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The Silex compliments Swing's successful paraglider product line
as they continue to expand their growth potential with an entry
into the powered paragliding market. |
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However, according to Manfred Kistler, the disigner at Swing, the Silex is a completely different wing than the Arcus UL. Swing has optimized the Silex for motoring by providing it with a higher trim speed and a faster roll rate for improved maneuverability. The result is a fast wing that has quick and responsive handling, which makes it a fun flying wing for the seasoned pilot. The wing is a natural compliment to their machine. THE COMPANY AND THEIR MACHINE Partners Markus Muller and Meikel Werner founded FB in 1989. Their single-place powerplant uses an enhanced version of the popular German Solo 210 engine. By adding an expansion chamber (also known as a tuned exhaust) to the engine, they have increased the available power by 50% (from 8 kW/10.7 hp to 12 kW/16.1 hp). To maintain engine life and compensate for the additional heating added by the power boost, FB has their own casting to produce an oversize cylinder head for additional cooling. With both an exhaust silencer and an intake silencer, their single-place machine is among the quietest PPG powerplants available. Efficient thrust is produced by their utilization of a carbon-fiber propeller that is light, strong, powerful and enhances the overall appearance of their product. This year they have released a tandem machine known as "The Monster", which uses a Hirth engine and appears to be the most powerful tandem machine I have flown. |
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CANOPY British Carrington Nylon cloth is used throughout the wing with type 1097 used for the top and bottom surfaces, while type 1099 is used for the ribs because of its greater resistance to diagonal stretching. The Silex uses V-ribs (diagonal ribs) to control the airfoil shape internally, thereby reducing the drag with fewer exterior lines. There is also a reinforcing strip of cloth running between each cell along the D-row, which strengthens and controls the wing shape in the aft chord area. The vertical ribs are reinforced with Mylar (polyester sheet) for stiffness to keep the air inlets open and provide good inflation characteristics. The stock colors are red, blue or yellow. Other colors are available by special order. Running the full span of the leading edge is a series of alternating black and white stripes which gives the impression of a piano keyboard. This layout is very distinctive and suggestive of an aerobatic color scheme. The standard Swing center cell marker, a small black circle, is inconspicuously placed at the trailing edge though the center of the wing, distinguished by being the only chord line with two lines attached at each row. LINES The lines have two cascade points converging to three lower A, B and C-lines and two lower D-lines. The stabilizer line is attached to the B-riser. Two different materials are used for the lines. The lower and middle are Cousin Technora (aramid), while the upper and brake lines are Edelrid Dyneema (polyethylene known as Spectra in the U.S.). As is standard in the industry, the lines vary in diameter for drag and cost savings. The lower lines are of two different diameters. Thicker diameter 2.2-mm lines are used where the loading is highest, along the leading edge (the A and B rows), and thinner 1.7-mm lines are used for the C and D rows. The middle lines are 1.2 mm while the upper lines are 1.0 mm. RISERS The Silex has a four-riser configuration with both a speed system and trimmers. The accelerator has a 3:1 pulley ratio with 9 cm (3.5 inches) of pulley line travel, moving the A-riser 3cm (1 inch) and the B-riser half as far. The trimmers allow only lengthening of the rear risers with no shortening possible. There are no split A-risers but the short riser length (43 cm/ 17 inches) allows the lines to be accessible in flight for performing big ears, even when flying with high attachment points above the pilot's shoulders. The rear risers have two pulleys available for the brake lines, with the lower one primarily intended to restrain the toggles from contacting the propeller. Routing the brake line through the lower pulley may be useful for pilots with short arms, particularly if motoring with a high suspension attachment point, but I found it to be awkward and uncomfortable. Since I fly with my brake lines shorter than most pilots do, I also found use of the lower pulley unnecessary with regards to propeller contact. If you choose to not use the lower pulley for routing the brake lines, be sure to conduct a thorough ground check before flying with this configuration since getting your toggle caught in the propeller will surely result in a spin to impact. |
