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Trailing edge dilemma - 1/31/2002 9:24:39 PM   
pukinbuzzard


 

Posts: 32
Joined: 1/3/2002
From: Tampa, FL
Status: offline 		Hi, I've been working on plans for a scratch build on a 33% Extra. I'm working on ribs and having a problem with my design. This is a built up wing, with ribs sheeted with 3/32 balsa.

At the trailing edges of ailerons, elevators and rudder I plan to make the ribs taper to a fine point and the sheeting extend to that spot. when I glue the sheeting on, the edges get glued together. that makes the trailing edges 3/16 thick (which I like rather than a delicate razor edge).

My problem is in lofting this. I use Drafix CAD. I can resize my airfoils, but (of course) that 3/16 trailing edge keeps resizing. I looked at the trial version of Compufoil. Everything seems to come out with a razor edge - I don't see any way to truncate it to 3/16. If I truncate it, I'm now at the wrong chord value....so I have to increase that. it all seems to be a hit or miss kind of thing.

Any suggestions?


thanks, David Soniat - [email]dsoniat@admin.usf.edu[/email]
       Post #: 1

Trailing edge dilemma - 2/1/2002 12:15:07 AM   
pukinbuzzard


 

Posts: 32
Joined: 1/3/2002
From: Tampa, FL
Status: offline 		Maybe a picture will help. these are "blow ups" of just the trailing edges of ribs. One has the taper to nothing (which as you can see makes the chord almost an inch too long.

the other has the edge truncated to the thickness of the sheeting (3/32" .





Attachments
Click to see the file in new window.Attachment.bmp

(in reply to pukinbuzzard)
       Post #: 2

Trailing edge dilemma - 2/1/2002 12:20:52 AM   
pukinbuzzard


 

Posts: 32
Joined: 1/3/2002
From: Tampa, FL
Status: offline 		Here is the second one with the truncated trailing edge.....

Attachments
Click to see the file in new window.Attachment.bmp

(in reply to pukinbuzzard)
       Post #: 3

Compufoil - 2/3/2002 12:28:46 PM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		You use the Trailing Edge Flair Wizard to correct your trailing edge from being a razor edge. Leave the Flare Coefficent alone and use the Trailing Edge Flare Amount to size your edge.

Just one question:

Why are you making a built up wing? I used Compufoil and printed my root and tip airfoils, cut out the templates and cut the cores in about 2 hours. I have since cored out the foam cores, sheeted them with 3M 77 and covered them in 3.5hrs.

So now I have a set of wings done in 5.5hrs and all my equipment is homemade from the hardware store, the power supply is a car battery, and the foam is from Home Depot. Nothing fancy. But I would like to have a Feather Cut system after using a friends. It makes creating a core so simple!!!

I used to make built up wings, but even using a jig was a nightmare if the wing is tapered, let alone the problems on the jig if it is a large wing.

The best thing is if I do not like how the wings fly, I can just make another set in a evening.

Just things to ponder,
Darrin Cash

(in reply to pukinbuzzard)
       Post #: 4

Trailing edge dilemma - 2/6/2002 11:38:05 PM   
pukinbuzzard


 

Posts: 32
Joined: 1/3/2002
From: Tampa, FL
Status: offline 		Darrinc, thanks for the reply. I only had an older demo verision of compufoil (and it didn't have the trailing edge wizard). I've now got the latest version.

Haven't done it yet, but from your description, it sounds just like what the doctor ordered.

RE: your question. I haven't done many foam wings, but they all seem to be heavier than built up. (i need to build 2 exactly the same and measure to confirm that).

the building process is easier for me with built up. (it takes longer, though). I think I may do several wings on my next project (33% extra) and may do some built up and some foam.....

thanks, DS

(in reply to pukinbuzzard)
       Post #: 5

Check this out - 2/7/2002 12:22:28 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		DS,

Check out what these guys have done to lighten a foam wing. They are quite amazing!!!

http://www.geocities.com/CapeCanaveral/Cockpit/3328/

Darrin

PS. If your interested, I'm in the process of making hollow core wings for a 33% Extra. Each complete wing should weight around 1lb!!!

(in reply to pukinbuzzard)
       Post #: 6

Yet another option - 3/6/2003 6:21:01 AM   
CompuFoil


 

Posts: 10
Joined: 3/6/2003
From: Brighton, MI, USA
Status: offline 		Hello,
CompuFoil has another option for a thick trailing edge. Under Utilities, there is the "Clipped Trailing Edge Chord Length Calculator" The way it works is this. Say you have an 8" airfoil and need a 1/8" thick trailing edge. The calculator will compute the required chord length such that when you cut it back to 8", the trailing edge will be 1/8" thick. Whether you use my Flare Wizard, or this Calculator, keep in mind that that TE thickness is only valid at that chord length. When you change the chord length, everything, including this TE gap is scaled as well. There simply is no way around that.

Hope this helps!
Regards,
Eric Sanders
[url]www.compufoil.com[/url]
Current version 3.21t

(in reply to pukinbuzzard)
       Post #: 7

Trailing edge dilemma - 3/6/2003 6:28:33 PM   
DICKEYBIRD



Posts: 2675
Joined: 4/8/2002
From: Collierville, TN, USA
Status: offline 		Hello there Eric! Good to have you onboard! Now we can ask all kinds of dumb questions!

When I do tapered wings in Compufoil, I do all the initial design decisions in "Gen. Lofted Full Set of Ribs." When all the basics are in I go back and open the desired airfoil and flare the trailing edge at the root with the chord at it's specified length & save it as a .cor file with a slightly different filename. Then I do the same with the tip airfoil, again flaring the T.E. to the same thickness with the smaller chord, saving it with a different filename.

Now, when you load those new .cor files back into your .lft file, VOILA!....the ribs are lofted with a consistent T.E. thickness all the way out, root to tip!

HTH!
Milton Dickey

_____________________________

"He who dies with the most good Cox engines wins!"

(in reply to pukinbuzzard)
       Post #: 8

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