NACA Airfoil Rails?

General Discussion
1

Inspired by stoneburner (http://bgboard.blogspot.com/2014/03/march-82014-afterr-seeing-recent.html) and the rails,rails,rails…rails-thread (http://www.swaylocks.com/forums/railsrailsrailsrails) I have taken up the idea of using the NACA 4415 Airfoil for building a rail profile:

Now I’m quite unshure if this will work for a modern, more performance orientated noserider. Especially the bevel worries me.

In the middle a little too much? In the nose a little too little? How to combine the best with concave in the nose? What do you think?

Best regards, Andi

2

The front half of the foil already looks like a rail profile to me, and guys like Stewart and Walden have been using the bevel or chine rail on their longboards for years.  Check out a Stewart Hydro Hull or a Walden Magic.

3

PM John Mellor (johnmellor).  I am pretty sure he uses airfoil profiles for longboard rails.

There is little doubt in my mind that Dick Brewer used airfoil profile as a core concept for rails.  He designed and raced RC airplanes at one time.

4

“I am pretty sure he uses airfoil profiles for longboard rails.”

Hi stoneburner -

Thanks for that but I just sort of make them up as I go.  I’ve always been intrigued by the concept of trying to match the lengthwise foil of the rail to something approximating an airplane wing but from what I see in the diagram posted, he’s more concerned with the cross section profile and how it might match the leading edge foil of a wing.  

I’m not saying the cross section isn’t important.  I just think the overall ride might be more influenced by how the rail entry, thick point, and exit help balance everything and allow the rider to pivot on the outline of the board.  The thick point becomes a sort of fulcrum in that regard and how the foil tapers behind and in front of that thick point can greatly influence how the board rides. 

 

 

 

5

Shhhhh.     ‘‘Nothing to see here, move along.’’   (Obiwan Kenobe) 

6

ok, I think I understand…

but I want to come back to the bevels. Is there some sort of rule of thumb? How much beveled should it be? width? angle?

7

I’m no expert on bevels, but the reason I suggested you look at the Stewart Hydro Hull or Walden Magic is to get a good idea of what has worked well for those two longboard shapers.  

You could also try a search here using “bevel” and “chine” for more discussion of the subject.  

But in the end, if your rail profile is going to be true to the airfoil leading edge cross section you have chosen, then that will dictate the amount and degree of bevel.

8

Trying to wrap my head around this, do you all mean designing the deck and bottom rocker based on the NACA foil, or just looking at the rails from the front and the rocker is separate?

9

 

10

 

my initial question was concerning the slices of a board. Maybe the drawing was a bit confusing…

 

11

“do you all mean designing the deck and bottom rocker based on the NACA foil”

I can’t speak for the others but that’s kind of the idea.  Specifically, the rocker/deck lines around the edges, not the stringer.   I’ve never been very aware of NACA specific foil designs… just kind of ‘winged’ it on my own. 

FWIW, the cross section contours you’ve presented in the diagram looks good… not necessarily modern shortboard but functional enough on a longboard.

12

I’ve been trying to match the lengthwise foil of the rail to something approximating an airplane wing for a few years. I didn’t like the way some boards kept trying to straighten out in bottom turns. You’ll see it in videos where guys constantly redirect. I decided that the effect was due to thick point of the rail being too far aft.

I moved volume forward and took it to the rails at about 2/3 way up the board. Then foiled the rail thickness out to the tail. It’s not a NACA profile, but I think having the thicker part of the rail up front helps “pull” the board through the water when on rail (in my mind ;-0 )

PS it took a few tries to get the volume forward without a bump in the rail. I’ll generate a rail profile next time I’m on the design computer.

Cross section to equal a NACA profile? It will be interesting to see how theoretical profiles match current state of the art

13

Back in 2002(?) I posted a photo of a rail contour gauge I made and the resulting template after placing it at the midpoint on a Skip Frye longboard.  It seemed to be a perfectly functional rail contour but the overall foil aspect of it is lost without a lengthwise photo which i don’t have.

It’s still in the archives:

http://www.swaylocks.com/node/62208

 

14

I remember that tool. That thing is awesome.

15

Thanks… rather difficult to fabricate from scratch. I cut all the ‘feelers’, ran them through a thickness planer, drilled a hole in each end of each feeler and hand cut each slot with a utility knife.  HAHA - what a pain in the ass!

16

That is either focused dedication, or OCD, I can’t tell which.    Either way, it’s well done.     Frankly, I’m not sure I’d undertake a project like that.

17

Aeroplane wings don’t have a nose and tail…they also move through their intended medium (the air) , in the opposite orientation to a surfboard… I think they only have implications for fin design…I remember a conversation I had years back with Peter Drouyn /Westerly Windara , where he said his rails were shaped in likeness to the sharper end of a watermelon…as usual , nature shows the way , whereas , computers just do as their told.

18

Boy, isn’t that the truth.       In the Balsa era, and early foam era, the ideal rail was described as an ‘‘Egg Rail.’’    Some folks liked the big end of the egg, others liked the small end.   

19

I dunno since leading edge of airfoil so similar to rail shape, it makes me think there are similarities in the requirements for both. Airfoils are from nature too!