Anyone want to explain the physics why increasing FOC will decrease trajectory, given constant weight, velocity and arrow dynamics. Thanks for your input.
I can find bits and pieces of info on FOC and trajectory on internet, but I prefer to to have TradGang members explain it.
http://tradgang.com/noncgi/ultimatebb.php?ubb=forum;f=24
There is actually a whole section of this website devoted to Dr Ashby and his studies.
It's pure physics at it's best. One of the best arguments I've personally heard and can grasp onto is that having the balance point farther forward gives the fletchings a longer lever arm to control flight.
Just wanted to add, I feel a well tuned Lower FOC arrow will out perorm and probably out penetrate a poorly tuned Higher FOC arrow and obviously you need a really sharp broadhead to cap it all off:)
Have utilized 32% Ultra-EFOC set-ups and have not encountered abnormal trajectory vs. normal FOC arrows of similar wt.
Inclined to believe that utilizing 5 1/2" feathers would experience such a substantial increase in drag due to Ultra-EFOC that excessive drop would be the result.
Agree with Friend, both points. I have not seen high or extreme foc setups drop more. In fact since it stabilizes quicker do to the longer lever arm working on smaller fletch it may shoot higher.
Some build a high foc arrow and result in a very heavy arrow and complain it drops lock a rock. With light weight shafts you can get high foc and remain 9-10gpp.
I know I've been up to long but I'm having trouble wrapping my brain around how foc effects feather drag. Wouldn't the drag be constant regardless of arrow weight dynamics?
My observations with going EFOC...And I ain't no rocket surgeon..
With EFOC, The point is less effected by the drag of the fletching... I think of it as the balance point (is moved farther forward towards the tip...) is where the arrow pivots as the tip and fletching work to oppose one another.... so in principle it takes less correction from the fletchings to correct the arrow into flying straight because the fletchings get a longer lever... Thats why many EFOC arrows can get away with lil 3in fletchings... With less drag and I believe that it flies straighter quicker as well...
It will out penetrate a low FOC arrow... and that was the draw for me... as I had hurt my shoulder and was shooting my Turkey bow well, but my heavier deer bow not so well...
I went to EFOC and began getting better accuracy and much better penetration!!!
Just my observations and experience...
I have be shooting arrows between 22% and 25% foc, don't remember if that is efoc or not, just know it makes it heavy up front. It allowed me to get the light carbons up to 10 gpp. Arrows fly as flat as any I shoot. I'll compare it with some aluminums with 125 gr. tips when the rain stops. see if I can tell any difference.
This is a link to Tuffhead's site and some audios of Doc Ashby speaking at kalamazoo.
http://www.tuffhead.com/education/kalamazoo%20jan%202012.html
If you go dow to "EFOC Offers Many Advantages" he talks briefly about trajectory and why it is affected by FOC and other aspects about FOC.
Thanks JimB, apparently FOC can have a flatter trajectory due to it coming out of paradox faster. The bottom frame of Ashby's talks is the "EFOC Offers Many Advantages"
One test I did was to set up paper between me and the target 30yds away. I set it high enough that I could still see the target. Since I shoot gap it allowed me to test the arc of the arrows. Both arrows weight was 800gr. One with 12% FOC, the other with 33.3%.
End results were the lower FOC arrow punched a hole thru the paper alittle over 3" higher than the high FOC arrow. Both arrows were pretty close to side by side in the target.
Troy
Troy,
That's interesting... That would mean that the EFOC arrow shot flatter than the standard. I wonder how far out that trend lasts. At some point, the heavy point surely must start to pull the trajectory down hard.
I've never done testing but I have noticed that some heavy pointed arrows will fly great initially but at some point, it looks like the hand of god reached out and slapped it to the ground.
I usually do not get into this subject but will add what I have noticed. I do not see any real difference between my FOC carbons and my alum. arrows of same weight at ranges out to 40 yards. I do have 4in feathers on the carbons and 5in on my alum. arrows. So I am happy because both bare shaft very well.
M60,
That's why I did the test. Until I did the test I would have thought there wasn't a hill of beans differance. Three inches isn't much and I never tried it any futher because I don't like to shoot much futher than that.
I didn't try it any closer because I couldn't see the target and didn't want to have obscured results. Thirty yards was the only distance that worked for me to do the test.
Troy
Troy, I like shooting 3d and that is why the 40 yards. It would seem to me at hunting yardage, say 20 yards at the most, the difference between the two shafts would not be an issue. Then I guess we would consider the higher FOC in relation to penetration. Maybe that is where my liking skinny shafts comes in along with high FOC. IMHO that is the best combo.
At some point, the heavy point surely must start to pull the trajectory down hard. Dave
I believe this is a common misconception, gravity pulls at the same 32 ft/sec/sec for both 800gr arrows.
