Primitive Archer
Main Discussion Area => Bows => Flight Bows => Topic started by: joachimM on December 10, 2017, 01:32:28 pm
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I did quite some flight exercises lately, and was rather appaled by my results.
Bow-arrow combinations that gave me OK results last summer, yielded absolutely awful distances the past few days.
It has been awful weather, however. Lot of side wind, which increases drag quite a bit.
But still, I started to look for variables that could affect flight path, especially how local environmental conditions affect drag.
I knew altitude had and effect, but had no idea how large that effect was. The Bonneville range is at 1286 m asl. The air density at this altitude is about 15% lower than at sea level, which reduces drag by 15%. Say you shoot an arrow at the Bonneville flats and it flies 205 m (supposing a broadhead), it would fly some 8 m shorter at sea level.
Next, there is temperature: the higher the temperature, the less drag there is. At 25°C, there is c. 10% less drag than at 5°C (my current temperature).
Summer versus winter temperature alone would reduce my distance by c. 6 m.
Combining temperature and altitude, a flight shot of 205 m at the Bonneville range at 25°C versus at my place at 5°C would make a difference between 205 and 192 m.
That's rather considerable. And it makes me more comfortable not closing in on the 300 yard mark in flight with flight arrows yet ::)
Sources:
https://fogmountaintennis.wordpress.com/2014/06/05/atmospheric/
https://sites.google.com/site/technicalarchery/technical-discussions-1/trajectory
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I don't think it is that simple. You have less drag going into the direction of the arrow but you also have less drag that keeps the arrow from falling out if the sky downward. Cooler moist air tend to give better results that hot dry air for instance.
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At high temperatures, moisture reduces drag, indeed. Bur at low temperatures the effect is much smaller and close to negligible. See attached graph, from the tennis paper.
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Joachim
I wonder if the combined effects are worse than you estimate? Not all the corrections you cite are linear, (and I do not presume that your calculations/numbers are), but when combining factors to estimate drag, are the results simply additive?
https://www.faasafety.gov/files/events/NM/NM09/2013/NM0951144/Density_Altitude.pdf
the pdf has a nomograph that you might find interesting for comparision .
I realize not walking as far as hoped to get your arrow, can be disappointing, but not near as bad as failing to clear the tree at the end of the runway. ;)
but you also have less drag that keeps the arrow from falling out if the sky
Steve, are you saying arrows might "glide" better with higher air density?
Edit: it is not exactly clear in the FAA publication if the displayed nomograph is adjusted for engine performance reductions.
this interactive nomograph might be more fun to play with. https://www.takeofflanding.com/
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Not necessarily glide but it seems to equal out advantages and disadvantages. Arrows are cutting through the air forward but also falling. Thin air is nice to cut through but it also doesn't give the good drag you want to keep the arrow from falling as fast.
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I am at a bit of a disadvantage from Steve and Alan, in that I can only participate in a somewhat theoretical discussion about arrow flight, and have not actually been on the ground at a flight shoot to observe arrows in flight from a down range perspective. I hope you guys don't think that I am trying to put you "on the spot" when asking so many questions, as I know it is not easy to put observations into words.
But... when I read from... http://www.primitivearcher.com/smf/index.php/topic,61455.msg863183.html#msg863183
In other words it is descending a bit nose up, causing drag. This drag slows the descent, keeping it in the air longer and giving it more time to travel a little farther
OK, I think maybe Alan could also have said "lift" but chooses to describe it as "a type of drag that keeps it in the air longer". Not worth quibbling about, really. as drag and lift are sometimes two sides of the same coin. But now Steve seems to imply that there is an "ideal" air density. Not too thick to slow the arrow too much, but thick enough to somehow keep it in the air longer. But it's not "glide". My mind is clocking in some over time to get a grasp of how that can be.
Once again, I am not finding fault with the observations of others, but I wish to ask more about this aspect of "beneficial drag". Having drag in the right places, such as feathers, seems to me, to be a "necessary evil" to be managed. Is there also an existence of another "useful drag", (for other than control), Perhaps an accepted concept in flight community discussions? Can I read more about it somewhere else? What are it's different attributes? Is it controversial or even discussed much?
curious
willie
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I tend to stay out of arrow discussions as it seems to me that there are too many variables to take into account to make a definitive conclusion. That said I would be inclined to think that heavy moist air would be detrimental to distance shooting
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I always like a good discussion. Takes me out of my comfort zone, and forces me to dig deeper. In the end I always feel I’ve learned something.
Is drag additive relative to air density? Increase air density by 10% and drag will increase by 10%.