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The accelerator, often referred to as a speed system, is common on paragliders, but not popular for use when motoring. I suspect that this is because the motor harnesses have historically not been available with the pulleys required for accelerator use, and that training in their use has typically not been provided to the motor community. The system is activated and deactivated by the foot stirrup, so the action is nearly instantaneous if the pilot's feet are resting on the stirrup, as is usually the case. An accelerator affects both riser sets equally and simultaneously, so the changes are always symmetrical and no turning tendency is introduced. A speed system is simpler for the manufacturers to get gliders to pass the certification tests because a glider with trimmers requires twice as many tests since each test must be performed at each extreme setting. The owner's manual states that when flying from an area of lifting air into an area of sinking air (as when exiting a thermal), "it is essential to take your foot off the speed bar in order to prevent a possible collapse. If a leading edge collapse occurs while the accelerator is engaged, it should be "released immediately". REAR RISER TRIM The rear riser trimmers on the Silex are configured to only allow the wing to speed up from what is termed the neutral trim position. Neutral trim is the position the risers would have if the trimmers weren't present, that is, all of the risers are of equal length. Some paragliders with trimmers also allow shortening the rear risers from the neutral position. An advantage of trimmers over an accelerator for the motoring application is to compensate for right turning during climb caused by propeller torque. With the Silex trim system, there is not only adequate trimmer travel to fly straight during climb, but there is additional trim available to make a climbing left turn without use of the toggles. This is accomplished by fully lengthening the right riser for maximum speed while simultaneously fully shortening the left riser for minimum speed. A thoughtful feature of the trimmers is that each handle can be Velcroed to the rear riser so it doesn't flop around in your face. |
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The brake travel is appropriately long for the higher suspension position typically used for motoring. This also makes it forgiving for beginner pilots. The factory brake length setting activates the brakes after 12 cm (5 inches) of travel. When paragliding using the Silex, you may want to shorten the brakes, but note that the minimum brake length recommended by the factory is 7 cm (3 inches). IN-FLIGHT HANDLING The Silex has a rapid roll rate but with high roll dampening so the canopy rolls into and out of a turn very quickly. The brake line tension is light despite the somewhat high wing loading when flying with one of the two smallish sizes of this glider, particularly with the added weight when motoring. As a result, roll reversals can quickly get away from the inattentive pilot. The wing will pitch quickly, both fore and aft but the leading edge remains quite stable during surges. The quick response in these two axes and the high wing loading allow the Silex to generate steep spirals with an accompanying rapid descent rates so caution is advised. PERFORMANCE The Silex, as with other modern paraglider wings, is trimmed
to fly at the speed for maximum L/D (lift to drag ratio). This is equivalent to the maximum glide ratio in still air. According
to the owner's manual the minimum sink rate is achieved with
20 % to 30 % brake. No performance polar was published or measured,
but the published airspeeds are listed below. I was able to soar
the Silex equally well while sharing the air with another pilot
on a DHV 2-3 (intermediate-advanced) wing in combined thermal
and ridge lift conditions. |
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DESCENT TECHNIQUES There are four common descent techniques: big ears, big ears with speed bar, B-stall and spiral dive. Since the Silex also has trimmers, these can be used with big ears and/or the speed bar for two additional combinations. BIG EARS Big ears is a symmetrical wing area reduction technique used to increase descent rate by increasing wing loading. The Silex does not have split A-risers to facilitate this, however the risers are short enough to allow the pilot to reach above the quick links and up to the lines to perform "ears". The owner's manual recommends pulling two outer A-lines on each riser set until the wing tips fold in and under, yielding a sink rate of four m/s (800 ft/min). I suggest pilots use a progressive approach when becoming familiar with a new wing by first inducing "ears" using only a single line per side before stepping up to two lines per side. The tips usually