Glider stability fin design

[gliders]

Any rocket scientists about ? I've recently been re-designing and refining some of my gliders that have tail fins for stability. Having used rounded manatee style fins which work well,and recently tried various rocket fin shapes with similar results, I'm inclined to think that technically the rocket shape fin ,all else being equal,and not considering aesthetics should be a more efficient shape. Any thoughts anyone? 

[gliders]

Unable to upload pics to illustrate, can someone remind me of rules for doing so? Says only allowed  0.42MB.  Is there a limit on picture size ,quality or quantity per month or suchlike ?

[SW Lures]

Yes there is a limit in the size Gliders. However here lately I have been able to load off my phone rather then using Photobucket. I used this to reduce the size from my computer. Some phone's can reducer the size while taking the pic. As far as the tail, don't know.

Dale

Edited April 25, 2017 by DaleSW
Added to comment

[gliders]

Thanks dale,not had any issues till now....glider

[Musky Glenn]

My thought was, do we really need any fins? A lot of good glide baits don't have any fins. Weight placement might be the answer. $.02

 

Edited April 25, 2017 by Musky Glenn

[gliders]

Musky glen,the gliders I make for my own use have no fins. They are however built on the edge of stability to maximise glide, if not worked precisely they are very unforgiving. With slight modifications and the addition of a fin they become far more forgiving if your not experienced working them. They tend to hold an even depth better which I find good for boat fishing. Personally I prefer without fin for my own use more often than not. Friends like my finned version cause it's easy to use. I should add ,I'm not talking about glider stability regarding lure shape or ballast or anything else, purely fin shape theory  if a fin is used........glider

Edited April 25, 2017 by gliders

[mark poulson]

16 hours ago, gliders said:

Musky glen,the gliders I make for my own use have no fins. They are however built on the edge of stability to maximise glide, if not worked precisely they are very unforgiving. With slight modifications and the addition of a fin they become far more forgiving if your not experienced working them. They tend to hold an even depth better which I find good for boat fishing. Personally I prefer without fin for my own use more often than not. Friends like my finned version cause it's easy to use. I should add ,I'm not talking about glider stability regarding lure shape or ballast or anything else, purely fin shape theory  if a fin is used........glider

Are your fins vertical or horizontal?

[gliders]

Horizontal mark,in practical terms there's nothing really between them, the manatee style is probably more aesthetically pleasing though. Theoretically I would have thought rocket type should be more efficient . Dont seem able to make pics correct size to illustrate, no probs till now. Is 0.42mb always been max size ? Must be missing something,not good with such like! 

[gliders]

[gliders]

No idea how that worked ! 

Edited April 26, 2017 by gliders

[mark poulson]

It looks to me like the horizontal tail fins act as a planing surface, giving the tail of the bait more lift on the pull/pause.  Kinda like the planing plate people put on their outboards to help their hole shot.

Could you change the angle of the tail fin to get the bait to rise or fall on the pull?

 

[clemmy]

Gliders:

I think tail fins are about stability. If the body starts to drift to a side, the surface area of the tail fin helps to resist that action. The righting force would be dependent on surface area of fin, speed and distance of the fin from center of motion in that plane.

 

I think rocket style fins are shaped to try to avoid increased drag while still providing stability.

 

Mark:

 

Yes, some baits actually make the tail fin out of metal to make it user tunable for that reason. The most obvious example likely is the classic musky bait the "Suick".

 

[gliders]

Mark, you could. This style of fin as clemmy says is about stability. Clemmy- thats what I'm talking about,for a given size/surface area you would think rocket shape fin should be a more efficient shape for stability /minimal  drag. In practice I dont see much difference. The  more rounded style is maybe  a little less prone to damage and possibly more forgiving  .......glider

[Anglinarcher]

Quote

 

Gliders, this is another one I almost don't want to get involved in, but I can't help myself.  Sorry.

As an engineer, and an avid archer, this question has haunted me for a long time.  A ballistic rocket, like and arrow, is not a bad analogy to the glider issue, except that you have a boundary layer, water/air, to deal with that arrows and rockets don't have.  That boundary layer would determine how you orient your fin depending on if your bait is yawing, rolling, or pitching.

The problem is that the answer to your question is "it depends".  OUCH, I know that is a bad answer and I am sorry for it.  There is no 'one' answer to all glide bait designs.

Lures like the Suick use the tail fin as a control surface, not as a stabilizer.  The adjustability is nice but the use is different.  The Suick tail fin is designed to stop the dived lure from backing up on a dive but to rise head first and glide forward.