In a world without friction and drag, an arrow would should a symmetrical, parabolic curve. The only force countering movement is gravity. With drag, however, the horizontal distance during the downward path is shorter than the upward horizontal distance, because drag slows the arrow down from the moment it leaves the bow.
Since drag is quadratically related to velocity (arrow speed), this asymmetry becomes more and more exaggerated with faster and faster launch speeds. Arrows being shot very fast will fly further, but will also fall out of the sky in a more vertical manner (landing at much more than 45° relative to the ground) since drag reduced the initial velocity more. I’m sure the experienced flight shooters have witnessed this.
Under exceptional circumstances, Alan’s theory about beneficial drag in a mildly rotating arrow might be valid (with a change in drag behavior due to different arrow movement through the air beyond the apex), but I don’t think when I shoot it matters a lot ;-). In general, the less drag, the more the arrow follows the drag-less path, and the further it will shoot. Drag that slows the descent also slows down the horizontal speed. With no horizontal speed, the object falls vertically.
How did I calculate the distances? I didn’t do complex calculus. I modified the spreadsheet presented in the technical archery page I linked to. Through the spreadsheet I track the vertical distance, Y (column AC). The horizontal distance is read at the moment the value in column AC reaches zero again.
I didn’t have input for drag coefficients (which differ for each arrow). For the calculations this wasn’t necessary either: I just needed to see how an increase in drag of 10, 15 and 23 % influenced a regular shot. Still, I used Steve’s rule of thumb’s relation between 10 gpp arrow speed and distance: 170 fps will yield c. 200 yards (183 m), 205 fps will yield c. 300 yards (274 m). From this, you can calculate the expected drag coefficient. If you know initial arrow speed (chronograph) and distance, you can calculate drag.
If you then increase the drag coefficient by 10% (effect of 5°C versus 25°C), 15% (effect of altitude) or both (23.5%) you can track the max distance in the spreadsheet. This teaches me that for a typical 200 m shot, the effect of altitude or temperature isn’t negligible at all.
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I tend to stay out of arrow discussions as it seems to me that there are too many variables to take into account to make a definitive conclusion. That said I would be inclined to think that heavy moist air would be detrimental to distance shooting
Actually, moist air is beneficial, as it reduces drag. Counter-intuitive, but it's neatly explained here https://fogmountaintennis.wordpress.com/2014/06/05/atmospheric/ (under the heading "humidity")
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Joachim, nice read about the tennis ball. It covers a lot of the factors in an easy to understand way.
Is drag additive relative to air density? Increase air density by 10% and drag will increase by 10%.
yes, at least the coefficients commonly used to define form drag are linear by definition. But is density linear to elevation and temperature change? I asked earlier because the scales used in the nomographs are not linear, they vary slightly from end to end. Density effects lessen as temps get higher, but increase as elevations goes up.
Your question made me ask myself "what factors affecting drag are not near so linear?" And attitude appears to me to be the biggest non linear player. Out of attitude flight increases turbulence, where drag coefficients can increase rapidly.
One question that keeps coming to mind, is that when considering an arrows total flight down range, different drag factors may have different importance as velocities vary. it's not quite like the simple momentum vs time of a trajectory in a vacuum. I often think we might be better served if we split the flight into a few different components.
1. Launch... where acceleration is obtained from the bow, velocities are high and attitude induced drag "makes or breaks" the shot.
2. The turn at the apex... where gravity causes a substantial change in flight direction and attitude and velocities are low.
Is this where the "less drag that keeps the arrow from falling out if the sky" examination needs to comes in?
3. Decent..... acceleration due to gravity along a new course with a new attitude and starting from a much lower velocity.
A few different problems, each with their own criteria?
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I notice that one of the problems we have is dealing with the lighter arrows around 200 grains or less. They come of the bow very fast but the slightest sideways motion kills the speed right out of the bow. Arrows around 300 grains from 50# bows can pretty regular hit the 300 mark but not good enough for records. I am moving my arrow weight up to about 250 or 260 this next year and see how it does.
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Steve,
what is the spine of the 200 and 300 you are comparing?
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I don't measure the spine on 200 rain arrows, I just test with my finger, with no point weight it doesn't take much, It would be cool to video tape in slow motion just to check it. On a tapered arrow I think the dynamic spine point is well behind center. If I were to guess I would say about 20# spine some as high as 35#
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I don't measure the spine on 200 rain arrows, I just test with my finger
If the lighter arrows are having trouble, wouldn't you want to have an objective way to test stiffness? I realize that stiffness measured at the center of a tapered arrow doesn't tell the whole story, but it is always part of the story. What am I missing here?
