Ye Olde Rocket Forum

Go Back   Ye Olde Rocket Forum > Work Bench > Building Techniques
User Name
Password
Auctions Register FAQ Members List Calendar Today's Posts Search Mark Forums Read


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 05-06-2009, 01:53 AM
BEC's Avatar
BEC BEC is offline
Master Modeler
 
Join Date: Feb 2009
Location: Auburn, Washington
Posts: 3,643
Default Rounded fin edges out of fashion??

In the three and a half months or so of my having become a BAR I've noticed something that makes me wonder a little. I see many pictures of rockets here, on makers' web sites and elsewhere that have square-edged fins. Has trying to reduce drag by rounding leading edges and tips, or even shaping fins to a thin symmetrical airfoil section fallen out of favor, or has someone just demonstrated in the past 35 years that it's wasted effort?

In the few model rockets I've built in these past few months I haven't been able to bring myself to leave LEs in particular square, I had to round them. I've generally left trailing edges square because I know that TEs on small model airplanes also can be left square at no real performance loss...even though the fly rather more slowly.

So....is it building simplicity, or aerodynamic research, or what that has led to this trend of square fin edges?
Reply With Quote
  #2  
Old 05-06-2009, 02:00 AM
Der Red Max's Avatar
Der Red Max Der Red Max is offline
MOTORVERKENS
 
Join Date: Aug 2008
Posts: 315
Default

Quote:
Originally Posted by BEC
...what that has led to this trend of square fin edges?
Laziness!
(at least in my case)
Reply With Quote
  #3  
Old 05-06-2009, 02:58 AM
Leo's Avatar
Leo Leo is offline
German Model Rocket Builder
 
Join Date: Sep 2005
Location: Germany
Posts: 1,313
Default

You are not the only one that noticed it.

I'm rather disappointed that some real nice builds are "tarnished" because the leading edges have been left square. I'm sure in most cases the instructions state otherwise.
__________________
Leo

My rocket fleet and more @ Leo's Leisure Site and on YouTube - My latest project: ALTDuino
Reply With Quote
  #4  
Old 05-06-2009, 06:37 AM
Rocketflyer's Avatar
Rocketflyer Rocketflyer is offline
Member in Good Standing!
 
Join Date: Sep 2006
Posts: 1,209
Default

Quote:
Originally Posted by BEC
In the three and a half months or so of my having become a BAR I've noticed something that makes me wonder a little. I see many pictures of rockets here, on makers' web sites and elsewhere that have square-edged fins. Has trying to reduce drag by rounding leading edges and tips, or even shaping fins to a thin symmetrical airfoil section fallen out of favor, or has someone just demonstrated in the past 35 years that it's wasted effort?

In the few model rockets I've built in these past few months I haven't been able to bring myself to leave LEs in particular square, I had to round them. I've generally left trailing edges square because I know that TEs on small model airplanes also can be left square at no real performance loss...even though the fly rather more slowly.

So....is it building simplicity, or aerodynamic research, or what that has led to this trend of square fin edges?



Good question. I too have noticed this. I can't leave mine squared. At the minimum they have to be rounded and somewhat tapered at the trailing edge. I dislike sanding, but will do it on the fins.
__________________
Enjoy life, it has an expiration date.
Reply With Quote
  #5  
Old 05-06-2009, 07:01 AM
motley16 motley16 is offline
advanced rocketeer
 
Join Date: Aug 2008
Location: pa.
Posts: 143
Default

I have also noticed the trend. Lazy or just different to be different. Not sure. I follow instructions and at times still round the leading edges. Do what YOU like and feel looks best!
__________________
craftsman, builder of exotics
Reply With Quote
  #6  
Old 05-06-2009, 08:09 AM
Nuke Rocketeer's Avatar
Nuke Rocketeer Nuke Rocketeer is offline
Knuckle Draggin' Engineer
 
Join Date: Mar 2005
Location: Minooka IL
Posts: 349
Default

I have noticed that too. I think it is laziness

I round and taper the fins on all my rockets, unless there is a scale reason not to. I just have to get that lst bit of efficiency out of it, or the engineer in me will nag me awake at 3AM.
Reply With Quote
  #7  
Old 05-06-2009, 08:23 AM
jetlag jetlag is offline
Old BAR
 
Join Date: Aug 2006
Posts: 2,279
Default

Quote:
Originally Posted by Nuke Rocketeer
I have noticed that too. I think it is laziness

I round and taper the fins on all my rockets, unless there is a scale reason not to. I just have to get that lst bit of efficiency out of it, or the engineer in me will nag me awake at 3AM.


