I'm sure that most of you are familiar with the foam "chuck" gliders that you can buy from toy and craft stores. They are lots of fun in their intended role, but I've always enjoyed modifying these inexpensive airframes into RC models. My knotted "Airplane!" model from 2014 is a recent example. While my chuck glider projects lean toward the whimsical and unusual, I figured out early on that these same models can also serve as low-stress trainers for new pilots.
The traditional path to earning your RC pilot's wings is to purchase an almost-ready-to-fly kit and then have an experienced pilot provide instruction over the course of several weeks or months. Even though prices for these types of models are as low as they've ever been, the cost of entry is at least $150 dollars…usually much more. That's a significant investment for someone who probably isn't quite sure if RC flying will be something they want to stick with.
Modifying a chuck glider for RC will probably cost about $50 for the airborne components. That is still not an insignificant sum, but it certainly relieves a lot of the crash anxiety that most new pilots feel. Furthermore, you can complete the conversion in a single afternoon. So there isn't much sweat equity required to get off the ground.
Bill of Materials
Air Hogs Titan glider, qty. 1, $10
Tactic TTX850/TR624 radio, qty. 1, $190 (any 3+ channel radio will do…go cheap!)
4-cell Receiver Battery, qty. 1, $13 (use any 4-cell NiCad/NiMH 1.5-3.0 ounces)
Tactic TSX5 Micro Servo, qty. 2, $9 each (use any 5-9 gram analog servos)
Great Planes Clevis w/12" Pushrod, qty. 2, $4/pair (use any pushrod ≈12")
Great Planes Nylon Clevis, qty. 2, $1/pair (use any lightweight clevis)
Great Planes Small Control Horn, qty. 2, $1/pair (use any lightweight control horn)
Foam Board for control surfaces, qty. 1 sheet, $1/sheet (use any sheet foam 4-6mm thick)
Optional V-tail mixer, qty. 1, $15 (only necessary if radio does not have mixing functions)
Less is More
I think that the majority of chuck glider conversions that I've seen are massively over-engineered. The designers seem to approach their project with the mindset of making this rudimentary toy store glider in the image of a traditional RC airplane. I've definitely been guilty of that in the past by adding lots of servos, wing spars, heavy power systems, even landing gear. In retrospect, my most successful conversions reflected a minimalist philosophy. The less you stray from the airplane's simple roots, the more it rewards you with its flight performance.
Simplicity was my overwhelming priority when sorting out this project. Cost was a close second. This often meant that I had to make concessions regarding weight, aerodynamics, and aesthetics. Suspend your sense of vanity and resist the urge to make changes for the sake of looks. This airplane is ugly for a reason. I think that the tradeoffs are worthwhile and will be appreciated by first-time builders and pilots.
The chuck glider that I used as the core of this project is the Air Hogs Titan. I can't find reference to it on the Air Hogs website, but they are still available from Wal-Mart, Amazon, and other stores. This was my first time converting this particular model and I found it to be an ideal subject. It is large enough to easily carry the necessary equipment and be seen from a distance. Also, the mold quality of the parts is very good compared to some others I've seen.
Resist the urge to buy smaller gliders. Those with 24" wingspan and smaller are fine for tossing around the back yard, but converting them to RC isn't easy.
Resist the urge to buy smaller gliders. Those with 24" wingspan and smaller are fine for tossing around the back yard, but converting them to RC isn't easy. It can certainly be done, but success requires building and flying skills beyond that of most rookies.
The most expensive part of this project is the radio system. Going to a hobby shop and buying a modern radio will probably cost you at least $150. The good news is that you don't need a new radio. Just about any radio with 3 or more channels will work fine. The advent of 2.4GHz radio systems has made the previous generation of 72MHz radios nearly obsolete and practically worthless (think VHS vs DVD). But those older radios are still a completely valid option. In fact, with most RC pilots using 2.4GHz these days, the 72MHz band is virtually empty.
Check your area for potential sources of old radio equipment. I would venture that most active flyers have one or more old radios sitting unused. Also check pawn shops, Craigslist, or the consignment area of hobby shops. A quick scan on e-bay shows a number of 72MHz radio listings at bargain prices. I even saw some new-old-stock radios with a quick Google search. Just ensure you get both the transmitter and receiver, and that the duo works before buying. While 72MHz radios are cheap to buy, there is no cost advantage when it comes to repairing them.
