Author: Curtis Mattikow
Edition: Model Aviation - 2008/08
Page Numbers: 65,66,67,68,69
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Large EDF Comes of Age

by Curtis Mattikow

I lived through the bad, old days of glow ducted fan. I have shoeboxes full of old, burnt Rossi and O.S. .91 pistons to prove it. Some modelers achieved reasonable reliability with the large glow systems, but my experience and that of most others was 10 flights at best before a pipe seal, glow plug, or something else went; then you were testing the rather limited gliding abilities of a 15-pound jet (or brick).

I got a lot of flying in, but I made numerous smoking holes along the way. I did not enjoy the noise, the fuss, or the gallons of glow fuel, but it was the only way to fly a jet without sticking a propeller on the nose.

When turbines came out, I jumped right on that — not so much because of the performance increase, but mostly because of the increase in reliability. Even at their worst, turbines are tenfold more dependable than glow ducted-fan (DF)-powered models.

Turbines have their own limitations, though. They are expensive, intimidating, and unwelcome at most fields for any number of reasons.

But now there is an alternative. Several large electric-ducted-fan (EDF) systems will drop directly into those old glow DF airplanes hanging from garage ceilings across the country and fly them as well as the old Rossi and O.S. engines did.

This did not happen overnight; it has been a constant process of incremental development. But there were a few milestones, a couple of which were when powerful-enough motors and controllers became commonly available. That, combined with steady improvements in battery technology, has led us to where we are today.

Many individuals have spent a considerable amount of time and money developing this technology. However, driving large EDF into the mainstream took the availability of complete plug-and-play (PNP) systems you can buy and stuff directly into an airplane without needing an electrical degree, a machine shop, or contacts at secret underground ESC factories in the Czech Republic that have a two-year waiting list.

This article is not meant to be comprehensive, but more of a primer covering where we are today and the most popular PNP large-EDF systems out there. If you are a jaded old hand who winds your own motors and shows up with Horten flying wings at the Aspach EDF meet every year, this article is not for you. If you are an average sport modeler who might have a hankering to get into this new field, read on.

Keep in mind that this is not a product comparison guide. I am neither endorsing nor rating various systems — just showing you what is out there, proven, and readily available.

I had an epiphany about large EDF a few years ago at a jet rally. A friend showed up with a Viper and a Yellow Aircraft Starfire powered by EDF, and they were identical to the "glow jobs" when they took to the air, only without the noise.

I queried him and learned that he had been experimenting for quite a while with components he had to get from all over the planet. I was kind of turned off but intrigued by the performance.

The next year several people showed up with BVM Vipers — all with a PNP system from Bob Violett Models (BVM). These pilots were just fliers, not electric experts, and they flew the heck out of the stuff. That was when I realized that the large EDF had arrived.

Who Has 'Em?

There are several large EDF units available, including the following.

BVM Electric VioFan (EVF)

The VioFan represented the pinnacle of efficiency for glow DF units. Both the fan unit and the engines for the EVF went through constant evolution and refinement to extract the most performance from the glow-DF format.

The VioFan has been converted to electric power and is available as a PNP unit, consisting of fan, ESC, and motor, all factory installed and balanced. The EVF comes in five varieties, from one with 4,000 watts designed for 10S Li-Poly cells to one with more than 6,000 watts, designed around 16S packs. The EVF puts out 14 pounds of static thrust (20 for the 16S), well exceeding that of the old glow versions.

Good, clean airframes have been routinely seeing 170–200 mph with the EVF. Twenty pounds of thrust on tap opens up possibilities for all sorts of larger airframes that were originally designed around 18- to 27-pound-thrust turbines.

The EVF costs $1,195–$1,695. However, it is well proven and the support from BVM is unmatched. This unit is also a drop-in fit to the many superb BVM ducted-fan airframes, such as the Maverick, Viper, and Sabre. They have proven to fly extremely well using the EVF system instead of glow.

Another great advantage is that you can get every part you need from one source: BVM. You can buy a complete airframe, fan parts, and specifically made saddle-type Li-Poly packs that will drop directly into the spaces where the old glow saddle fuel tanks used to be. In addition, the BVM website contains complete documentation and instructions for the care and feeding of your fan and batteries.

This system may be pricey, but notice how many happy BVM customers you see out there and how many of them are successful. Bob Violett does the tinkering and experimenting, so you get a refined and proven product for the money.

Jet Hangar International E-Turbax

Larry Wolfe of Jet Hangar International (JHI) has been at the leading edge of ducted fans since the earliest days, and his son, Chris, has joined him. Chris was one of the earlier proponents of high-performance EDF models, with his remarkable F-14 twin and their neat Skyray for the WeMoTec 480 MiniFan.

JHI has gone into the large-EDF ring with a conversion of its venerable Turbax fan, called the "E-Turbax." It comes in 10S and 12S varieties, rated at 4,000 and 4,500 watts and 13 and 14 pounds of static thrust respectively. The electric units handily outrun the .40–.46–powered glow versions.

