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Dymond Tiger Moth Electric Conversion

"Iíve always liked the challenge of converting a model designed for glow engine power to electric power, and ever since flying the ever-so-popular GWS indoor/parkflyer Tiger Moth, I decided to be on the lookout for a larger biplane kit...The Dymond fit the bill, and this conversion was born."

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Introduction


Wingspan:52"
Wing Area:900 sq. in.
Listed Weight:89 oz.
Actual Weight:90 oz.
Length:42"
Wing Loading:14.5 oz/sq. ft.
Recommended engine:.46-2stroke, .52-.56-4stroke
Motor Used:Kontronik Fun 500
Battery:12-cell 1700mah nicd
Available From:Dymond Model Sports

No matter how many model airplanes a modeller builds and flies, thereís always an itch to try something new and different. Iíve always liked the challenge of converting a model designed for glow engine power to electric power, and ever since flying the ever-so-popular GWS indoor/parkflyer Tiger Moth, I decided to be on the lookout for a larger biplane kit.

My son and I attended the 2003 Mid-America electric funfly near Detroit last summer. There were several hobby dealers set up selling their products. One of the dealers, Helmut, of Dymond Modelsports (in California and Wisconsin) had a reasonably large ARF biplane kit of the Tiger Moth that he had designed and had manufactured in China and imported to the USA. It was a balsa and plywood built-up model, covered in Oracover iron-on covering, includes aluminum struts and fiberglass cowl, and including most hardware needed to finish the model -- even the engine mount and aileron servo extensions are installed!

It is intended for a .40 to .50 size glow engine, but, and this is the best part, Helmut told me that he had already converted one to electric power using a direct drive brushless motor and a 14-cell 2400mAh NiCd battery pack. He did warn me that the plane was heavy and flew fast, but did emphasize that it flew well.

Assembly and Electric Conversion

I bought the kit (for about $140 in US funds) and brought it home. I started work on it soon after. I had decided to use a geared Kontronik brushless speed 500 motor with a 12-cell battery pack, which I had used successfully in other airplane models of this size before.

Installation of the motor was not too difficult as I simply widened the wood engine mounting area, and bolted the motor into place with brass straps around the motor. The brass straps had holes drilled through the ends to allow the bolting to the mount.

As always, I was concerned about the added weight from the battery pack, so I proceeded to eliminate some weight from the fuselage structure. It is very common that glow-intended models have added structure not needed when e-powered. Upon visual inspection, I could see that the aircraft was fully sheeted from behind the cockpit to the tail. I removed the plastic covering, cut the sheeting from between the formers, and recovered the fuselage. I also cut a large opening in a very thick piece of plywood from the firewall, to allow for air cooling over the area that the battery pack would be mounted (see photos for details). I used lightweight wheels and mini (but strong torque) servos.

The entire cockpit section is made removable, and this was where the radio equipment was mounted, as well as the battery pack. I cut the top of one former to allow easier access to insert and remove the battery pack for charging.

After completing the model I did have one main concern. The wings were difficult to assemble, and I didnít want to take them apart for transportation. I decided that the model would have to transported in one piece, or with the two wings removed as a unit.

I was not too worried with the weight and power system. The instructions indicated that ready-to-fly weight of a glow powered version was supposed to be 5Ĺ pounds, this likely with an empty fuel tank. My model weighed 6 pounds with the battery pack.

Ready to Fly

The power system had previously powered a similar size 3-D model airplane capable of flying straight up, so I was confident that it could at least fly this model in a reasonable manner.

The first flight took place in July at the Richmond Hill RC club. The plane took off from the grass field almost immediately, climbing up at a 45 degree angle. This was corrected with some down elevator. The plane flew quickly at first, but was soon trimmed and slowed down a bit. After a few laps, I had built up enough confidence to try a loop. There was plenty of power. I cut throttle on the down side of the loop, and reapplied full throttle at the bottom of the loop. Power came back and was lost instantly. The plane was landed without power with only slight damage to the motor mount. Inspection later showed that the motor had twisted in the motor mount due to torque from the sudden application of power, and this twisting motion had pulled the connection loose from the speed control. A few small pieces of rubber band between the motor and the brass mounting straps solved this problem.

Subsequent flights were less eventful, and the model was trimmed further for slower (but still somewhat fast) flight, and was able to perform loops and rolls. Despite the drag from the two wings, the model glided far and required a reasonable amount of ground for landing. Some actual landings were a bit rough and bouncy but the plane never actually tipped or rolled over.

