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As a scenario, let's say that a group of heroes is traveling in a hot air balloon as a proof-of-concept for bandit-proof travel. Some particularly well-armed bandits naturally have taken an issue with this, and are trying to shoot the balloon down with crossbows and/or longbows.

The heroes' hot air balloon is moving along at a pretty good clip, such that the bandits only have time for 1-2 good crossbow volleys, for a total of 8-10 bolts.

Assuming these conditions:

  • Could they shoot down a hot air balloon with crossbows or longbows?

  • How high must our heroes be to survive about 8-10 crossbow shots?

RonJohn
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ZaWarudo
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    Hi, and welcome to the Worldbuilding Stack Exchange forum! You're asking several questions here, which is normally not allowed on this site. However, you're new and they seem to be related to each other, so mum's the word. – In Hoc Signo May 31 '21 at 22:51
  • That said, how far away are the air balloons from the bandits? Are the bandits shooting straight up? If not, what is the approximate angle? Are they using incendiary bolts/arrows? – In Hoc Signo May 31 '21 at 22:53
  • If they were to fire at 75 degree or 60 degree would the velocity be enough? Let's make our characters job harder and the arrows or bolts should be incendieary too. They are approximately far away like the one is most high, or the one close up in this picture. https://i.pinimg.com/originals/fe/68/49/fe684991c1085da0c98e4afabee2d677.jpg – ZaWarudo May 31 '21 at 23:06
  • See also https://outdoortroop.com/what-happens-if-your-hot-air-balloon-gets-a-hole-in-it/ – sch Jun 01 '21 at 07:28
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    The answers already state that your balloon is pretty safe. and i agree with them. But, provided your ballon for some reason gets within firing range, while the ballon can tolerate punctures pretty well, it's passengers respond a lot less tolerant to such a treatment. – Burki Jun 01 '21 at 09:56
  • Looks like hot air baloons are pretty safe even against modern handheld firearms. Good to know. – fraxinus Jun 01 '21 at 11:02
  • It's reasonable to miss 8-10 arrows/bolts even from a moderate or relatively close range, especially with a moving target. – NotThatGuy Jun 01 '21 at 11:59
  • Even if they hit the balloon, so what? A slow puncture that deflates the balloon 2% faster? – PcMan Jun 01 '21 at 15:11
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    You should know that there are other fairly serious problems/threats involved with travel by balloon, especially in medieval times. Specifically, 1) bad weather is very dangerous, and 2) you have no real control over where you go, and 3) going too high is a dangerous problem and it can be very difficult to get back down again safely. – RBarryYoung Jun 01 '21 at 16:39
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    "How high must our heroes be to survive about 8-10 crossbow shots?" – 8-10 crossbow shots to the balloon, or to their bodies? – Tanner Swett Jun 01 '21 at 19:43
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    Nice question! You probably thought about this already, but just be aware that Bandits at some point will also use the new technology ;) – Lichtbringer Jun 02 '21 at 07:08
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    During WWI the British were irritated to discover that a hail of bullets had absolutely no effect on Zeppelins; the bullet holes were just too small to make a difference. Then they tried bullets coated in phosphorus which ignited the hydrogen lift gas, and that was the end of Zeppelins in warfare. – Paul Johnson Jun 02 '21 at 10:37
  • @PaulJohnson Even on hydrogen Zeppelins, incendiary was not very effective. It required a combination of explosive and incendiary. Besides, incendiary bullets on a "hot air balloon" as OP specs would be much less effective still. – PcMan Jun 03 '21 at 06:42
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    safe from arrows? Sure! Too bad some bandits are into falconry. . . – Aww_Geez Jun 03 '21 at 21:28

7 Answers7

74

They are safe.

A 1000lb medieval crossbow has an initial velocity of around 150 fps (~45.7m/s). Oddly increasing the poundage of the crossbow does not increase the velocity just the allowable weight of the projectile, the distance traveled by the bowstring and the speed the bow can flex act as limits.

I will use the the formula for firing straight up because it gives the maximum possible height and is pretty simple because stuff cancels out

$$ h_\text{max} = h_\text{initial} + \frac{V_0^2}{(2\times g)} $$

fired straight up with no air resistance, comes out to about 360 feet (110m).

