All articles are based on electric flying machines.
About EDF Jets
By Carl Tulanko
“Man, did you see that?” or “That looks cool!” are terms you often hear at meets when R/C jets take to the air. Whether you are a Turbine pilot, ICDF junkie or EDF flier, you have to admit that jets are indeed pretty cool and usually are associated with a fair amount of that good old “wow” factor! Electric Jets in particular have recently come of age and jumped the gap from toys to now serious competitors with the larger fuel powered models. For this reason, some basic knowledge is required in order to be successful and enjoy the benefits of flying EDF jets.
We will see if we can help clear some of the mystery around flying electric ducted fan jets. The first thing you want to ask yourself is “are you ready?” Only you can answer this question, but I must warn you that once you start down the path of EDF’s, you may never go back as it is extremely addictive! Your next questions should be “How do they fly”… “What kind of EDF?” … “How do it all work” and “What do I need to buy?” Hopefully this document will answer all these questions and give you a better understanding of Electric Ducted Fans.
Whether you’re a new pilot or an old timer, you cannot help but appreciate the advancements we have made in flight. From the very first radios and high wing models to today’s turbine jet aircraft, our hobby has grown in leaps and bounds, advancing with new technologies that now make available and affordable Electric Ducted Fan flight.
Jets in themselves are a unique breed and fly much different than standard prop aircraft. Both Prop planes and Jets require a propulsion system, but that is where the similarity ends. Airplanes have the advantage of being able to fly slower than their stall speed as the blast of air across the flying surfaces from the propeller can cause enough lift to keep them flying. Also, prop aircraft for the most part have thrust produced at the front of the aircraft. This allows them to “hang” on the prop for hover maneuvers, something that is not possible for jet models.
Jets require constant forward motion to fly and they could almost be considered as gliders being pushed around the skies from the thrust produced at the rear of the aircraft. If speeds get to low, below stall speed, you cannot throttle up and get a quick blast of air across the flying surfaces to keep it airborne as you can in a prop airplane. For this reason, you have a higher chance of crashing once you fly below the jets stall speed. This is very important information that needs to be known by all jet pilots and it is the primary difference between Prop and Fan flight. Speed must always be kept above stall! During landings, you should use the elevator to adjust your speed and the throttle to adjust your rate of decent. EDF’s land best when using a shallow angle of decent.
There are a couple final points to make; since Jet models propulsion is produced as thrust at the rear of the model, they do not require much in the way of torque compensation as you would do with angling the firewall or using the rudder on a prop aircraft. You can however, adjust the thrust angle, either up or down, to produce different flight characteristics for the model. You have to be careful when doing this though as a bad angle can cause the plane to fly into the ground. The Mfgrs of these aircraft usually have this all worked out for you, so there is little concern about this happening; I just wanted to make you aware of this if you decide to design your own jet in the future.
Ducted Fan Jets
Well, electric ducted fan jets have been around for a very long time, so it is not surprising that we see so many different models out there. Many of them have improved and progressed over the years and these improvements, along with the advances in technology have brought us into the new millennium with some very high tech hardware and made available the technologies that enable use to fly high performance Electric Ducted Fan Jets.
There are small, hand launch able and what I refer to as "toy" EDF's you can buy under $90; while these are slow, under 40mph models, they do make good park fliers. I have a few myself and they are good for a lunchtime break or quick fly. One of the more well known would be the GWS A-10 Warthog.
Next in line would be the high-end Foam EDF's such as the Alfa Mig-15 and F-86. They are ARF's that require smaller brushless motor setups for good performance, are hand launch able and run in the $250-350 range for a complete setup. They average 60-70mph and are very good acrobatic fliers. The big disadvantages are they are made from soft foam, there are no replacement parts, which makes them hard to repair and the internal parts are not very re-usable as there are very few models available that can reuse their fan.
Next are what I call performance EDF's, the Minifan series. These are models that fit the 69mm Wemotec Minifan 480 and this is what could be considered the foundation size for all EDF models. There are many different models available, allowing you to re-use your fan, motor, ESC and batteries and move them from model to model, which is a HUGE plus. I think this is a great place to start for anyone, but there are a few things yet to discuss that will allow you to make a better decision.
The ESC, brushless motor and batteries cost a bit more, with the majority of the cost going to the larger batteries that are required. Speed is normally in the 65-110mph range, depending on your choice of plane and setup and some of them can be hand launched however most Minifan models are bungee launched or modified for fixed gear. Unfortunately, the majority of Minifan 480 jets are too small for retracts, although there are a few that can be converted at a cost. However, the right ESC (on the larger size) and battery can be re-used in even the larger aircraft, such as the Midifan and HW series when you decide to take that step later, so it’s a good starting point when investing in re-usable equipment.
Now we come to the Midifan series of models. There are several models of Midifan jets available, although no where near as many as the MF480. The Midi models are larger, heavier, many can handle small retracts and they are fast, in the 100-160+ mph range. Performance comes at a cost though, with the ESC's running around $130-300 each, the motors around $120-250 and a larger quantity of batteries are also normally required. These jets cost around $1000-$2000 or more to completely set up, but are stunning in the air.
Finally, you have the Conan of EDF's, the HW730 and HW750 jets. Some of these could also be powered by twin 90mm Midifans I mentioned earlier and most of them are Glow conversions or scratch built. They are the coolest of the EDF's, however, cost of setup with light airframe, scale retracts, fans, motors and batteries can run thousands of dollars for a single model, making them cost prohibitive and not very popular in the EDF world. However, the market is continuously growing and even old timer experts like Bob Violett are getting on board as they are now seeing a value and market for these models.
To begin, the Electric Ducted Fan, otherwise known as EDF is the propulsion system that allows us to fly more realistic models, without the inconvenience of visible and distracting propellers. The fan unit consists of a Shroud to which you motor is mounted, a Rotor and a Hub. The Shroud is either glued, taped, or mounted with screws if it has side tabs. The Motor itself mounts inside the Shroud to a center plate with two or three small bolts. It is important to make sure you use short bolts, otherwise they may protrude inside the motor casing and hit critical parts or prevent the motor from turning. Usually the manufacturer will supply you with the proper bolts or indicate the size and length you need to use.
