Author Topic: Virtual Mass revisited  (Read 1976 times)

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Online DC

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Re: Virtual Mass revisited
« Reply #45 on: September 29, 2020, 10:04:47 am »
I'm going to do this test again with a couple of shots for each weight. The 548 was a definite jog in the graph. The 650 is just an arrow that I threw together to get a heavy one. It doesn't have any fletching and hit the target sideways. I think I got an error on the second chrono with it.
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Online DC

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Re: Virtual Mass revisited
« Reply #46 on: September 29, 2020, 12:23:15 pm »
I did it again and the changes aren't worth typing. The 548 dropped 4fps and the 667(fletched added 4 grains) came up by 2 fps. My second chrono seems to be about 5 fps slower for some reason.

I guess that spot in the bag got a little soft :-[ :-[ :-[ :-[
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Offline sleek

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Re: Virtual Mass revisited
« Reply #47 on: September 29, 2020, 12:36:54 pm »
I did it again and the changes aren't worth typing. The 548 dropped 4fps and the 667(fletched added 4 grains) came up by 2 fps. My second chrono seems to be about 5 fps slower for some reason.

I guess that spot in the bag got a little soft :-[ :-[ :-[ :-[

Consider that the weight of the arrow allows the harmonics ( wave theory ) of the bow to be maximized.  That weight arrow 548 grain, allows the return wave of the bow limbs to perfectly sync up, delivering the most efficient energy flow possible.

In support of this consider an off balance tire. It will vibrate worse up to a certain speed and then smooths out to be unnoticeable at a specific rpm, then as you pass that rpm range you get bad vibrations again. All these other arrows don't allow your bow to be in its proper vibration range. But the one heavily arrow puts it right there, picking up ALL the bows energy.

I know its just a theory of mine, but it explains a lot, and has worked for me in getting good performance from my bows. Also, there is usually 2 ranges that fall 180 ( i think ) from eachother that allow good performance.  You may find another arrow weight that also joggles the graph, either by more or less, but i dont think the same amount as this arrow.
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Online DC

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Re: Virtual Mass revisited
« Reply #48 on: September 29, 2020, 12:52:56 pm »
It is strange. I've run the test twice and even with the the readings from the second chrono being different that hump for the 548 one is there. If your wave theory is right wouldn't you think that the 556 one would show some improvement?
The 501,548 and 556 are all the same Tiger shafts. the 501 and 556 are both 60# spine and the 548 is 55#. Could that one be getting a cleaner launch?
I think I'll sand down the 556 to 55# spine. I'll take 5 shots before and 5 shots after.
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Offline sleek

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Re: Virtual Mass revisited
« Reply #49 on: September 29, 2020, 12:55:02 pm »
That 550 arrow has 47.87 foot pounds of energy,  which is more than the heavier arrow has at  44.19 foot pounds with 650 grains. If it were only hysteresis as an energy loss factor,  this energy difference wouldn't make any sense. For certain, sometimes else is working to allow this random arrow to absorb more energy contrary to standard thought.
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Offline sleek

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Re: Virtual Mass revisited
« Reply #50 on: September 29, 2020, 01:06:46 pm »
It is strange. I've run the test twice and even with the the readings from the second chrono being different that hump for the 548 one is there. If your wave theory is right wouldn't you think that the 556 one would show some improvement?
The 501,548 and 556 are all the same Tiger shafts. the 501 and 556 are both 60# spine and the 548 is 55#. Could that one be getting a cleaner launch?
I think I'll sand down the 556 to 55# spine. I'll take 5 shots before and 5 shots after.

Certainly a cleaner launch is a very good possibility and could completely explain this. I assumed you had all the arrows spined for the bow so similar flight would be hoped for. If you can try different spines all in the same weight range that would be an interesting test. Are they arrows all hitting the target fairly straight?

I wouldn't expect the 556 to show much if any improvement,  because i don't know where the harmonic range on this, or any, bow is. and chances are, its a narrow range. The difference from 548 to 556 is 8 grains, and thats enough to make a noticeable difference in flight distance. 

Id like to see the speed differences as the grains go up one at a time, then down from 548 one at a time. That would help you dial right in and you may even be able to plot the results of the wave as a wave. You should be able to if my theory is correct.
« Last Edit: September 29, 2020, 01:13:09 pm by sleek »
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Online DC

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Re: Virtual Mass revisited
« Reply #51 on: September 29, 2020, 01:29:09 pm »
Foiled! I started scraping down the shaft and realised that I was removing weight as well as spine. I took off 10 grains of arrow and lost 2.5-3# of spine. I gained about one or two fps which 10 grains of weight could explain so that's a bust. I've never really worried about spine as it didn't seem to have that much effect in the speed and it's a PITA to have to make equal spined arrows in every weight. This is where the mathematical method would shine because you can change one thing(I think). I think where the cleaner launch would help is in equalising the two chronos readings.

The arrows are hitting the target pretty straight.
With a real arrow you can't change the weight without changing the spine and vice versa. Maybe you could increase the weight by wrapping tape around the middle of the arrow so it wouldn't change the spine but then you'd have to wonder if the bumpy surface going across the bow would have any effect. More thinking required :D
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Offline sleek

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Re: Virtual Mass revisited
« Reply #52 on: September 29, 2020, 01:33:16 pm »
Foiled! I started scraping down the shaft and realised that I was removing weight as well as spine. I took off 10 grains of arrow and lost 2.5-3# of spine. I gained about one or two fps which 10 grains of weight could explain so that's a bust. I've never really worried about spine as it didn't seem to have that much effect in the speed and it's a PITA to have to make equal spined arrows in every weight. This is where the mathematical method would shine because you can change one thing(I think). I think where the cleaner launch would help is in equalising the two chronos readings.

