# Forget planes on treadmills, here's a sail-cart out-sailing the wind! **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [November 7, 2010, 8:17am UTC](https://boards.straightdope.com/t/forget-planes-on-treadmills-heres-a-sail-cart-out-sailing-the-wind/559778 "2010-11-07T08:17:09Z")\ **Posts on this page:** 7\ **Page:** 6
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 13, 2010, 8:38pm UTC](https://boards.straightdope.com/t/forget-planes-on-treadmills-heres-a-sail-cart-out-sailing-the-wind/559778/101 "2010-11-13T20:38:43Z")
I think I might have overstretched my analogy there - I accept the correction. ---
**Author:** ![ziploc](https://avatars.discourse-cdn.com/v4/letter/z/bbe5ce/32.png) [@ziploc](https://boards.straightdope.com/u/ziploc)\ **Post date:** [November 13, 2010, 8:43pm UTC](https://boards.straightdope.com/t/forget-planes-on-treadmills-heres-a-sail-cart-out-sailing-the-wind/559778/102 "2010-11-13T20:43:22Z")
> [@Mangetout](#): > > I think I might have overstretched my analogy there - I accept the correction. Times are changing in the world of DDWFTTW. You’re supposed to call me an idiot 😃 It’s probably been mentioned above, but the secret to this thing is simply that the wheels are rolling over the ground faster than the cart is moving through the air-mass. That means the amount of energy harvested at the wheels is greater than the amount of energy needed by the prop to pull itself through the slower moving medium (the air). Of course like most problems, there are other equally valid ways to look at it. But there are also some invalid explanations that yield the correct conclusion. ---
**Author:** ![ThinAirDesigns](https://avatars.discourse-cdn.com/v4/letter/t/df705f/32.png) [@ThinAirDesigns](https://boards.straightdope.com/u/ThinAirDesigns)\ **Post date:** [November 13, 2010, 8:57pm UTC](https://boards.straightdope.com/t/forget-planes-on-treadmills-heres-a-sail-cart-out-sailing-the-wind/559778/103 "2010-11-13T20:57:06Z")
> [@GargoyleWB](#): > > I’m still wrapped up on wind car though…help me out here, where is the car’s energy coming from in these two regimes… There are two regimes, but they are not “below wind speed” and “above wind speed”. They are “when propeller is stalled” and “after propeller is spinning fast enough to come unstalled and generate thrust”. This mode change begins _well below_ windspeed when the Blackbird is moving just a few mph. Initially is is just the bluff drag of the vehicle that causes it to blow downwind. As the prop spins and comes unstalled, the thrust of the steadily increasing in speed propeller begins to climb faster than drag of the steadily slowing apparent following wind slows. > [@](#): > > Below wind speed: I assume the car is building and storing energy from the rotation of the fan blades? Then it regears itself to boost itself past wind speed? The vehicle is equipped with a fixed ratio transmission so it’s impossible for it “regear”. Thus, it’s impossible for it to use the stored energy in it’s rotating components to accelerate. One of the very specific rules of NALSA is that the vehicle cannot be built such that it uses such stored energy but rather must all of it’s power at any given moment from an energy exchange with the wind. The Blackbird complies with this rule. JB ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [November 13, 2010, 9:41pm UTC](https://boards.straightdope.com/t/forget-planes-on-treadmills-heres-a-sail-cart-out-sailing-the-wind/559778/104 "2010-11-13T21:41:42Z")
> [@ThinAirDesigns](#): > > One of the very specific rules of NALSA is that the vehicle cannot be built such that it uses such stored energy but rather must all of it’s power at any given moment from an energy exchange with the wind. Where’s the fun in that? How fast could Jenkins make the Greenbird go if it could store wind energy in a flywheel or something and then dump it into the drivetrain all at once? Stupid killjoy rulemakers grumble grumble. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [April 7, 2026, 2:25am UTC](https://boards.straightdope.com/t/forget-planes-on-treadmills-heres-a-sail-cart-out-sailing-the-wind/559778/105 "2026-04-07T02:25:52Z")
Interesting link, made me think of this thread. > **[Veritasium on Instagram: "How something can go faster than what's pushing...](https://www.instagram.com/reel/DWyDqcmgKaT/?igsh=NTc4MTIwNjQ2YQ==)** > > 24K likes, 133 comments - veritasium\_daily on April 6, 2026: "How something can go faster than what's pushing it... > > \#veritasium #science #physics #engineering #bet". ---
**Author:** ![Al128](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/al128/32/16541_2.png) [@Al128](https://boards.straightdope.com/u/Al128)\ **Post date:** [April 8, 2026, 12:46am UTC](https://boards.straightdope.com/t/forget-planes-on-treadmills-heres-a-sail-cart-out-sailing-the-wind/559778/106 "2026-04-08T00:46:51Z")
It’s safe to say that the vehicle design did not catch on over the last 15 years. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 8, 2026, 1:29pm UTC](https://boards.straightdope.com/t/forget-planes-on-treadmills-heres-a-sail-cart-out-sailing-the-wind/559778/107 "2026-04-08T13:29:46Z")
It was never meant to be practical, just a fun and interesting engineering challenge. [Previous page](https://boards.straightdope.com/t/forget-planes-on-treadmills-heres-a-sail-cart-out-sailing-the-wind/559778.md?page=5)