Commercial aviation questions

During a commercial flight yesteray I pondered the following items, offered here to the SDMB in hope of receiving answers:

-How does a commercial pilot find his way around an airport to the correct gate? Suppose I’m a pilot who has never landed at Denver International Airport before, and now I touch down there with a plane full of passengers. How do I get to my gate? I assume I’m under tight supervision from the folks in the tower, but are they giving me instructions on how to get to my assigned gate, or am I expected to know how to find my gate, and it’s up to me to request permission from the tower to turn left here and right there and so on until I’ve arrived at my gate?

-Presumably the crew on a long-haul cargo flight must eat from time to time. Do they get hot food, or is it cold box lunches from the fridge? If hot food, who preps it? Is there a flight attendant to take care of these things so they can focus on flying the plane, or does one of the pilots just step out of the cockpit and throw a couple of Hot Pockets™ in the microwave?

-why are spoilers on a commercial airliner so much closer to the trailing edge of the wing than the leading edge? Given that their purpose is to disrupt airflow across the upper surface of the wing, it would seem desirable to have them located much nearer to the leading edge. There’s rarely (if ever) a need to eliminate the vast majority of lift in mid-flight, but I would have expected that this would be useful as soon as the wheels hit the runway. As it is, the spoilers pop up as soon as the wheels touch down (to get the weight on the wheels and allow heavy braking), but it seems like if they were nearer to the leading edge, they could kill even more of the lift, thereby getting more weight on the wheels ASAP.

  1. They are given instructions by aircraft controllers especially when crossing active runways. Once near the gate, a ground crew member marshals them into the specific gate.

  2. Cargo crews don’t include flight attendants. Most likely a boxed lunch.

  3. Spoilers are also used in rolling and turning the aircraft on many aircraft. If you watch closely you may seem them open up a little every once in a while. Also remember that spoilers work by disrupting the airflow over the wing and not by blocking airflow. They can disrupt the airflow just fine where they are.

Some aircraft, mostly fighters, have speedbrakes which are designed to block airflow but these are seldom on the wings. They are mostly on the fuselage and usually behind the center of gravity.

On the last commercial flight I was on, one of the pilots stepped out of the cockpit and put a Marie Callender frozen dinner in the microwave and heated it up.

He then took a seat in first class ( which had been held open for this purpose.) I knew this because it was next to my seat and I had been told it wasn’t a “real” empty seat when I put my coat and purse on it after the cabin door closed.

He ate his microwaved dinner while doing airline related paperwork and after the “dinner break” he went back to the cockpit.

I really don’t know if this was a typical situation or an unusual one but it was interesting. I wonder if he had to bring his own dinner because of budget cutbacks or if he took that route because it didn’t suck as much as airline food. If he hadn’t been an a**hole* I would’ve asked him.

*Dude seemed like he didn’t much care for my hippie appearance and demeanor – in first class, no less:), said something snarky to me about “lounging around in my sock feet in a public place like it was my living room” then he decided I was contagious and moved.

So I wouldn’t need to know where gate C27 is? I just tell the tower that that’s where I need to go, and they give me step-by-step directions to guide me there?

Yes, I understand the intent of spoilers (decrease lift), as opposed to speedbrakes (increase drag). My point was that the spoilers I’ve seen on commercial airliners only seem to disrupt airflow over the final ~20% of the wing’s chord. Example, this A-380 schematic shows the spoilers located just in front of the flaps. Wouldn’t it make more sense to have them farther forward than that?

If you needed detailed instructions, they would give them - they don’t want you wandering around, getting lost, blocking other traffic, etc.

But airport layout diagrams are readily available to pilots, and it would be normal for a pilot not familiar to refer to one.

Which has much the same effect on lift and drag as if they were located further forward.

OK, can you 'splain why this is so? Assume I’m an engineer with extensive education and practical experience with fluid mechanics.

I was going to say this - I’ve certainly seen such maps. Would it be standard practice for the crew to have a plan of the destination airport in the cockpit so they can check the layout? I kind of hope so.

The blockage of air flow over the wing effectively pushes air back toward the leading edge, much like a dam pushes water back upriver. They spoil lift over the entire airfoil that way, like a dam blocks river flow for a long way upstream. The downward force caused by deflecting air upward is about the same no matter where it happens.