A very low flying hot air balloon flies at over 500 feet (152m) -- legally they cannot fly this low today; during the civil war 500ft was considered flying low, 1000ft (~334 yards/ 305 meters) was more common.

so even if the balloon is flying low, you are more than a 100ft short, If it is flying at a reasonable height the bolt does not even make it half way. And that is firing straight up to get the maximum height, firing at an angle means it gets even less height.

As long as they are flying more than about 360 feet up they are perfectly safe from crossbows.

As a side note longbows actually preform a bit better, they have a slightly higher max velocity, crossbows lets you fire heavier projectiles at similar velocities not faster ones. Longbows can manage 177 fps (54m/s) or around 495 feet (165 yards, 151m) straight up.

So stay around 600 feet/200yards/183m/9chains or roughly a furlong and even the best archer on the planet can't touch them.

John
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  • Comments are not for extended discussion; this conversation has been moved to chat. – L.Dutch Jun 03 '21 at 03:02
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    According to this site, https://www.museumofflight.org/Exhibits/montgolfier-brothers-balloon, the first manned free flight had an elevation of 3000 feet. If that's accurate then John's numbers are realistic for a balloon prototype with 1700s tech. – Jetpack Jun 03 '21 at 03:37
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    While a bow can generate faster projectile speeds than a crossbow it is much more difficult to fire an arrow from a powerful bow straight up. Firing an arrow from a war bow requires a lot of muscles working together including much of your back. Being able to point straight upwards without ruining that form seems like it would be much more difficult than shooting one normally. On the other hand shooting a crossbow straight upwards is trivial – Kevin Jun 03 '21 at 21:04
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    The other good part about firing arrows/bolts straight up is that they come straight down too. Makes arrow reuse easier, but has a slight negative downside of landing with as much velocity as it left with. Not good for the archer. – Criggie Jun 04 '21 at 01:44
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Even if the balloon flies low enough that you can actually hit it with a crossbow or longbow (and it is surprisingly difficult to aim at a moving object above your head) you won't do much damage.

First of all at the top end of its trajectory the arrow or bolt won't have much penetrating power left.

And you will mostly be hitting the bottom and sides of the balloon envelope and holes there make hardly any difference to buoyancy.
Remember: hot air rises, so little would escape in downward/sideways direction anyway.
In fact: The envelope already has a wide opening at the bottom for the burner!

You best bet is to aim at the people manning the balloon and hope that they loose control of the burner when they duck for cover in the basket.

Tonny
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    Although, fire arrows/bolts might set the envelope material on fire which might have a significant effect on balloon envelope. Also, flammable liquids that make it to the balloon envelope might drip down to the burner causing flames to spread. – Arluin Jun 01 '21 at 15:15
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    @Arluin Yes, but fire arrows tend to also have a lot more air resistance than normal arrows so your likelihood of even reaching the target goes down with them. – Nosajimiki Jun 02 '21 at 20:57
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They are safe but for another reason than people have given

The balloon will be squishy and will flex went hit by an arrow. Think of poking a plastic bag.

If the arrow or quarrel pierces the bag it will get snagged and fill the hole it just created.

The balloons need to be fire retardant to avoid burning up from the fire keeping them aloft so even flaming arrows or bolts would likely be in effective since the flaming part would go out because (A) the oil or naphtha burns off and (B) the inside of the balloon is hot smoke so already has lower $O_2$ content

Counter strategies by groundlings might be to fire weighed hooked arrows. if enough can be snagged in the balloon, the added weight will force the balloon lower and slower. making it easier to hit.

