HGFA Skysailor Magazine

SKY SAILOR 29 March | April 2019 number of lines and risers used in order to optimise performance – so the latest gliders are unlikely to use a trim system. Some entry level gliders, such as the Advance Alpha 6, have an optional ‘power risers’ configuration. The good-natured handling and stability of the wing makes it suitable for both powered and unpowered flight – therefore a hybrid riser system that locks out the use of the trimmer system while in free-flight mode is used. Paraglider tandem wings – due to the pilot and passenger configuration under a tandem paraglider wing, the pilot cannot effectively use a speedbar system (the passenger is in the way), so a trim system is fitted to most tandem paragliders. Here is a diagram of the riser system on an Ozone Magnum3 tandem wing: Not all trim systems are the same! Back in 2011, Adrian Thomas said this in the paragliding forum: “What the trimmers actually do depends on the riser set. Some trimmers do exactly the same as the speedbar. Some trimmers do different things – changing the camber or the wing twist, for example. If the trimmers do the same as the speedbar, then I tend to just set them to some useful average for the day – faster for strong conditions, slower for weak conditions. The idea is that for glide, this is the same as going on a bit more bar. In climb, if the thermals are strong then they are also generally rough, so you need to have a good speed range between full brake and hands off, partly to allow you to counter surges, but mainly to allow you to speed through the ‘sinky’ bits of the thermal by going hands up – so setting the trimmers a bit fast gives you more dynamic range on the brakes which helps in strong and rough climbs. On the other hand, if the climbs are weak then they are generally also smooth, so I set the trimmers slow because most gliders get a slightly better minimum sink rate if you slow them down by using the trimmers to change angle of attack rather than using the brakes to slow them down. Having used the trimmers to slow the wing right down, you have to thermal with very little brake – because you have trimmed the wing close to stall/ spin – and obviously this only works if you can rely on the climb being smooth enough to allow you to climb comfortably without touching the brakes. If the trimmers change camber, and especially if they change twist at the same time (slowing the middle more than the tips), then they improve the maximum lift coefficient and improve the spin resistance, without any real downsides. With trimmers like that, I just jam them on full for every climb, and release them to neutral for speed. Usually, trimmers like that are slow-only. Sometimes they also allow you to add reflex at higher speeds. In that case they are intended to be released for high speed glide in rough air, because reflex sacrifices glide for stability. I generally leave that sort of trimmer on neutral because I am chicken, and don’t think I have enough practice in flying full speed with reflex trimmers fully released, finding where the stability limit is, and finding out how well the wing recovers in that trim condition when it does go. If I had the chance, I would practice that and make a decision about where to put that sort of trimmer for fast flight, having gained the relevant experience on that particular wing.” What can go wrong with trimmers? Trimmers add complexity to the riser system and also add parts that can fail. Asymmetric trim settings (one trim full open, other trim full closed): Although some paramotor pilots might use asymmetric trim settings to counteract torque from the motor, flying a paraglider wing with asymmetric trim settings would be annoying at best and dangerous at worst. Checking trimmer settings has to be added to the pre-take off check. Trimmers wear out and/or slip: Trimmers have been known to slip due to the riser webbing wearing, or the jaws of the clamp in the buckle wearing out. Worn out trimmer parts: Some risers are designed so that the trimmer webbing can be replaced as well as the trimmer clamp and buckle – but some risers are not, requiring the whole riser system to be replaced if the trimmer components wear out. What else can go wrong? As trimmer systems can differ (particularly in PPG), it is vital to read the owner’s manual before flying a wing with trimmers fitted. There are some configurations that are dangerous, e.g. on some PPG wings the application of speedbar and fully closed trimmers will lead to a large collapse. Adrian Thomas suggests (for trimmers on a paraglider wing): “You need to know what your trimmers do, and it is best to find out while ground-handling. Jam them on full slow – does the wing hang back on launch, or fall back to the ground really easily? If so, you may have an issue with deep-stall in thermals. Lots of higher performance wings do. On the other hand, do your trimmers make the wing less spin prone when ground-handling when they are jammed on full? Also, when they are fully released how much easier is it to pull a frontal? If they add reflex, when you release them, then sharply pull and release the A-risers, does the wing recover to normal flight even though the lines go slack?” Summary ➲ A collapse with trimmers open will probably delay recovery. ➲ Trimmers may be encountered by a paraglider pilot moving from entry level wings to speed- wings, freestyle wings, PPG/hybrid wings and tandem wings. ➲ Not all Trimmer systems are the same – you need to be fully aware of the use and limitations of the trimmer system you intend to fly with. Check the owner’s manual and ground handle the wing with different trimmer settings. ➲ Trimmers that are misconfigured or worn out can also present problems to the paraglider pilot. References: [www.bhpa.co.uk/documents/safety/formal_ investigations/index.php?doc=2016_03_22_ ppg-selsey.pdf] [www.par agliding forum.com/viewtopic . php?t=36775]