
Ram air turbine - Hooke
https://en.wikipedia.org/wiki/Ram_air_turbine
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dingaling
They make an horrific noise when deployed, the blade tips are highly
supersonic. I've heard one once as a groud observer and I can only imagine the
racket they make in the cabin. For that reason they're not tested in routine
service but there are ground-testing rigs that spin them up to a fraction of
their maximum rotation speed.

The A320 series have RATs but the 737s ( all series ) don't since they remain
manually-flyable without electrical power.

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unwind
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?

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JorgeGT
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!

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toomuchtodo
You'd think the RAT would charge a battery acting as buffer. But who am I to
armchair quarterback an entire aerospace industry.

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astrodust
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.

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JorgeGT
> 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.

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chinathrow
Here's one of those RATs in motion on a 777:

[https://www.youtube.com/watch?v=FfB2EP71hqY](https://www.youtube.com/watch?v=FfB2EP71hqY)

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PhantomGremlin
Be sure to follow the link to Pinnacle Airlines Flight 3701. That's a double
Darwin Award, well deserved.

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goldenkey
Wow, that was quite a legendary chain of fuckups. Link for others:

[https://en.m.wikipedia.org/wiki/Pinnacle_Airlines_Flight_370...](https://en.m.wikipedia.org/wiki/Pinnacle_Airlines_Flight_3701)

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astrodust
It takes a lot of gall to double down on your mistakes in a situation like
that. These two should've been stripped of their license had they survived
that stunt.

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goldenkey
It seemed like they were hoping the 2nd engine wasn't totally cashed. So they
lied to the ground about having only 1 engine failure. I would imagine being
alive is worth embarrassment but given the prestige of a pilot, I really can't
say more than, bad choice.

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InclinedPlane
Deep ocean sailing yachts used to use these for electricity generation (for
powering things like navigation equipment and radios) but now it's more common
to use battery backed solar power.

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HerpDerpLerp
I would say that boats have Wind Turbines rather than RATs.

[https://en.wikipedia.org/wiki/Wind_turbine](https://en.wikipedia.org/wiki/Wind_turbine)

The power comes much more from the wind than the vehicle moving through the
air (though I am very aware that the speed of the boat affects the apparent
wind the generator will experience)

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bnegreve
Actually water turbines (aka hydrogenerators) are also an option, but it's
less common.

[http://cdn.streamlike.com/secure/Covers/68/17853.jpg](http://cdn.streamlike.com/secure/Covers/68/17853.jpg)

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boxctim
Hooke was this by any chance inspired by a reddit discussion?