EDL
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    If you replace the feathers with thin blades i think you could slice a decent cut open, no? – Hobbamok Jun 01 '21 at 08:27
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    I think hot air baloons are already designed to produce more hot air than necessary, and let air out through a hole in the top. The pilot can probably just reduce the hole size, unless it's a really serious, sustained assault. – user7868 Jun 01 '21 at 08:37
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    @Hobbamok it still wouldn't be a very large cut if limited to the size of the feathers. You'd need to start a rip. The fabric is already a little porous over a huge area as well as having a vent hole at the top, more so in early balloons than with modern fabric. – Chris H Jun 01 '21 at 09:19
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    In a medieval setting and given the balloon is a prototype, i doubt there are many safety precautions in place. Particularly, fire retardants on any cloth are a very long shot, i think. So apart from the height / weapon range problems, i think burning arrows are the only chance to get the balloon down. – Burki Jun 01 '21 at 09:52
  • I wonder what would happen if you added upturned hooks to your bolts/arrows so that upon penetrating it snags the fabric and rips at it? – Doktor J Jun 01 '21 at 14:00
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    @Burki Flaming arrows would probably be ideal - except for the fact that flaming arrows will not fly as far - the weight and added aerodynamic drag of whatever you have burning on the end of the arrow will reduce your range somewhat, particularly an issue when firing in an upward direction. (If you have a high point to stand on, such as a cliff, tower, or maybe even another balloon, you could get considerably more effective range.) – Darrel Hoffman Jun 01 '21 at 14:03
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    @hobbamok but... those blades would just get caught on your bow/send the arrow flying recklessly? Feathers are used for fletching because they can give/not interfere when being shot – TCooper Jun 01 '21 at 18:23
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    And while a particularly stupid bow-man might be willing to fire one arrow with razor-blades substituting for feathers, they wouldn't want to fire a second one after the blades sliced past their bow-hand on the first shot. – Penguino Jun 02 '21 at 01:33
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    Regarding the balloon's squishiness, I think, you might have forgotten to count with inertia: it may indeed behave squishy when you poke it with your finger. But when an arrow hits it at speed, causing an abrupt impact, the inertia of the stretched-out material, but even the air pressing against it (like wind filling out a sail), could represent enough inertia to hold the thing in place enough for the arrow to pierce it. Disclaimer: I'm not an archer though. – Levente Jun 02 '21 at 21:27
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    @Hobbamok The way to do what you're suggesting would just be to shoot a broad-head arrow, which was already very much a thing used for hunting. Putting the blade on the front of the arrow also makes it more likely to puncture its target. – Kevin Jun 03 '21 at 21:09
  • @TCooper wasn't the question about crossbows? – Hobbamok Jun 07 '21 at 09:57
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Of course they can. If it's very dry, anyway...

The archers don't wait for the balloon to arrive. As it appears on the horizon upwind of their chosen hunting ground, they strike! They shoot bolts at the dry grass of the opposite hillside. From powerful incendiaries, flames spread quickly, climbing the bone-dry hillside as the horrified passengers of the Bandit Proof Balloon's maiden voyage watch helplessly. The wind draws them ever forward to the fire, at first with indifference. As flames tower high into the air, cold air is sucked in beneath, creating a windscape of treacherous downdrafts that suck the balloon toward the worst part of the fire. No hot air balloon can remain aloft in a column of superheated air.

Bowing to inevitability, the captain makes an emergency release of air, setting down to pay the ransom rather than chance his fate to the flames.

Mike Serfas
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    This is probably the only way to do it. – Charles Jun 02 '21 at 20:22
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    This is the sort of tactic you only get to use a few times before you run out of suitable hillsides. Plus once an area is burned it becomes a safe passageway for subsequent flights because it can't be burned again – Kevin Jun 03 '21 at 21:15
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    He said a hot air balloon. If you want me to stop an army of hot air balloons then I need that army of crossbowmen prepared with razor kites and exploding sky lanterns to help even the odds. I make no promises... – Mike Serfas Jun 04 '21 at 21:24
5

Please note, this was done with "seems right" figures. There is actual maths performed elsewhere, including the base of my answer. I am intentionally leaving it here, without editing my "seems right" numbers, both for archival purposes and to not have 3-4 homogeneous answers.

First, the distance

So according to a random page from google a medieval style crossbow had a total range of 380-390 yards.

So shooting up will take some distance out of it, but the bolt is "relatively" light, so lets round it to a nice 350 yards.

Now, could it take down a balloon?

The answer is "that depends". In short you'll want to have it puncture/tear a hole/several holes that leak more hot air/floaty gas than can be replaced.

I should imagine the hole made by a standard crossbow bolt is rather small and the material should be rather durable, both as defence and necessity to prevent "minor wear and tear" type things from causing a critical failure on the balloon.

Your bolts could have a very sensitive mechanism that will cause it expand into some claw like fashion for maximum tear potential upon hitting the fabric/balloon. This will increase weight, and cost, of the bolt so we'll now round the range further down to 300 yards.

Can 8-10 bolts take down a balloon?

Ultimately, it's your story so if you say it can, it can.

However, bolts are rather slow to reload so you're better to have 8-10 people fire once rather than 1 person firing 8-10 times.

With the assumptions above, it definitely seems plausible, presuming they're in range.

