I had the privilege of reviewing the Great Planes Sequence 1.20 in the January 2015 issue of Model Aviation. The review used a Rimfire 120 electric powerplant, which was inadequate for the demanding vertical turnaround maneuvers in the 2015 Advanced RC Aerobatics schedule.
The Sequence 1.20 is a good-flying airplane and worth the investment of time and money to improve vertical performance.
Reducing weight and adding more power is a difficult proposition. Adding more power generally results in more weight. The first step in solving the power/weight conundrum was to replace the 4.9-ounce metal motor mount with a 1-ounce custom wood/carbon-tube motor mount. The motor mount change shaved nearly 1/4 pound from the airframe.
With a couple of ounces saved, it was time to select a new powerplant. Typically, low Kv motors are used for Pattern applications, allowing for a quieter, slower-turning propeller with less cavitation noise.
Flying at 3,300 feet above Mean Sea Level, in 90°-plus temperatures, creates interesting power and cooling considerations.
After researching several 8S-rated motors, I chose the Himax HC6320 250 Kv motor. The Himax in my Prolog has been reliable, leading me back to the brand. At slightly less than 16 ounces, the Himax benefits from being one of the lighter 110- to 120-class motors. In comparison, the 6S-rated Rimfire 120 weighs a scant 14 ounces. Half of the motor mount weight savings was quickly gone.
Great Planes sells a wood mount for the Sequence 1.20, but it’s a front mount and the larger-diameter Himax 6320 did not fit into the aftermarket mount. I chose a 4.2-ounce Castle Creations Phoenix Ice2 HV 80 ESC to replace the 5.1-ounce ElectriFly Silver Series 80-amp ESC with a weight differential of nearly an ounce.
Castle ESCs have fallen out of favor with many Pattern pilots. I have (knock on wood) never had a problem with Castle ESCs; however, I have seen several descend from the sky bellowing smoke. My best guess as to why they fail is the brake function. From what I have read and heard, problems seem to occur when the brake function is set above 30%.
My first electric motor was an AXI 5330, which loudly dinged every time the brake engaged. At one time I wrongfully thought judges downgraded my landings because of the dinging. I turned the brake off and have opted to use an idle ever since.
It turned out that non-level wings were the reason for downgraded landings. Judges downgrading my wings for not being level? Gimme a break! My flying deserved to be scored better than it was! Hug a judge the next chance you get. They work hard.
The 1.8-ounce Futaba S9151 rudder servo used in the review is not rated for 6-volt operation and required a .4-ounce Castle BEC to regulate voltage to an acceptable 5.1 volts.
Looking to save weight everywhere possible, the BEC had to go along with the massive 2.7-ounce 1,100 mAh LiFeSource receiver pack. This rudder servo needed to be swapped for one rated at 6 volts.
A 2.15-ounce Turnigy TGY-9150MG servo replaced the Futaba S9151. International Miniature Aerobatic Club (IMAC) friends claim the TGY-9150MG is a brute on 6 volts. A Castle BEC weighs roughly the same as the weight difference between the heavier Turnigy and lighter Futaba servo, netting close to zero gain/loss.
A 1.44-ounce Zippy 700 mAh LiFePo4 battery receiver pack replaced the 2.7-ounce 1,100 mAh LiFeSource receiver pack to reduce weight by more than an ounce. If used, a 700 mAh redundant battery system setup would have approximately zero weight gain/loss and is a future consideration.
Experience has shown a typical electric Pattern flight uses anywhere from 50 to 75 mA, theoretically making a 700 mAh receiver pack good for eight flights: 80% of 700 mAh capacity, 70 mA multiplied by eight flights. My practice is to charge every six flights.
I had every intention of replacing the aluminum stabilizer tube. I removed the stock aluminum tube and cut the new carbon-fiber tube to length. Big surprise! Both tubes weighed the same.
I had inadvertently purchased a thick-walled 10mm carbon tube instead of a lighter, thin-walled version. With zero weight savings, the aluminum tube was reinstalled before leaving the workshop for the evening. Using published weights, the substitutions shaved a respectable 4.21 ounces from the airframe.
Finally, I swapped the 21/2-inch plastic review spinner for a 21/4-inch transparent one. The smaller-diameter transparent spinner is my preference. It’s slightly lighter, allows direct motor cooling, and I like the look!
Spinner/propeller weights are not a consideration until the optimum propeller size is determined during the trimming process. Ideally, a lightweight carbon propeller/spinner will be purchased after trimming, although lately I’ve had a bit of a wood propeller renaissance.
Motor Batteries
Airframe weight savings is good, but it overlooks the fact that going from 6S to 8S batteries of the same capacity is a weight gaining proposition no matter how you cut it. Two 13.7-ounce Thunder Power G8 5,000 mAh 3S LiPo batteries were used in series for the review. With connectors, this combination weighed 27.4 ounces—approximately 20% of the takeoff weight.
The new 8S setup consists of one 3S pack connected in series to one 20.8-ounce Power Unlimited 5,100 mAh 5S LiPo pack for a combined power pack weight of 341/2 ounces: a weight gain of more than 7 ounces. Ouch!
Wow! Where did those 4 ounces of airframe weight savings go? The takeoff weight is almost 3 ounces more than the review weight. Swapping the 3S Thunder Power packs for 3S Zippy Compact packs saves another 11/2 ounces for a gain of less than 2 ounces.
Conclusion
Weight is the worst enemy of any airplane. In this case, adding a couple of ounces to an already heavy airplane is not an optimal solution. The increased battery weight is partially offset with the reduction of airframe weight helps, but ounces still add up to pounds.
Increasing takeoff weight by 2 or 3 ounces will negatively impact flight performance. The gamble is that additional power will compensate for the extra weight, achieving the desired goal of improved vertical performance.
I’ll begin flight trimming as soon as the weather warms up.
Flight complete.
SOURCES:
National Society of Radio Control Aerobatics (NSRCA)
http://nsrca.us
IMAC
www.mini-iac.com
Great Planes
(800) 637-7660
www.gpdealera.com/cgi-bin/wgainf100p.pgm?I=GPMA4382
Castle Creations
(913) 390-6939
www.castlecreations.com
LiFeSource Batteries
(800) 637-7660
www.lifesourcebatteries.com
HobbyKing
www.hobbyking.com
