  SPORT • GLOW • ELECTRICS • AEROBATICS • SCALE • TRAINERS • HELIS |
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  return to the sample articles listEsprit Model's 400 ARF A custom-configured, lightweight aerobat for any park or schoolyard  by Dave Baron daveb@flyrcmag.com t all began while touring the vendor area at the Neat Fair… I was especially looking for extra-extra light sport models for schoolyard flying. First of all, it had to look like a plane. More importantly, I really wanted a classic low-wing sport model, definitely not a profile. Secondly, I wanted to explore a theory I had about flying models whose behavior in the air are more obviously affected by drag than gravity—that is, about models with very lightly loaded wings. I wanted this plane to fly like a feather on steroids! To achieve this, my quest was to get a model into the air that would have a wing loading of less than five ounces per square foot. I new that such a plane would be able to ROG well, even from grass, and be able to maneuver so aggressively as to seem to defy gravity, but all the while, be flying on it's wings.
 The second half of my task was now to equip the plane with servos, receiver, power system and motor in less than eight ounces. Here is how it ended up.
Receiver: .6 oz. Battery: 2.6 oz. Motor, gearbox, prop and controller: 3.8 oz. Total added weight: = 7.8 oz. I selected each component carefully, and I'll explain my thinking. Servos—There are a lot of great mini servos out there, but FMA's little PS20 makes the most sense to me because of its incredible ratio of low weight to available torque. Keep in mind that this model is for sporting around and general backyard barnstorming, so the 13 ounces of torque that this servo delivers makes it a top choice. This servo is also very attractively priced, and is available from many sources for about $20. It has been my experience that hardware such as pushrods, clevises and control horns can end up weighing as much as a servo, so I began to calculate the location of the different control surfaces and came to the conclusion that I might be able to squeeze a performance edge out of my system installation. I am a true believer in separate aileron servos for each aileron, even though this would mean an extra servo. I like the simplicity of the installation and the ability to mix flap coupling to the elevator. Receiver—I have grown tired of micro receivers that I can't use safely when flying with lots of other transmitters in the area. I have settled down on two great receivers that have yet to give me any conflicts.
Speed Control and Motor—There are a lot of neat, small and efficient motors available, and after much consideration, I settled upon AstroFlight's "improved" 010 Geared motor. The "new" part is the gearbox; AstroFlight has pared it down to a substantially lower weight than previous versions and that lets us modelers better enjoy the tremendous efficiency that this motor produces. The AstroFlight 010 system comes stock with a 10-amp controller that is light and probably one of the most efficient available in this size. Propeller—Never take your prop for granted. I have seen planes that are dogs, turn into awesome performers by a simple prop change. I played with a few props to achieve the desired affect with this plane, and had two reasons to do so. First, and most important–I could not load the motor to the point that I exceeded the "C" limit on the batteries. I used my AstroFlight Whatt Meter to establish the largest prop that I could swing without exceeding six amps.
Batteries—I chose Li-Poly batteries because of the project's weight requirements. After choosing the Astro 010 system, I established that the FMA / Kokam 1200 cell would be the smallest and lightest pack in my inventory that would fly the plane for the 10-minute duration that was my goal. The 1020mAh Kokam is limited to 6C discharge (hence the 6-amp current limitation).  Flaperons—I really like a lot of deflection and dedicating a servo to each aileron gives me the power that I need to achieve nearly the same deflection in flight as I get on the ground. I also like to be able to mix flaperons. I find this to be indispensable for hot dogging with planes large and small. I can reduce the loop diameter of the Angelis from 8 feet to around 5 feet by using a flaperon to elevator mix (the control surfaces swing in opposite directions). I use this mix "full time," and do not program it in onto a switch. The reason is that the first time you do a loop close to the deck and don't have flap-coupling engaged, you are setting yourself up for an embarrassing crash. Trust me, I've done it! Besides, the plane does everything better with flap coupling. It takes off better because of the additional lift generated as the flaperons descend, and it lands sweeter and slower for the same reason, and the flare feels much longer and smoother. CONCLUSION If you'd like a good-looking, low-wing aerobat that is so maneuverable and light you can easily do "carrier style" touch and goes on a picnic table, consider outfitting an Angelis with a low-weight power and control system as discussed here. It's a great configuration for sharpening your flight skills. It's also too much fun! Links APC Propellers, distributed by Landing Products, www.apcprop.com, (530) 661-0399. Astro Flight Inc., www.astroflight.com, (310) 821-6242. Esprit Models, www.espritmodel.com, sales@espritmodel.com, (321) 729-4287. Hitec RCD USA, Inc. www.hitecrcd.com, (858) 748-6948. JR, exclusively distributed by Horizon Hobby Distributors, www.jrradios.com, (877) 504-0233. Kokam Li-Poly cells are distributed by FMA Direct, www.fmadirect.com, (800) 343-2934. For more information, please see the source guide in the magazine. |
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