Holy DFC Batman...

[williwaw]

  Yah kinda lost me Willi...  Maybe you can give me an example in numbers how bow efficiency is measured and how I can use that to make a faster bow...  If it makes sense to me I could use that as a tool also...

Shredd,

If you are shooting lightweight arrows, flightshooting for instance, or building short bows that stack, then you might concern yourself with efficiency.  Basically you would measure the arrow weight and speed and calculate the energy it has. This energy compared to a "perfect" dfc gives some idea of how efficient the limb is. 

[avcase]

Willie,
This is a good explanation of the importance of dynamic efficiency.

A bow with very high dynamic efficiency is able to safely shoot low ggp arrows because very little energy is left behind in the bow.  So dynamic efficiency will probably influence where you decide to set the minimum arrow weight requirements for your bow warranty.

A bow shooting 3ggp arrows at 80% or better dynamic efficiency has a good chance of lasting many thousands of shots with no ill effect.

Alan

[Mad Max]

 This is a question I asked the guy in the picture holding the  Manchu composite bow

Question--There is a topic on Trad Gang forum about this bow, some of them are saying the DFC is very inaccurate and all over the place. Can you help them understand? Question from me The two 14# gains at 13/14", is  that the point when the string lifts off  the bridges ?. I love it myself. Thanks

Answer--Yes indeed, that's where the string leaves the bridges, giving it that distinct two-stage draw.

People say a lot online, haha. This graph has been questioned a lot but people with similar bows came to similar results. It's inherent to this design.

But I must admit the first time I pulled one I was also quite flabbergasted, once you get over the hump it feels like letoff.

It's not actually letoff of course, but as your body gets in a better position to pull it, it gives the perception of being lighter.

[Shredd]

Looks like he misunderstood your question about the graph being accurate...  I think he assumed you were saying people doubted the shape of the curve in the graph...  Just to be clear... I am not doubting the general shape of the graph, it's just not totally accurate that's all...  You can draw a circle freehand and you can draw a circle with a compass...  Let's just say that graph was drawn freehand... Nothing wrong with that it's just not accurate and you really can't use the numbers to compare to another bow with a similar dfc...  It would kinda be like running a drag car and having a guy at the end of the track counting and not using a stopwatch... 1 mississippi, 2 mississippi... You can't compare the two cars times fairly... I know I am speaking chinese to most out there because I have never heard of anyone else comparing a bow's numbers from a dfc with another bow except for myself... Most just look at the curve and compare curves...  Most are not concerned with the numbers, to them the numbers are just there to make the curve and that's about it...

[Mad Max]

No

This graph has been questioned a lot but people with similar bows came to similar results. It's inherent to this design.

[Shredd]

Yeah, so... What's your point??   Guess you don't understand Chinese...  I could hand draw a bunch of graphs that look similar...  I look at all this from a perspective of performance... That's why the the graph was created in the fist place... When you make a bow you are so concerned about a thousandth of an inch... A couple of extra thou here and there could make or break a bows performance... You worked so hard and was so accurate in making that bow bend perfectly... Now that you got it bending perfectly lets record exactly how the limbs are bending on a graph... I ask you... Should you record it as accurate as possible so you can compare it to other bows, in the possibility of improving performance?? You say, No... It's okay just round it off to a half an inch...    Makes perfect sense to me...     

[Shredd]

Mark...  Go back to the beginning of this thread and look at the reason why this whole thread was started... Why the heck did this guy take the time and effort to make a super accurate dfc?? He doesn't even know yet... I could tell by the way he talks that he is inexperienced with them... But he is smart enough to know that making an accurate dfc is important and a step in the right direction...

[Shredd]

Sometimes it sucks being in world where no one understands your language...    

  Wait until y'all see my latest discovery on the smoothness of draw of bow limbs...  And yes, it takes some understanding of a DFC, which will be explained...  And Yes...  To see what is exactly going on, you need an accurate DFC...    

[Shredd]

Here is another analogy / riddle that may help you understand...

   You have two nice high performance cars...  The original car was painstakingly made by the manufacturer...  The second car was a knock-off of the first and they cut a few corners but the car looks great and looks exactly like the first car and even has the same engine and transmission... However at high speeds the first car is faster and seems to ride more smoother and better on gas consumption...  Now to you everything looks the exact same...  Even the Lines and Curves look exactly the same... 
  Here is the riddle for you...  Can you tell me what the difference is between these two cars??  Can anyone of you solve this riddle??

[Mad Max]

If you read the article the bow was built because people were saying horn bows are not that fast. This horn bow needs to be 80# or more to preform and it did.
You can t compare to any thing except another horn bow.

Maybe I should have said Check out the poundage gains on this horn bow?
The original bows were built to cast a heavy arrow threw more than 1person.
The DFC was done in today’s world because, why not do one.
I have asked you if you read the article but you did not answer?

