Beveled Fin - performance impact due to burr grooves?

[MichiganJohn]

Seeking wisdom:

I cut out these fins and then beveled them to 15° on the leading and trailing edges. I did some moderate sanding on the bevel, but there are still grooves present from the burr.

Wondering if this will significantly impact the flow over the fin at all - ie will it impact performance significantly versus if I fill in the grooves? My intuition says No, but I'm not sure what the Science would say - I did some initial googling but couldn’t find info to answer that question specifically.

This is a 3 inch minimum diameter rocket, that will likely see top exposure of Mach 1.5-2.0.

Thanks in advance.

 

[SolarYellow]

No personal experience, but I would definitely get them smooth, either additively or subtractively.

 

[Banzai88]

A quick heavy coat of filler primer and sandpaper application and they're gone.

Same with a wipe coat of epoxy of your choice.

 

[David Schwantz]

Each grove is drag. Each grove will cause a shock wave over mach. Since this is a MD rocket and sounds like you are seeking high performance. Sand them out. The filler may peel out over mach. Also, each grove is a place for the ply to start to delaminate.

 

[rfjustin]

Seeking wisdom:

I cut out these fins and then beveled them to 15° on the leading and trailing edges. I did some moderate sanding on the bevel, but there are still grooves present from the burr.

Wondering if this will significantly impact the flow over the fin at all - ie will it impact performance significantly versus if I fill in the grooves? My intuition says No, but I'm not sure what the Science would say - I did some initial googling but couldn’t find info to answer that question specifically.

This is a 3 inch minimum diameter rocket, that will likely see top exposure of Mach 1.5-2.0.

Thanks in advance.

Pardon the Monday morning QB, next time when using the burr style bits, hit the bevels with a block sander 80 grit. Knock down those higher areas, takes a few seconds on each bevel with a firm grip and angle.

These fins below are have not been knocked down yet:

 

[rfjustin]

These were knocked down before installation:

 

[MichiganJohn]

Thanks for responses folks! It's hard to get a sense in the photos, but I did sand down the burred-edges after beveling (I happily copy your beveling process Justin), and the remaining grooves looked minimal until I put on the silver paint - which added a heavy contrast and makes them really stand out.

And that's what got me thinking about what effect, if any, the edge produces if it's not smooth. I was thinking along the lines of: is a beveled edge going to do what it does at supersonic speeds based entirely on the final profile shape (regardless of minor grooving) or will those grooves maybe cause turbulent flow (or higher degree of turbulence) than a smooth edge surface? AND does that translate into any significant performance difference, either in max altitude or flutter etc?

Maybe it's a question that doesn't need an answer . I'm probably going to tweak these edges a little more and call it good.

 

[MichiganJohn]

Each grove is drag. Each grove will cause a shock wave over mach. Since this is a MD rocket and sounds like you are seeking high performance. Sand them out. The filler may peel out over mach. Also, each grove is a place for the ply to start to delaminate.

Thank you!

 

[rfjustin]

Thanks for responses folks! It's hard to get a sense in the photos, but I did sand down the burred-edges after beveling (I happily copy your beveling process Justin), and the remaining grooves looked minimal until I put on the silver paint - which added a heavy contrast and makes them really stand out.

And that's what got me thinking about what effect, if any, the edge produces if it's not smooth. I was thinking along the lines of: is a beveled edge going to do what it does at supersonic speeds based entirely on the final profile shape (regardless of minor grooving) or will those grooves maybe cause turbulent flow (or higher degree of turbulence) than a smooth edge surface? AND does that translate into any significant performance difference, either in max altitude or flutter etc?

Maybe it's a question that doesn't need an answer . I'm probably going to tweak these edges a little more and call it good.

It going to mess with airflow a little bit, but not significantly. Clean them up best you can, and let it rip.