The spoilers fit better into the same portion of the airfoil as the ailerons and flaps mainly because the thicker, more-forward areas are occupied by spars, other structures, fuel tanks, plumbing and wiring. There’s still enough room further back for the hinges, brackets, and actuators without competing for space elsewhere.

An airline wouldn’t normally send two crewmembers to an airport for the first time. More typically, somebody who hasn’t flown the route before goes there with a pilot who has. If he’s a captain, he gets a ride back in the right seat. They will also normally have an airport diagram, either on paper or (increasingly an iPad). A general-aviation pilot who doesn’t have that option is encouraged to tell the ground controller “Unfamiliar, request progressive taxi instructions” and he’ll be talked through it turn by turn rather than clog things up.

Cargo planes vary - some are converted airliners, some built as freighters - and if there’s any room left after fitting in every possible container, there might be a small microwave, fridge, and coffeemaker there. Or there might be a cold sandwich or two in an insulated bag, and a thermos. Or nothing.

The unobstructed shape of a wing is the answer to the question “How do we produce lift with low drag?” Air passing over the top of the wing is accelerated aft and downward, and in normal flight is responsible for something like two-thirds of the total lift. This will be true as long as air is free to flow smoothly over the wing.

When you block this flow with a spoiler spanning part of the wing, you cancel nearly all of this lift. This also leads to a large increase in drag, as energy is dissipated generating turbulence in formerly smooth-flowing air. This effect will be seen if the flow is disrupted anywhere on top of the wing - it will be much the same if the disruption happens near the front of the wing, or near its trailing edge.

Back in the olden days, we used a map, called “sectionals” to get around. Then, when you got to the airport, pilots had a set of books called “Jeppesen charts” to navigate. Jepp charts contained data on all airports, so you had frequencies, elevation, ILS data, and maps.

Nowadays, it’s all electronical, so pilots will have them loaded on an Ipad or in the aircraft computer itself so they can just pull up the proper map from a menu.

This finally jogged my brain. Lift happens when the air coming off of the back of the wing is moving downward (compared to its angle of attack at the leading edge); if air coming off of the back of the wing isn’t moving downward, then lift is not produced. The part of your post that I quoted above nails it: spoilers at the back of the wing can kick prevent that departing airflow from going downward, or spoilers at the front of the wing can prevent air from following the shape of the trailing portion of the wing’s upper surface. Either way, air is no longer leaving the back edge of the wing with a downward trajectory anymore, and lift is gone.

Thanks!

Here’s one for Raleigh (RDU). All the little letters on the taxiways on the map are on signs at the airport. It’s easier than finding your way around a typical suburb with a street map.

Many airlines are still using paper charts.

For me personally, unless I know an airport really well or it’s layout is very simple, I will have the aerodrome chart (Jeppesen 10-9 chart) on the chart holder that makes up part of the window sill. All of the taxiways are identified with a letter and sometimes a number. Prior to descent we will have contacted our company rep on the ground and been told what bay we’ve been given. I will then, as part of the approach briefing with the other pilot, brief the parking bay position, any taxiway closures notified by NOTAM (notice to airmen), and the expected taxi route to the bay. After we land and vacate the runway the first officer will immediately contact the ground controller and advise what bay we are for. Then the ground controller may do anything from a simple “[callsign] taxi to the bay” in which case we follow the route I briefed, or if they want something specific they may give more detailed instructions. Most of the time it is brief and to the point such as “[callsign] taxi Bravo 6, Bravo, Charlie 8 to the bay”. Any points where you cross a runway must be specifically cleared, otherwise you hold short of the runway. E.g, “[callsign] cross runway 34, taxi Alpha, Yankee to the bay.” If you get lost or don’t know your way around, you just ask for help and you will get it.

3/4 of my flying is in cargo aircraft. Even on short haul we get fed. We will have a cooler box (Esky to an Australian) filled with water, soft drinks, sandwhiches, snacks etc. enough for a full meal plus a snack. If we don’t get that provided then we are entitled to claim meal allowances for that duty. Providing food is cheaper than paying allowances so the company provides food. Our aeroplanes don’t have any provision for hot food so it is all cold. One of our freighters is a converted passenger jet and it still has a galley with hot water brewers. The others were built as freighters and just have a powered urn for hot drinks. We fly with just two pilots so if we want something to eat or drink, one of us, normally the “pilot not flying” for that sector will go back and get food / make tea and coffee.

