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Jeff Goin

 

 

Yuneec ePac Pre-Production Prototype

Flown 04/08/2008, Reviewed 04-09-2008, Photos by Jeff Goin, Susan Mitchler

This is a revolutionary machine. I feel like a part of history�and a part of the future.

Forgive my enthusiasm, I realize its not becoming of a reporter and admit to being a huge fan of electric paramotors. I've wanted to see them succeed since Csaba's machine (first practical electric) purred aloft. But it's all been dreams and promises. Csaba did a good job but never wanted to go into production. Producing and supporting a motor in quantity is a huge deal.

Others have made good inroads, with tested machines and promising schedules, but they haven't come to market yet. One effort was all talk and no show. So you can imagine my elatation at finally getting to fly one. A real one. From a company with the wherewithal to produce it.  And in conditions that pilots will use it. The only special instruction they gave me on its use was "when it hits 53 volts, you need to land." Not because it would hurt the machine, but because the battery would shut off in two minutes to prevent excessive discharge.

Three of us flew it in two days.

Yuneec International is driven primarily by two individuals who are bringing their success to bear on an effort that has cost probably well over $100,000 so far. Tien brings the expertise of a top manufacturer of electric Radio Control models in China. Clive brings success in other design and marketing efforts (see the X-Pole). Both are well-enough heeled to see it through completion of a quality, easy-to-use product.

Just after day one of Sun-N-Fun, Wayne and Susan Mitchler, the Yuneec team and I headed for a nearby flying haunt. This site, under development, won't be available for much longer but would do one more time.

You can see the machine's specs on their website. The unit we flew had a 49" prop, weighed 59.5 pounds (measured on a certified scale by Stanley Kasica), and used the Parajet harness. Elevation was 100 feet MSL. There was a strong but reasonably steady wind of between 14 and 18 mph on a 78 degree afternoon with light to moderate thermal conditions. A huge advantage of electric is that there is no power loss at high elevations. Unlike gas engines, whose thrust withers with increasing temperature/altitude, the electric produces the same torgue regardless. High elevation will entail some loss due to the propeller pushing against thinner air, but it will be much less than a gas engine.

Weight

Wayne weighs 160, Eric about 185 and I'm around 150 pounds. Wayne and I flew it under a 22 m� Spice and the next day Eric flew it under a 25 m� Power Pluto.

The unit tested weighed 52 pounds and the harness added another 8 pounds. But it felt much, much lighter because the weight was concentrated up high and right against your back. We weighed the machine and harness first on Eric's large fish scale then put it on Mike Britt's certified scales to insure accurate reporting. Stanley Kasica is pictured modeling the scale just before putting the paramotor on.

Harness & Suspension: The harness, designed by Parajet, is a low hook-in, moving underarm bar system just like what's on the Parajet 2-stroke machine. It's thrustline is above the pivot point so it tends to tilt forward a bit under power, especially before the pilot is seated.

Starting (10): This is tough�squeeze the throttle! Actually, for safety you must first press the green button then, after it beeps, the motor is armed. Initial throttle up is programmed to come up gradually to reduce the likelihood of a surprise wind-up.

Ground Handling & Kiting (8): The electric motor is great for ground handling because, just like clutched machines, the prop isn't spinning. Several advantages are that: 1) In lightish wind reverse, the motor doesn't push against your effort. 2) There's no prop blast to disturb the wind's airflow over your wing. 3) You can feel exactly what the wind is doing on your face. 4) Being completely silent (prop not spinning) means that you can also hear your buddy yell that the wind has switched.

As to how it actually handles, it's easier than a regular paramotor because the weight is so close to your back. It's not trying to pull you over backwards.

Launch (8): The reverse launch was standard for strong winds and having the weight so close to your body was nice.

Since an electric motor naturally spins up dangerously fast, they've slowed it down with software. It wound up being a bit too gradual�an issue they were already planning to address by making it more "perky." We could easily compensate by squeezing a little throttle to get it coming up to speed, then turn around. This same technique is required of many gas engines, too, in real strong winds.

Climbout (5): About the same climb rate as a Snap 100. As with all low hook-in machines, be careful not to get a brake toggle into the prop. The motor tends to tilt forward a bit. This problem can be reduced dramatically by adding a short length of rope so that the risers cant tilt back.

Flight (8): Flying the machine was comfortable and, of course, quiet. Throttle response was perfect once the machine was running at over 20% power but the delay to come up from off was excessive. That is merely a software change that they already plan on making.

The harness is pure Parajet. For pilots used to high hook-in machines it will take some getting used to. The legs have separate straps that get cinched up fairly low on your leg. That makes it easy to get into the seat but it feels a bit like they're tugging your legs while running.

The throttle display was easy to read and provided a wealth of information, especially the voltage. It starts at about 68 volts and, when it gets down to 53 volts under a load, you have just a few minutes. The display starts off displaying voltage, motor temperature, controller temperature, and RPM to put chosen data items in large numerals, making them easy to see. Or you can look at all values at once in smaller fonts.

