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I'm confused. It looks like a turbine powered by the movement of ambient air, in this case due to the aircraft's movement through said air. But the article sa

by unwind 11y ago

I'm confused. It looks like a turbine powered by the movement of ambient air, in this case due to the aircraft's movement through said air. But the article says: The RAT generates power from the airstream by ram pressure due to the speed of the aircraft. How is this dependent on the pressure, rather than just the speed of the air? Would a RAT from an aircraft not work on a stationary object subject to wind? Or is such an object also experiencing ram pressure (just the other way around due to reference frame shifting), i.e. all (wind) turbines work due to ram pressure?

jonsen 11y ago
"ram pressure" is a link to its own explaining wiki-page.
- unwind 11y ago
  Yes of course, I read that and it didn't help. It talks about the drag experienced by an object moving in a fluid. I guess I'm just dense.
  - jonsen 11y ago
    You are right, not really informative. Maybe Ram Air Turbine is a bad name. A turbine driven by the airflow from "ramming" through the air?!
JorgeGT 11y ago
Aerospace eng. here, you are right in that is a confusing terminology. Ram pressurein this context is a way to refer to the available kinetic energy due to airflow: 1/2 x density x speed^2 (also called dynamic pressure). A point to stress is that the energy delivered to the plane systems by this auxiliary turbine is thus varying with the square of the speed of the plane. That means that as you slow down for landing, the RAT delivers less and less energy... and the commanding authority of the hydraulic-actuated control surface lowers, making the plane less and less controllable. Not fun!
- toomuchtodo 11y ago
  You'd think the RAT would charge a battery acting as buffer. But who am I to armchair quarterback an entire aerospace industry.
  - astrodust 11y ago
    Having a sufficiently large battery introduces another point of failure, something undesirable in a situation where you're already in bad shape. You don't deploy the RAT unless shit is going sideways.
    - JorgeGT 11y ago
      > You don't deploy the RAT unless shit is going sideways. We can't also confirm nor deny that RAT is a hand-picked acronym to make the "rats leaving the ship, we're doomed" joke.

by unwind 11y ago

jonsen 11y ago

"ram pressure" is a link to its own explaining wiki-page.

unwind 11y ago
Yes of course, I read that and it didn't help. It talks about the drag experienced by an object moving in a fluid. I guess I'm just dense.
- jonsen 11y ago
  You are right, not really informative. Maybe Ram Air Turbine is a bad name. A turbine driven by the airflow from "ramming" through the air?!

JorgeGT 11y ago

Aerospace eng. here, you are right in that is a confusing terminology. Ram pressurein this context is a way to refer to the available kinetic energy due to airflow: 1/2 x density x speed^2 (also called dynamic pressure). A point to stress is that the energy delivered to the plane systems by this auxiliary turbine is thus varying with the square of the speed of the plane. That means that as you slow down for landing, the RAT delivers less and less energy... and the commanding authority of the hydraulic-actuated control surface lowers, making the plane less and less controllable. Not fun!

toomuchtodo 11y ago
You'd think the RAT would charge a battery acting as buffer. But who am I to armchair quarterback an entire aerospace industry.
- astrodust 11y ago
  Having a sufficiently large battery introduces another point of failure, something undesirable in a situation where you're already in bad shape. You don't deploy the RAT unless shit is going sideways.
  - JorgeGT 11y ago
    > You don't deploy the RAT unless shit is going sideways. We can't also confirm nor deny that RAT is a hand-picked acronym to make the "rats leaving the ship, we're doomed" joke.