There's just something about a vintage biplane. They have a certain magnetic attraction that causes many people stop what they're doing and watch on that rare occasion when a full-scale one might happen to fly by. Maybe that explains why the GWS Tiger Moth, a semi-scale version of the British WWII basic trainer, has become one of the most popular slowflyers around. Go ahead and run a search in the RC Groups discussion forums for the word "Tiger Moth." I have one word of caution if you do. Be prepared for a whole evening's worth of informative reading, that is, if you're a fast reader. You'll find many useful construction tips and worthwhile ideas for a wide range of functional, quasi-functional, and/or purely cosmetic Tiger Moth modifications, like adding Calvin & Hobbs in the cockpit.
The Tiger Moth kit box contains:
- Airframe Components
- Motor (with connector), Gearbox and 9x7 Prop with spinner
- Landing Gear
- Full Color Instruction Manual with Photos
What you'll need (that's not in the kit):
The GWS instruction manual is one of the best that I've ever seen. The 17 pages of step-by-step directions with full-color photos illustrating most construction steps take much of the guesswork out of the building process. A beginning builder of reasonable intelligence and fine motor dexterity (i.e., can tie his shoes without tying both of them together) should be able to, with the help of this excellent manual and with the right tools, build a Tiger Moth with minimal difficulty in about 6-8 hours.
Fuselage and Motor MountWork begins on the fuselage and its various components. The fuselage comes pre-painted in two halves split down the centerline. Before gluing these two halves together, a few basic preparatory steps are needed. The IPS motor system mounts on a 5x8x87mm wood piece (looks and feels like basswood) that glues into the front of the nose at the proper offset angle (1mm differential on the stick) to give a bit of right thrust. Instructions direct you to check to be sure that the motor mount will slide all of the way (22mm) onto the stick before gluing it into the nose. Mine fit well with no trimming.
After you poke a couple of control rod exit holes through the fuselage and cut down one of the control horns to serve as a tailskid, which mounts between the two halves, the fuselage halves are ready to join. A tube of GWS glue is included with the kit. Now is the first, but obviously not the last, time to remember that weight is critical. Apply just a thin layer of glue spread on the contact areas. Gooping on extra glue throughout construction will only result in an overweight plane that won't fly as nicely as a lighter one. You can use some masking tape to hold the halves together for 30 minutes while the glue dries. Some E-Zone members prefer to use several rubber bands to accomplish this, being careful not to make them too tight, since tight bands can dig into the foam. This avoids the possible problem of the tape removing some of the yellow paint when it's peeled off.
Six little white plastic tabs (4 for the cowling screws and 2 for the wing struts) are then glued to the fuselage. The directions say to use the GWS glue for this and I did at first. I found GWS glue great for certain applications (foam to foam). It isn't up to the task of keeping the plastic cowl tabs secure, even after I scuffed them a little to help the glue stick. I ended up having to go back later and re-attach them with a dab of ProBond polyurethane glue.
Wing WorksThe next step involves fixing the proper amount of dihedral for both wings. Simply put, wing dihedral exists when both wing surfaces angle upward. Wing dihedral causes part of the lifting force of both wings to pull inward at the same time that it lifts the wings up. This effect increases the inherent stability of the plane in turns and generally makes it gentler to fly.
This is one of those steps in the Tiger Moth assembly process where you'll want to consider a departure from the instructions. The amount of wing dihedral indicated by the instructions is fine. The problem is getting it to stay where you want it, especially for the top wing. The instructions call for the use of double-sided tape included in the kit. An alternative method, as detailed in the discussion forums, uses small amounts of either ProBond (available at Wal-Mart) or some 5-minute epoxy mixed with some baking soda (or micro balloons) to lighten it.
I had first faithfully followed the directions by setting dihedral with the GWS tape. The bottom wing held at first, but I noticed a short while later that it was beginning to pull away from the plastic wing joint cover. I went back, and without pulling it apart any further, used a toothpick to spread a very thin layer of ProBond on the surfaces to make them stick for good. The two pieces of joint tape for the top wing didn't work well at all, so I whipped up a batch of 5-minute epoxy with an equal amount of baking soda. This mixture was spread into the gaps where the tape had been and worked fine.