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I measure on occasion. I feel like there are so many factors at work and so little available testing time or space, so many arrow style variations that I am better off just working intuitively basing everything on small samplings and then going in the right direction. I have had a steady improvement in arrows. I feel like if I could practice 1 time per month it would speed up my progress by dozens of years.
I am starting to think longer draws will pay off in primitive flight as well. Use the extra stored energy of a full 28" draw to beef up arrow weight.
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Steve, increasing your sample size never hurts if experiments don't go as planned. your intuition just needs more information. ;)
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There’s some really great info here. There is always something new to learn. In the 1960’s and 1970’s, one popular theory was that it was best to shoot in very cool and still conditions. Flight shooting would commence early in the morning.
Here is a bit of an article from 1977 in the Freemont Argus newspaper. It was about George Alavekiu, who was preparing for the US Flight Nationals. George was describing the role the atmospheric conditions played in his first mile long shots.
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George had hit a "weather window," as flight shooters call it. "At these speeds the air is practically solid, like water when you jump into it from a high place. If things are off just a little then your arrow will jump and roll and lose all its power to wind resistance." Looking for the "weather window", flight shooters every year converge on the Bonneville Salt Flats (where high-speed cars are tested) for the national flight tournament. The next one is scheduled for September. Before the shoot the arrows are registered. Actual shooting begins at dawn in order to take advantage of the still winds of early morning. Everything is important -- the temperature, the humidity, wind velocity and direction. Even shooting at higher elevations makes a difference because the air is less dense.”
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It is kind of funny that the article mentions the still winds at dawn as being the most desireable conditions. There may be other reasons for this belief at the time. Perhaps it was because the bows simply held together better in colder temperatures. Unfortunately, George never did make it to Bonneville that year.
A couple years ago I did some practice shooting at Bonneville during the winter and the temperatures were not that far above freezing. My distances seemed to be much worse than usual, although it was hard to know if it was influenced more by the temperature, or if it was due to the strong unpredictable winds that were blowing that day.
Alan
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I am not sure how much arrow shaft drag can be exploited to get farther shots. It seems theoretically possible and I have made efforts to see if I can get something out of it with my footbow arrows. What I have observed is that these arrows land the softest. In contrast, my high forward balance arrows seem to punch a lot deeper hole in the ground and fall short. My longest shots have been with the arrows where I have tried exploiting this concept of using shaft drag to keep the arrows in the air longer, but that may be due to a lot of other factors. I just haven’t been able to do enough shooting to draw any conclusions.
Alan
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I notice that one of the problems we have is dealing with the lighter arrows around 200 grains or less. They come of the bow very fast but the slightest sideways motion kills the speed right out of the bow. Arrows around 300 grains from 50# bows can pretty regular hit the 300 mark but not good enough for records. I am moving my arrow weight up to about 250 or 260 this next year and see how it does.
Good info. The other day I tried shooting 25” 160 gr stiff carbon arrows that gave me 220 fps and I expected or rather hoped they would shoot more than 300 m. They didnt even make it halfway... but it was pretty windy weather though. I hadn’t expected the effect to be so dramatical!
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I tend to stay out of arrow discussions as it seems to me that there are too many variables to take into account to make a definitive conclusion. That said I would be inclined to think that heavy moist air would be detrimental to distance shooting
Actually, moist air is beneficial, as it reduces drag. Counter-intuitive, but it's neatly explained here https://fogmountaintennis.wordpress.com/2014/06/05/atmospheric/ (under the heading "humidity")
So then shooting an arrow during a rainstorm should produce great distances :)
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except for the detrimental effects of extra drag by wind and rain itself (-S
Actually, it's pretty difficult to combine all ideal conditions of humidity, temperature and wind.
in the early morning the humidity is high (closest to the dew point), but temperature is low. Wind speeds are often lowest in the morning, especially in summer, when winds rise in the afternoon due to convection of warm air, heated by the sun.
Overall, I can imagine that early summer mornings provide the best overall conditions to flight shoot.
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Well I shot the same arrows and the same bow the other day that I shot at the flats last summer. I was disappointed to say the least . It was cold probably around 40 degrees . My arrows flew 25 yds shorter than they did here or at the flats. No wind to speak of. Maybe cold air falls and hot air rises has more to do with it than we thank. .??? Arvin
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I also think maybe that the water that comes off the flats in evaporation in the heat there makes the air more wet. Could be wrong about though. The water is shallow at the flats. Arvin
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Arvin, I think rising thermal air currents help a lot.
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I am not sure how much arrow shaft drag can be exploited to get farther shots.
Alan, I know you covered some FOC principles in an earlier thread where gliding was discussed, but maybe there are thoughts for other possible exploits out there? Have most of your efforts been limited to the "If we can delay the decent, then the arrow might go further" concept?
