fly line speed

[hairwing]

Can anyone give us an idea how fast in layman's terms (mph) a fly line is moving during a normal say 30 to 40 foot cast?

And at the crack of a missed-timed backcast is the fly moving at the speed of sound (768 mph)?

[Bobinmich]

Hair

Around 80 ft/sec (55MPH) would ball park it. This is at the start of loop formation. Depending on the drag of the fly, the fly line can actually increase in speed as the loop unrolls. Distance casters speeds are much higher sometimes approaching 200 or 300 ft/sec.

The crack in a missed time cast is a sonic boom. Same as in a bull whip. The direction change is such that the tip swings around and actually breaks the sound barrier. That's why the fly sometimes parts company with the rest of your gear.

Bob

[WarrenP]

Now that we know that fact, is there anyone who questions how a beaded fly can destroy your fly rod when it strikes it on the forward cast????!!!

[rainbowchaser]

Of course thats for a decent caster with a reasonably fast rod. For me with an old South
Bend boo it's more like eighty feet a day. If someone will hold the rod I can take time out for lunch between the backcast and the foreward cast.

[BSwan]

... If someone will hold the rod I can take time out for lunch between the backcast and the foreward cast.

Fine, I'll do it. I'll also bring the salami sandwiches.

[rainbowchaser]

Hi Bob. Are you dug out yet? I think you should have left this snow with Marco on the wrong side of the lake.

[hairwing]

Thanks Bob,
You've got me thinking now. The fly line actually speeding up went over my head. Is the reason this happens because the force remains the same but the weight of the moving top half of the loop decreases?

Been thinking about this while repairing my frozen plumbing. LOL.

HW

[OliveScud]

The line speed should be increasing because the casting stroke is a smooth acceleration. As one accelerates, the rod is going to bend and store energy (like a spring). When you get to the end of the casting stroke and stop, the rod is going to unbend and release that stored energy, causing the final acceleration.

Just think of sitting on a compressed coil spring. As it uncompresses, you are going to accelerate that whole time until it's completely extended.

The reason distance casters can cast with so much speed is they can get the rod to bend a lot farther than most.

[fishbum]

There is no acceleration of the line after the stop. Once you stop the rod you stop adding energy to the system and acceleration stops. The unloading rod just keeps up with the line and gets out of the way as the loop forms. There is some acceleration towards the center of the loop but that does not contribute to the the speed of the fly line that is behind the caster and moving forward.

fishbum

[Bobinmich]

And that is what I thought too, fishbum. Got into the physics of it when I read some articles by Noel Perkins and Bruce Richards. Turns out, energy is not being added to the loop but it is already there. As the loop turns over, the kinetic energy of the moving line segments that turn over and stop is transferred to the part of the line that is still moving. This translates into a force at the end of the moving line ahead of the loop and is resisted by the aero drag on the moving line and fly. Add to this the fact that the mass of the moving line is also decreasing and viola, F=ma and if F is constant and m goes down, bingo. The physics is relatively complicated but if you like, I can dig up some of those articles. If you have someone stand out to the side and you cast a nice tight loop w/o a leader or fly, you can actually see it speed up by watching the loop which is traveling at 1/2 the line speed. I thougth it was nutty too until I started playing with the equations. There are some real physics mavants over on Sexyloops but you will have to deal with some (one in particular) real narcisists. I don't go there anymore because of that.

Bob