Ask The Pilot

[jb747]

This surprises me.I would've thought that your reaction to a nose up or down attitude would've been reflexive. Similar to how you'd react to say, a car starting to slide. That, when you feel the aircraft go into a nose up attitude that you want to correct that you'd do it manually. But if the FBW control system is doing it for you then your manual input would be less than say, on the 744.

I don't think you quite understand. I'm flying an approach, with a pitch attitude of about 2.5º. To go around, I need about 15º and TO/GA power. Without any backside application, the increase in power will push the nose up. This effect is so strong, that once it gets to the desired attitude, I'll have to hold some forward force until I've trimmed it out, and I won't have had to pull to get it there. In the FBW aircraft, they don't pitch up by themselves, so you have to pull. Basically, FBW removes, or at least reduces, many of the secondary effects of controls. It's all about moment arms. The engines are very powerful, and lower than the drag line. So, any increase in power pitches the aircraft up, and a reduction pitches it down. When you next fly in a 767 doing an approach on a gusty day, every time the power is changed, the control column has to be pushed or pulled to counter the engine couple. Especially fun engine out, when you add rolling and yaw couples to the game as well.

Finally, getting back to your earlier statement regarding QF's sourcing of its A380 crew from 330s, I'm still surprised that you aren't senior to these guys given your background. ie. weren't 744 drivers senior to the 330's?

Yes...but they went to the 330 from the 744. And since then quite a few people have transferred over as well, so they've slotted in both above and below me.

 

[warpspeed]

I don't think you quite understand. I'm flying an approach, with a pitch attitude of about 2.5º. To go around, I need about 15º and TO/GA power. Without any backside application, the increase in power will push the nose up. This effect is so strong, that once it gets to the desired attitude, I'll have to hold some forward force until I've trimmed it out, and I won't have had to pull to get it there.

I think I know what this is like. I got to try out a basic 737 sim a while back (not a full on sim, so not sure how real this is). Flying a manual approach, when you select flaps 30, you need to push the control column forward progressively as it takes effect, otherwise the a/c goes nose up, loses speed, then the a/t increases power, which just exacerbates the issue even more. Completely unsettles the aircraft and approach. A progressive push input as the flaps take effect, smooths the whole thing out into a non issue.

I'd never realised that before in messing around in Ms flight sim.. Not until I was in this sim and the instructor pointed it out to me.

 

[mjt57]

I don't think you quite understand.

Well, I understand now. And I sort of did anyway.

Doesn't matter. Next question.

Watching Airport Live (I've only watched Ep 1 so far), they're towing the A380 to a terminal and are interviewing the "Brake Rider". When the tug turns the aircraft do the bogeys assist in turning as they do when you're steering it using the tiller? If so, what controls them?

As for the poster's comments about the B737 sim (which sounds like Flight Experience which I did last year), I'm still trying to wrap my head around why lowering the flaps lifts the nose. My initial thoughts on this was that drag underneath the wing would want to tilt it downwards. Obviously it must have something to do with lift, right?

 

[jb747]

Watching Airport Live (I've only watched Ep 1 so far), they're towing the A380 to a terminal and are interviewing the "Brake Rider". When the tug turns the aircraft do the bogeys assist in turning as they do when you're steering it using the tiller? If so, what controls them?

The body gear steering on the 747 and the 380 are substantially different. On the 747, the entire pair of body gear bogies twist in the opposite direction to the nose gear (once the nose gear is past about 20º, and at low speeds). It's very much like the rear wheel steering that was a fad on motor cars about 20 years ago. It makes a very substantial difference to the aircraft's willingness to turn, and the power required in the turn. It is an item that can be MELed, and the aircraft feels very different without it.

The A380 on the on the other hand, only has very limited body gear steering. In fact, calling it steering at all is a misnomer. All that happens is that the rear set of wheels on the body triple bogey are unlocked and driven off centre. It doesn't help the steering at all, but it does reduce the wear on those tyres. The 380 feels roughly like a 747 with no body gear steering, and as I'm sure some of you have noticed, it's quite prone to stopping in turns...in part due to the drag from the body gear.

In neither aircraft does it come into play when being towed. Part of the towing procedure is to actually lock out the system, and disconnect the nose gear from the steering system.

As for the poster's comments about the B737 sim (which sounds like Flight Experience which I did last year), I'm still trying to wrap my head around why lowering the flaps lifts the nose. My initial thoughts on this was that drag underneath the wing would want to tilt it downwards. Obviously it must have something to do with lift, right?