Whichever method you choose, be sure to wipe all surfaces to be joined with rubbing alcohol to clean off any left over mold-release agent. If you decide to use ProBond (great foam-friendly stuff), mix a small amount of water (just a drop or two) into the glue and stir it vigorously with a toothpick or similar object. It should change from a clear amber color to a creamy off-white. This will also cause some changes in the way this glue cures. First, it'll cure much more quickly, as without water, it takes six to eight hours. Plus, as it cures, it will foam up and expand to fill the gaps. Because of this, be careful to use a small amount of ProBond/water for each joint, since the ProBond can grow to about twice its original volume.
Set the two wings aside in a safe place where dogs, cats, small children, and spouses who despise R/C planes can't damage them. You won't need them for a while.
Tail FeathersAttaching the Tiger Moth's elevator and rudder is easy and straightforward. Don't be surprised, however, if flexing the elevator similarly the recommended amount, 40 degrees each way, causes it to crack. Mine did. It's really not a problem since you're going to secure it with hinge tape anyway. After marking the centerline, the horizontal stabilizer glues to a flat area on the fuselage using the supplied GWS glue. The vertical tail has a tab that slides into a slot in the back of the fuselage and another one that fits into a slot at the front of the horizontal stabilizer. Confirm with a triangle that the tail is straight up (90 degrees) before the glue cures.
The bottom wing is connected with rubber bands to a pair of bamboo sticks that run through the fuselage and out the other side. Just run them through until both sides are equal and secure them with a bit of GWS glue.
Under the HoodRemember that wooden stick glued into the nose at a slight right angle? The IPS (Indoor Power System) now slides into it and the wires to the motor through the lower hole in the nose. Some E-Zone members have suggested that enlarging this hole to allow for more airflow to the battery and ESC. I carved the hole to about twice its original size. Sufficient airflow can help increase motor life, especially during the hot summer months. For a couple extra bucks, GWS offers a heat sink that clips onto the motor for additional cooling. Use computer heat sink compound (available at Radio Shack or Best Buy) for better heat conduction.
The plastic cowling comes in two pieces. You have to cut off the excess plastic on these parts then glue the halves together. I initially did this "by the book" with the GWS glue. I shouldn't have wasted the effort. The cowling stayed together for a few flights, but it soon began to work loose along the seam. After pulling it the rest of the way apart, I glued it with some ProBond and added strapping tape inside the seam. A Dremel tool can be used to smooth the edges of the plastic and to neatly finish out the holes in the front. The cowling that came with the kit was black. I thought that the bright yellow might look good with a red nose and struts. I later gave it a few light coats of red enamel and was pleased with the result.
The cowling mounts with four very small screws into the four plastic tabs. I suspect that a few of these tiny screws have been lost in the carpet (that is, until the wife vacuums). With the cowling aligned, drill starter holes in the tabs before inserting the screws. The instructions tell you to attach the prop now, but I figured that it could wait until later.
Landing GearThe wire for the landing gear comes pre-bent and the wheels are easy to attach. The thin rubber tires glue to the wheels with some CA (superglue). The gear wire fits into a slot just behind the battery compartment and forward of the wing. The directions tell you to glue the gear wire into that slot, but hold off on that for now. After using it for a few days, I began to dislike the stock gear. While lightweight and easy to install, it's too flimsy and not scale. The right tire developed a nasty habit of coming off the wheel even after I had re-glued it a couple of times.
Following yet another E-Zoner's suggestion, I picked up some .055 music wire for 50 cents at my local hobby shop, and bought a pair of the better-looking, ultra-light 1-11/16" foam wheels (part #LYT43) from Hobby Lobby. Using the original wire as a pattern, bending a new gear wire wasn't difficult. To lessen the tendency of the gear wire to spread apart on landing, I added black sewing thread wrapped a few times around the gear wire, secured with a drop of CA, at the 90-degree bend by the wheels. With this much-improved gear, the Tiger Moth looks better and can more easily lift off from short grass. In some of the flight photos, you'll see that the foam does tend to pick up a few of our Texas grass burrs.
Finally, I wanted to be able to remove the wing easily for transport, so I never glued the landing gear in. The tension of the wire against the sides of the slot, which I reinforced with pieces of scrap plastic, keeps the gear in during flight. If you're going to transport the Tiger Moth around in the trunk of your car, removing the gear keeps the plane from rolling around as you drive. You'll have to run the motor and battery wires over the top of the gear wire instead of under it. A "V" bend in the wire allows for the needed space between the wire and the fuselage.
