Buying a bungee; Bungee Rubber; Parachute; Line; Joining it; Pegs & Poles; Storage; Laying it out; Winding it up; Launching; Weaving; Tips & Tricks; Repairs; Flying Wings; Launching into Thermals
There are a number of different ways of launching gliders from the field up to a height which is sometimes referred to as "thermal territory".
This article provides an overview of these, plus details and hints for the purchase, use and care of bungees.
Bungees (or Hi-starts as they are known in the U.S.) consist of a tent peg, rubber tubing, fishing line and a parachute. The chute is pulled back a number of metres, the ring on the top of it is slipped on to the tow hook which is on the bottom of the glider's fuselage (approximately 20 degrees ahead of centre of gravity) and the plane is launched forward about 30 degrees up, quickly rotating to about 60 degrees and upwards into the wild blue yonder.
As the plane gets close to above the point at which the rubber is secured to the ground, the drag of the parachute will cause it to fall off the tow hook and gently to earth. Bungees are suitable for launching LIGHT gliders, up to 2.5 metres, slightly more if the glider is particularly light and/or there is a reasonable breeze.
BUYING A BUNGEE
Bungees are available in hobby shops for around $100 (sometimes more, sometimes less). If your local dealer does not have one ask if he can get one in or check out the suppliers listed in the magazines. To ensure you get an appropriate bungee to suit your flying requirements, speak to fellow fliers and ask to try out your plane on their kit.
Approximately 30 metres of what is known as "surgical rubber" is required and it comes in different thicknesses. As a guide, 8mm tube with a 1.6mm wall is regarded as "medium" and suitable for models up to around 1.8 to 2.5 metres span which will range in weight from 700 to 1700 grams. The rubber used for the two metre Prelude Plus gliders used for training at VARMS in Wantirna (Victoria) every second Sunday is the medium and this provides several hundred launches in a year. 9.6mm diameter with a 2.4mm wall is on the heavy side and should cope with the heavier models that the medium bungee might just carry along with models which are stronger and/or bigger/heavier - up to a bit over 3 kg. Trying to pull a Ricochet up on a medium bungee will be a struggle unless the wind is strong, but the heavier bungee will sling it up fast and the fuselage and wing is more able to take this, unlike a Gentle Lady which would simply fold its wing because of the stress.
The chute ensures that when the line comes down it can be blown back towards you, meaning less distance to walk, little likelihood of tangling and making it easier to find the end of the line. It also assists the line to drop off the tow hook at the top of the launch. It may be supplied with the bungee kit or bought individually. Chutes are made of nylon and cord and have rings attached to each end. In theory it is possible to make one out of an old umbrella but for all the effort and frustration it is easier to buy one. Chose a colour which will show up easily on the field.
If you are putting the components together yourself, it is possible to use fishing line as light as 12 kilogram (25 pound) but, after a short time, you will find yourself spending more time repairing that you do flying. The 25 kilogram (50 pound) line will give you a better run and is very popular. The line used for training at my local club (VARMS) is actually 50 kilogram and this rarely breaks. Around 120 - 150 metres of line is the norm, any longer and you'd need a pretty big field to lay it out and allow for stretch!
One of the things that will weaken a line considerably is inappropriate knots. To join a broken line, use a "fisherman's knot". It actually consists of two simple knots on the lines and these are pulled together. An illustration appears at the bottom of this page.
JOINING IT ALL
Fishing "snaps" (they are the fisherman's equivalent to a safety pin) will enable you to easily dis/connect the line and the rubber. They can be supplied with or without swivels. To save weight and complexity I tend to cut off the swivels and don't have trouble with twisted line. Always have rings attached to the ends of the rubber as fishing line or snaps attached straight on to the rubber will cause it to be damaged and to fail. A snap can also be used to hold the lower chute ring to the fishing line.
PEGS AND POLES
If the field is flat and the grass forgiving, a simple 40mm tent peg will be sufficient to peg down the far end of the rubber. Belt the peg in (through a marker, as described in the hints section below) then place the ring at the end of the rubber over the peg before giving the peg its final couple of taps, to avoid damage to the rubber. If the environment is less forgiving, use a short (1 to 1.5 metre) metal pole with a couple of stays held by tent pegs to keep the rubber off the ground in the launch, so that there is less likelihood of damage to it.
The rubber tubing (or rubber bands - see below) will last a LOT longer if it is kept in a dry plastic container, such as a sealable bucket (eg a nappy bucket) or a plastic storage box with a lid and plenty of talcum powder. This is where the fishing snaps are handy as they allow the line to be easily clipped off the rubber.
