Equipment weight savings greatly affects flight performance
John Glezellis [[email protected]]
LAST TIME, I wrote about the benefits of using both Flight Modes and Flight Conditions. This month we will look at a few different ways in which a person can improve his or her aircraft's performance.
When I built my 38% Great Planes Extra 330S, I used one servo synchronizer per aileron, one servo synchronizer per elevator half, and one servo synchronizer on the rudder. This resulted in the use of five servo synchronizers.
In addition, I used two servos per elevator half (I used the Futaba S9155, which offers 192 ounce-inch at 6.0 volts). I used two nine-channel receivers on the airplane for redundancy.
However, I recently converted this aircraft to 2.4 GHz and selected a 14-channel receiver. Therefore, the need for servo synchronizers diminished.
All in all, each servo synchronizer has a total weight of approximately 0.46 ounce. That may not seem like a lot, but it can have a great impact on your model's flight performance, depending on its location within the aircraft.
A few additional ounces of weight on the CG will not change how your model transitions from upright to inverted flight. But a few ounces in the tail will, because of the greater moment from the tail to the CG point.
Servo Talk
When considering elevator servos for your giant-scale aerobatic aircraft, look at the servo's torque at 6.0 volts. When 40% airplanes were first introduced, it was common to use two servos per elevator half (and it still is, in some circumstances), because the servos did not have enough output. Today, many manufacturers have servos with more than 300 ounce-inch of torque at 6.0 volts.
Examples:
- JR 8711 — total of 403 ounce-inch at 6.0 volts.
- Futaba S9156 — total of 340 ounce-inch at 6.0 volts.
- Hobbico CS-170 and Hitec HS-5955 — each about 333 ounce-inch at 6.0 volts.
By selecting the right servo for a given application, you can reduce the number of servos you employ for a given control surface.
In the 38% Extra 330S, I went from using two servos per half (roughly 192 ounce-inch of torque each) to only one servo per elevator half (each giving 330 ounce-inch of torque). Now, not only does the modeler save weight by reducing the number of servos, but he or she also reduces the number of servo extensions and the number of servo synchronizers that are needed. (Two servo synchronizers were originally used; now none are required.) Let's take a look at the weight savings.
By reducing the elevator servos to only one per half, a total weight of 14.4 ounces per stabilizer half was obtained (compared to the original weight of 18.2 ounces). A total weight savings of 4.2 ounces was reduced per stabilizer half, which results in a total savings of 8.4 ounces.
The aircraft's flight characteristics change quite a bit when this amount of weight is taken out—especially when it is taken out of the tail.
Using Your Computer Radio Wisely
Today, it is common to see many fliers use a nine-channel or more radio system. It is important to take full advantage of a given radio system and the mixing capabilities it offers. By using a 14-channel receiver (and the 14MZ radio system), I was able to mix all four aileron servos so that no servo synchronizers were needed. The same was done for the elevator servos. (One channel was the "master" elevator channel and one channel was the "slave" elevator channel.) Using a computer radio's mixing capabilities is important when it comes to trimming your aircraft.
I often see modelers use a "Y harness" to make two servos work together for a given function. However, if a Y harness is used, a modeler cannot adjust each servo independently. Although this is suitable for a trainer or sport model, it is unacceptable for a giant-scale aerobatic aircraft, because the pilot cannot adjust the aileron differential that is needed to make the airplane roll axially.
I have written about aileron differential before. As a recap, it is when the aileron travel has more deflection in the "up" direction or more deflection in the "down" direction to make the airplane roll axially. Models that are top-hinged primarily have less deflection in the "up" direction, because the aileron surface has more area on the top of the aileron when compared to the bottom of the aileron.
Advantages of Lithium Batteries
Weight can also be saved with the battery chosen for a given application. I use Li-Ion (or LiPo) batteries in all my giant-scale and F3A models. A great amount of weight can be saved on a giant-scale airplane.
Example comparison:
- A five-cell, 4200 mAh NiMH battery weighs about 12.6 ounces.
- A 5200 mAh Li-Ion battery can weigh about 6.8 ounces — nearly half the weight.
However, remember to use a voltage regulator so that the voltage going to the receiver is 6.0 volts (unless otherwise specified by your radio manufacturer).
You have learned about the benefits that can be obtained by choosing your electronic equipment wisely, which ultimately results in improving your aerobatic aircraft's flight performance.
By taking full advantage of your computer radio's mixing capabilities, the need for servo synchronizers can be eliminated (depending on the airframe and the number of servos needed compared to the number of channels the receiver contains). That will result in a lighter overall airframe.
Since summer is finally approaching, get back to the flightline and keep practicing! Until next time, fly hard!
MA
Sources
- JR
(800) 338-4639 www.jrradios.com
- Futaba
(217) 398-8970 www.futaba-rc.com
- Hitec RCD USA
(858) 748-6948 www.hitecrcd.com
Transcribed from original scans by AI. Minor OCR errors may remain.
