There is a massive amount of information here and I have done my best to try and put some order to it. All italics are my text, the order of the text is not how it happened exactly. But that didn't make much sense either! So what I have done is try to discover Nicks current knowledge and lead him into a fuller understanding. The last part of this latest information does just this. I respect the fact that Nick has been so open and willing to publicly do this.

The Questions

a) what is a loop and how is it formed?

"Loop" is the description given to the shape of the fly line while being cast.  During to and fro casts this shape is visible on both the forward and back casts.  During continuos motion casts it is only seen during the forward section.

??? do you mean like roll casts?

Yep, continuos motion, roll cast, spey, switch etc.

Ok never heard the term. Mind you roll cast doesn't have to be continuous motion...

What else can it be? They certainly aren't to and fro.

Well you can set up a roll cast and wait 5 minutes before the delivery. That's not a continuous motion!

Yes I see your point.  But, I think that it is quite a nice way of splitting up the Speys etc.  Although you can wait 5 minutes to do a roll cast, most anglers would not and if you look at the whole cast there is certainly more "continuous" motion than "to & fro".  Do you see my point here or not ?

No, the roll cast needs a pause to anchor the tip of the line.

The loop is formed by the caster loading the rod with the line.  The rod travelling backwards/forwards in a horizontal position then tows the line backwards/fowards, in short the rod acts as a catapult.  Technique and to less of an extent, tackle, will determine how successful these loops are.

The loop is formed when the flyline passes the tip of stopped rod.

Right, but hang on here.  Technically your question is "how is the loop formed" which I answered above, several movements are needed prior to stopping the rod, right ?

Yes but you didn't mention the above bit :) and it's a really good thing to think about. The flyline is being pulled by the tip of the rod. The tip of the rod stops. the flyline passes the tip of the rod. A loop is formed. Forget about shooting line. This is absolutely key. This is flycasting. It's about loops. This is how the loop is formed. That one point, the moment when the rod tip stops and the flyline continues is so important.

See this.That's why it is good practice to take the rod in one hand, trapping the line with a finger and then practicing loop size by varying tip stops. Find this helps me relax my casting and provides some nice looking loops.

b) What causes a tight loop, open loop, tailing loop?

A tight loop is created by a small rod arc.  Tighter loops come from well timed double hauling and by speeding the rod up with an abrupt stop.

An open loop is caused by a wide rod arc, but can also be caused through bad timing.

A tailing loop is caused by the rod top dipping below the path of the line.  The rod top dips below the line through common errors such as uneven power application and miss timing the back cast.

A tight loop is caused by straight line path of tip   and open loop by convex path of tip. By matching the flex in the rod     to the size of the arc you can always throw a tight loop.    With a through-action rod or a deeply loaded progressive rod     you have to open the stroke to accommodate the increased flex.     Loop shape is determined by the path of the rod tip (although a low     backcast followed by a horizontal forward cast will also throw an     open loop)

I'm a bit lost here.  O.K., so let us take a rod that I have used, the T&T Paradigm.  Described as an "ultra smooth progressive action fly rod"  I have cast good loops with this, in my mind by slowing down my action to compensate for the action, yet still using a small arc.  I was NOT opening the arc.  This does not follow with your statement above. Can you explain further what is going on here. And Can you clarify the brackets.  I will play with this theory on the field tomorrow.

The brackets first: a low back cast will deliver either a high forward cast or an open loop. check out the 3rd drawing on this page

Will check in a mo.

There are two things going on. One you need to know, one is beyond apgai exam.

The one that you need to know is this... firstly I don't know how small your small arc is, but if you were to cast with half the amount of fly line outside the tip you would use a smaller arc still right? This is because you have half the weight and therefore the rod bends less. Less flex in the rod means that in order to get a straight line path the arc must be smaller... right? This is what I mean by adjusting the size of your stroke to match the bend in the rod.

Bingo! Got it. Explained simply this is why (some) beginners have such a problem when casting small amounts of line, their arc is often huge. However with a more experienced caster once the loop has been formed and sent on it's way the rod can be sent to the point required for maximum flex in the rod. Have I got it, or am I dreaming?

You've got it! :-)

The second thing that is going on here is not widely discussed. It's simply this: When we fly cast we do two things, we pull the line through the air with the tip of the rod - leverage - and we flex the rod by pulling it against the mass of line - the catapult effect. Both are important. An anchored rod in a field will not cast very far. A broomstick is also a pretty poor tool. The catapult effect is important since it imparts velocity as the rod straightens. That's the bit you need to know - it's how casting works and everyone should know this and why I've asked certain questions. So when you cast you are doing two things. You are moving the line in the direction you want to cast and you are storing energy in the rod which (when you make the stop) will be transferred to the line to get it moving quicker still.

Here's the crunch and is related to you slowing the stroke down. If you make the stroke too quickly what happens is that the line moves through the air and the rod doesn't flex as much. Most flycasters do this.They use too much leverage and not enough flex. Slowing the stroke down will allow the rod to flex and this is why you are getting narrower loops for your given arc when you slow down. The rod flexes more and the tip travels a straighter path.

Easy.

But I thought you said yesterday that the catapult effect had nothing to do with it. Your statements above fit exactly with my own thinking. I understand each section no problem. Where I am slightly confused is on the rod stopping section of your thoughts. When you make your initial backcast,where are you expecting the rod to stop? And then for the forward. What about for a fast rod, and a slow?

Give me some ideas about slowing down. Would I be right in thinking that casters who push are working on more leverage rather than flex?