Mythbusters
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Junior Member
Registered: 05-13-09 | In the myth that when you go 40 mph you get double the arrow penetration; the myth-busting team got it wrong by:
1. The had the wrong type of arrow shaft,
(wood not carbonfiber/graphite).
2. The archers of that time would have used:
Broad-headed tips for the arrows. |
Senior Member
Registered: 02-18-07 | Would make no difference. As long as other variables stayed the same, the only thing that mattered is velocity. And as long as we stay well below light speed, velocities simply add. |
Senior Member
Registered: 01-18-04 | Here's a question:
Would simply doubling the velocity necessarily double the penetration?
Think about it: as flesh is compressed and/or displaced, the modulus of friction would not remain the same, it would increase. (Try dipping a spoon into a pint of frozen ice cream to a depth of 1", and then try the same thing in an identical pint of ice cream, but try to reach 2". See what happens!) It follows that the energy needed to penetrate twice as far must be greater than 2X.
I'm just guessing, but I doubt that a horse moves faster than an arrow. Even if the horse could at full gallop, the archer wouldn't be very likely to hit the target. Not at all practical, IMO. |
Junior Member
Registered: 05-12-07 | I agree that they got it wrong, because:
1. the crossbow is more powerful than a regular bow (40mph added to regular bow would be a higher percentage of total velocity)
2. the types of bows and arrows at the time could have had even slower velocities than regular ones now.
the only problem is: to double the speed of the arrow it would have had to have been travelling at 40 mph in the first place. I doubt there bows were that bad. |
Junior Member
Registered: 05-12-07 | [QUOTE]Originally posted by b00mb00m:
Here's a question:
Would simply doubling the velocity necessarily double the penetration?
Think about it: as flesh is compressed and/or displaced, the modulus of friction would not remain the same, it would increase. (Try dipping a spoon into a pint of frozen ice cream to a depth of 1", and then try the same thing in an identical pint of ice cream, but try to reach 2". See what happens!) It follows that the energy needed to penetrate twice as far must be greater than 2X.
QUOTE]
you forget, people are squishee inside, much easier to get thru the innards |
Senior Member
Registered: 01-18-04 | quote: Originally posted by ringo3:
you forget, people are squishee [sic] inside, much easier to get thru [sic] the innards
No, I am not a cartoon character in "The Simpsons". My "innards" are made of actual flesh and bone. |
Junior Member
Registered: 05-14-09 | It would be harder for the arrow to penetrate the muscles and bone of the rib cage than the soft, almost hollow material of the lungs. The added velocity may have given the arrow the momentum to penetrate double the distance as it traveled through the lungs. |
Junior Member
Registered: 10-16-08 | OMG these guys are so lame. As usual, they take an old 'myth', translate it into modern terms, and then disprove the modern interpretation. The original myth IS NOT that firing from a horse will double the penetrating power - IT IS that doing so will double the penetration... into the target. And the target is not foam or ballistics gel. The 'target' is an human being, WEARING ARMOR! Probably leather armor. If a "standard" arrow shot penetrates the leather armor, plus three inches of flesh, it is entirely reasonable that the 'horse fired' arrow would penetrate the leather armor, plus SIX inches of flesh. Double penetration! |
Junior Member
Registered: 05-14-09 | No one mentioned the most obvious miscalculation, the bolt of the crossbow is about half of the mass of a bows arrow. I am no scientist but the more weight you have traveling faster will penetrate deeper. Although I am not sure twice as deep with a slight (relative to the static shot) difference in arrow speed, but I am sure it would make a differance |
Junior Member
Registered: 03-22-09 | WOW people omg DID ANY OF YOU HEAR THAT THEY CALIBRATED THE CROSS BOW TO BE THE SPEED OF A HAND BOW !!!! watch the show again and listen a lil better and speed is the only factor in the difference between a cross bow and a hand bow it dosent matter how it is shot as long as its going a certain speed |
Junior Member
Registered: 03-22-09 | i believe they do need to revisit. If the arrow is a pointed than the resistance in front f the arrow is less which true will send the arrow farther in. BUT the difference between the round edge at stand still and jeep is not going to be the same difference as the pointed stand still and the jeep because the farther the round tip went in the harder the resistence stopping it sooner if they wouldve shot the round arrow stay still then shot the same arrow twice as fast the arrow would NOT have went in double the 1st arrow because of the extra resistence but with the pointed arrow it reduces the resistence and less resistence with more speed is a greater penetration ratio than the round arrows penetration ratio. |
Junior Member
Registered: 05-14-09 | Hello there, love the show guys. But i hafto say that sometimes you guys really just don't think outside of the box it feels like. Do you really think that back in the days of where this myth is supposed to occure, they had a good scientific method of seeing a 50% increase of penetration? Isn't it more logical that the soldiers that had used both standing still bows and mounted fireing would have noticed an increase of people DIEING, not the accual penetration. Sooo, what could that then mean? Well logically and most likely they at that time had some kind of protection against arrows, like chainmail or tough leather or something like that. Here is what i'm thinking, and this is something you could have done in 5 minutes before doing the myth. You could have just googled arrowspeeds and used the horse max speed and clearly seen that there is not double penetration. So here is what i think that they meant when they said that mounted archers had double penetration. A "Leather harness" has lets say 100 points in average resistance to arrows. An arrow of that time had an penetrationpoint from around 80-120 points. The increase in mounted speed increased the penetrationpoint with maybe 20 points leading it to have for the soldiers point of view a 50% more likely penetrationifactor. Well thats what i think at least...great show guys..  |
Senior Member
Registered: 10-03-06 | The test was perfect. They had a crossbow properly calibrated, consistent speed, and distance.
