2013 Updates

Late February of 2013.  I took the KR out for a nice warm up flight and was once again so pleased with the way this plane flies, and the way this engine runs.  I have a number of updates I'd like to do to the plane, but just can't stand to ground a plane that flies so nice.  By afternoon, that tune had changed.

I pulled the plane in to start on what should have been a quick and easy annual inspection.  First thing was to do a quick compression differential check.  Nearly perfect, 79/80, 78/80, 79/80, and 58/80.  What?  That can't be right!  I checked a little closer and the news was not good.  It was leaking past the rings.  That does explain why the engine has been  pushing a bit more oil than expected.  One of these tired old  +.015 over cylinders has finally given up.  Surely it must be a broken ring.  I pulled the cylinder and saw nothing obviously wrong.  But measuring the cylinder, it has gone well beyond service limits and was showing some cylinder wall distortion.  It's time for new cylinders.

So, I got in contact with my friends at Aircraft Specialties and ordered a new set of Superior cylinders and a set of O-200-D pistons (8.5:1 compression rather than the 7.0:1 compression in the O-200-A).  Wow!  That was a surprise.  I didn't think Continental was going to make those pistons available.  I got into a real snag with the rings as Continental changed the top ring in the D pistons, then made them pretty much unavailable.  Finally resolved it by having my friend Doug machine the top ring groove to fit the ring set from the C-75 through O-200-A ring set. 

Now that the plane is already down for major maintenance, it's time to do all those little things I've been thinking about ever since the last major refit in 2005.


March 10 -Here's the lower cowl with my thoughts of how I want to cut down the cowl.  I have an unusual problem
in that my engine runs too cold in cruise, so I'm thinking I'll cut down this area, then perhaps add a cowl flap.

March 13 - I laid up a flat sheet of glass on a waxed tabletop to use as the bottom for the cowl.  Then I cut
off the bottom off the cowl.  The lines of the bottom of the cowl should match the lines of the fuselage and
reduce drag a bit.   I attached the new bottom onto the cowl with a finger fillet of milled fibers and West Epoxy.

March 13 -I bonded in the new bottom with some milled fibers.  I'll shape and glass the inside after this bond
line cures.  Clearly this is not the first or even the second time I have carved on this cowling. :o)  The "duckbill"
that extends beyond the back of the cowling is what will eventually become a cowl flap.

March 16 - Cowl bottom feathered in.

New cowl profile on the plane.  Compare this to the old lower cowl profile below.

March 17 - I bonded in an extension on the sides to match the length of the bottom of the cowl.

March 23 - Marking and cutting out cowl flap.

Mounting piano hinge for cowl flap.

Riveting piano hinge to the flap.  Cowl flap servo installed with plywood stiffener.

Preparing to rivet cowl flap control arm.

My old MAC trim servo mounted as the cowl flap actuator.

March 24 - Added composite stiffeners to the cowl bottom and cowl flap.  These are made with 1/4" Clark
foam bedded in a slurry of micro, and 2 laminates of BID 4.5 oz cloth, with one laminate at a 45* bias.

March 25 - Cowl and cowl flap stiffeners after peel ply was removed.  They really did the trick as the bottom
of the cowl is now rigid.  I cut more flat sheet fiberglass and added to cowl flap and cowl opening as edges.

March 26 - Cowl Flap completed.  Fully open.

Cowl flap flush with bottom of cowl.

Cowl flap retracted up to close off the center of the air outlet.  This might be useful during winter months to
bring the oil temps up a bit, but generally, I probably won't fly with the cowl flap in this position much.

Update: After a year of operations, I found that once I level out at cruise, unless the oil temp is too warm, I
always close the cowl flap into the fully retracted position as it is aerodynamically cleaner making the aircraft
fly faster.  Additionally, even under the hottest summertime conditions, the CHTs still stay around 300°F and
the oil temp will usually slowly cool back down to 205 during cruise.

Update: After 2 years of operation with this configuration I find that I only fully open the cowl flap on extremely
hot days.  Most days I have it just slighting more open than flush.  As soon as I level off at cruise, I pull it fully
closed.  The cowl flap makes a huge amount of drag when fully open, but there is even a significant difference
in the speed of the aircraft between flying with the cowl flap in the flush position, then pulling into the fully retracted
position.    Generally speaking, in this position my worse case scenario has the left side CHTs at 300º and the right
side CHTs at 200°.

March 30 - Cowl mounted while wiring cowl flap servo.  Cowl flap in the full open position.

Cowl flap in the fully retracted position.  I'm not likely to fly it with it in this position, but we'll see.
Se update above.  I use this position a lot!

April 22 - When it came time to paint, the bottom of this cowl was full of pin holes.  Not at all unusual for a
newly laminated glass sheet.  Every time I do glass I end up struggling with filling the pin holes.  This time I
decided to try something different.  I was thinking about ordering some "Smooth Prime" to fill the pinholes
when it occurred to me that it probably isn't the primer, so much as the technique for filling the pinholes.  I
stopped at the auto parts store and bought a can of cheap high fill primer, then spent about 30 minutes stirring all
the solids back into solution.  Then I painted the bottom of the cowl with a 2" brush, making it a point to stipple
the primer into the pin holes.  As the primer started to dry, I squeegeed the primer solids around on the surface,
then painted with another coat and allowed it to dry for 90 minutes before sanding with 220 wet.  It only took
about 5 minutes to wet sand the cowl.  It did a really nice job of filling the pin holes. It may require a second
pass with the primer to get all the pin holes, but this method seems to be quick and simple, fills the pin holes,
and sands quite easily.  I don't see any reason why I wouldn't be able to do one complete side of a wing in an

After a quick 5 minutes of wet sanding, the pinholes are filled.  The white on the bottom is the first coat of
polyester primer I shot which really exposed all the pinholes before I filled them.

April 26 - After shooting with PolyEster primer after filling the pinholes.  There are no pinholes now.

May 1 - Everything that needs to be shot white is now white.  I used Acrylic Urethane for the finish coat.  I
really like the Acrylic Urethane.  Much better than the Acrylic Enamel I've worked with in the past and much
easier to paint with than PolyUrethane.  I have some minor sags in the paint on the cowling that I'll need to
sand and reshoot, but overall, I'm just glad to have it painted.  This weekend I'll shoot some trim paint as
well.  The graphics package is on order now as well.

Feel free to email me with comments or questions at jscott.planes"at"gmx.com.

Stay tuned.  More to come...