How to Apply Mylar

What is Mylar?

Mylar is a thin strip of flexible, curved plastic that is used to seal the gaps around control surfaces. It is one of the most effective performance modifications that you can do.

Since air can no longer leak behind the hinge line, it can also make the controls more responsive, especially at low speeds. Mylar is most commonly used to seal ailerons, flaps and elevators on gliders, but on certain models, it can also be used on the rudder and sometimes even undercarriage doors. A Mylar seal consists of three tapes:

• At the bottom, you have the Tesa Double-Sided which bonds the Mylar tape to the glider
• In the middle, you have the Mylar tape which seals the gap
• On top, you have capping tape, which seals the leading edge of the Mylar tape creating a smooth transition.

Sealing your glider is not a particularly difficult task, but it is time-consuming, requires a bit of patience and using the wrong size will ruin your day as you’ll have to start again… As I found out the hard way…

1. What you'll need.

• A clean rag
• Cleaning Solvents:
  • Industrial Cleaner
  • Cleaner 191 (OPTIONAL: With 191 you have to be careful as it contains acetone which will melt cellulose paint and when we filmed our guide, we didn’t use it all)
• A heat gun
• Wizz Wheel (Stripe off tool)
• A drill (or any rotary tool that the wizz wheel can be attached to)
• A pencil
• A ruler (or ideally steel rule)
• A razor blade/utility knife
• Scissors
• Masking Tape
• Mylar
• Tesa Double-Sided Tape
• Capping Tape
• PTFE Tape (glider dependent)

Capping and Tesa Double Sided tape has to be sold as a roll for obvious reasons, but for smaller jobs, the other tapes are available by the meter. When it comes to measuring, which we'll cover further down, you may find our sizing guide helpful.

2. Preparing the surface.

If you are replacing old mylar, before doing anything, measure the mylar, the capping tape and the double-sided tape that’s already on there. It will save you a considerable amount of time later on.
You can then start removing the old stuff. If it’s been on there for a while then the tape will probably flake off rather than come off in one long strip. You can use a heat gun to gently warm the area (not too hot) and soften the tape until it starts coming off in long strips. Avoid pulling up as that may pull the paint off the glider, instead pull back along the surface of the glider. Like Jake is doing in this picture.

Once you remove the tape, you will probably find most of its adhesive remains on the surface. If you’ve ever tried to remove tape adhesive with chemicals, then you know they are excellent at turning a sticky mess into a soggy and sticky mess. It then becomes a battle of attrition between your thumbs and the entire wingspan of your glider. Save your thumbs and use a Wizz wheel (stripe-off tool) instead. It’s astonishing how much easier it makes the job.

When using the Wizz wheel it is crucial that you know which way the wheel is spinning and that you always orientate it so the wheel is running off an edge and never onto an edge. Even a household drill has enough torque to rip the trailing edge off your wing or worse a control surface. It is vital that you keep the wheel moving, staying too long in one spot can burn the surface.
Once you have a clean surface you can then look at sizing the tapes.

Now may also be the perfect time to hard wax your glider, as there are no obstructions. You can watch our guide on hard waxing here.

3. Sizing the tapes.

Mylar

If you can't get the information from the old Mylar or the manufacturer, then you will need to work out what size Mylar you need on your own. The first thing to look for is the biggest cutout or the biggest obstruction on the control surface. On most ailerons, for instance, you will see cutouts for the hinges or even large cutouts where the aileron linkage connects up.

You need to make sure that once Mylar is laid on top, there's no chance of it fouling the cutout and obstructing the control surface movement. If Mylar doesn’t cover the gap at full deflection, then it could sink into that gap. That's dangerous. So this size of Mylar is too small:

The next size up you can see that at full deflection, it's not going to fall into that gap and obstruct the control surface. So that's a good size:

Generally, we recommend you try and use the smallest size you can get away with. That usually results in a tighter seal. If you go too large, like in the photo below, you can see the Mylar doesn’t sit flush to the surface and there’s a large gap at the back:

Tesa Double Sided

When you look at the edge of the Mylar, you can see that it’s curved. You want the middle of that curve to be close to the middle of the hinge line of the control surface.
If you use double-sided tape that’s too thin, the Mylar will sit too far over the control surface or aileron in this case. You won’t get the trailing edge to sit nicely on the aileron. If you use double-sided tape that’s too thick, then it won’t cover the cutouts and could end up obstructing a control surface. The sizing here doesn’t have to be perfect as long the mylar is seated correctly.

Capping Tape

This one is the simplest. You simply want a width of capping tape that covers the portion of Mylar that is in contact with the double sided tape, with at least five mil overlap in front of the leading edge of the Mylar. 25mm is the most popular size.

4. Applying the tapes.

Gliders are handmade, and this becomes very apparent when you examine any “straight” edges closely. Coupled with age, trailer rash, and repairs, you may find that your control surfaces and trailing edges are quite wibbly wobbly.

