rendezvous
Topic Author
Posts: 531
Joined: Sun May 20, 2001 9:14 pm

ATR Throttles

Sat May 19, 2012 3:52 am

Hello,
I recently flew an ATR72 simulator and I noticed the 1 and 2 throttles are different widths. What is the reason for this? The left one is bigger, and that's the critical engine, but that didn't seem like a reason to have a wider throttle.



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jetblueguy22
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RE: ATR Throttles

Sat May 19, 2012 4:00 am

Quoting rendezvous (Thread starter):
The left one is bigger, and that's the critical engine

I'm just a single engine guy so I'm not up on this, but what makes the number 1 engine more critical than the number 2? Thanks in advance.
Blue
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rendezvous
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RE: ATR Throttles

Sat May 19, 2012 4:56 am

The critical engine is the engine that produces the most yaw when it fails. More yaw requires more rudder input to counter it, which increases drag and reduces climb performance. The critical engine is the one you don't want to lose.

The left engine is more critical (to lose) than the right engine because of asymmetric blade effect. This is something you may have heard of in a single engine too - part of the reason you hold right rudder in during a climb. Essentially the down going blade travels faster than the up going blade (assuming an aircraft nose up attitude). This results in the down going blade producing more thrust than the up going blade. As the down going blade is producing more thrust, the thrust vector from the engine is offset from the hub in the centre slightly towards the down going blade.

As both engines and propellers rotate the same direction (clockwise when you're sitting in the plane looking forwards) the thrust from the left engine is slightly offset towards the centre of the plane, and the thrust from the right engine is offset slightly away from the centre of the plane.

In a situation with the left engine running and the right engine failed all the thrust is produced from a point inboard from the left propeller hub. This creates a moment around the centre of gravity and the plan will yaw. This is corrected with rudder.

In the opposite situation with the right engine running and the left engine failed all the thrust is produced from a point slightly outboard of the right propeller hub. This once again creates a moment arm and yaw, but this time the moment arm is larger because the point where thrust is produced is further away from the centre of the plane (centre of gravity). A larger moment means more yaw, and therefor more rudder required to counter it.

Diagram of Yawing Moments
 
Max Q
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RE: ATR Throttles

Sat May 19, 2012 5:10 am

Wadrs, RV did not get his question answered.
The best contribution to safety is a competent Pilot.
 
C46
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RE: ATR Throttles

Sat May 19, 2012 3:56 pm

Just a wild guess but I'd wonder if it is to allow enough space between the power levers (left side) and the condition levers (right side) so as not to unintentionally move both or jam a finger/thumb between the two?
 
B6JFKH81
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RE: ATR Throttles

Sat May 19, 2012 6:06 pm

Quoting C46 (Reply 4):
Just a wild guess but I'd wonder if it is to allow enough space between the power levers (left side) and the condition levers (right side) so as not to unintentionally move both or jam a finger/thumb between the two?

...or maybe to help give a touch-based queue to differentiate between the power levers and condition levers in the event of visibilty issues in the flight deck? Much like how the landing gear lever has the little "wheel" on the end, maybe this helps the flight deck drew differentiate between the two diferent sets of control levers that are right next to each other so if there is smoke in the flight deck and the flight crew is flying blind, they know they are grabbing onto and adjusting the correct levers?
"If you do not learn from history, you are doomed to repeat it"
 
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sturmovik
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RE: ATR Throttles

Tue May 29, 2012 4:53 pm

A guess.
Quite often, I've seen ATRs taxi with engine no.1 shut down, and using only engine no.2. I believe this saves time in pax on/off boarding, since ground personnel can approach the A/C from the port side as soon as it taxies in, without having to wait for the engine to spin down. The A/C has doors on both sides, however the cargo door is on the port side up front ahead of the no.1 propeller, hence the loading/unloading almost universally happens from port side. As a consequence of this, the no.1 engine often has to be shut down (and maybe even started up, though I've never seen that happen) while the aircraft is in motion on the ground, and considering it has to be operated in a possibly bumpy environment (not to mention the fact that an earlier poster mentioned that no.1 is the critical engine), the no.1 throttle lever's larger size could be of help in identifying the correct engine and reducing the possibility of a mistaken operation.
Again, just a guess.
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rcair1
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RE: ATR Throttles

Tue May 29, 2012 5:15 pm

Quoting B6JFKH81 (Reply 5):
or maybe to help give a touch-based queue

That was my thought -but I have no idea if it is correct.
rcair1

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