The Rotor is the working part of the Ducted Fan Assembly. Some are pressed on the motor shaft, while others require a Shaft Adapter. In the latter case, the Shaft Adapter slips over your motor shaft and is locked in place with set screws. There are different Shaft Adapters for different diameter shafts and they range from just over 2mm through 6mm or more for the largest motor shafts, so make sure you get the correct adapter that will fit your motor. The outside of the Shaft Adapter is used to secure the Rotor, which is the actual bladed fan unit. Rotors can vary from 3 blades to 7 blades with various blade pitch, depending on the EDF unit you purchased. The Rotors that use the Shaft Adapter have a larger hole in the center that slips over the adapter and is locked in place with a large nut and washer. There are even some shaft adapters that clamp on the motor shaft and are tightened using a bolt at the front, that causes the clamp to compress on the shaft.
The Hub is a round or conical, aerodynamically shaped “nosecone” that covers the Shaft Adapter and nut and its purpose in life is to provide smoother air flow through the intake of the fan unit. Some fan Rotors have the hub built or machined in place, while others use a separate Hub that is retained to the front with a bolt that threads into the center hole of the Shaft Adapter. You can run the fan without the hub if it is removable with slightly decreased efficiency; some fliers will leave the hub off the Minifan 480 if they are approaching or slightly exceeding the fan’s maximum rating in fear of it being “thrown” from excessive forces. However if you wish to get the maximum performance out of your EDF, the hub should be used. No matter which Rotor you use though, make sure you choose the correct motor that will work for your EDF.
Before you choose a motor, you need to select the fan you will be using for your application. There are several different terms you will hear, microfan, mf480, minifan, midi, or even HW730 and 750. These are all slang terms for the size of the fan from the largest manufacturer of ducted fan units, Wemotec of Germany. Wemotec makes the 40mm Microfan, equivalent to a EDF50 size (50mm outer diameter), the Minifan 480 (69mm), the Midifan (90mm), the HW730 (105mm) and HW750 (120mm). There is also a HW609 (75mm) fan, which is a cut down version of the midi and there is a HW620 (85mm), another cut back version of the 90mm midi, but with steeper blade pitch, hence higher thrust velocity.
Other types of fans include the DS30 (69mm) or DS51 (90mm); these are fans made by another manufacturer, Schuebler. They are equivalent to the Minifan and Midifan from Wemotec, but they are made from carbon fiber, pre balanced and have a $250 or higher dollar price range just for the fan. There are a couple more manufacturers such as Vasa, who makes a 55mm and 65mm carbon fiber fan, Wattage, who makes a fan specific to their EDF’s and the Alfa fan, which is included with the Alfa Jet kits. Two others include the Jepe 90mm Spyder Fan and the entire family of low end fans from GWS.
The measurements in mm that were given in parentheses indicate the diameter of the Rotor/blade unit; the larger the fan, the larger the model it will power. The smallest EDF’s are used in jets weighing under a pound, while the largest HW700’s and sometimes Twin Midi’s are able to produce 19+lbs of thrust and have been known to power up to 14+ pound models.
Intake and Exhaust
This brings us to Intake Ducts. Intake size really does matter with EDF and for good reason; a larger fan in a smaller jet probably will not work without modifying the intake. Larger fans require sufficient intake airflow in order to provide the best thrust levels. I have seen a high thrust fan placed in a smaller jet and the draw from the fan was so strong, it actually collapsed the intake duct. It’s like putting your hand over a vacuum sweeper hose and watching the hose collapse from the suction because it cannot breath. That is why you will see tips from fliers that include using fiberglass intake ducts, or wrapping the outside of the duct in carbon fiber strips for extra strength and support. Sometimes cheater holes are cut from the bottom of the aircraft so the fan can draw the air it needs. It is very important that your aircraft can breath properly and that your model’s intake is strong enough to support the fan you use. Intake ducts equal to the diameter of the fan shroud are a good start and should guarantee the proper inflow of air.
Exhaust ducts are a bit different. Unlike their intake duct counterpart, they do not require strengthening as the air output flowing through the duct will keep it expanded. Also, they can vary in size from those equal to the output diameter of the fan shroud to ducts that are smaller than the fan shroud output diameter. The larger the diameter, the more static thrust, hence making them easier to hand launch, however you will loose some top speed. The smaller the diameter, the higher the velocity of thrust, hence your top speed will increase. However smaller diameter thrust tubes produce less static thrust or “push”, so they are more difficult to hand launch and may require a bungee launcher or landing gear for take-offs. There is an optimum setting for each exhaust duct and the model manufacturer will usually tell you what works best for their jet; for the Minifan 480, an exit diameter of 53-55mm is normal.
Before we begin discussing the electronic components used in EDF, it is important to understand some basic electronics theory. Now before you panic and say “there’s no way I can learn that!”, you need to realize it’s really not difficult to understand as I describe it and you have probably been using items around the house for years that could better explain the theory.
There are four basic terms your will hear when discussing any electronics and you have probably already heard of them. They are Volts, Amps (or current), Watts and Resistance. Let us see if we can put them more into perspective to help us see how this all interacts. We will use an analogy that is better understood by everyone…the old water hose theory.
We will relate Volts to the amount of water pressure applied to a water hose. Current, measured in Amps, would be the water itself and the wire could be seen as the water hose.
The higher the water pressure, the faster water will be pushed through the hose. The same applies to electronics; the higher the voltage, the faster electrical current, measured in Amps, will be pushed through the wire. There is eventually a limit though where only so much current in Amps can pass through the wire. This would be similar to the limit with a water hose when it is turned to full, only so much water can pass through the hose at one time.
From this theory we realize that all three major components are interlinked. If you want more water to pass through, you can increase the pressure, but eventually you will reach a saturation limit where the volume of water cannot increase, causing the hose to heat up or eventually split under too much pressure. The same happens in electronics. With too high a Voltage, you will saturate the amount of Amps the wire can handle and the wire will heat up and eventually burn out like a fuse and break the connection. This stops the flow of current and prevents the device, in our case, the motor from turning.
This is where the size of the wire that is used comes in to play and it could be compared to the inside diameter of a hose. The larger the water hose diameter, the more water in volume can pass through it at any one time. In retrospect, the larger the wire, the easier it is to pass a specified amount of current, or Amps through at any one time. That is why you will see different wire sizes used for different sized electric R/C models. It is, however, important to match the wire to the model and while you could use the largest wire on a very small airplane, you loose efficiency due to the excess weight of the heavier wire. Larger wires on EDF models however are usually a good idea.
