Lift force acting on a fly line

[Graeme H]

A bunch of boring tethered loops:



A bunch of boring casts with shooting line:



Enjoy.

Cheers,
Graeme

[Dirk le Roux]

Thank you for sharing both the velocity and acceleration vectors, Graeme.

The purple and red paths tell tails' orientation at the time, the fluff having mass, appear to be influenced by motion dynamics and direction of acceleration at top of the loop and as such are not a direct reflection of the relative airflow there, which should be more parallel with the velocity vectors?

Regards,
Dirk

[Graeme H]

Yep, torn between the need for no mass and the need to be able to see them. If you have an idea for a material that is robust enough to cast, visible enough to see and light enough to not be thrown around, I'm all ears. Easy enough to reshoot.

[gordonjudd]

Graeme,
Thanks for taking a shot that shows the direction of the opposing wind vector on the inclined section of line.

You can see it has an upward tilt, and thus will produce some +y lift just as Torsten showed in his diagram.

No pixies required.

Gordy

[gordonjudd]

So what does Newton's Third Law of Motion suggest about that? I believe Newton would say "If tension in the string is pulling something down then something is pulling the string up."

Graeme,
And of course the opposite is also true. If the angle of the rod leg has some positive angle as it did at that point in the Rowen's cast then the rod tip is pulling down on the line. That is the counter example that shows the upward lift on the loop could not come from the force from the rod.

Does that make sense to you?

Gordy

[Torsten]

Graeme,

That's interesting. The proposed attack angle (α) at that point is well in excess of 20° there, maybe 45°. Can you explain why you think lift might be occurring there? Which direction and velocity do you think the line is traveling there? The tell tales here and the tracking data I've worked with show the line surrenders the vast majority of its forward movement at the loop nose. Or are you saying this because the line is moving downwards and there is resistance to movement in the vertical sense?

Both skin friction and and form drag contribute there to an upward force component (e.g. your indicator is not parallel to the line).
We have usually two components; one tangential directed (skin friction) and second a normal to the surface directed component (form drag).
Or to make things simple: friction is directed against the movement - so if line segments move downward you can expect a force in opposite direction.

The magnitude is another question; that's why I'd like to have measurements for these points.

Sorry Torsten, but you implied that to be the case in your first post of this thread with this sentence:
If you can spot a section of a fly line in a video, with an inclination and you know the velocity, you can compute the lift force.

This is still the basic idea; but it needs to be adapted to the relative flow velocity direction. Goal was to check first, if there is a relevance and compared to the gravity we can see a significant influence for some cases. We know that line speeds ~30m/s are possible, and so further research is useful.

Your goal may well be to quantify a lifting force for certain cases, but if we can't demonstrate those conditions even exist in a cast, why give people hope that there is a case for lift in a cast?

Don't agree, it's very likely that such conditions exist. Simplest case is casting against the wind.

The conditions discussed in the referenced paper are not honoured by line in the rod leg. If someone thinks they are, please explain where it exists in the cast and one of us can devise an experiment to prove those conditions are met (or not). The only place I can find those conditions is in the leading edge of the fly leg, but that would force the line down, wouldn't it?

.. relative flow speed, you have to adapt it to the direction. As I've written I'll extend the simple equation - input parameters are then the velocity and position vectors of two markers and output is then the resulting force or better forces. I think I'll write that down on the weekend.

Okay, well who is doing this work? Is it going to be peer reviewed? How long before the results are published?

This was a proposal for a systematic approach to our work.

Because I've often read this killer argument here: The (traditional) peer review is used to determine if a paper is appropriate to publish in an academic magazine. First I don't think that the innovation level is high enough for publication and second I think the review process is flawed - opaque, not transparent, slow. There is in my opinion no warranty that such an review process would improve the quality of the publication (for our purposes). I'd support the idea of an open peer review and that's basically what we're doing here.

Call it handwaving if you like, but at least we can see evidence of progress by doing experiments.

We made progress by the overall contribution of the members, not just by the experiments.

So far we're up to 27 pages of discussions without any support for the proposed lifting force. Ockham's Razor suggests that we have 26 pages more than we need.

Now 29 pages .. that's a compliment for me and shows the interest in the subject. So thanks to all.

[Graeme H]

Hi Torsten,

Placing the results of your work here on SL is publishing. The peers are the people who contribute here (and those who read this but won't post.)

You have enough people who think there is lift. These people should do the scientific research work to support their view.

You have enough people who would critically review the work you do.

You have a platform on which to publish.

So I suggest the systematic approach you are proposing should be enacted. Someone who believes in this must get team together and get started.

Cheers,
Graeme

[Graeme H]

Graeme,
Thanks for taking a shot that shows the direction of the opposing wind vector on the inclined section of line.

You can see it has an upward tilt, and thus will produce some +y lift just as Torsten showed in his diagram.

No pixies required.

Gordy

Gordy,

Yes, I can see it has an upward tilt. I put it there intentionally to give the theory the best chance of being proven.

Did you watch the video? Did you miss the part about shooting line into these casts? The rod leg is moving forward in these casts, unlike in every other example we've been discussing for 29 pages.

Did you observe the rod leg falling in every shot cast? Shot casts are the only example where the conditions for Torsten's diagram are met, and yet the rod leg falls out of the sky like a stone. Pixies were required but they were missing in action here.

How does that compare with the tethered casts, where I maintain tension in the rod leg but still develop a sloped leading lower edge of the loop? They both have inclined leading lower edges in the loop. The shot cast has more form drag in the rod leg than the tethered one. And yet, the cast with more form drag falls faster than the one without.

What is the crucial element missing in the shot casts that keeps the rod leg suspended in the tethered casts? (I'll give you a clue: It starts with the letter T.)

Cheers,
Graeme

[gordonjudd]

You have enough people who think there is lift. These people should do the scientific research work to support their view

Graeme,
What is your reasoning that says the fly line wind gauge experiment does not show there is lift on an inclined section of line just as Torsten descrubed in the opening of this thread?

I expect you understand that the steady state tilt angle of the line is achieved when with torque from the upward force from form drag balances the opposite torque produced by the downward force of gravity. Thus as the velocity of the incoming air stream increases the tilt angle required to get a torque balance decreases just as Torsten described.


To me that experiment does just what you are asking to see although the concepts involved are so basic I would not characterize that experiment as "scientific research".

Gordy

[Paul Arden]

I’m pretty sure that casting into a strong wind will create some lift on the loop, as maybe even would shooting line, but after the line has turned the nose of the loop on a non-shooting cast it has for all purposes stopped all horizontal movement.

Perhaps aerodynamic lift explains why the nose of the loop can travel to the top of the loop, as Merlin wrote somewhere, but most of the line in the fly leg is just hanging there.

Anyway I’d be very interested to see if lift or DOG can actually be proven due to aerodynamics and not trajectories. Trying to isolate the two is going to be challenging especially when trajectory (line inertia) appears so dominant.

Cheers, Paul