Finally Back on the Robin
I finally have cleared the decks to the point where I can get back on the Robin. It took 9 months to order and receive my new Casler 1/2 VW. Then I was named the lead engineer on the Embraer 190/175 Rudder/ Elevator program. That took a lot of my spare time and required quite a bit of travel to Brazil. That program is winding down and I started to have more time in the evening. In addition to the Robin, I have been redesigning the nose landing gear of a Tiafun Motor Glider and the fabrication of a new 1-26 sailplane Nose Cowl. All of the heavy work is finished so I set to work on the Robin. The first task was to locate the engine in its proper location relative to the center line of the fuselage and in the correct vertical position. My main criteria for the location was to have the old prop spinner contour blend into the existing fuselage contour. So I set up a three strap hanger from the overhead of my shop. I used three turnbuckles on each strap so I could fine tune the positions.
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| Casler hanging from ceiling |
the thrust line was set 1 degree downward. I used a piece of long welding wire as a spline. once the curves blended from the cowl to the fuel tank fairing, I knew I had the correct vertical height. On this new cowl, the cheek cowls will be functional like the original Limbach installation in the Fourier RF4D. If you look carefully at this side view you can see the welding rod spline.
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| Welding rod Spline |
Once I had the engine in position I added temporary wood trusses to keep the engine from moving. I used Hot Glue to temporarily attach them.
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| Temp braces |
In this picture you can see round aluminum pucks that were fabricated to dummy up the rubber engine mount. Since I intended to build in place, I want to be able to tack weld the engine mount together. I am using a thru bolt style Lord Mount that was available thru WD Granger industrial Supply. This mount is inherently safe because there is a thru bolt that will keep everything in place should a rubber bushing fail. The most common style of engine mount used on light engines have a section of rubber bonded between two plate with a threaded stud. These mounts require a safety strap should the rubber fail.
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| Lord Mount |
I mentioned this in my previous post from the original engine mount for the 2 stroke, but this is worth repeating . The basic principal of designing a proper engine mount is to ensure that on the airframe side of the rubber isolator, there exists a stiffness path for all 6 degrees of freedom. in order for an isolator to absorb engine vibration, it must convert the vibratory energy into heat. It can only do this when the vibration input node is being reacted by a stiff load path. Consequently, there will be a series of tubes that will supply the needed stiffness. The first being a square pattern that ties all 4 mount pads together.
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| corner mount pad |
I fabricated four corner mount pads. The two tangs extending outward are the weld pads for the trus. The corners are made of 3 pieces of 1/8" 4130 steel. I used a hole saw to cut two circular pads to be welded to the main base. The mounts require 3/8" of spacer per the mount spec. I have just finished fabricating the square backing and I will cover that in the next blog update. But before I sign off tonight I want to share a trick that an old machinist taught me 35 years ago when I was a safety crash test technician at Ford Motor Company in Dearborn Mich. There is a trick to drilling a large hole in thin material. I have what is known as a Deming Drills. Large diameter drills with a reduced shank. These drills will tend to chatter and elongate the hole when they are used. Except if you use the "Trick"
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| "The Trick" |
use a small piece of cloth soaked in cutting oil. I like Tap Magic. Center the drill on the work piece and then place the folded rag between the drill and the work piece. Apply pressure with the drill press and then turn it on. The rag will stop all chattering and create a perfect started hole.
Until next update
Mark