Now that you can relate Volts to water pressure, Amps to the water volume and the Wire to the hose, you are probably wondering about the other two terms, Resistance and Watts.
Resistance should be self explanatory and is indeed the amount of counter pressure applied. In a water hose, the inside walls of the hose could be considered a resistor to water because as the water passes through the inside hose wall, the wall causes friction and slows it down. The same applies to electronics; as current in Amps passes through a wire, the composition and diameter of the wire resists how much current is allowed to pass through. Electronic components such as resistors usually consist of small diameter wire or carbon that is calibrated to resist the flow of current. It is important to realize though that resistance exists in a multitude of components.
Resistance is important in EDF as it is a determining factor in batteries, motors and Electronic Speed Controller functionality. In batteries, those with the least internal resistance produce higher current flow and more power. Motors use wire inside to make them work and a motor with smaller wire on its windings allows less current to turn the motor, hence it resists the current allowed to pass.
Something else to keep in mind is the amount of wire needed. Just like a heavier, thicker water hose would require fewer wraps to fill a storage spool when compared to a smaller hose, heavier, thicker wire has fewer wraps inside a motor when compared to thinner wire. The smaller diameter, longer length wires have more resistance to them as current has to travel longer through them. This means you need more pressure, or voltage, to push the lesser amount of current through the wire. While the large wire uses less voltage with more current and hence low resistance, the small wire can handle a higher voltage with less current and higher resistance. There are quite a number of motors available in these various styles so you can customize your setup to meet your needs.
When using speed controllers, resistance inside the ESC is used to control the actual speed of the motor…the Esc has internal electronics that resist how much voltage and current is applied to the motor and the unused portion is consumed by the Esc..
It is important to remember resistance produces heat and you will see this referenced many times throughout this document. Heat is the killer of all electrical components and heat in itself causes resistance, thus adding to what could be described as a “runaway effect”. For this reason, you will notice that may different methods have been developed and used to insure proper cooling of electronic components for our EDF aircraft.
Finally, we come to Watts…what the heck are watts??? The Watt is a measure of power that is produced by your electronics setup. It is the product of Volts and Amps; by multiplying the two together, you get the Watts of power consumed in an electronic circuit. Pretty simple, huh? An example we will use is an electric ducted fan motor that is connected to a 10volt battery. If the motor is drawing 5 Amps from the battery, the Watts would be 10volts x 5amps or 50 watts of power.
It is important to understand this as the Fan/Motor/ESC systems that power our EDF jets are usually referenced to in Watts. You will often hear terms such as “400-500 watt power system” to describe the range of components used to power a specific model. Smaller motors, lower Amp ESC’s (electronic speed controllers) and smaller batteries are used in smaller models to produce a low wattage range while more powerful and heavier motors/esc/batteries are used in the larger models to produce some serious power in the 1000 watt (otherwise known as kilowatt) range. Each is matched to the model to produce the necessary power, measured in Watts, to propel the aircraft for which it was designed.
Now is a good time to talk about motors. There are hundreds of different motors currently available for electrics. Some can be used for prop aircraft, some can pull double duty and will work for both Prop and EDF units and some are EDF only motors, custom built to provide maximum performance for your model. With so many choices, it can get very confusing as to which one to choose. For the most part, we will be concentrating on Brushless motors that can be used for EDF. They are now available for every size and model of Fan and they are more powerful and more reliable. Also brushless motors have no parts to really wear out, so they should last a very long time. What is a brushless motor? Glad you asked.
Electric motors have been on the market for almost a hundred years and vary in size, shape and application. When our hobby was at its young stage, brushed motors were pretty much the norm and were used and shipped with many different models of aircraft. To understand how a brushless motor works, we will first look at the brushed motor.
A brushed motor for electric flight consists of a case, with magnets lined on the inside walls, a center Rotor that has wire wrapped around it with these wires leading to cylindrical contact plates (commutator) at one end, a set of brushes to transfer power from the source to the commutator and a set of end caps with bearings in the center to support the Rotor shaft ends. The motor uses two leads that supply power to make it turn. Power travels through the leads to the motor tabs on the case end cap, then wires from the tabs connect to the brushes. The brushes are usually square or rectangular carbon rods that protrude into the motor and make contact with the cylindrical rotor commutator plates. Power is transferred from the brushes to the plate contacts to the Rotor coils, which creates a magnetic field. This magnetic field opposes the field of the magnets around the inside lining of the case and this opposition causes the Rotor to turn.
The problem with brushed motors is that they are constantly wearing down with every second they run. The brushes will eventually grind down to the point that they need replaced. The springs that keep pressure in the brushes can overheat and loose their strength over time and the rotor commutator plates can wear down from the brushes pressing on them, which would require turning them like you do with rotors on your car or replacing the Rotor if they are worn too much. Moreover, the physical contact causes drag and inefficiencies in power transfer, which consumes some of the useable power that could otherwise be used to power the model.
Brushless motors are almost the complete opposite of the brushed motor. The coils actually line the inside wall of the case, while the rotor is essentially a magnet on a shaft. When power is applied to the coils, the opposing magnetic fields from the coils to those of the Rotor magnet core cause the Rotor to turn, or “push away”. There are no brushes to wear and no contact of any kind between the rotor and the outside case. This method makes the motor worry free with no wearing parts, which in turn allows the motor to produce more useable power. You will often see efficiency ratings for a brushless motor that show very high percentages of power transfer with low loss.
There are similarities as to how both kinds of motors operate. Brushed motors have two leads that are attached to the end cap; while the motor spins, the commutator plates rotate and are moving and alternating contact between the brushes, which helps cause motion in one direction. To reverse direction on a brushed motor, you simply reverse the two leads.
Brushless motors can easily be identified as they have “three” leads protruding from them that come directly from the coil windings. Since the Rotor is essentially a solid magnetic core with no brushes or contact plates, there is no alternating of power to rotor plates and motion cannot normally be achieved using the brushed motor system. Instead of plates, the motor windings on the inside of the case have power applied to them in a way that causes motion.
