Thoughts about ... the speedbar

speed bar "A mechanical device that allows the driver to increase the speed of the vehicle."

In paragliding, a speed bar exactly the same function: to increase the airspeed of the aircraft. This accessory, which can be intimidating for novice pilots, can also prove to be a formidable ally in many cases. Like any tool, it is necessary to understand it well in order to learn how to use it properly and not fear it unnecessarily.
We will try to explain how it works, its effects on the wing's behavior, and ultimately when and how to use it.

I.- A few notions of aerodynamics ... :

To fully understand how thespeed bar worksspeed bar the consequences of its use, it is important to have grasped certain aerodynamic concepts, particularly those relating to the speed polar curve, trim, and angle of attack.

I.1- Speed polar :

The speed polar is a graph that describes vertical airspeed as a function of horizontal airspeed for an aircraft in steady level flight (paraglider, hang glider, glider, etc.). This curve illustrates the different flight regimes of a free-flying wing and determines its overall performance within each regime: speed, sink rate, glide ratio. Although its shape remains broadly the same, there are certain specific features depending on the type of wing (recreational, performance, mini, etc.) and the flight characteristics expected at the design stage.
This curve is considered to be a graphical representation of the wing's performance. A good understanding of this curve will enable you to better understand the effects of usingspeed bar described below. We will focus on this curve, without going into too much detail.

The different flight regimes are each defined by a zone on the graph:

Notable features include

- Speeds above the minimum sink rate, known as the "1st regime" (downward part of the curve).

- Speeds below the minimum sink rate, known as the "2nd regime" (rising part of the curve).

- The stall speed (Point A):
Located at the extreme left of the curve, the stall point corresponds to the minimum speed required to remain in the flight envelope. Below this speed, the wing stalls and stops flying!

- The speed corresponding to the minimum sink rate (Point B):
This is the highest point on the curve, where the curve intersects its horizontal tangent. We're in the flight regime that allows us to descend (vertically) as quickly as possible.

- The maximum glide speed range (Zone C):
Located at the junction of the straight line passing through "0" and tangent to the curve, this zone corresponds to the best possible glide for the designated wing. We'll see later that this zone of max glide can be more or less important depending on the wing, as the polar curve can be likened to a straight line over a certain portion.

- Max speed (Point D):
This point, at the extreme right of the curve, corresponds to the maximum speed that can be reached by the glider, after using all possible acceleration systems. There is no exit from the flight envelope just after this point, but we are approaching the acceptable limit for safety.

This polar curve therefore teaches us that there is a direct link between speed, finesse, and sink rate (in other words: performance).speed bar therefore be used with a clear understanding of the interaction between these three parameters.

I.2- Basis and incidence :

To allow aerodynamic forces to come into play and make flight possible, it is necessary for the air streams coming from the relative wind to attack the glider at a given angle: the angle of incidence. This is formed by the plane of the sail and the direction of the relative wind (which also corresponds roughly to the paraglider's air path). This angle is directly related to the glider's trim, which corresponds to the angle between the wing plane and the horizontal.

At the design stage, and depending on the purpose of each model (competition, hang glider, school, cross-country, etc.), the designers calculate a pitch (and therefore an angle of trim) which will define the glider's nominal flight characteristics, i.e. without pilot action. There is no standard for this setting: it is specific to each glider model. You can find this "neutral" point on the polar chart, and determine the nominal parameters: cruising speed, sink rate and glide ratio. On modern paragliders, this point is generally located at the beginning of the maximum glide zone (Zone C), whether on recreational or performance wings. On mountain or speed-riding/flying mini-sails, this point may lie a little further down the curve (between C and D), in which case you'll need to apply a good dose of brake to find the maximum glide ratio.

II.- Accelerate ...

Now that we have reviewed (briefly) the aerodynamic principles related to the speed of a paraglider, we will take a closer look at the "acceleration" aspect.
If we want to increase the speed of a wing, we will therefore have to increase its angle of attack to make it more nose-down. There are currently two systems for doing this:speed bar and trims (also known as indicators). Both use the same principle: bending the risers to vary their relative lengths in order to change the nominal trim.

speed bar is the most common device found on modern paragliders. Consisting of one or more bars, it is connected to the risers by a system of cords that slide through pulleys located on the sides of the harness. The principle remains the same regardless of the harness, but it is up to you to find out about the specific features of your harness and how to assemble your speed bar correctly. If in doubt, do not hesitate to consult a professional.