TL;DR

8-10 people shooting a specialist bolt should be able to take down a balloon from within 300 yards with a solid degree of plausibility. Their effectiveness is increased the closer they are as it's likely they can punch through both sides of the balloon.

Addressing comments

Hot air balloons fly between 1000 and 3000 feet

According to google, 1000 feet is 333 yards, so that puts the lower bound of flying into the upper bound of "lucky shot".

If this is going to be a hard constant, it turns "plausible" to "highly unlikely".

You mentioned this is a prototype, so I'd wager they'd be rather hesitant to fly too high for fear of coming down hard. That would mean your bandits stand a chance if they stay just above the treetops or lowish over hills/plains.

Can a medieval person find wind currents?

Predictably, maybe not. But it won't take that experienced a pilot to quickly figure out that different heights tend to have winds that blow different directions and act accordingly. This method is used by birds so I'm sure a human can figure it out.

A skilled pilot may be able to predict these with more accuracy. Even if it's "mountains tend to make the balloon want to go direction" rather than a scientific reasoning.

Please note, no maths was actually performed so actual results may vary significantly. I just applied some common sense "fridge logic".

For actual maths, please see John's answer, the result is quoted below:

As long as they are flying more than about ~ 120yards up they are perfectly safe.

As a side note longbows actually preform a bit better, they have a slightly higher max velocity, crossbows lets you fire heavier projectiles at similar velocities not faster ones. Longbows can manage 177 fps or around ~165 yards straight up. So stay around 200 yards and even the best archer on the planet can't touch them.

