I've been on an airfoiling kick recently because I dislike square edges facing the wind.
I do balsa fins by hand, and prefer to use a sander of some sort with 10 or lower grit on plywood fins.
I don't have a sander currently so I had to do my Leviathan's by hand. (BroncBuster II in the Mid-power forum)
Definitely was an opportunity to practice consistency. I apply thin superglue to the trailing edge in order to stiffen them up.
I start by sanding the green (~10-20 deg off vertical), then the yellow (~10-20 off horizontal), then the red (~30 off horizontal), and finish by working it into a curve. Trying to get as close to en ellipse's profile as i can by eye.
View attachment 306992View attachment 306993View attachment 306994
I offer no illusion that my foils are perfectly consistent on a fin to fin basis, but they work perfectly well for general sport flying.
And in an ideal case you may get up to 70% drag reduction! (SG force corresponds to rearwards force on the fin)
View attachment 306999
I've been on an airfoiling kick recently because I dislike square edges facing the wind.
I do balsa fins by hand, and prefer to use a sander of some sort with 10 or lower grit on plywood fins.
I don't have a sander currently so I had to do my Leviathan's by hand. (BroncBuster II in the Mid-power forum)
Definitely was an opportunity to practice consistency. I apply thin superglue to the trailing edge in order to stiffen them up.
I start by sanding the green (~10-20 deg off vertical), then the yellow (~10-20 off horizontal), then the red (~30 off horizontal), and finish by working it into a curve. Trying to get as close to en ellipse's profile as i can by eye.
View attachment 306992View attachment 306993View attachment 306994
I offer no illusion that my foils are perfectly consistent on a fin to fin basis, but they work perfectly well for general sport flying.
And in an ideal case you may get up to 70% drag reduction! (SG force corresponds to rearwards force on the fin)
View attachment 306999
I did the same with my Leviathan fins, using a sanding block. I think I used 150 grit paper, so it did take a little while, but wasn't any more difficult than doing it on balsa - just a little slower.
I try to airfoil most of my fins. I just can't help myself.
And now I see a major typo....that was supposed to be 60 grit not 10.....
Now I've done it once and have the experience to say its not something I want to repeat.
Especially since I see a 4" Phoenix in my future that has ~ 6 ft of 1/4" leading edges.....
It's also worth pointing out that trailing edges are just as important as leading edges, especially for subsonic flight.
On the trailing edges, it provides more time (via distance) for molecules to impact the surface to impart their (upward directional) momentum onto the surface.
And now I see a major typo....that was supposed to be 60 grit not 10.....
Now I've done it once and have the experience to say its not something I want to repeat.
Especially since I see a 4" Phoenix in my future that has ~ 6 ft of 1/4" leading edges.....
There's a guy in my club that makes fun of me for airfoiling all my fins now when I leave tape ridges on masked paintjobs.
I'm about reducing drag in some ways, but really don't care about others
It is actually a turbulent pocket that forms behind the square edge of the fin, effectively where the air has to fill the gap (coming in from either side) as the fin moves forward. Turbulence equates to wasted energy. The thinner the edge the smaller the patch of turbulence.
@BDB, I wish I had a router, but I think I'll get the apartment fully furnished before investing in shop equipment lol.
I think part of troy's point is illustrated with my rough simulation, but I want to push back on the idea that Pressure increases as flow velocity increases. The increase in pressure is the result of Deceleration of the flow as it is diverted by the fin. Since we're talking airfoils, we're in the subsonic realm of incompressibility. I have a feeling Mr Bernoulli may back me up here. We're you referring only to the dynamic pressure?
Plus, I have a hard time grasping that molecular impacts to the trailing edge of a Rocket's fin will have any practical effect. If we were talking Lift from an airplane's airfoil, I could see your point, but the streamline model is better for such cases than a particle model.
About 3D printed leading edges glued to leading edges (this was before I ditched my crappy Kickstarter M3D 3D printer):I've been on an airfoiling kick recently because I dislike square edges facing the wind.
I do balsa fins by hand, and prefer to use a sander of some sort with 10 or lower grit on plywood fins.
I don't have a sander currently so I had to do my Leviathan's by hand. (BroncBuster II in the Mid-power forum)
Definitely was an opportunity to practice consistency. I apply thin superglue to the trailing edge in order to stiffen them up.
I start by sanding the green (~10-20 deg off vertical), then the yellow (~10-20 off horizontal), then the red (~30 off horizontal), and finish by working it into a curve. Trying to get as close to en ellipse's profile as i can by eye.
View attachment 306992View attachment 306993View attachment 306994
I offer no illusion that my foils are perfectly consistent on a fin to fin basis, but they work perfectly well for general sport flying.
And in an ideal case you may get up to 70% drag reduction! (SG force corresponds to rearwards force on the fin)
View attachment 306999
I agree. Pressure is only a small component of the equation.I still hold the position that boundary layer reduction and streamline management have more influence than merely the presence of the varying fluid pressure (ie. particle collision) and change of momentum.
Great idea!I also made a 3D printed sanding block over which was applied wet sanding sandpaper
Interestingly, experiments have shown that a flat trailing edge (1% of chord approximately) can be beneficial in some circumstances!
The more I read the more I realise it is not a very intuitive subject. It is able to be learned, but not intuitive just out of the box.
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