Radio GearFor the inner workings, I installed the GWS 4-P Pico single conversion receiver, a pair of GWS Pico series servos, and the GWS ICS-100 (5 amp) ESC. The GWS Pico Flight pack for the Tiger Moth comes with the ICS-50 (2 amp) ESC and includes a 6x150mAH NiCad battery pack. I figured that the 5 amp ESC would allow for possible motor upgrades in the future.
Installing the radio gear and control linkage is fairly simple. The instructions tell you to attach the servos to the inside of the fuselage before cutting and bending the linkage. Instead, note and mark where you are going to mount the servos with the double sided tape, but don't secure them until you have the control rods and horns set up. Being able to adjust the servo location with everything else in place might be handy. Since the rods are not adjustable, a "V" bend is placed in each rod about 1" forward of where they attach to the control horns. The receiver and ESC can be mounted with small pieces of Velcro.
Wings & StrutsTwo sets of plastic struts hold the wings in place. The center struts attach to the top wing beneath the dihedral bends, and fastened to the fuselage just forward of the cockpit. The side struts, of course, join the two wings together. The strut material is a thin white plastic that's just a little too flexible. I laminated 1/16" balsa to both sets of struts before painting them. (That's another RC Groups, Park Flyers forum hint.) Wherever the strut material is to be attached to the wings or anything else, it's important to roughen the contact surfaces to help the adhesive stick. If that is done, the GWS glue may be adequate to hold things together, but ProBond or epoxy will give a stronger bond.
For additional wing strength, and because they looked nice on the photos of other Tiger Moths in the forums, I added flying wires. This requires the addition to just a few anchor points and four small holes in the corners of the side struts. The rear anchor points are a dowel rod with a hole drilled in each end and run through the upper rear of the center struts. I made the front anchors from the tips of a couple servo horns glued into slots that I'd cut through the bottom wing joint cover at the front of the wing root. I used black sewing thread because my wife already had some handy. There are many different ways you can do this, but the basic concept is the same.
If you opt for a non-removable wing and landing gear, the wing assembly goes over the tail feathers to the wing saddle where you rubber band the bottom wing to the bamboo sticks and attach the center struts with four screws into the tabs glued earlier to the fuselage. Wanting an easily removable wing, I drilled holes, and ran a couple of hardwood dowel rods through each of those mounting tabs and out through the tab on the other side. Matching holes on the center struts slide over those rods to hold the center struts in place. I thought that I might have to secure the center struts with a rubber band, but they hold fine without them. To remove the wing, simply remove the landing gear, take the two rubber bands off the bottom wing, slide the center struts off the rods, and work the wing off the nose of the plane. This works even with the flying wires on the wing and the prop on the motor.
A decal sheet is provided to give the Tiger Moth some semi-scale British trainer markings. When adding the markings to the top of the wing, the irregular wing surfaces make it necessary to use a pin or sharp blade to poke holes in the decals to get rid of the larger bubbles. Some modelers have painted their Tiger Moths with either foam-friendly paint or very carefully with light coats of the regular stuff. It's a personal choice. I like the bright yellow, as it's very visible at dusk or under floodlights, and I didn't wish to add any more weight to the plane.
Setup and Flight
The CG on the Tiger Moth is set at 35-45mm aft of the leading edge of the bottom wing. With the Qualcomm 830mAh Lithium-Ion 7.2V 2-cell packs I used, a couple of different battery placement, including in the front cockpit, are possible. I ended up placing it in the battery slot, secured with Velcro, just behind the bottom of the cowling. The total flight weight with the lithium pack was 8.3 ounces.
When bench testing of the electronics, I experienced some intermittent, but significant receiver glitching. I ran the problem by a flying buddy, ("realglow" on the E-Zone) who's a retired electrical engineer. When I mentioned to him that I was using a non-GWS crystal, which operated flawlessly in the receiver it came in, he suggested changing to a GWS crystal. A quick e-mail to Gerald at www.officeshops.com, and I had the crystal in just a few days. The GWS crystal completely solved the problem and I learned a valuable lesson. Meanwhile, I discovered that the Tiger Moth will handle the extra 7/10ths of an ounce added by using a Hitec 555 receiver instead of the GWS 4-P, but that it doesn't climb or loop as well.
