Slipstream
Slipstream is a zone of lower wind speed on the leeward side ( leeward ) of a flow obstruction. The historical use of the slipstream consists in the creation of rows of trees or hedgerows in the field , where the slipstream - six to seven times the length of the tree height - prevents erosion . In a broader sense, slipstream refers to the zone behind a moving object, even when there is no wind. The slipstream behind moving objects plays an important role in various sports. In the case of a moving object with an additional crosswind , the slipstream lies diagonally behind the object in accordance with the vectorial addition of the wind speeds (compare: parallelogram of forces ).
Sailing
In the sailing ships of the effect of the wind shadow is basically negative: On the leeward side of islands or coasts , the sailors less wind and less driving - when sailing race which extends between the increases counterparty and the wind direction shifting ship to the enemy the wind out of the sails , because it creates a slipstream.
Cycling
The slipstream plays an important role in cycling , as the air resistance is greater than the rolling resistance on flat terrain from around 15 km / h . When drafting (engl. Drafting or slipstream) is likewise a traveling ahead cyclist as a wind breaker used in the shade of the air resistance and thus - with the same speed - also necessary to overcome it proportion of the performance is up to 30 percent lower.
In most disciplines this is allowed and also desired - the speed of the field and the tactical variety increase.
Slipstream driving in groups
In a special form of slipstream driving, the so-called Belgian roundabout , the drivers take turns constantly so that the management work is distributed equally to all drivers and also to the drivers who are in a second row in the backward movement towards the end of the group drive in the slipstream. Disadvantages of this formation: Due to the frequent change of leadership, the leading driver has to drive significantly faster than the speed of the overall formation (because he gives up the lead and thus about 1.80 to 2.00 m again and again when changing leadership), and the formation only works then smoothly when all drivers are almost equally strong.
Other formations are the wind relay, in which the leader falls back to the end of the group after about 250 m, or (only during training) the double row, in which both leading riders fall back past the group.
In crosswinds, all forms of slipstream travel are carried out sideways. For example, when the wind comes in from the front left, the first driver drives on the left side of the road, the others line up to the right of the person in front, whereby the front wheel should be on average roughly at the level of the pedal bracket of the person in front, depending on the angle of the inclined wind . As a result, due to the limited width of the road, only a limited number of riders can participate in the group (20 to 25), so that in the Belgian spring classics there is an inclined wind from the Atlantic on the long straights comes quickly to the division of the field into many groups. In order to force this, the leading driver can also drive in the middle or almost to the right on the road instead of on the wind incidence side (in the example on the left) in order to “take” only a small part of the group with him. This technique is therefore also called “ hanging on the edge of the wind ”.
Outliers who want to break away from the peloton usually only have a real chance of success against the peloton if they take turns in the slipstream.
Exact investigations with the mobile SRM training system have shown that
- the air resistance reduction at different positions of a number of drivers - for example in a four-wheeler - is different. The last driver has to overcome up to 15 percent higher air resistance than that in the slipstream of the first man in front;
- Even the leading driver - surprisingly and in contrast to sailing (see above, taking the wind out of the sails ) - experiences a reduction in air resistance.
Even on touring trips, especially with strong headwinds, it can be important that less powerful or more wind-prone people - for example because with wide, fluttering clothing or bulky luggage on the side of the bike, or simply physically smaller - use the slipstream of the first rider as much as possible to stay together as a group.
Triathlon and individual time trial
Only in the triathlon (on the long and middle distance as well as in many competitions on the Olympic distance and the sprint distance (is in the respective event announcements and, for example, in the regulations of the German Triathlon Union)) and in the individual time trial , slipstream driving is prohibited and will result in disqualification or Punished time penalties because it is seen as a falsification of one's own performance. Especially with the long straights of the Ironman -distance to Hawaii by the volcano - desert in strong head winds and high temperatures occurs slipstreaming due to the very different performance levels of all participants very often and was just in the last two years to the controversial issue, as real margins were prescribed .
Pacemaker races and record attempts
Due to the slipstream, special sporting disciplines such as B. the standing race , in which behind special motorcycles, which are equipped with a steel spacer, the roller, speeds of up to 100 km / h can be achieved on cycle tracks . In Germany , this sport enjoyed particular popularity from the 1920s until the 1980s , when mostly Germans were the world champions. A standing train still exists in Solingen today .
On October 3, 1995, the Dutchman Fred Rompelberg reached a speed of 268.831 km / h on his special bike behind a dragster racing car with a huge windshield on the Bonneville Flats in the Great Salt Flat in Utah ( USA ) .
See also: Stayer world records on the Grenzlandring .
in-line skating
In inline skating , the slipstream - despite the lower speed - has a greater suction effect than in cycling due to the smaller possible distance to the person in front . However, in order to make optimal use of the slipstream, a uniform step is required by those involved. Therefore, the skate movements must be performed in a uniform rhythm so that the slipstream group can minimize the distance to the person in front and thus maximize their speed. Favorable positions within a slipstream group are the first positions after the leader. The so-called "accordion effect" does not only occur in the rear of the slipstream group when changing tempo. Small speed differences in the group create "holes" between the skaters further back in the group. When the pace increases, the skaters can often no longer close the gap to the person in front and therefore have to let go.
As with cycling, the slipstream has a decisive influence on the course of the race in inline skating.
In speed skating with a mass start or in team pursuit races, slipstream plays an important role, while slipstreams are largely avoided when running in pairs (and alternately) on the inside and outside lanes.