The E-Turbax system has been flown extensively and proven to be reliable. It is also affordable, at $895 for a factory-test-run and balanced unit including the Castle Creations Phoenix 110-HV controller.

There are a vast number of Turbax-powered airframes out there; they were (and still are) sold by the thousands. Most are slightly lighter and smaller than the average jet because they were designed around .45-size engines rather than the .91. This makes them particularly suitable for EDF conversions.

JHI has everything a jet pilot could need, including its own line of Falcon-brand Li-Polys, made precisely for the task, and a large range of fiberglass-and-foam jet kits. Exciting news is that the company is gradually releasing ARF versions of its whole range of jets. The A-7 ARF has been out for a year or more and has been successful. The F-86 should be available soon.

Stumax SM110-52

The Stumax fan differs from the others in many ways. It was designed from the ground up as an electric fan, and it has a pusher configuration (motor in the front) rather than the tractor configuration of the others. It has also benefited from a long, careful development process using computational fluid dynamics to extract the maximum efficiency from the available power.

The SM110-52 is almost silent when it runs. Noise equals wasted power, and if silence indicates efficiency, this fan is extraordinarily efficient.

It has a 110mm diameter, which is slightly smaller than the others, and requires only 80% of FSA (fan swept area) for inlets. That means it is suitable for converting many turbine airframes that have smallish inlets designed for turbine use.

The Stumax fan represents more of the future, with carefully designed EDF-specific shrouds and rotors. It is currently set up to produce 3,500 watts at only 77 amps, but it puts out the same amount of thrust as the other fans while using less power. Future versions will have even more power; a 165mm fan with perhaps 18 pounds of thrust will probably be released soon.

The SM110-52's design is neat, easy to install, and has tremendous long-term potential. And the price is reasonable for such a carefully thought-out and sophisticated unit, at $750.

Static Thrust

Static thrust is something of a red herring when it comes to comparing fans. I have measured 16 pounds of static thrust on my old Byron Sabre, but it would be lucky to top 110 mph on the downhill. However, I had Dynamax-powered models that measured only 8 pounds of static thrust but would approach 200 mph in flight.

Manufacturers need to list static thrust because there is no other way to give some idea of the fan's performance. But the user shouldn't read static thrust as a true indicator of what a fan can do. Thrust may go way up or down in the air, exhaust velocity may be dramatically different, and some fans perform better or worse on the bench or with or without the proper inlet or exhaust ducting.

Each fan performs differently in the air, and I don't want to make a point-by-point performance comparison of the three I've listed. It depends on the airplane and how you fly.

Be careful about reading bench-test reports in magazines and on the Internet. All bench-test results seem great, and what a fan will do hooked up to a test bench (usually with a power supply instead of a battery) is often completely different from what it will do in the air.

Do your research! Get out to the field and see what models pilots are flying, with what fans, and how they go in the air.

ESC

The EVF, E-Turbax, and SM110-52 use the Castle Creations Phoenix 110-HV controller. There are alternatives, but most are expensive and come from Europe, which can mean long wait times if you need service; Castle Creations is located here in the U.S. The 110-HV is well proven against several others, which is a great reason why it is the controller of choice.

And there is good news on the horizon. Castle Creations is about to release a new version, the 110-SHV, which will be capable of handling as many as 20 Li-Poly cells. When motors that handle that become available, you will be able to increase the voltage and reduce the amperage and get the same or more power, while being able to use less-expensive battery cells.

Motors

All three systems I've mentioned also share motors — made by Steve Neu of NeuMotors — but they are different. Each fan uses a particularly tweaked winding configuration to handle the various loads of assorted rotors.

There are alternative motors, such as Lehner, Plettenberg, and other brands, but what will work well in your fan is an open question. There are good reasons why these manufacturers have settled on NeuMotors as their standard fitments; they work, and if something goes amiss, service is right here in the U.S. rather than an ocean and a language away.

Li-Poly Cells

For these applications you need excellent batteries that will produce at least 25C. With lesser batteries, the voltage sags too much under load and performance suffers or the pack puffs.

I use MaxAmps batteries. There are many brands, but batteries' C ratings are often exaggerated. This is not a big factor in most circumstances, but these fan units are pushing the limits, and the price of an inferior battery may not be a bargain if it puffs on the first flight. Stick with name brands that have good warranties.

Also, most cell manufacturers suggest that you don't discharge your batteries more than 80% so they will have long, healthy lives. Be aware of that when you are flying; a flight timer is a must, and you need to keep flights short at first. After every use measure what you put back into the battery and increase the flight times incrementally until you have a good idea of how much is being taken out in what period of time.

Running a battery all the way to the low-voltage cutoff is bad in mainly two ways: it shortens battery life and turns your jet into a glider, as in the bad, old days of glow.