Plus, it looks so much nicer when all is filled and finished. Though when I was a tyke, I never filled the grain and spent little time rounding; just get 'er finished by the weekend!
Allen
Reply With Quote
  #8  
Old 05-06-2009, 08:32 AM
GregGleason's Avatar
GregGleason GregGleason is offline
U.S. Manned Space Program Buff
 
Join Date: Mar 2009
Location: Houston
Posts: 1,298
Default

Fin symmetry has been a pet issue for me for last couple of years. On my latest mid-power build, I bought some carbon rod with the same OD as the fin thickness and glued it to the square leading and trailing edge, then filled in the gap with a mix of epoxy and microballoons for ease of sanding. The nice thing about carbon rod is that it is uniformly round and straight, along with being dent/ding resistant. It turned out pretty well, too.

My dream is to get my own CNC machine and mill my fins to +/- 0.01 inch tolerances. That way I can get those nice contours for V2 fins or multiple faceting for Astrobee D fins. Now as to how I plan to seal/paint to keep those tolerances …

Greg
Reply With Quote
  #9  
Old 05-06-2009, 09:28 AM
Jerry Irvine's Avatar
Jerry Irvine Jerry Irvine is offline
Freeform rocketry advocate.
 
Join Date: Jan 2008
Location: Claremont, CA "The intellectual capitol of the world."-WSJ
Posts: 3,780
Default

The actual optimum shape for strength and performance is ogive on the fins. Both leading and trailing. Especially trailing.

Just Jerry

http://v-serv.com/usr/pubs/air10.htm

http://v-serv.com/usr/kits/micro-sentraSRB.htm
Reply With Quote
  #10  
Old 05-06-2009, 10:10 AM
Doug Sams's Avatar
Doug Sams Doug Sams is offline
Old Far...er...Rocketeer
 
Join Date: Mar 2005
Location: Plano, TX resident since 1998.
Posts: 3,965
Default

Quote:
Originally Posted by BEC
I've generally left trailing edges square because I know that TEs on small model airplanes also can be left square at no real performance loss...even though the fly rather more slowly.
My understanding is the opposite - the trailing edge affects drag more than the leading edge. While the blunt leading edge certainly presents more drag than a taper, the blunt trailing edge causes swirling airflow that significantly adds to the drag.

That said, I'm guilty of squaring mine off. Trying to recall why I went to that, I believe it's because I wanted the fins to be stronger and less susceptible to damage along the edges.

At one time, I would not only round the edges, but put aggressive tapers on them. The result was fins that were very thin over much of their surfaces which left them weaker and more prone to landing damage. Also, somewhere I learned that clipped tips were more aerodynamic than rounded (or elliptical) tips which tend to cause swirling airflow and thus drag. Once I started leaving the tips alone, it was not long before I began leaving the entire fin completely square along the edges.

About that time, it also occurred to me that, since I'm not a competitor, I didn't care about performance, so there was really little motivation for airfoiling anyway, and skipping that step saved some time and kept some dust out of my lungs

OTOH, I hate blunt launch lugs - they make me cringe. So I always bevel the leading and trailing ends of the lugs to make them look more aero. I don't really care if they are more aero, but they gotta look like it

Here's a pic which illustrates my point about the lugs. Doug




.
__________________
YORF member #11
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump



All times are GMT -5. The time now is 12:04 PM.


Powered by: vBulletin Version 3.0.7
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Ye Olde Rocket Shoppe © 1998-2024