Steep face (fair)

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A steep wall rider sitting across the saddle of the motorcycle during the show. Red line near the top of the web.

First Saudi driver Saeed Aldouweghri , 2003.

The steep wall or drum is a fairground attraction . The cylinder wall of a large wooden drum four to five meters high and about 7 to 10 meters in diameter is used on the inside by one or more motor vehicles, usually motorcycles.

Steep wall

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Four drivers at the same time on the steep face

parade

In front of the large wooden drum, a motorcycle is made to roll on a roller stand as an advertising measure , usually an old American motorcycle, e.g. B Indian . Its throttle can be locked in one position. The driven rear wheel rotates on a pair of rollers and, via this and a chain drive, also drives the likewise cylindrical roller that carries the front wheel. With the wheels spinning quickly and movement stabilized, the artist now does gymnastics on the motorcycle. These simpler feats, which can be admired freely, promote the steep face, for which the audience has to pay admission.

boiler

The audience climbs the outer stairs of the boiler, then stands on stage stairs and looks into the boiler from above to watch the performances.

Driving inside on the vertical wall is physically possible because the centrifugal force when driving in the drum points radially outwards from the center of gravity (vehicle and driver) and presses the tires against the wall and above a certain speed (depending on the diameter of the track and the coefficient of friction (Tire to wooden track) approx. 40 to 60 km / h) is so large in comparison to gravity that, thanks to static friction (transverse to the direction of travel), it is possible to drive on the inside of the boiler wall in a corresponding inclined position without sliding down in the direction of the gravity of the earth.

idea

The steep wall rider starts on the circular inner platform. A cone slope of around 45 degrees all around allows the transition and entry into the vertical wall as a steep curve .

In this cylindrical wall it is now accelerated further up to a steady and relatively safe speed, at which tricks are then performed. A steep face demonstration runs for a total of 5 to 10 minutes.

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Acrobatic feats on a steep wall motorcycle

Several artistry numbers take place in the sequence of a performance in the boiler. Common numbers are:

• The co-driver or the driver of a motorcycle shows acrobatic feats.
• Overtaking race: Several motorcycles ride around each other.
• A powerful motorcycle accelerates to twice the speed, which generates four times the centrifugal force and makes the entire boiler vibrate.
• A go-cart race is being held.
• Loops: The artists curve “sideways” in the drum so that they are once near the bottom and then again at the top of the bowl.

hazards

Driving on the steep face is exhausting and dangerous. High forces act on the driver, often three times or more his weight. A high level of concentration is required, carelessness can lead to falling into the boiler or being blown out. Driving close to the top of the boiler is particularly dangerous. Even if the spectators are protected with safety fences, the driver is at risk.

There are only a few troops around the world who perform these fairground arts.

Death ball

The death ball of the Flic Flac circus

A variant and further development, on the fairgrounds around 1964–1969 in Wels , is the ball - " death ball " - made of steel, which can be dismantled into segments that are formed from a network of bent sheet steel strips in segment frames made of L-profile. The spectators in the tent can see through gaps of around 4 × 4 cm that leave out the mesh, which is also around 4 cm wide. These steel strips are curved according to the spherical shape and attached to the segment edges so as to be resistant to tensile force. From interwoven driving, slightly different from the equatorial circle, 2 drivers can switch to driving on circles at right angles to each other.

As a highlight, even three drivers can drive on circular paths that are orthogonal to each other, two of them meridional and one equatorial. Or all three at the same incline of a little more than 45 ° horizontally, corresponding to the rolling directions of a cube standing on a corner. The latter configuration has the advantage that all tracks are geometrically and physically the same, that is, "equally fast". As a complication, the 3 orbit levels can slowly rotate around a vertical axis.

Each of these 3 drivers can be accompanied by another driver, side by side or one behind the other. As a result, the space in the sphere becomes increasingly narrow.

In February 2014, a team of 7 put together by Freddy Nock experienced a new world record in terms of the number of riders in the sphere in a sphere 4.9 meters in diameter. In April 2010 several drivers of the "Russian State Circus" had an accident in a sphere with 32 meridian segments due to a blown rear tire. On March 19, 2013 six drivers of the Flic Flac circus were injured during a training session in Cologne , two of them seriously.

In Graz, Circus Safari showed a motorcyclist in a death ball.

Physical estimates

A high coefficient of friction allows centrifugal forces to be struck even at low speed. At best, however, a coefficient of friction of 1.0 can be assumed.