Think of a brushless motor as an AC motor you run from 3-phase house power, like one used in a dryer or for a large machine tool. With three wires, you apply power to leads 1 & 2, then 2 & 3 then 3 & 1, and continue to repeat the process all over again. This method creates magnetic fields in the coils that push the magnetic core around the inside of the case, chasing it in a circle. You can see that this could not very well be achieved with only two wires, because you would loose the “chasing” effect and the ability to specify direction. For these reasons, brushless motors normally use three leads for power. In order to reverse direction, you can switch any two leads; some brushless ESC’s may also have a programmable “reverse” setting, in which you can change direction through the ESC.
As you learn more about motors, you will hear terms like “Timing”, “Advanced” and “Soft”. These terms, along with others are various ways to modify or optimize the performance of your motor. Timing is probably the most popular of the modifications and can be set on both brushless and some brushed motors. With a brushed motor, the end cap plate on one side of the motor that holds the brushes is actually rotated to a different position inside the case, which changes the position of the brushes relative to the magnets. This causes the motor to run faster (advanced timing) or slower (retarded timing). As you advance the timing, you draw more current in amps to turn the motor faster and amps create heat, which is bad for all motors. Using this method though allows you to tune a motor to the maximum output that your battery can supply.
Brushless motors also use advanced timing, but since the coils inside the motor are fixed, the timing is actually set in the Electronic Speed Controller. It can provide advanced timing, slow or fast start, frequency in kHz and various brake settings. Most brushless motors do require larger power setups and they will draw more amps compared to an equivalent setup for a brushed motor. This is primarily due to the fact these motors are more efficient in the way they run.
Heat is the destroyer of motors and ESC’s. Heat in a brushed motor causes springs to deform and loose their power, thus causing contact failures between the brushes and the commutator rotor plates, resulting in a damaged or dead motor. Heat also damages the brushes where they ride on the rotor plate. The tips of the brushes can soften and wear down to nothing in minutes or they can pit and build up carbon, causing the brushes to loose contact and the motor to stop working. Heat in a brushless motor can cause the enamel on the wire windings to separate, thus causing shorts in the windings and even higher amp draws, which eventually can spiral out of control. Worse yet, excessive heat will also demagnetize the rotor core magnet of a brushless motor, making it worthless. In ESC’s, heat has been known to actually cause components to de-solder themselves from the circuit board.
For this reason, care needs to be taken when cooling your motor and ESC. Some motors come with heat sinks to help dissipate the heat, while others are automatically cooled by the passing air from the fan when mounted to the fan shroud. You will notice that many fliers mount their ESC’s right behind the motor in the exhaust ducting, just to keep it cool. This is a great way to cool down that expensive ESC and the minimal amount of thrust you may loose from doing so is worth keeping your Motor and ESC alive.
Electronic Speed Controllers
With electric motors in powered flight, you need a way to control their speed, hence came the birth of the Electronic Speed Controller, or ESC. These devices have been around for a long time now and can be as simple as a mechanical Rheostat controlled by a servo, which is a variable coil similar to ones used for volume controls on your stereo or for throttle power to an electric train set. They can also be made from advanced electronic components, with no moving parts. Most of the ESC’s we use are completely electronic with multiple features to help us get the most out of our setup.
All ESC’s have a set of two wires that run to your battery, a three wire plug that goes to the throttle channel on your receiver and a set of wires that run to the motor; some may also have two extra leads with a power switch to turn the ESC on and off and a few have an additional momentary push button switch to “start” the motor. Remember this though…even if you have an on-off switch, ALWAYS disconnect your battery from the ESC leads. I have heard of people that left their batteries plugged in with the switch off, thinking everything was fine only to find out that when they tried to charge the model again, the main battery is completely drained and ruined.
Different types of ESC’s can be identified by the number of wire leads that go to the motor; Brushed ESC’s have two wires that run to the motor, while Brushless ESC’s have three wire leads that run to the motor. You cannot interchange these ESC’s with each other and if you do, you risk damaging the ESC, the motor or both. Always make sure you get an ESC that matches both your motor type and required performance level.
If you are using multiple fans and brushless motors in a Jet, ALWAYS use a separate ESC for each brushless motor. Note this only applies to brushless motors…multiple brushed motors run fine on a single ESC. It is also a good idea to use separate battery packs for each brushless motor/ESC combo.
Also note that you will need to connect multiple ESC receiver cables to your receiver channel by using a Y-Connector to your receiver. If however each of your brushless ESC’s have BEC, you need to unplug the red/orange center wire from the ESC’s receiver plug on all ESC’s except for one. A small piece of heat shrink tubing can be placed over the loose power wire to prevent shorts. Only one ESC should supply power to the receiver at any time. Please note this only applies to ESC’s that use BEC to supply power to your receiver. Opto or optically coupled brushless ESC’s do not have this problem and power is normally supplied by a U-BEC or small receiver battery.
One of the more popular features of Brushless ESC’s is the “Timing” feature. This sets the timing for different motors as each manufacturer uses different timing values for their product. You need to read the data sheet that came with your ESC or motor to find the value you need to set for timing. Certain ESC’s like the Hacker brand even allow you to advance timing one degree at a time through a programming box. As previously discussed, timing can make the motor run stronger and faster, or it can be set to soften the speed and amp draw in order to match a smaller battery pack.
Most ESC’s have additional features including Soft (slow) or Hard (fast) Start/Acceleration when throttle is applied. With a soft start, changes in the throttle settings will build up over a second or so, while a hard start will instantly apply power to the motor. The same goes for braking. Hard Braking will stop the fan motor rapidly, while no braking will allow it to freely spin at the same speed as the breeze passing through it. Another setting that is used is Frequency, which is also a setting that must be matched to your motor specifications.
Other important settings include the “Type” of battery you are using, the “Voltage Cutoff” per cell, which turns power off to the motor when the cells get low, “Aircraft Type” for airplanes or Heli’s, Number of Battery Cells and “End Point” adjustments for your throttle setting. Most of these can be set through a button or two located on the ESC. The “Kontronik” models use the button type, while the “Hackers” use a programming box. Castle has an optional cable you buy that connects to your PC and you program them from software. Others like Jeti can be programmed using a special jumper board. Some ESC’s are set through your radio stick movements and some will completely auto detect your setup so you need to do nothing. Modern ESC’s have become very advanced, with the inclusion of onboard microprocessors and now have features unheard of a decade ago.
