Thanks, Machine Elf for a lovely explanation. I loves me aerodynamics and that’s a good example of an intuitive look at mass flow and momentum change. Well done.
Here is a good example of this:
Thrust reversers always amazed me, and remind me of the “astern elements” of a naval steam engine (i.e. in a nuclear powered vessel), in their effectiveness, if not their actual implementation.
They typically have two small turbine sections at the ends of the low-pressure turbine that are designed to work in reverse, and those provide about 10% of the power as the main engines, and are highly inefficient. If your ship has a total of 200,000 shaft horsepower going forward, you probably have 20,000 going in reverse.
So when you want your ship to stop, you shut the forward throttles and pour loads of steam in the very poor astern turbines, but efficiency just isn’t what you are looking for at that point, you just are trying to slow down.
No. There is no such thing as “suck air”. Its pushed. Its pulled by gravity though, but then that creates air pressure, which means it can push itself… So anyway the push from the engine requires the inbalance of pressure from front to back… So if the system reduced pressure at the front and produced pressure at the back, that represents a force forward…
Thats why everyone talks about thrust, its the increase in pressure , which creates higher pressure behind , that pushes…
When at idle the engine’s intake isn’t acting as a dumb static air brake. But when they put it into reverse, it starts to act as an air brake, braking about the same amount as if a flaperon of that size was there.
After considering all the ineffeciencies, it seems “reverse” is just to get that extra braking surface for free. (no extra weight,etc)
It’s not *just * a brake. As mentioned earlier aircraft can (but typically don’t anymore) taxi backwards using reverse thrust.