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Pilot Zone / Re: Fly in the car
« on: September 14, 2022, 02:43:54 PM »
I object to the phrase “sucked out of the car”.
The fly voluntarily flies through the window.
Let the direction of car travel be along axis x. Assume no wind outside. Assume no turbulent boundary layer, but a sharp instantaneous change of airspeed from zero inside the car along the x axis to 60 mph relative to the car. Assume the fly crosses that threshold along the y axis, perpendicular to the airflow. I don’t know how fly wings work so assume they work like airplane wings, needing forward angle of attack. It doesn’t matter what speed he is flying along the y axis, although that may affect his final resting spot.
Therefore:
A. There is no forward movement to use as “excess thrust”. The forward movement is relative to the ground and the fly knows nothing of the ground. He only interacts with the air. His “forward movement” is along the y axis. All he knows is he encountered a sudden wind sheer 90 degrees to his direction of travel.
B. Pretty much. The sudden crosswind likely flips him all around and he falls to the ground (now involving the z axis) somewhat near where he left the car, but farther along the x axis, because his forward movement (in the x direction) does becomes relevant with respect to the ground at that point. But not too far because as soon as he leaves the car the force moving him along the x axis ends and his inertia is quickly met with air and ground friction. The trajectory of his trip to the ground within the x-z plane and maybe a little in the y direction can be calculated with a formula involving coefficients of friction, gravity, the mass of the fly, and the speeds of the air and his initial exit, but I’m too lazy to work that up for you.
C. Flies have legs?
The fly voluntarily flies through the window.
Let the direction of car travel be along axis x. Assume no wind outside. Assume no turbulent boundary layer, but a sharp instantaneous change of airspeed from zero inside the car along the x axis to 60 mph relative to the car. Assume the fly crosses that threshold along the y axis, perpendicular to the airflow. I don’t know how fly wings work so assume they work like airplane wings, needing forward angle of attack. It doesn’t matter what speed he is flying along the y axis, although that may affect his final resting spot.
Therefore:
A. There is no forward movement to use as “excess thrust”. The forward movement is relative to the ground and the fly knows nothing of the ground. He only interacts with the air. His “forward movement” is along the y axis. All he knows is he encountered a sudden wind sheer 90 degrees to his direction of travel.
B. Pretty much. The sudden crosswind likely flips him all around and he falls to the ground (now involving the z axis) somewhat near where he left the car, but farther along the x axis, because his forward movement (in the x direction) does becomes relevant with respect to the ground at that point. But not too far because as soon as he leaves the car the force moving him along the x axis ends and his inertia is quickly met with air and ground friction. The trajectory of his trip to the ground within the x-z plane and maybe a little in the y direction can be calculated with a formula involving coefficients of friction, gravity, the mass of the fly, and the speeds of the air and his initial exit, but I’m too lazy to work that up for you.
C. Flies have legs?