The answer to all our secrets
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Originally Posted by NW1
...it's only a chat...
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Double engine failure
Hi,
What are the possibilities of a quad engined airplane (744, 340s only) having a simultaneous or one after the other engine failure during takeoff and the speed is v1-10~20kts? Would the airplane be able to climb on 2 engines if its fully loaded? if so what would be the biggest rate of climb in feet per min? what is the biggest of climb on these airplanes if only one engine fails?
Another question kind of relating to the above is what if the PF is the FO and an emergency occurs while taking off, would the captain immediately say "i have control" and perform the takeoff, and do the rest of the emergency, while the FO just helps with ATC and checklists?
What are the possibilities of a quad engined airplane (744, 340s only) having a simultaneous or one after the other engine failure during takeoff and the speed is v1-10~20kts? Would the airplane be able to climb on 2 engines if its fully loaded? if so what would be the biggest rate of climb in feet per min? what is the biggest of climb on these airplanes if only one engine fails?
Another question kind of relating to the above is what if the PF is the FO and an emergency occurs while taking off, would the captain immediately say "i have control" and perform the takeoff, and do the rest of the emergency, while the FO just helps with ATC and checklists?
Last edited by xxgunnerxx; 5th Oct 2007 at 02:58. Reason: forgot to add something
G'day xxgunnerxx,
Years ago when I first started on the B747-400 we finishd a sim session a little early and had a bit of time to play. The instructor set the a/c at MTOW and the temp 30 degC then during the takeoff run had an engine fail after V1 and the other one on the same side fail at VR. So a double asymmetric engine failure at max weight on a hot day.
It was a handful to say the least and if you followed the flight manual it resulted in a gradual descent into the ground, however if you selected the flap up from F20 to F5, regardless of the speed, then there was a huge reduction in drag and the a/c would eventually accelerate and climb away as you cleaned up further. Once you got it clean there was more than enough thrust to complete the approach.
Second paragraph, if the take off is rejected the captain takes over, however if the take off is continued and the FO is handling things well he continues to fly and set up for the approach, though in my company the captain has to do the actual landing.
Regards,
BH.
Years ago when I first started on the B747-400 we finishd a sim session a little early and had a bit of time to play. The instructor set the a/c at MTOW and the temp 30 degC then during the takeoff run had an engine fail after V1 and the other one on the same side fail at VR. So a double asymmetric engine failure at max weight on a hot day.
It was a handful to say the least and if you followed the flight manual it resulted in a gradual descent into the ground, however if you selected the flap up from F20 to F5, regardless of the speed, then there was a huge reduction in drag and the a/c would eventually accelerate and climb away as you cleaned up further. Once you got it clean there was more than enough thrust to complete the approach.
Second paragraph, if the take off is rejected the captain takes over, however if the take off is continued and the FO is handling things well he continues to fly and set up for the approach, though in my company the captain has to do the actual landing.
Regards,
BH.
Warning Toxic!
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Gunner- you need to understand what V1 means. In the scenario you suggest, no chance, therefore you should already have abandoned your take-off. Particulary with both on one side out, you would not be able to maintain runway direction at that speed. As Bullethead stated, at V1 you have a severe struggle on your hands, but it can be done. In real life, a significant number, probably a majority, of such failures would result in a crash.
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757-200 Spoilers Question.
A less aviation inclined acquiantance of mine posed to me a question about something he observed on a flight home from LAS.He noticed the spoilers being deployed while in what appeared to be normal flight.What situations would exist for the spoilers to be deployed in flight?
Landing is the only time I've seen spoilers active, but then I can count on the fingers and thumb of one hand how many times I've flown. <G>
Thanks for your time..............
Landing is the only time I've seen spoilers active, but then I can count on the fingers and thumb of one hand how many times I've flown. <G>
Thanks for your time..............
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I'm no expert, but I think if the pilot/ATC made a (big) mistake and they had to make a steep descent or quick deceleration, they can be extended to increase drag, but you don't see it done very often.
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I've seen them deployed in flight on a 737 IIRC.
If you are asked to get a move on by ATC before starting a descent, or if you are given a late descent, why not use them?
Ideally probably would not want to as its effectively 'wasted' energy, but if it gets the desired effect for the situation, I don't think anyone has made a 'mistake'.
Disclaimer: I've never flown anything with spoilers on.
