B747 Back up Hydraulics
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The Classic has an electrical pitch control that only a handful of pilots and flight engineers know about, and few practice with it in the sim, but it does work and I recommend you try it. Never know if you will need it.
The elevators are powered by hydraulics, with no manual reversion. The stabilizer trim system is powered by hydraulic motors, without an electric reversion. What electric system are you talking about?
Pilot input controls hydraulic actuation of the inboard elevators, and the inboard elevators control the opposite outboard elevator by cable to a hydraulic actuator...There isn't an electric motor to the inboard or outboard elevators, and the motor moving the horizontal stabilizer is composed of two hydraulic motors.
Electric input from the control wheel switches only signals the stabilizer trim drive units to operate, but there's no electricity moving the stab; it's commanding sequence valves for the hydraulic motor to operate, and it's operated hydraulically. Take away the hydraulics and the electric trim switches can be moved all day long, to no avail.
Likewise, the pedestle manual trim levers do nothing more than sequence hydraulic fluid to move the stab trim unit motors, and involve no electrical motors.
With this in mind, how is electric pitch control available? If a trim runway occurs, electrical input to the stab trim can be interrupted by pushing on the control column in the opposite direction of the runaway travel, but the solution there ultimately involves hydraulics, too; the cutaway switches on the pedestle to cut hydraulic power to the hydraulic trim motors. With that cut, or lost...what's left to drive the stab trim unit?
Usual disclaimers apply!
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Actually squire boofhead is sort of right! The classics alternate T/E flaps switches IIRC were marked 'pitch up' for the outb'd and 'pitch down' for the inb'd, so I guess there would be a pitch change albeit extremely slow. However whether it would have been useful or not if used in anger I don't know.
Or indeed if the alternate motors lasted long enough, they don't take too kindly to being run up and down continiously.
Or indeed if the alternate motors lasted long enough, they don't take too kindly to being run up and down continiously.
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I imagine that in extremely calm conditions, the alternate flap switches could be used to effect pitch change, though that might make for an interesting approach and landing. Travel on the normal flaps takes about 45 seconds. Go to the alternate switches, and the rate is greatly reduced; full travel takes five and a half minutes. That's a little long to be making corrections while flying an approach. Certainly if it's all you've got, it's all you've got...but you're going to get faster changes by trimming for a speed and using power.
Further, if you do indeed have a full hydraulic loss, and power is a big part what you're doing, then you also have no roll control beyond splitting the flaps...again, better hope for a calm day, an extremely long runway and very uniform engine response.
Further, if you do indeed have a full hydraulic loss, and power is a big part what you're doing, then you also have no roll control beyond splitting the flaps...again, better hope for a calm day, an extremely long runway and very uniform engine response.
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Trim problems, nose up/down
In the 707, we had an alternate procedure extending inboard flaps to get the nose up, or extending outboard flaps to get nose down in case of trim problems. Panel overhead captain's head was even indicating what switch to use. Also we could use partial spoilers, inboards or outboards. Although such procedure does not exist in 747, it could be achieved. I will play that game in a simulator one of these days, to see what can be done.
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After all a 747 is just a big 707 with a lot of extra goodies.
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Happy contrails
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After all a 747 is just a big 707 with a lot of extra goodies.
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Happy contrails
Last edited by BelArgUSA; 1st Oct 2008 at 23:13. Reason: Typing error - fat fingers
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But before I did, I would be climbing into the roof space with the crash axe and trying to pull those bloody control cables with my asbestos gloved hands until I got the right one!
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Al Haynes could have used this system in the DC10 except that that airplane does not have the electric backup to the flap. One point of the Boeing system is that an airplane will fly the speed at which the failure occurred, unless you can change the trim setting somehow. The DC10 did not have that option, but the 747 Classic does. As the flap is extended, the trim speed reduces. As the gear etc is moved, the trim speed can be changed to adapt by extending the inboard or outboard flaps accordingly. With engine power to assist in turns, rate of descent and speed adjustments, it is possible to set up a slow approach with flap set and by moving one set of flaps to even maintain a glidepath. It is an exercise you can try in the sim. Turbulence would be a bad thing, but still better than just sitting there on your hands.
One note of warning; do not pulll the throttles closed for the touchdown, or else the airplane will nose in. Wait until you are on the ground.
In the 744 you can achieve the same effect by pulling either the inboard or outboard flap circuit breaker (just behind the FO seat) and extend or retract one set to achieve the same thing, but with a hydraulic fuse, that should not be necessary.
