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The struts for Dean Gradwell’s Ka-3 fuselage and wings is now faced and fitted. While at it both sets of struts were completed, meaning one less task when assembling my Ka-3 when the time comes. Flying season is soon approaching so a set of wings from the Ka-1 kit is next on the bench as time permits.
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That's sweet!Gunny
Aviation Concepts rcComment
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After fitting a set of prebuilt Ka-1 wings to Dean’s Ka-3 fuselage it was time to start the kit side of this build for my Ka-3 fuselage. This build is a collaboration with Dean to fit Ka-1 wings and stabs from a CNC Modellbautechink Bayer kit to a 40% Ka-3 fuselage as they are the same on both airframes. Dean already had the set of built-up wings from one of a few Ka-1 kits in his hanger.
An inventory of wing parts brought out some exceptional kit features like full length and width D tube and trailing edge sheeting. The D tube sheeting is also finger spliced and finished sanded. The 5mm x 10mm spruce spar material is already beveled for splicing, when glued and laminated to the full length 3mm x 10mm spruce spar material it will provide one of two very strong wing spars per wing. All the ribs are precisely CNC routed lite ply, no burn marks to sand clean. The shear webbing in both ply and vertical grain balsa is pre sized and keyed for assembly. To finish it off the mounting hardware is water cut 11 ga stainless steel. A little light sanding to clean up the routed edges and it will be ready to start building.
If you would like to try building a 40% Vintage Ka-1, I’m sure Dean would be happy to sell you one of the kits he has left. dean@xcsoaring.comComment
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With time limited now to start on any thing large, attention was turned to the wing tip construction. Over the years I found it easier to deal with the wingtips as a separate item from the wing when possible. The reasoning is that the large tip pieces can then be laminated using a flat surface and assembled to the end rib with a 90 degree block instead of hanging off the end of a 6-8ft plank during the process. The only important thing to remember is one tip is right and the other left, "not that I ever have made that mistake". When setting the wing ribs on the spars the last rib also will have a nearly completed tip assembly, saving a lot of possible hanger rash on the wing structure with less hassle.Comment
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After reviewing the tip geometry again on the both the full scale and model plans a new train of thought was needed. This required the remaking of new vertical grain spacers to be fitted. Now it only needs to be glued together remembering to make one right and one left.
Thanks to the loan of Larry’s oscillating belt sander the skid thickness was easily tapered smooth from thick center to thin ends after rough sawing off some of the excess wood. I have to make a note to get me one of these in the near future.Comment
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Now that the wing tips are nearly finished it was time to turn my attention to the spar lamination. To keep the Spruce spar material straight and level an aluminum channel was screwed to the top of my level workbench. A 6’ straight edge was used to insure it stayed straight while the drilling and screwing was done. A test fit and procedure check was also done so no unexpected surprises would show up when the gluing started. A applicator was made from 1/32 ply that laid down an uniform glue pattern on the 10mm wide spar surfaces after first running a glue bead down the spar. Before placing the lamination on the bench for clamping a paper towel was used to remove any excess glue. Cleanup was also repeated on the exposed side after clamping and tapping the spar edges down to the table surface with a wooden block. Waxed paper was used as the release agent and worked great.
With three of the four wing spars done and the last to be removed from the clamps tomorrow they will have at least a week to cure before any wing assembly, as another aerotow will take me away from the shop.Comment
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On the drive back from the Visalia aerotow Dean and I were discussing a hatch concept for the Ka-3 I had though of earlier. The bottom of the wing has a round inspection hatch for the aileron pulleys so why not use one on the bottom of the wing and stab to access the control servos instead of the one provided in the it that is square, bulky and just screwed on. The problem was I had no idea of how it worked, or what it looked like, but a trip to the hanger the next morning allowed me to take photos of one on Dean’s full size Rhonbussard under construction, so when I got home it was easy to draw up using scaled dimensions for the inspection hatch from the full size drawings. My son was kind enough to laser cut the parts out of 1/32 ply to run the test concept. With a little refinement it should fit the need and be true vintage scale.Comment
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Had the opportunity to doodle in the shop this weekend so a few other concepts were completed. First two scale total energy probes for the Ka-3 were turned out of 3/8 dia brass rod and soldered to a 1/8 dia brass tube for testing on the Grunau Baby II this next weekend at the Yakima Aerotow. One has a slightly smaller vortex opening in the front to see any difference in performance, that is if it works at all. Revamped the drawing for the inspection hatches and cut four new wing leading edge ribs to match the full scale drawings in two of the wing bays. Finally fitted the skid to the Ka-3 airframe. The arc required some tweaking but soaking the ends in hot water and with some gentle persuasion overnight did the trick. The front mount will be sandwiched between the 1/32 ply nose and the skid mount plate. The rear of the skid floats just like the full size. A lot of finish work left to do later.Comment
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Gone are the days of the coping-saw, file and sandpaper. This was before even the scroll saw was available to a kid. Now what would have taken hours is done in less than a minute and a half. I had a chance to watch the cutting of the wing and stab hatch parts for the Ka-3 today. I was impress with the process but there was some tweaking of the program to reduce the burn width as my son set up and cut the parts. I may give it a try sometime.
The scale total energy probe with the 0.98 dia venturi opening worked so well that there was (0) stick lift between lift and it was easy once a count too five was made when lift was indicated before turning into a possible thermal too ensure it was big enough to turn in. Once in lift the matter of coring the thermal was a synth using the probe. The 1/3 scale Grunau Baby test bed was turning within a 20ft radius up to the point of deploying spoilers, even then it gained another 179 ft before flying out of lift. Besides it looks cool on the nose of the Grunau Baby. A brass mount will have to be made for the nose of the Ka-3 to keep with a scale appearance.
After the late June aerotow hopefully work will begin on the Ka-3 wings.
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Following with interest. I have a 1/3 scale Grunau Baby and 1/3 scale Ka1 short kits from Island Models in Ireland. They are in my “to be built list†right behind my 1/4 scale 2-33.Comment
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The test venturi on the Grunau Baby worked so well new parts were made for the two Ka-3's. The base uses a silicon tube to prevent any air leakage between the venturi post and base. A test fit on the Ka-3 sub plate looks about right. The venturi tube on the test unit was shortened to better fit the Grunau's scale and will come in handy this next weekend at the Vernon B.C. Aerotow.Comment
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Worked on the stick control for the Ka-3 with an issue showing up right off. When the stick was moved from side to side the clevis at the rear for the fore an aft drive rotated more than expected. To correct this a rotation coupling was made using a #1 flat washer, brass tubing an a modified 2-56 x 0.074 brass rod end connector. Fore an aft play is zero but the clevis can rotate 360 degrees smoothly. The clevis may be changed to a Sullivan Ball Connector as once this area is covered it will not be as easy to access so having a quick release to the servo makes since.
The short video will explain it with a glance.
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Now that there is a window in the aerotow schedule it's back to the Ka-3 build. Final coats of Schooner 96 varnish have been applied to the seat and floor plate. The servo drive bracket for the control stick needs painting before the servos are permanently attached. Then a functional video of the control stick assembly can be made.Comment
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Found some 1†dia smooth foam balls to make the tail skids tennis ball out of. First coated in West Systems 105 epoxy in preparation for the yellow plastic coating. This was to protect the foam from the solvent base of the plastic coating. After dipping, the balls are left to cure before mold lines are drawn on them. As for a name that will be left blank.
Servos were epoxy in place and the seat, floor and control stick temperately mounted to check the servo actuation of the control stick movement. So far all is well.
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