Here is an interesting article about trimming for basic pilot trainees: Pagea5Trim and Holding the Yoke

If we just look at an aircraft in level flight (actually any steady state will do, but this is easy to imagine). The aim is to decelerate from about 200k to about 130k. We will need all of the high lift devices to allow us to do that. But, as the aircraft will be in level flight at both ends of the exercise (and hopefully at the same height), the actual amount of lift needed will be exactly the same across the entire deceleration.

Devices normally consist of leading edge flaps, leading edge slats, and trailing edge flaps. The effect of flap is the same no matter whether it is leading or trailing edge...it makes the wing more curved, and so for any given speed it produces more lift (and more drag).

Slats actually don't produce lift...they simply create a slot; a gap that air can flow through. The slot tends to delay the stall to a higher angle of attack. Slats can be extremely simple. On the A4, they were full span, but automatic. They popped out as they felt like it, and were pushed in by air loadings. Springs and air...early digital. If you were pulling the aircraft towards max g, it would start to buffet (shake), the slats would come out, and the buffet would stop...so you pulled harder until it started again.

Back in our airliner, decelerating from 200 to 130 in level flight. As we take each stage of flap, our minimum speed will reduce by about 20 knots. As the first stage is selected, the aircraft is at the attitude and speed for 1 g level flight, so the wing immediately starts making more lift than we need. A push forward is needed...but as it decelerates the lift reduces, and you need to progressively select a higher attitude. If we stop the deceleration, we'll find that the final attitude will be lower than the initial level attitude, but the power will be higher. This will continue with each stage initially making more lift than needed, giving us the push forward/pull back cycle. Later stages tend to produce more drag increase than lift, so the pitch response isn't as obvious.

In the real world, we don't do this flying level, but incorporate it into the approach, which certainly tends to mask the attitude and power changes. If we get it right, much of an approach will be flown at idle (but NOT below 1,000 ft).

 

[mjt57]

In neither aircraft does it come into play when being towed. Part of the towing procedure is to actually lock out the system, and disconnect the nose gear from the steering system.

So, does that mean that the gear gets dragged around as the aircraft is turned by the tug?

Here is an interesting article about trimming for basic pilot trainees: Pagea5Trim and Holding the Yoke

Thanks for that.

And thanks for the "aerodynamics 101" lesson.

 

[jb747]

So, does that mean that the gear gets dragged around as the aircraft is turned by the tug?

Basically yes. When I first looked at it, I thought it might passively castor, but there's some nasty reasons not to allow that going backwards. I expect the pilots are way harder on the tyres than anything the tug can manage.

 

[Moody]

..... If we get it right, much of an approach will be flown at idle (but NOT below 1,000 ft).

Is it possible to do so all the way to touchdown? I have had some landings (particularly early morning) that felt like they were at idle all the way. Perhaps A/T was engaged but never needed.

 

[mjt57]

JB,

Yesterday the government announced changes to FBT laws surrounding novated leases for cars. Last night Qantas has suspended its car leasing program for employees. This morning they're discussing it on the radio and the commentator, Neil Mitchell mentioned pilots salary sacrificing cars.

I seem to recall that you said that you guys don't have this. Is what Mitchell said wrong?

 

[QF WP]

A more correct term is "salary packaging" which can encompass items like novated leases (for cars).

 

[jb747]

Is it possible to do so all the way to touchdown? I have had some landings (particularly early morning) that felt like they were at idle all the way. Perhaps A/T was engaged but never needed.

Part of what you'll have been hearing with regard to Asiana, is the requirement to be 'stable'. The point at which you have to be 'stable' varies (500 ft VMC/1000 ft IMC), but the upshot is that you have to be on the correct approach path vertically and laterally (whether it be visual or instrument), fully configured, speed within the allowed tolerance, and the power at approximately the normal approach setting. Outside any of those, and the approach isn't stable and you should go around.

Idle power most definitely isn't a normal approach power, at least below 1,000 feet. On the 767/747 engine N1 is about 64%. The 380 displays 'thrust', and that is around 23%. Let the power go too low, and you get into the zone from which the engines take time to accelerate, so the aim is to keep well above that point.

A/T engaged but never needed? No, the only reason that an engaged A/T wouldn't come off idle would be because you're too fast (in speed mode), or simply hadn't given it a mode to follow. In any event, most landings are manual, and Boeing pushes that autopilot out should go with autothrust out as well. Airbus, on the other hand, mean for the A/T to be engaged at all times, even when manually flying the aircraft.

I expect that what you've felt are landings on calm days, where the power has basically stayed at the one point. We tend to notice changes, not steady states.