open on their own when the lines are released, but the owner's manual states that should this automatic reinflation fail, pump the brake on the side which remains closed. It should be obvious that if both sides were to "stick", then both brakes should be pumped simultaneously if needed. Also, "ears" should never be combined with a spiral dive due to the potential for structural failure. BIG EARS WITH ACCESSORIES While ears do not provide an increase in forward speed, it can be combined with use of the speed bar and/or trimmers to do so. The owner's manual indicates that this combined action can increase the descent rate of the Silex to six m/s (1,200 ft/min). I had occasion to utilize this mode after launching in winds that were locally increased by the presence of a venturi (a narrow gully between two hilltops). I was concerned about getting blown back (getting sucked into the venturi), so to remain low in the slowest portion of the wind gradient I used big ears. Also, to penetrate upwind and get out in front of the band of ridge lift, I trimmed full fast and applied full speed bar. The combination proved effective for not only getting me down and out in front, but it also stopped the small asymmetric collapses I was experiencing in the turbulence at the mouth of the venturi. The Silex vividly demonstrated its stability in this descent configuration and it felt secure in this maximum-speed dive. B-STALL B-Stall is a paraglider rapid descent technique that is popular because of the canopy's effective yet benign behavior. A symmetrically executed B-stall can provide a smooth and steady descent rate of up to 10 m/s (2,000 ft/min) with the Silex according to the owner's manual. But it also cautions that a front horseshoe of the canopy can occur if the B-risers are pulled down excessively. It further cautions that the risers should be released evenly for recovery. And, it warns that if the risers are released too slowly, you may enter a parachutal stall. If this occurs and does not immediately correct itself, the manual advises to press the A-risers forward as is recommended in the section below titled "Parachutal Stall". I performed only one B-stall with the Silex but found it to be easy to execute, effective for descending, and it behaved predictably throughout the maneuver (initiation, descent and recovery). |
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COLLAPSE PREVENTION AND RECOVERY Consistent with the two principles of "active flying" for resisting turbulence-induced collapse, the owner's manual recommends flying with about 20% brakes and responsively adjusting the brakes to keep the canopy centered overhead. Flying with brakes on maintains a higher angle of attack than flying brakes off while also dampening canopy movement. According to Swing, the Silex would probably receive a DHV 2 (intermediate) rating without the accelerator and a DHV 2-3 (intermediate-advanced) rating with full accelerator and trimmed full fast. This is accentuated by the small wing size. So, in addition to the light handling, the collapse recovery characteristics which would be the source of these certification ratings reinforce that the Silex is especially inappropriate for the beginner-level pilot for flight in turbulent conditions when a collapse is most likely. ASYMMETRIC COLLAPSES The owner's manual states that "you must not attempt to inflate the canopy by "pumping" the brake until the glider is stable and you are flying straight and on the correct course." It further states that if an asymmetric collapse does occur, use the opposite brake to stabilize and straighten the canopy, and notes to "brake too little rather than too much!" The manual warns that the Silex may require 180 degrees - 360 degrees of rotation for recovery from an asymmetric collapse. I had the opportunity to perform only a single 50% asymmetric collapse on the Silex and noticed that it required nearly 180 degrees to recover without pilot input and that the rotation occurred very quickly and was associated with a rapid loss of altitude. FRONT TUCKS A front tuck, also known as a leading edge collapse, can occur when sinking air is entered abruptly, as when exiting a thermal. Flying slower than trim speed and timely braking to dampen dives will reduce the probability of frontal collapses. The Silex recovered promptly without the need for pilot input from the full frontal I performed. A firm and rapid pump of both brakes can accelerate the recovery. The owner's manual suggests reducing the throttle to aid recovery. I performed my full frontal collapse at idle to minimize the influence of thrust. PARACHUTAL STALL A parachutal stall, also known as a deep stall or as a constant stall, is when a paraglider wing looses enough airspeed that the air simultaneously flows around the trailing edge as well as around the leading edge of the wing. When this happens, it