I did some steepish maneuvering and it pushed enough to keep me level in up to 45� banks. That's about where the wingtip is on the horizon.

Weight Shift (8) Weight shift, which uses a pivoting arm, is quite effected. A combination of lean and leg cross achieves the maximum result. Weight shift is not affected by having an electric drive train. The Parajet harness is much like the current crop of pivoting arm machines. It could probably be improved slightly by moving the arm's pivot points aft about 2 inches.

Torque (8): Minimal. Torque from the prop is identical to a two stroke of the same power. It's related to prop drag and harness setuphaving an electric drive train doesn't matter. But torque steer can be adjusted out and this particular harness was well adjusted. None of the pilots complained of it.

We were hanging it from the most aft hook-in point available on the left and the second to farthest aft on the right. The most aft hang point was unavailable due to the design of a special piece that moves the hang point outboard. That's done so the thrust line is more centered under the twisting point (middle of the risers). That helps. We adjusted the harness so the motor hung quite vertical which also helped. Moving the attachments aft like we did does make it tilt forward more with power application, but it becomes easier to launch and has less torque.

Thrust (5): We didn't get to measure the thrust but it felt like about 100 pounds�roughly the same as a Snap 100 with wood prop. At the end of the flight it still seemed like it would do pretty good, maybe 90 pounds.

Circuitry logic protects the batteries from overheating, reducing current to maintain the temperatures (controller and motor) below 200C. 

Endurance (1): This is what you trade for all the benefits. We put 40 minutes cumulative on one charge with 3-5 minutes to spare. An average pilot, flying an average wing, will get a good 30 minutes of play. If you hammer it, expect about 12 to 15 minutes. But then after gliding for a while, the batteries will recover a bit and you'll get several more minutes of level-flight power. Pilots at high elevations will probably get about 90% of the performance. Since power required is a function of sink rate and weight, if you sink at 300 fpm at sea level but 350 fpm at 5000 feet, then you're requiring more power out of the motor. That will use the battery faster.

Adding batteries will enable more run time. And given the comfort of having its weight so close to your back, another 20 pounds of batteries would produce about another 30 minutes of flying time. That option is not planned for the initial offering but they indicated it was possible in the future. That would be an hour of flying time for a pilot of average weight on an average wing.

One cool feature that will be on production models is a sensory low-battery alert. When approximately 5 minutes of power remains, the throttle grip will vibrate. As it runs down, the vibrations will get more frequent until they become continuous just prior to its last gasp. You'll be hard pressed to be surprised that it's running low. I suggested that it provide a little electric shock but they didn't think that would go over well.

Vibration (10): This was sweetness, pure smooth sweetness. What little vibration there was obviously came from the prop.

Sound (10): Second only to vibration, this was pure sweetness. Neighbors will be far less likely to object since the noise, all of which comes from the prop, is fairly low pitched. And they're fine tuning the prop to make it even quieter. It's obviously quieter to the pilot and, when I asked two pilot observers, they said the noise was 30% quieter than the quietest machine they'd ever heard (Fresh Breeze usually). Its certainly not silent, especially at full power, but it's tone and intensity are the least objectionable of any other paramotor by a hefty margin. 

Safety (7): A big concern with electrics is how harmless they seem just sitting there. To prevent a casual squeeze of the throttle from spinning the prop unexpectedly, a green button on the throttle stem bottom must be pressed first. Plus there will be a master switch on the frame, within reach of the pilot. If someone gets by all that, the motor won't just go immediately to full power the first time someone hits the throttle. It spools up slowly.

The cage is a compromise. It must be efficient so there is no netting but it is quite rigid. And the tubing would stop an open human palm in most cases from surprise thrust. There are gaps in the cage that would be nice to close a bit but at a price in drag. The cage seems sufficiently stout to prevent lines from pulling the hoop into the prop.

Batteries are another concern with electrics. Lithium Polymers have a nasty reputation for burning impressively, but these folks have years of experience working with the technology in R/C applications. They have found that nearly all fires come from overcharging. So their charger (the production version wasn't here) forces proper polarity and monitors each cell individually to both prevent an overcharge condition and warn of a bad cell. The other cause of fires has been physical damage. So they have placed the batteries up high in a place where the prop cannot strike them and in an aluminum case so that survivable impacts are not likely to breach any cells. If a pilot crashes bad enough to breach a battery, the breach probably won't matter.

Construction (9): This machine included a test of several production processes but it's really a pre-production prototype. Even at that it was beautifully built and worked flawlessly. Their well-equipped factory in Shanghai, China comes complete with a CNC machine, molding and many other accouterments of manufacturing.

Most of the cage uses teardrop shaped tubing to reduce drag through it's 51" diameter.  The 49" prop averages about 3 inches behind the rim. It's closer at the top than the bottom but I would expect a power forward inflation would not be a problem.

Several parts used production molds but with non-production processes. The cowling around the motor, for example, was extremely thin. The production version will be appropriately thicker without being excessively heavy.