LAYING OUT THE BUNGEE
When laying out your bungee, ALWAYS lay it out with the peg upwind as all launches need to be into the wind and the wind is always going to blow the chute back to you. Consider also the needs of the other fliers and how far apart bungees will need to be to avoid being crossed. Also, consider where everyone will be wanting to land, and don't set up in the middle of it. Ask the fliers present about the prevailing conditions and preferred placement. Sometimes, when a few bungees are out, we actually prefer that as more fliers come onto the field they share the bungees that are laid out rather than having to spend the afternoon undoing "bungee macrame" caused by too many lines.
Mark your measurements/paces on the side of your winding device so that you can drop your gear, pace out the required distance to allow for length of line plus stretch, plant your bungee and walk back to your launching place beside your gear at the flight line with your bungee appropriately stretched and ready to place on the peg near your gear. As a guide, the 30 metre rubber is stretched a further 60 to 80 metres (about 80 to 100 paces). The stronger the breeze, the less stretch is needed as the plane will "kite" up with less forward pull from the bungee. In fact if the nose is pointed up too far, your bungee may be stretched even further than it can cope with so you will need to be prepared to input some down elevator. Ask an experienced pilot to assist you to ensure you get the best out of your bungee without risking damage to it.
WINDING IT UP
You will usually be winding up from the parachute end and there are a variety of methods used. A simple winder consisting of two oval plywood "plates" held apart by three dowels inserted in a row, with the middle dowel sticking out one side and one of the outer dowels sticking out the other, enabling the line to be easily wound up. The distance between the two outer dowels needs to be about 200-250mm. Variations on this theme include placing plastic conduit over the handles so that they will rotate; having the outer dowels both short and a sliding bolt as the winding handle, set slightly inside the outer dowel, this taking up less room for storage and allowing "gearing" as the distance between the centre handle and the sliding bolt handle is less than the distance between the centre and the outer dowel.
This winder can be big enough to temporarily take your rubber as well or it can be made small enough to take the line only. You will need to take the rubber off the winder for storage in the talcum powder, as described above. If you have been clever enough to have snaps on the rings on both ends of the rubber and the fishing line then you can start winding from whichever end you happen to be standing.
Other methods of winding the line include a large 30cm hand reel or a reel attached to a battery drill. Another method is to use the type of winder used for garden hoses. In my opinion these are a but cumbersome and one would be tempted to leave the rubber on the spool rather than placing it in the talcum powder.
As mentioned, all launches are into the wind. Take care to launch forward, not sideways, and hold the plane far enough away from you so as to not wipe out its tailplane on your head!! ALWAYS loudly call "launching!" and WAIT for any reply before heading up. NEVER launch from downwind of a fellow flier (ie the flier is ahead of you) as a simple mistake may cause your plane to collide with him/her at high speed.
ALWAYS flick a control lever to ensure you have turned on your transmitter and receiver before letting go and try to be in the habit of watching out of the corner of your eye where the chute dropped.
MAXIMISING YOUR LAUNCH
I mentioned how the winch lads can flick (or "ping") their plane off the line to gain extra height. This is also possible with a bungee but to a far lesser extent. Practice with a slight dip just before you would expect the plane to come off the line followed by a little up - but be careful to give down again before the plane loses speed and stalls, otherwise your gains will be lost.
Also, gradually work on (safely) increasing the power of your throw so that the plane moves into the climb earlier, particularly on light days.
There are differing schools of thought on this, some pilots find that with some planes in some conditions it is possible to get greater height by "weaving" left and right up the line, thus keeping up the line tension whilst still gaining height. This is not something that should be experimented with until the pilot has had considerable experience. Also ensure that the conditions allow it, that you are well clear of others and that other pilots are aware of your intentions.
BUNGEE HINTS, TIPS & TRICKS
If you are supplying your own line, consider getting the fluorescent coloured line as it is easier to see in the grass. Also, if the line easily gets lost at your field, think of using fluorescent builders' line instead of fishing line in the 20 metres closest to the chute so it's easy to see.
If the rings supplied on the parachute are heavier than you are ever going to need, consider swapping them with sturdy keyrings as the lighter the chute the slower it will come down and the further it will drift back if the breeze is light.
PAINT your pegs brightly and insert them through an ice-cream container lid, a plastic bag or attach a rag to them, so that if the rubber comes off or you drop them in the grass they can be found by you rather than by the mower blade(!). NEVER use a screwdriver as a stake as there is a high risk of it coming out and causing injury.
If the budget will not yet stand the purchase of a bungee, consider the cheaper alternative of three 500 gram bags of number 64 rubber bands and loop two and a half bags of them together in threes. (For a very light glider you may get away with them being looped in twos.) Then add the keyrings and line (and possibly the coloured string) and, while waiting to save for a parachute (about A$25), use a piece of mum's brightest scarf to mark the end of the line.