The arrows are hitting the target pretty straight.
With a real arrow you can't change the weight without changing the spine and vice versa. Maybe you could increase the weight by wrapping tape around the middle of the arrow so it wouldn't change the spine but then you'd have to wonder if the bumpy surface going across the bow would have any effect. More thinking required :D

Wrap tape around the nock end. If you can do ALL your weight adjustments back there, spine won't be an issue.
Tread softly and carry a bent stick.

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Online DC

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Re: Virtual Mass revisited
« Reply #53 on: September 29, 2020, 01:40:01 pm »
It takes a lot of tape. Half the length of the arrow is just a few grains and I'm not so sure that putting the weight on the back doesn't increase the spine. If weight on the front decreases it, I dunno.
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Offline sleek

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Re: Virtual Mass revisited
« Reply #54 on: September 29, 2020, 01:47:04 pm »
It takes a lot of tape. Half the length of the arrow is just a few grains and I'm not so sure that putting the weight on the back doesn't increase the spine. If weight on the front decreases it, I dunno.

We are over thinking this. The arrow doesn't care how much it weighs. So, don't add weight to the arrow, add it to the string right at the nock area using split shot fishing weights. The bow will handle it fine, just a little hand shock, but it will force the bow to push the correct weight, and you won't have a variable in spine to worry about.
Tread softly and carry a bent stick.

Dont seek your happiness through the approval of others

Online DC

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Re: Virtual Mass revisited
« Reply #55 on: September 29, 2020, 02:04:02 pm »
I've got chores to do so it's going on the back seat. It's the Vancouver Island Wooden Bow Makers Gathering this weekend. Got to get the trailer(RV) ready ;D
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Offline sleek

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Re: Virtual Mass revisited
« Reply #56 on: September 29, 2020, 02:11:24 pm »
I've got chores to do so it's going on the back seat. It's the Vancouver Island Wooden Bow Makers Gathering this weekend. Got to get the trailer(RV) ready ;D

Have fun man! Thats awesome yall have an event, lots of folks dont. Im prepping to go out of state on a big hunt with my son for his first hunt. He has made his bow for this specific hunt. Going on an 8,000 acre ranch for trophy bucks. Otherwise I'd try to do the testing myself. When I get back, I will build a shooting machine. to do some testing also. I do appreciate your willingness to do all these experiments. Your dedication to precision and testing is invaluable.
Tread softly and carry a bent stick.

Dont seek your happiness through the approval of others

Offline willie

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Re: Virtual Mass revisited
« Reply #57 on: September 29, 2020, 02:39:24 pm »
Quote
I guess that spot in the bag got a little soft :-[ :-[ :-[ :-[
Damn.  the door looks pretty good otherwise. though.

are you shooting with one of your best bows? It could be there is not much hystersis to detect :)

maybe test some really light arrows, and then repeat the test with an otherwise similar bow, but is doggy with set, when you have a chance.  I will try to plot any data you generate on a graph this evening to see if we can "see" any hysteresis.

Offline avcase

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Re: Virtual Mass revisited
« Reply #58 on: September 29, 2020, 11:43:19 pm »
Consider that the weight of the arrow allows the harmonics ( wave theory ) of the bow to be maximized.  That weight arrow 548 grain, allows the return wave of the bow limbs to perfectly sync up, delivering the most efficient energy flow possible.

In support of this consider an off balance tire. It will vibrate worse up to a certain speed and then smooths out to be unnoticeable at a specific rpm, then as you pass that rpm range you get bad vibrations again. All these other arrows don't allow your bow to be in its proper vibration range. But the one heavily arrow puts it right there, picking up ALL the bows energy.

I know its just a theory of mine, but it explains a lot, and has worked for me in getting good performance from my bows. Also, there is usually 2 ranges that fall 180 ( i think ) from eachother that allow good performance.  You may find another arrow weight that also joggles the graph, either by more or less, but i dont think the same amount as this arrow.

This is an very good analogy and very true. You will see this if you very carefully test a bow over a wide range of arrow weights.  In a plot of virtual mass versus arrow weight, the virtual mass may increase with less arrow weight and then reverse and start decreasing, or sometimes it is the other way around.

Alan

Offline bownarra

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Re: Virtual Mass revisited
« Reply #59 on: September 30, 2020, 02:31:56 am »
Waves involve the transport of energy without the transport of matter. In conclusion, a wave can be described as a disturbance that travels through a medium, transporting energy from one location (its source) to another location without transporting matter.

:)

DC just make some selfnocked test arrows. You can fine tune the weight quite a bit without affecting spine.  You can also get sticky backed lead strips. Airgun pellets are another way to alter weigh easily. Use screw on field points and drop the melted lead in the head (soften spine + add weight). Sanding just the middle will reduce spine without affecting weight much. Stiffen an arrow whilst reducing weight - sand both ends, don't touch the middle.
Many ways to play about with arrow dynamics.