Rehash - conflicting info re: jet critical engine
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Rehash - conflicting info re: jet critical engine
G'day all
Was doing some reading from "Ace the technical pilot interview" on jet critical engines..
One of the questions asks:
"If you had an engine failure between V1 and Vr and you had a maximum crosswind, which engine would be best to lose, i.e. upwind or downwind engine?"
The answer states:
"Upwind engine. This is so because the crosswind would then oppose the yawing moment of the downwind engine"
I found this very hard to believe and thought it might be a typo. However in another question in the same book it asks:
"How does a crosswind affect the critical engine?"
Answer: "..a failed number 1 engine will cause a yaw to the left. A crosswind component from the left will apply a restoring force to the aircraft's fuselage, whereas a crosswind from the right will aggravate the yawing moment further to the left due to the sideways force experienced on the right side of the aircrafts fuselage (which is from right to left)"
I did a search on here and read some past threads where everything seems to match up with my thinking....The book basically suggests that the fuselage has more influence on the yawing moment than the veritcal fin/rudder?...
Pages 60 and 195 for anyone who has it.
Thoughts please? Really want to nut this one out...it seems straight forward.
Was doing some reading from "Ace the technical pilot interview" on jet critical engines..
One of the questions asks:
"If you had an engine failure between V1 and Vr and you had a maximum crosswind, which engine would be best to lose, i.e. upwind or downwind engine?"
The answer states:
"Upwind engine. This is so because the crosswind would then oppose the yawing moment of the downwind engine"
I found this very hard to believe and thought it might be a typo. However in another question in the same book it asks:
"How does a crosswind affect the critical engine?"
Answer: "..a failed number 1 engine will cause a yaw to the left. A crosswind component from the left will apply a restoring force to the aircraft's fuselage, whereas a crosswind from the right will aggravate the yawing moment further to the left due to the sideways force experienced on the right side of the aircrafts fuselage (which is from right to left)"
I did a search on here and read some past threads where everything seems to match up with my thinking....The book basically suggests that the fuselage has more influence on the yawing moment than the veritcal fin/rudder?...
Pages 60 and 195 for anyone who has it.
Thoughts please? Really want to nut this one out...it seems straight forward.
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Yep,
Looks wrong to me too... upwind engine is the critical one in a crosswind. Will run out of rudder a lot quicker if you lose the upwind engine (twin engine jet a/c) and have to counter max crosswind.
The whole weathercocking thing seems to be taught differently in this book than most others.
Looks wrong to me too... upwind engine is the critical one in a crosswind. Will run out of rudder a lot quicker if you lose the upwind engine (twin engine jet a/c) and have to counter max crosswind.
The whole weathercocking thing seems to be taught differently in this book than most others.
Bottums Up
Ovum,
The AFM of the venerable BAe146 states that the critical engine is the outboard engine on the upwind side.
I guess with types like DC9, 727, 717 with a lot of fuse forward of the C of G it could be the down wind engine but stand ready to be corrected.
The AFM of the venerable BAe146 states that the critical engine is the outboard engine on the upwind side.
I guess with types like DC9, 727, 717 with a lot of fuse forward of the C of G it could be the down wind engine but stand ready to be corrected.
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Cheers for the replies so far.
Capt. Claret
I see what you're saying with the amount of fuselage foward of the CG however surely the vertical fin would more than offset any amount of yaw generated by fuselage forward of the CG?
The book seems to suggest that the downwind engine is critical because (assuming the aircraft is perfectly balanced) the wind from the same side as the live engine will effectively 'push' the aircraft back in the same direction as the wind - hence the mention of sideways force. Still doesn't match my understanding of the definition of yaw.
Capt. Claret
I see what you're saying with the amount of fuselage foward of the CG however surely the vertical fin would more than offset any amount of yaw generated by fuselage forward of the CG?
The book seems to suggest that the downwind engine is critical because (assuming the aircraft is perfectly balanced) the wind from the same side as the live engine will effectively 'push' the aircraft back in the same direction as the wind - hence the mention of sideways force. Still doesn't match my understanding of the definition of yaw.
The book's wrong!!!
One, you're not balanced. Nor will you ever be in asymmetric flight - have a look at the balance ball next time you're flying in steady, unaccelerated asymmetric flight. The forces may be in equilibrium but there will always be some sideslip. The key is to minimise it.
