Propeller falls off Rex plane

[jb747]

A bit of trivia:]

In comparison jet engine turbofans typically have a rotational speed of Mach 1.5 at the tips (> 550m/s at altitude)

What's your reference for that? I don't think so.

 

[Quickstatus]

Rotational speed of tips = circumferential speed.
So it's just mathematics. As always happy to be corrected
What's the rpm of T900 in cruise? And fan diameter?.

Diameter x Pi x rpm/60

Speed of sound at 35000 feet (10000m) = approx 300 m/s

 

[NM]

I assume the term "feather the prop" is not supposed to relate to the weight of the prop.

 

[trooper]

I would be quite certain that the prop would have a RELATIVELY low terminal velocity.....What I do wonder is whether it would spin as it falls... I would assume so....

 

[Quickstatus]

Yes The free falling prop would spin if the blades are not in the feathered position.
A detached prop may actually go into the feathered position with the blade edges parallel to the direction of airflow (assuming that force is required to change the blade pitch). Due to the twist in the prop blade not all of the blade edge will be in the airflow direction and so there will/may be a bit of spin. Of course it may be spinning due to the torque imposed on it prior to detachment but it should slow down due to drag.

 

[jb747]

Rotational speed of tips = circumferential speed.
So it's just mathematics. As always happy to be corrected
What's the rpm of T900 in cruise? And fan diameter?.

Diameter x Pi x rpm/60

Speed of sound at 35000 feet (10000m) = approx 300 m/s

I've been trying to write this in a couple of paragraphs, but failing, so I might leave you to do some research.

The upshot, and I know that it is totally non intuitive, is that the flow through an engine is not supersonic. The makers will go to extreme lengths to ensure that it isn't. Curved blades (which is simply a form of swept wing) are part of this. Intake design, even very short intakes, is an extremely complex science, the ultimate aim of which is to take any air flow, from whatever speed, and reduce it to subsonic speed. Part of that may include manipulating the local speed of sound (that speed varies at literally every point on the aircraft).

Taking this to an extreme example...if I'm ripping along in an F15 at mach 2, the flow through the engines is still subsonic.

Supersonic flow would produced dramatically less lift (thrust)...about 20% of subsonic, have hugely more drag (fuel flow), and make lots more noise.

 

[Quickstatus]

....I descended into a moment of inane trivia after someone triggered something in my brain by commenting on the spinning propellor...

those interested in the OT comment about propellor speed carry on and read the fine print:

Yes understand that flow through an engine (front to back) is not supersonic and that supersonic air speed in an engine or for that matter across airfoil, fan blade results in terrible inefficiency and noise.

However I think the reason might be supersonic spinning of the turbofan blades (though inefficient) allows for very high dynamic pressure across the turbofan blade resulting in todays high thrust high bypass jet engines with an ability to operate at altitudes like 40000 feet while allowing for a smaller diameter engine.... Seems like a trade off.

The subsonic flow in an engine makes sense with Bernoullis equation - pressure changes with square of velocity. Not sure if this can be validly applied to a spinning turbofan blade. But looking at it another way the design forces air flow into an engine to slow down - and in some aircraft from supersonic to subsonic.

And the design of the turbofan blades - very knifelike and slim is I suppose optimised for supersonic (spinning) operation across a range of Mach numbers including <1. Look for the curve diagram:
http://www.enginehistory.org/Allison/XF-84Propulsion.html


Back to topic:

Rex grounds several Saabs with the same batch number propellor gear boxes and shafts http://www.abc.net.au/news/2017-03-...rounds-five-planes-amid-investigation/8369958

 

[astrosly]

News in that they've found the propeller: Missing propeller found in Revesby bushland after falling off REX flight
In Revesby in bushland off The River Road (from Google Maps looks like in the Georges River NP).

 

[Quickstatus]

Melburnian1 you were not far off. Reports are that its around 100kg.

other reports citing the FO suggest the prop travelled outward and over the wing

 

[Dr Bob]

9news reports the engine was shut down & propeller feathered before it separated. Their photo on the ground suggest it was feathered.

 

[Quickstatus]

9news reports the engine was shut down & propeller feathered before it separated. Their photo on the ground suggest it was feathered.

Possibly but would a separated propellor be naturally in a "feathered" position as that is the position of least drag as it falls through the sky?. It takes applied force to change the propellor blade pitch to anything other than feathered?. My speculation.

 

[love_the_life]

Rex is not having a good trot - an emergency landing at Dubbo :shock:
Rex Airlines flight makes emergency landing at Dubbo airport after engine shutdown - ABC News (Australian Broadcasting Corporation)

 

[Himeno]

ATC recording.
[video=youtube;povLEP6CmZM]https://www.youtube.com/watch?v=povLEP6CmZM[/video]

 

[AVC]

I was interested to hear in an Air Crash Investigation episode that a B747 was designed such that if an engine became detached, it was designed to go forward, then flip over or under the wing (I can't remember which) and avoid the wing, tail and fuselage.

If the engine is at a high power level, and detatches, it's going forward, regardless of design. At least for a short time.
I seem to recall an ACI episode where a 747 (cargo) had a pylon failure during climb out. The (inboard) engine took off (i.e. shot forward) but obviously once detached lost power. It then slowed down and hit the outboard engine on the same wing. After that, they were screwed.

 

[Melburnian1]

The ATSB has issued a preliminary report finding a 'fatigue fracture' and 'corrosion':

Fracture linked to propeller falling off plane: investigation | The Border Mail

Where the above says 'Rex has quarantinerd all propeller gearboxes', should we take this to mean that the five aircraft temporarily withdrawn cannot return to passenger flights until GE Aviation's analysis and inspections are complete?

 

[jb747]

The ATSB has issued a preliminary report finding a 'fatigue fracture' and 'corrosion':

Fracture linked to propeller falling off plane: investigation | The Border Mail

Where the above says 'Rex has quarantinerd all propeller gearboxes', should we take this to mean that the five aircraft temporarily withdrawn cannot return to passenger flights until GE Aviation's analysis and inspections are complete?

No, it just means the gearboxes. If they have sufficient spares, the aircraft can fly.

 

[Quickstatus]

No, it just means the gearboxes. If they have sufficient spares, the aircraft can fly.

including spare propellor gearboxes?

 

[Melburnian1]

including spare propellor gearboxes?

Yes, that's the bit that's confusing. It would be helpful if bureaucrats like those who work for the ATSB used plain English.

 

[jb747]

I'm sorry, I must be having an obtuse morning. I don't see the issue with the gearbox.

 

[Quickstatus]

Interesting marketing "blurb" from Saab:

Saab 340B

They seem to suggest ongoing support/enhancements for the 340 for the "next 15 years and beyond:".
The manufacturer suggests a 99% despatch reliability.

Why do passengers prefer new aircraft?