Being in the navy for 26 years, I consider myself a frequent flyer. Today was my first ride in the A380. On climb out and descent (and for a while at alt of 37k) she felt like she kept surging without any discernible change in engine tones. If we were in a car the feeling was like when you start starving the engine of fuel and she “stutters”. For as much as she displaces, she felt like she was moving around quite a bit and the takeoff rollout seemed to take forever— not acceleration like a 747...but I am a ship driver and well outside my wheelhouse on this one. Just curious! Thanks guys.

If I was there, maybe I’d have a better feel for specifics. It sounds like you rule out external forces, like turbulence or annoying chop?

With engine changes, maybe some type of ‘harmonics’ as power changes occur? Another possibility is how the climb & descent is set up in the ‘flight management computer’. Since it’s a foreign carrier, many lean autopilot over manually flying the plane a fair portion of the departure or arrival. Power changes as one meets restrictions, level offs & climbs can be less than smooth as auto-throttles adjust power.

There are several schools of thought as one settles in for a 14 hour flight to the Far East. Most will do a ‘cruise climb’ where the passengers hardly perceive the plane is climbing. At the most there is a slight pressure change in the ears, then a peek at the flight map.

I have seen a few who do a higher power climb at a quicker rate. The reasoning is, ‘to let them know we’re awake up here’. That thought is rather rare.

As to the takeoff roll, most are done at a ‘reduced power’, less than max thrust. Of course one has to have excess thrust available for conditions. Many factors go into the computer driven calculations for T/O thrust for given departure. That would give you a longer roll, which you also expect with a heavy plane on a longer international flight.

While there are the general conventions for operations, various exceptions are sprinkled throughout. There is also room for ‘individual technique’, even though it may be a rather structured environment.

That’s my story & at this point I’m sticking to it.

quote:

Originally posted by KP93:
Being in the navy for 26 years, I consider myself a frequent flyer. Today was my first ride in the A380. On climb out and descent (and for a while at alt of 37k) she felt like she kept surging without any discernible change in engine tones. If we were in a car the feeling was like when you start starving the engine of fuel and she “stutters”. For as much as she displaces, she felt like she was moving around quite a bit and the takeoff rollout seemed to take forever— not acceleration like a 747...but I am a ship driver and well outside my wheelhouse on this one. Just curious! Thanks guys.

A takeoff at gross weight in the 747 is a long, slow, laborious process that takes a bit chunk of the runway. It was always common for me to see the red lights at the far end...up close.

When powering back for descent, turbine or compressor vibration isn't uncommon. If you've looked on the inside of the engine inlet, you've seen the fan blades; these blades are small airfoils like a wing, and just like a wing, they work best at a certain angle between the airflow and the blade ("angle of attack). Like a wing, they experience drag at other speeds and angles, and as speed changes so does the angle of the airflow as it meets the blade. These blades are found throughout the engine; airflow through the engine isn't consistent, and various means of changing the angle of the airflow relative to the blades are used. At low powersettings at high speeds, you may sometimes hear a bit of a rumble. In the cockpit, vibration sensors are displaying values to show how much vibration.

This sometimes occurs at high power settings, too. Air is sucked in the front of the engine nacelle, and what isn't pushed out the back by the fan, goes through the engine and is burned to make power to drive the fan. That air is compressed considerably, and slowed, to increase pressure, before being mixed with fuel in burner cans, ignired, and blow through the rest of the engine to produce thrust, and to turn turbine wheels. The turbine wheels turn the compressor and the fan. With all that turning and burning going on, slowing and increased pressure, there are a lot of changes happening; there are times when they get "out of sync" such that you'll hear that rumble or feel that vibration. It's normal.

As noted above, vibrations can reinforce one another and produce a cyclic or rhythmic "harmonic" vibration that seems to pulse or come and go. sometimes it will stay doing that for a while, sometimes it will seem to drift around. In the C-130, a good engineer could actually put the harmonic vibration in a specific place...like under the captain seat, if the captain was an ass. In airline operations, it's just a by product of two, three, or four engines working together.

Enroute climbs are done on a profile; increased rate climbs are only done when requested by air traffic control. The climb is a combination of efficiency in forward speed, and efficiency at altitude; turbojet (and turbofan) aircraft are inefficient at low altitudes, and need to get to higher altitudes. We never do anything to let others "know we're awake."

Climbs are restricted by air traffic control, and the cruise altitude by winds and weight and temperature aloft; there will be an optimum altitude for the flight for a given weight, and any flight above that altitude will cause a signficant increase in fuel burn, as will flight below that altitude. As the flight gets lighter and fuel is burned off, it can climb to a higher optimum altitude. Optimum is also limited by the maximum and minimum speeds; for a given weight and temperature, there reaches a point where the flight can't climb higher because those two speeds come together. Climbs are done periodically on a long trip; these are called "step climbs" and are based on decreasing weight and enroute conditions of weather, winds, and temperature.