Rounding off the leading edge of fins?

[danmic]

I came across this video and he mentioned that rounding off the leading edge of fins lower drag by a substantial amount for low powered, balsa fin rockets. I was wondering if this makes sense on HPR rockets that use wooden fins or if the gains are much more insignificant relative to other factors. Is there any reason not to do it such as structural concerns?

 

[dhbarr]

I came across this video and he mentioned that rounding off the leading edge of fins lower drag by a substantial amount for low powered, balsa fin rockets. I was wondering if this makes sense on HPR rockets that use wooden fins or if the gains are much more insignificant relative to other factors. Is there any reason not to do it such as structural concerns?

The faster you go faster, the more those corners drag.

 

[Scott_650]

Shaping fins can give you better - if higher/faster is your definition of better - performance. You can play around with fin profiles in Open Rocket and (I believe) RocSim and see if it’s worthwhile to you. It’s a personal choice as far as the aesthetics go - I think some designs look better with square, chunky fins but that’s me, I’m not concerned with overall performance. The lowest drag is typically from fully air foiled fins though that takes a fair amount of skill, practice and patience.

I suppose there could be some structural advantages to rounding - square edges aren’t typically as resistant to cracks from impacts and stress as rounded ones, but I doubt it’s a huge advantage.

 

[Hobie1dog]

it seems most logical to round them off

 

[waltr]

Yes, rounded does lower the drag resulting in higher velocity and altitude.
If you want a low & slow rocket then leave them square.

I do an angle on leading edges just so they are not square. This is mainly for looks but does lower drag.
I'm not going for altitude or speed.

If your rocket is expected to go faster than Mach then fin profile becomes important.

 

[dr wogz]

I like rounded leading edges, just because they look more "finished". (Also shows you've put some time to their prep.)

I've seen a few fins (LPR & HPR) where the edges ae still brown, and the 'tab' is still evident. "Rushed to build it?!?"

 

[cls]

I've seen a few fins (LPR & HPR) where the edges ae still brown, and the 'tab' is still evident. "Rushed to build it?!?"

I think the Boy Scouts get a merit badge for this. And, glue everywhere, including the MMT and launch lug.

 

[samb]

... Is there any reason not to do it such as structural concerns?

No reason IMO. To round, taper, or leave square is an aesthetic decision left to the builder. While the aerodynamic efficiency of the fin will differ the basic job of stabilization won't be affected by the choice.

 

[Lt72884]

I came across this video and he mentioned that rounding off the leading edge of fins lower drag by a substantial amount for low powered, balsa fin rockets. I was wondering if this makes sense on HPR rockets that use wooden fins or if the gains are much more insignificant relative to other factors. Is there any reason not to do it such as structural concerns?

sure does the drag coefficient equation has Area as part of the function. The faster you go, the more force the fluid pushes on the object. In HPR, that would be air, especially when its colder, the air is "thicker". If you reduce the amount of area the fluid has to interact with, you lessen the drag. When you lessen drag, you also can increase the efficiency of the rocket or whatever vehicle you are dealing with.

 

[KenECoyote]

Also if you have fins that are forward or extend forward, rounding them should help move the cp back a tiny bit.

 

[sriegel]

Your choice. Some I round, others, not. Depends on the aesthetic I'm looking for.

 

[MClark]

When I RSO if the fins have square edges I look to see what else is wrong

 

[KenECoyote]

When I RSO if the fins have square edges I look to see what else is wrong

For my recent Madcow 4" Patriot build, I actually purposely chose to leave the fins untapered/square. This was because the fins on a Patriot are so small that I figured the bit of extra drag would help with stability and airfoiling could actually hurt.

 

[cls]

Rounding helps, but some fins have a shape that is difficult to consistently round each edge. If they are not all the same, the rocket will likely have a lot of roll, more than I like.

Good reason to not airfoil the fins, that demands even better quality work, and the edges are delicate, seem to get road rash.

None of my square fin rockets have ever flown away.

 

[blackwing94]

I like split fin rockets that whistle. I always leave the edges square and flat! And I also prefer the additional drag to keep the altitude down. What ever floats your boat.

 

[Paul Howard]

Altitude and Speed advantages aside (yes, it works!), and airfoiled fin (or wing) will keep the air moving more smoothly around it and have less separation when the rocket starts to "wobble" in any direction, since there is less separation and less messy vortex's forming there "should be" more rapid return in alignment to line-of-travel. However, there is the argument of adding drag behind the CG for stability which might have some merit. Without extensive wind-tunnel testing with all sorts of metering, it's hard to tell. Is it enough to notice? Maybe, maybe not - I think other stability factors would come into play possibly more so such as the CP to CG distance, Fin-size, etc. I pretty much airfoil all my fins and often put hardwood leading and trailing edges on, but that comes from a history of nit-picking "squeeze the most performance out" approach to RC Gliders and small Freeflight gliders I build. That's my 2 Cents.

 

[bjphoenix]

I round the edges because it looks better and because I think a rounded edge looks reasonably finished and is the most resistant to damage from handling, storage and landings. I used to airfoil edges but they were a lot more prone to getting dinged.