Coverings

last updated 12/24/2006

Regardless of how you cover your wing, there are a few simple things to remember before you begin.

The Color of a Wing

It is not uncommon to lose a fast wing in flight.  During the building phase, most beginners will completely forget about the color of their aircraft from a functional perspective.  This is very understandable since sharp looking aircraft always fly better!  My car even runs better when it's clean, it's simply a universal constant.  However, what looks outstanding on the ground may very well disappear at 100ft on an overcast day.   And if you start doing aerobatics, being able to tell where your plane is in relation to the ground can mean the difference between completing a roll or beginning an abrupt landing.

Flying wings have a further disadvantage from their shape.  How many times have you become disoriented by your wing?  If you have flown at all, most likely at least once.  Even if you are extremely good at spatial relationships, all it may take is a comment from a watching friend and you run the risk of losing your orientation.  It happens quickly.

Ultracote® and film coverings

Ultracote is a great option for covering foam wings.  Ultracote is also marketed as Oracover although apparently through different manufacturers now.  It might be said that Ultracote is in reality the only film option for easily covering foam.  Easily is the key word here.  The rational being that the temperature required to activate or melt the adhesive needs to be lower than the melting point of the foam itself, yet still retain shrink capability without also melting the foam.  Ultracote fits that requirement nicely.  As shown in the graph below, Ultracote has a very well defined adhesive and shrink behavior based solely upon temperature.  If you are searching for an extremely stiff and sharp looking aircraft and you do not feel like playing with fiberglass or bags, then a film covering such as Ultracote is your best solution.  And if that is not enough it is easy and fun to do.

There exists several different kinds of iron-on films and all have different prices and availability.  Some individuals use Econokote® or Monokote®, others use Coverite® Black Baron (low temp), Oracover, Ultracote® or Ultracote Plus. Regardless of which one you choose,  make sure the adhesive temperature of the film is below the melting point for your type of foam as well as some shrinkage temperature.  Weight is the other consideration.  Two weight tables can be found at CharlesRiverRC and FatLion.  Tensile strength is another variable and it pertains to how tear or puncture resistant the film is.  

It is easy to get confused.  After much heated debate on eZone, most people settle on Ultracote, Coverite or Econokote depending upon their cash flow at the time.   After all, "money saved means more toys played."

price versus foam melting point table, condensed weight and tensile strength table to be inserted here.

The following table was compiled by 02ViperTwin on the eZone thread found here  Be aware that different colors of the same film may weight different amounts.

You can find more weights at http://www.fatlion.com/sailplanes/weights.html

To apply the heat, use an iron specifically designed for it.  The 21st Century Iron from Coverite is a good choice.  It has a digitally controlled thermostat that is accurate and you will find this to be an important feature when applying the film.   Purchase or borrow some type of iron designed for film.   They are specially shaped for getting into corners, are usually teflon coated and come with cloth socks to prevent scratching of your film.

If you cannot find a covering iron, a normal household clothes iron will work in a pinch but I would avoid the clothes iron method at all costs unless you are an expert and understand the risks.  If you go this route make sure you calibrate it before you begin.  One easy method is to set the iron on the lowest temperature possible, wait 10 minutes and place a drop of water on it.  Since water will boil at roughly 212 F degrees (100C) when at sea level, slowly increase the heat until the drop begins to boil.   Mark the iron setting.  212F  is just below the adhesive point of Ultracote and there is a designed in buffer before it will begin to shrink at 300F (148C).

Stay away from hair dyers.   If you practice a lot you can get away with it but it requires a lot of practice.  While you will save yourself $30, you will most likely ruin your plane.  Hair dryers and other hot air blowers focus extreme heat into a very small area.  You will melt your foam and only melt  a small area of covering onto it.  If you move the dryer quick enough to avoid melting the foam, you are most likely not activating the adhesive either. If you apply too much heat, you might wind up with a modern art sculpture that cannot fly.  

(The graph above is for Ultracote.  A similar temperature chart for Coverite can be found here at the Coverite web site.)

The trick is to only shrink the covering as much as you need to make it look nice.  Save as much shrinkage as you can for future events and this means to use the lowest heat setting possible. After flying a few times you may notice bumps and wrinkles that appear.  These can be removed through a judicious use of heat.  Starting with the last heat setting used during the initial covering, slightly increase your heat and work the wrinkles out.  Remember that once a heat setting is used, Ultracote will not shrink any more at that same temperature.  You must increase the temperature to create more shrinkage, and once you hit the maximum, it will not shrink anymore.  If you need to remove the covering to fix something, try heating your iron up to 220F and carefully pull on it.  If you shrunk it before to make it look nice you will most likely have to do that again to retain the nice look.  

