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 trying to describe.
Specifically my understanding is as follows -
The wind powers the vehicle initially.
The wheel's (through gears and chain) drive the propeller.
It would be safe to assume that until the vehicle reaches the wind speed, its powered by the wind and as such builds up inertia (and consequently can accelerate).
However the explanations (in the veritasium video) tend to focus on the power generated by the wheels to explain the vehicle going faster than the downwind. The problem with this explanation is that it holds only to the extent that the vehicle has expended (exhausted) the potential energy it initially built (from it rolling when it was slower than the wind). Friction would eventually slow it down back atleast to the same speed as the wind. It does not explain how the vehicle is able to sustain it.
The question is - what is the force that is allowing the vehicle to sustain the speed ? It definitely can't be the power from the wheels - its built on inertia and friction would cause it to drain its energy back to zero.
My understanding is that there should be some physical 'link' that would be between the wind generated from the propeller (propeller-wash?) that compensates for and allows for the 'link' to be re-established between the downwind and the vehicle - analogous to a boatman pushing the boat in shallow rivers/lakes using a stick, the wash from the propeller is the 'stick' and the downwind forms the 'lakebed/riverbed'.
Is my understanding correct? If not then what is wrong with my understanding ?
My question is similar to the question posted here - How to sail downwind faster than the wind?
It also has a fairly good answer in the past few days (which I believe draws insights from the videos linked below) but does not clarify on point #5 (on sustainability) - https://physics.stackexchange.com/a/651106/31729
- (A Physics Prof Bet Me $10,000 I'm Wrong) https://www.youtube.com/watch?v=yCsgoLc_fzI
- (Risking My Life To Settle A Physics Debate) https://www.youtube.com/watch?v=jyQwgBAaBag
- (CNN Early Start - Blackbird upwind cart) https://www.youtube.com/watch?v=b8MWCvKIi7E
- (DDW.mov) https://www.youtube.com/watch?v=5CcgmpBGSCI