Teth•er (teth' er) n. 1. A rope or chain for holding an animal (balloon) in place, allowing it a short radius in which to move about. 2. To fasten or restrict.
Given the above definition of tethering, one wonders why one would ever attempt such with a balloon. Indeed there are those pilots who when asked about tethers will offer the sage advise, "don't do them." Yet we all know how immensely popular balloon glows (which are nothing more than night tethers) have become. And there is the issue of commercial tethers where the balloon is used as nothing more than an attention grabbing billboard. For many, there is no choice when it comes to tethering; for them the question becomes not whether they should be done, rather how to do them safely?
Unfortunately, like so many things in ballooning, expertise comes only with practice and experience. Fortunately, whether a novice or veteran balloon pilot, you need only look to your flight manual for guidance on how and when it is best to tether your system. Beyond those instructions only common sense and expertise will save you.
For this report Balloon Life did just that. We have examined the flight manuals for the major manufacturers to compile the following recommendations for tethering. Where specific differences between manufacturers were found, these cases are so noted.
Site Selection
The same general rules apply here that would apply to selecting a suitable launch site. A wide, open area, free of obstructions and downwind hazards works best. However, because the balloon will remain on site, and given that wind directions can change, attention must be given not only to downwind obstructions, but also any obstruction around the perimeter of the intended tether or "display area."
Cameron goes a step further in their flight manual. They recommend you:
...leave space downwind so that an equipment or planning failure will leave
you space to recover control without catastrophic consequences. Never tether upwind
of powerlines closer to the lines than the separation recommended for inflation (100 feet
for each mile per hour of wind speed).
Weather
Again some of the same common sense judgment used in making the "go-no go" decision for flight should be applied to tethering. Yes it is possible to tether in more wind than you might normally fly in, but does that mean it's safe too? When judging how much wind to tether in, consider not only your experience level, but also that of your crew. If the wind begins to gust unexpectedly, can you and the crew execute an immediate deflation safely?
Obviously one condition to avoid when considering a tether is the proximity of thunderstorms. The presence of thunderstorms anywhere in your area should immediately rule out any tether... the danger of being struck by a completely unseen, unexpected and unannounced gust front is too severe. Many pilots draw their own limitations at to the nearness of thunderstorms, but most that I know will not consider a ballooning operation if storms are within a 50 to 100 mile range.
Certainly the most critical element of weather to be considered for a tether is wind speed. Aerodynamic forces on the balloon increase roughly as the square of the wind speed. In other words higher wind speeds mean significantly higher forces acting on your balloon. For example, if the wind is blowing at 5 mph and then increases to 20 miles per hour, the wind speed has increased by the power of four. However, the forces exerted by the wind have increased 16 times.
Check your flight manual for any limitations your manufacturer may place on your system, for example:
Thunder & Colt
Cameron on the other hand does not establish a definite minimum, but does suggest the following:
Avoid more than 15 miles per hour of wind. Balloons are not designed to
withstand safely the forces which can develop in more than 15 miles per hour of wind.
To tether in wind stronger than 15 MPH risks equipment damage and serious or even
fatal personal injury.
The most effective and positive means of ensuring stability in windy tether
operations is the utilization of a Superpressure system with top tether and basket tether
attachments. Relatively safe tethering can be accomplished up to 15-18 mph. It is not
recommended to tether in winds in excess of 18 mph due to the extreme tether forces
which occur.
The Balloon Works does not address tethering in their flight manual but has prepared a publication entitled Tether Harness Instructions. Here they offer the following:
Wind and weather conditions for tether operations are critical. Such operations
must be done only under the strict supervision of a commercially licensed balloon pilot
with specific tether training and experience. No operations should be conducted in gusty
wind conditions, at a time of day when the thermal triggering temperature is likely to be
exceeded, when or where turbulence is likely, or when peak (not merely average)
surface winds are above 10 MPH.
Ropes
Everyone uses something different. There's nothing new in ballooning about that. However, another quick review of your flight manual might be in order. Lindstrand Balloons requires ropes with a strength of 4000 kg (approximately 8,800 pounds) as a minimum, Cameron says lines should be able to withstand a load of at least 7,500 pounds. Thunder & Colt requires ropes of 4-ton strength.
