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PostPosted: Wed May 29, 2013 8:31 am 
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Joined: Wed May 05, 2010 8:28 am
Posts: 684
Location: Clinton Lake, KS
I like woodworking, and have a fully appointed woodshop.. I want to build a set of rudders for my H16, just because it sounds like a fun project and I could use a set.



Where I am hung up is on profile shape. Well... I am not so much hung up on it as I have found there is a LOT to learn. This only serves to further my interest in this project.


At first the idea was just glue up a blank and use a copy mill to make my own replication of an EPO...

The trouble I have found is small inconsistencies in rudder profiles.. On both the EPO and EPO2 rudders.. So I ain't sure exactly which to copy, or how I should go about exactly 'perfecting' the rudder before I copy it.


The standard answer seems to be to use the NACA 0012 profile... Which is easy enough to do... But is it the best for a H16?

I also see many discussions about the NACA 63 series being used on similar craft.

Based on what little I know the planform is the most critical part of the whole thing... and it is pretty much defined by class rules... I think.. I have an email into the IHCA requesting the profile plans.






Any thoughts? Or links to what profiles F16, F18 guys are using... I figure if I am going to give this a go, I might as well make it right.


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PostPosted: Wed May 29, 2013 12:44 pm 
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Joined: Mon Jul 14, 2003 7:11 pm
Posts: 4589
Location: Detroit, MI
You can't use the NACA 0012 profile because of the thickness restrictions in the class rules. The first two numbers in a NACA section describe the camber (0%, because it's a symmetrical foil) and thickness (12% of the chord).

From the class rules:
The maximum thickness of a rudder blade(s)
shall not exceed 1.015 in. (25.8 mm), tapering
over a distance of 2 ft. (60.96 cm) to a maximum
thickness of 1/2 in. (12.7 mm), 2 in. (50.8
mm) from the bottom tip of the rudder.

The maximum chord is ~ 9.75 in, so the max thickness is 10.4%

The planform is dictated by class rules - and doesn't have a linear chord progression (like the thickness is required to), so the section changes as you progress down the foil.

Having fun yet?

Beware the "low drag bucket" sections, like NACA 63 series. They're meant to operate at a low angle of attack - they will stall at higher angles - and well before a 0010 section. The laminar flow characteristics are useless in a disturbed flow regime - like the flow coming off a Hobie 16's leeward hull.

This was one of my textbooks in naval architecture school 30 years ago, and it's still applicable today - http://www.amazon.com/Theory-Wing-Secti ... g+sections

Get the Kindle edition for only $15 and your head will explode with information.


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PostPosted: Wed May 29, 2013 2:12 pm 
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Joined: Wed May 05, 2010 8:28 am
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Location: Clinton Lake, KS
Thanks Matt! I have really been enjoying researching foil shape and design... any input you have is very much appreciated..

I sent an email to "IHCA rules" and within minutes Erik Olsen sent me the drawings for the EPO rudder... I can't seem to import into anything to just trace and scale it up... but all the numbers and profile drawings seem to be there... But it feels like cheating to just copy it... :lol:

Even if this doesn't come to fruition it has been a fun exercise... I'll have to try and see if I am smart enough to understand that textbook... :mrgreen:



I worked in the plastics industry for some time, and called an old friend today who is an excellent machinist and fabricator, and during the course of the conversation bounced this off of him..

He thought I should just use a foam core and go for it... Pointed me to a couple videos explaining the "hot wire" method of foam cutting, and then came back to me telling him about the EPO rudders... He said " I would have to guess EPO stands for Expanded PolyOlefin , the type of foam used for the core... :D Well gee... I guess you learn something new everyday! So was the original EPO designer/builder an RC airplane guy?


http://www.youtube.com/watch?v=SCbEeW_n7OU

Then Vac bagging resin is old hat around here... Hummm....


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PostPosted: Wed May 29, 2013 2:28 pm 
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Joined: Fri Apr 13, 2012 7:35 pm
Posts: 607
Location: Tuscaloosa, AL
if you will email it to me I can print it in large format (To Scale) and mail it to you.


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PostPosted: Wed May 29, 2013 2:55 pm 
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Joined: Sat Oct 29, 2011 4:27 pm
Posts: 553
Location: Central Oregon
Used to be into high end RC Gliders. This is the software we used to make templates for hot wire cutting the foam cores.
http://www.compufoil.com/index.shtml hmmm or maybe it was this... http://www.profili2.com/eng/default.htm
I have been tempted to try some home brew hobie rudders. :twisted

_________________
1980 H16
1997 Wave


Last edited by hobiesrock on Wed May 29, 2013 3:00 pm, edited 2 times in total.

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PostPosted: Wed May 29, 2013 2:56 pm 
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Joined: Sat May 02, 2009 5:22 am
Posts: 459
Location: Columbus, Indiana
here is a photo of a rudder I made from mahogany some 10 years ago .... :D

Building these rudders was a fun and easy project.

Image

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Bill 404 21SE
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PostPosted: Wed May 29, 2013 3:49 pm 
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Location: Clinton Lake, KS
sxrracer... email sent!


Thanks for the enabling Bill.. Hope to catch you at an event sometime.. That rudder looks GREAT!


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PostPosted: Tue Jun 25, 2013 5:32 pm 
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Joined: Wed May 05, 2010 8:28 am
Posts: 684
Location: Clinton Lake, KS
Well... I ripped apart some old pallets I found in the ditch, and I think this firewood should do quite nicely...


:mrgreen: :lol:



Image


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