If you are asked to get a move on by ATC before starting a descent, or if you are given a late descent, why not use them?
Ideally probably would not want to as its effectively 'wasted' energy, but if it gets the desired effect for the situation, I don't think anyone has made a 'mistake'.
Disclaimer: I've never flown anything with spoilers on.
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On a 757 the spoilers are used to increase drag and reduce lift in flight and on the ground. However they also supplement the ailerons in roll control depending on the amount of control wheel input. Therefore in a turn you will very like see them deploying without any direct input by the pilot other than through the normal control wheel input.
In a descent, or when slowing down in level flight, or when slowing down and descending they will be selected by manual input of the speedbrake lever. This is an almost every flight occurance at some point or other.
Finally the spoilers are fully deployed automatically ( normally ) or manually on landing to reduce lift and transfer weight to the main wheels (and brakes). This occurs as soon as the main gear trucks untilt, or when either thrust reverser is activated, or when manually applied.
It is not likely to be the case they were deployed my mistake, as to do so would be very difficult and extremely unlikely. They are used very often and normally to achieve a desired profile by either increasing a rate of descent, or increasing the drag to slow the aircraft down. The 757 is quite a slippery ship, and often needs assistance in reducing speed particularly in busy traffic environments or where absolute restrictions apply, such as in the USA (and other locations) where a mandatory 250 kts or below is a requirement below 10,000 feet for example.
In a descent, or when slowing down in level flight, or when slowing down and descending they will be selected by manual input of the speedbrake lever. This is an almost every flight occurance at some point or other.
Finally the spoilers are fully deployed automatically ( normally ) or manually on landing to reduce lift and transfer weight to the main wheels (and brakes). This occurs as soon as the main gear trucks untilt, or when either thrust reverser is activated, or when manually applied.
It is not likely to be the case they were deployed my mistake, as to do so would be very difficult and extremely unlikely. They are used very often and normally to achieve a desired profile by either increasing a rate of descent, or increasing the drag to slow the aircraft down. The 757 is quite a slippery ship, and often needs assistance in reducing speed particularly in busy traffic environments or where absolute restrictions apply, such as in the USA (and other locations) where a mandatory 250 kts or below is a requirement below 10,000 feet for example.
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Angle of Engines on MD-80
Why are (at least some) airliner engines mounted at an up angle to the horizon--the intake end higher than the nozzle end? I first noticed the design element on the MD-80.
Apologies if the question is answered elsewhere on Pprune--I did look, and couldn't find it addressed.
Many thanks.
Lax Pax
Apologies if the question is answered elsewhere on Pprune--I did look, and couldn't find it addressed.
Many thanks.
Lax Pax
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Why are (at least some) airliner engines mounted at an up angle to the horizon
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So then wing-mounted engines would not be angled because there's no fuselage and associated air stream to deal with(?).
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Not meaning to hijack the thread but I've recently noticed an MD80(2/3?) with engines removed; there are 3 windows aft of the left main door (assume same on stbd side). Having not noticed them before I presume they are masked when engines mounted. What would be located inside the cabin here? Thinking a galley perhaps?
Thx.
Thx.
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Sometimes there's a galley or such there, but mre likely there are SLF seats behind the engine inlets.
If you want something of an education in fluid flow, sit back there during a night takeoff in light snow, and watch the snowflakes change direction as the ship accelerates down the runway. REALLY interesting!
If you want something of an education in fluid flow, sit back there during a night takeoff in light snow, and watch the snowflakes change direction as the ship accelerates down the runway. REALLY interesting!
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Flight idle and ground idle
What are the reasons for having different idle speeds for jet engines in different flight regimes? I note that there is a ground idle, which seems to be about 25% N1, and a flight idle, which seems to be around 40% N1, and both seem to be automatically set for idle in recent aircraft (I suppose pilots of older aircraft set these speeds manually?).
I've read of two potential reasons for the difference: (1) Higher idle speeds at high altitudes reduce the possibility of a flameout; and (2) flight idle is designed to match the drag of engine nacelles so that an aircraft can glide in a descent with the drag of the nacelles "erased."
Are these the real reasons? Are there others? Is the notion of flight idle and ground idle common to all jet aircraft, or only certain aircraft? Are there other idle speeds?
