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View Full Version : Fabric V@ Plastic as covering material?


intruderdave
08-23-2006, 12:45 AM
I am in the planning stages for my next disast... I mean project, and need a little input. All my sailplanes to date have used one of the many heat-shrink, smooth as glass, plastic coverings. Can anyone tell me how a fabric covering worked out for them, particularly on a large (12 ft and up) sailplane? Of course, there are a some fabrics intended for RC use, but I'm also considering the lightest weight Ceconite or Polyfiber such as used on ultralight aircraft. Sure, there would be a weight penalty compared to the plastics, but I have read some studies showing the slight turbulence induced by the weave of the fabric can actually improve the wings performance. Any input will be appreciated.
Thanks
Dave

olmod
08-23-2006, 02:24 AM
Well I havent built quite as large as that :) but back around1970ish I did have a glider with 2 identicle wings one covered with monocoat the other a nylon type curtain material and in light air conditions the nylon won out , I might add they were a polyhedral wing built up construction,its interesting to note that golf balls have a dimpled surface to give a better range:) when it all comes down to it I suppose that it depends on the type of aircraft. cheers.

ForestCam
08-23-2006, 02:29 AM
Have you considered the ripstop nylon they use in preformance kites? It's quite strong and light.

Grasshopper
08-23-2006, 04:09 AM
I've been playing with a new non-woven polyester material for covering. It's super light and very strong. I'm not sure how it will work on an open span but it covers very well over foam and is much lighter than a fiberglass cloth or silk span. Several of the guys on the forum have been doing some tests for me and maybe thay can chime in with their thoughts about it.

Once I had some input from the guys that were testing it, I was going to offer it for sale. I'd be happy to send you a sample if you'd like to see it or answer any questions you have. I covered my Magpie AP with it. FiremanBill is covering his A10 and Skysharkster is trying it out with very good results so far. You can see a photo of it in my thread on my Magpie build. http://www.wattflyer.com/forums/showthread.php?p=94090#post94090 Look at post #41.

Tom

Tom

Sky Sharkster
08-23-2006, 11:50 AM
Hi Dave, I've been reading this thread with interest; For many years of flying gliders (as well as various other types of models) I've wondered if the covering material could be used to increase glide efficiency.
Tom has sent me a sample of the material he's described and so far, it looks like a very good lightweight alternative to F/G cloth. I'm using it over foam on a GWS Spitfire, with Minwax Poly as a bonding agent. It forms a hard, but sandable, shell and conforms to normal aircraft contours easily. The texture is a unidirectional weave and appears to need at least two coats of Minwax, plus sanding, to achieve a smooth surface. It is white and of course will need some type of color application.
Whether it would be a viable covering for an open structure is another question entirely. I'm sure it would be stronger than silkspan + dope and being unidirectional would minimize any tears, unlike tissue or silkspan, which tends to lengthen holes along the grain direction. It appears to need a fair amount of "filler' to obtain a smooth surface but for artifically-induced turbulance this may not be an issue.
My limited knowledge of model aerodynamics seems to indicate that at very low Reynolds numbers an induced flow breakaway in front of the airfoil high point aids the sink rate; For pure duration and again, at low speeds, this would be useful. For thermal duration R/C gliders, which have a greater speed envelope (although still smaller than most model aircraft) and also need to "cruise" between thermals, make headway upwind at minimum sink rate and often have camber-changing devices like spoilers, flaps and combination functions like spoilerons I doubt whether a turbulated airflow would be helpful and might even be counter-productive.
Turbulating the entire airfoil surface seems risky. Most turbulators or inducers are placed at a specific point, dependent on the individual airfoil, glide speed and size (R/N). Full-sized Sailplanes are normally very smooth, although this may be a more a function of the strength ratio of F/G vs open structure.
I certainly don't want to influence you to not try a textured surface covering. there could very well be unknown benefits but personally I don't believe a better overall glide performance at all speeds will be one of them.
JMO
Ron

intruderdave
08-24-2006, 11:28 PM
I failed to mention that this will be an E-powered sailplane. It is not intended to compete with the high performance planes, I just want a fun flyer. One thing I am interested in is the apearance of fabric vs plastic. Sometimes I get a little tired of the 'plasticky' appearance of many of our coverings. It is true that a lot of full size high-performance sailplanes are super slick, but many good performers of the past were fabric covered. I guess the best way to see is to try it!? Thanks to all for the valuable input.

Dave

TLyttle
08-25-2006, 02:22 AM
I use ripstop for hinges (yeah, I'm old), and the first thing I noticed was how thin it is, and how quickly it fills. A couple of yards of this stuff is light; I imagine there is some comparative information out there that covers it, along with tissue, iron-ons, silkspan, galvanised iron.... oh, wait, maybe not the last one...

Turbulence is a plus-minus thing, depending on what you desire from the model.