Joshua
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  • So i looked it up and: Hot air balloons normally fly between 1,000 and 3,000 feet in the air. When balloons fly over populated areas, they legally have to be flying above 1,000 feet in the air. Because of the harsh conditions at higher altitudes, hot air balloons normally don’t surpass 3,000 feet. The highest a balloon has ever flown is 68,986 feet. So 300-350 yards make it around 1.000-1.050 feet. If it were to go around 1.500-2.000 feet than they would be safe, i suppose. – ZaWarudo May 31 '21 at 23:15
  • How would they maneuver it then becomes another question at such high. As long as i know: The pilot catches different airstreams at various heights as desired. Through the study of wind currents, a pilot can determine the overall direction of the flight. But in a medieval setting, can a pilot know wind currents at those highs? – ZaWarudo May 31 '21 at 23:24
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    Note that with mass-volley fire if the bolts can actually reach the balloon I would think there nearly as much chance of fatally wounding the crew. And hot-air balloons are very mass-sensitive so armor doesn't seem like a particularly feasible response when flying out of reach is so much easier. – SoronelHaetir May 31 '21 at 23:26
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    @ZaWarudo I have updated my answer with your follow-ups – Joshua May 31 '21 at 23:38
  • Thanks, i understand your points and will try to take different approaches at the situation. I know it will be easy way but i guess i will first make my bandits stay in flatlands to prove their points. When our characters try to reach upon a city, they will be in danger as castle archers might shoot them down. So they will force themselves to either go higher and abandon their fears, or will go down before coming to the cities. – ZaWarudo May 31 '21 at 23:47
  • @ZaWarudo that was a thought I had, that the landing spots and/or hills would be vulnerable points as the balloons are likely to be lower to the ground. Furthermore you could easily extend the range by having more powerful crossbows for taking down balloons. Either fixed ballistae or smaller "man portable" versions designed to shoot further but are too cumbersome to use for "general" use. – Joshua Jun 01 '21 at 00:05
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    Even if 300+ yards is the maximum range, the bandits have to actually hit the balloon. Some quick searching shows that the accurate range of a modern crossbow is ~50-80 yards, so for the bandits it would be significantly less. Out of two salvoes of 8-10 bolts, it's unclear if they'd even reliably get 1 hit on a hot air balloon at 300 yards altitude. – GrumpyYoungMan Jun 01 '21 at 00:14
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    I should imagine that accuracy is vs a human, not a balloon which is generally larger than a human [citation needed]. They just need to shoot up-ish and ahead-ish to lead the large balloon rather than pick off a 40cm wide person from a hundred paces. – Joshua Jun 01 '21 at 00:34
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    how lite the bolt is does not matter, the bolt is not going anywhere near its maximum horizontal distance in the vertical. It will be lucky to make 200 yards. – John Jun 01 '21 at 00:36
  • as i said, no maths was applied, just "distance is somewhat a function of force and mass" therefore the weight does matter somewhat, but gravity i likely the bigger player so i fudged the numbers a bit. – Joshua Jun 01 '21 at 00:38
  • @Joshua The accuracy is against deer, which is much wider than a human. And, again, that's with a modern crossbow with modern sights. The much cruder crossbows of untrained bandits don't even come close to that kind of range or accuracy. – GrumpyYoungMan Jun 01 '21 at 00:39
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    @josh it matters for horizontal difference, for maximum vertical the mass cancels out. maximum horizontal distance many times larger than maximum vertical distance. – John Jun 01 '21 at 01:09
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    If the max range is X, the maximum height is X/2. There is no way for a crossbow with range 390 yards to reach 300 yards when firing vertically. And the mass has no relevance at all in the calculation for range. – L.Dutch Jun 01 '21 at 04:30
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    Agree with above: As a matter of ballistics, maximum upward height is exactly half the normal horizontal distance. – Daniel R. Collins Jun 01 '21 at 13:08
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    A balloon big enough to carry "A party of heroes" could take dozens, possibly hundreds of punctures before the balloon operator notices. The whole operational principle of a hot air balloon even involves the operator periodically opening a large, multi-meter diameter hole at the top to vent hot air, and a few finger-sized holes aren't gonna do jack. – Dragongeek Jun 01 '21 at 15:14
  • the hole isn't closed. it relies on the hot air rising and the balloon being a mostly closed system so the hot air is contained while the cold is forced out through the bottom. Its a pressurised system. Any holes would mean that the pilot would need to burn more fuel to maintain altitude. – CaptainBumbleFudge Jun 01 '21 at 23:51
  • According to google, 1000 feet is 333 yards, do you really need to tell us that you had to use Google to divide 1000 by three? – JDługosz Jun 02 '21 at 19:56
  • @JDługosz: Freedom Unit conversion is ridiculous. I can totally believe that someone forgot how to convert feet to yards. – Mooing Duck Jun 03 '21 at 17:03
  • You've updated your answer to respond to many comments. Why not edit initial bad assumption "So shooting up will take some distance out of it... so lets round it to a nice 350 yards" to correct it based on the information from comments and other answers that the maximum vertical range is more like 360 feet (120 yards)? – Gregor Thomas Jun 03 '21 at 18:56
  • @Dragongeek -- indeed, this AV.SE answer confirms that redneck AA fire has hit balloons before with very little ill effect on their airworthiness – Shalvenay Jun 04 '21 at 00:31
  • @MooingDuck I encountered a lab tech at a medical testing place that didn't know how to convert milliliters to liters. – JDługosz Jun 04 '21 at 14:25
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If you compare a medieval archer to a real balloon, the balloon will win. But real balloons were made in the 1780s and your balloon is made in the medieval era.

Your balloon was was created by an inventor who does not have the scientific background, technology, supply chain, or infrastructure that the Montgolfier brothers did. The fact that it can lift a person off the ground at all is an astonishing futuristic marvel centuries ahead of its time. If the balloon can fly so high and so reliably that there is drama about whether archers will threaten its flight, then that is the sort of epic achievement that is worthy of a story.

All in all, a medieval balloon that can carry a person is in the realm of suspension of disbelief. If you want a balloon that can barely lift, or that sinks at the least convenient time, that's at least as believable as a balloon that keeps people successfully out of range.

Jetpack
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Archers can't reach you once you're aloft, but you're far from bandit-proof. Balloons are extremely slow. Average balloon speed is under 10 mph for safe operation (during liftoff and landing you want it as close to zero speed as possible). A horse can trot at 8-12 mph, and gallop close to 30 mph. Your balloon is also quite large and has nowhere to hide while aloft. That means that your bandits won't have much trouble following you (modern balloons typically have a "chase crew" that does exactly this, to give the passengers a ride back to the starting point). You have to land eventually, and the bandits will be right there waiting to shoot you down the moment you get low enough.

The only way to be bandit-proof is if you escape over mountains, a large body of water, or some other impassible terrain. You're at the mercy of the wind, however, so there's no way to know in advance if you'll sail over the impassible mountains or into the very-passable prairie. There's also the inherent danger in being blown towards a mountain (crashing or being swept up higher than your balloon can handle) or out over a sea (stuck with no way back to land).

bta
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