Arrow Speed Explaination Needed Please

[Badger]

     Lots of things you can do to improve the speed of your bow without becomming a speed freak. Start with a good string, if you want to stay all natural use a good quality linen for starters so you don't have to make the string too fat. This makes a huge difference right there. Your draw length is what it is but practicing good form will give you the best draw length you can expect and still stay accurate. A good release can make as much as 15 fps difference, common to see 8 or 10 fps difference just using a proper release and not creeping forward or slowly slipping it off the fingers. I have seen many bows go from 136 fps to 166 fps just by using a decent string and draw and release. I have always believed our ancestors did what they could to tweak out the performance a bit. Steve

[Del the cat]

To me the speed is an indicator of the properties of the materials used and the bow design.
Just for fun I've looked at speed divided by draw weight as a generalised sort of design performance indicator. (It does indicate you speed vs the peak effort you put in to shoot).
Basically the power put in is the area under the draw weight vs length curve, (The wheelies, or Asiatic composite ultra recured bows input most energy under the curve).
Of course what goes in doesn't necessarilly come out, which you will find if you make a bow with real long heavy limbs, also stability is better in some designs...longbows are generally smooth and stable.
Out of interest, if you look at speed/weight.
My Yew longbow (my fastest bow) is 169.7/75 =2.26   The experimental bow beats it 165/55 = 3
This shows that the flat bows are more a more efficient design (As clearly explained in TBB), and also the law of diminishing reterns, as you increase the draw weight, it becomes harder to gain speed, what you gain is power...e.g You can shoot a heavier arrow, which is only really relevant if you are trying to penetrate armour (or maybe shoot a Bear which is driving a car )
There are often too many variables to get a coherent picture, so sensible comparisons need to be made by looking at bows with the same drawlength or draw weight.

This Longbow is also beaten by several others, my Hazel bow and even the 'One Hour' rawide backed bow beatsit at about 3.4 ! , these have the same draw length as the longbow.
Why are these even higher than the experimental bow??? Probably due to the much longer draw, 28" against 24". If you subtract the bracing height, the actual 'power stroke' is 19" on the experimental vs 23" on the other two, which is about a 20% increase.

Having an engineering background I like to mess with this stuff, but it's easy to get a bit obsessive...but hey, I like drawing graphs.
To answer the original question your speed looks fine to me for an Elm self bow.
Don't get hung up on speed, else we'd all be making the same style bow. It's the properties of the different woods and design which is half the fun.
Who would want to make the same bow every time?...not this Cat.
Del
(BTW, The real reason I use the Chrono is that Mrs Cat doesn't like me popping over to the playing field to test my bows...   )

[Badger]

        Something else about bows to keep in mind is that heavier arrows will extract more eneregy from the bow and are always more efficient. An arrow that weighs only 5 grains per pound may extract less than 50% of the bows energy while an arrow that weighs 20 grains per pound may extract 90% of the energy from the same bow. Instead of plotting force draw curves I started just testing bows with extremely heavy arrows like 5 or 7 ounces. These will extract almost 100% of the energy and tell me how much energy a bow is storing. Some designs are better suited for lighter arrows while others are better suited for heavier arrows. Each civilization had a particular job expected from their bows and the bows were designed accordingly.
       I enjoy looking at ancient designs and trying to figure out what may have been expected from that particular bow. Steve

[George Tsoukalas]

That is a good tiller but I can't see how thin and trim the last 8 in are. Just looking to help for the next. Jawge

[Diligence]

thanks for the tiller comment Jawge.  I think I got lucky, but I tried to go slowly and be deliberate like El-D and Pat suggested.

Regarding the dimensions:

The bow is 65.5" nock-to-nock and 67" tip-to-tip.

The nocks are 1/4" wide, and the limb at the shoulder of the nocks are 1/2" wide.  The tip thickness at the nock shoulder is 7/16".

The width of the limbs at a point 8" away from the nock shoulder is 1-1/16" tapering evenly to the width at the nock shoulder.

The thickness of the limb at a point 8" away from the nock shoulder is 9/16" (measured from the crown of the back to the belly), tapering evenly to the tips.

Both top and bottom limbs have the same dimensions +/- 1/32".

I'm using a home made 14 strand b50 string with beaver ball string silencers.

Cheers,
J

[George Tsoukalas]

Dilligence, that sounds good. You'd be surprised how much you can narrow those tips. Took me years to get up the courage and it happened quite by accident while making a bow. I just accidentally narrowed it more than I thought I should have. The bow shot quickly. Jawge

[Diligence]

On the next bow I finish, I am planning on trying to go very very small at the nocks to minimize mass as much as I can,  and use a sinew wrap to hold the string in place.....but we will see how it turns out, might be an adventure.

[tetaxidermy]

I have killed deer with wheelies and fiberglass recurves not self bow yet, this year hopefully, but from experience a slower quiet arrow beats a fast loud one any day. Shot placement is key not speed. If they can't hear it coming they can't jump it.

[TBod]

Using a chrono can be very addicting. Soon you will find the need to buy your own. I`m totally hooked on it`. Just a warning