747 - Outboard engine failure- why no bank?
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747 - Outboard engine failure- why no bank?
I'm curious how the heavy drivers actually do this.
I have a sim briefing document in front of me that says "Control wheel level, rudder as required" for an outboard engine failure.
Why no roll inputs/bank angle for optimized climb performance?
Is the point of keeping a neutral control column just to ensure the spoilers stay retracted? Even during a V2 climb?
In the medium turboprops I fly, we would also keep the wings level (except for the initial climb) during an engine failure. But I always thought there was a bit of aileron input along with the rudder input to maintain this.
Thanks,
fpt
I have a sim briefing document in front of me that says "Control wheel level, rudder as required" for an outboard engine failure.
Why no roll inputs/bank angle for optimized climb performance?
Is the point of keeping a neutral control column just to ensure the spoilers stay retracted? Even during a V2 climb?
In the medium turboprops I fly, we would also keep the wings level (except for the initial climb) during an engine failure. But I always thought there was a bit of aileron input along with the rudder input to maintain this.
Thanks,
fpt
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Wheel "level" -
According to the FCTM 747 - this technique results in minimizing the sideslip angle, and thereby, reduces drag. Drag of course is created by spoilers that are raised by the wheel lateral inputs.
xxx
Except at lower speeds (which are closer to VmcA), I never use any "bank" technique to improve directional control. So try to minimize bank in 747s...
Happy contrails
xxx
Except at lower speeds (which are closer to VmcA), I never use any "bank" technique to improve directional control. So try to minimize bank in 747s...
Happy contrails
Moderator
Zero slip will approximate minimum drag and is achieved with a few degrees into the operating engines. Unless things are really critical, the effort is not worth the gain, especially when a bit of hamfisted roll control will bring up the boards on the jets. Hence, the general Boeing guidance is nil wheel input and rudder to maintain heading.
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Thank You
Thanks for the replies guys.
Informative as always.
I guess it will take a bit of chair-flying to change some of the second nature techniques I have from my current background.
Informative as always.
I guess it will take a bit of chair-flying to change some of the second nature techniques I have from my current background.
Remember in a 4 Engine jet you've only lost 25% power on one side and not 50%.
That's why the 777 has such a big rudder
However you still need to have a slight wing down in the 777 ( maybe 3 deg ), it is very hard, if not impossible with full thrust to keep the wings level ( yes the yoke is zero and the spoilers are down ) while climbing out in the second segment. Once it's clean around 220 kts there is no problem keeping everything straight.
In the 744 with 2 engines out it was the same I think.
That's why the 777 has such a big rudder
However you still need to have a slight wing down in the 777 ( maybe 3 deg ), it is very hard, if not impossible with full thrust to keep the wings level ( yes the yoke is zero and the spoilers are down ) while climbing out in the second segment. Once it's clean around 220 kts there is no problem keeping everything straight.In the 744 with 2 engines out it was the same I think.
Moderator
(a) rudder is sized to suit the aircraft. Doesn't matter whether you have two engines or four, the OEM is only going to give you enough rudder to meet the design standards and certification process requirements.
(b) bank has two important considerations. (There is no particular problem flying constant heading with varying bank angles provided that rudder capability is adequate and the resulting sideslip angle doesn't cause you problems).
(i) Vmca is VERY bank sensitive which is why one generally can presume that the quoted certification figure relates to 5 deg bank into the operating engines. This certification bank limit covers considerations of keeping a level playing field and avoiding side slip related handling problems. Any bank delta back towards wings level and beyond pushes the Vmca up - rapidly - if I recall correctly from a course in years past, a well-known many-engined strategic bomber saw something in the vicinity of a 30-40 kt increase in Vmca in this adverse bank configuration. It is important to note that Vmca considerations do not include climb capability.
(ii) best climb (or least descent, as the case may be) will occur for a bank angle of around 2-3 deg into the operating engines where the side slip angle is zero. I am reliably advised by those who have vastly more experience in such matters than I .. that this is a pretty general across the board bank angle regardless of Type. It is not overly simple to fly this sort of bank angle using a typical A/H and, when one considers the penalty on aircraft for which wheel angle is linked to spoiler deflection, the small climb penalty with wings and wheel level is a better option than trying to get the last bit of performance and making a hash of it. With a slip string stuck on the nose (or a side slip gauge for those who flew Concorde) it is, at least conceptually, a much easier exercise. I note Bellerophon's comment in the hyperlinked post about endeavouring to fly OEI zero slip in Concorde.