I've read of two potential reasons for the difference: (1) Higher idle speeds at high altitudes reduce the possibility of a flameout; and (2) flight idle is designed to match the drag of engine nacelles so that an aircraft can glide in a descent with the drag of the nacelles "erased."
Are these the real reasons? Are there others? Is the notion of flight idle and ground idle common to all jet aircraft, or only certain aircraft? Are there other idle speeds?
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Another reason is a safety buffer, since it takes a LONG time for a CF6 (for example) to accelerate from 25% N1 to 40%.
There is also a consideration in some airplanes of reliably providing enough bleed air for all the systems airborne.
There is also a consideration in some airplanes of reliably providing enough bleed air for all the systems airborne.
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Anthony,
Some aircraft use different idle settings, others don't. Generally that's an engine function, rather than an aircraft function; airframes tend to use a variety of engines either as a customer choice or just as the airplane evolves...and what's an option on one engine installation may not be the same on another...even though it's the same type airplane. The B747, for example...three different basic engine makes to hang on it, with differnt models engine from different manufacturers.
I flew the C-130. The early models I flew didn't have a ground idle. These were turbopropeller airplanes; the T-56A-9 engine had no ground idle, but the T-56A-14 engine did. It was quieter, cooler, and burned less fuel on the ground. As previously mentioned, in flight, a higher idle speed means the engine spools up faster, and is less likely to flame-out...as well as producing more bleed air for pressurization, air conditioning, anti-ice, etc.
At low engine speeds, small openings have to be used in the engine, sometimes called acceleration bleeds, which dump air out of the compressor to keep it from stalling. As air enters the engine, it's compacted or compressed, and pushed through a series of stages which continue to do so, before it's slowed, pressure increased, and then fuel added to burn. In those compression stages, an orderly flow of air is necessary; increase the pressure too much without enough airflow, or allow the blades to turn slowly enough, and the airflow in there stalls; it can reverse direction in the engine, the flame in the engine can go out, and somewhere in there, engine damage can also occur. The acceleration bleeds are small valves which open to let some of that pressure out when the engine is operating at low speeds.
Wasting this compressed air in flight is pointless...especially when the bleed air is used for so many functions in the airframe. Preventing the engine from going so slowly as to open these bleeds is an important operational consideration, then, and is designed into the operating design of the engine. Some engines revert to ground idle on their own after touchdown, others must be put there manually.
Some aircraft use different idle settings, others don't. Generally that's an engine function, rather than an aircraft function; airframes tend to use a variety of engines either as a customer choice or just as the airplane evolves...and what's an option on one engine installation may not be the same on another...even though it's the same type airplane. The B747, for example...three different basic engine makes to hang on it, with differnt models engine from different manufacturers.
I flew the C-130. The early models I flew didn't have a ground idle. These were turbopropeller airplanes; the T-56A-9 engine had no ground idle, but the T-56A-14 engine did. It was quieter, cooler, and burned less fuel on the ground. As previously mentioned, in flight, a higher idle speed means the engine spools up faster, and is less likely to flame-out...as well as producing more bleed air for pressurization, air conditioning, anti-ice, etc.
At low engine speeds, small openings have to be used in the engine, sometimes called acceleration bleeds, which dump air out of the compressor to keep it from stalling. As air enters the engine, it's compacted or compressed, and pushed through a series of stages which continue to do so, before it's slowed, pressure increased, and then fuel added to burn. In those compression stages, an orderly flow of air is necessary; increase the pressure too much without enough airflow, or allow the blades to turn slowly enough, and the airflow in there stalls; it can reverse direction in the engine, the flame in the engine can go out, and somewhere in there, engine damage can also occur. The acceleration bleeds are small valves which open to let some of that pressure out when the engine is operating at low speeds.
Wasting this compressed air in flight is pointless...especially when the bleed air is used for so many functions in the airframe. Preventing the engine from going so slowly as to open these bleeds is an important operational consideration, then, and is designed into the operating design of the engine. Some engines revert to ground idle on their own after touchdown, others must be put there manually.
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Keeping a constant taxi speed
Is there some secret to getting a large aircraft to roll at a constant speed during taxi? I'm having a terrible time getting my aircraft to taxi at a reasonably constant speed, and I'm wondering if airline pilots have some special technique for doing this. Or is it just practice?