How long should the ropes be? I found no specifications from the manufacturers, but 125 feet seems an average length I've discovered from talking with other pilots. It is also a good idea to have someone splice "eyes" into the ends of your ropes because any time you tie a knot in a rope you weaken its strength at that point.
Rigging
How many tethers should you use, 1-2-3 or 4? Certainly the most common one- point tether occurs when you land and spontaneously decide to take the landowner or the neighborhood kids for a quick ride. This is most commonly achieved by utilizing the balloon's drop line, with or without a second line deployed for crew handling. When conducting this type of operation it is a good safety measure to be sure the downwind area is clear of obstructions and that you have enough fuel to fly on for another ten or twenty minutes in the event your line breaks.
The manufacturers unanimously recommend use of at least a 3-point tether. This system features two upwind lines spread anywhere from 60 to 120 degrees apart. The third line, downwind, is set opposite the other two lines so as to form a sort of equilateral triangle. When used, all three lines should be secured to a satisfactory anchor point (more about that in a moment). Do not allow crew members to "work" the downwind line. If necessary, a fourth line can be run from the basket to the crew which can be manned and used for positioning of the basket.
As to the attachment points, it is critical you refer to your flight manual or seek your manufacturer's advice. Generally the attachments will be at or near the burner frame, but make no assumptions. The last thing you want is catastrophic failure of the balloon system because you attached a line to a point unable to withstand the necessary stress.
For systems that carabiners additional equipment may be required. For example, both Thunder & Colt and Lindstrand require the use of tether rings. These rings allow the tether attachments to mate with the balloon system at the conjunction of the burner frame and the flying wires, but without putting undue side stresses on the carabiners and also allowing the attachments to move freely of one another. If not using tether rings, you should at least attach ropes to the side of the carabiner away from the carabiner gate.
For ground attachments or anchor points you can use large vehicles (such as a chase truck). Be wary of small pick-up trucks or trailers which can be moved and sometimes jerked aloft in strong winds. Other suitable points would include fence posts and large trees. Light standards are also suitable if you anchor around the concrete base.
Finally, care should be taken to assure that the ropes will not chafe against any rough surface such as a vehicle bumper, metal fence post, etc.
Top Tethers
Most certainly recommended for high-wind tethers and quite possibly the safest all around tether system for any conditions, top tethers are not as difficult as they may seem.
Three (or four) ropes are attached to the crown ring. Cameron warns:
This attachment must never be made with metallic clips directly to
the crown ring. The metal may scratch the aluminum crown ring
causing roughness that can damage the envelope's vertical load tapes.
For added safety, three additional lines can be deployed and attached to the
standard tether points recommended by your manufacturer. However these lines are
only for backup. It is the top tether lines which should control the balloon's movement.
In other words, the lines running to the burner frame should never all go taut at the
same time.
A variation of this system is recommended by The Balloon Works. The rope from the crown line taken directly to the basket attachment point. Then a second line is attached to run from the vertical rope to the ground anchor. Where the two ropes join, the ground line has a ring on it allowing it to slide up and down the vertical rope as the balloon rises and falls.
The Role of the Crew
While the manufacturer's flight manual do not directly address this issue, each makes it clear that the safety of persons and property on the ground is paramount in any tether operation. When planning a tether it is good to consider doubling your usual crew since in most cases it will fall to you, the pilot in command to provide adequate crowd control. This also allows for the positioning of one crew member at each tether line to assist in adjusting the line if necessary and warning passers-by of walking over or under the rope. Additional crew may be needed if tether rides are being given to assist you in the loading and unloading of passengers.
As a final thought, plan your crew with both muscle and knots in mind. If adjustment of a tether line becomes necessary after inflation it may require some muscle to keep a pull on the line until a crew member can untie and retie the line. And be certain they can tie a reasonable bowline or other substantial and sufficient knot.
Experience
Another subject not covered by any flight manual. As mentioned earlier, expertise in tethering in gained through experience. However, know your limitations and expand them carefully. If you are a novice pilot with 10 or 15 hours you probably would not register to fly at Albuquerque with 800+ other balloons in the sky. Likewise, don't make your first tether in 15 mph winds just because the book says the system can handle it. Tethers offer much greater risks of personal injury and property damage, so build your experience accordingly.
