RCU Review: Greg Covey's Amp'd Issue 5: EDF Goes Mainstream


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    Contributed by: Greg Covey | Published: February 2008 | Views: 64171 | email icon Email this Article | PDFpdf icon

     

     

     

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    Issue 5
    Article By Greg Covey

    Print Issue 5 "EDF Goes Mainstream"


    When my interest in electric flight first started about a decade ago, we struggled as pioneers in our hobby just to get planes to fly. The brushed motors and NiCd packs had so much weight that we were happy for even a 5 minute flight. We found a few combinations of inexpensive components that seemed to work well; the most popular using a Speed 400 motor. Still, there were others that wanted to push the limits even further. They created the first Electric Ducted Fan (EDF) units using the limited resources of the time and toiled over making smooth surfaces to help improve the air flow efficiency. Although these early EDF Jets barely flew, my respect for their efforts and enthusiasm remains to today.

    Over that 10 year span, I kept my own focus on more efficient prop driven flyers and watched first hand as the technology changes flooded the hobby market. It was no longer much of a challenge to make any plane fly and fly well. The combination of new materials, brushless motors, lighter components, and higher density battery technologies could bring new life to any design.

    Once the prices dropped, the new technology was incorporated into mass produced products and sold through major distributors.

    With brushless motors sustaining 30,000 to over 40,000 RPMs under load, EDF units started performing very well. We first saw a series of "fun" jets where the EDF unit was merely used to replace an existing prop design, almost as an afterthought. We also saw many streamlined jet designs that were powered by pusher props. Then, it finally happened...the first high performance ARF ducted fan jets hit the market. This month's issue of AMP'D is all about jet fever as EDF goes mainstream.

    First Mainstream EDF Performance


    The Alfa Models MIG-15 could be easily hand-launched or even take-off right from grass.

    Alfa Model in the Czech Republic has always been one of the top designers of smaller foam Almost Ready to Fly (ARF) warbirds. I have reviewed several of their models in the past and they always flew as well as they looked. It was little surprise that they carried the same mastery of foam design over to EDF jets. The first one that caught the attention of many R/Cers was the little 29-1/2" wingspan MIG-15. The model could be easily hand-launched with a little toss and even had enough power to Rise Off Grass (ROG) by sliding on its belly. When equipped with the recommended brushless motor and LiPo pack, the MIG-15 could climb at a remarkable rate and tear up the sky with excellent speed. The popularity of this model was enhanced by a dynamic range of speed and performance that allowed it to slow to a crawl for easy landings.

    In addition to great value and performance, what made this EDF design popular in the mainstream of R/C hobbyists is that it included the ducted fan as well as the smooth ducting. The overall design made it simple to construct and when the recommended power system components were used, you could expect success on your first EDF model.

    While this 150-200 watt class EDF jet model set the bar for other mainstream designs, the weakened U.S. dollar
    provided opportunity for other manufacturers to compete.

     

    German Engineering Meets Elapor Foam


    One of my favorite materials to work with is the ELAPOR (pronounced el-a-pore) foam used by Multiplex. It is designed to use CA and kicker for fast, easy assembly time and it also resists damage compared to many other types of foam. My previous reviews of Multiplex models combined with my new passion for EDF dictated that I had to buy a Twister.

    What made this purchase even more exciting was that the Twister came with a completed Ready-To-Run (RTR) EDF unit.

    The 70mm unit (EPF69BL) is a Himax Brushless RTR Ducted Fan that comes with a HA2825-3600 Himax motor and is dynamically balanced (which means the blades are balanced with a quick dry component and tested while spinning).

    My Twister turned out to be a great looking EDF Jet that flies fast but still slows down for easy landings. It is an excellent choice for your first EDF model but does require intermediate flying skills. It can be hand-tossed straight out with some zest.

    The foam packing that so cleverly keeps the Twister protected during shipment can also be used as a stand for the completed model by simply cutting out a "U" channel at one end.


    Twister Hop-ups


    Although the Twister is a great overall design for mainstream R/C, there are some of us that feel the need for more speed. Unfortunately, the Himax HA2825-3600 motor is limited to a 3-cell LiPo pack and about 350 watts.

    As an easy upgrade, the Ammo 28-45-3600 Inrunner Motor can be used in place of the stock Himax motor. This motor allows the use of a 4-cell pack like the FlightPower EVO 25 3700mAh 4-cell (14.8v) LiPo battery which easily provides the needed 55 amps. The resultant power output is doubled at about 700 watts providing unlimited vertical performance without stressing the parts.


