Critical engine - B747
Thread Starter
Joined: Oct 2005
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From: North of Antarctica
Critical engine - B747
Hi there to all the tech gurus!
I have an interview coming up, and I believe one of the questions in the past has been the critical engine on a 747.
I can tell that it is the up wind engine, but why? I assume it has to to with the remaining thrust on the opposite side providing a yawing tendecy; But primarily because the weathercocking effect. Anyway, I am just speculating and would appreciate an educated input.
Thanks guys
I have an interview coming up, and I believe one of the questions in the past has been the critical engine on a 747.
I can tell that it is the up wind engine, but why? I assume it has to to with the remaining thrust on the opposite side providing a yawing tendecy; But primarily because the weathercocking effect. Anyway, I am just speculating and would appreciate an educated input.
Thanks guys
Joined: Mar 2006
Posts: 171
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From: Southern Turkey
Absolutely correct I believe, though I've never flown a 747. Upwind outboard engine is normally the critical eng on a 4-jet, since yaw due to failure and weathercocking due to crosswind are additive in their effect.
regards,
rts
regards,
rts
Gender Faculty Specialist
Joined: Mar 2002
Aviation Qualifications: ATPL
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From: In your head.
Seconded, from a handling point of view.
However, you can have a critical engine in terms of systems that you lose. Dunno 'bout the 747 in that respect though.
However, you can have a critical engine in terms of systems that you lose. Dunno 'bout the 747 in that respect though.
Joined: Jul 2001
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From: Gold Coast
From a weathercocking point of view that is correct, but the 747 otherwise has no critical engine.
You can lose any engine and there will be no loss of electrical, pneumatic, or hydraulic power at all. There is no difference in Vmca with either inboard or either outboard engine failed.
You can lose any engine and there will be no loss of electrical, pneumatic, or hydraulic power at all. There is no difference in Vmca with either inboard or either outboard engine failed.
Fleet Manager
Joined: Apr 2001
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From: various places .....
Suggest a search on the topic in the archives ..
(a) certification (AFM) Vmcg ignores wind (older UK certificated aircraft use a 7kt crosswind basis which will increase the value compared to the US value)
(b) crosswind considerations are pragmatic and should be considered by pilots, especially in the case of low weight, ferry type flights. The certification Vmcg will increase by (typically something in the vicinity of) 0.5kt/kt (twins), 1.0kt/kt (four engines) so, in the case of a takeoff at low V1 in a strongish crosswind, the "actual real world" Vmcg easily can exceed the book figure .. good case for delaying the takeoff until one gets better conditions or use a higher speed schedule.
(c) better to keep the "critical engine" term (for Vmcg) to apply to the certification case and use some different or qualified term to distinguish the real world crosswind consideration ..
(d) for Vmca (once the aircraft is away from the ground and stabilised), steady wind should have no effect ..
(a) certification (AFM) Vmcg ignores wind (older UK certificated aircraft use a 7kt crosswind basis which will increase the value compared to the US value)
(b) crosswind considerations are pragmatic and should be considered by pilots, especially in the case of low weight, ferry type flights. The certification Vmcg will increase by (typically something in the vicinity of) 0.5kt/kt (twins), 1.0kt/kt (four engines) so, in the case of a takeoff at low V1 in a strongish crosswind, the "actual real world" Vmcg easily can exceed the book figure .. good case for delaying the takeoff until one gets better conditions or use a higher speed schedule.
(c) better to keep the "critical engine" term (for Vmcg) to apply to the certification case and use some different or qualified term to distinguish the real world crosswind consideration ..
(d) for Vmca (once the aircraft is away from the ground and stabilised), steady wind should have no effect ..