(c) handling, especially during the dynamic initial failure, is very speed sensitive. In the cruise - no sweat - during the takeoff flare for a min V1 schedule takeoff - wholely an animal of a different kind. In the latter situation, be prepared for rapid and substantial control inputs (rudder and aileron) to keep the aircraft under control while you are sorting things out. It was just for this exposure that I used to work folk up to this exercise in 737 endorsement training play time. While the wide eyes were typical in the first couple of tries, the smiles of satisfaction were real once the trainee had the beast under control after several goes at the exercise. As an aside, it really caused/causes me some concern that the majority of airline aircrew have never had any exposure to min speed climb out failures and the rapidly escalating stick and rudder problems which attend keeping the dynamics under control ....
(b) bank has two important considerations. (There is no particular problem flying constant heading with varying bank angles provided that rudder capability is adequate and the resulting sideslip angle doesn't cause you problems).
(i) Vmca is VERY bank sensitive which is why one generally can presume that the quoted certification figure relates to 5 deg bank into the operating engines. This certification bank limit covers considerations of keeping a level playing field and avoiding side slip related handling problems. Any bank delta back towards wings level and beyond pushes the Vmca up - rapidly - if I recall correctly from a course in years past, a well-known many-engined strategic bomber saw something in the vicinity of a 30-40 kt increase in Vmca in this adverse bank configuration. It is important to note that Vmca considerations do not include climb capability.
(ii) best climb (or least descent, as the case may be) will occur for a bank angle of around 2-3 deg into the operating engines where the side slip angle is zero. I am reliably advised by those who have vastly more experience in such matters than I .. that this is a pretty general across the board bank angle regardless of Type. It is not overly simple to fly this sort of bank angle using a typical A/H and, when one considers the penalty on aircraft for which wheel angle is linked to spoiler deflection, the small climb penalty with wings and wheel level is a better option than trying to get the last bit of performance and making a hash of it. With a slip string stuck on the nose (or a side slip gauge for those who flew Concorde) it is, at least conceptually, a much easier exercise. I note Bellerophon's comment in the hyperlinked post about endeavouring to fly OEI zero slip in Concorde.
(c) handling, especially during the dynamic initial failure, is very speed sensitive. In the cruise - no sweat - during the takeoff flare for a min V1 schedule takeoff - wholely an animal of a different kind. In the latter situation, be prepared for rapid and substantial control inputs (rudder and aileron) to keep the aircraft under control while you are sorting things out. It was just for this exposure that I used to work folk up to this exercise in 737 endorsement training play time. While the wide eyes were typical in the first couple of tries, the smiles of satisfaction were real once the trainee had the beast under control after several goes at the exercise. As an aside, it really caused/causes me some concern that the majority of airline aircrew have never had any exposure to min speed climb out failures and the rapidly escalating stick and rudder problems which attend keeping the dynamics under control ....
John thanks
On the basis of your fine words I wonder if you could put a perspective on the AWACs Multiple bird ingestion accident in Elmendorf for me.
They completely disabled two engines on one side just after lift off. On the CVR one of the people in the cockpit says rudder overboost more than once and the pilot in command says thank you .
I believe that this aircraft sideslipped and rolled down into the dead engines somewhat as it intersected a rising hill.
What is the purpose of the rudder overboost that was being called for?
On the basis of your fine words I wonder if you could put a perspective on the AWACs Multiple bird ingestion accident in Elmendorf for me.
They completely disabled two engines on one side just after lift off. On the CVR one of the people in the cockpit says rudder overboost more than once and the pilot in command says thank you .
I believe that this aircraft sideslipped and rolled down into the dead engines somewhat as it intersected a rising hill.
What is the purpose of the rudder overboost that was being called for?
Moderator
I presume you are referring to the 1995 mishap ? I don't have any reports on that accident and can only presume that the outcome related to Vmca-2.
In general, lose two on the one side too early into the takeoff and the aircraft is going to reacquaint itself with terra firma shortly after .. about all the crew can do is manipulate the operating engine(s) thrust to avoid a cartwheeling return to earth .. if they are quick enough and have a bit of Lady Luck on their side.
