The discussion centers on the physics behind why a flying disc, such as a Frisbee, rolls in the opposite direction of its spin, particularly when thrown by a right-handed individual using a backhand release. The primary factors include the differential lift generated by the spinning edges of the disc and the resulting pitch torque, which leads to a gyroscopic roll reaction. Specifically, a clockwise spin from a right-handed thrower results in a left roll due to the pitch down torque associated with the cambered airfoil design of the Frisbee. The Aerobie, a flying ring, minimizes pitch torque and can be tuned to fly straight without rolling.
PREREQUISITESAerodynamics enthusiasts, Frisbee and disc sports players, physics students, and anyone interested in the mechanics of flying objects will benefit from this discussion.
Jeff Reid said:The disc normally experiences a pitch down torque due to it's shape (cambered airfoil) and forward movement. The gyroscopic reaction to the pitch down torque is an inwards roll.
A flying ring would normally have a forwards center of lift, resutling in a pitch up torque, resulting in a outwards roll. An "Aerobie" is a flying ring is designed to keep the center of lift close to the middle, minimize any pitch torque, and if properly "tuned" (before throwing it you flex it in the concave or convex direction), will fly straight without rolling.
http://en.wikipedia.org/wiki/Aerobie
http://www.aerobie.com/Products/Details/RingScientificPaper.htm
It should roll to the right, which is what mine do. For a frisbees (cambered disk), the roll is such that the forwards moving edge moves upwards while the backwards moving edge moves downwards, but this is more related to pitch down torque related to a cambered airfoil and the gyroscopic roll reaction to pitch torque than any difference in lift. For a flat flying ring, the pitch torque is upwards, resulting in the opposite roll response. The Aerobie is a flying ring designed so that the airfoil and center of lift don't produce a pitching torque.apollo100 said:Why does a Frisbee delivered by a right handed thrower with a back hand release tend to roll to the left?
I corrected my previous post.djeitnstine said:I would just like to rephrase this as since the torque is negative it experiences a left roll. Oppositely if the torque is positive it experiences a right roll.
Pitch torque results in roll reaction and vice versa. The control inputs for a helicopter are set 90 degrees out of phase to compenstate for this.apollo100 said:Just to make sure I understand. This effect is caused by the gyroscopic response to torque and not the aerodynamics?
A discus is a symmetrical airfoil, so I wouldn't expect a pitch down torque. If you look at the video below, the discus mostly maintains it's angle of attack with respect to the ground, although the camera angle make some of them appear to pitch up. You probably want to turn off the sound.As another example: Olympic discus throwers experience a similar effect. Throws either land fairly flat or roll inwards. Based on what I've read so far then: Because right handed discus throwers produce clockwise spin, when viewed from above, the downward pitch torque produces a gyroscopic reaction that causes a roll to the left.
A discus probably doesn't roll, or at least not significantly. Looking at the video, the discus seems to maintain it's attitude until it impacts with the ground.apollo100 said:So a discus rolls inward because the leading edge is being pushed up?
Olympic style discus? In the video above, the top throws didn't appear to have much roll at all. It's possible that a right handed thrower initiates a left roll in addition to clockwise spin at release. I'm not sure how much affect areodynamic pitch related torque would have on a 2kg discus.apollo100 said:Actually, being very familiar with discus throwing, they very often roll into some degree. In fact, with a little help from a quartering head wind, record throws almost always land vertically, frequently rolling inwards 45 degrees.
If you look at any videos of a discus thrower, they hold the discus so the outside edge is down and the inside edge is up, in order to keep the discus from falling downwards out of the hand of the thrower. A bit before release, the thrower lowers the inside edge and/or raises the outside edge of the discus, imparting an inwards roll before any significant spin is imparted to the discus. The momentum of the inwards roll will be conserved during the toss. The 2kg mass of the discus is enough that aerodynamic torque / roll coupling is probably very low.apollo100 said:I've often wondered why so many throws (at all levels) roll inwards.