An Electric Aerobat from the UK

[G2:459 n=1 class=left]A few months ago, I was looking for plans for a small electric aerobatic plane and stumbled upon Flymodels.co.uk. There, a Brit by the name of Philip Rawson described a speed 400 electric aerobat he'd designed that looked and sounded like just the ticket. He provides a PDF version of plans for download and a series of photos and description for some of the construction details, but other than that, you're on your own. Construction looked straightforward enough, so I decided to give it a try. If you're not reasonably comfortable with scratch-building techniques and meager instructions, I suggest perhaps trying something else first. However, this is a fun build for someone with at least some experience.

Building

[G2:477 n=1 class=right]Along the way, I made a few modifications - some planned, some not. As Philip admonishes, the theme here is "build light". The plans called for 1/32" balsa ribs, but Philip warns that these can be very difficult to work with. So, I opted for 1/16" balsa and added lightening holes to each rib to compensate a bit. This turned out to work very well and the straight, symmetrical wing came together very quickly. The ribs ended up being about 1/16" thicker than planned, which required a commensurate heightening of the fuselage sides, but it was easy to accommodate during the initial lay up of the fuse. The rest of the fuselage and tail feathers came together as planned.

Philip's original design called for a geared inrunner motor, but I wanted to use a direct-drive outrunner, so the firewall did not require the hole and mounting tube. I simply bolted the motor directly to it and threaded the power leads through the firewall to the ESC. The next major change I made was to the canopy. Philip originally carved it from blue foam and secured it with a leather strap over the top. I wanted something a bit more spiffy and decided to try to mold a more "traditional" canopy from clear plastic sheeting. Not having done this before, I was a bit skeptical of my ability to pull it off, but in the end it came out surprisingly well.

Using instructions gleaned from a forum thread on RCGroups, I first created a balsa mold and attached it to a wooden stick I could secure in a vise. I then heated a sheet of PEC plastic using a heat gun and stretched it over the mold. It took a couple of tries (and sheets) to get the technique right, but the third one was perfect. The hardest part was then trimming the plastic, building a balsa floor that fit perfectly and then gluing the two together using canopy glue. The canopy is positioned at the front and bottom with small balsa blocks and secured to the fuselage with a pin through the fuselage rail and one of those blocks.

I built the entire canopy before completing the front and back sections of the upper fuselage. This ensured that I would end up with a seamless fit. In other words, I build the canopy and then built the mating pieces around it. All in all, I'm very happy with my first scratch-built canopy. My only regret is not securing a pilot into it before gluing the base in.

[G2:465 n=1 class=left]I decided to use two micro servos for the ailerons, rather than the single one used in the original. This enabled me to use my radio's aileron mixing feature and implement flaps. With weight always a consideration, I covered it with Hangar 9's Ultracote film. I really like it's variable shrinkage capability and light weight. To show off the pretty structure, I used transparent yellow.

There were no details in the plans for the landing gear, so I improvised a triangular structure, wrapping the back braces to the main gear with 26 ga. wire and soldering. The whole thing is attached to the fuselage with small ply hold-downs, since I didn't have any of the suggested lithoplate.

Flying

With a Hitec micro receiver, an 800Kv speed-450 outrunner motor, a 20A ESC and a 700mAh 3S lipo battery, the entire model weighs in at almost exactly 16 ounces - 2 ounces less than Philip's target weight! Diligent attention to keep weight out of the tail, helped to ensure the CG was just behind the wing spar as intended. By simply shifting the battery slightly forward, I can easily achieve different CG positions without the need for dead weight up front. All in all, I think I've achieved a light model.

I've completed 4 flights so far using several different propellers. My favorite right now is an APC TE 11x8. It seems to provide an excellent balance of speed and thrust. Originally designed for a 400-class motor, the 450-class I'm using provides outstanding performance. With a 1000mAh 3S pack, I'm getting in excess of 12 minutes of flying time, with a pretty solid dose of aerobatics. I'm really thrilled with this plane and am looking forward to really honing my aerobatic skills with it.

The ability to use flaps on landing has turned out to be a nice feature. My Airtronics radio has a flap/elevator mixing feature which allows me to maintain pitch attitude at any flap setting. I've fine-tuned this mixing and with one notch of flaps on final approach the model slows incredibly while still maintaining the proper attitude. I can hit "spot landings" that require only about 2 feet of rollout.

Thanks, Philip, for designing a fun flyer!

If you'd like to see the results, check out the photo gallery.