Sometimes the numbers are stacked against the aircraft and the crew on the day ... no guarantees ... only probabilities.
Although I considered bidding for the 707, I never flew it (much to my later regret) so I can't offer comment on the overboost question. I have no doubt that others who have Type experience will be able to answer the question.
In general, lose two on the one side too early into the takeoff and the aircraft is going to reacquaint itself with terra firma shortly after .. about all the crew can do is manipulate the operating engine(s) thrust to avoid a cartwheeling return to earth .. if they are quick enough and have a bit of Lady Luck on their side.
Sometimes the numbers are stacked against the aircraft and the crew on the day ... no guarantees ... only probabilities.
Although I considered bidding for the 707, I never flew it (much to my later regret) so I can't offer comment on the overboost question. I have no doubt that others who have Type experience will be able to answer the question.
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707 VmcA-2
The AWACS (E-3) is a 707-300...
It can be equipped with JT3D or CFM-56 engines.
xxx
I flew the 707-300s with JT3D-3B of 18,000 lbs thrust.
Typical VmcA-1 was about 120 Kts, and VmcA-2 was about 145 Kts.
I never flew 707s with CFM-56, but I flew DC8-70s with such engines.
Fitted on E-3, with increased thrust, I would expect VmcA-2 increased by some 10 Kts...
Was more than 150 Kts in the DC8-73...
xxx
The 707 had a boosted rudder (hydraulic system).
Full 3000 psi was available when flaps were 14 and speed was low.
At higher speed, and flaps up, the boost pressure reduced to 750 psi...
Hope my numbers are correct, my last flight on 707 was 20+ years ago.
xxx
Happy contrails
It can be equipped with JT3D or CFM-56 engines.
xxx
I flew the 707-300s with JT3D-3B of 18,000 lbs thrust.
Typical VmcA-1 was about 120 Kts, and VmcA-2 was about 145 Kts.
I never flew 707s with CFM-56, but I flew DC8-70s with such engines.
Fitted on E-3, with increased thrust, I would expect VmcA-2 increased by some 10 Kts...
Was more than 150 Kts in the DC8-73...
xxx
The 707 had a boosted rudder (hydraulic system).
Full 3000 psi was available when flaps were 14 and speed was low.
At higher speed, and flaps up, the boost pressure reduced to 750 psi...
Hope my numbers are correct, my last flight on 707 was 20+ years ago.
xxx
Happy contrails
The 707 had a boosted rudder (hydraulic system).
Full 3000 psi was available when flaps were 14 and speed was low.
At higher speed, and flaps up, the boost pressure reduced to 750 psi...
Hope my numbers are correct, my last flight on 707 was 20+ years ago.
Full 3000 psi was available when flaps were 14 and speed was low.
At higher speed, and flaps up, the boost pressure reduced to 750 psi...
Hope my numbers are correct, my last flight on 707 was 20+ years ago.
I always thought that the rudder performance was limited by airspeed, fin area and fin deflection. If the airspeed is low (AWACs accident) then it shouldn't take unusual pedal pressure to fully deflect it??? or am I all screwed up
John.......
From my experience the 777-300ER is basically the same size as the 400 ( with similar total thrust ) but it has a much bigger rudder that deflects futher and has a tab. This from From the 777 FCOM 1
Yaw control is provided by a single rudder, which is almost the same height as the
vertical tail. The lower portion of the rudder has a hinged section (tab) that deflects
twice as far as the main rudder surface to provide additional yaw control authority.During takeoff, the rudder becomes aerodynamically effective at approximately 60
knots
I always understood that a big twin with very big donks on both sides needed a bigger rudder than a similar sized quad simply because of the huge thrust loss. Also the 400 only has 1 VMCA speed that caters for 1, 2 or 3 Engines out as far as I know.
take a look at the B52, it has a very small rudder.
(a) rudder is sized to suit the aircraft. Doesn't matter whether you have two engines or four, the OEM is only going to give you enough rudder to meet the design standards and certification process requirements.
Yaw control is provided by a single rudder, which is almost the same height as the
vertical tail. The lower portion of the rudder has a hinged section (tab) that deflects
twice as far as the main rudder surface to provide additional yaw control authority.During takeoff, the rudder becomes aerodynamically effective at approximately 60
knots
I always understood that a big twin with very big donks on both sides needed a bigger rudder than a similar sized quad simply because of the huge thrust loss. Also the 400 only has 1 VMCA speed that caters for 1, 2 or 3 Engines out as far as I know.
take a look at the B52, it has a very small rudder.
