scsmith
Well Known Member
Quite a discussion ensued from a question about spinning from a slip.
You may not realize how thin a line there is between a slip and a skid while doing a forward slip.
Lets establish a forward slip. Lets say about 2/3 to 3/4 left rudder, and just the right amount of right aileron to maintain a straight-ahead flight path.
Now, suppose we add a little more right aileron. The extra bank starts to turn us to the right. We are in a slipping turn to the right. Not much of a turn, lots of slip. Everyone feels very safe here.
Now, instead, suppose we take away a little bit of right aileron. Not enough to keep the flight-path straight, we start a turn to the left. We are in a skidding turn to the left. Oooh, skid = bad - stop that.
The forward slip - straight flight path, is just a thin dividing line between the slip and the skid. Is either one really worse than the other?
For most airplanes, without generating any significant yaw rate, just developing the turns as described here, I don't think a spin will develop from a stall. For some airplanes, it will.
From conventional wisdom, the skidding side is arguably more risky than the slipping side. Here's why.
For a normal wing with some dihedral, in the slipping turn, the whole right wing sees a higher angle of attack than the left. The aileron input to maintain roll trim reduces the effective angle of the outer wing panel, leaving the inboard panel of the right wing at the highest angle of attack.
On the left wing, the whole wing is at a lower angle, but the aileron input is increasing the effective angle on the outer panel. But we are also turning, so the left wing is moving faster, making more lift, so it doesn't take very much aileron to maintain roll trim.
The same wing, in a skidding left turn, still has the whole right wing at a higher angle of attack. Still the right aileron is reducing effective angle, and the left aileron is increasing effective angle. But the turn to the left means that the left outer panel sees reduced velocity, requiring more right aileron input to maintain roll trim than the equivalent slipping turn. More likely that the left wing tip will stall first.
The forward slip, as the boundary between a skidding turn and a slipping turn, still has the left wing outer panel at a relatively high angle of attack, balancing the extra lift on the right inboard wing panel. Depending on the details of the wing design, such as taper, twist, airfoil design, the left tip can still stall first, dropping the left wing. As I mentioned in the other thread, the Schweizer SGS 2-32 is a great airplane to demonstrate this in.
Whether the wing drop develops into a full spin or a 1/4 turn entry that evolves into spiral dive may not matter if you are 200 ft off the ground and don't respond by checking the stall immediately.
Remember too that the static source for the ASI will probably not read correctly in a slip - especially if the static taps are on the fuselage. So keep the nose down, OK?
You may not realize how thin a line there is between a slip and a skid while doing a forward slip.
Lets establish a forward slip. Lets say about 2/3 to 3/4 left rudder, and just the right amount of right aileron to maintain a straight-ahead flight path.
Now, suppose we add a little more right aileron. The extra bank starts to turn us to the right. We are in a slipping turn to the right. Not much of a turn, lots of slip. Everyone feels very safe here.
Now, instead, suppose we take away a little bit of right aileron. Not enough to keep the flight-path straight, we start a turn to the left. We are in a skidding turn to the left. Oooh, skid = bad - stop that.
The forward slip - straight flight path, is just a thin dividing line between the slip and the skid. Is either one really worse than the other?
For most airplanes, without generating any significant yaw rate, just developing the turns as described here, I don't think a spin will develop from a stall. For some airplanes, it will.
From conventional wisdom, the skidding side is arguably more risky than the slipping side. Here's why.
For a normal wing with some dihedral, in the slipping turn, the whole right wing sees a higher angle of attack than the left. The aileron input to maintain roll trim reduces the effective angle of the outer wing panel, leaving the inboard panel of the right wing at the highest angle of attack.
On the left wing, the whole wing is at a lower angle, but the aileron input is increasing the effective angle on the outer panel. But we are also turning, so the left wing is moving faster, making more lift, so it doesn't take very much aileron to maintain roll trim.
The same wing, in a skidding left turn, still has the whole right wing at a higher angle of attack. Still the right aileron is reducing effective angle, and the left aileron is increasing effective angle. But the turn to the left means that the left outer panel sees reduced velocity, requiring more right aileron input to maintain roll trim than the equivalent slipping turn. More likely that the left wing tip will stall first.
The forward slip, as the boundary between a skidding turn and a slipping turn, still has the left wing outer panel at a relatively high angle of attack, balancing the extra lift on the right inboard wing panel. Depending on the details of the wing design, such as taper, twist, airfoil design, the left tip can still stall first, dropping the left wing. As I mentioned in the other thread, the Schweizer SGS 2-32 is a great airplane to demonstrate this in.
Whether the wing drop develops into a full spin or a 1/4 turn entry that evolves into spiral dive may not matter if you are 200 ft off the ground and don't respond by checking the stall immediately.
Remember too that the static source for the ASI will probably not read correctly in a slip - especially if the static taps are on the fuselage. So keep the nose down, OK?
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