I've given away all of my working 72MHz radios, so I used one of my 2.4GHz systems, a Tactic TTX850 transmitter and TR624 receiver. In addition to the transmitter and a receiver. You will also need two micro servos and a battery to power the onboard gear. The micro servos I used are Tactic TSX5 9-gram units. They're actually a little larger than necessary for this project…5-gram servos would work fine. But 9-grams servos are typically easier to find and less expensive.
The battery is by far the heaviest component on the airplane, so it is important that you choose wisely. I used a 4-cell, 4.8-volt, 1100mAh pack consisting of 2/3A-sized NiMH cells. At 2.9 ounces, it's on the heavy end of what I would recommend for this project. Any 4-cell NiCad or NiMH battery in the 1.5 to 3-ounce range should work fine.
Choosing a receiver battery can be tricky. In addition to the NiCad and NiMH options above, there are also 2-cell LiFe batteries. Such batteries have a higher nominal voltage and are lighter for a given capacity than NiCad/NiMH cells. LiFe batteries are acceptable options as long as they fit the weight range and you don't mind the cost.
Avoid using LiPo batteries to power the receiver. Although many LiPo packs are advertised as receiver batteries, the voltage of a 2-vell LiPo is too high for most receivers and servos. These batteries require a voltage regulator to prevent burning up your radio gear.
The last bits that you will need are basic RC hardware items such as pushrods and control horns. I've listed the items I used in the bill of materials. I could have saved a few grams by going with specialty components that I have in my stash. But I decided to go with items that can be found in any hobby shop and purchased cheaply in small quantities.
You may have noticed that I have not listed a motor or speed control for the Titan. That's because this trainer will be a glider, at least to start with. Flying without a motor will help you to learn the basics of piloting with fewer variables and less risk. I'll show you how to add a power system in a later article.
The first step in the conversion process is to remove the glider from its packaging and assemble the pieces together. Note that the horizontal stabilizer can be installed either of two ways. Use the orientation that results in the least upward angle. You may want to place a piece or tape or a subtle mark on the stabilizer so that you can easily determine top from bottom later on.
Do not apply the stickers since they'll just add unnecessary weight. Once the glider is ready to toss, determine where the fore/aft balance point is. This is easy to do by balancing the glider on two fingers, one under each wing. Use a Sharpie to mark the spot where the glider rests horizontally or slightly nose down. It will be necessary to maintain this balance point (center of gravity - CG) as you add the RC components. The CG on the Titan should be 5" behind the leading edge of the wings where they join the fuselage.
Now disassemble the model. You won't need the wings again until you are ready to fly.
As a glider, the Titan will be a 2-channel model…meaning the radio system will drive two control functions on the airplane. This would normally translate into adding a rudder for yaw control and an elevator for pitch control (you'll utilize a third channel if/when you add a motor). That path is certainly an option here, but the geometry of the Titan's tail feathers makes adding a rudder and elevator a little more complex than the method I propose: tailerons.
Tailerons are much like elevons, which are the control surfaces commonly used on flying wings. In both cases, electronic mixing allows two independent control surfaces to work together to provide pitch and roll control. I don't want to dive too deep into explaining why it's okay to choose between yaw or roll control. So I'll just say that, despite the differences in physics, the control inputs for the pilot are the same whether you are flying a model with rudder/elevator or tailerons.
The only catch with using tailerons is that you need the correct channel-mixing capability to make it work. Most computer radios (and many analog radios) have this mixing feature built into the transmitter. If the transmitter lists "Elevon", "Delta Wing", or "V-tail" mixing, you're all set. Again, to avoid any lengthy tangents, I'll just say that V-tail control is not the same as elevons or tailerons. But a radio with V-tail mixing can be used to provide the same end result.
If your radio has none of these mixing options, you can utilize an onboard V-tail mixer. The result is the same. You just end up with a little extra weight to carry and more wires to manage.
I decided to make the control surfaces out of foam board. I would normally use sheet foam that does not have a laminate, but that material is tougher to find. As it turned out, the laminate on the foam board was advantageous here.
