Some examples:
120" span 1/2" x 0.028" uni carbon - 1.00 safety factor - 203# line pull at failure
120" span 1/2 x 0.014" uni carbon - 1.00 safety factor - 105# line pull at failure
80" span 3/8 x 0.028" uni carbon - 1.00 safety factor - 118# line pull at failure
There is a great dependence on the distance between the caps - it is a third power relationhip. If you have a choice of putting the cap at the wing surface or under D-box sheeting, go with the wing surface - the extra 1/8" (2 x 1/16") will make a tremendous difference.
I can also tell you - from experience - that a 2M with 50# pull designed wings without flaps can take a full pedal zoom. I do not think that wing could generate much more than 50# of lift. Guys who have seen my 2M at the Nats can attest to the abuse that wing took. I built that one with a wood spar, but it was 1" wide at the root. I also ignored the added strength of the carbon joiner and the full wing balsa sheeting, using any added strength as safety factor.
The failure will occur on the top surface where the spar is in compression. Failure is by buckling - separating from the wood spar. The wrapping is very important in preventing this, as the carbon does not accept the glue as well as more porous materials. Lightly sand the the carbon on the glue side to five it some "traction". I've been told that any thread wrapping will do, but the kevlar is cheap insurance.
The Excel spreadsheet is available (finally) at http://users.adelphia.net/~sliderule. Follow the link to Radio Controlled Model Sailplanes, then right click and choose "Save Target As" to download a copy of the "Spar Cap Stress Calculator". Standard disclaimers apply.
----- Original Message ----- From: "Harley Michaelis" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; "RCSE" <soaring@airage.com>
Sent: Monday, January 24, 2005 12:20 AM
Subject: Re: [RCSE] Carbon fiber reinforced spars
Wes. . .it will be easiest to work with the rigid, pre-made laminated spars. They come in several lengths, widths and thicknesses. If this is a 2M RES the .014" thickness should be fine. If somewhat larger, a bit thicker would be better. You do want these to be flush with the top and bottom of the wing, so will have to deepen the spar notches in the ribs to accommodate the thickness of the CF spars. if it is that kind of construction. You should also get the Kevlar thread from CST for wrapping around the spar system to keep things together.
File 3 of the Genie pages at http://genie.rchomepage.com/ has pix and text in it about CF spar use, attaching, wrapping, weighting down, etc. This file is going to be updated again shortly, so check it out again in a couple of weeks.
----- Original Message ----- From: "Wes Gibson" <[EMAIL PROTECTED]>
To: "RCSE" <soaring@airage.com>
Sent: Sunday, January 23, 2005 8:27 PM
Subject: [RCSE] Carbon fiber reinforced spars
Building a new woodie RES and this time I want to reinforce the top and
bottom spars with carbon fiber. I've been looking over the CST and Aerospace
Composite Products web sites ending up with more questions than answers. I
know I should use unidirectional carbon fiber, but what's easier to use:
tapes or tow? What thicknesses are recommended? I don't have a vacuum
bagging system, so I'll have to use old fashion phone books to weight the
stuff while the epoxy dries. I did find an informational article by Bob
Vixie which helped out a lot, but he didn't talk about thicknesses. Anyway,
what does everybody recommend out there.
Wes Gibson AMA 607029 LSF 7533 -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.300 / Virus Database: 265.7.0 - Release Date: 1/17/2005
RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
