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Balloons, by their very nature, are at the mercy of the wind, and can’t maneuver out of the way of other objects except by (very slowly) climbing or descending. For this reason, mid-air collisions are fairly common whenever and wherever large numbers of balloons occupy small volumes of airspace (especially because this inability to take evasive action essentially restricts most balloons to uncontrolled airspace, which, in most places, is a very small layer immediately above the ground); fortunately, as balloons are very slow1 and very soft, balloon-balloon MACs are, generally, completely harmless (except in the extremely rare cases where a balloon rises into the basket of a balloon above it and gets its envelope ripped open).

Birds, on the other hand, are not necessarily at the mercy of the wind, are largely concentrated at the low altitudes where most balloons operate, are far more numerous than balloons (which is probably still the case even in the middle of a balloon gathering), and tend to come with a lot of inconsiderate pointy bits (beak, claws, probably other things too). Unlike with heavier-than-air aircraft, where a birdstrike usually just means a few dents, or, at worst, some unscheduled engine maintenance (although, as always, there are exceptions), a balloon could, if hit by a bird, easily suffer a catastrophic envelope rupture, followed quickly by (at best) a hard forced landing, or (at worst) rapid unscheduled lithobraking.2

How do balloons and birds avoid each other?


1: Not necessarily slow relative to the ground, but definitely slow relative to each other (since they’re being pushed by the same, or mostly the same, wind), which is what counts in a MAC.

2: Like the chapter in The Twenty-One Balloons where the protagonist’s houseballoon is punctured by a seagull, and he has to make a forced landing on a beach.

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  • $\begingroup$ What is the maximum horizontal speed of a balloon? The maximum (horizontal) relative speed is very low when compared to airplanes, I assume. $\endgroup$ – Rodrigo de Azevedo Mar 16 at 20:57
  • $\begingroup$ Hot air balloons have a huge amount of air in them. Would a bird-sized hole in one really be such a catastrophe? $\endgroup$ – David Richerby Mar 16 at 23:12
  • $\begingroup$ Planes go very fast. A bird could easily not see one coming or would be unable to react in time. A large, slow, round balloon on the other hand? A bird would have to be an idiot to fly into it. $\endgroup$ – forest Apr 29 at 8:26
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I've got over 100 hours in balloons, crewed for around 200 more flights and used to work at a hot air balloon MRO. I have never noticed or heard of a bird strike or seen any damage from one. I have had multiple mid-air collisions with other balloons. Have seen a balloon with bullet holes (from someone who thought it would pop) and many other tears and rips.

Hot air balloons are made of ripstop nylon and are not pressurized, they do not pop like latex balloons and can handle some pretty extensive damage and still fly. The ripstop fabric has strong reinforcement threads woven into it in a diamond pattern, this helps prevents rips/tear from propagating once the tear hits a reinforcement thread.

Balloons are made from many panels of ripstop (see figure below). These panels are sewn together using a French Fell seam (the same stitch that is used on the inside seam of jeans). If a rip does run the full length of the panel, it will almost always be stopped by the seam and will not transition to the next panel, just like cracks in riveted aircraft skin rarely jump to the next panel.

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Running on top of every vertical seam, and many of the horizontal seams is a thick nylon webbing called Load Tape. This load tape is what actually carries the majority of the structural loads of the balloon. Due to the strength of the load tape, it is very hard to tear, and provides strain control for the envelope, which would further prevent any rip from running past a seam with load tape.

A balloon will also not deflate or lose altitude from a hole any bird could put into it. When the burner runs, not only do you add the burner exhaust into envelope, but you also heat the air around the flame and cause it to flow into the envelope. A good way of visualizing this is to watch a balloon "standing up," although a fan is used to put air in the envelope, it is often less than half full when the pilot starts the burner to stand it up, the rest of the air is provided by the burners exhaust and the flow of hot air into the envelope. To put in to perspective how big a hole would have to be to affect a balloon, the parachute vent valve at the top of an average size (90,000 cubic feet) balloon is about 35 feet in diameter and can be pulled down several feet in flight in order to descend (and it doesn't cause you to fall out of the sky).

Of course there are limits to how large holes and tears can be before you take off, but there isn't much risk of a bird tearing a large enough hole to prevent continued safe flight and landing. And of course, a bird is more likely to land on the balloon than fly into one.

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The airspeed of a hot air balloon is always... zero. So it's completely up to the bird to do the avoiding. Which shouldn't be too difficult for the bird, on account of this humongous giant brightly coloured monster thing floating in its way. Ya gotta be a pretty dumb or drunk bird to run into one.

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    $\begingroup$ Nitpick: the airspeed is only zero in equilibrium. In reality, the wind gusts and changes direction. But, yeah, close to zero and what you said. $\endgroup$ – David Richerby Mar 16 at 23:09

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