High gear/low gear

[DC]

Just because the arrow goes 300 fps it doesnt mean anything if the bow is only putting 50% its energy into it.

It does mean something, it means the arrow is going 300 fps and it's going to go farther than a 200 fps arrow no matter how much energy was gained lost or wasted up to the time the arrow left the string.

[sleek]

Just because the arrow goes 300 fps it doesnt mean anything if the bow is only putting 50% its energy into it.

It does mean something, it means the arrow is going 300 fps and it's going to go farther than a 200 fps arrow no matter how much energy was gained lost or wasted up to the time the arrow left the string.

I guess if your only goal is speed no matter how it got there, then you have a solid point. But with how it relates to gearing, to hold a more solid comparrison, keeping draw weight and length the same, you need to work with effeciency.

[DC]

Tru nuff

[avcase]

But a bow that shoots a 2 grain arrow at 250 fps will always shoot a 1 grain arrow a little faster. Right?

Yes, speed will increase all the way to a dry-fire, similar to what Del’s graph shows, but not all designs do this at the same rate. This is why it is possible for a design that is good at flinging heavy arrows to be bypassed by a lower energy storage bow when shooting lighter arrows.

Del,

Is the graph an extrapolation based on virtual mass?  Virtual mass is also not so constant either.  If you do a lot of testing over a wide range of arrow weights, some designs will show a pretty consistent virtual mass regardless of arrow weight, others show decreasing virtual mass with progressively lighter arrows, and some designs will show the increasing virtual mass with lighter arrows.

[sleek]

Last mojam i upped my arrow weight and was shootung further with 13 grain vs 10gpp. It may have been the arrow, idk, but anobody else notice arrows gping further with heavier weight?

[avcase]

Nope, if it is too light the drag will overpower it's momentum/kinetic energy.
I't the old ping pong ball vs golf ball thing.
Fastest tabletennis ball smash is about 70 mph, but it wouldn't go as far as a golf ball travelling at 70 mph.
Del
[/quote]

50 ft-lb kinetic energy to a golf ball will send i the down range at 121.7 mph.
50 ft-lb kinetic energy in a ping pong ball is 502.3 mph. That will still hurt!

Now make the ping pong ball smaller in diameter so it has the same density as the golf ball, then the diameter of the 41.6 grain projectile is now just a bit over 5/16”, and that is going to punch a pretty nasty hole into just about anything it hits. 

Alan

[avcase]

Last mojam i upped my arrow weight and was shootung further with 13 grain vs 10gpp. It may have been the arrow, idk, but anobody else notice arrows gping further with heavier weight?

It really depends on the bow, arrow, and release method.  When I last went to the desert to flight test my foot bow, the lighter and faster 115-125 grain arrows always out-distanced the heavier 145-165 grain arrows.

Over the last couple of years at the Bonneville Broadhead flight tournament, Jim Martin got much better distances shooting 650+ grain arrows than he did with the minimum 450 grain arrows.

Alan

[Del the cat]

@Alan:-
The graph on my post is just raw experimental data, no extrapolation, no fudge, no sprinkles 
I made the lightest projectile I could.
I s'pose could have tried a dry fire, but the non existent projectile wouldn't register through the chrono' 
Del

[DC]

Either that or it would be going infinitely fast

[DC]

Alan, with all your shooting and testing do you ever think that you're getting a handle on this stuff or is the carrot still out of reach?

[Tuomo]

Virtual mass is also not so constant either.  If you do a lot of testing over a wide range of arrow weights, some designs will show a pretty consistent virtual mass regardless of arrow weight, others show decreasing virtual mass with progressively lighter arrows, and some designs will show the increasing virtual mass with lighter arrows.

Could you please elaborate this? Surely there is some kind on trend? For example, it seems that high gear bows is the design, which shows decreasing virtual mass with progressively lighter arrows? What are the design features, as general?

Nope, if it is too light the drag will overpower it's momentum/kinetic energy.
I't the old ping pong ball vs golf ball thing.

That is true but what is the real effect with real arrows? For example, what would be theoretically difference in distance with two dimensional identical arrows - 150 grain and 200 grain - if the speed is for both 200 fps? Or other way around, how much faster 150 grain arrow should be that it would fly as far as 200 grain arrow?

I think that difference is insignificant and thus the fastest arrow arrow has the most potential in flight shooting.

[Selfbowman]

Toumo i agree with Alan . That's what I have seen at the flats. Light is not always faster. The first five feet and where the arrow lands is two different critters. I've shot enough to witness this. And I have only been doing this a couple years. Maybe I did not understand your post either. It don't take much for you math guys to get over my head. .  Arvin

[Del the cat]

Virtual mass is also not so constant either.  If you do a lot of testing over a wide range of arrow weights, some designs will show a pretty consistent virtual mass regardless of arrow weight, others show decreasing virtual mass with progressively lighter arrows, and some designs will show the increasing virtual mass with lighter arrows.

Could you please elaborate this? Surely there is some kind on trend? For example, it seems that high gear bows is the design, which shows decreasing virtual mass with progressively lighter arrows? What are the design features, as general?

Nope, if it is too light the drag will overpower it's momentum/kinetic energy.
I't the old ping pong ball vs golf ball thing.

That is true but what is the real effect with real arrows? For example, what would be theoretically difference in distance with two dimensional identical arrows - 150 grain and 200 grain - if the speed is for both 200 fps? Or other way around, how much faster 150 grain arrow should be that it would fly as far as 200 grain arrow?

I think that difference is insignificant and thus the fastest arrow arrow has the most potential in flight shooting.

If the speed for both (dimensionally identical arrows) is the same, the heavier will fly further.... (but their speed won't be the same from the same bow).
Second question is possibly unanswerable! Prob' depends on the dimensions and properties of your "dimensionally identical arrows).
I don't think you can really separate the bow from the arrow except in thought experiments...
Del

[avcase]

Alan, with all your shooting and testing do you ever think that you're getting a handle on this stuff or is the carrot still out of reach?

Ha!  Yes-Still out of reach, but if it was easy then it wouldn’t be nearly as fun.  I feel the bows are fairly straightforward. Not necessarily easy, but the physics are straightforward using the same kinds of basic physics like those used to launch a car in space.  Haha!

I don’t feel very confident that I have flight arrows figured out. I just don’t have enough data points. The only good news is that I have made a lot of progress with distances this last two years, after years of almost no improvement. But I can’t say for certain why the changes I have made seem to work. I just have a lot of semi-educated guesses.

Alan

[avcase]

There is one major drawback as far a small flight shooting is concerned, the efficiency is relatively low and it starts to run into a wall below 8-9ggp. This is one design where the faster bow with heavy arrows is not the fastest with lighter arrows. Alan

Why? What are the physical reasons of that?

I can send you a link to a video, and it will pretty clearly show a tremendous amount of energy left in the limbs when the arrow leaves the string. The physical reasons have to do with the distribution of mass and stiffness in the limb. It uses a long flexible limb with many high energy vibration modes, and this allows the limb to flex and buckle rather than force its own kinetic energy through the string and into the arrow.  At slower speeds, this isn’t a problem. When I say slower speeds, I mean slow by flight shooting standards, but it is an incredible performer at typical hunting arrow speeds.

Alan