Changing out wing root tape periodically and an oil mystery

[edwalker]

Since it's in a hangar, I've had the same wing root tape on the Phoenix since its last annual a year ago. It's some of the high quality tape offered on Wings and Wheels. I had to remove it today to track down a leak, and to my surprise it was almost impossible to get off. Apparently the adhesive had dried out and formed a more steadfast bond with the gelcoat. I had to gently use a small plastic scraper to slowly get the vinyl tape off and then use some GooGone to soak and remove the yellowed, hardened adhesive. After wiping with a dry cloth I removed the final residue with some acetone. It took about an hour just to do one root.

My guess about how this happened is that the tape adhesive gradually dries out over time. It probably didn't help that I had the plane in hot conditions in Ephrata last summer where it sat out with its covers in 90+ degree heat for several days. The W&W tape has a good reputation, but most sailplane owners are using it for shorter periods of time since it is removed at disassembly. I'm going to change it out more often.

Additionally, in case this happens to anyone else...

What got me started on this was that I found a small puddle (maybe 2 teaspoons) of oil under the bottom of the plane this morning. The drip point was the centerline of the fuselage about 9 inches in front of the trailing edge of the wing. There is nothing there that should be dripping except it is the low point of the belly at rest. What was weird was that there was a faint residue of oil from that drip point back to the trailing edge of the left wing root tape on the underside of the wing. Several very smart people spent an hour looking at this and trying to figure out what was happening until we realized the mechanism.

I'm sure you're all familiar with the oil system breather tube that vents to a small slot just in the fuselage centerline just ahead of the landing gear. I've been practicing a lot of no spoiler landings in the pattern, and there is a very slight residue from the breather hole to the midpoint of the wing root underside. Some oil from the breather tube got under the wing root tape edge in the angled flow of the slips and then gradually tunneled back in the tape to the trailing edge where it slowly dripped out after I left, working its way by gravity to the fuselage centerline where it accumulated until a drop could form and create the tiny puddle. Very subtle. What was puzzling was, although we all thought it was oil, there was no direct residue path from the breather slot down the centerline to the drip point. Apparently the slips created the ideal conditions for this anomalous pathway. The tape from the underside midpoint of the wing all the way back was still adherent, but when I pulled on it the tape came off easily and was clearly soaked with oil.

 

[Jim Lee]

In cool conditions (anything other than Florida or Arizona in the summer), use a heat gun first, and bring the temperature of the wing to about 80 f degrees.  Then peel the tape sideways at a 45 degree angle.

From Cumulus Soaring:

Important Safety Note: "Gap Seal Tape" is Not Designed for Use on Control Surfaces
This stretchy plastic tape is perfect for use sealing fixed gaps - such as the gap between the wing and fuselage.  I do not recommend using it on control surfaces such as the gap between the wing and aileron or the fin and rudder, or the horizontal stabilizer and elevator.  Plastic tape will shrink over time and especially when it gets hot in the sun.  If it is connected to a control surface it may contract over time and not allow full travel of the control surface.  Or as it gets tight it may pull off as it is stretched by the control surface - which could lead to high drag or reduced control of the aircraft as the tape flaps in the airstream or changes the airflow over the control surface.  Using plastic tape secured on both sides and across a control surface gap is unsafe and may be an illegal modification to the aircraft.

Notes on Cleaning Tape Residue

"Any adhesive residue should always be cleaned up with lighter fluid, never MEK, acetone or lacquer thinner.  Lighter fluid will not harm paint, gel coat or canopies.  Never get anything near any airplane that will harm the canopy!  I have heard of guys dropping a container and having lacquer thinner splatter on a canopy, NIGHTMARE!". - Mike Bowlus

[Eric Greenwell]

Good reminder - it's been at least three years since I've changed the tape on mine. Next time I'm at the hangar, I'll warm up a tape end on the wing root, then lift enough off the surface to see how much residue is left. I've always (30+ years) used 3M General Purpose Adhesive Cleaner #08984 to remove tape residue (and more, not just on gliders).