    FlightPower EVO25 4s 3700mAh


    Ammo 28-45-3600 Motor

    The AMMO upgrade provides twice the power over the stock motor.

    Keith Sparks, the custom plastics guru, has a canopy upgrade for the Twister that costs only $14 including shipping. The kit contains the canopy, instrument panel, pilot and ejection seat.

    The finished canopy upgrade looks fantastic and you can use your imagination to make it as detailed as you like. You can e-mail Keith at parkflyerplastics@att.net to order this canopy upgrade or any of his other scale enhancements.

     

    New Mainstream Releases


    ElectriFly L-39 Albatros EDF ARF

    Great Planes has responded to the demand for mainstream EDF models with the ElectriFly L-39 Albatros Jet EDF ARF. The 25" span jet comes with
    an Ammo In-runner motor, HyperFlow Ducted Fan unit, detachable armament, a display stand, and, instruction manual.

    The L-39?s smooth surface is made from AeroCell?
    foam which comes already finished with a militarystyle camouflage trim. Decals are also factory applied and detachable display magnetic armament is included. AeroCell? foam offers the structural strength and rigidity of traditional structures without building. It offers the weight advantages of foam without the brittleness and breakage so a smooth, paintable surface comes right out of the box factory-finished and decaled.

    The HyperFlow ducted fan unit was designed using flow analysis and state-of-the-art computer modeling to identify the parameters for high performance. The result is the ultimate ducted fan design that, when combined with an Ammo brushless motor, produces impressive thrust and speed.

    ElectriFly's sport-scale version of the L-39 Albatros Jet combines extreme brushless motor performance with advanced HyperFlow ducted fan technology. Assembly time is quick and the wide-open flight envelope will be enjoyed by all jet pilots.

    Now that's what I call mainstream EDF!


    E-flite F-15 Eagle DF ARF

    E-flite?s new sport scale F-15 Eagle DF ARF (EFL7050) is designed to emulate the flight characteristics and response of the full-size tactical fighter. The versatile foam model shows off an attractive Edwards Air Force Base Safety Chase trim scheme in orange and silver with pre-applied custom decals.

    • Designed to use two E-flite Park 400 DF motors
      (EFLM1320DF) to match the included ducted fan units
    • Performs basic aerobatics, such as loops, rolls and split-S
    • Made from lightweight injection-molded EPS foam that?s easy to repair
    • Retracts included

    The low wing loading and twin ductedfans allow superior maneuverability and acceleration to perform basic aerobatics.

    While this plane is capable of flying a tight flight pattern, it can still be flown at your local park. The wings are each reinforced with a carbon fiber tube spar for added stability. This model also has full flying horizontal stabilizers for pitch control and stability.

    An ARF Jet design with Matching Components and retracts is a great example of mainstream EDF!

     

    Off the Beaten Path


    Since mainstream EDF is relatively new, it doesn't take long until your interest goes off the beaten path. You want a larger model, more power, and maybe a good building fix. One example is the Hayoe F-18 twin EDF kit made by Tak Lee Industrial Company in China. This kit is sold by several U.S. distributors but comes with little instruction and many ways to power it.

    I will detail my build and testing of the big F-18 foamy in a future column.

    At this time in the EDF revolution, you have a handful of U.S. distributors selling unique products from around the world. These smaller distributors support a niche part of the market and often represent a company overseas. The choices for EDF sizes are generally 50mm, 70mm, 90mm, and 120mm. The prices go up with size and power but new entries in the market are constantly lowering the cost through competition.

    Shown above are some new products from Great Planes that fit nicely in my 90mm EDF application and provide a very cost-effective solution. The AMMO 36-56-1800 In-Runner Brushless Motor fits perfectly in any 90mm EDF unit. When combined with the ElectriFly Silver Series HV 60-amp ESC and a 5-cell FlightPower EVO30 4500mAh LiPo pack, the 1200 watt result produces about 4lbs of thrust without stressing the components.


    F-16 Fighting Falcon ARF

    Nitro Model?s newest addition to their electric-powered lineup of quality ARF aircraft is an exciting replica of the F-16 that flies as well as it looks! The ARF kit features a beautifully prepainted fiberglass fuselage with balsa sheeted wings.

