Size Requirements for Different Aircraft Metal Decals with Cellophane Backing Metal Decals With Paper Backing Decals Metal Decals with No Adhesive Paper Decals Vinyl Film Decals Almost universally for U.S.-registered, standard certificated,  fixed-wing aircraft, the marks must be at least 12 inches high.  A glider may display marks at least 3 inches high. In all cases, the marks must be of equal height, two-thirds  as wide as they are high, and the characters must be formed  by solid lines one-sixth as wide as they are high. The letters  “M” and “W” may be as wide as they are high. The spacing between each character may not be less than one- fourth of the character width. The marks required by 14 CFR  part 45 for fixed-wing aircraft must have the same height,  width, thickness, and spacing on both sides of the aircraft. The marks must be painted or, if decalcomanias (decals),  be affixed in a permanent manner. Other exceptions to the  size and location of the marks are applicable to aircraft with  Special Airworthiness certificates and those penetrating  ADIZ and DEWIZ airspace. The current 14 CFR part 45  should be consulted for a complete copy of the rules. Markings are placed on aircraft surfaces to provide servicing  instructions, fuel and oil specifications, tank capacities, and  to identify lifting and leveling points, walkways, battery  locations, or any areas that should be identified. These  markings can be applied by stenciling or by using decals. Decals are used instead of painted instructions because  they are usually less expensive and easier to apply. Decals  used on aircraft are usually of three types: paper, metal, or  vinyl film. These decals are suitable for exterior and interior  surface application. To assure proper adhesion of decals, clean all surfaces  thoroughly with aliphatic naphtha to remove grease, oil, wax,  or foreign matter. Porous surfaces should be sealed and rough  surfaces sanded, followed by cleaning to remove any residue. The instructions to be followed for applying decals are  usually printed on the reverse side of each decal. A general  application procedure for each type of decal is presented in  the following paragraphs to provide familiarization with the  techniques involved. Immerse paper decals in clean water for 1 to 3 minutes.  Allowing decals to soak longer than 3 minutes causes the  backing to separate from the decal while immersed. If decals  are allowed to soak less than 1 minute, the backing does not  separate from the decal. Place one edge of the decal on the prepared receiving surface  and press lightly, then slide the paper backing from beneath the  decal. Perform any minor alignment with the fingers. Remove  water by gently blotting the decal and adjacent area with a  soft, absorbent cloth. Remove air or water bubbles trapped  under the decal by wiping carefully toward the nearest edge  of the decal with a cloth. Allow the decal to dry.  Apply metal decals with cellophane backing adhesive  as follows: Metal decals with a paper backing are applied similarly  to those having a cellophane backing. However, it is not  necessary to immerse the decal in water to remove the backing.  It may be peeled from the decal without moistening. Follow  the manufacturer’s recommendation for activation of the  adhesive, if necessary, before application. The decal should  be positioned and smoothed out following the procedures  given for cellophane-backed decals. 1.  Immerse the decal in clean, warm water for 1 to 3  minutes. 2.  Remove it from the water and dry carefully with a  clean cloth. 3.  Remove the cellophane backing, but do not touch  adhesive. 4.  Position one edge of the decal on the prepared receiving  surface. On large foil decals, place the center on the  receiving surface and work outward from the center  to the edges. 5.  Remove all air pockets by rolling firmly with a rubber  roller, and press all edges tightly against the receiving  surface to ensure good adhesion. 1.  Apply one coat of cement, Military Specification  MIL-A-5092, to the decal and prepared receiving  surface. 2.  Allow cement to dry until both surfaces are tacky. 3.  Apply the decal and smooth it down to remove air  pockets. 4.  Remove excess adhesive with a cloth dampened with  aliphatic naphtha. Apply decals with no adhesive in the following manner: To apply vinyl film decals, separate the paper backing from  the plastic film. Remove any paper backing adhering to  the adhesive by rubbing the area gently with a clean cloth  8-18