mansoor_
I'll help you out since you don't read, a normal P/E is 20-30. To say it is not a great financial investment is unequivocal. It is effectively a write-off for the foreseeable future.
But that is not to say you shouldn't invest in difficult problems and try to solve them, even if they don't make money. This is one of them. I hope people do the same for other challenging problems.
Yeah, they don't pay drivers, but their cars' hardware costs mean that they won't break even with human-driven taxis for quite some time (unless they manage to decentralise the computing).
To put some rough numbers to this, the sensor set in each car, is probably ~$75K (was initially $150K).
Drag = 1/2 * fluid density * velocity^2 * C_d * Ref. Area
It approximates the drag experienced by objects as they move within a fluid (atmosphere). You can see that drag is proportional to the square of velocity, so going twice as fast induces 4 times the drag.
Ergo, when you speed up, you produce a lot more drag. This will slow you down until you reach an equilibrium between thrust and drag (unless you apply more thrust).
Even if you don't see an immediate benefit in CI times, it may still be a good idea to clean up unnecessary includes.
- Yes the efficiency of the laser is poor and modern tech is more efficient, but not enough to make it an energy producing process. The best lasers are ~50% energy efficient.
- This can only be maintained for short periods of time and the time to restart the process in long. Not only that, tritium is a rare isotope. These are probably the largest challenges to overcome.
- The energy is released in the form of high-speed particles, and there is no efficient energy capture process.
The significance of their achievements is overblown. Yes, they achieved ignition, but no it is just an incremental process towards commercial fusion power.
To clarify the physics, the "conservation of momentum" idea explains all of the lift, not just some of it.
If you draw a bounding box around the wing and measure the momentum at either end, the lost momentum will be because of the wing, some of that will be lift generation (there is also drag + other turbulent losses).
Downwash (in the context of lift generating wings) refers to the downwards motions of air generated by tip vortices (look-up "induced drag" for more details). This is not the same as the net downwards motion of the air in the wake, relative to the free-stream air. Take for example, an infinite wing (or a 2D wing). Here, there is no downwash but we still generate lift and have a net downwards motion of the air in the wake. You can see this with online fluid simulators for airfoil sections, many of them are 2D.
To summarise: Any statement to the effect of "aircraft lift generation is complex" is probably wrong. It is wrong because a high-level picture given by Newton's third law (momentum conservation) is correct and adequately explains lift generation. You do not need to go into the details of velocity or pressure distribution on the wing. You can step back and look the overall airflow and reason about why lift was generated.
> You haven't explained why there is "circulation generated by the wings", you have just stated that there is.
I only mention circulation, to state that both the arguments are similar, just from a different perspective. In my initial post, I reference only Newton's third law (the conservation of momentum). Naturally the source of the circulation is the same as the source of the velocity/pressure distribution. As stated earlier, you do not need these details to explain lift. You do need them to explain phenomenon like stall or drag.
Can you clarify what you mean? Which evidence?
>In particular, we know that fluid flows faster over the upper surface[0], so we know from Bernoulli that the pressure over the upper surface must be lower. That appears not to be included in, or covered by your statement, which suggests that your claim that "It is really that simple" is wrong.
These two perspective are in fact congruent. I decided to explain lift by reasoning about the circulation generated by the wings (https://en.wikipedia.org/wiki/Circulation_(physics)). In this picture, the motion of the air in the wake of the wings has a net rotation (clockwise when the wind is coming from left to right) that generates an upwards resultant force on the wing. This is analogous to the pressure argument. I feel this perspective provides a clearer understanding. With the pressure argument, you have not explained why the air is faster over the top surface of the wing, you have just stated that it is.
As I stress, it really is a simple and well understood problem. Complexity with fluid dynamics arises from problems like turbulence, multi-phase flow and computational modelling.