    As you can see, this 41" wingspan F-16 is designed to be a pusher-prop jet with a 600-800W brushless motor and fly at about 3.5lbs.

    With a little work, a 90mm EDF unit can easily fit inside the fiberglass fuselage and provide a 1200 watt ducted fan solution.

    Here is a list of some vendors that provide EDF solutions...off the beaten path.

     

    General Rules of Ducted Fans
    The aerodynamics and rules of thumb of the ducted fan remain the same regardless of the power source. Jet Hangar International has compiled a list of items and frequently asked questions that should be helpful to you in your EDF jet flying. Here is their list of general rules for ducted fans.

    How a ducted fan works - Ducted fans operate as they sound: they are an internally ducted high performance fan which takes in air from the inlet opening and blows air out an exhaust tube to generate forward thrust. The air enters an impeller spinning at high RPM which propels pressurized air out of its exhaust at increased pressure and velocity. A ducted fan thrives on the air fed into it so too little air will starve the fan, thus preventing it from perform at its optimum design point. Conversely, inlets that are grossly oversized can have the same effect: a ducted fan can only process a given amount of air at any particular time, so too much air will hamper performance --not to mention the increased drag from the larger inlets.


    Requirements for Ducted Fans - Ducted fans need inlets sized to approximately 95%-110% of the Fan Swept Area (FSA) with an exhaust outlet sized to approximately 75% 85% FSA. Choking down airflow at the exhaust, increases exhaust velocity. This in turn will increase top end speed of the aircraft. There is, however, a point of diminishing returns: choking down the exhaust too much will back pressure the fan resulting in degraded performance. Additionally, a larger outlet area will increase the static thrust of the system, but lower the top end speed of the aircraft. The areas suggested above represent a good compromise between static thrust and exhaust velocity.


    External Inlet Shape - The ideal inlet lip shape for a ducted fan aircraft is a 2x1 ellipse. This represents the most aerodynamic shape while maintaining good airflow into the inlet system.

    Fan Swept Area - The fan swept area is calculated by subtracting the area of the impeller hub from the area of the inside of the shroud. The equation is shown below:

    Duct Area - Impeller Hub Area = Fan
    Swept Area

     

    Tractor vs. Pusher EDF

    Almost all EDF's are the tractor configuration in which the motor is aft of the rotor so the air flow is pulled towards the motor. A pusher configuration has the motor (or engine) in front of the fan assembly and pushes air through the duct. This configuration can be seen in Glow Ducted Fans (GDF) but is still not very common due to efficiency and cooling concerns.

    An exception to the overwhelming use of tractor-style EDF designs is the Stumax Aircraft SM110-52 EDF system. In this design, the motor is forward with its wires pointing towards the battery, which means the 180 degree bend and longer wires (typical in tractor style designs) are no longer needed. The ESC is now placed in between the fan unit and the battery. This technique is more space efficient and provides less ducting losses.


     

    Extreme EDF

    There are some of us with deep pockets and equally abundant confidence. When you mix those attributes with master craftsmanship the result is extreme EDF performance and appearance.

    Bob Violet Models or BVMjets.com is the place to go for extreme EDF. The new Electra Jet provides top of the line performance.

    The BVM Electric VioFan uses a Neu 1521 motor, Castle Creations HV110 ESC, and FlightPower EVO 30C 12s2p 6400mAh batteries to exceed 200mph!

     

    Summary

    This column was not meant to be an extensive dissertation on EDF but rather an eye-opening introduction to the ongoing evolution. The constant changes in technology have increased the power-to-weight ratio in EDF power systems. At the same time, prices have dropped and complete Ready-To-Run (RTR) systems are now available through major distributors.

    I find it a very exciting time to get into the EDF craze. As more products become "mainstream", you can spend less time building and more time flying as you are almost guaranteed success!

    When you fly electric, fly clean, fly quiet, and fly safe!

     

    Special thanks for contributions by:
    "Papa Jeff" Ring and Paul Weigand

     

    This section of AMP'D covers some of the questions that our readers have sent in and I thought would be interesting for others.

    Juan V. asks: "Greg: First, congratulations on the AMP'D segment in the rcuniverse magazine. It is what modelers are looking for in the vast jungle of electric products being offered. Recently burned a brushed electric motor on my ECO 8 helicopter, I knew I was having heat problems but not as much as burning it.

    HOW MUCH IS HOT IN AN ELECTIC MOTOR?

