Q1 Plans Chapter 19 Page 19-7
- Category: Quickie Plans
- Published: Monday, 12 May 2008 10:28
- Written by Dan Yager
- Hits: 1665
Step Four: Primer
The ultra violet radiation barrier is provided by the heavy carbon black content of the dried primer (Dupont 70S). The primer gives the whole surface a flat black color and the sanding should never remove it completely, exposing the light gray feather fill below. The primer is sprayed on, allowed to dry, and sanded lightly to achiev.. a smooth surface. The lirsi primer coal is sanded using 220-grit and the second coat very lightly wet sanded with 320-grit. When complete, the primer is very saiooth, dark, and ready for finish paint.
Step Five: Finish Paint
Follow the manufacturer’s directions for the type of finish paint that you have chosen.
Cockpit Interior Paint
A light color(light grey, green, or blue, etc.) is recommended on the cockpit interior to avoid high heat buildup when the aircraft is parked in the summer sun with the canopy locked. It is not necessary to fill the glass weave and some very light sanding may be done to smooth the surfaces slightly. Apply one coat of the Dupont 70S primer to the interior glass surfaces for ultra violet protection and then the color.
CANARD SURFACE SMOOTHNESS IS CRITICAL. During the Quickie program we built and installed a canard that resulted in very poor low-speed performance. Stall speed was 10 mph higher than predicted and tuft tests showed stall angle-of-attack over three degrees lower than estimated. We later traced the problem to a wavy upper surface; the canard must be smooth.
Of course, the big question is “how smooth”? The best way to check this is with a steel pocket ruler, the flexible kind that’s only .02” thick, or with a plastic drafting ruler. Hold the ruler as shown in the sketch, pushing it to the surface with two fingers 2 inches apart. If the surface is a smooth curve between your two fingers the ruler will lay down following the curve with no gaps. If the surface is bumpy or wavy the ruler will touch the surface only in 3 or 4 places. Take a feeler gauge to measure the gaps between the ruler and your surface. If you have a gap of more than .005 inch, your surface is too wavy. Check this in several places from the leading edge back to 50% chord. The bad Quickie wing had gaps of about .012 inch. After refinishing with gaps of less than .005 inch, its stall angle of attack increased from 8 deg. to 12 deg!
The best time to use the ruler and check for smooth surface is when sanding the Featherfil with the spline. Recheck after sanding the 70S black primer. It will not change when white paint is sprayed o.