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I am not sure how much arrow shaft drag can be exploited to get farther shots.
Alan, I know you covered some FOC principles in an earlier thread where gliding was discussed, but maybe there are thoughts for other possible exploits out there? Have most of your efforts been limited to the "If we can delay the decent, then the arrow might go further" concept?
Short answer is yes. One of my biggest challenges at our Flight competitions is that some portion of the arrow remains above ground so it can be found and measured. A soft landing is pretty important, and it is even better if I can get a little extra distance in the process.
I do want to better understand the role of atmospheric conditions. I think this is useful. One of my current obsessions is trying to understand how Harry Drake shot an arrow over 2000 yards in 1971. It doesn’t seem possible given the equipment he was using, yet I do not doubt his distances were completely legitimate. My theory is that he was a master at knowing when and where to shoot in order to get as much help from the atmosphere as possible. Another part of the mystery is that this record was set at a lower altitude location than Bonneville, and the recorded temperature was a very cool 59 degrees F. The wind was noted as a gentle but steady off-angle tail wind of 5mph.
Alan
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Short answer is yes. One of my biggest challenges at our Flight competitions is that some portion of the arrow remains above ground so it can be found and measured. A soft landing is pretty important, and it is even better if I can get a little extra distance in the process.
A little aside for a sec. What would happen if you got a real soft landing. So the arrow hit flat and skipped along the surface. Does it not count in scoring?
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A little aside for a sec. What would happen if you got a real soft landing. So the arrow hit flat and skipped along the surface. Does it not count in scoring?
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According to the Flight rules: “An arrow that’s comes to rest in other than the usual position may be measured from the tip of the arrow if visible, or from the point which it enters any object other than the ground.”
In this case distance wouldn’t be measured to the point of the arrow where it came to rest. But this is where the acting judge may need to get involved. For instance, if there was a chance some external forces act to continue to move the arrow after it has landed, such as high winds, or flash flooding, etc., then it will not be possible to score the arrow.
We have had rare instances where an arrow may have hit a rock below the surface and bounced out, but I am not aware of any time that this resulted in a much of an advantage.
I don’t think an arrow can descend at such a high angle of attack that it would land flat on the ground. If it did, then there probably wouldn’t be enough forward motion to carry it forward very far. In fact, if this happened then the arrow will descend in a long slow spiral, and may end up traveling the wrong way by the time it hits the ground. What usually happens is that the arrow picks up speed as it descends, and this moves the center of pressure further rearward, eventually forcing it into more alignment with the trajectory path before striking the ground.
Alan
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Alan
Lots of light powder snow has been hanging in the branches of the spruce trees here. When a pilot friend stopped by, I commented how we hadn't had any wind for 2 weeks. He said it seemed unusual because just a few hundred feet up, it has been a steady headwind for days on end. His (airplane) trip home each afternoon is slowed, while he he looks out over a forest of undisturbed snowy trees. He observed that it seems like when the wind is the other way, the trees are swaying and the ride is bumpier.
Having worked on deck for many years, most of my observations about wind and waves were more about the waves, but I can say that all waves are not created equal. Sometimes sea conditions weren't near as poor as one would expect (for the given wind), and sometimes just the opposite. Could the same be true for the atmospheric side of the boundary? Are there vertical flows to be considered besides the of mentioned "thermal uplift"?
https://en.wikipedia.org/wiki/Secondary_flow#Wind_near_ground_level
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Releasing balloons might give you some indications but I am not so sure what you would do to make adjustments for it.
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Ballons reminded me of flying a kite. sometimes there are surprises just a little ways up. Guess if you want to break records at matches, you gotta shoot when its time for everybody to shoot. But if its a personal attempt, then you could take the kids picnicking and kiteflying and learn a bit more about the winds aloft.
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There is a lot of good info on the subjects discussed above in "Archery, the Techical Side." There are articles on arrow flight beginning on pages 122 and 185. (Note that the second article says that drag varies as the square of the velocity. This is wrong. IT varies as the cube of the velocity.)
There is also an article on the effect of feather size and center of gravity, beginning on page 77.
I think there are places where it can be read online.
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Jim, could you explain why drag relates to the cube of the velocity instead of the square?
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Jim, could you explain why drag relates to the cube of the velocity instead of the square?
Nope. Can't explain gravitational acceleration being 32' per second, per second either, but text books and even wikipedia agree on both drag and gravity.
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I was WRONG! (A) Too long since I was casually studying aerodynamics. Drag does increase as the square of velocity. It's power required to maintain velocity that varies as the cube.
Sorry. I hate being wrong because I try not to be.
Jim