Now for a little history lesson…batteries. EDF is where it is today thanks to technology, with a primary focus on batteries. It was but not a couple years ago most of the fliers were using heavy NiMH and Nicads and now have turned to lightweight and powerful Lipos. While the old cells are still out there, the Lipos are worth the investment in performance. When they were first introduced, there were all kinds of problems with packs venting and catching fire and almost always it was due to improper handling, charging and use of the packs. There is a ton of data to back this up a everyone was doing their best to report these issues.
Since then however, there have been several changes, the foremost was education of the user. Manufacturers are including caution instructions regarding the proper charging of Lipos and we as users are actually reading them. Public awareness, along with a tainted past history, have actually made users more aware, thus increasing safe usage and decreasing the amount of problems.
Moreover, there is a very large variety of DEDICATED Lipo chargers now available and I am actually seeing the variety of other chargers decrease, at least for electric flight and the trend is spreading, even into the R/C car arena. Mfgrs are even making specialty chargers, custom made for certain Lipo packs. These chargers not only charge the packs correctly, they balance the cells within hundredths of a volt. Someone mentioned the cells are not matched and this is no longer the case! There are now available pocket sized cell balancers for perfect matching, with monitors and more...even temperature gauges are being applied to batteries so they can easily be monitored. Technology for Lipos has changed what seems like a hundred fold since just a couple years ago and all of it for the better. For these reasons and more, there are now very few incidents with Lipos these days compared to the past and I believe it is only getting better with time.
While I am not trying to make this a sales pitch, I did want to make you aware of the tremendous amount of energy, time and expense the industry has put into making these batteries safer and more user friendly. Through education and the proper tools, we have moved forward into a new generation of electric power.
Using them for powered flight, the distinct advantages of
this power source are much more than just a weight savings. Someone stated
the weight of Lipos is a factor, since larger capacity packs of the same
weight as older cells are allowing much longer run times. While this is a
plus, their physical size is also important as due to the much
In addition, USABLE capacity is in the 20C range, with single packs that can supply over 64 amps continuous throughout their run, a much greater capability than the old technology cells and the supplied current does not decrease as rapidly under load as the other cells. But one of the greatest advantages is working voltage! While NiCad and NiMH packs steadily decrease in voltage during their use, Lipos hold a steady voltage until they are nearly exhausted!!! This is a BIG plus for those of us running high RPM's or someone who wants to fly hover or other aerobatic maneuvers; they can now rely on a battery to provide more consistent RPM's during flight, not one that tapers with every passing second.
Almost every Electronic Speed Controller has Lipo cutoff safety settings and there are even ESC's now strictly for Lipos with many built-in safety features. There are even cutoff modules you can use externally of the ESC and safety modules that prevent incorrect overcharging charging. Also, with the performance increase from 3C years ago to now 20C, ESC's are now large enough to easily power 12- 14 lb models or larger...a big advantage over the old days.
My whole point is that, while there is still a higher risk of fire using Lipos and you may still see an occasional problem, safety education, excellent support products, better storage methods and better packs have redefined the battery in the electric arena, and as someone else mentioned, in everyday life, making their use much safer with far fewer problems. While NiCad's and NiMH's may still have their purpose for our hobby, it is a fact that their use has much diminished in Electric R/C compared to a few years ago and the trend continues with time into all aspects of R/C.
With Lipos you will see 8C, 10C, 15C and 20C along with numbers like 1350, 1500, 2100, 2450, 3200, 3700 and more. An example would be the ThunderPower 3S 2100, rated at 10C. What does all this mean? The 2100 is the first number to consider; this means the pack stores 2100mah (milli amp hours) of power, or 2.1 amps continuously for one hour. The 10C means the pack can be discharged at ten times it’s “Capacity”, or you can safely discharge the pack at 2.1amps x 10 = 21 amps continuously. Some Lipos such as the Kokam 3200 series are rated at 20C, which means they can be discharged at 3.2 amps times 20C, which equals 64 amps continuous discharge.
As your rate of discharge increases, your flight time decreases. A ThunderPower 2100 can supply 2.1 amps for an hour, or for a typical EDF motor 21 amps for a six minute flight time; the flight time decreases as your current requirements increase. Using this information, you can calculate average flight times for a specific power setup.
Batteries provide an enormous amount of stored energy that you have at your disposal, so it is recommended you leave a little play in there for safety. If your power plant will be drawing 40 amps, use a 60-80 amp ESC and a battery pack rated at 45-60 amps continuous draw. Using only 80% or so of your battery and ESC’s potential will keep them cooler, allowing them to last a long time. The same can be said of your motor. Try to purchase a motor that will perform well within your requirements, without you having to advance the timing or overstress the motor. Finally, provide cooling for all components by positioning the ESC in the exhaust duct or by adding ventilation holes in your battery compartment to keep them cool.
The ESC is an essential component of the EDF system and your choices are abundant. There are so many different models, it becomes almost impossible to choose. No matter what you settle for, there are a couple things you will want to know before making that choice.
As far as electronic speed controllers go though, I would invest in the biggest and best one I could afford that fit my style of flying. The larger the ESC, the higher the power output you will produce. If you ran a 45 amp ESC and a 70 amp ESC side by side with the same motor and battery, the 70 amp would produce more watts of power. They have a lower internal resistance and run cooler, while a 45 amp ESC may be at or near it’s maximum amp level…it’s always good idea to buy your ESC with some play in there. For Minifan 480 and Midifan models, I recommend 60 amp ESCs or higher for all applications and prefer to use the Hacker 70’s or 77-O myself.
So what do I choose? I have used all the controllers I mentioned and really like the Kontronik and Hackers, not because they are two of the most expensive (the Kontronik are also top-of-the-line), but because of their programmability. As I mentioned before, you can program a Hacker ESC to advance the timing on a motor “one degree at a time”, something no other ESC can do and I like that feature. This allows you to “Tune” the battery to the motor, getting the maximum performance you can possibly squeeze out of the setup. Also, they are built extremely well and with ESC’s, you really get what you pay for; the Castles are lesser breed, but very popular because of their price and features. One other ESC which I have not yet tried but plan on doing so are the Hyperions…they are pretty new and I would have to test their ESCs before I recommended them.