Centrifugal force (outwards) in the cylinder at the level of gravity (downwards) is then just sufficient for adhesion. The resulting total force on the vehicle results as the diagonal of the square of forces 1.41 times as large as the force of gravity and with the motorcycle tilted at 45 °. Additional forces in or against the direction of travel cannot be absorbed by the adhesive force at the tire contact point, accelerating or braking would lead to the loaded tires being smeared down towards the cone.

If the vehicle and the driver are exposed to a total acceleration of 1.41 g , the centrifugal force has a stronger effect at a greater distance from the axis of rotation of the orbit, but it has a lower effect closer to the center of the cylinder. On the one hand, this means that the vehicle alone experiences a higher centrifugal force acceleration than the driver, whose center of gravity is closer to the cylinder axis. This relieves the driver a little of the amount of g-force , especially with small cylinder diameters or when he is crouching or standing on the motorcycle saddle. Standing on the saddle reduces the centrifugal load on the driver when the motorcycle is at a fixed speed, but requires a certain increase in driving speed in order to maintain the minimum centrifugal force to maintain grip.

Compression clothing, especially in the lower half of the body, can help the driver to maintain his blood circulation under higher loads.

When a rider who stands relaxed on the motorcycle relaxes his "soft spine" without muscle strength, this will draw a slight arc when viewed from behind; like a link chain that the driver holds up from his point of view: near the center of the cylinder, running closer to the direction of gravity, somewhere in the center of the chain 45 ° at an angle and further out, i.e. close to the inner cylindrical roadway more horizontal than 45 °, because there the Centrifugal force must be greater than gravity.

Anyone who drives a sphere meridionally on the inside must achieve a centrifugal force at least equal to the force of gravity at the upper apex of the track in order not - from his point of view - to lift off the road or not to lose contact at the upper pole of the ball from the outside view. At the top, he needs the speed of a driver in the equatorial lane with a coefficient of friction = 1. The driver accelerates downwards on his meridional path through gravity and has reached his highest speed at the lower vertex, at which the resulting force from gravity and centrifugal force is more than that Reached twice the acceleration due to gravity. By using the motor drive necessary against rolling and air resistance more strongly on the upward branch of the meridional path, the driver can reduce this load peak somewhat at the lower vertex.

When traveling along the meridian, gravity below the equator supports the pressing of the motorcycle against the track by centrifugal force; at the equator it has a neutral effect because it is parallel to the track, above it it reduces the pressure, as the vectorial addition of the components shows. Assuming constant motor drive force and air resistance, there is an ups and downs in speed, because part of the kinetic energy is converted into positional energy (altitude in the earth's gravity field) or is recovered again. This fluctuation in speed has the effect of decreasing the centrifugal force during the upward journey, so that good traction for powerful engine thrust is more likely to exist under the equator than afterwards. The driver will try to start his short motor drive phase by turning the throttle in good time below the equator.

If the driver notices that he is too slow to remain on the ground while sitting at the “North” pole, he can increase the height of the center of gravity by standing up and thus - from outside - lift the motorcycle a few centimeters. Alternatively, it can steer away from the pole and reach a lower-lying apex.

Motorcycle types

Indian 750 Scout from the 1920s and 1930s are still popular with steep wall drivers thanks to their stable frame and good power development. In the future, lighter electric motorcycles - it can be driven with a small battery - have application potential.

Web link

• Ball with 9 drivers at the same time . A group of 5 men starts, one behind the other they take a horizontal orbit to the left rather a little above the equator. The remaining 4 also start later as a group and travel on an orbit about 30 degrees lower, also counterclockwise and with the same period of about 1.5 seconds. 8 are then grouped more closely together, for example in a circumferential hemisphere and make the 9th place for 7 more vertical (from position 1/2 8 to position 12 o'clock in the ball, fixed in space) the path of the group synchronously crossing rounds . If It Were Not Filmed No One Would See These Events - 2 Entertainment Box, youtube.com, October 11, 2017, accessed October 30, 2017. - Video clip (8: 23–9: 04/11: 08)

Individual evidence

1. ^ First Saudi driver (ar) . In: newspaper . Retrieved September 15, 2018. 
2. ↑ Drama in the "Death Ball" by FlicFlac artists neuepresse.de, March 20, 2013, last accessed October 30, 2017.
3. ↑ http ://www.mein Bezirk.at/graz/ People /circus-safari-graz-m5667978,808597.html Graz Circus Safari, (picture 19 + 20: death ball) photo report Marie Ott, week, accessed January 13, 2014

Web links

• Physics exercise with a steep face driver ( LEIFI physics)