Airframes

There are scores of suitable airframes. Thousands of glow-DF kits have been sold through the years, and many are still new in the box and available at swap meets, just as many are hanging, gathering dust, from ceilings at hobby stores. Some of the designs are unsuitable for turbine conversion because of structural issues or lack of room for fuel and can be purchased for reasonable prices.

In addition, a goodly amount of new kits are available from various sources, particularly BVM and JHI, although there are not nearly as many as there were five years ago. Nowadays the trend is to go ARF. There are many out there, and they are mostly for the turbine market; but if you can keep the weight down, some are eminently suitable for EDF conversion. A successful conversion is the Cermark F-16. It's light, inexpensive, and goes well on EDF power.

You may have to work on making proper inlet ducting if you are converting a turbine model. Exhaust ducting is simple — a rolled plastic tube is basically all you need — but inlet ducts may involve making a foam form and then fiberglassing it and removing the foam.

If you have doubts about an airframe's suitability, ask your dealer for the bare airframe's weight and inlet and exhaust diameters. Keep in mind that you don't need a wheel-brake system with EDF, so you can save some weight and expense by using conventional wheels and wire struts rather than the heavier turbine landing-gear systems.

In the end, you can get almost anything airborne with these systems, as you could with an O.S. .91. But carefully selecting an airframe and ducting is required to get outstanding performance.

After the magic of seeing the model fly has worn off, most pilots want it to perform like a jet. Many of the older airframes weren't sized properly for the old glow fan systems in the first place and flew marginally on them. That won't improve much with EDF power.

Charging

You need a good charger! Actually, you'll probably need two. Most batteries are set up as a pair of five- or six-cell packs rather than a 10- or 12-cell pack. Few chargers will handle a 10S pack, so you are probably best off getting two chargers that will handle 6S.

I like the Hyperion EOS 0606i, available from MaxAmps, which has a balancer built in and is AC/DC. But the new 0606i Duo will accommodate two packs at once, which is much nicer than waiting two hours between flights. You need to balance your packs for every charge cycle.

There are some terrific chargers out there, such as the new FMA Direct Cellpro 10s. It will charge and balance automatically with a push of a button. I highly suggest that you make a modest investment in quality chargers. They are useful for all your batteries, not just Li-Polys, and a good charger will take care of your batteries.

Charge times are typically 40 minutes to one hour, depending on how far you have discharged the cells. So unless you like waiting, consider investing in an extra set of batteries to get more flight time.

Generators and Gel Cells

You are throwing anywhere up to 6,000 mA into your model batteries on each charge. That's a lot of power. And if you hook a charger up to your car battery, you have a good chance of needing a jump-start before the end of the day (and having to figure out how to reset the clock on your dashboard). So what do you do?

It's rare to have access to 110-volt house current at most fields, so get a marine-type, deep-cycle, 12-volt battery to feed your chargers. Some pilots use a small gasoline-powered generator to top off a 12-volt battery. It's noisy but effective, and it's handy to have around the house anyway.

Don't be the last person at the field if you have been charging from your car. Make sure it starts at the end of the day before everyone else leaves and you are stuck without a jump!

Off-Brand Fans and Motors

Some other fans out there are European and of very high quality, and a few are from the Far East and of somewhat doubtful quality. However, all lack the PNP functionality of the EVF, E-Turbax, and SM110-52.

You may get the fan unit but have a hard time finding the right motor with the right shaft diameter to drive it properly or the ducting to match your airplane. There are all sorts of potentially expensive variables.

If you are a neophyte, stick with a proven PNP system such as the ones I've mentioned. You shouldn't ignore other systems — some are outstanding — but unless you feel comfortable matching components and potentially toasting batteries, controllers, or motors, leave the bleeding edge to others.

The Future

Maybe the biggest hurdle for large EDF aircraft is limited flight duration. Six minutes is usually the maximum. But that was the case with turbine-powered models only a few short years ago. It isn't anymore, so expect the same improvements in big EDF airplanes. The motors, and the batteries in particular, keep improving (and getting cheaper), and performance and duration keep increasing. EDFs might supplant turbines in popularity within five years. I don't claim that turbines will go away, only that EDFs will be more popular. There are more places to fly them, less intimidation, lower cost, and not as much noise. I have watched the smaller EDFs gradually come to meet and then greatly exceed the power and duration of their glow counterparts, and I'm confident that the same will happen with the large versions.

The 200 mph barrier is already broken, 1:1 thrust ratio is possible, and scale flight of almost any airframe is doable, so not much needs to be proven. From here on there will be only refinement and improvement; the large EDF has "arrived"!

When you see one of these units in action, I think you'll be convinced. Visit a jet or electric rally where you know a big EDF is being demonstrated; seeing is believing.

Curtis Mattikow [email protected]

Sources

Transcribed from original scans by AI. Minor OCR errors may remain.