I used to fly Dash 8 maritime surveillance aircraft, those had microwaves but we still typically had cold food. I always thought they’d have been better off fitting the aeroplanes with a fridge than a microwave.

Spoilers: As long as you block the airflow being accelerated off the trailing edge of the wing you will spoil the lift. It’s similar to blocking the thrust of a jet at the exhaust or at the intake, both methods will kill the thrust.

The FAA publishes airport diagrams, which pilots bring along with all their other charts (usually using some kind of electronic system today). They are essentially required by regulation to have a copy of the diagram for any airports they’ll be using (most electronic charting systems have copies of all of them anyway). Here is the diagram for DIA:

http://155.178.201.160/d-tpp/1403/09077AD.PDF

However, it is not up to the pilots to decide which route they’ll take. Once they are clear of the active runway, the control tower transfers them to the ground controller, who gives them specific directions on which route to take through the taxiways to get to their gate. The taxiways are all clearly labeled using very visible signs (e.g. https://www.google.com/search?q=taxiway+sign&client=safari&rls=en&source=lnms&tbm=isch&sa=X&ei=jNw6U8TTIsruyQHS8YCoDA&ved=0CAgQ_AUoAQ&biw=1324&bih=764) and so it isn’t all that hard to follow the instructions.

Taxi instructions might be something “Taxi to gate C33 via Foxtrot Golf-3 Alpha Alpha-6”, meaning to take the taxiways marked F, G3, A, A6 (the numbers identify short connectors between larger taxiways).

If the pilot is not familiar with the airport, he can also request “progressive taxi” instructions, in which the ground controller will essentially give him the directions one at a time as the plane arrives at each taxiway intersection.

Most large airports will have supplementary charts that show the positions of the parking bays themselves as well.

If the above link has worked it shows the parking bays at Melbourne Airport. The taxiway centre lines also have bay numbers marked on them. So when you get to the right area you will see yellow lines peeling off the line you are following and each one will have the parking bay it leads to written on it.

Sure is. Every taxiway has a letter designation, to distinguish them from runways, which have numbers. A sign showing which taxiway you’re on is in yellow on a black background, while signs showing a direction to a taxiway are black on yellow. Runway signs are white on red. Here’s the FAA guide, but it’s almost or exactly the same anywhere. You may also notice white-on-black signs alongside a runway - those show how much runway length is left in thousands of feet.

A major airport like DIA will often have ramp controllers, who work for the airline the uses a particular ramp, and take over from the tower-based ground controller when the airplane is not in a movement area, away from the gate. That person coordinates movement of tugs, fuel and catering trucks, jetways, etc.

A wing produces lift by reducing the pressure on its upper side compared to its lower side. The airfoil shape does this by accelerating it, and Bernoulli’s Principle takes it from there. It isn’t about downward angle at the trailing edge, sorry, that just makes the upper and lower sides come together.

It depends. As a freighter pilot I’m flying during very low traffic periods and if there is no conflicting traffic we will be given no instructions on how to get to the bay, we just go whatever way seems most efficient. The taxi instruction will literally be “taxi to the bay”. The assumption is that you’ve been around long enough to know where to go but new captains may need to ask for directions.

As an aside, unfamiliarity with an airport’s taxiway layout – and/or fog obscuring a taxiway sign – was a factor in the 1977 Tenerife mother-of-all-plane-disasters. Due to major on-the-ground congestion (lots of planes grounded by fog simultaneously), a runway was also serving as a taxiway. One taxiing plane was supposed to turn off the runway at point “C,” but they turned off at “B” (or something to that effect), and thought they were at “C” – so, in the fog, the control tower and a plane about to take off thought they were at “C,” too. Turning at “C” would have gotten them off the runway before the second plane took off. Would have.

You need downwash for lift. No downwash means no Bernoulli, no Bernoulli means no downwash, they are intrinsically linked.