It has been nearly a year since the RAST system was first presented to the public. During this time we have tested it in various gliders, a number of versions and in all conceivable conditions. We would like to summarise our findings and experiences from this:

Swing Rast

Position in the paraglider: between the B- and C- loops.

There are currently two versions of RAST available…

RAST 1.0 IN SERIES GLIDERS

RAST 1.0 is a vertical partition system with a permanent outlet opening and is already being successfully used in the series gliders
MITO MITO (LTF A) and TWIN RS (Tandem LTF A).

Swing Rast

RAST version 1.0 without valves (green)

RAST 1.0 is particularly suited for paraglider designs with a large area and/or where the control pressure is relevant. RAST 1.0 has performed very well in practice:

  • the paragliding schools which use the MITO confirm the advantages for launching: the middle of the canopy does not collapse and inflation behaviour is simpler. In addition, in the event of student errors or in strong winds, there is much less tendency to launch the pilot unintentionally than there is with conventional paraglider designs.
  • the glider no longer overshoots if there is no wind or a tailwind – although the pilot should adjust his launch technique a little to the RAST system. When inflating the glider with a tailwind, he should not race off impulsively, but start running gently only after some impetus. Thus the front section fills and quickly generates the lift needed. If too much force is used while the glider is inflating then the rear section fills too quickly and launch run-up is extended approx. 20%. The new inflation and launch technique developed by the DHV instructors team also recommends a measured run-up and subsequent calm on deploying the glider.
  • in the event of a front stall, no longer do we see the dreaded stable front rosette even in the most stringent test conditions. With the RAST system, this problem finally seems to be history.
  • the way in which RAST 1.0 behaves in asymmetric collapses depends on what caused them:

1. Collapses caused by strong turbulence without the pilot braking shortly beforehand: the glider collapses, but the depth is usually much less than would have been expected from the turbulence. The opening behaviour here is typical for its class.

2. Collapses where the pilot actively applies the brakes during the disturbance: the pilot is able to specifically prevent a collapse with high collapse area. By pulling the control lines, the internal pressure increases in the rear section, which can then virtually no longer collapse.

3. Simulated collapses: with the correct technique (slowly pull down and briefly hold down the riser) a collapse with high collapse area can also definitely be simulated with RAST 1.0. The reactions to collapses caused in this way can be dynamic. Nevertheless, in our experience, the collapses simulated in this way are unrealistic and are at best relevant for safety training.

NOW FOR RAST 2.0

RAST 2.0 has non-return valves as well as the vertical partition used in RAST 1.0.
This variation allows the air to flow rapidly into the rear section on launch as with RAST 1.0. The valves close almost completely if the internal pressure in the rear section increases, for example by braking or in turbulence. This makes the rear section even more resistant to deformations.

Swing Rast

RAST version 2.0 with valves (green)

Launch

To date there are no differences between RAST 1.0 and RAST 2.0 in relation to launch behaviour.

Collapses

The difference between RAST 2.0 and RAST 1.0 is most evident with asymmetric collapses: the more quickly and more vigorously one pulls, the less widespread the collapses become.
Its performance is as for RAST 1.0 for the other manoeuvres.

Feeling during flight

The wall stabilises canopy movements.
Advantages: the canopy feels more direct, the pilot has more control over steering, the canopy is once again much more stable in turbulence and manoeuvres are easier to control. Disadvantages: higher control pressure if the brakes are applied very quickly.

Improvement in performance

However, a further unexpected effect is evident, especially with the high performance prototype currently in use: gliders with RAST 2.0 have much better performance in turbulence than those without RAST. The more turbulent the conditions, the greater the advantage. However, in calm conditions there is no noticeable difference in performance which could be attributed to RAST.

Swing Rast

We can see in film footage that with RAST 2.0 the rear section has hardly any wave action in turbulence and the profile stays clean. Without RAST the profiles become deformed behind the B-hangpoint, try to adjust to the air movement and disrupt the airflow.

It is noticeable that RAST 2.0 prototypes are more likely to generate thrust in turbulence, while their counterparts without RAST have a tendency instead to brief surges and thus lose speed and momentum.

Something which was very apparent to us time and again with both RAST systems during the test flights is this: control through the steering lines is much more direct and more efficient than without RAST. There is hardly any time lag and the whole canopy responds immediately to control input. Where other gliders can hardly be controlled, for example where there are high climb rates, in strong turbulence or when flying at full throttle, the pilot has total control over the canopy. Clearly, the control pressure becomes somewhat stronger with rapid steering movements, but one notices clearly that the entire canopy follows immediately.

There will no doubt be much more discussion about performance and safety with RAST, however the control through the steering lines is definitely convincing.

We have noticed the following difficulties – if you could call them that:

  • Collapse simulation is much more difficult and unrealistic. This is a problem particularly in certification.
  • RAST calls for a measured launch technique when there is a tailwind.
  • When there is a full stall, initially the glider flies backwards noticeably, pitching feels somewhat more dynamic. RAST gliders thrash around much less in very large full stalls though.

Which gliders will have RAST next

Currently our test team is continuously flying RAST prototypes in the high performance class, in order to transfer to high performance gliders the refinements to the design of RAST 2.0 and additional experiences with improved performance through RAST 2.0.

In addition, RAST prototypes are at present flying in lightweight designs and as speedriders. Here, the stabilising effect in particular could prove to be an advantage for the target group.
Besides that, work is underway on the Acro glider TRINITY.

2017-06-11T23:01:43+00:00 August 7th, 2016|0 Comments

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