Dear god people, do you have to complain about everything? |
Senior Member
Registered: 01-31-08 | I didn't like the color of arrow they used either  So many stupid objections. First off they calibrated the speed of the crossbow to that of the original bows. In earlier episodes they showed that penetration is almost identical between an arrow with a simple point and a broadhead arrow. The material has to be uniform to accurately measure depth of penetration. If you shot into an actual body with an arrow you would get different penetration depending on where you hit it, not the best medium for basing this myth. When they gave you the speed of the horse and the speed of the original arrows it was pretty obvious that you would not get twice the depth of penetration. You need to remember that people exaggerate, "he hit it a mile" and thousands of other everyday exaggerations we accept, knowing that they are not true, they are just an indicator that something was out of the ordinary. Yes the arrows did go in deeper, but not twice as deep. Twice as deep is not too unreasonable as far as exaggeration goes in a story from the past. |
Junior Member
Registered: 05-14-09 | I think the spirit of this myth is true. they got 3" of extra penetration going at speed. in regards to killing people 3" extra probably helped. and i think they should have done it with a human analog.
but how i think they messed up the most is that the didn't replicate the myth. they never saw what it would take to get twice the penetration. what would happen if they went 60 or 70 mph in the jeep? |
Junior Member
Registered: 05-15-09 | Arrow Penetration is (largely) driven by Kinetic Energy. To double the penetration, you would double the KE. Since KE = mv^2/2, you would need to increase the velocity by a factor of sqrt(2) in order to double the KE. This means the on-horse velocity has to be 1.414x that of the still shot velocity. If a horse is moving at 40 mph, in order for that to be an increase of 41.4%, the still velocity of the bow would have to be 96.6 mph, which is pretty darn slow.
Of course, there are many more complex factors actually at work, but when you break it down to the basics, you would need to double the KE to double the penetration and shooting from a horse does not double the KE. |
Junior Member
Registered: 05-13-09 | Ok....Sheesh... Love it when math folks have no working knowledge or practical usage of equipment and try to explain things. Ive seen SO many incorrect statements in this thread it's dang near hilarious. 1rst off the material that the bolt was made of DOES and WOULD make a difference in the penetration factors. We have discovered that carbon fiber shafts have a better penetration factor than aluminum or wood because of friction and deflection factors. To get the same spine on an arrow shaft, you need approximatly 25% less weight with carbon fiber than you would aluminum and 43% less verses wood. This entails more speed but LESS kenetic energy at the SAME velocities. BUT...since they used the carbon shafts for the complete test medium then they are NOT messing up. The test results would have been the same. Now lets talk about broadheads versus Target Points. Will Broadheads penetrate further that targ. points? Its according to the material that you are firing into! Foam stops an arrow by friction not blunt force stop. A broadhead could and would penetrate further BUT AGAIN....They used Target points for the full test medium!! I am a professional hunter and most concider me an expert in Archery (even though I dont believe in anyone being an expert) I feel like they did this test in the only way that would be practical in todays time. You have to remember many things in a test such as this. 1) The bows of yesteryear were Longbow and recurves. And MOST underestimate the power of these bows and the skill that the men of that time had with them. They LIVED on their abilities to use this weapon for war and for food! 2) There is no way that we could CONSISTANTLY reproduce this test while using the old weapons because there are few people left in the world that could use them as adeptly as the men of the time. If there are ANY! 3) There is absolutely no way we could consistantly reproduce the equipment used in that time because THEY didnt even produce a consistant product! They didnt have the high tech equipment for production like we do.
