FOC

[morphymick]

Furface - 19/9/2005 7:31 PM

OK, on the basis that there is no such thing as a stupid question
What is "FOC"?

Forward of Centre.

It is the %age of the length of the arrow, "Forward of Centre" at which the arrow balances. See 2nd post on this thread for Determination of FOC.doc, includes a useful Excel titbit.

Mick

[Marcus26]

Sorry Joe I know all too well the AIS stance on FOC and their processes as I coach one of their shooters and visit there often. They do not measure it at the AIS, they don't care, full length points.
If they turned to my archers and told them to not use full weight points in their arrows then I would support their closure quite happily.

If you read my post carefully you will see my requirements for a well tuned arrow, these are recurve requirements and there isn't more than that. This has been backed up by Australian representative recurve archers in field testing.
Recurve Arrow flight is governed by matching bow poundage to the spine of the arrow. Compound arrow flight is governed by contact to the rest. No voodoo to it and no secret combination that will suddenly produce a 'forgiving' setup.

[joetapley]

Furface

OK, on the basis that there is no such thing as a stupid question

agreed - there are only stupid answers

If you download the (free) Easton Shaft Selector program (a useful thing to have anyway) it includes an FOC section including an arrow FOC calculator.

Unfortunately understanding the importance of FOC requires some basic understanding of mechanics. Just to present the highlights FOC affects arrow flight in two ways, it controls how drag forces act on the arrow and it effects the fishtailing/porpoising behaviour of the arrow. The basic rule is that the higher the the FOC the smaller the arrow groups become (this like all one line statements is a bit of a simplification). That's the reason elite archers will use specially made heavy tungsten piles, you get a few percent more FOC.

The one slightly dubious information you come across regarding FOC is to do with distance. In the Easton Tuning and Maintenance Guide for example Don Rabska says that FOC becomes important at longer distances (70/90m). This is not strictly correct. FOC mainly 'does its thing' in the first 20 metres of flight. However the further distance you shoot the bigger the error becomes in where the arrow hits from what happened in the first 20 metres. FOC is still marginally relevant shooting 18 metres.

[Mick]

"FOC is still marginally relevant shooting 18 metres."
Joe so it's not a complete waste of time to add loads of weight to my X7 2114 points for the indoor season? (shooting 29 1/2", 47lb on my fingers)

[Marcus26]

Unfortunately understanding the importance of FOC requires some basic understanding of mechanics. Just to present the highlights FOC affects arrow flight in two ways, it controls how drag forces act on the arrow and it effects the fishtailing/porpoising behaviour of the arrow. The basic rule is that the higher the the FOC the smaller the arrow groups become (this like all one line statements is a bit of a simplification). That's the reason elite archers will use specially made heavy tungsten piles, you get a few percent more FOC.

Having talked to a number of engineers about FOC and they disagree with you.

The one slightly dubious information you come across regarding FOC is to do with distance. In the Easton Tuning and Maintenance Guide for example Don Rabska says that FOC becomes important at longer distances (70/90m). This is not strictly correct. FOC mainly 'does its thing' in the first 20 metres of flight. However the further distance you shoot the bigger the error becomes in where the arrow hits from what happened in the first 20 metres. FOC is still marginally relevant shooting 18 metres.

Again, our top recurve archers have proven that the FOC is not important, the arrow mass is. What the heavier weight does at long range is increase your downrange velocity and prevent the arrow from being hit by drag closer to the target. A light pointed arrow starts off fast but gets moved off course easier. This all has NOTHING to do with FOC and all to do with mass. Result may be the same, but it isn't going to suddenly make you group better. You might reduce the effects of wind drift, but chances are the reason you missed the 10 last end would be the same next end.

Once again, grouping is determined by draw weight in relation to spine. You get this right and the arrow will straighten up very very fast and totally negate the reasonings you have for FOC. Too many archers fail to tune their arrows correctly and then try to hide the effect by messing with plunger tension and searching for the magic FOC percentage value.
My wife has been ranked #1 in Australia recurve and can change between spin wings and flex fletch without effect on her groups at 70m. This is with recurve. There is a few extra FOC % points right there.

I'm not an enginner, but I do train some top compound and recurve archers and talk alot with many others. Not a single one of them cares about FOC. None of them even bother checking what their FOC values are. Yet they are world class archers shooting over 1340 FITAs. (compound and recurve)
Now I may well be wrong in all this, but at the end of the day, the actual physical testing I have seen does not support you.

[joetapley]

Mick

so it's not a complete waste of time to add loads of weight to my X7 2114 points for the indoor season?

Well you will get a marginal improvement assuming you can get a good tune with the heavy points (That's why people do it). Result in most cases would be better by using cheaper carbon arrow e.g. ACC/Triple. The idea that very wide arrows are better for recurves (line cutting) is rarely true. The amount the better arrow will hit nearer the X for a given shot is greater than the difference in the diameter with the worse performing fat aluminium arrow.

[Mick]

Cheers Joe, think I'll stick with the ACEs indoors then. Less hassle

[joetapley]

Mick
Good advice from Vittorio F. on Sagi

This subject comes out every year, and many people continue to say that they switch to aluminum for indoor for budget reasons.
Well, In my club,for the same reason, nobody (recurve) changes anything at all. Affording a second set of arrows, a change of the arrow rest, a second plunger and string (if you want to shoot outdoor as well) is really too expensive not only in terms of money, but time, too. And, aluminum arrows are much more fragile than ACE/Navigator/ACC and bend quite easily, so need a continuous maintenance.

[TJ Mason]

The other side of this, though, is that the horrible hard materials used for indoor bosses can abrade carbon, leading to the arrows becoming steadily less precise. Not that you'd notice with my shooting...

[Marcus26]

Exactly correct TJ.
An archer I know tested his X10's before and after using them into stramit for 3 months. He lost 5 grains of weight per arrow. I did the same test with alloys and obviously lost nothing.