Micro-Flying

Author: Joe Malinchak

Two small counterrotating motor drives with propellers

BUILDING SMALL INDOOR MODELS

By Joe Malinchak | joemal@echoes.net

MY QUEST TO BUILD the smallest indoor F3P/3D model continues. A few years ago, I built a 13-inch wingspan version of Devin McGrath’s Anubis that features a coaxial motor and foam propellers. The airplane is still a great-flying model, but I wanted to see if I could go smaller. In order to do this, I needed a biplane design.

I built an 11-inch wingspan, all-balsa version of the Tensor 3D biplane back in 2005. The model flew but was very heavy. I thought it would be neat if I could design an F3P model with the combined looks of the Anubis and the Tensor biplane!

The F3P/3D Twin-Motor Biplane

This 10-inch wingspan model features the wings of the Tensor and the tail of Devin’s Anubis, with the rest of the model being my design. I was trying to figure out a way to build a smaller, lighter coaxial drive for the airplane then I thought, “Why not try using a twin-motor system with counterrotating propellers?”

I did a search on YouTube and found that someone had already done this with great results on a larger-scale F3P model. I thought that by using two high-performance 4mm motors and counterrotating propellers that I would have a lightweight drive for the model.

I didn’t want to spend too much time on the drive units, so I turned to my friend Nick Leichty, of Micro Flier Radio, for help. He has a small, lightweight 4mm drive on his website that can put out up to 10 grams of thrust with a 4-inch propeller. I had him make me 3.25-inch right-hand and left-hand propellers for the drive units. The two-gear drives, with propellers, weigh only 2.5 grams. With my drive-system problem solved, I could concentrate on building the model.

Micro Flier Radio receiver and wiring — Micro Flier Radio has made an optional upgrade to the DT Rx43d and Rx31d receivers by adding a soft motor stop.

To build the lightest model possible, I had to use carbon fiber for construction. I drew the design in Adobe Illustrator and laser-cut molds out of thick cardstock paper. I used 1.5k carbon-fiber tow that is coated with slow-drying epoxy, allowed it

Carbon-fiber parts in laser-cut cardstock molds — To make the carbon-fiber parts, the author used 1.5k carbon-fiber tow that was coated with slow-drying epoxy, placed into laser-cut cardstock molds, covered with glass, allowed to dry, and then baked in an oven to cure.

to dry, and then baked in an oven to cure.

Covered and painted micro-aircraft parts arranged on a sheet — The completed airframe was covered with 2µm Mylar and painted with Createx translucent paint.

Completed colorful twin-motor micro biplane — The model uses two Micro Flier Radio 400 mg servos on the rudder and elevator and one 500 mg servo for the ailerons. The completed model weighs only 7.9 grams.

translucent paints and used UHU Por glue to attach the wings, tail, and all of the .3mm carbon-fiber rod bracing.

On this model, I used a DT Rx31d twin-steer receiver, Micro Flier Radio 400 mg servos for the rudder and elevator, and a 500 mg servo for the ailerons. The completed model weighs only 7.9 grams. It flies quite slowly on a 30 mAh LiPo cell. The model can perform loops, rolls, and most F3P/3D maneuvers. You can see some videos of the model flying on my YouTube channel.

Micro Flier Radio Upgrade

The DT line of receivers is among my favorites for use in my micro RC projects. One minor flaw, however, is that when the battery runs down to the low-voltage cutoff, you can lose all control of the model unless you remember to cut the throttle. This will give you control back so that you can land.

Micro Flier Radio has solved this problem by adding an optional soft motor stop to the DT Rx43d and Rx31d receivers. I tested this feature in a recent build and it worked great. Please see the company’s website, listed in “Sources,” for more information.

Two lightweight model airplanes photographed on a floor — The author’s 13-inch wingspan, carbon-fiber Anubis and his new, smaller, 10-inch wingspan, carbon-fiber, twin-motor biplane. Both are great-flying micro models.

to dry for approximately 90 minutes, and then placed it in the molds while the tow was still flexible. After drying overnight, the parts were baked in my oven at 150° (when my wife was not home) to complete the drying and hardening process!

If you would like to learn more about how I molded my carbon fiber, I am planning to make a video for my YouTube channel that is under my name, Joe Malinchak. It should be available by the time that you read this.

I constructed the model over my plans using a magnetic building board, much the same as building a balsa model. I used Bob Smith Industries Maxi-Cure CA glue to build the airframe. I found that this glue works well on carbon-fiber joints. When it was complete, I covered the airframe with 2µm Mylar. I painted the Mylar with Createx translucent paints and used UHU Por glue to attach the wings, tail, and all of the .3mm carbon-fiber rod bracing.

Sources:

Micro Flier Radio
(941) 377-9808
www.microflierradio.com

Joe Malinchak’s YouTube channel
www.youtube.com/user/joemal214/featured

Bob Smith Industries
(805) 466-1717
www.bsi-inc.com

Createx Colors
(800) 243-2712
www.createxcolors.com