For Mylar to seal, it has to be laid in a straight line. Any deviation will cause it to bulge or kink and lift from the surface. This doesn’t matter so much for the double-sided tape but trying to apply mylar in a straight line, over wonky double-sided tape is tricky. There are different methods for finding a straight line, I liked using masking tape the most. You use it as you would use string: Stick it down at one end of the control surface, roll it out to the other end, pull it tight and stick it down. Make sure you stick the tape edges a width of your double-sided tape away from the trailing edge. You may need to adjust it slightly to compensate for how wonky your wings are.

Applying the double-sided tape is simple, just do it in stages and apply it gently. You may need to adjust the placement and if you pressed it down, you’ll have to get the wizz wheel out again.

If you’re right-handed, start to your left, working to the right and vice versa if you are left-handed. Apply the double-sided tape against the masking tape edge and stick down in about seventy centimeter sections at a time. Repeat this until you reach the end. At this point, we recommend you check that the mylar will sit nicely over the double-sided tape along the entire length of the control surface. Adjust accordingly and then push the double-sided adhesive down with your rag, removing most of the air bubbles.

Now the Mylar itself. Cut a slightly oversized length of mylar for the surface you’re working on first. Make sure both ends of the mylar are cut cleanly at ninety degrees. Stick the mylar to one end of the control surface with masking tape and roll it out to the other end.

If you don’t stick it down, there’s a high probability the mylar will slide off the wing onto the floor and all the dirt in the world will static itself onto it.

You now need to be very precise. Peel back approximately thirty centimetres of the red backing from the double-sided adhesive and carefully align the corner of the mylar with the edge of the control surface. You will probably have to trim it later so going over a bit is better than not pulling it close enough, which you can’t fix.

Keep the Mylar taught, you want quite a lot of tension. Pull back more of the red backing, align the mylar and press it down with your fingers or the cloth. Repeat to the end. It is particularly important to maintain that tension, even when changing hands or moving further along the wing - if you let the tension off, you will get kinks!

Screwing up at this stage usually means new double-sided and mylar tape. Mylar doesn’t like being reseated and usually damages the double-sided in the process as well.

Using the razor blade and steel rule, you can now trim the ends of the mylar. Be very careful not to score the paint or gelcoat underneath!

Capping tape is the most forgiving tape of the whole lot, but you do need to move the masking tape to accommodate it. Position your new line of masking tape so that the capping tape covers the portion of the mylar in contact with the double-sided tape. A pencil is handy for marking where the masking tape should go.

And then just apply it with gentle tension. The capping tape is easy to adjust and shape.

Finally, PTFE or Teflon tape can be used in different ways when it comes to sealing gliders. There are two types of tape used for this purpose – glass backed PTFE tape, and Teflon tape (no glass weave). The type you need will be specified in your maintenance manual or you should ask the manufacturer or an inspector for guidance. These tapes have a brown or grey colour to them, but this will fade when exposed to UV over multiple years.

In some gliders the PTFE/Teflon tape is used as an aerodynamic seal between the bottom of the control surface and top, it physically bridges the gap between the control surface and the trailing edge of the respective part of the glider (e.g aileron and wing). In this application, it can only be used on gliders with a hinge on one side of the control surface (i.e not centrally hinged to avoid restricting the movement of the control surface).

In another example of a PTFE/Teflon installation, looking at an LS8 aileron which is centrally hinged, a blind PTFE seal is used on its own, without any Mylar. This blind seal is a wide length of PTFE tape used in combination with two lengths of double sided adhesive. This seals the gap with all of the excess pushed inside the recess of the aileron, see picture below as an example.

PTFE tape can also be used to reduce friction through the control surfaces by preventing the Mylar from sliding and scratching the control surface paint, instead if applied correctly it can be used to provide a slippery surface for the Mylar to slide over. This reduces friction through the controls and also creates a better seal between Mylar and control surface.

Usually PTFE tape is installed first – before any double-sided tape, Mylar and capping tapes. Whenever installing any sealing tape, make sure the control surface is fully deflected down or away from you before applying the tape.

A top tip – apply a little lubricating oil to the hinges with your fingertip – this will stop the tape from sticking to the relative moving parts of the hinge and restricting the movement of the control surface, it will also stop it kinking as badly.

When installing, it needs a minimum of 3mm overlap with the trailing edge of the wing/tailplane/fin to provide a secure bond. You may wish to use the masking tape technique to give you a straight reference line to work against. Apply the tape to the trailing edge of the wing first in small sections at a time, being careful to keep the remainder from sticking onto the control surface. Once applied to the trailing edge, then push a little excess tape into the gap of the hinge, you can use your fingertip, or a small wooden mixing stick. This crease of excess tape within the gap, makes sure that this tape never restricts the movement of the control surface allowing for some shrinkage of the tape. Once a small crease has been pushed into the gap all the way along the surface, then the remainder of the tape can be stuck down onto the control surface and all bubbles carefully pushed out with a cloth into the hinges or the gap.

In all cases when working with any sealing tapes, you must follow the instructions from the manufacturer or type certificate holder. Not following instructions can adversely affect the movement and behaviour of the control surfaces and as such, the flight characteristics of the glider. A full deflection test must be carried out following the installation of the tapes and a BGA or approved inspector must sign off the installation once completed.