FanFacts
by greg moore You can reach Greg Moore via e-mail at
jetflyr@comcast.net
PHOTOS: DAN EATON
It’s the middle of January, you have a reasonable weather day, you have been working on a particular model for 2½ years and it is finally all ready to go so you haveto attempt a test flight! That’s what Kevin Cox (at left) did and poses with his very long labor of love, the X-32B designed around a 120 mm fan (TF-4000). This 67-inch long, 11S powered bird sports 1300 square inches of wing area. Wisely, Kevin chose to leave the fillers and primers as his colors of choice for his maiden. On the takeoff roll for the first time, Kevin’s X-32 (above) shows its interesting underside curve and long-ish nose gear. The flight was aborted on the takeoff roll due to the several year old, 20C battery packs sagging and not providing enough power to the fan.
W
elcome back! It is the middle of winter and, as I write this, only a very few states are not in a deep freeze, so I guess it’s build- ing season! My day job seems to take more and more of my evenings, so I am in awe of some of the builds that I have seen on the web, (I can check at lunch) and some of the designers! It seems as if everyone now knows how to use CAD programs, and I’m envious!
To start off, regular readers are aware of my attraction to, and approval of, scratch- building, so we will start off with a familiar name in the edf community, Kevin Cox. Not being able to leave well enough alone, he has started a large model—67 inches long with a 45.5-inch wingspan—and traveled a time- consuming path—it began in the fall of 2011—with his TF-4000 powered Boeing X- 32B. The 120mm fan/Neu 1521/2y motor combo needs an 11S battery to reach its needed thrust, which one would think would
not be a problem with an airplane this big. But having the entire center of the airplane comprised of the intake ducting and the fan unit does make for some head scratching about pack placement.
One interesting aspect of reading scratch- building threads is finding out little pieces of information that help explain some of the minutia of thrust line placements along with gear length (especially the nose gear) to offset the inefficiency of the scale location on our models. It’s really rather neat stuff! The thread is only seven pages long (as I write this) but has some good all round informa- tion in it, so I can heartily recommend it as a good read! The thread can be found on RC Groups at:
www.rcgroups.com/forums/show thread.php?t=1543953.
Moving on, Kevin has designed his 1300 square inch wing area X-32 with permanent- ly attached wings, so servo connections are rather simple, but what if you have remov- able wings? I think we have all “been there”
connecting aileron and flap connections and, even though we have color coded our connec- tors, we still end up plugging in the wrong leads, which we only find out about after we have secured the wing(s), flipped the airplane over and aired the retracts up … arrgghh! Well, I decided a few years ago to use the Multiplex 6-pin connectors as a two-servo connection for removable wings so that I did not have to worry about an improper connec- tion and possibly stripping a gear set or even worse, burning out a servo. An advantage to doing the connections this way is that the length of each wire can be determined and precise, so that you don’t have bundled up wire “stuffed” somewhere. The drawback to this system is that you must be (or become) confident about soldering small wires to small pins, and wires together (for the ends), or you need to become comfortable with var- ious connectors and crimpers.
One of the manufacturers of do-it-yourself, locking connectors was Ashlock, which is no
PHOTOS: GREG MOORE
Let’s see—two ailerons, two flaps and two air line connectors (above left)— what can go wrong here? The air line connectors are impossible to connect backwards when the connections are opposite of each other, but color coding, numbering and otherwise marking identically shaped servo connectors always goes wrong when we can least afford it to. A simple solution to the four servo
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connection conundrum is the use of a multi-pin connector. Here (above right), Greg has used two six-pin Multiplex connectors for four servos. Using opposite connectors for each pair ensures that the correct pair gets plugged into each other. The downsides to this connector are that you must be able to solder small wires to small pins neatly, and the connectors do not have a locking mechanism.
MARCH 2014
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