The maiden flight was in an appropriate spot for this kind of plane, on the street in front of my house. Now, in this part of Texas (equidistant between Dallas and Louisiana), instead of tumbleweeds and cactus, there are plenty of plane-grabbing trees, not to mention poles, mailboxes, and power lines. Using the 9x7 prop, the Tiger Moth rose from the asphalt in about 6 feet and began a gentle climb. I leveled off at about 20 feet and flew a few tight ovals up and down the street. For an elevator/rudder only plane, it turns nicely, which is good considering the number of solid objects that I was forced to avoid. I had initially set it up for moderate throws on the servo/control horns, but later switched to full throws for tighter turns and better loops.
The Tiger Moth does what they designed it for, which is slow cruising with lots of class. This is a plane that is soothing to fly. Put it into a moderate bank and let go of the stick, and the inherent stability built into this plane becomes evident. So long as it's not close to anything that it might run into (including the ground), you can confidently take your eyes off the plane for a few seconds. When you look back, it'll still be cruising along gently straight, level, and on course. This is a model that you can take to a safe altitude, and let a new flyer try without too much worry since it's difficult to get it too far out of whack before you reclaim the sticks.
The Tiger Moth is predictable and stable on approach and landing, with some power is left on until touchdown. Simply leaving the channel three (throttle) trimmed in the "up" position seemed just about right. When power is reduced, the nose immediately drops and the Tiger Moth begins its descent. It's no floater, which makes small area landings much easier once you become familiar with the glide path. The addition of a steerable tail wheel, yet another worthwhile forum suggestion, allows the Tiger Moth to taxi well on hard surfaces. I fabricated one from a small wheel stolen from my 10-year-old son's Playmobile toys, and a bit of leftover control rod that I bent and glued into the bottom of the rudder. (He didn't mind since he gets to fly too.)
While the Tiger Moth will loop on the 7.2V lithium pack, it's not a nice round loop unless some additional speed is first added with a shallow dive. Its undercambered wings don't fly inverted well at all. It doesn't roll, and as for outside loops, forget it. Level flight speed tops out at less than 10 mph, making flight on a moderately windy day akin to flying a remote control kite. "Harrier" (vertical) landings in the wind, however, can be fun. Using the Qualcomm 830mAh lithium packs, flights in excess of 30 minutes are possible. Other battery packs in the Tiger Moth achieve hotter performance, including seven or eight-cell 300mAh NiMH packs. Be forewarned that over-stressing/over-heating that little GWS DX-A motor can lead to its premature demise.
After changing the prop to the GWS 10x4.7, I tried flying the Tiger Moth inside the gym/auditorium at church after a meeting. It is a very enjoyable indoor flyer. You just have to ready to turn quickly and often. The reaction of the other guys present (all non-flyers) was interesting. Everyone stopped what they were doing to watch the Tiger Moth fly circles around the gym. It was the first time that any of them had seen, or even heard of an R/C plane flying indoors. Whether indoors or at the park, it seems that whenever the Tiger Moth is in the air and visible to passers-by, someone is going to stop and watch. They sometimes approach to ask questions.
For a very light foam biplane, I found the Tiger Moth to be decently hardy. During an early street flight, I let the wind push it into my brick mailbox. The soft rubber spinner did a great job of absorbing the impact, as there was no damage. Later, while working with my 14-year-old son on approaches and landings on grass, the Tiger Moth flipped forward over its nose a few times. It seemed no worse for the wear. I also found out the hard way about the need to make certain to strengthen the wings for aerobatics. When I attempted a normal loop during a recent lunchtime flight, the left side of the top wing decided that it didn't want to be a part of the plane anymore. It snapped off just inside the dihedral bend, and pulled lose from the outside strut. Using some 5-minute epoxy and a slice of yellow Zagi tape, I was able to put it back in good shape.
This is obviously not a model for tearing giant holes in the sky, but it's perfectly wonderful for loafing around a schoolyard or doing "touch and goes" in a parking lot. The kit builds easily with the help of an easy-to-follow instruction manual. It would even be suitable for a beginning builder, especially one who isn't afraid to stop and seek help on the RC Groups Parkflyer forum if needed. Flying the Tiger Moth is a relaxing pleasure, whether at the R/C field or on a neighborhood street. It's an excellent plane with which to develop good approach and landing skills. The ability to run this model on lithium-ion (surplus cell phone) batteries allows for very long flights with decent performance. All that you need to toss in the trunk for an hour's worth of easy flying is the plane, your transmitter, and a couple lithium battery packs. It's hard to get more convenient than that. It's no big surprise that the Tiger Moth has become one of the most popular and most loved slow/parkflyer planes today.
Floyd "DaJudge" Getz
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