Two, taking off with a crosswind from the right, left rudder is applied to counteract the yawing moment generated primarily by the vertical stab. (Note: the moment generated by the vert. stab. is enough to overcome any yawing moment generated by the fuselage forward of the CoG (surface area is huge and moment arm is also huge in comparison to most of the fuselage forward of the CoG - even on an aircraft with rear mounted engines)).
Failure of the upwind (right) engine will require additional left rudder to counteract the yaw generated by the engine failure. Failure of the downwind (left engine) will require some right rudder but nowhere near as much due to the yawing moment to the right created by the crosswind.
Seems you already knew the answer to the question!! Treat the rest of the book carefully and good luck.
Cheers.
PS. Is Gary Bristow a former Navy or an Airforce pilot?? It may be different on an aircraft such as a fighter with rear-mounted engines very close to the longitudinal axis and substantial "vertical" surfaces ie. engine intakes, forward of the CoG. As an airline pilot though he should really know better, unless part of the book was "ghost written".
One, you're not balanced. Nor will you ever be in asymmetric flight - have a look at the balance ball next time you're flying in steady, unaccelerated asymmetric flight. The forces may be in equilibrium but there will always be some sideslip. The key is to minimise it.
Two, taking off with a crosswind from the right, left rudder is applied to counteract the yawing moment generated primarily by the vertical stab. (Note: the moment generated by the vert. stab. is enough to overcome any yawing moment generated by the fuselage forward of the CoG (surface area is huge and moment arm is also huge in comparison to most of the fuselage forward of the CoG - even on an aircraft with rear mounted engines)).
Failure of the upwind (right) engine will require additional left rudder to counteract the yaw generated by the engine failure. Failure of the downwind (left engine) will require some right rudder but nowhere near as much due to the yawing moment to the right created by the crosswind.
Seems you already knew the answer to the question!! Treat the rest of the book carefully and good luck.
Cheers.
PS. Is Gary Bristow a former Navy or an Airforce pilot?? It may be different on an aircraft such as a fighter with rear-mounted engines very close to the longitudinal axis and substantial "vertical" surfaces ie. engine intakes, forward of the CoG. As an airline pilot though he should really know better, unless part of the book was "ghost written".
Last edited by DirectAnywhere; 29th May 2005 at 11:13.
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As far as I can tell it is the upwind engine. See the explanation in "Flying the Big Jets" (not HTBJ the one about the 777).
There are a few apparent errors in "Ace The Technical Pilot Interview". There is a question about wide cord fan blades that says the cord is from the engine hub to the blade tip. That's not what Rolls Royce reckon and they invented them.
It's a useful book but only a start on the more in depth questions.
There are a few apparent errors in "Ace The Technical Pilot Interview". There is a question about wide cord fan blades that says the cord is from the engine hub to the blade tip. That's not what Rolls Royce reckon and they invented them.
It's a useful book but only a start on the more in depth questions.
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The book's wrong!!!
DirectAnywhere said of "Ace The Technical Pilot Interview" by Gary Bristow.....
I agree totally with you DA.
I bought this book on a recommendation from a colleague preparing for a Dragonair interview.
There are a substantial number of outright errors in his book.
There are also a lot of incomplete or very poorly explained 'answers' to many other questions.
This book might have once been a useful set of notes for Mr Bristow, but it is a pretender when it is aimed at professional pilots.
About all it is really good for is asking a few questions. Readers should source their answers from HTBJ, Fly the Wing and Aerodynamics for Naval Aviators.
The book's wrong!!!
I bought this book on a recommendation from a colleague preparing for a Dragonair interview.
There are a substantial number of outright errors in his book.
There are also a lot of incomplete or very poorly explained 'answers' to many other questions.
This book might have once been a useful set of notes for Mr Bristow, but it is a pretender when it is aimed at professional pilots.
About all it is really good for is asking a few questions. Readers should source their answers from HTBJ, Fly the Wing and Aerodynamics for Naval Aviators.
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Use the book only for the questions. If you have already bought it that is, otherwise don't waste your $$. Like the others say, it is FULL of mistakes. Have a look at what he has to say about the HF req'd freq at night for another fine example. 
The Ionosphere increases in altitude at night due to a lack of things like solar winds!!
Don't buy these books to get the "answers" for an interview, because you will be shot down when they ask for more info.
You need a good understanding of the subject, not just a memorized quote from a dodgy book.
The Ionosphere increases in altitude at night due to a lack of things like solar winds!! Don't buy these books to get the "answers" for an interview, because you will be shot down when they ask for more info.
You need a good understanding of the subject, not just a memorized quote from a dodgy book.
