Frame of reference - forces in a turn (airplane)

In summary, the conversation discussed two different ways of depicting forces in a turn. The first picture shows unbalanced forces from a stationary reference frame, while the second picture shows balanced forces from a rotational reference frame. The purpose of the second picture is to illustrate the resultant load or "g-force" experienced by the airplane, while also highlighting the concept of centrifugal force, which some consider to be fictional.
  • #1
italia458
6
0
Hi,

I've seen the forces in a turn depicted two different ways:

http://selair.selkirk.ca/Training/Aerodynamics/images/lf-turn.gif

http://www.free-online-private-pilot-ground-school.com/images/forces_during_turn.gif

Which one is correct?

I think the first one would be since it's analyzing it from one reference frame and the second picture appears to analyze it from multiple reference frames.

Regarding the second picture: if the forces are all balanced (as depicted), the airplane wouldn't be accelerating. How can it turn then?

Cheers!
 
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  • #2
I think the second picture is merely showing how the centripetal force increases in a sharper turn, where the plane is banked more. IMO, both pictures show the same thing, only slightly different.
 
  • #3
italia458 said:
Hi,

I've seen the forces in a turn depicted two different ways:

http://selair.selkirk.ca/Training/Aerodynamics/images/lf-turn.gif

http://www.free-online-private-pilot-ground-school.com/images/forces_during_turn.gif

Which one is correct?

I think the first one would be since it's analyzing it from one reference frame and the second picture appears to analyze it from multiple reference frames.

Regarding the second picture: if the forces are all balanced (as depicted), the airplane wouldn't be accelerating. How can it turn then?

Cheers!

The first picture shows unbalanced forces and it says "Force of centripetal acceleration" centripetal means "towards the center" if I recall. So, the plane is accelerating towards the center of the axis of its turning radius. The frame of reference, in this case, is stationary, from the ground, or a stationary observation tower, looking towards the airplane in that instant that it was facing away from the viewer.

The second picture is from a rotational reference frame. The forces are balanced, in this case, because it is a non inertial reference frame. The forces are balanced, but in relation to a reference frame that is already rotating. The airplane is "stationary" relative to the rotational reference frame, but is still rotating. A centrifugal force is mentioned, so, in this case, it means "from the center." Relative to the rotational reference frame, the forces the plane experiences are trying to push it away from the axis of rotation.

At least, that's how I interpret it.
 
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  • #4
The forces are balanced, but in relation to a reference frame that is already rotating. The airplane is "stationary" relative to the rotational reference frame, but is still rotating.

Is there any benefit for a pilot to see acceleration relative to a rotational reference frame... that is rotating at the same velocity as the airplane?! Meaning zero acceleration. To me it seems at least useless and just wrong, in some way.

Relative to the rotational reference frame, the forces the plane experiences are trying to push it away from the axis of rotation.

How do you know which forces the airplane is "experiencing"? I thought all the forces drawn on that airplane were what it was experiencing. If that's correct, then it's experiencing a force away from the axis of rotation (as you stated) but it's also experiencing a force towards the axis of rotation (centripetal force) and they're equal and opposite.

I understand that if you decide to have your reference frame move in the exact path of your object then there isn't any acceleration. But what's the point of that? Every force would be always balanced then and there would never be acceleration.
 
  • #5
The point of the second picture is to show the resultant load or "g-force" experienced by the airframe.
 
  • #6

Related to Frame of reference - forces in a turn (airplane)

1. What is a frame of reference?

A frame of reference is a set of coordinate axes used to describe the position and motion of an object. It is a point of view or perspective from which observations and measurements are made.

2. How do forces affect an airplane in a turn?

In an airplane turn, forces are constantly acting on the aircraft. The lift force generated by the wings is responsible for keeping the airplane in the air, while the weight force pulls the airplane towards the ground. The thrust force from the engines propels the airplane forward, and the drag force opposes this motion. When turning, the lift and weight forces are unbalanced, causing the airplane to bank and change direction.

3. What role does the center of gravity play in a turn?

The center of gravity is the point where the weight of an object is concentrated. In an airplane, the center of gravity is crucial for maintaining stability and control. During a turn, the center of gravity shifts towards the inside of the turn, causing the airplane to roll and bank.

4. How does the angle of bank affect the forces in a turn?

The angle of bank, or the angle at which the airplane is tilted during a turn, has a significant impact on the forces acting on the airplane. As the angle of bank increases, the lift force also increases, allowing the airplane to maintain altitude. However, a steeper angle of bank also increases the drag force, requiring more power from the engines to maintain speed.

5. How do pilots use the frame of reference to control an airplane in a turn?

Pilots use the frame of reference to monitor and adjust the airplane's attitude and direction. They rely on instruments and visual cues to determine the airplane's orientation and make adjustments to maintain a desired heading and bank angle. By constantly assessing the frame of reference, pilots can effectively control the forces in a turn and safely navigate through the sky.

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