GWS Tiger Moth Park Flyer

I discovered electric powered RC airplanes in July this year and received a GWS Pico Tiger Moth as a gift in late August.  It has been a great plane from which to learn to about the electric flight hobby.  The Tiger Moth is a WWII biplane trainer. The model incorporates wing dihedral with rudder, elevator, and motor speed control, requiring a 3-channel transmitter.

The Real Tiger Moth

For more information on the Tiger Moth history and photos of the real thing is avaiable at the following links:
www.geocities.com/CapeCanaveral/Lab/3455/tigermoth.html.
www.airliners.net --search for dh82 in the airplane selection box. Very nice photos of lots of airplanes.
sres.anu.edu.au/associated/fpt/nwfp/tigermoth/tigermoth.html
www.dhmothclub.co.uk/
www.duncanhutson.co.uk/your_model.htm

Other GWS Tiger Moth web sites

About the kit

The kit comes with a GWS DX-A motor geared at 5.9:1 turning a 9x7 prop.  To the basic kit, you must add a receiver, battery pack, speed controller, and two servos.  GWS markets two kits of all the necessary flying electronics: a Naro and a Pico.  The electronics kits differ in the size of the servos (the Pico kit uses smaller servos) and the size and length of the receiver antenna (the Pico kit’s antenna is thinner wire and is one-half the length of the Naro’s receiver antenna.  The supplied battery pack is a 150mAh 6-cell NiCd pack (7.2 volts).

The GWS Tiger Moth kit is somewhere between a kit and an ARF in that the fuselage and wings are foam yet they require assembly.  Depending on your expertise and up-front modifications to the kit, it will take anywhere from two to six evenings to assemble.  Ron at GPA Hobbies in Crofton recommended that I use 6-minute epoxy to speed the assembly – definitely a good idea as the glue in the kit takes a long time to set.

When assembling the model, pay attention to the alignment of all components. I didn't keep the fuselage straight when I glued it together. It has a slight bend (like a banana) that causes the rudder to be slightly offset. As a result, I have to use a little right rudder to make my TM fly straight.

Make sure the tail pieces are at 90-degrees to each other and that the horizontal stabilizer will be even with the wings when the wings are mounted.

Modifications (improvements?)

I performed a number of modifications to the kit during and after assembly:

• Sanded the rough leading and trailing edges of all lifting surfaces.
• Lightly sanded the fuselage to remove the burs left by the injection points in the mold.
• Used 6-minute epoxy during most of the assembly. The glue supplied with the model requires about 30 minutes to set.
• Replaced the bowed plastic struts with 1/16-inch balsa, making sure to retain the proper incidence of the wings relative to each other. Note the bow in the plastic in the left picture. Stiff balsa also eliminates the need to strengthen the wing with thread (or fishing line) to prevent the top wing from flexing too much. Other modellers have increased the plastic strut stiffness by laminating balsa or carbon-fiber rod to the plastic struts. I've also not needed to install any reinforcing strips under the center of the wing. With the plastic struts, other modellers report of having much stronger wings by epoxying thin strips of balsa or bamboo across the center of the upper wing. Whichever method is used, a wing with less flex will break less often from flex stress.
• Added 1/32" plywood motor mounts (the motor mount stick broke in a bad nose-in crash). This modification also allows me to adjust the angle of the motor. See below for more details.
• Used epoxy to replace the tape that holds the dihedral in the top wing. Use a popsicle stick or rounded piece of balsa to smooth the epoxy. Other modellers (tigerothsquadron.com) have used microballoon fillers in epoxy to make a strong, light joint.
• Epoxy the lower plastic reinforcing to the wing. The supplied double-sided tape didn't stay stuck for very many flights. When it started to come appart, I used a thin piece of balsa to push some epoxy between the plastic and the wing. It hasn't come appart since.


• Mounted the servos on balsa supports instead of using double-sided tape.
• Enlarged the battery compartment to allow the use of larger capacity batteries. Note the 270mAh NiCd battery toward the left end of the electronics cavity in the photo below. I've flown my Tiger Moth with battery packs up to seven 720mAh NiMh cells (about 100 grams of batteries).
• Added Dubro E-Z adjusters to the servo arms so it is easy to adjust the rudder and elevator trim. You can see the Dubro adjustors on the servo control arms in the photo to the right.


• Replaced the GWS wheels with balsa laminated wheels of the same weight. The wheels are made from 1/16-inch balsa laminated with the grain perpendicular. The hub is 3/8 dowel glued into the center of the wheel. Other modellers have used foam wheels from Hobby-Lobby to obtain a more scale-like model.
• Added a reinforcing wire between the wheels. I used .025-inch wire, crimped around the landing gear wire and epoxied in place. You can see it in the photo of my pilots ready for morning takeoff at the top of this page. Carbon fiber rod is a better light-weight alternative to piano wire. Attach CF rod by wrapping the joint in a few turns of cotton thread and applying a little thin CA glue.
• Reinforced the thin webbing part of the horizontal stablilzer where the rudder straddles it
• Added a heat sink to the motor and cut a notch in the bottom of the fuselage firewall to allow more air to flow out of the motor compartment. High heat will significantly reduce the lifetime of the GWS motors. If you have to replace a motor, make sure to get the carbon brushed motors (available from www.toddsmodels.com). If you're learning how to fly with the Tiger Moth, buy a couple of replacement motors and gear boxes. Toddsmodels.com also has these - look under "Brushed Motors" on his web page.

