1/4" Plywood Fins - What airfoil technique?

[Green Jello]

I'm working on my first build with 1/4" plywood fins (Madcow Super DX3):



What method do you guys use for airfoiling?

- Round leading edge and taper trailing?
- Diamond pattern?

 

[JohnCoker]

For me, the edging is cosmetic, so I tend to do bevels because it looks cool. Of course, a true airfoil profile would be better for reducing drag (rounded leading edge, tapered trailing edge).

Here's a couple of techniques for beveling fins.

 

[thobin]

I mark the leading edge 1/2" down then draw a center line down the middle of the leading edge and bevel it to that point. I leave the leading edge a little smaller than a 1/16 thick, you don't want to sand it to thin or it will just break off all the time. Then I just round over on all the trailing edges.

Of course I do this with my edge sander so its quick and painless, it can take some time if you do it by hand. Its reverse and isn't as involved as an airfoil but it looks good.

TA

 

[Green Jello]

Of course I do this with my edge sander so its quick and painless, it can take some time if you do it by hand. But it looks good and isn't as involved as a full airfoil.

TA

What do you mean by "edge sander?"

I have a palm vibrating sander, or just hand stuff I've made with blocks.

 

[MClark]

I have a jig to hold the fin and run use a table saw. Takes about 5 minutes to do a set of fins.

 

[thobin]

What do you mean by "edge sander?"

I have a palm vibrating sander, or just hand stuff I've made with blocks.

This. :headbang:




TA

 

[BLKKROW]

I have a jig to hold the fin and run use a table saw. Takes about 5 minutes to do a set of fins.

Any details on this? What kind of blade are you using and chance for a pic of the jig?

 

[GDJ]

I just do a simple wedge on the front and wedge on the back. That knocks down drag by a fair bit. It's not ideal for subsonic flight, but it's pretty good.

 

[Coop]

I usually just round the leading edge. If I'm feeling particularly froggy, I'll give the trailing a bit of a taper (read: infrequently, but has happened once or twice). I have no jigs or specialty tools for this... usually just some coarse-grit to knock it down until it looks right. Yeah--super HiPo stuff, that's me. Heh.


Later!

--Coop

 

[Sully]

it can take some time if you do it by hand.

Not only that, but if you have your sandpaper on a table and are moving the fin held at a fixed angle, it's pretty easy to sand your thumbnail off! And not the edges like a manicure, but a hole right in the middle of the nail. This is not as pleasant as it sounds.

 

[MClark]

Any details on this? What kind of blade are you using and chance for a pic of the jig?

No pictures, not sure where it is after moving
It is made of wood and went over the fence, slides. The fin is clamped to it, vertical, edge to be cut against the surface. Blade at desired angle, adjust fence to leave a small flat.
After setting up a few times I made a gauge to set the fence. Put gauge between blade and fence with the blade straight up, remove then tilt blade.
Blade is whatever came with saw.

Mark

 

[tjsnakez]

1/4" ply is pretty easy to bevel in my opinion. I usually just free-hand on a belt sander turned upside down. You have to be careful to not "let it eat" too much.
I usually put a nice tapered point on the leading edge and round the trailing edge or leave it square. It's mostly cosmetic.

 

[thobin]

Not only that, but if you have your sandpaper on a table and are moving the fin held at a fixed angle, it's pretty easy to sand your thumbnail off! And not the edges like a manicure, but a hole right in the middle of the nail. This is not as pleasant as it sounds.

Oooh that doesn't sound pleasant at all.


TA

 

[asheriff]

This. :headbang:

View attachment 140064


TA

THIS I need. BUT! No way can I sneak that in the garage and swear to my wife with a straight face that is been there for years. My old man could do it, but he's the master of sneaking in large tools.

 

[Voxels]

I sand mine to a rounded leading and trailing edge for less subsonic drag, though I was thinking of trying using an angled table saw to create diamond, mainly because it looks cool.

 

[Green Jello]

This is what I ended up going with:

https://www.rocketryforum.com/showthread.php?56811-Madcow-Super-DX3-Build-Thread&p=571946#post571946

They came out pretty well.