Rounding the leading edges of fins...necessary?

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TexasAndy

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Greetings all, I am currently working on the Estes Yankee which ironically was the first rocket I built in my teens. The instructions called out for "rounding" the leading edges of the fins and I don't remember them requiring that on past projects. My question is this; is it really necessary? I know it would reduce drag somewhat but how necessary is it?
 
Agreed, not necessary unless you're working on a HPR and need to start worrying about shredding of the fins.
 
Necessary? No.

Visually appealing? Yes, I think so.

I found it does seem to make a difference in altitude, in real life. I have done a few LPR where I rounded over the leading edge, and made a sharp knife trailing edge. I'm quite certain there was a marked improvement, but no concrete evidence to prove it.

In simulations, it adds a -considerable- amount of altitude, but, alas, it's just a simulation.

I think Micromeister has done extensive real world testing, maybe he'll chime in.
 
If your just a week end warrior then it's not needed------from a performance point of view--- That said, it is like comparing a barn door to a tennis ball. Rounding the leading edge will smooth the air flow and , frankly , it looks better. It's a detail thing that you may not care about but others will notice. If you want to go higher, faster , farther, worry about weight first and then tweek the fins and finish--that's my 2 cents worth. --H
 
It's simply a case of how high do you want to go and how do you want it to look? Your rocket, your choice. Sometimes I build in extra drag to my rockets just because I get sick of losing them. I always know I'm going to get my MDRM back! :wink:

The only thing that is necessary when building a rocket is that it be safe--fins stay on, motor stays retained, NC separates at apogee, recovery system brings it down slowly. Everything else is arbitrary.
 
I agree with all of the above.

Not necessary.

Useful, can fly higher, but not necessary.

I especially agree with this:

Bat-mite said:
The only thing that is necessary when building a rocket is that it be safe--fins stay on, motor stays retained, NC separates at apogee, recovery system brings it down slowly. Everything else is arbitrary.
Click to expand...

And..... LUGS stay on. Sigh.

Now if we were talking gliders, it would be different. Most gliders can glide with square edges, but not very well. And many can have major problems with glide trim. But this thread isn't about gliders, so....

- George Gassaway
 
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Not by definition. Something that floats or descends slowly cannot be said to be gliding unless it is along a lateral path. The descent of a rocket is more akin to leaves falling off of a tree than to the gliding of a bird or a hockey puck.
 
TexasAndy said:
... My question is this; is it really necessary? I know it would reduce drag somewhat but how necessary is it?
Click to expand...

Good info so far which all boils down to your rocket - your rules as far as finishing is concerned. For myself, squared off leading and trailing edges on a "finished" rocket cause me physical pain, emotional distress, and spiritual turmoil. I simply have to round them for health reasons. :wink:

Back in the day, we had things like the Centuri Design Manual that provided this guidance, without a whole lot of aerodynamic theory:

Centuri_Model_Rocket_Designers_Manual.jpg

https://sargrocket.org/documents/centuri/dm-1.pdf

I suspect you could find more technical studies on fin profile and drag reduction if you surfed around a bit.
 
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I was just doing some searching on the Estes Magician.

Estes claims the max altitude of a Magician is 1600'. I air-foiled (rounded over, and knife edge) the fins on mine and got 1768' according to an AltimeterOne.

If some time spent on sanding fins will get me an extra 168', I'll take it!
 
geez, I just wish I had someone who would sand the fins on my rockets :> Heck, even build them. Dang motor holders.
 
As others have said, not it's not necessary. And honestly, dealing with LPR, you're not really risking losing fins to flutter if you don't. High power, that could be a different story, but not with LPR. I feel they look much better, and you can get a better finish on them with the leading edges rounded a bit, and the trailing edges tapered a bit. All personal preference, but certainly not required.
 
georgegassaway said:
Now if we were talking gliders, it would be different. Most gliders can glide with square edges, but not very well. And many can have major problems with glide trim. But this thread isn't about gliders, so....

