Altitude change in straight flight

In summary: Changing gravity direction or some other factor would change the angle of attack and cause the aircraft to fly an arc like path which is parallel to underlying Earth surface.
  • #1
pbaumer
1
0
Hi,

Assume an aircraft starts flying to east with zero pitch and roll, would this aircraft slowly move away from Earth surface due to Earth being a sphere ?

Or would changing gravity direction or some other factor cause this aircraft to fly an arc like path which is parallel to underlying Earth surface?

Thanks!

Paul
 
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  • #2
Welcome to PF!

The curvature of the Earth is so gradual it has no impact here. Straight and level is straight and level.

But I suppose if it mattered, the changing direction of gravity would help, since that is the reference point for "level".
 
  • #3
russ_watters said:
But I suppose if it mattered, the changing direction of gravity would help, since that is the reference point for "level".

The question obviously "matters" in terms of geometry, for long distance flights.

But air traffic control "flight levels" are defined in terms of local air presssure, not distance above the ground level. For example "Flight level 100" corresponds to 10,000 ft above sea level for the International Standard Atmosphere, but at any moment in time it can vary from about 9,000 to 11,000 feet over different parts of the Earth's surface, depending on whether it is summer or winter, or day or night, at a particular place.

The basic reason for defining it that way was historical, since all "mechanical" flight instruments work with reference to air pressure. It stiill makes sense even when location systems like GPS are available, because the aircraft's performance (fuel consumption, etc) depends on the air it is flying through, not its distance above the ground.

So "level flight" actually means "keeping the air pressure outside the plane constant", not "flying along a mathematical straight line".
 
  • #4
pbaumer said:
Assume an aircraft starts flying to east with zero pitch and roll, would this aircraft slowly move away from Earth surface due to Earth being a sphere ?

Or would changing gravity direction or some other factor cause this aircraft to fly an arc like path which is parallel to underlying Earth surface?

My vote: the aircraft would rather quickly fall towards the ground. Zero pitch means zero lift.
 
  • #5
The wings can be at angle of attack relative to the airflow but the aircraft is not pitched.
 
  • #6
AlephZero said:
The question obviously "matters" in terms of geometry, for long distance flights.
Since a plane is constantly pitching, yawing and rolling by a small amount, any amount due to the geometry of the Earth is lost in that noise. Increasing the distance doesn't change that.
 
  • #7
RandomGuy88 said:
The wings can be at angle of attack relative to the airflow but the aircraft is not pitched.
As well, if the zero point for angle of attack is geometrically defined, the wing will have lift even at zero angle of attack.
 

1. What factors affect altitude change in straight flight?

The main factors that affect altitude change in straight flight are air density, weight of the aircraft, and angle of attack. Air density decreases with altitude, so the aircraft needs to fly faster to maintain lift. Weight of the aircraft affects how much lift it can generate, and a higher angle of attack can increase lift but also increases drag, causing the aircraft to slow down.

2. How does altitude change affect airspeed?

As altitude increases, the air becomes less dense, resulting in decreased airspeed. This is because the same amount of air passing through the engine produces less thrust, causing the aircraft to slow down. Pilots must account for this decrease in airspeed when flying at higher altitudes.

3. Can altitude change affect aircraft performance?

Yes, altitude change can significantly affect aircraft performance. As mentioned earlier, air density decreases with altitude, which can cause a decrease in airspeed and lift. This can also result in a decrease in engine performance, making it more difficult for the aircraft to maintain speed and altitude.

4. How does altitude change impact fuel consumption?

Flying at a higher altitude can reduce fuel consumption due to the decreased air resistance. However, this is only the case if the aircraft is flying at a constant speed. If the aircraft has to increase speed to maintain lift at a higher altitude, it can actually result in higher fuel consumption.

5. What is the best altitude for fuel efficiency?

The best altitude for fuel efficiency varies depending on the aircraft and the flight conditions. In general, flying at a higher altitude can be more fuel-efficient due to reduced air resistance. However, pilots must also consider factors such as air density, temperature, and engine performance when determining the most fuel-efficient altitude for a specific flight.

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