Motorsport
In many categories of motor sport , the slipstream is used to gain a speed advantage when overtaking almost equivalent racing cars or motorcycles. Here, the behind running end in the leaves quiet zone of the person in front of this approach eye and then tries to use the excess speed of up to 25 km / h past him forward.
Driving in the slipstream is particularly advantageous on straights and in banked turns . For this reason , slipstream duels can be observed almost constantly , especially on oval courses , such as those still used today in the IndyCar Series and the NASCAR Series. However, dangerous collisions can occur here.
In sports car races , such as As the 24-hour race at Le Mans with its long straights, is drafting an important element to fuel saving, since each extra pit stop cost.
In touring car racing, the slipstream is sometimes used to achieve a better lap time in qualifying. To do this, several cars (usually from a team or a manufacturer) drive one behind the other over a long distance at a short distance. An extreme form, pushing the person in front of you, which also increases your own speed, is called bump draft in the NASCAR scene .
In Formula 1 , the slipstream used to be more important because it could be better used for overtaking maneuvers. Since around the mid- 1980s , diffusers and other air control elements (e.g. winglets) have increasingly been creating treacherous turbulence at the rear ( dirty air ), which makes it difficult for those who follow immediately to check the vehicle, especially on the front axle, and thus make overtaking more difficult.
Winter sports
Mass starts are now being carried out in more and more winter sports, so the question of running or driving in the slipstream is becoming increasingly important. With ski cross there is also the problem that it goes steeply downhill. As a result, it is necessary to step out of the slipstream as late as possible before the target, so that the opponent has no chance until the target to attack again than the following. Here one must also take into account the force of gravity, which favors the corresponding overtaking maneuvers.
swim
The reduced flow resistance in drafting also plays a role when swimming . Even if the medium is not air, but water, z. T. the term slipstream used.
Road traffic
What well-rehearsed truck drivers can already practice when driving in a convoy is to save fuel by being considerate and driving behind one another, which is limited by law (maintaining distance). Systems for utilizing the slipstream without impairing road safety and in accordance with the Road Traffic Act, so-called platooning , are currently being developed. In other words, with the emergence of autonomously controlled vehicles and their networking with the vehicles in front, slipstream driving between trucks and cars will become safer and therefore practicable.
aviation
In contrast to cycling or motor sports, where the slipstream has a positive effect, it is negative in aviation and air sports. If an aircraft were to fly in the slipstream (“ wake vortex ”) of another aircraft, this would result in the wings of the “pursuing” aircraft no longer receiving sufficient flow and the aircraft sagging or, in the worst case, falling into a tailspin. For this reason, planes that fly in tight formations, as is sometimes seen in flight displays, fly at minimally different altitudes. Sometimes even the slipstream of an aircraft can become a problem for the aircraft itself. The design of the Lockheed P-38 Lightning made it difficult or impossible to intercept during a long dive because the wings between the engine and the nacelle created such a large slipstream that the elevator was no longer flown against and therefore not more worked. The problem was solved with dive brakes, which slow the aircraft down so far that the elevator is flown against again.
The so-called deep stall is also a problem that can be traced back to the effects of the slipstream. If the flow stops in an aircraft with a T-tail and the pitch is large enough, the wings cast a slipstream on the tail . It cannot contribute to the control because it is no longer flowed against. Then it is practically impossible to end this dangerous state.
It is similar with parachutists . For example, a skydiver is not allowed to linger over another's parachute, because the slipstream of the lower one reduces the air resistance of the upper skydiver and causes the parachute to collapse. In the worst case, the upper skydiver falls on the parachute of the lower. However, this "attraction" with the artistic jump offers the possibility that the upper one stands with his legs on the cap of the lower one, provided that both umbrellas also make a certain forward movement.
Bird flight (analogy)
Like an aircraft, every bird in flight causes a downward current in the track behind it, a characteristic piece to the right and left of it, however, a compensating upward current, which makes it easier for a bird flying to the side just behind it to generate sufficient lift. A group of birds flying together will therefore tend to form an arrow formation, especially when pulling evenly in one direction. Here, the air resistance is not reduced as in the classic slipstream, but the lift is facilitated through synergy .
Use of language
Very often in the German-speaking area one finds the usage that person B would have found success in the "slipstream" of person A, which as a rule should not mean anything else than that person A had prepared the way for B and B less resistance had to overcome.
The tendency of journalists to use figurative language does not necessarily mean that it is used appropriately if it is only meant in the sense of “in the wake of”, such as B. in "Social plans in the slipstream of Hartz IV ".
Web links
- Slipstream on wissenswertes.at ( Memento from March 7, 2016 in the Internet Archive )
Individual evidence
- ↑ JJ Isler, Peter Isler: Sailing for Dummies. Wiley-VCH Verlag, Weinheim 2013, ISBN 978-3-527-70949-6 , p. 111.
- ↑ a b Constant rotation of the group. In: wissenswertes.at. Retrieved May 31, 2013 .
- ↑ Rule violations in triathlon - and how to avoid them. In: triathlon-tipps.de. Retrieved May 31, 2013 .
- ↑ Skating in the slipstream - the key to success. In: skating.bmw-berlin-marathon.com. Retrieved May 31, 2013 .
- ^ WTCC in Monza: The preview. In: motorsport-total.com. March 10, 2012, accessed January 9, 2013 .
- ↑ The winglets should go. In: motorsport-magazin.com. May 9, 2007, accessed January 9, 2013 .
- ↑ Arnd Krüger . Slipstream. Competitive Sports 49 (2019), 2, 25.
- ↑ Best Drafting Distance in Swimming svl.ch, Swimming Club Limmat Zurich, May 1, 2005, last accessed July 7, 2017.