All of these are good choices, but you need to learn a bit of the lingo to become more fluid and make a better choice for your needs. Kontronik ESC’s name designates their style, quality and features. In the order of low end to high end they have the “Smile” series and the “Jazz” series. Kontronik numbers for their ESC’s actually mean something too! The first number is the maximum continuous amps they can handle, while the next two numbers indicate the lowest and highest number of Nicad cells they can handle.
Yes, I said Nicad cells! This means that the Kontronik Smile 45-6-12 can handle 45 amps and 6 to 12 Nicads, or 2S to 3S Lipos. If you are wondering about NiMH’s, Nicads and NiMHs can be interchanged in the numbering system as they are nearly the same. So that about sums it up for Kontronik, except for one important point; ALL of the Kontronik ESC’s have BEC circuitry that works with any number of cells you use.
The Hacker and Jeti ESC’s have a different numbering system. The Number indicates the amount of amps the controller can continuously handle, while the name indicates whether or not they can use BEC, along with their maximum cell range. The “B-Flight” series supply BEC to the receiver, hence the “B” and they are limited to 3S Lipos maximum, where as the “O-Flight” requires separate receiver power. The “O” stands for Optical, which means the signal wires to the receiver are optically coupled. This is a feature required for some “twin” motors or applications using high cell counts that produce more RFI (radio frequency interference). The signal from the ESC uses an optical circuit for input from your receiver; using this type of circuit, the throttle line is isolated electrically, so feedback from the second ESC’s receiver wires in the case of using twin motors when connected together at the receiver will not affect the first ESC as there is no real electrically wired circuit. The same goes for RFI, as noise that may be passed electronically through the wires has less effect on the ESC. Some of the “O-Flight” ESC’s can handle 16 cell or 5S, while others can go to 32 cells or 10S … some are even higher.
Castle Creations “Phoenix” series of ESC’s are pretty simple to understand; the number indicates the number of amps the controller can continuously handle. They also have a feature the other ESC’s do not…they all come with BEC, which works when using a 2S or 3S Lipo pack and is disabled when you use a Lipo pack larger than 3S. The advantage of this is that one ESC can be used for non-BEC or BEC powered models, where the other ESC’s can be purchased only either with or without BEC…so it’s like getting two ESC’s in one, with BEC supplied. Oh…What is BEC? Glad you asked.
BEC- Powering my Receiver
BEC stands for Battery Eliminator Circuit. In R/C, we use receiver battery packs to power our receiver and servos. However, in the electric world many of the ESC’s have built in circuitry to power your receiver from the main motor battery. The power is taken from you cell pack or Lipo, then output through the signal wires that you plug into the receiver for throttle control. This way weight is saved by eliminating the need for a receiver battery pack as the receiver and motor are powered off a single battery. Moreover, you do not have to worry about charging your receiver battery as it is now your main power pack and gets charged every time you charge your main pack. Also note there is safety circuitry included, where the ESC will turn off power to the motor if the battery pack is getting to low; that way you still have receiver power for a dead stick. Smart little suckers, those ESC’s.
Not all ESC’s have BEC though…you need to read about them first. Most ESC’s that go up to 12 cells (except for Opto’s) will have BEC, but once you go beyond that, things change. If you need to run a 4S Lipo, like for the 700 watt Minifan power system we have yet to cover, you will need to supply some form of power to your receiver from another source, as ESC’s normally do not support BEC beyond 3S Lipos or 12 cells. The Exception is Kontronik…they have BEC that works for all their ESC’s at any range … good German engineering.
Since you still need to power the receiver, you can use a small NiMH or Nicad 270 mah 4-cell battery pack, or you can opt for something called the U-BEC, otherwise known as the Ultimate BEC. This is a device you tap off the main battery leads and it powers your receiver independently of the ESC. The added weight (1.5 oz) is less than that of the smallest Nicad receiver battery pack and the weight is compensated by the fact that you are using them in a higher power motor system. Moreover, you do not have to worry whether or not you charged the receiver battery pack. These U-BEC units are good all the way up to 42+v or 10S Lipos and that’s a bunch! There are other versions out there now like the S-BEC that work with small servos and micro receivers, but only the U-BEC can provide up to 5 amps of power for your receiver and servos…a must for larger EDF jets.
So Many Motors
There are more motors on the market right now than I have time to type, so I will narrow the field a bit. Typhoon, HET-RC, HiMaxx, Mega, Hacker, Kontronik and Lehner, from lowest to highest quality are the motors I recommend to use for EDF. Some of the names may already look familiar and that the last three are all about the same in both quality and price, although the Lehners seem a bit overpriced. There are other motors out there, but for EDF, these are pretty much the standard and the most popular of choices for your EDF setup. For this scenario, we will be discussing motors for the most popular of EDF’s, the Minifan 480.
HET-RC just introduced their motors over the last year and they have gone gangbusters with sales. For $55 you get a motor that does the same as the others, at near half the cost or less, or for ten dollars more, you get the 700 watt motor. Their reasoning is they plan on releasing some twin Minifan jets in the near future and wanted to provide a twin power plant that was as affordable as a single motor jet with the other brand motors. It worked and they are worth every dime, which is why I recommended them in my price quotes. The 2W for the HET-RC motors stands for 2 wind…it’s the number of windings used for the electromagnet and the lower the number, the higher the RPM’s per volt (rpm/v), but also the higher the current draw…it’s a give take situation. The motor is rated around 4600 rpm/v.
Mega came out with their 16-15 series of motors for the minifan when the market needed an inexpensive, very dependable motor. They are a step up from the HET-RC, although the HET motors perform nearly as well. The 16 number I think stands for the internal rotor diameter while the 15 does stand for the Rotor length, which is 15mm. The 16-15-2 is similar to the HET-RC 2W and it is a 2 turn (wind) motor with around 4600 rpm/v (rotations per minute for each volt of battery power) .
The higher the last number for the motor, the lower the rpm/v will be. For example, the Mega 16-15-3 is rated at 3000 rpm/v, so in order to make it turn the same RPM as the Mega 16-15-2, also known as the Mega 2-Turn, you need to use a 4S battery pack while the Mega 2T only uses up to a 3S Lipo. RPM limits for both motors are similar, it just takes different batteries to match the motor for the same rpm range.
