September 2000
Page 4...
| Before installing the motor to the Aero Vee mount, I lined the bed of the mount with 1/32-inch plywood, and epoxied a 1/16-inch plywood ring to the motor's endbell. This completely isolated the motor from the motor mount, and its attaching cap screws, thereby eliminating another possible source of RF noise. The motor is then secured to the mount using the supplied hard nylon hold-down tubes on each end of the motor, using four screws. However, before installing the hold-down tubes I slit two 1 V4-inch lengths of silicone fuel tubing and installed them between the tubes and the motor, thereby providing some additional friction to prevent the motor from possibly turning. | |
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Battery design Installing 20 Sanyo 3000CR cells in the Scout would be difficult all by itself, but to install them and have the center of gravity (c.g.) correct would be a real challenge. By pre-assembling the Scout and doing a mockup of the RlC gear, I determined that eleven cells needed to be located just in front of the firewall and nine cells behind. Because of the motor's location and the electronic speed controller's location (just below the motor, attached with Velcro@ to the firewall for maximum forced air cooling), a crescent shaped forward pack was required (see Figs. 1 and 2). To allow for adequate clearance for the rudder and elevator servos and their pushrods in the upper and lower compartments, and to assure symmetrical left and right balance for the total battery assembly, a three-cell flat pack had to be installed in the upper compartment and a sixcell rectangular pack had to be installed in the lower compartment (see Figs. 1 and 2). Sufficient fore and aft movement of the rear sub-packs is available to allow for fine c.g. adjustments. Steve Belknap at Diversity Model Aircraft volunteered to assemble the subpacks using "zapped" Sanyo 3000CR cells. I believe the zapping process is vital to assure peak voltage for the pack, especially at higher amperages. This increase in available voltage can be translated into added flight duration because fewer amps (mAh) are needed for a given throttle/power (watt) setting. A "zapped" pack can add 30-60 seconds to an eight-minute flight. Gold Stecker connectors were used to connect the battery pack components, for ease of assembly and disassembly. |
| One of the leads from the three-cell flat pack in the upper compartment was replaced by a NAPA Belden mini-fuse holder, part no. 784667. A 30A minifuse was installed, with easy access through the upper hatch cover. The leads from cells #1 and #20 were connected to a female Deans Superplug. Three pairs of eyehooks were used to anchor nylon Tye Wraps to secure the forward pack to the firewall, after a soft rubber pad was installed as a cushion. The two smaller battery packs were installed using the same procedure. | |
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Fortunately I was able to try the new Hitec Flash 5 "System X", with dual rates, mixing, exponential and 5-model memory for the Scout E-con. The dual rates and aileron/rudder mixing came in handy with this project, especially for the first flights. Hitec/RCD HS-225BB servos were used for the elevator and rudder because of their moderate torque, 54.6 ounce-inches; their speed, 0.14 seconds/60 degrees; and their light weight, 0.98 ounces each. A Hitec/RCD HS-605BB was used for the ailerons because of its hefty 77 ounce-inches of torque; its fast speed, 0.16 seconds/60 degrees and its weight, only 1.73 ounces. For a receiver, the lightweight compact 5-channel Hitec/RCD Micro 555 (0.70 ounce) was installed. A 1000 mAh 4-cell receiver battery pack was used. The RlC installation was straightforward with "Z" bends used at the servo arms and ball links used at the rudder bellcrank and elevator tiller ends. I will say that reaching inside to hand drill a hole in the brass elevator tiller for the ball link was a real chore. There was adequate room for each servo, and even the supplied, pre-bent aileron pushrods fit perfectly. Care must be given to isolate the receiver and its antenna wire as far away from the servos, power batteries, and motor wires as possible. To do this I used Velcro@ to install the receiver on a small shelf on the lower, aft, right inside wall of the lower compartment. A charging jack and micro on-off toggle switch, for the receiver battery, were installed on the instrument panel in the cockpit, as it was inconspicuous and provided easy access. |
