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NRCF

Department of Physics, Lund university

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Front, middle or back?

Click on the images to enlarge them. 

The upper graphs above show the "vertical" component for rows 2, 6, and 9. The coordinate axes have been rotated from the raw data so that the vertical axis is orthogonal to the track (and essentially along the spine of the rider). The elevation data are measurer through air pressure, and is sensitive to air speed (Bernoulli's law), which seems to affect the data from row 2 most. (The data were collected using the WDSS sensor from Vernier.

The numbers below refer to the overview picture on the Project Helix blog: (http://projekthelix.se/).

 Predrop (1) + korkskruv (2)

As in the picture on the top of the page, the red graph corresponds to Row 2, the blue graph to Row 6 and the green graph to Row 9 (just in front of the last row.) 

Note that the time difference between the different position is smaller for high g's, where the train moves faster.

Launch 1 (3) - corkscrew (4) - airtime hump (5)

 

The Launch is clearly visible in the graph as a long period (15-17 s) of about 1g, as well as a relatively straight ascending line in the elevation graph. (Since the speed is well above zero when the train enters the launch, the deviation from a straight line, expected for accelerated motion, is hardly visible). After the launch the train enters a corkscrew and then an airtime hump at 24 sec. 

Pretzel-loop (6) + airtime hump 2 (7)

 

First, note that the largest forces on the rider are not at the bottom of the Pretzel-loop (32s) but just before and after. Also, note that the graph in the Pretzel-loop is relatively symmetric for a rider close to the middle of the train, whereas a rider close to the front of the train experiences the largest force occurs at the exit from the lower part of the Pretzel when the rest of the train is still lower, giving a higher speed. The tail of the train instead approaches the lowest point with higher speed than it exits.

Around 38-40 s, the train passes the second airtime hump where you are weightless or experience negative g's. Since the middle of the train passes the top with lowest speed (since the center of mass is highest there), a rider in the middle experiences less negative g's, but is, instead closer to weightlessness. Both front and back of the train move faster over the top, making the centripetal acceleration (v2/r) larger.

Zero-g roll (6), dive och helix (9)

The zero-g roll is a long period of near weightlessness, while you rotate around an imaginary line at heart level. 

Launch 2 (10), Inverterad top hat (11), Airtime Hump (12) 

The long period of 1g (54-58 s) corresponds to the second launch. Note how the front part has more g's (at around 58s) approaching the  inverted Top Hat that the middle and back. (After leaving the launch, the train loses speed on the way up to the top.) Also note the long period of near weightlessness, while your are upside down in the highest point of the Helix track. After the Top Hat the direction of motion changes on the way into the largest Airtime Hump. Giving a long period of negative g's around 65 s. Again, there front and back move faster over the top, leading to more negative g's.

S-kurvor (13) och Heartline Roll (14)

Finally, the S-curces offer some slalom, before the heartline roll, where tho body moves in essentially uniform rectilinear motion, while rotating around the heartline. During the heart line roll it is also interesting to consider the lateral (sideways) component. In the graph below we have added an expected cosine curve for the vertical (red) component and a sine curve for the lateral (blue) component. The green curve gives the force in the direction of the track, where the break following the heart line roll is clearly visible. 

Also, watch a movie showing the forces in the  Heartline Roll.

Coming to a stop

The brake is clearly visible in the graph of the "longitudinal" component. Since the whole train brakes at the same time, this part of the graph can be used to synchronise the three graphs from different places in the train.

Read more about magnetic brakes and about the brake in Helix (in Swedish)

A movie from the tour synchronised with accelerometer data.

By chance, there is a POV movie, which is possibly from the same tour I measured (row 9) during the press day 23 April. The program Logger Pro, allows the data to be synchronised with the movie. View the resultat  (Note, however, that in that case, the accelerometer data are the raw data, before rotating the coordinate axes)

Why does the position in the train matter?

Read more in "Student investigations of forces in a roller coaster loop" (with examples from the Kanonen loop).