I remember wondering out loud why those arrows showing the trim change were on the electric switches for the alternate flap in the Classic and was lucky enough to be flying with a smart South African fellow who explained it all to me. He said they used to include it in the type rating courses but dropped it when told the chance of such a failure was so low. A few hundred people might, if they were able, correct that opinion.
One note of warning; do not pulll the throttles closed for the touchdown, or else the airplane will nose in. Wait until you are on the ground.
In the 744 you can achieve the same effect by pulling either the inboard or outboard flap circuit breaker (just behind the FO seat) and extend or retract one set to achieve the same thing, but with a hydraulic fuse, that should not be necessary.
I remember wondering out loud why those arrows showing the trim change were on the electric switches for the alternate flap in the Classic and was lucky enough to be flying with a smart South African fellow who explained it all to me. He said they used to include it in the type rating courses but dropped it when told the chance of such a failure was so low. A few hundred people might, if they were able, correct that opinion.
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Al Haynes could have used this system in the DC10 ...
Face it folks, the 'ole TriStar was so far ahead of its time, it's unreal.
Speaking with a (now) retired Boeing design engineer a few months ago, he related that when Boeing looked at the L1011 years ago, they found the systems integration/redundancy so very good, it was a huge wake-up call to the folks in Seattle.
Lockheed, simply the finest, straight out of the factory, years ago.
PS: and yes, one can split the spoilers for pitch control, just like on the 707, years before.
A superb design.
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Hey all couldn't resist this post. I don't have the wealth of knowledge to add to this post - I'm just a professional pilot wannabe.
But I really enjoyed learning in this post. Thanks for sharing everyone!
But I really enjoyed learning in this post. Thanks for sharing everyone!
SkyGod
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If Al Haynes had been in an L1011 instead of a DC-10, he would have had a much better chance of landing the airplane in one piece...
Superior design, but no autopilot disconnect warning?
Or the L-10 aborting after V-1 in JFK due to false stall warning?
Good bird but not invincible...
Not fair to blame Easterns L1011 crash on the aircraft really, perhaps there should have been a louder autopilot disconnect warning but what happened to 'FLYING THE AIRCRAFT' someone should have been dedicated to that task exclusively.
And at JFK what kind of Pilot reacts to a stall warning after rotation by PUTTING IT DOWN ON THE RUNWAY ! by any standard that was irrational behaviour to a spurious warning, the aircraft was flying, the only appropriate response would have been to push the power up and lower the nose a tad.
Had the stick shaker go off a few time myself over the years after rotation, not that unusual with gusts or a 'sticky' aoa vane, putting it down again is unthinkable and disastrous in any aircraft.
Ridiculous to blame these accidents (officially attributed to Pilot error) to design deficiencies.
The Tristar never had a design caused accident, quite incredible really, Douglas could have done a lot better.
And at JFK what kind of Pilot reacts to a stall warning after rotation by PUTTING IT DOWN ON THE RUNWAY ! by any standard that was irrational behaviour to a spurious warning, the aircraft was flying, the only appropriate response would have been to push the power up and lower the nose a tad.
Had the stick shaker go off a few time myself over the years after rotation, not that unusual with gusts or a 'sticky' aoa vane, putting it down again is unthinkable and disastrous in any aircraft.
Ridiculous to blame these accidents (officially attributed to Pilot error) to design deficiencies.
The Tristar never had a design caused accident, quite incredible really, Douglas could have done a lot better.
Usual disclaimers apply!
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As good as it was/is didn't an EAL L1011 come very close to a hull loss when the 'fail safe' shaft failed?
Due in part to a location bearing failure caused by an oil fire inside the LP shaft.
IIRC the fan and shaft assy crawled its way up the 'S' duct and caused the loss of 3 hydraulic systems. I guess in that case the damage was upstream of the hydraulic fuses?
Not long after that a (Fan Catcher) mod. came out. Still it is one damn clever bit of kit...dunno why the RAF make such a meal of it.
Due in part to a location bearing failure caused by an oil fire inside the LP shaft.IIRC the fan and shaft assy crawled its way up the 'S' duct and caused the loss of 3 hydraulic systems. I guess in that case the damage was upstream of the hydraulic fuses?
Not long after that a (Fan Catcher) mod. came out. Still it is one damn clever bit of kit...dunno why the RAF make such a meal of it.
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Another 'almost' for the L1011 was over the Arabian Gulf, enroute KHI.
A wheel burst in the wheel well at FL290, ruptured the pressure hull, and disabled three of four hydraulic systems.
