Slow climb during long flights, in atmo.

[TimePeriod]

Quick question, why do aircraft slowly pitch upwards during long duration flights?

[ineon]

Have you got a specific example? Can you post a screenshot of one of these aircraft?

[TimePeriod]

[IMG]http://i357.photobucket.com/albums/oo19/TimePeriod/2015-11-19_00001_zpsnown54k8.jpg[/IMG]
Here.

[Snark]

Is it that the aircraft is pitching upwards? Or is it that the planet is pitching downwards?

For example, a craft that's in orbit will keep the same absolute orientation (if you don't manually rotate it or tell SAS to hold a particular orbit-relative direction). So if you point the nose prograde, and then just hands-off the keyboard, the nose will appear to "pitch up", but the craft isn't rotating at all-- it's just that the navball is displaying the orientation relative to the [I][U]planet[/U][/I], which of course changes as you follow the curve of the orbit.

Is it possible that there's something similar going on with aircraft as well? Not sure whether the game has a code switch to make "hold orientation" mean surface-relative rather than orbit-relative, or whether this would be relevant at all due to aerodynamic forces on the craft.

Or is this a particular effect of the aircraft design? Do you notice this on all aircraft, or only certain designs? (I don't fly aircraft enough myself to know...)

[Val]

[quote name='TimePeriod']Quick question, why do aircraft slowly pitch upwards during long duration flights?[/QUOTE]Assuming you have SAS on, it is because of the curvature of a planet's surface.

SAS keeps pitch in absolute terms, so as you move across the surface, SAS will try to maintain a straight line, but the surface curves down, so it appears as if the craft is lifting it's nose.

[IMG]http://i.imgur.com/AkgVSyL.png[/IMG] Edited November 19, 2015 by Val

[RCgothic]

If you're talking about pitching up during atmospheric flight it could be that your centre of mass is moving as fuel burns. That will affect the trim of your aircraft.

[KerikBalm]

See val's post, #5....
Thats almost gauranteed to be what the OP is talking about

[KerBlammo]

You're burning fuel and changing the COM.

Or in other words what RCgothic said :)

[Beetlecat]

"You're both right!"

:D

[A_name]

[quote name='Snark']Is it that the aircraft is pitching upwards? Or is it that the planet is pitching downwards?[/QUOTE]

[quote name='Val']Assuming you have SAS on, it is because of the curvature of a planet's surface.

SAS keeps pitch in absolute terms, so as you move across the surface, SAS will try to maintain a straight line, but the surface curves down, so it appears as if the craft is lifting it's nose.[/QUOTE]

This.

[Tourist]

These are all [B]seemingly[/B] rational explanations. But that's what [B]they [/B]want you to think. But beware, they are all thralls of the Kraken.

Be careful, we are a long way through the looking glass now and we're fresh out of croquet mallets.



That or the curvature thing... its probably that.

[Venusgate]

I'm afraid if you want to dependably hold a certain altitude over the course of a long flight, you're going to need a mod plugin.

[Octa]

May i suggest a third explaination: :sticktongue:

Fuel consumption -> less mass -> higher TWR -> higher accelaration and speed -> more lift

Edit:

Try Pilot Assistant, i use it to keep heading and vertical speed/altitude

[KerikBalm]

More lift doesn't explain a change in pitch.
Its the curvature thing, that fully explains the observations, and there's no need to suggest additional explanations

[Kobymaru]

There's a mod that's basically "SAS on steroids": [url]http://forum.kerbalspaceprogram.com/threads/138332-PLUGIN-AtmosphereAutopilot-1-1-%28Fly-By-Wire%29[/url]
If the Master Arm is on and your Navball is in surface mode, it will keep the nose at a constant pitch relative to the ground.

[stormdot5]

[quote name='Octa']
Fuel consumption -> less mass -> higher TWR -> higher accelaration and speed -> more lift
[/QUOTE]

-> Less trim required, but not actually adjusted -> Pitch up due to trim

[Octa]

[quote name='stormdot5']-> Less trim required, but not actually adjusted -> Pitch up due to trim[/QUOTE]

oh, yeah....i forgot the last steps in the equation.

From what i read about autopilots IRL, keeping a plane at a constant altitude or speed is rather simple, but requires constant adjustments. Constant altitude [B]and[/B] speed is where the fun starts.