behaves like a parachute, producing only drag. This is caused by a loss of airspeed due to excessive braking. The owner's manual states that "if your glider engages into a continuous parachutal descent, give the A-risers a short downward pull until the canopy resumes its forward flight". In searching for deep stall using the brakes while ridge soaring, the canopy exhibited a significant increase in sink rate but maintained adequate airspeed for control. Upon release of the toggles, the wing resumed normal flight with no tendency to enter constant stall. This reinforces the industry standard that modern gliders cannot enter a parachutal stall simply by using the brakes. Pilots must recognize, however, that any paraglider can enter deep stall during collapse recovery such as a B-stall, particularly when it has a light wing loading. Also transient turbulence may be able to induce constant stall with brakes alone, especially if the glider has trimmers that are capable of and set an airspeed slower than "neutral". MAINTENANCE AND INSPECTION A soft sponge and clear water or warm water and a mild soap are recommended for cleaning the canopy. The owner's manual cautions against the use of chemicals, scrubbing or hot water, which can weaken the fabric and dissolve the surface finish. For German certification the wing requires a professional inspection ever two years. OTHER FLIGHT MODES Towing The Silex is not specifically certified for towing, however, there is no caution against it either. According to Swing, the manufacturer, there is no problem with tow launching the Silex. I did not have the opportunity to tow launch it, but Eric Dufour of Paratour in Quebec Canada, the North American FB importer/distributor has extensive experience towing the Silex and recommends it for this launch method. MOTOR FLIGHT The Silex was designed for auxiliary power and is well suited for this flight mode. The only adverse factor, which I have noticed, is related to its small size. Some pilots when flying at a high wing loading, as with a wheeled undercarriage (commonly referred to as a trike), have found that this high speed wing requires a higher throttle setting to maintain altitude than the larger wings which they usually use. As a result, I think the new large size Silex will be a welcome addition to accommodate big pilots and those with heavy machines. For motoring, I like the rubber O-rings used on the quick links as line retainers on the Silex and other wings because the open link allows me to increase the success rate of my forward inflations. By inserting the tip of each index finger into the A-riser quick link, I use it as a handle to complete the inflation. When I perform a forward with a motor, I apply a secondary application of riser tension by pulling down firmly but gently with my index fingers to bring the canopy fully overhead. COMPATIBILITY WITH OTHER THAN FB MOTOR UNITS The Silex paraglider wing is recommended by FB for use with any PPG motor unit, which uses two attachment points and is within the recommended weight range. SUMMARY The Silex is the first successful paraglider designed for the motor market. The Silex was preceded by the first PPG-specific wing, the Reflex, which proved to be fast and stable but had heavy handling, was not a good soaring performer, and was difficult to inflate in light winds. By contrast, the Silex combines the best features of a motoring wing with those of a soaring wing. It excels in handling, speed and stability. However, the Silex compromises the flat turning efficiency of a soaring wing, and its collapse recovery characteristics make it less than user-friendly for the beginner pilot if it collapses. The trimmers and short risers make it well suited for the motoring application, and its light and responsive maneuverability make it very fun to fly. I am personally looking forward to the release of the large size Silex. If it retains the handling and of the smaller sizes while retaining the top speed, the increased wing area should reduce its power requirement for motoring while improving its sink rate performance as a soaring wing.
About the author: Alan Chuculate is an EAA UFI and began flying ppgs in 1993. He has been a USHGA paraglider pilot and instructor since 1990 and has been a hang glider pilot since 1974. He has been a hang gliding instructor since 1977 and is a USHGA Tandem Instructor for both hang gliding and paragliding. He is authorized by the USHGA to train and certify both paragliding and hang gliding instructors. He first flew a powered ultralight in 1980 and he has trained pilots to fly the Mosquito powered hang gliding harness. He resides in San Diego CA and has trained ppg pilots on four continents. If you have questions or comments regarding this article you're welcome to contact him directly by email or telephoning at <g_achucu@qualcomm.com> or 858-292-1552. |
