Hot Air Ballooning
Today’s use of hot air balloons is generally similar to the use seagoing yachts. Quiet morning or afternoon flights drifting cross country to enjoy the view, competitive sporting events and record setting attempts are popular. A balloonist may fly alone in the basket, or carry several friends. Often several balloons meet to launch together without any competitive goals. Individual flights generally last from one to two or three hours and may go ten or twenty miles but often land very close to the take off point.
In normal fair weather the wind shifts some forty degrees in the first thousand feet of altitude. This enables the pilot to control the balloon’s course within that range. In some special terrain locations, drainage winds can create a “Box” where there is consistent three hundred and sixty degree direction variation within just a few hundred feet from the ground. By judicious use of these conditions the astute pilot can often land very close to the launch site or maneuver to a pole erected as a target. Pole grab prizes have often been for a new car or chase truck.
After flight, newcomers are often “Baptized” with a Champagne toast, purportedly provided to placate disgruntled landowners in memory of Prof. Charles’ first unmanned balloon which was destroyed by the local peasants upon landing.
Balloon Rallies may consist of just a few balloons for a one day outing or up to several hundred for a week long festival. Competitive events include distance within a time limit, spot landing and Hare and Hound races. The hare and hound is easy to organize and judge since it only requires one extra “Hare” balloon to launch first and fly a reasonable distance. The competitors attempt to land as close to the hare’s landing as possible. In crowded conditions a marker is often dropped to simulate the landing and the balloon flies on to a more open location.
Commercial ride operators are in business almost everywhere in the world. Some ride balloons carry ten or twenty passengers at once in gigantic partitioned baskets. The California and French wine country flights are popular tourist attractions. African Safari flights, at low altitude over vast game preserves, are perhaps the pinnacle of ride ballooning.
Hot air balloons vary considerably in design and materials. Light weight coated nylon and polyester fabrics are the most common. Cotton duck is very serviceable but has a comparatively poor weight to strength ratio. Some home built balloons have been made using plain polyethylene film and spun bonded polyethylene fabric such as Tyvec ®. Special shaped balloons, which are literally pneumatic sculptures, are especially popular at public events. They utilize special tailoring and many internal baffles and cords to attain the desired designs.
Normal sport balloons all have a silhouette similar to the fully inflated natural shape gas balloon. They can be assembled with many vertical gores of straight material, fewer gores made up of horizontal bands of fabric or gores sewn together of strips on the bias, like flat canopy parachutes. If straight gores are used, excess material can be tailored in to create a fluted pattern providing some flexibility. The bias pattern gores provide a natural flexibility. With the horizontal bands, the individual panels can be tailored to provide the bulbous gore which gives even greater flexibility. Because of the greatly reduced radius of curvature, the bulbous gore balloon has considerably decreased skin stress.
With the bias gore system the load tensors are generally sewn loosely into ducts formed into the vertical seams, much like the shroud lines are sewn into a parachute’s radial seams. With other balloons the load is carried in tapes sewn directly to the vertical seams. One load tape can have enough strength to carry the whole load with a safety factor without excessive weight penalty. The stress in the skin of the balloon is so low that normal handling will cause visible damage if the fabric is weakened by wear or exposure long before it would fail in normal flight. The importance of load tapes and adequate excess strength in them in balloon construction cannot be over emphasized. Catastrophic failure in a properly designed balloon is an extremely remote possibility.
Landing a bag with some four tons of air in it at twenty miles per hour without wheels, steering gear or brakes presents some real problems. Prior to John Wise’s discovery of the rip panel deflation system in the mid 19th century, a landing dragging several miles before coming to a stop was not uncommon for a gas balloon. Balloons on extended flights seemed to be drawn into low pressure systems which often resulted in stormy landings. Fortunately there were no electrical transmission wires stretched across the countryside.
The rip panel in Ed Yost’s first hot air balloons was a simple large sleeve at the apex drawn into a bunch and tied off with a cord which could be cut remotely by an electrically actuated explosive squib cannon moments before touchdown. This has been called a “Pop Top”. His later models used a circular panel held in place by hook and pile adhesive closure (Velcro ®) that could be opened progressively for a gradually decelerating landing. That system is commonly used today but is more often replaced with Tracy Barnes’ “Parachute Top” venting and deflation panel.
The parachute top venting and deflation panel has several advantages over the original Velcro ® rip out panel. First, it has a reversible action and is even highly suitable for in-flight partial operation for buoyancy control where the Velcro ® top and the Pop Top are very final. The parachute top consists of a simple hole at the apex of the balloon, usually about one quarter of the balloon’s diameter, plugged with a parachute of slightly greater diameter. The parachute is positioned by radial “Centering cords” radiating from the parachute’s edge out a few feet to anchors located on the puffy gore centers. A venting cord leads from the juncture of the parachute’s shroud lines to the basket. Sometimes a mechanical advantage is gained by a pulley system. Pulling the cord draws the parachute down into the inside of the balloon letting hot air escape. Releasing the cord lets the parachute snap back into the closed position by the force of the hot air.
If the parachute is pulled far enough into the balloon it will collapse letting the balloon completely deflate rapidly. This is a great advantage in a high wind dragging landing where it might be difficult to maintain tension on the cord. Naturally, care must be taken not to over vent at altitude. Newer versions use separate retracting cords to positively close the opening, redundant cinch cords to bunch the parachute for hands off deflation and elastic centering cords to provide automatic rapid setting and resetting of the parachute.
Hot air balloon burners are now exclusively liquid propane fed vaporizing burners almost identical to Bacon’s “Roarer”. The vaporizing coils are generally made of stainless or exotic steel alloys, but plain copper tubing has been used with good results. Naturally the copper tubing is much cheaper and can be fabricated easier. It is also a better conductor of heat. A secondary system without vaporization and slower air mixing can provide much quieter operation and give redundancy. Many designers call for multiple duplicate burners and fuel supply set ups for added safety. There has been a history of leaking seals on control valves and occasionally contaminated fuel.
The passenger car varies as much in design as the balloon itself. The FAR’s allow for the use of a simple trapeze, some one man balloon just have a chair or seat attached to the burner system along with a fuel tank, but most have a traditional wicker basket. For easy transportation, collapsible tubular frames with stout fabric covers can meet minimum requirements. Originally, wicker baskets had Manila rope woven into the basket for suspension, but because of the potential for rot, these have been replaced with synthetic or steel cables. The heavy wickerwork frame, using rattan up to an inch in diameter has also been replaced with metal or plastic framing.
Wicker construction has the advantage over metal skeletons and hard fiber glass shells of non-resilient energy absorption on impact. It is also favored for its nostalgic artistic appearance. Any basket can have closed cell foam padding on the inside for passenger safety and comfort.
Metallic components present hazards in the event of electrical power line contact. Wickerwork, by itself, provides little protection to the passengers or fuel tanks from such contact.
by Don Piccard
©2005