Whatever material I use for control surfaces, I almost always use some type of tape for the hinge. Blenderm medical tape works best, but I've used all types of tape with varying success. With my recent experience building the Flite Test Mini Arrow (which is made entirely of foam board), I decided to try using the foam board's own laminate as the hinge.
I wanted the tailerons to be about 1.5" wide. So, I initially cut two strips of foam board that were 1.75" wide and slightly longer than one half of the Titan's horizontal stabilizer. Next, I drew a line 1.5" from the trailing edge on the bottom side of each strip. I used an X-Acto knife to cut along this line with the handle tilted rearward about 45-degrees, being careful to not cut through the laminate on the opposite side.
When the cut was complete, I flexed the joint back and forth several times to put a crease in the top laminate. I then removed the foam and bottom laminate forward of the cut. I was left with a strip that has an angled leading edge and an overhanging lip of the top laminate. I attached the strip to the trailing edge of the horizontal stabilizer with a thin bead of hot glue applied to the lip.
Once I had the first taileron in place, I trimmed the ends to match the shape of the horizontal stabilizer. I then repeated the process to attach the second taileron. Standard screw-in control horns work perfectly in this situation. Glue-in type controls horns would also be fine. Just make sure that you install the horns so that the hole(s) for attaching the pushrod are aligned with the hinge line.
With both elevons glued in place, the next step was to permanently attach the horizontal stabilizer to the fuselage. Make sure that the stabilizer is oriented correctly. Avoid using any solvent-based glues here, as they will dissolve the foam. Also stay away from heavy glues to prevent adding unnecessary weight to the tail. I used a thin layer of fast-drying Gorilla Glue.
The pushrods I used are standard 12"-long metal units with 2-56 threads on one end. The particular pushrods that I used also come with a nylon clevis attached to the threaded end. It would be customary to solder a threaded brass coupler to the unthreaded end of the pushrod or twist it into a z-bend. With the light loads of this model, however, I was comfortable just gluing another nylon clevis in place. I drilled out the clevis to the diameter of the rod and used medium viscosity Cyanoacrylate glue (super glue).
For each pushrod, I attached one clevis to a taileron control horn and the opposite clevis to the servo horn on one of the TSX5 servos. I used hot glue to attach the servo to the side of the fuselage while making sure that the taileron and servo were both centered. Working with hot glue gave me a few seconds to fine tune the servo positioning before the bond set. I repeated this process for the other pushrod and servo.
It would have been a very simple matter to hog out a bit of foam in order to flush mount the servos. It would definitely look better that way. Yet, doing this would have created a weak spot in the fuselage that would make it more prone to failure in a crash. You want your trainer to be as tough as possible. So worry about flush mounting on a subsequent build. For now, Ugly is good!
I added a strip of self-adhesive Velcro to the top of the fuselage just behind the faux cockpit. The receiver and receiver battery are attached to this strip. Position these components so that the model retains its original balance point. Just make sure that you reinstall the wings before checking the balance. As long as the wings are a tight fit into the fuselage, there is no need to glue them in place. It's actually better for them to be removable.
If your battery is on the light side, you may need to place it further forward for proper balance. The CG is critical, so do whatever it takes to make it correct.
The final assembly step is to ensure that the control surfaces move in the correct direction. You will only use the right control stick on this model while it is a glider. Pulling downward on the stick should result in both tailerons moving upward equally. Pushing forward on the stick will have the opposite effect. Moving the stick to the right should cause the right taileron to move upward and the left taileron to move downward. Moving the stick to the left should make the left taileron move upward and the right taileron move downward.
If the control surfaces do not respond in the correct direction, you can often correct this by using servo-reversing options on your radio. You may even need to swap the channels that the servos are plugged into. I typically plug the right taileron servo into the aileron channel and the left taileron servo into the elevator channel.
Prepare to Fly!
At this point, the converted Titan is ready for glide tests. In the next installment of this series, I'll show you how to get the model trimmed. Then I'll discuss how to use the Titan to build your flying skills.
Terry is a freelance writer living in Lubbock, Texas. Visit his website at TerryDunn.org and follow him on Twitter and Facebook. You can also hear Terry talk about RC hobbies as one of the hosts of the RC Roundtable podcast.