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Old 6th Dec 2017, 14:27   #1 (permalink)
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Dash-8 Q400 Critical Engine

Very simple question, what is the critical engine on the Dash-8 Q400.
Really struggling to find something to verify this online from any official source, I have a feeling it does not have counter-rotating propellers...
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Old 6th Dec 2017, 21:39   #2 (permalink)
 
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Engine no.1
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Old 7th Dec 2017, 17:02   #3 (permalink)
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Thanks for the reply, do you know where I can find any official documents from Bombardier that confirms that its engine no.1 and that the propellers are rotating clockwise? Not sure where to find this...
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Old 8th Dec 2017, 07:48   #4 (permalink)
 
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No, but, just look at a video of one starting up, there are plenty available online. The theory is the same as other multi-engine prop. aircraft.
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Old 8th Dec 2017, 20:17   #5 (permalink)
 
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Something I have never really understood, who cares which engine is critical? I can understand test pilots worrying about this stuff but once certified being flown by a line pilot, why does anyone really care? Not like you say "oh it's number two that's failed, lets trim 5 kts or whatever off the speeds, we can make it over that hill".
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Old 8th Dec 2017, 23:09   #6 (permalink)
 
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Quote:
and that the propellers are rotating clockwise?
The vast majority of North American built propeller aircraft have clockwise rotating engines, and I've never seen a specific reference to this in any other propeller or turbopropeller AFM / AOM for the other types I've flown. Not saying the reference is not there in other manuals, but this is just put down to general knowledge (in fact, this side of the pond we're often told the only people doing counter-clockwise propellers are the Russians).

But, to identify which way the propeller will turn doesn't require one to watch an engine start; just look at how the props are bolted onto the hub, as the position of the blade face (and, consequently, the blade back) will tell you immediately which way the propeller will turn.

Quote:
who cares which engine is critical?
You're right that the average line pilot does not care. However, this knowledge is another tool in the toolbox that permits a pilot to know why they are "putting in more rudder input than would otherwise be expected." I've never subscribed to the idea that any knowledge is useless - who knows when you might just need to know that a certain engine is the critical engine? Better to know it than not.

Also, it helps to explain why some aircraft are constructed with a rudder that can travel a certain number of degrees further in one direction than the other.
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Old 9th Dec 2017, 09:50   #7 (permalink)
 
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Sometimes that knowledge can be too useful.
On the Electra #1 was the critical engine (IIRC) and during base checks (no sim) the EFTO was normally #1 pulled back to 200hp at Vr to simulate the failure. The young and keen F/Os would be all geared up for this.
Occasionally though #4 would be pulled back and that got very interesting when the wrong rudder was applied.
My job in the middle was to call "Engine Fail" but not identify which one.
Sometimes an inboard engine would be failed and that also caused issues as very little rudder was required.
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Old 10th Dec 2017, 04:12   #8 (permalink)
 
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Occasionally though #4 would be pulled back and that got very interesting when the wrong rudder was applied.
And that's what happened to Transasia 235. In the sim, the pilots always trained for the loss of the critical engine. When 235 had an engine failure for real, the pilots did what they had always trained for and shut down the critical engine - and crashed!

Be careful how you train!
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Old 10th Dec 2017, 06:09   #9 (permalink)
 
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Quote:
Originally Posted by adamlouis View Post
Very simple question, what is the critical engine on the Dash-8 Q400.
Very simple answer: none.

Due to P-factor (downgoing blade producing higher lift as it has higher AoA and a bit of forward velocity imparted by the aeroplane, when the aeroplane alpha is positive) the thrust centerline on the Q400 (and most western twinprops) is offset to the right, therefore No2 has longer moment arm and No1 failure requires more rudder than No2. Practically, the difference in handling is imperceptible.

There are some airframe/powerplant combination where the phrase "critical engine" really means something. It is kind of useless and potentially dangerous "knowledge" to assume that because your twin trainer behaved differently whether you lost left or right donkey, all the multiprops in your flying life will do the same.

BTW, there is no critical engine on ATR-42 300 either.
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Old 10th Dec 2017, 07:44   #10 (permalink)
 
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Quote:
Originally Posted by dixi188 View Post
Sometimes that knowledge can be too useful.
On the Electra #1 was the critical engine (IIRC) and during base checks (no sim) the EFTO was normally #1 pulled back to 200hp at Vr to simulate the failure. The young and keen F/Os would be all geared up for this.
Occasionally though #4 would be pulled back and that got very interesting when the wrong rudder was applied.
My job in the middle was to call "Engine Fail" but not identify which one.
Sometimes an inboard engine would be failed and that also caused issues as very little rudder was required.
I remember a less than young Captain doing this and the TRE taking the other side on the next departure, not a lot of room at Southend to correct that!
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