By looking at two good indicators of the flying characteristics of a model rc airplane: the “wing loading” and the “power loading”. Each of these are easy to determine using just a pocket calculator and by reading the rc airplane’s specifications listed in the ad or on the side of box. Once you get the “hang” of it, you’ll be able to estimate it in your head..I promise!
is the weight of the electric powered rc airplanes in ounces per square foot of wing area. So using the wing area listed on the box, say it’s 314 square inches, divide that by 144 (1 square foot = 144 square inches) to get 2.18 square feet. Then, take the weight number from the box or ad, let’s say it’s 19 ounces (including battery, radio, motor – everything) divide 19 ounces by the 2.18 square feet and you would get 8.7 ounces per square foot of wing area.
As a guide, for model rc airplanes, if the wing loading is under 10 ounces per square foot, they will be suitable for the slow flying, gentle handling that you need in arf electric rc airplanes used as basic trainers. From 10 to 20 ounces per square foot will include intermediate trainers, flying a little faster, having more power and being a little more demanding in terms of needing a bit more speed for landing and taking off. Above 25 ounces/sq. foot you begin to find the warbirds, military scale-type models, many of which fly wonderfully, but at the same time are not forgiving of letting the speed get too low while close to the ground. You need to be carefull “lest the ground rise up and smite thee”! Learn to Fly a Model RC Airplane
for rc electric models is watts of power output per pound of total airplane weight. Just take the battery and motor description – let’s say the box says it is a 7-cell, 600Ma battery with a carbon brushed motor. The battery can deliver (for a short time) 7 cells @1.2 volts x 600 milleamps (600 milliamps =0.6 amps). So we just multiply 7 x 1.2 = 8.4 volts x 0.6 amps = 5 watts. Since a brushed motor is at best only 50% or less efficient, that’s 2.5 watts of power at the propellor! If the complete model rc airplane weighs 16 ounces (I pound) then the power loading would be 2.5 watts per pound.
A rule of thumb is that a sport-type, advanced aerobatic trainer needs about 50 watts per pound and that 10-20 watts per pound is about right for intermediate arf electric rc airplanes. You can see that the performance of our sample airplane above is going to be very sedate! Just exactly what you want when you’re first learning! So as you probably guessed, with rc electric aircraft better performance comes with more battery capacity, less weight, and more efficient motors.
So let’s take a look at a typical recently tested basic trainer-type rc electric airplane. Wing area = 367 square inches, weight = 24 ounces (as tested) , brushed 400-size motor, and battery 7 x 1000 NiMH. Ok, doing the numbers: 367/144= 2.54 square feet, divided into 24 ounces = 9.4 ounces/ square foot; wing loading right on target! Power; 7 x 1.2 x 1000 (that’s 1 amp, right?) = 8.4 watts divided by 1.5 pounds (24 ounces = 1.5 pounds) will give us a power loading of 5.6 watts per pound, times the 50% efficiency of the motor, or 2.8 watts per pound.
As we expected from our number crunching, the tester found this arf electric rc airplane to fly quite well: very gentle handling and with nice slow landings and takeoffs. A nice model rc airplane to have!
TIP: How about when you don’t have the specs, and are just looking at the model rc airplane at a swap meet or auction? Just remember to “lose weight and add lightness”. For any model rc airplane, but particularly for electric powered rc airplanes, lighter is better! If it feels like a “lead sled”, it will undoubtedly fly like one!