Hi, all my drawings are made with " QCAD ".
There is a very complete free version of this software...

Hello everybody,
I am wondering about the design of the CD wings. It is clear that the thickness at the root constitute an irrevocably factor of strenght. However, it is probably disadvantageous regarding performances. Would it be possible to reduce the thickness of the wing and therefore increasing the performance of the CD? I was thinking of strenghtening the wings with brace like on the Moyes Tempest.
Looking forward to having any comments on this.
Didier

Hi Didier,

It shouldn't be necessary to brace the wings with external struts if you design them properly. All the compressive and tensile loads are carried by the carbon rods in the spar caps. Pultruded carbon rod has incredible load carrying capacity, and if you are worried about strength then you can safely use more rods than are strictly necessary with very little weight penalty. Your wings will also have less vertical flex under load. Adding support struts/trusses would significantly increase drag and reduce performance, negating any improvement in performance gained be redesigning the wing to make it thinner. The Carbon Dragon wings are purposefully thick so that they generate lots of lift even when flying very slowly - they're not designed for high speed performance like a sailplane!

I would strongly recommend that you get a copy of Jim Marske's Composite Design Manual and study it for a better understanding of the loads and stresses in a wing. The manual shows exactly how to calculate the loads in a wing and how to design both supported (trussed) and unsupported (cantilever) wings and spars.

www.marskeaircraft.com/flying-wings.html - Books & Manuals

I developed a spreadsheet for the Carbon Dragon wings based on Jim Marske's manual:

www.ihpa.ie/carbon-dragon/index.php/cd-b...rs/phil-lardner-s-cd
www.ihpa.ie/images/carbon-dragon/CD%20Bu...g%20calculations.xls

Jim Marske also supplies suitable pultruded carbon rod in continuous rolls.

You'll need to modify the spreadsheet if you change the thickness / airfoils of the wing.

You can't change the thickness of the wing without changing the airfoils and doing a full aerodynamic analysis of the wing - and that's definitely a non-trivial task, and way beyond my skills at the moment! That said, if you do redesign the wing/airfoils and the analysis looks good then do please share your results here! I'd recommend getting familiar with either/both Profili2 and/or XFLR5:

www.profili2.com/eng/default.asp

www.xflr5.com/xflr5.htm
- XFLR5 Youtube tutorials - not for the faint hearted!

www.mh-aerotools.de/airfoils/index.htm

I'm not an expert in wing design or analysis, but happy to help out where I can.

All the best,

Phil.

Depends what you mean by performance. This is not a "contest machine", but rather a "micro-lift" glider. I am not sure you can have the very high L/d (40-1 for example) and also have a glider that climbs in very light conditions. It has been reported (and maybe it is hype) that one does not need to thermal this glider as long as there is any lift at all. It would be interesting to verify that fact.