Hot answers tagged

44

When flaps are retracted they do nothing, which is the whole point. The byproduct of lift is drag, a larger wing will create more lift, but more drag as well. More drag equals a slower cruising speed, or bigger engines to power past the drag along with higher fuel consumption. Flaps let airplanes cruise faster by getting out of the way.


27

The autopilot pitches to hold the flight level when it captures the level at the top of the climb, so later on as the aircraft gets lighter and wants to climb further, the A/P will lower the nose as required to hold the flight level (the A/P is able to move the elevator through its servo's link to the elevator controls; it can also work the trim if the servo ...


25

Your concerns about heavy flaps are well founded. The designers try to get away with as few high-lift devices as they can afford to. But not fewer! If you observe the trend over the years, flaps became more complex with every new airliner generation, starting from simple split flaps in the 1930s to triple-slotted flaps on the Boeing 747 in the late Sixties. ...


13

Climb to cruise burns fuel. Adding additional drag burns fuel. Adding retractable mechanisms adds weight that burns fuel. More drag, even at higher cruise altitudes, requires larger engines for the same cruise speed. Larger engines burn more fuel (despite increases in modern engine fuel efficiency). Retracting high-lift, high drag devices reduces fuel burn ...


13

When airplane mass, altitude, N1 (engine spool speed) and Mach number change together, it is very hard to come to a meaningful conclusion what is better for fuel flow. However, you see that the grey boxes tend to show the smallest fuel flow and they sit at the upper altitudes, so altitude seems to help. Going above 90% N1, however, seems to increase fuel ...


12

White lights are usually off in the cockpit in night flights to protect pilots' night vision. Red lights are sometimes used as these do not impact night vision. One of the challenges you'll run into is knowing when it's night, as the start of night varies by latitude and the exact time. Phones generally set their time from the mobile network, which may be ...


11

The questioner seems to have noted that the basic wing with flaps retracted provides a high ratio of L/D (or Cl/Cd). Where L denotes lift, Cl denotes lift coefficient, D denotes drag, etc. We can certainly scale up the basic unflapped wing to provide as low a landing speed as we wish, although landing will be tricky due to the flat glide path. Flaps help ...


11

If you are asking about logging night VFR -time, you are not concerned with lighting conditions. Night time is logged according to regulation based definition of night (at least EASA), tables for night time are usually available from local aviation administration websites. Your logger simply needs to know your position, date and time, and refer to the ...


9

Here are the cruise performance tables for the Q400 at the heaviest and lightest weight (click to view larger): Source: from the Dash-8 Q400 performance manual, which came included with a simulator product I purchased. They probably got their data from a QRH (Quick Reference Handbook), which usually includes such tables in the In-Flight Performance section. ...


4

The main reason for the transition layer is to assure separation between the highest usable altitude (TA) and the lowest usable FL (TRL). That means it has to be at least 1000ft thick. If the QNH is 1014 or above the transition level is always just 1000ft above the TA (5000ft and FL60) because the whole FL system is shifting upwards above the MSL. This means ...


4

That's easy. Just push the nose down a teensy bit. (or rather, pull the nose up less.) That will reduce AoA, reduce lift slightly, prevent you from climbing and will hold altitude. "But then, we'll speed up!" Correct. So, reduce thrust as needed. Another option is to intentionally climb. Then, you enjoy the fuel economy benefit of higher altitude. ...


4

As pointed out by HiddenWindshield, the pilot will pitch the nose down slightly as the fuel load is burned off. The pilot does this using the elevator trim control and will from time to time in a long flight add nose-down trim to maintain zero vertical speed. With less load, less lift is required, and trimming away the unnecessary lift will cause the plane's ...


4

There are a lot of things that affect lift beyond just the speed and air density. For instance, the angle of attack. As the weight of the aircraft decreases, the pilot (or autopilot) will pitch the nose down slightly to reduce the AoA, and therefore lift.


3

To strictly answer the title question, at least in GA operations, we typically fly with the cockpit lights off to avoid ruining our night vision. We do sometimes use red lights to see stuff in the cockpit, though. However... It's unlikely that a photosensor will be very useful for determining which hours count as day vs. night. Lots of factors will affect ...


2

Yes, that is typical for high bypass ratio (HBPR) turbofans. But why? Because the entry impulse goes up while the exit impulse stays roughly constant. Thrust is the difference between both, derived over time. The moving engine needs to slow down the airflow for combustion to take place, and then needs to accelerate the air by more than it has been ...


2

The FAA's IFR handbook sheds some light on what they expect (page 2-48) If the pilot receives the term “climb at pilot’s discretion” in the altitude information of an ATC clearance, it means that the pilot has the option to start a climb when they desire and are authorized to climb at any rate, and to temporarily level off at any intermediate ...


2

As pointed out in other responses, there are many factors that influence how and why an aircraft will need constant adjustments made to maintain speed and altitude while cruising. You are correct in assuming that as the mass decreases as you burn off fuel, there will be less lift required to counteract gravity. It will also take less thrust to counteract ...


1

Takeoff thrust depends on many factors and needs to be calculated carefully. You can take the max values from the manufacturer in orther to have an idea. Cruise can be calculated roughly. Let's see an example. We know that during cruise phase all four forces are level. Lift = Weight and Thrust = Drag We also know that an airliner such as the A320 is very ...


1

A320 family's engine of choice is the CFM56-5B. Now there are multiple variants of this engine. But on average the takeoff thrust for the models -5B1/B2 and -5B3 are between 30,000 to 33,000 lbf. Other variants have a lower thrust rating between 21,000 - 24,000 lbf and 27,000 lbf. The cruise thrust is lower of course since the aircraft has already taken off ...


1

Your question says there is 1000ft between the TA and TL, but depending on how QNH compares to QNE from day to day and from place to place, the actual thickness of the layer will vary; it will always be at least 1000ft (though rarely more than 1999ft). This guarantees that an aircraft at the TL and an aircraft at the TA will always be properly separated. ...


1

To address what's discussed in comments... The East/West rule governs cruise altitude. When you're climbing to or descending from your cruise altitude, those rules don't apply. ATC obviously has to consider opposite direction traffic when they contemplate where/when to issue those climb & descent clearances, but for the pilot, that's just a matter of ...


Only top voted, non community-wiki answers of a minimum length are eligible