Speed / draw length

[Morning Star]

Just curious.

Given the "same weight" at each length, what kind of gains do you get out of longer draw lengths?

Compare....say

50lbs @ 27"

50lbs @ 28"

50lbs @ 29" and so on.

[vermonster13]

About 4% per inch

[KSdan]

4% of what??

[WESTBROOK]

Dan, say 50@27" goes 170 fps. 50@28" will go 176.8 fps, 4% faster.

Eric

[Dartwick]

Wouldnt be more sensible to have a % of energy?
I know this an off the cuff estimation, but it just seems odd to use velocity.

[O.L. Adcock]

Yep, Bows put out KE...Looking at fps is like looking at rpm of an engine..It's not tied to horsepower...Any given bow will gain of lose about 4% every inch up or down. At 9-10gpp that works out to about 4fps.....O.L.

[Morning Star]

Thanks guys.

[KSdan]

Help me understand power stroke then. . ???  I thought the longer draw meant longer power stroke which meant more "horsepower"?  No??  
Appreciate an explanation.  

I am shooting 55# at 31.5".  How is that better than 55# at 28"?  

Thanks for educating me guys.

[vermonster13]

The arrow is on the string longer and thus absorbs (for of a better term) more of the energy from the bow resulting in more KE/Momentum.

[John Havard]

Stored energy goes up with each inch of draw.  Calculate the area under a triagle.  One has a 50# peak at 27" and another has a peak at 28".  One-half of the base times the height equals the area of the triagle.  A longer draw with the same draw weight has more stored energy than a shorter draw.  Simple.  

Therefore, with dynamic efficiency staying about the same at most normal draw lengths (see our website's description of "energy storage") then the longer draw length (at the same draw weight) will shoot the same arrow faster because it stores more energy than the shorter draw length.  

As much as we'd love to, none of us can fool Mother Nature or the laws of physics.