Combining LiPos with Adapters

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Written by Dave Lockhart
Sport & Aerobatics
As seen in the Fall 2019 issue of Park Pilot

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Appearances can be deceiving! Commonalities and differences between the flight performance and power systems of these aircraft are described in the text. Pictured clockwise from bottom are a Park-Zone T-28 Trojan, a Fancy Foam Mx2 EPP, a Freewing Lippisch P.15, a Fancy Foam Extra 330S, a Hacker SkyCarver, and (center) a Tower Hobbies Slow Ride.

>> What do all of the airplanes in the picture with this column have in common? Could it be that they are all suitable park flyers? The answer to the fi rst question is, not surprisingly, that all of them are aerobatic aircraft. All are powered by three-cell LiPo batteries. The LiPo capacities range from approximately 300 mAh to 2,200 mAh. Using an adapter, it is possible to fl y a larger model airplane with two LiPo batteries that are sized for a smaller airplane. Two (or more) equal-size LiPos can be combined with adapters to produce a more powerful battery in two ways. One way is that they can be connected in series, which results in twice the voltage with no change to the capacity. A series connection between two LiPo batteries is accomplished by connecting the negative side of one with the positive side of the other. Measuring across the positive lead of the first LiPo to the negative lead of the second will show the combined voltage of the two batteries. A pair of 3S 850 mAh LiPos that are connected in series would function the same as a 6S 850 mAh LiPo battery. The second way to connect two LiPo batteries is in parallel, which results in twice the capacity with no change to the voltage. A parallel connection between two batteries is accomplished by linking the positive lead of one LiPo with the positive lead of the other, and the negative lead of the fi rst LiPo with the negative lead of the second. In this way, the capacity of the batteries is combined without changing the voltage. A pair of 3S 850 mAh LiPo batteries connected in parallel would function the same as a 3S 1,700 mAh LiPo. Pictured are a couple of parallel adapters for Ultra Deans-style plugs. Depending on the shape of the battery mounting area, it is possible to utilize a single 3S 1,800 mAh LiPo battery or a pair of 3S 850 mAh LiPos (with a parallel adapter). When connecting the batteries in parallel, it is important to use ones of equal capacity and C rating. The batteries should not be connected unless they have the same voltage (equal charge condition). Regarding the second question, Park Pilot Program aircraft are defi ned as ready to fl y at less than 2 pounds and limited to a speed of less than 60 mph. By that defi nition, four of the six airplanes in the photos are truly park fl yers—two are not.  A good park fl yer needs to be agile enough to fl y in a small space. Brief specifi cations and fl ight characteristics of each airplane follow.

ParkZone T-28 Trojan (horizonhobby.com)
• 44-inch wingspan
• Weighs 30 ounces
• Uses an 1,800 to 2,200mAh LiPo battery
• 200 to 250 watts  

A favorite for many pilots, the T-28 in stock form is easy to fl y and capable of all traditional (non-3D) aerobatics. With the landing gear removed and a relatively lightweight 1,800 mAh LiPo battery onboard, the weight and drag are reduced and aerobatic capability is substantially improved. Hand launches are easy, as are belly landings in less-than-ideal grass fi elds. Its performance can be further improved by upgrading the stock motor to an E-fl ite Park 480 1,020 Kv motor.

Hacker SkyCarver (hacker-motor-shop.com)
• 35-inch wingspan
• Weighs 9 ounces
• Uses a 700 to 900 mAh LiPo battery
• Hacker A10-7L motor
• 75 to 100 watts

Owing to their simple shape and construction, fl ying wings generally offer low drag, high lift, and light wing loadings. This gives them a wide speed range and good gliding capability. The SkyCarver is a good example that can even be flown in large indoor spaces. Its EPP foam construction is durable, making the SkyCarver a popular model for flying combat. Tower Hobbies Slow Ride (towerhobbies.com)64-inch wingspan Weighs 47 ounces Uses a 2,100 to 4,000 mAh LiPo battery Hacker A30-10L motor 500 watts
Belying its size, the SlowRide is capable of the slowest flight of all of the airplanes pictured. Despite its 64-inch wingspan and length, a carefully assembled Slow Ride can weigh less than 3 pounds.  Although it’s technically not a park flyer because 
it exceeds 2 pounds, the large control surfaces provide plenty of control authority for all aerobatics, including 3D, at relaxed speeds in small spaces. In light wind, the Slow Ride can virtually hover in place upright or inverted with a minimal angle of attack, or even while doing a rolling harrier. With the ailerons “drooped” as flaps, takeoffs and landings need only a couple of feet of ground roll.
 

combining-lipos-lockhart-2.jpegTwo examples of parallel adapters that can be used to pair two equal LiPo batteries and double the mAh capacity.

Fancy Foam MX2 EPP (fancyfoam-com.3dcartstores.com)
• 34-inch wingspan
•Weighs 7 ounces
•Uses 300 to 500 mAh LiPo
•Hacker A10-13L motor

The 34-inch MX2 is one of my favorite airplanes as a medium-size indoor flyer, but it is also well suited for flying outdoors in calm or light wind. Powered by a 1,200 Kv Hacker A10-13L motor and 3S Thunder Power RC 325 mAh LiPo (thunderpowerrc.com), the power is good and flight times are 5 to 6 minutes.  Fully 3D-capable, I often start flights with a vertical hand launch and end with a catch from a hover. The relatively lightweight EPP foam structure is durable for landings in short or tall grass.

Freewing Lippisch P.15 
(motionrc.com) 
• 30-inch wingspan
• Weighs 16 ounces 
• Uses a 1,000 to 2,200 mAh
• LiPo battery 200 to 250 watts

Rarely do small EDF (electric ducted-fan) airplanes boast decent performance and good flight times.  The P.15 is a notable exception. The efficient flying wing platform, paired with a 64 mm five-blade fan, yields eye-catching performance in a scale package. However, even at its small size and light weight, the P.15 is not an ideal park flyer because of its overall speed and relatively high landing speed that requires an unobstructed landing approach.  Still, if room is available, the P.15 can fill the need for high-speed aerobatics with towering loops and a blistering roll rate.

Fancy Foam Extra 
330S (fancyfoam-com.3dcartstores.com) 
• 42-inch wingspan
• Weighs 24 ounces
• Uses 1,500 to 2,200 mAh LiPo battery
• RimFire .10 motor 200 to 250 watts

Without question, this is my go-to park flyer. The 42-inch Extra is capable of 3D flight in tight spaces and is equally at home flying big-sky precision loops and long, slow rolls. Compared with airplanes of a similar size and weight, the Extra handles wind with ease, making it a versatile airplane.

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