|Mar 19, 2010, 08:12 PM|
Bagged wing layup spreadsheet
Ever wondered how much layers of fiberglass, carbon or Kevlar your bagged wings really need?
The answer to this question is probably yes. If you’re an inexperienced builder, the solution will most likely be to look and ask what other builders with comparable models have used. Other than that, there’s the wonderful “Wing Layup calcs” spreadsheet by Joe Wurts. Joe’s sheet (Excel says the Author’s name is “David F. Taggart”) does have it’s limitations, and can sometimes be hard to grasp.
Enter Jay Decker who published results from his own developed Excel spreadsheet. (http://www.rcgroups.com/forums/showthread.php?t=451571)
Jay was contacted to ask for a copy of his sheet, as the results he showed looked very promising. It turned out that Bill Osberg was busy modifying Jay’s sheet, because data input at that time was quite basic and time consuming. Bill send me a copy of what he had at that time.
After several months of hard work, the sheet has been transformed to provide a user friendly interface, with all of the composite material specifications included. The sheet calculates the wings basic aerodynamic properties, Cl- and lift distribution, bending moments resulting from hard turning or winch starting, wing stresses from up to four different kind of skins, stresses of up to two darts, tube spars, square spars and capped spars. Wing bending slope and deflection is calculated. The weight and cost of each component is calculated too. It even tells you how much layers of reinforcement the wing’s top layer needs at the servo bay cut into the bottom surface of the wing. The sheet is available in a version with imperial units, and a version with metric units.
Read the supplied manual for more information.
Currently the spreadsheet is a Beta version, meaning it can contain mistakes that can lead to inaccurate results. It is advised to always double check the spreadsheet results by looking at what other comparable model planes use for their wing construction!
|Mar 21, 2010, 07:58 PM|
It seems that adding the torsional stiffness of the wing is not that hard, BUT...
First, I really should include CLT into the sheet, which makes results much more accurate (and makes the calculation a lot more complex). Currently the EI of the (up to 4) skins are simply summed up, basically treating them as separate layers, instead of treating them as a bonded set of different layers with their specific properties according to the CLT.
From the R&G Handbook:
The classical laminate theory (CLT) is a method for conducting calculations on multi-ply inhomogeneous laminate lay-ups. It includes a thorough deformation and stress analysis based on the specific stress conditions in fibre composite laminates and specific failure hypotheses.
Deformation and stress analysis
Using the classical laminate theory (CLT) to conduct a deformation analysis on laminates yields a solution to a statically indeterminate system which has to take into account not only the equilibrium conditions, but also additional constitutive equations as well as stacking assumptions.
The analysis assumes the following:
The ply is the smallest calculation unit in the laminate. The properties of the inhomogeneous ply are “smeared” over the ply, and so “homogenised”.
For the calculations on the laminate, the plies are “stacked” and firmly glued to each other to form the laminate (stacking assumptions).
Whereas the full CLT also considers bulges, twists, and bends that arise as soon as coplanar forces are applied to non-orthotropic laminate lay-ups, the method of treating the laminate as a plane considers coplanar stresses and deformations only.
|Mar 21, 2010, 11:23 PM|
Vincent, thanks for posting and working on the spreadsheet. I've downloaded it, but haven't had time to open it up and take a look. I look forward to giving it a wing.
Thanks for the work.
|Mar 22, 2010, 01:11 AM|
Gratitude for your efforts.
Still have to explore the spreadsheet - will have to get xls working.
Anyway that example wings can be saved for the RCG community to view.
I was thinking if the SuperGee11 was loaded we would have a standard to go from. Same with Taboo, Zone and Edge??
As I say this may already be there - just thinking out loud.
|Mar 22, 2010, 04:42 AM|
Appreciate your replies! I had anticipated that it takes time to get reactions on the sheet, as one typically only dives into it the night before you plan cutting cores.
I must say that Jay's original calculation only had one skin, and now I understand why. Even Joe's calculation doesn't show results from the two skins combined.
@Jeff: good suggestion. We might create a simple database/table with the results from a number of well known designs. That way you can set yourself design goals for a certain torsional stiffness or wing deflection.
Posting the results here as a saved .xls file will allow me to make that database, and eventually include it in the calculation.
|Apr 07, 2010, 06:48 AM|
Good news. I have included CLT and torsional rigidity in the sheet, and have received permission to use part of the Lamicens code!
Still working on implementing the changes to the Imperial unit version.
Expect this soon.
|Apr 08, 2010, 11:29 AM|
Joined May 2004
Thanks for developing such tool ,I will try to contribute if something arise.
A note in the gliders and high perf. forums may atract a lot of talkers
|Apr 08, 2010, 08:03 PM|
North OC, Ca.
Joined Jun 2005
Can you tell me where you got the material property data from? I looked at the r-g catalog of properties and something doesn't seem to make sense.
The mechanical properties look high in the spreadsheet. The E11 values on a bias fabric may not make sense. ( more like E12 IIRC).
I also see no mention of resin properties in the sheets I looked over. they did assume 50 % Fiber volume ( not resin content, there is a difference).
It is critical that the properties be what you can get with a wet lay-up laminate under a vac. bag. Foam cores will not stand much post cure and so the resin modulus and hence resin to fiber load transfer will suffer.
Let's see if we can get the material properties to agree with actual fabrication processess.
|Apr 09, 2010, 07:26 AM|
The material properties in the current spreadsheet version are taken from the free CLT software "Lamicens".
The software prescribes a Fiber volume fraction, which I didn't change.
Fiberglass cloth 25 g/m² is calculated with a Vf of 25%
Fiberglass cloth 163 g/m² is calculated with a Vf of 37%
To me these values look achievable in wet layup vacbag setup.
In the still to be published new spreadsheet version 0.8 you can specify your own Vf.
The E11 values on a bias fabric are also a direct result from the Lamicens software. For a Carbonfibre cloth 160g/m² the E11, E22 and G12 are displayed here:
Notice the dramatic impact of bias orientation.
The resin properties in the current spreadsheet are:
E_resin: 3400 MPa
G_Resin: 1019 MPa
In the new version, resin properties can be manually changed.
It would be nice to include properties of some well known resins.
|Apr 09, 2010, 02:39 PM|
North OC, Ca.
Joined Jun 2005
when I opened the Beta version( english) I noted the 3k twill laminate was 12.5 mils thick. Multiple sources ( albeit probably autoclaved and normalized to nominal CPT) put the thickness at "PLY THICKNESS: 0.0074-0.0085 in."- source http://snebulos.mit.edu/projects/ref...HDBK-17-2F.pdf
Mil handbook 17. Vac bag wet-lay-up is a bit thicker but that is alot thicker.
I have not yet been able to reference the link but I will check it later. Your resin properties are similar to the west systems physical properties (RT cure , no post cure)so that is good.
My main issue is the beta test spreadsheet properties, I assume the properties are the calculated output of the rule of mixtures E11= E11resin(1-Vf(fiber))+ E11fiber Vf(fiber).
My German limits my ability to use the lamicens software......
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