Other modellers have replaced the stock landing gear with removable gear, sometimes made from CF rod. The major reason for using removable landing gear is to allow the fuselage to be removed from a wing that uses flying wires (typically made from fishing line) to stiffen the wings.

Learning to fly

Reading about airplanes on the web really helped me get started.  I now know why all the small balsa gliders and rubber powered airplanes I built as a child never flew well – they weren’t properly balanced. After starting to fly, I found that when I glued the fuselage halves together, I didn’t keep the fuselage straight.  It has to have the rudder trimmed slightly to the right to fly straight.

Small electric airplanes fly much better when they are light and the Tiger Moth is no exception; it weighs 199 grams (7.1 oz) without battery.  But light also means that they can’t fly when the wind picks up.  Wind over about 5mph makes for very slow up-wind legs and any gusts make safe landings very interesting.

Motor & Prop Performance

The performance of the Tiger Moth out of the box is good, but can be easily improved. I've been using the 10x4.7 prop with good success. It is the prop that is noted on DX-A motor package as being the best match. My static thrust measurements show the 9x7 prop with about 90 grams of thrust and the 10x4.7 at over 100 grams of thrust (my guage measures up to 100 grams). The result is that the 10x4.7 prop performs better for at low speeds such as at takeoffs and at stall speeds.

Other pilots report that the 9x7 prop moves more air and provides more thrust in flight, even though the 10x4.7 provides more thrust when measured in static tests on the ground. At high altitudes, other pilots report success in using a 10x7 prop. Some pilots have taken the 10x4.7, heated the blades, and bent them to the 7 inch pitch when they cannot find the appropriate diameter and pitch prop at the local hobby shop.

There are two types of electric motors available for use in the GWS DX series systems. One motor, using a black plastic rear housing, uses a wiper brush made of metal. The other motor type, built with a gray plastic rear housing, uses carbon brushes. The carbon brushes last a lot longer than the metal brushes. Replacement motors (with or without the gearbox) are available from a variety of sources. I purchase most of mine from Todds Models.

The stick that the GWS motor is mounted on broke in a particularly bad nose-in crash. I had been wanting to change the motor offset anyway and took this opportunity to mount 1/32-inch plywood to the front of the firewall using epoxy. I screwed the motor to the plywood using small wood screws that come with some of the DX-A motors and with the smaller servos from various vendors. I can now shimm the motor to whatever offset I'd like. I'm currently using a fair amount of down-thrust.

Tiger Moth Batteries

I've also experiemented with batteries. Changing to a 7-cell battery pack provided a welcome improvement in full-throttle thrust. I don't consider the 6-cell 150mAh NiCd pack to be worth buying. I tried 8-cell packs and found that the motor life is significantly reduced when running at the higher voltages (the brushes quickly die).

I also invested in some 600-700 mAh NiMH batteries. These batteries weigh about 100 grams (3.5 oz), twice that of the 150mAh NiCds, but with 5 times the capacity. I've gotten flights of 25 minutes on these batteries. It is a lot of fun to practice a lot of touch-and-gos at the local baseball infield without having to change batteries!

I recently purchased 550mAh lithium-ion battery cells that weigh 20 grams each. A two-cell pack provides 7.6 volts, equivalent to a 6-cell NiCd pack) and weighs 41 grams. It drives the Tiger Moth very well, even though the voltage is equivalent to a 6-cell NiMh pack. The reason it flys well is because the battery weight is so small. NOTE: Lithium Ion batteries have special charging requirements. Please read up on them before buying and charging them.

Another very good batery choice is the 830mAh Lithium Ion cell, also taken from cell phone battery packs. Two cells provides 7.6 volts (6-cell NiCd pack equivalent) and weighs about 61 grams. It is easy to get 20-30 minute flights with these packs.

Tiger Moth on Skis

It snowed here last week and I decided to try skis on my TM. Here are the photos of the skis I made using the foam from construction board purchased at a local office supply store (soak the foam to remove the cardboard backing). I even made the rear ski steerable. The main skis are 6 x 1 inch and the rear ski is 4 x 3/4 inch. The mains were too narrow for very soft snow. I increased the width to 1-3/4 inches and they rode on the snow better. Flying from packed snow will always be better. I had to add thread from the leading and trailing edges of the skis to the wing hold-down dowel at the front of the wing.

The tail wheel (ski) is constructed from a 5/32 brass tube epoxied into a hole drilled into the tail foam. The wheel (ski) is mounted on a piece of bamboo skewer. A .025-inch hole is drilled through the bamboo and a piece of .025-inch wire is glued into the hole. A slight kink in the end of the wire helps hold it in the hole in the bamboo. The wire is taped onto the rudder with clear packing tape. The wire flexes back and forth in the loop of tape and doesn't stick. If the tape causes a problem, I intend to tape a piece of small tubing to the bottom of the rudder. I didn't glue a tube to the rudder so it is easy to change the wheel to a ski.

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