By pushing on the bars with his feet, the pilot acts on the cords, which then activate the system installed on the risers. This system then accentuates the angle of pitch and generates an increase in the wing's airspeed. The A / B / C risers can be shortened linearly or not. Some systems even allowed the rear risers to be released when the front risers were lowered. But this system was soon abandoned, as the phenomenon was amplified in the event of a frontal collapse! The 2-pulley pulley system (in blue on the diagram) reduces the effort required of the foot.

Trims (or displays) work in exactly the same way, but are operated manually and allow the risers to be locked in a certain position. They are generally fitted to wings where the use of a speed bar complicated or simply impossible, such as in tandem wings or speed riding (because of the skis!). They can also be found on paramotor wings. Trims can be used to set the wing in a more nose-up or nose-down position. They are positioned at the rear or front, and sometimes both. Their location and action are entirely dependent on the intended use of the wing.
In tandem flying, for example, this allows the flight regime to be adapted to the weight of the passenger. Or to make a wing more responsive during takeoff if there is wind.

WARNING!

The trimmers can therefore offer a relatively precise adjustment, but as they have to be operated by hand, they can present a major disadvantage in the event of bulk, as the wing will have to be managed with the brakes: your hands will already be quite busy! You'll then have to manage a wing in a more nose-up or nose-down configuration, and therefore potentially less easy to recover in stabilized flight. With a more nose-down setting, the glider will be much livelier, and collapses more violent.

III - Action - Reaction!

All you need to do is activatespeed bar trims to change the angle and trim, allowing the wing to pick up speed. There are many complex interactions between trim angle and angle of attack. In our case, concerning acceleration and speed increase, we will simplify matters and consider that the more nose-down the trim, the lower the angle of attack will be.

When we accelerate, we move a point along the polar curve to the right. Accelerating will therefore have the following direct physical consequences (see polar curve of speeds):
1.- Increase airspeed
2.- Change glide ratio
3.- Increase sink rate
4.- Reduce angle of incidence

More generally, flying a wing at a faster speed will accentuate all these effects, including reactions in the event of collapses. Certification tests subject our paragliders to all kinds of flight incidents at cruising speed (nominal trim), but also at different accelerated speeds (modified trim). The effects of these flight incidents are more violent at higher speeds. Managing these accelerated incidents will therefore be more complicated than at cruising speed. It is interesting to look carefully at the certification reports to determine the scenarios that ultimately classified the wing in a particular category (A/B/C/D). A single case may suffice, such as a large asymmetric collapse withspeed bar to its maximum. This is not necessarily a common occurrence, but it is important to be aware of it.

As soon as the angle of incidence is reduced, we see that the airflow attacks the profile more and more in line with the wing (decrease in incidence), and that the risk of it passing over (negative incidence) and causing a collapse increases. The sails are adjusted so that this does not happen in calm air, but more "vigorous" aerological conditions are quite conducive to this type of problem. This is one of the only risks involved in using thespeed bar.

IV.-speed bar  a tool for steering:

The main tool on a paraglider for controlling different movements is the brakes. They allow you to control the three axes (roll, yaw, and pitch). They are also used to control speed, but to a very limited extent and mainly to slow down. When you want to pick up speed, you have very little room for maneuver using only the brake handles.
But there are many situations where it can be useful to be able to pick up speed depending on the aerology, for example in the case of a poor analysis of the current conditions...
The four consequences of using thespeed bar Paragraph III) can then become valuable allies, either together or independently.

There are two ways to usespeed bar 
– As a safety tool
– As a performance tool.

IV.1-speed bar a safety tool:

Firstly, you should considerspeed bar an additional safety feature for your paragliding equipment. In theory, you shouldn't find yourself in problematic aerological situations, but who knows? It could well be useful if you need to accelerate and take advantage of some of the resulting effects (see above). It is not necessary to carry out this experiment in a secure environment (such as SIV training) since the wing is not supposed to leave the flight envelope, but to start off calmly, it is essential to carry out your first experiments in calm conditions, at sufficient altitude and far from any terrain or obstacles.

As we saw with the speed polar, accelerating can help degrade the overall performance of the wing, especially at its maximum. "Escaping" therefore remains one of the main reasons for usingspeed bar a safety tool. To get away more quickly from an "unpleasant" area, avoid being sucked into the cloud, or simply fight against the wind (or breeze) and reach your intended landing spot.speed bar also be combined with certain descent techniques such as big ears to make them even more effective. It is essential to consult professionals to learn more about these descent techniques and how to implement them.

