Roll torque created by anhedral during slips and skids

Roll torque created by anhedral during slips and skids

Steve Seibel
www.aeroexperiments.org

This page is still under construction!
This page was last modified on August 4, 2006

 

In "Definition of a 'slipping' turn", we noted the following: an aircraft is engaged in a "slipping" turn if the aircraft's nose is allowed or forced to yaw to point to the "high side" or "outside" of the turn in relation to the aircraft's actual direction of travel through the airmass at any given moment. In other words, an aircraft is "slipping" whenever the nose of the aircraft is allowed or forced to yaw to point to the "high side" or "outside" of the turn in relation to the actual direction from which the relative wind is blowing at any given moment. In a left turn, an aircraft is slipping if the aircraft's nose is pointing to the right of the actual direction of the flight path through the airmass at any given moment, i.e. to the right of the direction from which the relative wind is blowing at any given moment. (Diagram to be added.)

In "Definition of a 'slipping' turn", we also noted the following: when an aircraft is "slipping", there is a sideways component in the relative wind or airflow over the aircraft. This sideways component blows from the "leading" wing to the "following" wing, i.e. from the "inside" wingtip to the "outside" wingtip, i.e. from the low wingtip to the high wingtip. For example, in a left turn, if the aircraft is "slipping", i.e. if the nose is pointing too far toward the right in relation to the actual direction of the flight path and relative wind at any given moment, there will be a left-to-right component in the airflow over the aircraft. (Diagram to be added.)

In "Oblique views and side views of aircraft with anhedral", we explored how anhedral creates a roll torque in the "upwind" direction whenever there is a sideways component in the relative wind or airflow over an aircraft.

Putting all this together, we can see that when an aircraft with anhedral is turning to the left, if any sideslip is present, the resulting left-to-right sideways component in the relative wind will interact with the anhedral to create a roll torque toward the left. (Diagram to be added.) This roll torque will tend to roll the aircraft toward a steeper bank angle. As a general rule, during a slipping turn, the sideways component in the relative wind will interact with any anhedral that is present to create a roll torque that will tend to roll the aircraft toward a steeper bank angle.

**As a side note, when I flew this aircraft in a sustained slip, holding lots of right rudder to keep the nose of the aircraft pointing to the right of the actual direction of the flight path and relative wind, I actually had to hold a right aileron input as well, in order to keep the bank angle constant. This is opposite of the roll (aileron) input that is required in a sustained slip in a more "conventionally" shaped aircraft, as we explored in "Roll torque created by dihedral during slips and skids". The reason that I had to hold a right aileron input to prevent the bank angle from changing was that the sideways airflow from the slip was interacting with the aircraft's anhedral geometry to create a roll torque in the "upwind" direction, i.e. toward the left. Planform view of same aircraft (with wings adjusted to a flatter configuration).

 

In "Definition of a 'skidding' turn", we noted the following: an aircraft is engaged in a "skidding" turn if the aircraft's nose is allowed or forced to yaw to point to the "low side" or "inside" of the turn in relation to the aircraft's actual direction of travel through the airmass at any given moment. In other words, an aircraft is "skidding" whenever the nose of the aircraft is allowed or forced to yaw to point to the "low side" or "inside" of the turn in relation to the actual direction from which the relative wind is blowing at any given moment. In a left turn, an aircraft is skidding if the aircraft's nose is pointing to the left of the actual direction of the flight path through the airmass at any given moment, i.e. to the left of the direction from which the relative wind is blowing at any given moment. (Diagram to be added.)

In "Definition of a 'skidding' turn", we also noted the following: when an aircraft is "skidding", there is a sideways component in the relative wind or airflow over the aircraft. This sideways component blows from the "leading" wing to the "following" wing, i.e. from the "outside" wingtip to the "inside" wingtip, i.e. from the high wingtip to the low wingtip. For example, in a left turn, if the aircraft is "skidding", i.e. if the nose is pointing too far toward the left in relation to the actual direction of the flight path and relative wind at any given moment, there will be a right-to-left component in the airflow over the aircraft. (Diagram to be added.)

Bearing in mind again that anhedral interacts with a sideways component in the relative wind to create a roll torque in the "upwind" direction, we can see that when an aircraft with anhedral is turning to the left, if any skid is present, the resulting right-to-left sideways component in the relative wind will interact with the anhedral to create a roll torque toward the right. (Diagram to be added.) This roll torque will tend to roll the aircraft back toward wings-level. As a general rule, during a skidding turn, the sideways component in the relative wind will interact with any anhedral that is present to create a roll torque that will tend to roll the aircraft back toward wings-level.

 

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