3D Robotics

Multiplex vs HobbyKing Shootout!

I'm always looking for cheaper Chinese alternatives to our standard aircraft platforms, which is why I'm a fan of the Hawk Sky (EasyStar clone) and Busy Bee (good aerial photography platform). Most of them come really ready to fly these days, with pre-installed brushless motors and ESCs, servos and sometimes even decent LiPo batteries and chargers. Since many of these aim to offer cheaper alternatives to the excellent but expensive Multiplex line that are a favorite for UAV makers, I thought I'd check out two HobbyKing clones of our tried and true Multiplex Easy Glider Pro and Funjet: the Easy Fly and the Sky Fun. They've now arrived and the jury is in: the SkyFun is great and the Easy Fly is crap. At first glance, they both look very attractive. The HobbyKing SkyFun, at $63 with servos and brushless motor included and installed, costs less than a third of what the Multiplex FunJet and power pack costs. And the HobbyKing Easy Fly, at $70 with installed brushless motor, folding prop and servos, likewise costs less than a third of the Multiplex EasyGlider Pro and power pack. But are they really such a good deal? The answer is that the HobbyKing foam RTF kit quality varies pretty widely. The right kit is as good or better than the name-brand equivalent. And the wrong kit is no bargain at any price. First the good news: the SkyFun is a terrific replacement for the FunJet. As you can see from the photo above (the SkyFun is on the right), it's a bit bigger than the Funjet, but otherwise very similar. It comes with a smaller motor, which the commentators on the product listing say leads to pretty tame stock performance, but it has a very wide flight envelope, from slow to very fast (with a bigger motor). Most importantly for UAV uses, it has a HUGE equipment area. As you can see in the picture below, it has more than twice as much interior room as the FunJet, and the FunJet is known for having a lot of interior room. You could put an autopilot, a camera, a range of sensors, and all sorts of wireless video gear in there and still have room for loads of foam padding and movement to get the Center of Gravity right.

I haven't flown the SkyFun yet, but I'm pretty sure that this one will get a lot of UAV use, and possibly a motor upgrade if I get very confident in its flight characteristics.

Now for the bad news: the EasyFly. It's a joke, at least for UAV use. The quality of the model is far below Multiplex standards, and the cockpit area is a mystifying failure of design. Although the EasyFly is bigger than the Multiplex Easy Glider Pro, it's got only half as much interior space, due to some poorly placed servos, way too much useless foam and a ridiculously thick and deep canopy. Just look at it, compared to the Easy Glider Pro (the EasyFly is on the left):

You can see even more clearly from this angle that the EasyFly doesn't even have enough room for a decent-sized battery, much less an autopilot and other electronics:

Then there is the quality of the model. The folding prop and spinner don't fit the body, so they look bad and the prop blades hit the side. The motor is tiny compared to the Easy Glider Pro (which is, to be fair, pretty overpowered). And rather than proper horns on the ailerons and rudder, the EasyFly has these ridiculous lever things (I imagine that they're designed to lower air resistance, but they just have the effect of less solid control):

The comments suggest other problems, such as an unreliable wing mounting, but I think the cramped cockpit is simply disqualifying. I may end up using it to learn slope soaring (if I crash/lose it I won't be too sorry) but I can't see ever turning it into a UAV. Where would I put the gear?
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  • I wonder if it's possible to modify the fuselage so that the lovely clear cockpit bubble is on the underside, so we can put cameras behind it... I think I might have to buy a couple and attack one of them with a craft knife and glue.
  • Developer
    Probably depends on what you want. I'd expect that you will loose the nice rolling characteristics (ie the flys like a pig comments) while gaining payload and duration. A 747 flys like a pig compared to an F-16, but....
  • Moderator
    There seem to be differing opinions as to the effect of lengthening the wings of the EzStar. (either by using an EZGlider wing or thru surgery)
    At RCG some say it's a great mod, while others say it turns it into a pig!
  • 3D Robotics
    The Skyfun flies awesome. One of my favourite planes. A great UAV platform...
  • Developer
    I have been flying the SkyFun for a while now - Perhaps 20 flights. It has a very wide flight envelope. If you set the throws low and trim for a relatively slow speed it is nice and docile. If you replace the power system you can easily push it up beyond 100 kph. I have not had any crashes, although the other day I did throw a prop and tip stall at about 5 meters high. I had just enough recovery room to pull it from a vertical dive to impact at about 45 degrees on hard turf. No damage.

    The EPS foam is not as durable as EPP, but since it is more rigid I have been happily flying in the 80 kph range without adding a carbon spar. That keeps the airframe nice and light and aids in crash survivability. And the final "durability" consideration is with the low price you can buy 2 ;)
  • Hey Chris have you flown the Skyfun yet? If so, how did it hold up?
  • See you dusted it off Chris. lol. get her in the air.
  • 3D Robotics
    @Mook. My problem is just practical. It's too big for my car, my flying field, my workshop etc. And just unecessary, since a standard EasyStar or EasyGlider Pro has all the room we need. As far as flying goes, I don't know whether big gliders have any special dynamics that an autopilot needs to know about--we just haven't bothered to find out, since almost everyone is happy with smaller platforms.
  • @Chris
    what are the problems with too large of a wingspan?
  • 3D Robotics
    @Daniel: Yes, it's HUGE. 2m wingspan is way too big for our purposes.
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