I have had about a dozen flights with the model so far, and have come to enjoy it quite a bit. Once trimmed, it can fly at slower speeds and is extremely stable. Loops and rolls are easy to perform, and my landings are improving.

There are not too many biplanes of this size at electric funflys, and it stands out. I intend to fly it as much as possible during the upcoming 2004 flying season. It was an easy conversion to make and a real pleasure to fly.

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Jun 19, 2004, 05:02 PM
Registered User

little suggestion


hi, sometimes industrial plastic ties (those used for fastening cables) are better than rubber bands, when
it comes to fastening the mount etc. they are as light and handy.

your plane looks very cool.
Jun 20, 2004, 06:25 AM
E-flyer since 1981
Michael in Toronto's Avatar
The elastic bands are used as a "grip" to prevent the motor from spinning in the brass motor mount. I've found that motors can spin in cable-ties as well.
Jun 22, 2004, 04:04 AM
Registered User
icebear's Avatar
Great conversion Michael!
I converted the Ripmax Tiger Moth which is of the same size (51" wspan).
I decided to keep the weight down and went with a MEGA 22/20/4 direct drive with 10x5 wodden MA prop. On just 8 cells (1950 NiMH's) I get enough power for nice scale flight since AUW is only 64 ounces (4 lbs). This way I can fly really slow but I'm sure yours is more powerful!
I used cableties but put some sticky foam glue under and around them so that the motor keeps from spinning.
/icebear
Jul 05, 2004, 10:47 AM
Suspended Account
Which Fun500 was used?

Paul
Jul 11, 2004, 09:23 AM
Registered User
Fredy's Avatar
Hi everyone,

I'm wanting to convert a Carl Goldberg Super Decathlon .60 - .90 (glow size) to electric. I've looked at the Kontronik site but they don't have a contact link on it for my questions.
I'm failry new to electrics, I've flown small foamies and park flyers. So I've heard of motors like the Axi, Himax, Astroflight, CD-ROM, Razor, etc.......... Now for a larger model I'm hearing the Kontronik and Mega........... Any others???

I have the following questions;

1. Are the set ups in converted larger planes (.40 - .90 glow) the same as in small parkflyers/foamies?
2. Would the Kontronik 600 be a good choice for my Super Decathlon? On the Kontronik site it states it for a GP J-3 Piper Cub 81". That J-3 has a specified 10.5lbs flight weight and my super decathlon specifies 9.7 - 10.5lbs flight weight.
3. Are lipos also the way to go for larger electrics? Which ones?
4. Wil my Triton work for charging batteries of larger electric models?

Thanks in advance for you input.
Last edited by Fredy; Jul 11, 2004 at 09:31 AM.
Jul 14, 2004, 08:59 PM
Registered User
What is the prop use and whats the RPM and Amp? How long was the flight?
Jul 15, 2004, 11:31 AM
E-flyer since 1981
Michael in Toronto's Avatar
I'll get the exact Kont 500 series motor, prop, etc. info in a day or so. I'm really busy at work.

I'll try to answer these...

1. Are the set ups in converted larger planes (.40 - .90 glow) the same as in small parkflyers/foamies?
Not neccessarily. Most larger systems need an on board radio battery, and because they are heavier, need to be held in more securely.

2. Would the Kontronik 600 be a good choice for my Super Decathlon? On the Kontronik site it states it for a GP J-3 Piper Cub 81". That J-3 has a specified 10.5lbs flight weight and my super decathlon specifies 9.7 - 10.5lbs flight weight.
I use a Kontroink geared 600 in an 84.5 inch Piper Cub, weighing less than 8 lbs. Because of the very large wing and relatively light wing loading, it can take off at 1/2 throttle. I am using a 4S4P 8000mah lithium battery. In a heavier, more aerobatic plane, I think a motor that can handle more volts may be better, for example, a similar size Hacker B50L or XL motor geared 6.7 to 1.

3. Are lipos also the way to go for larger electrics? Which ones?
Lipos are a key in having longer flights, or saving a lot of weight (over a pound or more in some larger planes), or both. Cost is more though.

4. Wil my Triton work for charging batteries of larger electric models?
Yes. In most cases. Read the instructions for the cell count capabilities.


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