Estimation of Arrow Speed

[blindarcher]

For those who would like to get a bit nerdy, please find attached a spreadsheet I use for making rough estimates of arrow speed.  Two methods are used.  The  first is based on measured force versus draw data.  The second is a closed form equation to estimate arrow speed using using a prediction of force versus draw equation.  I hope the EXCEL spreadsheet is accessible.  Results have not been validated or correlated to actual test data of speed, so no promises on accuracy.

[blindarcher]

Just a clarification to my original posting.  The second worksheet in the spreadsheet has Fmax in the proposed force versus draw equation.  Fmax is the same as Fd used in the remaining equations, and is the draw force at design draw length.

[crooketarrow]

  None of that matters much when a 4,5 year old 200# 10 point standing at 10,12 yards.

  Buy a chono NO force versus draw length data. Point on with your arrow speed.

[blindarcher]

Sorry, I can't relate to your point of view.  I don't hunt.  I do know that others have asked about the subject on this forum.  I was just trying to help.  Did not expect such a response.

[jeffp51]

There are two kinds of people here--those that do everything by feel and practical experience-- and those that really dig the numbers and the physics and the theory.  I guess there is a third kind (me) that likes a little of both.  Don't mind old Crooketarrow,  he is just the most firmly entrenched in the practical experience and primitive camp.  He isn't trying to offend.


 I can't actually follow your math (I am a language teacher) but it would seem that you should try your equations out and see if they have any resemblance to reality.  That is when it starts to get interesting.

[blindarcher]

Thanks for all your input.  I would put myself in both camps as well.  I have been building my own equipment since the mid 1960s, and enjoy doing it by "feel" mostly.  However, having degrees in Aero/Astro Engineering and advanced degrees in Aerospace Engineering, I thought I could offer some help to describing the physics to those who recently posted questions about this subject.  I honestly do not design and build my primitive bows with the attitude of a meticulous engineer.  Doing it by "feel" provides the needed balance to my life.  By the way, the physics is sound.

It amazes me on how people can assume so much about a person from knowing nothing about them.

"Once an Eagle, always and Eagle"

[bubby]

The math is a bit much for me, and don't mind crooked arrow he's rightband everybody else is wrong lol.

[Tuomo]

Nice charts!

I checked the second method. I filled the inputs with measured real bow values and the output was 137,5 fps when the measured value was 138 fps. This is not a surprise, because the bow-arrow dynamics follows the laws of physics, as your equations too.

As for predicting arrow speed without chrono, the most problematic value is bow efficiency, as it depends on arrow weight (arrow weight per draw force). It has to be guessed. But, I think that bow efficiency is possible to estimate quite accurately with a normal flatbow.

Here is measured values for one of my simple flatbow:

Arrow weight / draw weigth    Efficiency
9 grain/lbs                              57 %
11 grain/lbs                            60 %
13 grain/lbs                            63 %
19 grain/lbs                            68 %

Same problem is in first method. The bow efficiency is a function of arrow weight per draw force, so the chart underestimate arrow speed at short draw length, because the bow efficiency is not constant along the draw.

One more thing - how you define draw length? AMO-standard, to belly or to back of the bow?

By the way, please use SI-units... Or, make at least conversion tables, or both versions.

[PEARL DRUMS]

Sorry, I can't relate to your point of view.  I don't hunt.  I do know that others have asked about the subject on this forum.  I was just trying to help.  Did not expect such a response.

Pay NO attention to any of it. Its normal. Keep up the good work and mostly, enjoy it.

[bow101]

At the end of the day its mostly about Noise.  Lately I have heard 70db in string twang, limb vibration and whatever.  It does not matter about speed in a hunting situation when your bow is Screaming Arrow Fling... Shooting targets with your buddies is irrelevant.

[stickbender]

 
     Blind archer, thanks for the input, and listing.  Unfortunately, it is wasted on me as once I get past my fingers and toes, math becomes Greek astrophysics to me.  But there are a lot of opinions on this site, and you will step on toes, of some, and be in good company with others.  Overall the people on this site are good people.  Some are not exactly tactful in their expression of their personal opinion.  And sometimes a misleading interpretation is the result.  Anyway, most of us when we want to slam your post, or opinion, will leave no doubt.  But then you will still get supporters and detractors on the issue.  Anyway, like I said after I go through counting my toes and fingers, math is just gibberish to me.  Just don't have the wiring for it.  Would like to, but is a bit beyond me.  But your theory has merit in that it can measure the variables that a Chrono cannot.  But then like it was said it all comes down to what form of archery you are into.  Hunting, target, flight, etc.  Your post will be very helpful to some, and of little to no use to others.  Sort of like an omni directional time tunnel, and the theory of space, time, bending.  Anyway, I for one thank you for your post, and your time and effort to work this out.  I admire those with great math skills, as I have mental block, or missing neuron for that skill.  Thanks,

                                    Wayne

[bow101]

Everyone has their own opinion.  Some people say that I snap shoot.  So what Howard Hill was a snap shooter.  Even if you shoot FG bows does mean you have to hold anchor for 3-4 seconds.  That seems to spoil my shot.  One fluid motion draw ~ anchor ~ release with a good follow thru.

PS. not trying to steal the thread just saying, but who listens to who around here.  I ask 7 different people and I get 7 different answers.  At the end of the day its whatever style and method that works for you, thats all that matters.