ParkZone Radian Electric-Powered Sailplane

After about a 12-month hiatus from flying any kind of model airplane, and having sold all of my RC gear prior to moving to Erie, PA, I looked around for something that would get me back into the air quickly.

My first inclination was to build yet another Spirit 2-meter sailplane and put a brushless motor in it like before, but I really didn't want to have to take the time to build it first. I also did not particularly care for most of the ARF gliders that were available, but seeing the ParkZone Radian sailplane on the Horizon Hobby website and watching the video of its flight convinced me to spring the $250 for the RTF version. There certainly is no better value out there - a nice-looking sailplane with brushless motor and controller, servos, a 3-cell Li-Po battery, and a charger, along with a 2.4 GHz spread spectrum radio system. You cannot buy the parts individually for that much.

See September 7, 2009 update:

Assembly was a piece of cake - just slide the horizontal stabilizer / elevator into place and secure it with the supplied clear tape, then connect the pushrod wire to the control horn. I didn't like the way the straight wire put a twist on the control horn, so I bent an offset into it to relieve the strain. The pushrod is plenty stiff to function with the bends. The four AA alkaline batteries were installed into the transmitter, the Li-Po was charged (only took about 15 minutes), and off I went to the flying field.

The recommended range check was performed on the radio, and controls were verified to be moving in the right direction. I slowly revved the motor up to about half throttle and launched the Radian into about a 5 mph wind and away she went. At about 3/4 throttle, the Radian will climb nearly vertically. It has a strong nose up tendency at more than about half throttle, so a significant amount of down elevator is needed to keep it from literally climbing into a straight up attitude. This can be a bit of a pain at altitude. A computer transmitter would be of great benefit because you could program in down elevator as the throttle is advanced. But, for a $100 savings, I'll feed in the down elevator myself (at least for now).).

I have to say that this Radian is the best 2-meter sailplane I have ever flown. It is amazingly stable even in gusty conditions, and floats like a butterfly in calm air. Each flight has lasted well over 30 minutes, and that is without coming anywhere near depleting the Li-Po battery; it typically has 11.5 V of charge left after flying around for 45 minutes to an hour. One time when I was flying over a school building and parking lot, I got over 30 minutes just on thermal lift alone - a record for me. The Radian was so high and in such a strong thermal that I put it into a spin to lose altitude. then, she went right back up again. That was at around 2:00 on a Saturday afternoon. I sure wished I had installed myI have to say that this Radian is the best 2-meter sailplane I have ever flown. It is amazingly stable even in gusty conditions, and floats like a butterfly in calm air. Each flight has lasted well over 30 minutes, and that is without coming anywhere near depleting the Li-Po battery; it typically has 11.5 V of charge left after flying around for 45 minutes to an hour. One time when I was flying over a school building and parking lot, I got over 30 minutes just on thermal lift alone - a record for me. The Radian was so high and in such a strong thermal that I put it into a spin to lose altitude. then, she went right back up again. That was at around 2:00 on a Saturday afternoon. I sure wished I had installed my HowHigh™ altimeter. It was so high that I could barely tell which way it was going.

My next trip out did not turn out so well. After flying around in weak evening lift, I decided to do some precision landing practice (which for me is landing within about 20 feet of the target area). On what was intended to be the last flight of the evening - and turned out to be so anyway - I launched as usual, then decided to do a full throttle climb-out. I had never had the Radian at full throttle, even just running it up on the ground. I eased in the juice and began to pull up vertically, when all of a sudden the canopy flew off and I heard a gosh-awful noise coming from it. I immediately throttled back, recovered from the stall, and circled back to the ground while keeping my eye on the descending canopy. I didn't know what happened. Upon landing, an inspection of the craft showed that one side of he folding propeller had broken off about an inch past the hinge point. Evidently the prop broke and the ensuing vibration shook off the canopy.

After getting home and pondering the situation, I decided to do a Web search to see if anyone else had reported such an occurrence. Well, it turns out that the Radians have had this issue since at least January of this year (2009). All have reported the exact same failure mode (see RC Groups  RC Universe). I contacted Horizon Hobby about it and the guys who wrote back (Nathan) said that ParkZone is aware of the problem and is working on a fix. This kind of a known failure mode that throws a thin, sharp blade seems like a lawsuit waiting to happen. I hope the fix it quickly and send out replacement props to all current owners, or at least broadcast a willingness to do so. It wouldn't be hard to find a large number of witnesses for convincing a jury of the negligence.

Here are a few photos of my broken Radian folding propeller blade. It's hard to tell from the pictures, but the break is clean along the cord. I did not recover the piece that separated, so I cannot tell whether it broke into more than two pieces.

ParkZone Radian Broken Propeller Blade Photographs

Amazingly, someone captured an in-flight video of a prop breaking on the Radian during a climb-out

September 7, 2009 Update:

Well, the new propeller was installed and the Radian is flying again. With the Winged Shadow Systems' HowHigh electronics altimeter installed, I launched the Radian at my Erie Tech Center flying site. After a powered climb to a couple hundred feet, I began searching for a thermal. It did not take long to find a boomer. In no time, the Radian was a small dot in the sky. My no-so-great eyesight caused me to to abandon the thermal and land to see how high it got. 1,122 feet, per the HowHigh. The altimeter was reset and up she went again. This time the Radian made 964 feet. Nice. I spent about 10 minutes just launching to about 50 feet and practicing landings. There is one spot at the south end of the approach that would be ideal for a hand-launched glider (HLG), because is seems every time I pass over it at low altitude I can circle a few times before landing.

Here is a little exercise to figure out just how big a 2-meter wingspan looks at 1,122 feet. The first step is to figure out how far away the Radian is. I estimate the Radian was about 20° off my vertical, so by the trigonometric relationship shown to the right, that makes the Radian 1,194' away (only about a 6.4% increase over vertical). So, the next thing to do is calculate how big the wing looks at that distance. Again, trig is used to calculate a subtended angle of around 0.33°. How big is that? Well, the sun and moon subtend angles of about 0.5°, so the Radian appeared roughly 2/3 the size of the sun.

Posted December 9, 2022
(updated from original post on 9/17/2013)