To figure maximum static RPM, take the RPM/v times the battery voltage; note that each Lipo cell is rated at 3.7v, so a 3S would be 3 x 3.7=11.1v. A good comparison would be the HiMaxx motors for smaller EDF’s. The HiMaxx 2015-5400 turns at 5400 rpm/v, and with a 2S Lipo pack, it will turn 39,600 rpm without load. The Himaxx 2015-3600 turns at 3600 rpm/v and with a 3S Lipo pack will also turn 39,600rpm without load. Here we have two motors with different ratings, different batteries and the exact same performance.
You may have noticed we did not use the 4S pack on the Mega 2T motor or the 3S on the HiMaxx 2015-5400. Each fan produces a fixed load on the motor and you match the motor to the fan unit you want to use. Also, the battery is matched to the motor and fan/load. If you try to use a higher voltage battery to power a specific motor combo, the higher voltage will cause the motor to exceed its recommended maximum RPM, causing high current draws, which will overheat and destroy the motor and possibly your ESC. For this reason, you never want to overpower your setup, no matter how tempting it seems.
The Kontronik motors are one of the best motors you can buy…period. The Kontronik numbering system is pretty easy… the first number is the case’s size, the second number is the rpm/v. For example, a Kontronik 400-36 would be a 400 sized case, which is the same diameter and length as the HET-RC 2W and Mega 16-15 series. The number 36 equates to 3600rpm/v. Pretty simple huh? Their 480 motors have a longer case and rotor than the 400 series and those such as the Kontronik 480-33 would be similar to the HET-RC 2W 20 or Mega 16-25 series of motors.
Hacker motors have a totally different numbering system and you actually need to read their tables for specs. A BL40 series is the Minifan size, similar to the Mega, HET and Kontronik mentioned above. They do use a system like BL40-7S, where the “S” indicates case length. They have “S” for short, “L” for long and “XL” for extra long. A BL40-7L is similar to the Mega 2T and HET-RC 2W. The 12S would be more similar to a Mega 16-7 series, while a 12XL would be more like the Mega 16-25 series or Kontronik 480 series. This brings us to another item to note.
The physical size of the motor is important. Larger or longer motors usually turn lower rpms because they have longer, heavier rotors to turn, so you need a higher voltage Lipo pack to power them, such as 4S-10S. Their size however does produce more torque, so they are more powerful out of the hole and they are capable of turning higher pitched rotors. Also, since they are larger, they can absorb and dissipate more heat, which in turn means they can handle more amps. Amps produce heat…the more amps, the more heat, which is why you want to keep smaller motors like the Minifan motors at around 40-45 amps max and larger motors under 60 amps max during use. Remember, heat is the killer of brushless motors; excessive heating will de-magnetize the core and ruin the motor.
For these reasons the HET-RC 2W, Mega 2T (16-15-2) and Hacker BL40-7L are rated for 400-450 watts using 3S lipos, while the longer motors such as the HET-RC 2W 20, Mega 16-25-2, Hacker BL40-9XL and Kontronik 480-33 are rated more for 600-700 watts using 4S Lipos. Any of those motors will work for the 450 watt or 700 watt power setups available with the only difference being the price, which is due to a higher cost battery like a 4S, more expensive ESC and higher price on the motor. I recommend the HET motors though for the price, or Hacker/Kontronik for quality.
I do recommend the FMA/Kokam packs as they are 3200’s that are rated at 20C and are just a good overall lipo pack. This means they can supply 64 amps continuous, more than enough for nearly any power application. Their only issue may be their size, where they are 1/3 larger than a single Thunder Power 2100, but smaller than two of the TP’s…see where different packs need to be used depending on aircraft size and room available? Also note that there is a give and take; while the Kokams are stronger, they are only 3200mah packs…the Thunder Power 4200 Pro Lites or 6000mah packs have more stored power, so you can fly longer. Moreover, they are top of the line and hold their voltage very well over time, so the Thunder Power Pro Lites are also highly recommended.
With batteries, balancing the aircraft needs to be considered, so do your research and make sure the model can be easily balanced with the packs you choose. The Sniper Jet had a few issues with this, balancing tail heavy with a pack next to each intake under the wing, yet it was nose heavy with the packs in the nose. The HET-RC F-18 takes the Kokam packs or smaller ThunderPower and the F-20 has tons of room for any of them.
Your current skill level will make a big difference as to where you start in the field of EDF’s, so you need to take everything you learned and decide which one is good for you and then make the purchase. If you are a beginner and park style slow flier, you probably will want something like the GWS A-10 with the EDF-55 fans and 300 series motors. This will get you in the air with a simple, fun and affordable aircraft that has many possibilities for modifications. There are many tips on upgrading this model to brushless, which brings is close to the next group of EDF jets. www.e-flighline.com pioneered the upgrade of the A-10 and actually sells them as brushless kits. It’s a good place to look and as with nearly all EDF vendors, they are very good at responding to questions.
Fast Foam Park Fliers
These are usually park fliers that are a big step above the slower aircraft we just mentioned. Such models would include the Alfa F-86 or MIG-15 and the Flying Styro Models like the all foam F-16. They are all good models, although the FS F-16 requires modification as it was not originally intended as a EDF. The Alfas are excellent ARF kits, and if you wish to buy a 60mph foam jet that flies great and looks good, they are a good choice. Most Vendors will recommend a power setup for them. A good starter setup would be using the AC 25-25-26 motor, 12-25 amp ESC and a ThunderPower 3S 11.1v 1320mah Lipo pack. A more popular and much better/hotter setup for them would be using a 3s Tanic 2220, Himax 2025-5300 and CC Phoenix 25 ESC. A Polyquest Lipo pack could be substituted for the Tanic if desired.
Minifan 480 EDF Jets
For hand launching, the Minifan 480 sized HET-RC FA-18 is a good startup model and it looks great in the air. Moreover, at $125 for the ARF shipped, you cannot beat the price! Another choice is the one I recently soloed...the new HET-RC F-20 Tigershark. It is much larger than the average Minifan 480 model, making it easier to locate the batteries and it is much easier to see in the air. Also, it is a good candidate for retract conversion in the future, however, it comes as a bungee launch model. I suggest you take a look at one of the best websites for EDF's, www.warbirds-rc.com and see what is available. He has a great selection of models, from ARF to ARC to build up and the best prices around to boot! Also note all his prices “include” shipping, which makes them a great deal. He also carries one of the motors you would want to start with, either the HET-RC 2W or HET-RC 2W 20.
