I’ve written several times about this pitch, and each of those posts reflected an evolution of my thinking on it based on recent results. Our results continue to get better, and my thinking gets more definitive. So I thought I’d write an update.
[If you are new to our measurements, you may take a minute to read here about vorticity (the colors in our plots), boundary layer separation and wakes]
First, this is a rare pitch that depends on the ball orientation. Conventional pitches do not. The depend only on the spin axis, rotation rate and ball speed. The only other pitch I know of that depends on orientation is a knuckle ball, but, somewhat ironically, no one attempts to control the orientation of a knuckleball. It’s random, and that is part of the appeal.
But, wait… maybe knuckleballs have something to teach us here. The “laminar express” is really an attempt to have the action of a knuckleball in a repeatable, stable way.
We’ve been testing MLB balls with no spin. I hesitate to call them “knuckleballs” because we launch them at 90 mph and a knuckleball is rarely over 70. With some regularity, I see this pattern.
As I have described previously in Post 17 and Post 27, seams on the rear of the ball within a certain range of angles pin the boundary layer separation location (visible as the red shaded region), and this is happening on the right rear of the ball. I have previously thought that this effect can cause the separation on the side with the seam to be delayed relative to the other side, but we see here the opposite is true. On the left side, the seam upstream of the hemisphere line causes the flow to become turbulent, and that significantly delays the boundary layer separation on that side (separation is the start of the blue shaded region on the left of the ball). The asymmetry results in a shift in the wake to the right side meaning the ball is being pushed to the left. I’ve updated my sketch below. This is what a “laminar express” from a right hander looks like.
One thing to note here is that there is nothing “laminar” about this pitch.
It’s also interesting to think about other orientations. First, consider a more counter-clockwise orientation.
This moves a seam just in front of the hemisphere line on the right (which will cause turbulent flow on that side) and just downstream of the hemisphere line on the right (which will cause the boundary layer to separate there). This is a more asymmetric wake and a bigger force than the original orientation.
OR, perhaps the seam near the front of the ball is in a region too stable to cause the flow to become turbulent on the right side. In that case, a laminar separation may form prior to the hemisphere line as sketched below.
This would result in a very large force. But strangely, it doesn’t seem to work this way. We found a case where laminar separation occurred on the the right, but…
The right hand side looks very similar to my sketch with a laminar boundary layer separation. For reasons I don’t understand, the left side separation point is much closer to the hemisphere line than we’d expect, and the wake is not as tilted as the case as it is in Figure 1. I’ve put them side by side below to make the difference more obvious. So, we have yet to see any evidence that laminar boundary layer separation enhances the “laminar express”, at least at this speed.
Now, let’s look at rotating the orientation of the ball in the other direction relative to Figure 1. If this pitch orientation was rotated clockwise in the sketch, the asymmetry in the wake should be smaller and the side force less. This is sketched below. The more gyro added, the more the right side resembles the turbulent separation of the left side and the less force. The range of angles where the seam causes separation is something we are currently mapping that out.
If the orientation was more counter clockwise, at some point, the seam is at the hemisphere line on both sides. Beyond that point, the force direction changes to the other side. I am told that throwing a ball in that way would hurt.
Conclusions
- Ball orientation (position of seams relative to axis) can strongly influence the wake and generate side force on a pitch.
- I believe that these phenomena found in non-spinning balls will also be present with the ball is spinning since the seams are in a similar location most of the time.
- So far, no evidence that laminar boundary layer separation enhances this effect.
Continuing my back reading, and our earlier conversation. I’m still perplexed by your hypothesis that you state in the post: “I believe that these phenomena found in non-spinning balls will also be present with the ball is spinning since the seams are in a similar location most of the time.”
We’re both absent data, so ¯\_(ツ)_/¯ but, I would expect that there would be a functional dependence on the vector that goes with the line where the two symmetry planes of the baseball meet in the case of the non-spinning baseball, but an *entirely different*, strongly nonlinear functional dependence on both that vector and the spin vector that’s involved. I can’t imagine that the functional dependence on a low-spin baseball would particularly inform us about the behavior of the high-spin one. What’s your thinking on how this relationship manifests?
That spin has nothing to do with this phenomenon. It only serves to keep the ball in the desired orientation. Spin is obviously central to Magnus force, which is in the other plane.
Ohh. So when you talk about spin, you strictly mean the O(1 rpm) spin rate as the ball tumbles? Essentially the random fluctuation you’d see with a knuckleball thrown by a Greek god?
From my experience, a knuckleball will never maintain any particular orientation. But, a slowly rotating ball can. Have you seen this? https://www.baseballaero.com/wp-content/uploads/2019/01/GarciaSplitter-desktop.m4v
I’m so confused. Wouldn’t this make the ball cut?
Nat, what do you mean by “cut?” I realize that is a very common term, but I’ve never been able to get a handle on what exactly people mean by it.
Sorry I just saw this. I think we’ve figured out what I was talking about since!
an axis like this with nearly backspin from an overhand fastball with a tilted axis of somewhere between 10-20 degrees made my but cut as much as Rivera’s cutter.
My cousin and I were watching Greg Maddux describe his two seam fastball. Now I believe that Maddux had a laminar 2 seamer. It seemed to move like a screwball that had a 45 degree sideways axis. Maddux on TV was saying that his natural fastball just does that with a standard two seam grip. Now my cousin then went outside and used that 2 seam grip Maddux showed on TV. We then went outside to test it out. However, since my cousin and I throw from an overhand/over the top arm angle(both of us are RH).. the ball cut to the left like Mariano Rivera’s cut fastball. Both of our fastballs nearly cut 7-8 inches when we threw it. I noticed a white dot on the left side of the ball when I would catch it. It seemed that the ball had a tilted axis somewhere between 10-20 degrees on the left side of the ball when I caught it. We just called it a natural curve. And anytime I was on the mound against a LH batter… I would use this suped up 2 seam cut fastball against them with great success! I never could get that running(to the right) and sinking action on a two seam fastball or change up like Maddux, Strasburg, or Bauer. But I could get as much cut on the FB just like Rivera’s cutter though. The catcher’s who caught me and my coaches just called it the Guzz Cutter… PS I also could never get a 4 seam cutter to move much either… all the cutters I threw were of the 2 seam variety!
I do think subtle changes in orientation can cause the direction of this effect to reverse.
Last year during the summer of 2019, I tried this with a two seam slider as well. The slider axis is pointed upwards at a 10 degree angle. This slightly upward axis causes the Magnus Effect to make the ball break laterally, but the red circular seam on the back of the ball catches the air and causes the ball to drop faster than normal during it’s flight. I only throw a slide between 65-70mph. I would imagine a pitching machine of MLB player with a great slider would have a much more dramatic effect on this type of slider.