    In normal operation they turn hot, but how much heat can they tolerate before the windings burn? Bought a brushless inruner motor as a replacement and there is no temperature range specification no where in the instructions.(ammo inruner) I can only tell the engine is over heating due to the bad selection of the engine pinion and poor performance of the helicopter.

    Thanks,
    Juan Vadillo
    Guatemala

    Greg: Thanks for the kind words. Your question about motor temperature is a difficult one since it has many answers that are dependant upon the motor quality, motor type, and duration of high temperature. I am not a heli expert but on my planes and EDF applications, I do not like the motor temperature to rise above 100 degrees C (212 degrees F). An outrunner motor can hide the actual inner temperature more than an inrunner motor due to the heavy metal case that is spinning. Therefore, the inner temperatures can be much hotter on an outrunner motor.


    My recent tests with the AMMO inrunner motors in EDF applications look very promising and their prices are very competitive. In the end, I guess that motor longevity tells us when we are abusing it too much. You seem to be able to tell when your performance suffers so give the Ammo motor a try. The increase in efficiency of the brushless motor will make a big improvement. In a demanding application like your ECO 8, it may be a trade off between the cost of replacing a less expensive motor and buying a more costly one meant for extreme performance.


    Ask questions by e-mailing me at greg@rcuniverse.com

     

    This section of AMP'D reveals some of the feedback or suggestions that our readers have sent in about previous issues.

    Jason Cole writes:

    Greg,

    Your RC Universe column, AMP'D - issue 4 - "Why Regulate?" was a great article for all electric enthusiasts. It is very important to know how all those electrons flow and make our airplanes work. Your diagrams and text explained it well. We will be recommending this article to our customers. Keep up the good work!

    Jason Cole
    Hobby-Lobby
    Advertising Director

    Make suggestions by e-mailing me at greg@rcuniverse.com

     

    The newly released Hobby Lobby Hacker ?Warbirds in Reno? flown by 15 year old Chris Hass won the Open Pylon race at the E FEST in Champaign, IL on February 8, 2008. Against a field of over 20 of the best pilots in the Midwest, Chris, a member of the Skymasters R/C Club of Michigan, flew the just released Strega. It is part of a family of easy to build, fun to fly EPP aircraft. Chris received the racer two days before the event, assembled it with the recommended motor, battery and prop, and did the test flights before leaving Friday morning for Champaign. With only a few flights under his belt Chris flew a very tight pattern around the pylons throughout the races. Chris took home a plaque and the $100.00 first prize.

    In addition to the Strega five other aircraft are available including Furias, Rare Bear, Red Baron, Blue Bear and Ferias. A complete package for your ?Reno Racer? is available from Hobby Lobby. See your local dealer, visit www.hobby-lobby.com or call 1-866-WE-Fly-RC (1-866-933-5972)

    Chris Hass poses with his Open Pylon
    Award and new EPP Strega at the Great
    Planes E-Fest in Champaign, IL.

    ?It is a fun airplane to build and fly? Chris said. ?It goes together quickly. It has a wide speed envelope so you fly it as fast or as slow as you like. Plus it is durable. I landed mine upside down during practice with no damage?.



    E-flite DHC-2 Beaver 25e ARF

    E-flite Intelligent Li-Po Balance Charger

    Stop Running in the Dark!

    XTRM 4120/06 - 900 watts

    XTRM 7035/08 - 4800 watts

    Print Issue 5 "EDF Goes Mainstream"

    Comments on RCU Review: Greg Covey's Amp'd Issue 5: EDF Goes Mainstream

    Posted by: truevine77 on 02/24/2008
    Would the Ammo 28-45-2700 work just as well with the Twister? It's a bit easier on an esc (mine is a Airboss Elite 45) http://www3.towerhobbies.com/cgi-bin/wti0001p?&W=001313602&I=LXLWY4&P=K Thanks
    Posted by: bleary on 02/27/2008
    Greg maybe you should check out extremerc in Australia for EDF stuff.Mark actually tests and modifys the planes that he gets,then will fly them with video...there are plenty of vendors out there,perhaps not that many that will stand behind the product.The stuff is made in China and Taiwan,yet tested and modified to work so that you do not have to reinvent the wheel...no commercial interest,just a happy camper. Cheers, Bleary.
    Posted by: kemetpharaoh on 07/13/2008
    what ammo motor would be a good upgrade for the eflite f15?
    Page: 1

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