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Final assembly was simple and fully covered by the supplied 3 Sea Bees' instruction manual. The dual pull-pull elevator assembly and the pull-pull rudder assembly both installed easily. I observed that one of the four wing panels (upper left) was warped, while the others were straight. Heating the warped panel with a heat gun and trying to twist out the warp was unsuccessful. My only hope was that final assembly with the rigging wire tension would straighten this panel (that is exactly what happened). The two lower wing panels were installed into their respective lower fuselage mounting tubes, using the supplied wing rods. The upper wing panels were joined with wing rods and fastened onto the four cabane strut fittings using 6-32 socket head cap screws. Mter installing the four interplane (between the wing) struts I noticed a potential problem. The pre-installed interplane and cabane rigging wires were made from 40pound plastic coated multi-strand stainless steel cable. The loop ends of the rigging wires were designed to pass through the crimping sleeve and loop around through the sleeve again, for added safety, before crimping (see Fig. 3). The second (safety) loop around and through the crimping sleeve was not done on any of these rigging wires or for that matter the pull-pull control cables. This problem was communicated to 3 Sea Bees and they indicated that it will be corrected on future models. This is especially dangerous for the high tension wing/cabane rigging wire application, where coated wire has been known to pullout of the non-safety loop crimped sleeves leaving the plastic in the sleeve. Because of this safety concern I re-wired the twelve interplane rigging wires and the eight cabane rigging wires using 50pound uncoated multi-strand stainless steel cable. At the same time I wrapped each sleeve end with 3/l6-inch shrink tubing to provide a cleaner appearance and to minimize the times that the bare wire ends would stab me. This re-wiring took five hours. Due to the low tension on the pullpull control cables I didn't think re-wiring was necessary. Final alignment of the wings and adjustment of the wing and cabane rigging wires was tedious, but uneventful, and took three hours. For safety and stability reasons I put l/2-inch of washout into each aileron by heating the Solartex with a heat gun and holding in the washout until it cooled. This is a very simple way to add additional flight stability. Once all of the R/C gear, batteries, motor and electronic speed controller were installed, cooling holes and slots were cut into the firewall anywhere that there was clearance fore and aft. The holes and slots allow cooling air for the battery packs in the rear compartments, which are vented to the cockpit, as well as a flow-through for cooling air in the cowl. Control throws were set as suggested in the instruction
manual: The first flights were made with 50% rud der mixed into the ailerons. Total assembly time was 18 hours. This included the time to fabricate the new rigging wires, but does not include the engineering time or paint modifications. The total weight, ready to fly, was 11 pounds, 8 ounces, just 4 ounces more than the estimate. This flying weight is identical to a wet-powered Scout using a Saito 0.65 4stroke. Why the same weight, and not 25% more? To balance the wet-powered version, 32 ounces of lead had to be added to the engine cowl. Judicious placement of the power battery pack eliminated the need for any additional balance weight with this E-con. What does this say about the manufacturer's specified flying weight of 9 pounds? |
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| The instruction manual calls for a c.g. location approximately 5.2 inches behind the leading edge of the upper wing. With all three battery sub-packs secured to the firewall, the completed Scout's c.g. was 5.1 inches behind the leading edge of the upper wing (it's very satisfying when a plan comes together on the first try), close enough for the first flight. | |
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Prop tests were performed in two phases, before and after the initial flights (24), but will be combined here for simplicity. These static tests were conducted using an AstroFlight Super Watt Meter to measure volts and amps (watts), while a 50-pound electronic fish scale was attached to the rear of the fuselage to measure thrust. I was interested in obtaining the most accurate relative performance data and knew that the absolute measured results might not be accurate. To help assure greater accuracy, only seven props were tested, at various throttle settings, on each battery charge. Additionally, on each test series, the last prop tested was the same as the first, and any performance (thrust) degradation due to lower battery charge level was added back into the results of the previously tested props on a pro-rata basis. |
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