 

[jb747]

Yesterday the government announced changes to FBT laws surrounding novated leases for cars. Last night Qantas has suspended its car leasing program for employees. This morning they're discussing it on the radio and the commentator, Neil Mitchell mentioned pilots salary sacrificing cars.

I seem to recall that you said that you guys don't have this. Is what Mitchell said wrong?

We didn't always have it. It came in a few years back. There are two schemes. One was a novated lease, while the other was called the 'executive' scheme. I think anyone could be part of the novated, but the other is restricted. Anyway, they've both been canned, for all employees.

I expect the 'law of unintended consequences' will ensure that this government decision has exactly the opposite effect to whatever was desired.

 

[flychrisfly]

Are there any major differences in configuration, apart from thrust, between an aircraft taking off and landing, assuming the conditions are the same?

 

[jb747]

Are there any major differences in configuration, apart from thrust, between an aircraft taking off and landing, assuming the conditions are the same?

Assuming the same weight and conditions, the difference would be the flap setting. The last two stages of flap on most aircraft are more for extra drag than extra lift, something you don't want taking off. So, a 747 would use flap 20 for takeoff, and 25 or 30 for landing, and the 380 would use 2 for takeoff and 3 or full for landing.

 

[Cynicor]

Ooh, while on flaps, from the tail cam on the MH A380 it appears that the flaps add a significant amount of surface area (obviously...)

Just how much do they give you? It looked like more than 50% increase?

And thanks for the excellent thread, really love the whole thing, esp the JB747 replies, and those of the other knowledgable folk.

 

[jb747]

Ooh, while on flaps, from the tail cam on the MH A380 it appears that the flaps add a significant amount of surface area (obviously...)

Just how much do they give you? It looked like more than 50% increase?

The area increasing component of flap extension happens with the very early stage selections. There is nothing written about it in the 380 manual, presumably as facts like the actual percentage of area increase have no relevance to flying the aircraft (I expect you'd all be surprised at how devoid of general information the manuals are). Looking at the diagrams though, I'd be very surprised if it was more than 10% of the overall area. Whilst the flaps look huge (and I guess they are), the rest of the wing is enormous.

 

[Cynicor]

Thanks!

Just seemed like they kept on going and going. Yeah, wasn't certain if you knew the answer. Mr Google probably does, might hunt later.

 

[mjt57]

... the rest of the wing is enormous.

That it is.

We sat about centre of the wing. When I looked out it seemed to go waaay back from where we sat and waaay forward. It was actually a rather poor seating position as much of the ground scenery was unable to be seen.

In comparison looking out of the window on the 744 that we flew on prior to our trip home on the 380 it looked positively skinny in comparison. I could see both leading and trailing edges.

 

[tuppaware]

That it is.

We sat about centre of the wing. When I looked out it seemed to go waaay back from where we sat and waaay forward. It was actually a rather poor seating position as much of the ground scenery was unable to be seen.

In comparison looking out of the window on the 744 that we flew on prior to our trip home on the 380 it looked positively skinny in comparison. I could see both leading and trailing edges.

It does! It looks like B747 wing is a higher speed wing ?

 

[mjt57]

Interesting article in the paper today.

Landing gear broken? Don't worry about it, says pilot

Interesting, the name of the author's website...

 

[jb747]

Interesting article in the paper today.

Landing gear broken? Don't worry about it, says pilot

Interesting, the name of the author's website...

Reality is that Patrick Smith was using the 'Ask the Pilot' tag for quite a while on Salon...so I think we borrowed it.

Whilst I don't always agree with his comments, he does speak common sense with regard to the various incidents, and I certainly agree with what he's said about this one. Looking back at various incidents over the last few years, I'd expect that the major items that I see most certainly aren't the same ones latched onto by the media...whose knowledge of events extends only as far as trying to find a way of using words like 'plunged'. I expect to eventually see that attached to a taxiing incident.

Think about...
BA777...the Captain thought to retract the flaps back to 20º, which resulted in the aircraft touching down about 50-100 metres later, and so missing all of the obstructions leading to the runway.
A320 ditching...the Captain decided to ditch, and not to attempt to save the aircraft by landing at Teterboro. That is why everyone survived. The ditching per se, wasn't any sort of miracle.
QF32, the crew took their time, and landed when they had properly contained and understood the situation.

None of those underlined points are what you'll see in the media, but they're the most important facets of those incidents. Of course, I'm sure that somewhere in these 450 pages, I've said what I think about most media reports, but they continue to get worse, not better, and yet they still seem surprised that nobody reads newspapers or watches the TV news any more.