I saw a youtube video (from a channel called Real life guys) where gum was used to join the ribs of their homemade plane to the skin and I saw another video where the wing skin(tedlar) was literally sown to the ribs of the wings,my question is what is the appropraite way to join the wing skin(tedlar/mylar)to the ribs?
The FAA offers a nice handbook on wing skin covering for fabric aircraft you can find here. They list, clips, screws, rivets and lace as the joining methods
Rib Lacing Cord
Rib lacing cord is used to lace the fabric to the wing ribs. It must be strong and applied as directed to safely transfer in-flight loads from the fabric to the ribs. Rib lacing cord is available in a round or flat cross-section. The round cord is easier to use than the flat lacing, but if installed properly, the flat lacing results in a smoother finish over the ribs.
In some cases, or even in adition to other methods fabric cement may be used.
Modern fabric covering systems utilize special fabric cement to attach the fabric to the airframe. There are various types of cement. Figure 3-9In addition to good adhesion qualities, flexibility, and long life, fabric cements must be compatible
Tedlar is DuPont's brand name for a polyvinyl fluoride foil. Chemically it is between polyethylene and PTFE (brand name Teflon), and the strong chemical bond of the fluoride atom gives it good weather resistance and gas tightness. In aviation its only use is in the decorative cover of internal cabin surfaces.
Mylar is DuPont's brand name for a biaxially stretched polyester foil which has high mechanical strength but low resistance to ultraviolet light. It is used for blister packages or soda bottles. For aerospace applications it is made gas-tight and UV resistant with a metallic layer of a thickness of only a few atoms. Such metallized films are used for thermal blankets, in spacesuits, on satellites and for toy helium balloons.
Both materials are sold as foils (or films), and this makes them rather unsuitable for covering aircraft surfaces. A proper cover material should be a fabric, for three reasons:
- Fabrics can be tightened after application, for example by the application of dope.
- Fabrics are better for draping around spherical surfaces. Depending on the type of weave, this capacity is rather limited, but still much better than that of films which need to be plastically deformed in order to assume a three-dimensional shape.
- In fabrics, stitching will not introduce local defects but leave the tensile strength of the material intact.
Bonding or glueing alone will not be sufficient to permanently attach a cover to a substructure, because in low-pressure regions the cover will be sucked away from the structure. This results in local peel stresses which are certain to destroy the bond over time. @Dave's answer gives a good overview how to avoid peeling - be sure to pick one of the methods it shows.
Model aircraft use special polyester foils which have been stretched and will contract under the application of heat. On one side they are covered with a hot-melt adhesive. Their easy application has made them supplant most other covering materials, and the web has many pages with instructions for their application. However, for man-carrying aircraft they are too thin and offer too little strength.