[Roy from Pa]

I'll have to call and ask the ole goat..

[avcase]

Looks like he misunderstood your question about the graph being accurate...  I think he assumed you were saying people doubted the shape of the curve in the graph...  Just to be clear... I am not doubting the general shape of the graph, it's just not totally accurate that's all...  You can draw a circle freehand and you can draw a circle with a compass...  Let's just say that graph was drawn freehand... Nothing wrong with that it's just not accurate and you really can't use the numbers to compare to another bow with a similar dfc... It would kinda be like running a drag car and having a guy at the end of the track counting and not using a stopwatch... 1 mississippi, 2 mississippi...

Very well stated!

I agree that the general shape of the force draw curve is believable, but the data doesn’t support the arrow speed or bow efficiency numbers that are reported with it.

Alan

[Shredd]

  Thanks Alan... 

  Mark...  I read this article years ago and I think I have read it a second time since then... Now I just touched over it again... 

 First off... Don't bet your house on everything you read...  Who is this expert any way...  How does a bow jump from 2# down to 1.5# back to 2# and then up to 2.5# back down to 2# on the DFC...  For the life of me I have never seen this before, actually I probably have...  Second...  Shooting that heavy an arrow at that speed doesn't sound right...  I am not gonna believe it or disbelieve it, it just does not sound right to me...  Third... This rule about heavier bows not shooting a lighter arrow fast, I believe applies to most bows...  I have heard your fastest fiberglass bows are around 50 to 60#...  Anything heavier the limbs start getting too heavy to shoot a 10 gpp arrow fast and start slowing down...  Fourth...  I have a huge respect for these composite bows...  I am amazed how they engineered these things back then...  And last but not least...  The DFC is fine...  It looks pretty much like what a bow that style would produce...  It's just not accurate, which is fine...  95% or more of DFC's out there are not accurate any way... 

   Ok...  I am over this...  If anyone can't solve this simple riddle that's Ok too...  Alan...  What about you??  Can you solve the riddle??

[Shredd]

He who completes the riddle will gain enlightenment to the DFC...  I Guarantee...  Or you money back...   

[avcase]

He who completes the riddle will gain enlightenment to the DFC...  I Guarantee...  Or you money back...   

What is the riddle again?  Is it the assumption that a heavy draw weight bow  (for example 100#+) will not shoot a 10ggp @ 28” draw arrow as quick as a 50# bow? 

The heavier bow will have the advantage with an identical ggp arrow most of the time.  This is especially true for shooting lighter arrows. It depends on the mechanical properties of the materials used, bow design, and ratio of draw weight to draw length. An all-wood bow and unidirectional carbon backed bow may not show a big difference at lower versus higher draw weights. A glass bow will generally show higher efficiency at higher ratio of draw weight to draw length. This is why an Excalibur recurve crossbow with solid glass limbs can have a higher dynamic efficiency shooting 1ggp arrows than some 40-50# glass or carbon backed recurves shooting 10ggp arrows.  The effect of the ratio of draw weight to draw length is even more pronounced with sinew-wood-horn composite bows.

Or is the riddle about the two cars, where the horsepower and torque curves are the same, but high speed performance and fuel mileage different?  This indicates a difference in dynamic efficiency.

Alan

[Shredd]

Yes... The riddle is about the cars...  All the mechanics are the same...

  I will read what you have to say about heavy weight bows later when I can contimplate on it...

[Longcruise]

IF two identical bows are constructed,  one 50# and the other 100#, it's my opinion that the 100# bow can't possibly shoot slower than the 50 given 10 GPP arrows.

So,  my riddle for y'all is why would this be so...... if my opinion is correct.  It’s a riddle in a riddle with a side of conundrum. 

[avcase]

Yup.  You may not see a huge difference with a 10 ggp arrow.  The gap in performance grows exponentially with progressively lower ggp arrows.

Alan

[williwaw]

A glass bow will generally show higher efficiency at higher ratio of draw weight to draw length. This is why an Excalibur recurve crossbow with solid glass limbs can have a higher dynamic efficiency shooting 1ggp arrows than some 40-50# glass or carbon backed recurves shooting 10ggp arrows.  The effect of the ratio of draw weight to draw length is even more pronounced with sinew-wood-horn composite bows.
Alan

Does the advantage of the higher efficiency limb come from working at a higher stress?
Or perhaps such a limb, when working at a higher stress, can store the needed energy with less mass?

[Shredd]

So, you are saying the statement is false... It is what I have heard and I believe most of the bows in the WTT contest were in the 50 to 55 lb. range... Why wouldn't someone make a 70 to 80lb. bow and blow the doors off the competition??

  And you are also saying that 100# bow is definitely faster than a 50# bow with 5gpp arrows with both bows being of the same design??