On the big things, the controller and motor, they've got it wired. It's taken lots of development work to come up with a low-heat solution that should withstand heavy use. The build their own brushless motors for this particular application, sizing them to spin a 48-50 inch prop. They make the controllers, too, which are upsized versions of what they build on thousands of large R/C models. It's a tradeoff. By doing their own motor this way they reduced the parts count by eliminating a redrive. That further improves reliability.

I learned about brushless motors. Current is sent to 20 or so fixed coils, arranged like a radial engine, in a tightly choreographed dance of pulses. Each pulse pulls or pushes on the rotating fixed magnets at just the right time to induce a torque. With stationary coils, the actual rotating mass, which has the fixed magnets, is quite small. The magnets are incredibly strong, too, and as long as they never exceed about 200�C, they won't demagnetize.

Reparability (10): The ten is for its drive train. There are surprisingly few moving parts and nothing got terribly hot. I was able to hold my hand on the motor and controller immediately after landing. The cage is no different than But the cage will require welding if it gets dinged and, in this case, replacing the aerodynamically shaped tubing will be harder. Such is the price of improvement.

Transport (10): Nothing spills. It comes apart in several pieces and, since the batteries can be removed, it's amazingly easy to transport via fedex or airline. I'm not sure what, if any, restrictions there are about carrying these batteries besides having their terminals taped. Check with the airline or carrier you plan on using.

The cage is about 50 inches in diameter so it will fit into a minivan without disassembly. They had a full sized van but the procedure still requires putting it in at an angle to fit.

Cost

It won't be cheap, especially for the first few years but isn't bad considering the development costs. It sounds like a unit will go for around $8000 (US) and $10k with a wing that's being developed specifically for Yuneec. Just like cell phones, the batteries will degrade with use. After 500 cycles, the batteries will have about 80% of their total energy capacity. So a battery that gave you 40 minutes when new, will end up giving 32 minutes after 500 full charges. Partial charges don't count as a full cycles since Lithium Polymer batteries have no "memory" like Nicads. Most pilots fly under 50 times per year so they'll want to replace the batteries after 10 years. No price was given but I'd expect the batteries to run around $2500. Compare that with gas, though--many motors have sucked up $2500 by that time, too. Time will tell regarding reliability. There will be growing pains but these folks are positioned to support the product. Yes, controllers and motors will be expensive, but in the R/C realm, these have proven highly reliable. And if they support the paramotor product like they apparently supprot the R/C products, we'll be in good hands.

One last thing about cost. There is some small offsetting benefit from the energy source. Electric power is cheaper than gas power. For example, if fuel is $3/gallon and you burn 1 gallon per hour then your energy cost is $3 per hour. I'm told the electricity to charge the batteries for an hour flight would be about $1. That's $2 per hour cheaper on energy so, after 500 hours, you will have saved $1000 in energy costs.

Water is not a factor for most pilots but there are always exceptions. So I asked how it would deal with submersion. "Not well" was the answer. Of course that makes sense; you wouldn't expect your far less sophisticated electric drill to handle it well, either. Light to moderate rain should not be a problem�they've designed it be protected, but still recommend against flying in rain.

Overall: I believe that electric will become a big part of paramotoring's future. It won't replace gas for a long time to come but will take an increasing share of the market. For good reason. Free flight pilots will love it, non-mechanics will love it, as will any pilot who wants to just squeeze and go which is about all of us.

It's not for long cross countries, real heavy folks (yet), or those that like to fly fast. Speed requires large amounts of continuous power and this won't put up with that for long enough to be useful.

The electric meets a mission for many pilots who A) don't want to be 2-stroke mechanics, B) tend to fly shorter trips around their local area or C) travel a lot and take shorter flights for a quick exploration of their surroundings.

It will have a plug-n-play battery system. The pilot snaps the batter in place and, when he's done, snaps it into the charger. They say it will take about 1.5 hours for a full recharge.

 

  

1. Conditions were strong but that was what we were dealt. I had some fun first to warm up.

2. The cage hoop and radial cage structure is made from this aerodynamic stock to reduce drag by several pounds. That's just like adding several pounds of thrust to your motor. It benefits free flyers, too, who want to motor to their soaring sites.

3. L to R: Clive, Jeff, Wayne, Tien, Guei. I'm clearly excited about this prospect. After hearing so much about the electrics and writing about them on ElectricPPG.com for several years, I've been hoping for success.  But effort after effort fell by the wayside so it's refreshing to see a company get this far. Far enough to bring a product that they let us use in real world flying.

There were no conditions given to us, they didn't ask us to baby it in a certain way, they just said have at it with as many pilots as want to try it while the charge remains. It went through two charge cycles during our testing and we may have one more session to play with it this morning.

Eric Dufour flew it in very rough conditions and had it on full power quite a bit to climb out of the turbulent tree-shrouded field. And he weighs 180 lbs.

We may get an extra session this morning (in Christmas, FL) and I'll hopefully get some aerial shots of it flying along with other comments about our experience.


Remember, If there's air there, it should be flown in!