For example, it seems that a lightly loaded 747-400 will lazily start rolling at 35% N1, but then it will speed up and up and in no time you're rolling along at 30 knots. And yet if you set power to 32% N1, it will gradually slow down and stop. The "sweet spot" seems to be about 0.00008 knots in width. Sometimes I hit it entirely by accident, but otherwise constant tweaking of the throttles is required. I must be doing something wrong.
Ditto for the 737-800, except that you see results a bit quicker when you adjust the throttles. A 767-300ER seems to want to roll even at idle, but it does seem to speed up and slow down more rapidly, which makes it a little easier to set the throttle.
So, how do you taxi at a steady speed in real life? Do you try to find the right spot for the throttles or just constantly adjust them. And is it cheating to set the throttles so that you gradually accelerate and then tap the brakes a bit to slow down when necessary? I don't know how much this heats the brakes. On a small plane I'd use differential braking to help in turns but I don't know if this is allowed or a good idea on large aircraft (and in any case differential braking doesn't seem to make a lot of difference in turns, at least in simulation).
For example, it seems that a lightly loaded 747-400 will lazily start rolling at 35% N1, but then it will speed up and up and in no time you're rolling along at 30 knots. And yet if you set power to 32% N1, it will gradually slow down and stop. The "sweet spot" seems to be about 0.00008 knots in width. Sometimes I hit it entirely by accident, but otherwise constant tweaking of the throttles is required. I must be doing something wrong.
Ditto for the 737-800, except that you see results a bit quicker when you adjust the throttles. A 767-300ER seems to want to roll even at idle, but it does seem to speed up and slow down more rapidly, which makes it a little easier to set the throttle.
So, how do you taxi at a steady speed in real life? Do you try to find the right spot for the throttles or just constantly adjust them. And is it cheating to set the throttles so that you gradually accelerate and then tap the brakes a bit to slow down when necessary? I don't know how much this heats the brakes. On a small plane I'd use differential braking to help in turns but I don't know if this is allowed or a good idea on large aircraft (and in any case differential braking doesn't seem to make a lot of difference in turns, at least in simulation).
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Keeping a constant taxi speed
Is there some secret to getting a large aircraft to roll at a constant speed during taxi? I'm having a terrible time getting my aircraft to taxi at a reasonably constant speed, and I'm wondering if airline pilots have some special technique for doing this. Or is it just practice?
For example, it seems that a lightly loaded 747-400 will lazily start rolling at 35% N1, but then it will speed up and up and in no time you're rolling along at 30 knots. And yet if you set power to 32% N1, it will gradually slow down and stop. The "sweet spot" seems to be about 0.00008 knots in width. Sometimes I hit it entirely by accident, but otherwise constant tweaking of the throttles is required. I must be doing something wrong.
Ditto for the 737-800, except that you see results a bit quicker when you adjust the throttles. A 767-300ER seems to want to roll even at idle, but it does seem to speed up and slow down more rapidly, which makes it a little easier to set the throttle.
So, how do you taxi at a steady speed in real life? Do you try to find the right spot for the throttles or just constantly adjust them. And is it cheating to set the throttles so that you gradually accelerate and then tap the brakes a bit to slow down when necessary? I don't know how much this heats the brakes. On a small plane I'd use differential braking to help in turns but I don't know if this is allowed or a good idea on large aircraft (and in any case differential braking doesn't seem to make a lot of difference in turns, at least in simulation).
For example, it seems that a lightly loaded 747-400 will lazily start rolling at 35% N1, but then it will speed up and up and in no time you're rolling along at 30 knots. And yet if you set power to 32% N1, it will gradually slow down and stop. The "sweet spot" seems to be about 0.00008 knots in width. Sometimes I hit it entirely by accident, but otherwise constant tweaking of the throttles is required. I must be doing something wrong.
Ditto for the 737-800, except that you see results a bit quicker when you adjust the throttles. A 767-300ER seems to want to roll even at idle, but it does seem to speed up and slow down more rapidly, which makes it a little easier to set the throttle.
So, how do you taxi at a steady speed in real life? Do you try to find the right spot for the throttles or just constantly adjust them. And is it cheating to set the throttles so that you gradually accelerate and then tap the brakes a bit to slow down when necessary? I don't know how much this heats the brakes. On a small plane I'd use differential braking to help in turns but I don't know if this is allowed or a good idea on large aircraft (and in any case differential braking doesn't seem to make a lot of difference in turns, at least in simulation).