- George Gassaway
Click to expand...
Didn't know that about gliders. Most of my scratch gliders have flat (non air foiled) wings and I haven't always bothered with rounding the leading and trail edges. Thanks for the info
 
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TopRamen said:
I need to do some edge shaping on a couple of builds, and saw this thread:

https://www.rocketryforum.com/showthread.php?132604-A-simple-balsa-fiberglass-fin-idea


He has a tool, in post #2, which is basically a T shaped aluminum plane that hold sandpaper.

I have a feeling I'll be wanting a tool like that, and needing some practice.

Does that tool have a name so I can find one to buy???

Found it!!!

https://www.onlinemetals.com/mercha...rm=1101000030095&utm_content=Primary Shopping
Click to expand...


Specialized sanding blocks like this can be had as well:

counter sander.jpg

https://www.hobbylinc.com/htm/gpm/gpmgpmr6190.htm
 
I discuss my favorite sanding block here:

https://www.rocketryforum.com/showthread.php?8648-Sanding-Blocks&p=71737#post71737

Composite Photo:

attachment.php


- George Gassaway
 
Thanks for all the links folks!!!
Looks like I'll be getting a few sanding blocks next month!
 
As many have already posted rounding the leading and trailing edges of our fins is NOT necessary. but doing so can increase achieved altitude by a good bit.

On most of my models I do round the leading and trailing edges of the fins regardless of profile. It's just what I perfer to do.

Teardrop symmetric Airfoiling fins will gain the most altitude if done correctly and aligned as nearly perfectly as possible. Perfecting teardrop Airfoils is almost an Art Form taking LOTS of time and many many failures to get done symmetrically. Getting the sanded fins to a matched set in the exact shape and on the model correctly will give the modeler perfectly straight NO Roll flights to the very best altitude. Failing to get them symmetric or mis-align a single one will cause spinning roll that will cost almost as much altitude as leaving the edges square.
 
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Square edges are also very easily nicked and damaged by minor contact. Rounding gives more area to spread the load.
 
Micromeister said:
Teardrop symmetric Airfoiling fins will gain the most altitude if done correctly and aligned as nearly perfectly as possible. Perfecting teardrop Airfoils is almost an Art Form taking LOTS of time and many many failures to get done symmetrically. Getting the sanded fins to a matched set in the exact shape and on the model correctly will give the modeler perfectly straight NO Roll flights to the very best altitude. Failing to get them symmetric or mis-align a single one will cause spinning roll that will cost almost as much altitude as leaving the edges square.
Click to expand...

John is right (as usual :wink:)

Downside of airfoiled fins for sport rockets (translated as anything you fly for fun and plan flying multiple times) may be durability. Those tapered fins don't hold up too well on landing. Rounding lead and trail edges seems to be a good compromise. on the other hand, for a sport rocket you will get a decent flight with squared fins. As for aesthetics, it is in the eye of the beholder. Some rockets like the flutter bye look pretty cool with squared edges.
 
From the Model Rocket Handbook, showing nose cone shapes not fins, a perfectly squared off leading shape has high drag, however with slightly rounded edges the drag drops to about 30% more than a perfect parabola shape. Likewise, from elsewhere, as long as laminar flow can be maintained a full trailing airfoil shape is great but as soon as there is turbulence, you can cut it off square right there without increasing drag (also, rounded trailing edge shape doesn't really help anything). So, I make sure the leading edges are least rounded a bit, and sand the trailing edges some at an angle. Never much more for ruggedness.

Back when I made model sailboats, I did carve a full airfoil (only 1 or 2 req'd), best I can remember mostly with a knife.
 
bill_s said:
From the Model Rocket Handbook, showing nose cone shapes not fins, a perfectly squared off leading shape has high drag, however with slightly rounded edges the drag drops to about 30% more than a perfect parabola shape. Likewise, from elsewhere, as long as laminar flow can be maintained a full trailing airfoil shape is great but as soon as there is turbulence, you can cut it off square right there without increasing drag (also, rounded trailing edge shape doesn't really help anything). So, I make sure the leading edges are least rounded a bit, and sand the trailing edges some at an angle. Never much more for ruggedness.


Rounding the trailing edge of fins greatly reduces the Base Drag on the model. We still have a good be from the motor but rounding those trailing edges helps. Also reduces the landing damage.
Click to expand...
 

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