Moderator
One would normally expect a bigger rudder on a twin, indeed, but you will only get what the OEM needs to achieve certification compliance .. ie the end result for the pilot is going to be similar.
Long time since I've looked at a 744 AFM but the Vmca certainly will be considerably greater for two out on one side than one.
Long time since I've looked at a 744 AFM but the Vmca certainly will be considerably greater for two out on one side than one.
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Some VmcA numbers for 747s
For info - VmcA numbers for 747-200/300 with JT9D-7Q.
These engines are 53,000 lbs thrust.
xxx
From my latest Boeing 747 FOM table.
VmcG sea level STD temperature (lowest V1 FAA tables) = 128 KIAS
Expect lowest V1 to be higher with the 7 kts CAA X-wind factor.
VmcA-2 sea level STD temperature is 159 KIAS.
xxx
I would therefore expect VmcA-2 in a 747-400 to be around 160-162 KIAS
This with engines JT9D-7R4G2 which are approximately 55,000 lbs thrust.
xxx
Happy contrails
These engines are 53,000 lbs thrust.
xxx
From my latest Boeing 747 FOM table.
VmcG sea level STD temperature (lowest V1 FAA tables) = 128 KIAS
Expect lowest V1 to be higher with the 7 kts CAA X-wind factor.
VmcA-2 sea level STD temperature is 159 KIAS.
xxx
I would therefore expect VmcA-2 in a 747-400 to be around 160-162 KIAS
This with engines JT9D-7R4G2 which are approximately 55,000 lbs thrust.
xxx
Happy contrails
Just looked at our 744's FCOM2 and no mention of VMCA 2 at all, it only mentions VMCG and VMCA in the definitions section. "Failure of the most critical engine at takeoff thrust etc........"
The computer Takeoff data we get in the flight deck from the ACARS system only mentions VMCG.
In fact there are no tables to calculate VMCA or VMCG in our FCOM 2 manuals for the 777 or the 744.
The computer Takeoff data we get in the flight deck from the ACARS system only mentions VMCG.
In fact there are no tables to calculate VMCA or VMCG in our FCOM 2 manuals for the 777 or the 744.
Moderator
I'll leave it to other 744 folk to comment on the specifics. However, in the AFM performance section (and probably in whatever performance data is in the FCOM) there will very definitely be some wisdom words about Vmca-2.
The Vmca to which you refer is Vmca-1 (ie Vmca with failure of the first, most critical, engine).
The Vmca to which you refer is Vmca-1 (ie Vmca with failure of the first, most critical, engine).
ahhhhhh Just slap me in the face John, I flew the 400 for 8 years and believe me I've never heard of VMCA2 we don't have the term in our manuals anywhere.......................ok
I'm just re-reading the FCOM2 for the 400 now and still can't find ANY ref to VMCA2 or VMCG2. The only thing close is 3 Eng ferry flights section where it mentions: The V2 chosen is the higher of VMCA or VMCG ( twp Engines inoperative ) blah blah blah..............
Now I'll look at the FCTM to see if it differentiates 1 or 2 Engines out.
I'm just re-reading the FCOM2 for the 400 now and still can't find ANY ref to VMCA2 or VMCG2. The only thing close is 3 Eng ferry flights section where it mentions: The V2 chosen is the higher of VMCA or VMCG ( twp Engines inoperative ) blah blah blah..............
Now I'll look at the FCTM to see if it differentiates 1 or 2 Engines out.
Nope VMCA2 OR VMCG2 is not mentioned apart from in the 3 Eng ferry section.
The takeoff perf charts have no mention of these at all.
The computer data we use has the VMCG for 1 eng only on it.
Eg: Boeing 744, DXB RWY 12R
290 tonnes
To 58 EPR 1.54
Flap 20 VMCG 123
V1 134
VR 145
V2 155
That's all we need I guess.
The takeoff perf charts have no mention of these at all.
The computer data we use has the VMCG for 1 eng only on it.
Eg: Boeing 744, DXB RWY 12R
290 tonnes
To 58 EPR 1.54
Flap 20 VMCG 123
V1 134
VR 145
V2 155
That's all we need I guess.