The airplane was diverted to DOH, with only system D fluid remaining, and landed very nicely by the First Officer...which was required, due to the Captains pole then being unserviceable.
SV trained for this procedure at each sim detail for F/O's...the quite good training showed when the chips were down.
A wheel burst in the wheel well at FL290, ruptured the pressure hull, and disabled three of four hydraulic systems.
The airplane was diverted to DOH, with only system D fluid remaining, and landed very nicely by the First Officer...which was required, due to the Captains pole then being unserviceable.
SV trained for this procedure at each sim detail for F/O's...the quite good training showed when the chips were down.
The "Pitch Up" and "Pitch Down" indications on the overhead panel on the 74C are reminers as to which way the aerodynamic trim goes when using the Alternate Flap extension. I'm pretty sure the intention wasn't to give the crew an alternate pitch control system. Having used them in the sim, I'm certain that pitch control would be near impossible.
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I'm not sure how deft one could be with those controls. As stated before, they take over five minutes to move full travel; they're very, very slow. Additionally, per some manuals, they work hard; a 20 minute cooldown period for the motors after having fun full travel. Working them back and forth sounds good on paper and in the simulator...but the airplane isn't the simulator. Imaginary motors in the sim have no duty cycle because they don't exist; real motors burn out, seize, burn brushes, fail where you don't want them to, and may not work out nearly as well as in the simulator.
Remember that for all it's training value, the simulator still pretends to show that which does not exist.
Remember that for all it's training value, the simulator still pretends to show that which does not exist.
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Additionally, per some manuals, they work hard; a 20 minute cooldown period for the motors after having fun full travel.
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Gear isn't really applicable to electric flap motors. In fact, the motors are working a lot harder under an airload to move the flaps, than they might on the ground.
Some motors? There are only two.
The Leading Edge Devices have separate motors for the groups, but for the trailing edge you have a choice; inboard or outboard.
I would imagine you would run all flap half way, then you could play with inboards and outboards separately to avoid overheating. If some motors did burn out, hopefully you would still have the other flap sections still working getting pitch up or down on that inboard or outboard section only.
The Leading Edge Devices have separate motors for the groups, but for the trailing edge you have a choice; inboard or outboard.
Last edited by SNS3Guppy; 2nd Oct 2008 at 20:45.
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I don't know how many motors each flap section has.
Also although they work hard in the air, with the gear down, cooling is much better.
The answer is the same in both cases...no effect.
They'd also not work very hard retracting.
Don't you think it would work?
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Why does putting the gear down cool electric flap motors?
I get the point about increased airloads, though (thanks for the reminder, Guppy)... However, I'm not sure how much they would increase in the flap ranges we are talking about for pitch control. I'd imagine extension would be more in the fore-aft plane, than the up-down plane.
Further, for a given airspeed, how does the gear have any effect on the load under which the flap motors are operating?
Rgds.
NSEU
Last edited by NSEU; 3rd Oct 2008 at 01:55.
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Not directly pertinent to the present discussion but an interesting observation -
In the early days of CRM work, my airline was a main player in Oz. One of the emergency refresher school exercises for a while involved role play with two people out of each other's sight co-operatively trying to achieve a goal involving difficult communication against the clock. A typical exercise was for one to communicate the arrangement of a set of coloured blocks with a goal that the other should rearrange his/her set to match.
I found it interesting in the extreme that, nearly to a (wo)man, the aircrew folk played it down to the wire. Conversely, the non-aircrew folk tended to "throw in the towel" when it became evident that the clock was likely to win .. think I would rather the former fighting attitude in the cockpit with an unusual, potentially catastrophic failure .. than the fatalism of the latter ?
I'm with Rainboe .. if nothing else at least it fills in the time before you die.
In the early days of CRM work, my airline was a main player in Oz. One of the emergency refresher school exercises for a while involved role play with two people out of each other's sight co-operatively trying to achieve a goal involving difficult communication against the clock. A typical exercise was for one to communicate the arrangement of a set of coloured blocks with a goal that the other should rearrange his/her set to match.
I found it interesting in the extreme that, nearly to a (wo)man, the aircrew folk played it down to the wire. Conversely, the non-aircrew folk tended to "throw in the towel" when it became evident that the clock was likely to win .. think I would rather the former fighting attitude in the cockpit with an unusual, potentially catastrophic failure .. than the fatalism of the latter ?
I'm with Rainboe .. if nothing else at least it fills in the time before you die.