TransAsia ATR crash in Taiwan.

[AshVX220]

Thanks for the replies.

[Countdown]

JuniorD said:

hornetrider said:

Legend83 said:

Wow, are you a pilot?

That is so cool.

Q. How do you know that there is a pilot in the room.
A. Because they come over and tell you.

And if he's naked and doesn't talk, you can tell by his big watch (and tiny penis).

With accountants it's the other way round.......

[Brother D]

On the topic of feathering, I would have thought logically a windmilling (provided it's not fine pitch causing the prop to exceed max RPM as mentioned) would have less drag than the prop seized in position say 'half' feathered? As a free wheeling prop can 'cut' thru the air providing less resistance? Rather than act as a stationary object impeding smooth airflow around it?
I'm pretty sure that's a wrong assumption, and that there is less drag having a stationary/seized un-feather prop than one that can move freely. - Just not sure on the physics behind it.
Is it a case of a free-wheeling prop having the effective drag of a 'dinner plate' towards the airstream vs 4 sticks where the majority of air passes thru?

[Ginetta G15 Girl]

AshVX220 said:

This maybe a really numpty question and I apologise, what's the different between a "feathered" prop and a "windmilling" prop

Essentially the prop on a Turbo-Prop a/c can be in one of 5 states.

1. Providing torque (thrust) - the prop is in the normal operating range and the blade angle is within the correct parameters for the airspeed. Any induced drag on the blades (lift dependant drag) is overcome by the torque (thrust) produced.

2. Stationary, Feathered - the prop blades are rotated such that they are parallel to the airflow thus minimising the profile drag. The term derives from rowing as in: 'feather your oars'.

3. Stationary, Un-feathered - the prop is producing profile drag based upon its shape and how it is presented to the airflow. Obviously maximum drag occurs when the prop blades are at 90 degrees to the airflow.

4. Windmilling - the prop is turning in the airflow but not under power. Given that the prop is turning through the air it will have an angle of attack and thus will be producing torque (thrust), however, because the prop is still connected to the engine it will be trying to turn the engine/gearbox. Thus the torque that it is producing is negative; that is to say it is producing an equivalent force to drag. The finer (flatter to the relative airflow) the blades are for any given speed the greater will be the drag. As the True Air Speed (TAS) reduces the prop will slow and the negative torque will reduce until the prop finally stops. A windmilling prop will produce more effective drag than will a stationary un-feathered prop until it stops rotating.

5 Decoupled. The prop is no longer coupled to the engine/gearbox. It will turn in the relative airflow and thus still have an angle of attack. It will therefore still produce some drag but as airspeed reduces the prop rotation will slow and drag will reduce. It is unlikely that the prop will stop turning.


Thus in terms of drag worst to best:

Windmilling > Stationary Un-feathered > Decoupled > Stationary Feathered > Providing Torque

[AshVX220]

Ginetta G15 Girl said:

Essentially the prop on a Turbo-Prop a/c can be in one of 5 states.

[snip]

Thus in terms of drag worst to best:

Windmilling > Stationary Un-feathered > Decoupled > Stationary Feathered > Providing Torque

Brilliant, thank you

[Eric Mc]

Countdown said:

With accountants it's the other way round.......

100% agree.

[Hilts]

Legend83 said:

Ginetta G15 Girl said:

Wow, are you an accountant?

That is so boring.

WACC, LIBOR, ASB, XBRL, ZBA, SOX etc etc.

That's a lot of acronyms you have there.

[Mojocvh]

The sad thing is it would appear they almost made it to the river..

[croyde]

Ginetta Girl would you start an airline, I'd feel safer in the air flying with you

Thanks for the VMC (not) exclamation. Looked it up and wondered what the weather had to do with it.

[Puggit]

This might mean more to other people!

[CAPP0]

kapiteinlangzaam said:

That means it looks a lot like a Kegworth.

i.e: they've had an engine failure (nr. 2 engine), but shut down (the healthy) engine nr. 1

indeed.

[TTmonkey]

News is saying they lost power to both engines, but attempted a restart on one.

Please tell me they didn't turn an operating engine off, in mistake.

[HoHoHo]

kapiteinlangzaam said:

Puggit said:

This might mean more to other people!

That means it looks a lot like a Kegworth.

i.e: they've had an engine failure (nr. 2 engine), but shut down (the healthy) engine nr. 1

Probably a mixture of bad luck and bad decisions.

Would it not be obvious on the flight deck which engine was having issues?

Do gauges not always show the truth or is it all happening so fast it's nothing more than mistakes are made?

[HoHoHo]

kapiteinlangzaam said:

HoHoHo said:

Would it not be obvious on the flight deck which engine was having issues?

Do gauges not always show the truth or is it all happening so fast it's nothing more than mistakes are made?

http://en.wikipedia.org/wiki/Kegworth_air_disaster

An interesting read.

If the information is processed correctly, then yes, it should be obvious where the problem is.

Thanks and yes, interesting.

I'm guessing a similar scenario (I'm not suggesting turbine failure obviously!) and then by the time you think oh...........it's too late

[Ginetta G15 Girl]

Puggit said:

This might mean more to other people!

Oh, that doesn't look good.

[Eric Mc]

Apparently it looks like a DOUBLE engine failure - according to the latest report.

[HoHoHo]

Ginetta G15 Girl said:

Puggit said:

This might mean more to other people!

Oh, that doesn't look good.

To those of us who may not understand the wiggly lines etc., can you please explain WTF was going on?

[Eric Mc]

Ssshhh - it's a secret within the brotherhood and sisterhood. They don't REALLY want to explain anything - just demonstrate their detailed knowledge of the subject.

Those of us who don't understand the code are outsiders and unworthy of inclusion.

[KTF]

HoHoHo said:

To those of us who may not understand the wiggly lines etc., can you please explain WTF was going on?

Timeline from left to right showing the data from the FDR relating to engine data, altitude, etc.

Engine 2 is blue and engine 1 is green. Engine 2 failed but power was also reduced to engine 1 - maybe by mistake, maybe not. Will need the transcript of the voice recorder to collaborate.

[Puggit]

Another pic from FlightRadar24