As velocity slows the farther the arrow flies, wouldn't the arrow with the bulk of it's weight shifted forward drop more at the front of the arrow shaft? Not trying to argue gravitational pull, just trying to understand how weight placement on the shaft wouldn't have an effect on flight when done to the EFOC extreme?
With a bullet easy to understand, but an arrow is more like an aircraft with the fletching being like small wings that help steer. Heck I don't know?
Gravity pulls at constant acceleration on objects, the front of the arrow and rear drop at the same rate.
Remember the test done on an Apollo mission where the astronaut dropped a hammer and a feather in an environment with very little air resistance, moon surface, both fell at the same rate and hit the dust same time.
I realize that gravity is a constant but I also believe that in actual "air" here on earth, the fletchings act almost like a wing and will "plane" through the air and thus either through lift or drag (take your pick) will have an effect on the arrow flight. Yes, I do realize that due to offset and or helical, while one fletch is lifting, another is diving which is what gives us rotation but sheer air resistance will hold the back end of the arrow higher than the front due to surface area differences.
Initially, the fletches are almost holding the arrow point back. That is, they are being drug through the air by the heavier point end. As the arrow looses speed, drop becomes more evident even though gravity is constant. As an arrow slows down it appears to fall faster but really it's just not going as far in the same time. Depending on the FOC, the arrow may drop "level", or it may drop nose first because of the difference of surface area and air resistance. A balanced arrow should drop fairly level but one with a heavy point will drop more tip first. Since virtually ALL functional arrows are heavier in the front than the back, we are used to seeing them drop point first but if the balance were farther back, they could be made to land flat or even tail first.
In extreme high FOC arrows, the balance point is nearly at the back of the head so the fulcrum is right up there too. When speed is sufficient, it'll drag the tail of the arrow level behind it but as speed drops, the balance point becomes the "heavy spot" and will start to fall while the lighter tail kinda "floats" due to lesser weight and greater drag. This is the point at which I think the heavy point will start to drag the arrow down suddenly.
I'm willing to concede that it may be an optical illusion though because it might just be a matter of the arrow "appearing" to be pointed down as opposed to a more balanced arrow that might be dropping at the same rate but you still just see that spinning ball of feathers and not the shaft taking a nose dive. I've never tested side by side with equal weight arrows of different FOC's. I honestly don't care enough to bother. I like the way cedars fly for me, I think carbons are amazing to shoot. In practice, I'll shoot either but if given only one choice, I'd pick the cedars just because I like 'em and they're certainly good enough for what I do.
Mind you some would say I only squeaked by my engineering physic classes :biglaugh: , but I THINK this is how it works. All objects ACCELERATE toward the earth at the same constant rate. Objects do not DROP at a constant rate, but rather ACCELERATE in a perfectly downward direction at a constant rate through the time of fall/flight. The longer the arrow is in flight the faster it is going toward the earth. The resultant velocity/force however(the sum of both horizontal and vertical aspects of the velocity/force respectively) will be less than the original velocity as well as determine it's flight path. This of course is within reasonable velocities.
A higher FOC is generally associated with a heavier arrow so it moves slower and therefore stays in flight longer prior to reaching the target. This "time of flight" affects the time in which the downward acceleration acts on the arrow. The longer an arrow is in flight the "faster" it is dropping by virtue of its downward acceleration. This flight of the arrow therefore creates velocity/force vectors, both horizontal and vertical components which are added together to produce a magnitude and direction resulting from both components.
The higher the downward velocity vector AND the lower the horizontal velocity vectors are (more time in flight), the more the resultant force/velocity points downward giving the perception that the arrow's point is dropping faster than the back. It is, however, not due to the FOC, but more so the resultant velocity vectors.
Hope this makes sense.
awbowman, sounds good for different mass/speed arrows, OP specified different foc with same weight 800gr arrow.
Now take the 800gr high foc arow and put tiny A&A fletches on and compare to the normal foc 800gr 3x 5". I would think the high foc would drop less at distance since it stabilizes earlier and retains more energy.
Here are my unscientific results to testing foc and efoc. I shot three arrows ICS Bowhunter 500's with a arrow weight of 535 gr, with 250 gr, upfront. Easton 2018's with 125 gr. up front and a total weight of 565 gr. And one cx heritage 150's with a total weight of 500 gr with 250 gr. upfront. I shot a group of 5 ICS, 2 Eastons and 1 cx per group. I could not find nay difference from 20 to 40 yards. Except for the brain fart fliers the arrows grouped well enough to not matter. At 40 if I had to call teh good shots ( and at 40 I am not good) the ICS's grouped about an inch or two higher. The Cx was about 6" lower. Total mass seemed to mean more than foc.
Is there data out there measuring trajectory with a "bow machine" for arrows with the same weight, same velocity, same profile, only different FOC?
QuoteOriginally posted by gordydog:
Is there data out there measuring trajectory with a "bow machine" for arrows with the same weight, same velocity, same profile, only different FOC?
This would be the test I'd like to see and I'd like to see it done into a test medium to study penetration too