VMG can be greater than the wind, steady state. (VMG being Velocity Made Good, or the downwind component of your ground track). [LINK] [LINK] #2 is pretty straight forward: Anytime there is relative wind over the chassis of a vehicle there is associated drag. When traveling slower than the wind, this drag on the chassis works to move
Cites ThinAirDesigns · 2021-08 · Physics Stack Exchange · on “Is a passive vehicle exceeding wind speed from rest possible with momentum conservation?”
If you're looking for math treatments, MIT professor Mark Drela does this one: [LINK] Here is an article by Kimball Livingston (at the time Editor in Chief for Sail Magazine) written about his experience when hired as one of the independent observers for the NALSA record runs: [LINK] And video from one of those runs: [this video] There are countless more resources regarding the Blackbird on the internet. [LINK] (wind-powered_vehicle)