The end of the bungee rubber can be looped and bound with string, with a drop of CA glue to hold it in place. Alternatively, a piece of dowel can be inserted in the rubber tube and, again, string can be bound over the rubber with a drop of glue. Drill a fine hole down the dowel and screw in a metal "eye", again using a drop of glue to add strength. Dowels, string and glue can also be used to repair broken tubing (keep some in your kit), but avoid tightly bound cotton as this will cut into the rubber. At each end of the rubber tube, attach a strong keyring, being careful not to nick the rubber in the process of putting it on.
LAUNCHING FLYING WINGS
Although designed for the slope, some people also try to launch these from the field, with varying degrees of success. Apart from the difficulties of trying to find the best place for the tow hook and their longitudinal sensitivity, they accelerate very quickly and the drag of the chute drags the line off the hook prematurely. Alternatively, by double hooking them, the drag is reduced and up they go - but then they won't come off the line!! (By double hooking, I mean hook the top ring on the line and then the bottom ring. This "folds" the chute and is a method often used by the winch boys.) The answer to this may be to double hook but to experiment with a bit of ribbon on or slightly below the lower ring of the chute.
WHEN TO LAUNCH
You will note from my article on catching thermals that when the breeze/wind strengthens and cools then the thermal has just passed. Better to launch when the breeze/wind is starting to die in the hope that the cause is that the wind you would normally have hitting your face is being sucked up by a thermal in front of you.
Finally, if you notice other pilots' parachutes are coming down very slowly - there is probably a thermal above - so launch into it!
OTHER LAUNCHING DEVICES
A winch consists of a 12 volt car battery driving a car starter motor which is attached to a drum. A length of heavy fishing line goes from the drum to a pulley or "turnaround" up the field, then back to the pilot standing beside the winch. The pilot holds down a foot pedal to operate the winch and put considerable tension on the line. From there the launch is similar to the bungee launch described above except that by "pulsing" the foot switch the pilot controls the rate at which the winch is wound in.
A brake is included in the device to ensure the drum doesn't free-wheel, as for it to do so would cause the line to tangle. Winches can provide an amazing amount of power and are generally used for your heavier, faster and more robust competition gliders (sometimes referred to as "plastic fantastics"). In competition, the plane is pulled up the line (with a little flap input to increase the rate of lift) and then pulled DOWNWARDS very rapidly before being flicked upwards and continuing up even further. A lightly built glider would be torn apart by this sort of treatment.
Next is the hand tow, which is occasionally the prescribed manner of launch in certain competitions. This could be a simple line pulled by one or two people. More likely, one end of the line will be attached to a peg near the pilot and the line then goes out to a pulley attached to a handle then back to the plane. The tow people run into the wind with the pulley, pulling the plane at twice that speed up the line.
Finally, there is the tow plane, being a reasonably powerful internal combustion engined machine with the tow-line attached to a point above the centre of gravity. These are used to launch large scale gliders, generally 3 to 4 metres plus in span.
This time the glider has a tow point at the front, with a servo controlling the release of the line. The controlling channel may share the undercarriage function, so that wheel-up is also tow-release.
The wings of the glider are held level, the slack in the line taken up and then the plane pulls the glider forward and into flight. The glider will leave the ground first and will be flown slightly higher than the tow plane so the line will not foul the tow plane's tail. At an appropriate height, the glider will drop the line and be sent off in search of lift and the tow plane returns to the strip.
Just as in real gliding, there will be a pre-determined arrangement in the event of something going wrong, such as the tow plane going right and the glider going left. The tow plane also has the ability to drop the line at its end in the case of an emergency and the line itself will usually have a ribbon attached to determine its position in the air and also to assist in seeing it come down if it is let go by both planes.
A cheap source of tow-line is 5mm packing tape.
This knot is the best to use to join broken fishing line as it won't slip and it won't squash the line and it won't cause the line to weaken.
NOTE HOWEVER that when you do the individual knots instead of winding the loop through once (at steps 1 & 3), wind it through 3 times. (Sorry I don't have a picture.)
Bungee kit, pegs, rubber line (on the reel) and chute.
Brian holds up the rubber and the winder for the fishing line. In this case a "star" post has been used upwind, to keep the rubber off the ground when launching.
Keep the bungee rubber in a sealed plastic box or bucket with some talcum powder, this will stop it from perishing.
Another picture of the launch - but the plane needs to be held high or the tail will catch the back of this lad's head! It happens, and I've done it!
Winches are NOT for beginners but are included here for completeness,
A winch made of a 12 volt car starter motor and using a 12 volt car battery. A brake is built in to stop the reel spinning which would lead to a tangled line.
The winch sits at the place of launching and the line goes out to a pulley and back to the glider.
Using a winch on a beginners' model would pull its wing off if not used carefully. Here we see a Ricochet, which is capable of taking this sort of punishment.
It is not essential that someone else launches for you but it can be helpful.