For giggles, I am going to give you a link to a friend's video and how he determined he need a stabilizer for his glide bait and how he determined how to do it.  It might give you some insights, but it does not tells us why he also chose the 'rounded manatee style fin' instead of another style. 

http://www.makelure.com/store/pg/54-How-To-Videos.aspx#prettyPhoto/7/

Now, back to theory only.  Rounded shapes, like circular styles, actually give more surface area per drag imposed.  Getting rid of sharp edges at the ends and corners reduces drag turbulence that, in arrows, causes noise and slows down the arrow some.  IN THEORY, it would do the same to gliders, "for the same amount of material".  Smaller or larger fins of another style can be used to compensate.

Theory only again, the traditional view of a rocket fin or an arrow fletch, that of a right triangle shaped piece, increases drag and pushes the center of pressure to the rear.  For an arrow, or a ballistic rocket, that higher friction or drag can increase stability but marginally increases drag (like having a mini parachute on the back).  In air, that drag is minimal and is a function of the square of the velocity and the coefficient of friction.  In water, because water is what, about 800 times denser then air (should have looked it up), the drag would be increased by 800 times, but......... the coefficient of friction is so low that at the low velocities of a glider it almost is not a concern.

If I wanted to create a low drag design that provided good stability, I might consider putting something on with a round shape that extended back, kind of like a lolly pop in 2D.  Yuk, but, it should glide really well, and if the lure starts to wobble or shake the profile would be exposed to more water flow as the fin rotates of the center of glide, pushing it back to true center of glide.

Still, depending on the cause of the instability, the interactions with the boundary layer, the specific design of your glider, or to go back to the rocket/arrow analogy the purpose of the projectile, different designs will give different results.  Not all rockets use right triangle fins, not all arrows use that shape fletch (most don't now), and I expect not all glide baits will either.

I hope this helps some.  Good luck.

[gliders]

Anglingarcher, that's the kind of detail I like ! Kinda backs up my practical tests that when it comes to an actual glider in water ,there's not much discernible difference. The shape on left is probably my final shape, slightly more rounded than what I was using ,same performance, nicer looking ! As a final test I will swim it with the amended rocket style on the right. Thanks for the interesting insight.......glider

[mark poulson]

Anglingarcher,

You must really understand what you're talking about, because you made it clear to me.

Thanks.

[surfk9]

I agree Mark... he definitely knows his stuff ...sounds like my youngest son  (32) a mechanical engineer...makes it clear to me..lol..michel

Edited April 27, 2017 by surfk9

[Chuck Young]

A note about posting pics. The higher resolution your camera is, the more of an issue it will be. Over zooming can help. So can the crop feature on  photo software.  If you zoom out then crop, you are effectually reducing the pixels in the image . As far as fins go, water is a high resistance medium. Your manatee fin style fins are probably more than sufficient. And aesthetics count.  

[gliders]

Thanks chuck, the manatee style works fine, I like to design and understand my own gliders, rather than just copy someone, so I decided to re-disign stability fin -and ended up with same 2 designs I started with !  That's actually o.k , means I had it good to start with . I don't trust when I design something and get it apparently correct ,without having made designs that failed . This shows me the parameters of the design. Thanks again ..........glider 

Edited April 27, 2017 by gliders

[Vodkaman]

Anglinarcher - another great read.

 

DAve

[SW Lures]

39 minutes ago, gliders said:

Thanks chuck, the manatee style works fine, I like to design and understand my own gliders, rather than just copy someone, so I decided to re-disign stability fin -and ended up with same 2 designs I started with !  That's actually o.k , means I had it good to start with . I don't trust when I design something and get it apparently correct ,without having made designs that failed . This shows me the parameters of the design. Thanks again ..........glider 

I agree 100% Gliders. To understand why things are better then another way makes you doing anything that you work on. Just to run up on a great way of doing something but not understanding. This drives me nuts, I have to know why and prefer to know before hand.  That's why I ask so many questions

The fin on a boat motor is referred to around here is a dolphin or stabilizing fin. From what I understand they are to plan out a boat quicker. With that being stated, this manatee fin would do the same. The rocket style would make it run straighter and plan out quiker, if I understand what you are saying. As long as the fin rest on the surface of the water. A little tweaking to the front of the lexan may help also.

IMO,

Dale

[gliders]

Cheers dale, the fin is for keeping sinking gliders on an even keel. .....glider