Santa Cruz Mk. III
Strength and weight are key factors in freeflight Endurance. The upper spruce dorsal longeron (above left) with carbon strip and lower fuselage balsa dorsal
formance by increasing rpm with hotter fuel and smaller props resulted in three crank- shafts cracking and two bent rods. Jerry Mur- phy suggested I take the remaining ones and put them on a trophy case on my mantle. I did. The plane flies fine but couldn’t be pushed too hard at this altitude. The HH set- up will get you back into flying without too many complications and at lower altitudes the HH is an excellent starting point. The next step was using TDs with red fuel tank and standard carburetion. You proba- bly have a couple of these lying around, there’s still a good supply of parts for them from Cox International
www.coxengines.ca. This configuration placed third in this year’s SWRs missing a fly off by two seconds using 35% fuel. I can push them to 24,000–25,000 rpm without any problems using Murphy Mist. Murphy Mist, a special 65% nitro ½A fuel, came by way of Johnny Shannon. Casey Hornbeck supplied it to the Texas folks and it is now available from RedMax in different strengths. I do not regularly use this in com- petition. You don’t need the “hot” stuff to get started. 25–35% will haul her up nicely.
longeron (above right), also with carbon strip keep the fuselage light yet strong during the models power on climb.
The piece de resistance was when all the Santa Cruz ships got upgraded to the pres- sure fuel system this summer with some great help from George Avila on operational considerations. You cannot hand start the engine with this setup as one needs an elec- tric starter with a foot switch or a third arm. Graduate to this system when you have mastered the other. Santa Cruz really scoots in this mode.
If you are an active flier, start with the pressure system and have your chase bike ready. The plans are shown with the pres- sure system configuration.
Construction Wing: A flat building board surface is a must. The Warren Truss structure resists warping, so if you build on a warped surface, you will not get it out.
Notch the inside of the leading and trail- ing edges where the rib attaches to provide a little extra support for the glue joint. Pin the leading, trailing and center spar and lo- cate the ribs. Use the lightest weight wood possible on the wing tips as it is important to
keep the extremities as light as possible. As- semble the rest of the wing and glue with your favorite. I use CyA for the first pass. Af- ter the wing is assembled, double glue every surface contact where two pieces of material meet. I use carpenters wood glue for this. Paint the entire wing structure with thin- down (50–50) clear dope. This adds a little more rigidity to the structure. Cover with your favorite covering. Hangar 9 Ultracote Lite is used on these models. Laser-cut ribs are available. Stabilizer: Use the same procedures as the wing. Use lightweight wood as it’s im- portant to keep the extremities light. Fuselage: This Linder-type fuselage is basically two sides separated by a pylon and two reinforced full length longerons. One is spruce for strength: the other, balsa for weight savings. Both have a piece of 3mm × 0.5mm carbon strip glued to their ¹⁄₈-inch surface to add lateral stiffness. Pin one side of the fuselage over the wax paper covered plans. Position the pylon and longerons in place and glue. Put glue on the exposed sur- faces and place the other half of the fuselage
Full-size plans available through Carstens Bookstore
www.carstensbookstore.com 44
Order Plan CD450 for $14.00 JANUARY 2013
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