FanFacts W
elcome back, and I hope you have gotten more accomplished in your workshops than I have over the last month. That is (un-
fortunately) what I said last month! But I did have the chance to visit with Mike War- ren from Performance-edf, to talk Hawker Hunters (edf) and to discuss some of the newer fans with their pros and cons. For the longest time, all we really had
were WeMoTec (Mini and Midi fans) and HET with their versions of 70 and 90mm fan units as our “fans for the masses”. The high- er end (and performance) Schubeler fan sys- tems were (and are) essentially limited pro- duction run, highly refined carbon fiber units that perform wonderfully. Recently, Stuart Maxwell designed a series of 110mm fans and then followed up with both 90 and 80mm units (as a drop-in replacement in Habu-32s), which have the Australian Postal Service hopping to ship his fans to fans worldwide (sorry, I couldn’t resist!). What has many lined up for the Stumax
units is their performance, and even more folks because of their sound. Huh? I hear you asking. Since sound is a perceived expe- rience, many things affect it, and for a long time we have been aware that “noise” is fre- quently wasted energy. Just as a musical oc- tave is eight notes, each note has eight sub tones (which is why a synthesizer’s “middle C” sounds so different than a pianos). Simi- larly, the sound a variable pitch propeller makes is dependent upon its pitch in the airstream, and the newer curved blades on some turboprop engines make a vastly dif- ferent sound than a traditional straight one. EDF units are no different. The aggres- siveness of their pitch determines load on the motor and thrust, as well as harmonic sounds (like the sub tones of a musical note) which can then exacerbate “noise” or blank it, which can then produce the commonly heard “hairdryer” sound. Add in airframe noises and ducting which can add, subtract, mask or
by greg moore You can reach Greg Moore via e-mail at
jetflyr@comcast.net
augment the fan sounds and things can get complex very fast! So why the recent demand for
the Stumax (and newer fans)? Stuart Maxwell, as an engineer, paid attention to the flow of air molecules and maximized his fan units’ impeller and stator design to maximize performance and minimize losses; therefore it is quiet, has good thrust and has a nice “swooshing” sound. All right, what about the Chi-
nese? We are seeing several fan units with marked similarity to previous designs. Hoaye fans have an uncanny resemblance to a BVM Viofan rotor and the new Change Sun designs look an awful lot like a Stumax. On The E-Zone forum huge numbers of pages have been written talking about trying to keep Hoaye fans togeth- er and to find the correct motor to maximize the power of the 70mm Change Sun fan, and the number of motors they have burned up in trying. All good stuff if you like to experiment and fiddle … but for me, see my first paragraph! Recently, an Austrian fan (Ejets) came on
PHOTO: GREG MOORE
The Schubeler DS-94HST in the upper left, DS-51HST in the upper right and the JetFan 90 (center) and 80 show the carbon fiber, 12-bladed impellers of the Schubelers, and the molded 9- bladed impellers of the JetFans. All utilize CF shrouds.
the market. The JetFan-90 (and the new 80mm version) were designed to be quiet (they claim to be half the sound-level of any German fan) and to have very good perfor- mance. Rainer Holzman (the owner) is con- stantly updating the performance data of his fans with various motors and publishing them both on his website, and in the forums. All reports are that the fans perform as ad- vertised: being both efficient and quiet, and that the motors run cool, which is a function of good design, allowing excellent airflow to the motor. Best of all, they are readily avail- able at a reasonable price. So, where does this bring us in our “Ford
vs. Chevy” debate? My take on things is that WeMoTec and HET are the family minivan. Performance is very good, “fuel” economy is very good and the price is very reasonable, even though their sound is not as “swooshy”. Equally acceptable are the Horizon Hobby fans as found in their Habu-32. Next up the price ladder are the excellent JetFan units. They are more of a perfor- mance crossover “sport-ute”, with the peppi- ness costing you a bit less motor efficiency, but not enough to be a deal breaker. The Stumax fans occupy the next rung, being ef- ficient, quiet and powerful and with a great sound, but like a Lexus, you do pay a pre- mium price for the excellent engineering. Fi- nally, the top rung is occupied by the Schubeler fans, which like a Porsche, deliv-
PHOTO: GREG MOORE
PHOTO: KEN PARK
These fairings (three in total) are on the outside of the Schubeler HST series fans (above left) with bullet connectors for the ESC hookup. With each wire passing through a stator, the airflow is kept very clean. The “business” side of Ken Park’s steering servo (above center). Notice that it sits lower (higher?) than
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PHOTO: KEN PARK
the strut so that it will not interfere with the retraction cycle and the short, straight steering wires. The “other” side of the steering servo is shown here (above right). Notice the popsicle sticks going completely across the plate to stiffen things up and ply plates for mounting the servo. Simple and neat!
JULY 2012
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