IV.2-speed bar a performance tool:

Less useful on recreational wings, as they generally perform best with the arms raised (particularly in terms of glide ratio),speed bar essential on competition wings to optimize the different flight regimes according to the conditions encountered. Performance wings have a "flatter" polar curve, allowingspeed bar to be usedspeed bar maintaining their best glide ratio over a more or less significant range.
In competition or cross-country flying, or more generally in performance flying, you have to constantly juggle your set goal, timing, and the aerological conditions encountered. Sometimes it is better to lose glide ratio in order to reach a generous updraft more quickly, or sometimes it is better to optimize your sink rate to gain height in thermals before transitioning to the next ridge. There are many different scenarios, which could be the subject of an entire course, but that is not the point here. For those who would like to explore the subject further, I recommend Baptiste LAMBERT's excellent video on Mc Cready. To simplify, you can remember that when flying into the wind,speed bar your glide ratio and ground speed. In accelerated transition, skilled pilots even learn to control the pitch movements of their wing by playing withspeed bar, pushing or releasing it at the right moments. When this is not possible, they use the rear risers because this generates less drag than using the brakes and allows them to maintain maximum performance. We will see later that the use of brakes should be avoided whenspeed bar activated.

V.- Precautions :

As we have seen previously, using thespeed bar that complicated, but its use inevitably affects flight. It is therefore essential to follow the instructions below carefully in order to use it safely:

–speed bar be correctly adjusted to ensure safe and optimal use. First and foremost, check that the adjustment length is not too short and will not activate the system without deliberate action by the pilot. The risk is that you will find yourself flying with a permanently accelerated wing. To be able to use it over the entire range of travel, the two pulleys on the risers must be in contact when your legs are stretched out. If this is not the case and there is still travel at the pulleys, don't worry, you can simply adjust it on your next flight. In general, the adjustment is not easily accessible in the air and you will need to spend some time on the hang glider to rough out the adjustment and refine it after a few flights to measure the adjustments to be made in real conditions (lengthen/shorten/symmetrize). It is important to use the risers of the wing in question to make the adjustment, and not the pulley system that may be present on the gantry straps, as it may be different (dimensions). In "performance" use, this adjustment is particularly important as it will allow you to adjust each flight regime according to the bar used, in relation to the polar curve of the wing in question.

– In the event of a stall, it is important to releasespeed bar immediatelyspeed bar not to amplify the effects. The same collapse (type and amplitude) will be more violent and difficult to manage ifspeed bar held down. Furthermore, reducing the angle of incidence during acceleration makes the wing more fragile and sensitive to collapse. You must therefore be particularly vigilant when flying close to the ground and terrain. When using trims, it will be very difficult or even impossible to neutralize them quickly in the event of a collapse, and you will therefore need to manage the situation more carefully.

– When usingspeed bar, it is essential not to touch the brakes, as this could cause a collapse! This may seem counterintuitive, but it is true. Without going into too much detail, applying the brakes will generate negative pressure towards the trailing edge, which will then cause the center of thrust to shift backwards. To realign this new center of thrust with the pilot's center of gravity (pendulum system), the wing will have to move forward and dive, creating the risk of an accelerated front collapse! This explains why adjusting the brake length is so important. If they are set too short, the trailing edge may be deformed when using thespeed bar leading to an accelerated front collapse without the pilot even having to apply the brakes.
And if you feel the need to brake, why did you accelerate in the first place? Well, to hold the wing steady, of course, if conditions are a little turbulent. So what can you do if you're not allowed to touch the brakes? You can hold the wing using the rear risers, which are often equipped with small handles (at least on recent wings). By pulling on these, you can hold the wing without risking a collapse. To steer the wing when accelerated (without using the brakes), it is recommended to use the harness the rear risers. For more experienced pilots, it is also possible to prevent collapses by adjustingspeed bar control pitch.

Conclusion:

speed bar should not be viewedspeed bar something frightening and complicated. It is a relatively simple tool to use, which deserves a little time to learn how to use it so that you can use it with confidence when needed. You need to take the time to install and adjust it correctly: its effectiveness will depend on this when needed (a bit like a reserve parachute...).

Now you've read enough!
Go fly and don't hesitate to test your speed bar make it your best ally!