For the benefit of those interested in the mathematical interrelationship between the main concepts of propeller driven electric powered airplanes, here are some real-world concepts that are easy to understand with a remedial knowledge of algebra.

Those of us that have posted online calculators understand that there is a mathematical relationship between current (Amps), voltage (v), Watts-in (Wi), Watts-out (Wo), torque (lb-ft or kg-m), horsepower (HP or lb-ft/sec), thrust (lbs or Kg), pitch and airspeed (mph or kph) , and propulsive force (kg·m/s).

These variables are all related mathematically to the point where every one of them can be calculated using a few widely accepted constants by knowing as little as two variables, such as Amps and Watts-in.

Known Efficiency:

Motor efficiency is the key to performance that separates motors within weight classes in our hobby. The term efficiency is defined as the margin between the power we need to drive the entire circuit compared to the actual power delivered to the propeller shaft. In electrical systems, we call the two power variables Watts-in and Watts-out. In other power systems, terms like Horsepower (HP), Brake Horsepower (BHP), Estimated Shaft Horsepower (ESHP), etc., are used to define the difference between how much gross power the system must develop in order to deliver a net power to the shaft with which to drive a propeller.

The reason why this power margin is so important is because by knowing the margin...Continue Reading

This thread's intent is to illustrate and explain the benefits that a StinGR gear reduction unit provides the electric RC aviation community.

The StinGR is a gear reduction, belt-driven, transmission unit that reduces the high RPM and HP of an RC helicopter motor to the lower RPM torque required to deliver peak propeller performance for giant scale airplanes.

The gear reduction of this unit increases the efficiency between Watts-in and Watt-out. This means that there is a smaller margin between the power needed to run the entire unit and the propulsive force the unit develops at the shaft.

Electrical power systems have always been efficient, and none-geared 3-phase outrunners can deliver as much as 45% more efficiency than gas engines. Additionally, gear reduction units can deliver as much as 15% more efficiency than a non-geared 3-phase outrunner.

This translates to 15% more flight time with the same power and same battery capacity, or more power at the same flight time with the same capacity.

Additionally, I have written at length about the clear advantage that the new C2E carbon fiber propellers that Falcon Hobby manufactures in the 'Power Systems for Extreme Flight Fanatics' thread here on RCG. The performance efficiency of these propellers can add as much as 11.2% more efficiency to the StinGR power system, bringing the total net efficiency to between 22%% and 25% compared to non-geared outrunnner of similar mass using other types and brands of...Continue Reading

102" Purpose-Built-Electric SU-26 with sheeted foam wings, stabs, and turtledeck, with high density foam and 1/16th inch balsa. It's covered in genuine Oracover and the ailerons can be cut to custom sizes for IMAC, 3D, or XA. 6800W of power and enough capacity for 5.5 to 6 minutes bring the plane to an AUW of 24.34 lbs RTF.

Covered weights:

Fuse + Rudder = 2165g
Battery Tray = 83g
Firewall = 101g
Motor Beam Top & Bottom = 103g
Wing 1 = 941g
Wing 2 = 944g
Wing Decals = 99g
Stab 1 = 236g
Stab 2 = 236g
Cowl = 528g
Canopy = 267g
Wing Tube = 169g
Stab Tube = 66g
CF Landing Gear = 197g
CF Tailwheel Assembly = 57g
KavanLite 5" Wheels = 147g (stock wheels are heavier)
Steel 6mm Axles & Hardware = 32g
Hardware = 39g
Triangle Stock and Doublers = 28g

Total Empty Weight = 6438g or 14.19 lbs

We now have a new StinGR gear reduction unit on the plane too with a 28x13 Falcon C2E with a 12S 8000mAh main pack. The power unit pulls 58 lbs of thrust.

StinGR 5035 Power System = 1548g
Tribunus II 200A ESC = 235g
2x 6S 8000mAh main pack = 2215g
Falcon 28x13 C2E = 125g
Falcon 5" Carbon Spinner = 108g
AR8010T = 24g
Ultra Guard BEC Backup = 41g
5x Servos with arms and extensions = 525g

Total Power & Control components = 4.821 kg or 10.63 lbs

Total AUW = 24.85 lbs

This is an 8.32 oz/cu ft cube loading and a 29.8 oz/sq ft wing loading.
MAC * Wingspan = 1921 sq in wing area
CG at 25% Static Margin = Center of the...Continue Reading

Here are some quick instructions for the PAR Calculator, which is still in beta. Some formatting changes and text corrections still need to be made, but I want to complete the beta testing so I can make all the semi-final changes at the same time.

I've also included an image illustrating the measurements that are required in order to calculate PAR values. These measurements should calculate to the exact same value as if we calculated the MAC (mean aerodynamic cord) and multiplied it by the wingspan. Anything close to a 100 PAR is very good, and you should find some that will be as high as 115.

Please remember that PAR is a highly subjective ranking, and you should instead focus more on the actual values associated with them, such as wing loading, wing cube loading, power loading (Watts per pound), pitch speed, stall speed, etc.

My suggestion is to add data for your favorite planes, and perhaps establish your own PAR. Then use the PAR Calculator to identify planes and power systems that share similar values with your personal PAR.

For more information about the PAR Calculator, PAR values, or to ask about a specific motor, prop, and cell count, configuration that you may be considering, feel free to ask.