These guys on mythbusters (and girl, sorry Kari) do what they can with what they have to produce as accurate of a reaccount of these tests as they can. Are they all going to be perfect? Of course not. ITS A TV show!!! Get over yourselves!!! |
Junior Member
Registered: 05-13-09 | hello, I was the one who posted (revisit) question. And I agree with there is no real difference between a cross bow and a riding bow as long as they travel to the same speed.
That was not the point i was trying to make. i was trying to make the point that if you get arrow from that time period it would most like have been a arrow head tipped arrow and would allow for the shaft to not have as much drag being caused when it goes into an object.
I have asked many range instructors if it makes a difference when they use broad tipped arrow v.s. just the pointed arrows into a board like one used on the show that the pointed is hit with drag all the way through the board since the penetration point is as big as the arrow it's self. As where the broad tipped arrow penetration point is bigger allowing for the shaft to have no or very very little effect as it goes into an object.
I also agree with those that said that they really didn't do this myth right because normally they go until they get the same results as to make the myth "true", then state that no one would be capable of reaching this speed, at that day and age.
and to yeahyeahyouwere, you have it mostly right with kinetic energy just that what happens when you add in factor of mass differences in the arrows (aka. broad tipped arrow mass v.s. a brand new pointed graphite shaft arrow) and also you have to add in cutting power in the object plus drag, this list goes no forever; but if the cutting difference between the two types of arrows broad v.s. pointed tip is that the pointed tip is greatly affect by drag through an object and has hardly no cutting power then yes you have to double the velocity, but if the broad tip has great cutting power with little or no drag then you do not need to increase the velocity by a factor of (2). |
Junior Member
Registered: 05-15-09 | The discussion has covered most of the outstanding issues but to complete the test of the myth the boys only need to do a little history research and one more lab test.
Penetration is a function of the material the arrow is striking, the shape of the arrowhead and the kinetic energy the arrow brings to the target.
First the target. Yes, we need to replicate the typical battlefield armor and the the warrior's body. Likely the research will yield something like a half inch of layered leather or woven reads etc. But something that is harder to penetrate than human skin. In the laboratory set up they'll need to cover the ballistic gel dummy with this type of armor.
Second the arrow head should be something similar to the original battle tips, i.e. broad-head steal.
For the test the crossbow can be used in the lab with it's speed adjusted for first a) speed of standing archer's arrow, then b) that speed plus the speed of a galloping horse.
If the myth is confirmed it will likely be because the energy need to penetrate the armor is more than half of the energy contained in the normal (non-mounted) arrow shot. Perhaps 80% of the energy is consumed to pass through the armor, leaving 20% for penetration in the flesh. With only a 20% increase in the kinetic energy of the arrow from the horses speed the energy remaining for penetration after passing though the armor is doubled.
Simple as that. They could truly test the myth and prove that it is confirmed or busted. But as it stands now... the question is still unanswered.
Come on guys. Finish the test. |
Junior Member
Registered: 05-15-09 | I'll skip the difficult problem of penetration as I have no knowledge of any armour used in that period, which would be likely more of a factor than flesh resistance, and instead look purely at KE.
We all know the ol' 1/2mv^2 formula. Keeping arrow mass constant (call it Ma, and assume it to be 0.5, so that 1/2m = 1 to make our equations easier, as we're only looking at relative KE):
Arrow speed from stationary: 135 mph = 60.35 m/s
Arrow speed from 40mph horseback: 135mph + 40mph = 185mph = 82.70 m/s
Arrow speed from 40mph horseback firing at another rider riding at the same speed in the opposite direction: 135mph+ 40mph + 40mph = 225mph = 100.58 m/s
KE is proportional to v^2 (remember, we're ignoring Ma as it's constant)
KE stationary : moving = 3642:6839 = 1:1.876
KE stationary : opposing = 3642:10116 = 1:2.778
That's a pretty significant increase. Having two riders riding towards each other at point-blank range (for a flat trajectory. Curved trajectories add a whole other layer of difficulty) isn't entirely out of the question for two armies meeting head on. If 1.9 times the KE increases penetration by 70%, 2.8 times the KE might increase the penetration by 100%. Or penetration my be limited more by the increase shaft friction than by initial KE. |
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