Another choice of models, the Sniper from HET-RC is a very nice Minifan 480 model with a glass fuselage and monokoted wings. It is a great performer and can fly near 110mph with the right setup, not bad for 3 lbs of jet. The disadvantages are that the Sniper, except for the rare one here and there, normally requires a bungee to launch. These are not bad systems to use and if you are getting into EDF, you really should get used to working with the Bungee. It is a system that’s easy to setup and use and pretty much a requirement anymore for launching performance EDF’s.
Some people have mounted fixed gear to the Sniper, so that is also an option. Note that retracts are not as popular because of the added weight they induce; when a model weighs 29oz dry without batteries, every bit of weight counts for performance, not to mention the problems you face trying to fit them in already restrictive spaces. For this reason, the Sniper and several others are not good candidates for retracts. Also, there are some issues with battery placement in the Sniper that are not as critical as in the other models...just something to keep in mind.
A good place to shop for parts is www.espritmodels.com and they have a great selection of speed controllers, motors and batteries, wire, connectors, etc... For batteries, receivers and more though, I get mine from Tower Hobbies, so those are the three places I shop for EDF. Unfortunately, there are no vendors anywhere nearby that carry EDF stuff. Markos at Warbirds-RC is fantastic though and has an excellent reputation, so I urge you check out his site. While you are there, look at the builds for the different jets in his "Research" section and check out some of the videos he has so you can get an idea of what to expect. The builds will show you how these birds go together.
What would I recommend for power? It depends on how crazy you want to get. It was just last year the average Minifan 480 EDF used 400-450 watt power setups (we measure power/thrust in watts for EDF). Now with the new HET-RC 2W 20 motor, everyone can step up to 700 watts and pass the 100mph barrier for Minifans for only $10 more than the old motor. The only inhibitor is more cost and heavier battery weight due to more cells. I will give you a rundown of two different power plants that work for ALL of the Minifan 480 models.
Wemotec Minifan 480 69mm ducted fan, HET-RC 2W Brushless Motor, 45-70 amp Brushless ESC and a single Kokam 3S 3200 Lipo Pack. With this setup, you can have fun flying all day and not spend a fortune. You will have a power plant that runs 400-450 watts and run times around 6 minutes on the pack I mentioned.
Cost as follows:
Wemotec Minifan 480 Fan $40 (68mm)
HET-RC 2W Motor $55 (Typhoon-EDF 2W-20) $75
45 amp 12 cell ESC $80 to $129
Kokam 3S 3200 Lipo $120
Total - $294 - $350
That is the cost of a good power system for the Minifan jets and it even includes the battery. Note that you can use different brands of Lipos, but the cost goes up as Tower Hobbies carries the FMA/Kokam brand and a killer price and they are fantastic batteries. Other good batteries would be the Polyquest 3700 or the newer Thunder Power Pro-Lites in a 3S or any others that can continuously handle 50 amps. Your choice may also depend on which jet you buy, as some packs may more readily fit in a specific aircraft; we can discuss that more once you have made a choice.
You can make some substitutions, using a Kontronik 480-42, Mega 16-15-2 or Hacker B40-7L for the motor. They all perform well with the above setup on 3S Lipos and give you some options for motor selection. I also recommend the following ESC’s in the following order from best to midrange performance:
Hacker Master 70-B Flight
Kontronik Smile 45-6-12
Castle Creations Phoenix 60
Wemotec Minifan 480 69mm ducted fan, HET-RC 2W 20 Brushless Motor, 70 amp Brushless ESC, Ultimate BEC (required for 4S or higher batteries) and a Kokam 4S 3200 Lipo Pack (2 of the Kokam 2S 3200’s in series). With this setup, you will smoke the skies. You will have a power plant that runs 650 - 700 watts and run times around 5 minutes on the pack I mentioned. Speeds just over 100mph are pretty much guaranteed.
Cost as follows:
Wemotec Minifan 480 Fan- $40
HET-RC 2W 20 Motor $65
60-70 amp 16 cell Opto ESC $119 to $159
Ultimate BEC $30
Two Kokam 2S 3200 Lipo at $82 each, Total $164
Total - $418 - $458
As you can see, you need to pay for the power increase, about another $120 or so, however the packs, ESC and U-BEC can be used in future Minifan models or even Midifan models. It’s your choice on where you want to start. This setup will give you excellent performance, with underhand launches possible followed by endless verticals.
You can also make some substitutions, using a Kontronik 480-33 or Hacker B40-9L for the motor. They all perform well with the above setup on 4S Lipos and give you some options for motor selection. I also recommend the following ESC’s in the following order from best to midrange performance:
Hacker Master 70-O Flight
Kontronik Jazz 55-10-32
Castle Creations Phoenix 80
Receivers and Servos
I like to use Hitec Servos for about everything…they are strong, light and priced well. The smaller HS-55 and HS50 servos can be used in the foam aircraft, while the stronger Hitec servos should be used in the Minifan and larger aircraft. The HS81-MG metal gear servo is a good choice as an Elevator servo and HS55’s, HS56’s, HS65’s or HS125 thin wing servos work well for the Ailerons. For Tailerons, either HS81MG’s or HS85MG’s for Minifan jets or the HS5245MG Digital Servos for Midi jets, it all depends on the model.
As far as receivers go, I have had great luck with the Hitec Electron-6 receiver on all my EDF jets. FMA also make good receivers, as does Berg and any of the Mfgrs receivers usually work just fine. Just be sure to use a good, high quality dual conversion receiver on Minifan or larger models.
I think that about covers most of it…sorry if this was way too long winded. As a wrap, here are my recommended places to buy… the Jets and HET motor I would get from Markos at Warbirds-RC, the ESC, batteries and wire/connectors from Northeast Sailplanes and the batteries, servos and receiver from Tower Hobbies as they have THE best price on Kokams. Your local shop could probably get the ESCs, receivers, servos, wire, and batteries in if they wanted, but you still need the kit and motor. I hope you found this information useful and wish you the best in your EDF endeavors!
Copyright © 2003 [BetterFly Crafts]. All rights reserved.
This WEB page was last updated:
2008 01 19.