Open vs. Taped Upper Aileron Gap
In 2004, while making drag measurements on my right wing aileron panel, I snuck in a comparison of the
open vs. taped aileron gap on the upper surface. The wing has lower surface Mylar seals as well as internal S seals, so
air venting up from below is not an issue.
I was using a drag probe on the trailing edge of the aileron with an array of miniature Pitot tubes extending above the wing
but not below. The array was about an inch high. The vertical axis in the graph is the voltage from a differential pressure
sensor measuring the aircraft Pitot pressure minus the average pressure of the miniature Pitot array. Thus, the greater the
voltage the slower the airspeed in the boundary layer compared to that impinging on the nose of the glider; i.e.,
the greater the drag. The black curve is from the clean wing with an open aileron gap. The orange curve is the same, but with
the gap taped. Ignore the red curve.
I don't recall clearly what kind of tape I used. I usually use a wide fabric tape on my upper aileron gaps.
That's a thick tape. I assume that, with the thickness of the boundary layer at the TE, a thick tape won't hurt.
In any case, the thickness of the tape's leading edge is a problem farther forward, such as in with tape competition
numbers on the bottom wing surface or the fin.
Bottom line: It appears that taping the upper aileron gap makes a measurable difference above 70 kts and the improvement
increases with speed.
Tom Shipp's Control-Rod Seals
Fabric # 2117232 WT BD BLKOUT. A closely woven material with a rubber like coating on one side.
Can be purchased at most fabric shops. Cost will be about $3.00.
Use Weldwood DAP Contact Cement to glue the seam and to the inside wing root.
Can be purchased from any hardware store, cost about $3.00.
Use a full size cone for the dive brakes and cut some (about one inch) off
the bottom for the aileron control. Install the dive brake first since there
will be a slight overlap on the aileron control seal. To insure the correct
length for the aileron, tape the cone to the control rod and determine the
correct length while holding the cone at the wing root and making full aileron
defections with the control rod.
Glue the large cone end to the wing root and use either a tie wrap or tape to
attach to the control rod. After dry, re-check the control rods for full travel
and adjust as required.
Some gliders may already have a fairly good foam seal on the left wing aileron
control so this may not require replacing. If so replace it with a new foam,
the hole size should provide some friction on the control rod to insure a good seal.
The tie wrap or taped end will extend the cone almost fully out with
the dive brake closed and extend through the hole when opened fully. The tie
point on the aileron will be about centered in the hole when in the neutral
In the pictures, the left wing has only the one seal for the spoiler rod because the existing seal
for the aileron control rod appears to do an adequate job. The end of the cone is secured to the
control rod by cable ties.
(Click for larger image.)
Comment by Jim Hendrix
I tried making a set of these seals for #60 using transfer tape instead of contact cement. This
failed for two reasons. First wrinkles in the fabric where it seals to the root rib made channels
for air flow (contact cement seals these), and, after one season, the seam that connects the two
sides of the seal together had come apart. So, this is a good idea not to try.
Ed Thunen's Control-Rod Seals
I have had my Cirrus for approximately 18 years. I have been using "punch-bag"
balloons for push rod seals. I cut the balloon across where its
circumference is slightly larger than the push rod hole in the root
rib. The balloon is glued to the root rib with contact cement. The
balloon stem is a snug fit on the push rod. Be sure the balloon is
long enough so it does not impede motion. They will only last about
a year but there cheap! Do not seal the close fitting push rod.
Apply the glue with care and you will have less mess to clean up next