The tutorial at Dave's Aircraft Works Covering Tips has a lot of great tips for covering foamies.  They have done this many times before and their tips include covering Coroplast as well. This is a 3C conversion project almost complete with Ultracote. Ultracote was applied to the Coroplast winglets and elevons.  Click on the pictures to see a larger image, it might take a while as they are large (1600x1200).

One of the more difficult challenges with covering a Zagi is determining the shape of the Ultracote before applying it to the wing.  To help with this, use some clean newspaper and experiment with different shapes.  Here are two shapes that can be used to cover each side of the wing with only two pieces of Ultracote, a total of four will cover the entire Zagi.  These will be rather large pieces and if you begin with the TE template first, the LE template will overlap creating a nice seal.

Before you begin placing the Ultracote, make sure that the surface is properly prepared.  Sand the surface with 150 grit sandpaper in one direction only to ensure smoothness of the finish.  This is important for covering over the strapping tape used in the initial construction.  Most tape is sold with an anti-stick coating on the non-stick side.  This is done to ensure that you can easily unroll the tape.  You do not want it to unroll your Ultracote, so sand it lightly to remove this coating.  When the sanding is finished, wipe down the entire wing with a damp cloth or towel and let air dry.  

There are many different ways to apply Ultracote but probably the single most important tip during application is to take your time.  It is not a race, and if you spend a few minutes removing the wrinkles and major screw ups first, the end result will be that much better.  Having said that, try not to fixate on minor wrinkles, bumps and air pockets.  These will generally disappear during the shrinking phase.  Concentrate first on getting the entire surface done and sealed before moving onto shrinking the Ultracote.  Air bubbles can be removed by poking a small hole with a needle or X-acto knife in the middle, then applying heat to smooth it out.

If you feel like covering your Coroplast winglets or elevons, thoroughly wash the Coroplast with Windex or soapy water first.  Spray the Coroplast with S77 and place the Ultracote down while it is still wet.  It helps to peel the paper backing off of the Ultracote just before you spray it.  You can use your fingers to press it down, however a towel works better to spread the wrinkles out.  It is not required to use heat, but low heat will shrink it a bit if you are careful to not let the iron sit for too long in one spot.  If you use an iron on Coroplast, be prepared to ruin one piece until you figure out what the melting point is.  Technically, the melting point for Coroplast is 324 degrees F (162C); but reality always wins.

As a last comment, several people have reported problems with using chrome film or tape.  Apparently this covering can be conductive and might effectively shield your antenna during flight.  Here is a thread on eZone which has reported this same phenomenon.

Here are some steps in a suggested order to follow:

The Tape

Using the supplied colored tape is the most convenient method. Hopefully you will have it included in the kit but it depends upon where you purchased it.  If you do not have any you can purchase it through  Trick R/C or www.uline.com and search for 'color coded tape'.  You can find 2.2mil x 2" or 3" rolls of tape for around $4 each.  Since weight can be the deciding factor between a good Zagi and a great Zagi, show some restraint in how much you apply.  Overlap the tape as little as possible to keep the weight down.  Begin at the TE (trailing edge or rear) of the wing continuing forward and ending with a single wrap across the LE (leading edge) with half of the tape above and below the LE.  

A trick that helps the taping process is to keep your scissors clean.  Every 5-10 cuts, wipe your scissors with a damp paper towel with Windex on it.  The residue from the tape can make clean cuts almost impossible and good quality scissors will make a difference.  If the tape adheres to the scissors you will most likely tear the tape instead of cut it and if it is already applied to the wing it will look ugly.

Several individuals have reported great success with shrinking the tape using a normal hair dryer or heat gun.  The hardest part to do correctly is the LE nose where the two cores meet.  There are several ways to fold the tape to keep it smooth, but it is non-obvious and difficult to do it without wrinkling it somewhat.  So, we try our best and get frustrated anyways.  One method that that works fairly well is to cut a split at the end of the tape.

(Try not to laugh at my old Zagi but I needed an example nose to use.  Believe me, new tape looks much better)  If you put the end of the split at the very tip of the nose similar to what is shown below, you can then fold it around the nose a little easier.  Another option is to cut a V shape in the end and fold that over the nose like this:

Yet another method is to make two slits from either end leaving an uncut section in the middle, about 1/2" or so.  You fold each side down or up as carefully as you can, overlapping the excess from one side at the top onto the same side at the bottom and visa versa.  It does not matter if you fold the top first or the bottom first, whichever one looks nicer for you.  Probably bottom first so the top overlaps, opposite of what is shown here.

I have yet to come up with a perfect solution so if you know of one, please let me know so I can put a link to your page that demonstrates it or post your idea here (with your name of course).

® UltraCote is a registered trademark of Horizon Hobby Distributors.