Formula Used
Wing area: S = span × ((root chord + tip chord) ÷ 2)
Aspect ratio: AR = span² ÷ wing area
Mean aerodynamic chord: MAC = 2 ÷ 3 × root chord × ((1 + taper + taper²) ÷ (1 + taper))
Wing loading: WL = aircraft weight ÷ wing area
Stall speed: Vs = √((2 × weight force) ÷ (air density × wing area × CLmax))
Power loading: PL = motor watts ÷ aircraft weight in kilograms
Dynamic thrust estimate: T = prop efficiency × motor power ÷ cruise speed
Safe flight time: minutes = battery Ah × 0.80 ÷ average current × 60
Tail volume: Vh = tail area × tail arm ÷ (wing area × MAC)
How to Use This Calculator
Enter the final flying weight, not the empty airframe weight. Include battery, propeller, wheels, receiver, servos, paint, and hardware.
Add wing dimensions in centimeters. For a rectangular wing, enter the same value for root chord and tip chord.
Use a realistic maximum lift coefficient. Simple flat-bottom trainer wings may use higher values than thin fast wings.
Enter motor power, battery size, current draw, and ESC rating. Then compare current margins and safe flight time.
Review the CG and tail volume values. Use them as early design guides. Always confirm balance before flight.
Smart RC Airplane Planning
A good model starts with balanced numbers. Wing area, weight, power, and battery size must support the same flight goal. A slow trainer needs gentle wing loading. A sport plane can accept higher loading. A glider needs clean lift and low drag. This calculator helps compare those choices before cutting foam, balsa, or printed parts.
Wing Loading and Stall Speed
Wing loading shows how much weight each unit of wing must carry. Lower loading usually gives slower landing speed and easier control. Higher loading can feel sharper, but it needs more speed. Stall speed estimates the point where lift can no longer hold the aircraft. The result depends on weight, wing area, air density, and maximum lift coefficient. Use conservative values for early designs.
Power, Battery, and Flight Time
Power loading tells how much motor power is available per kilogram. Trainers often fly with modest power. Aerobatic models need more power reserve. Battery energy affects flight time, but current draw matters more in real use. The tool uses a safe usable battery fraction. It also checks battery current limit and ESC margin. These checks help avoid overheated parts and weak climbs.
Balance and Tail Sizing
Center of gravity is one of the most important setup values. Many models begin near twenty five to thirty three percent of the mean aerodynamic chord. Tail volume is another useful guide. It compares tail area and tail arm against the wing. A low value may feel unstable. A high value may add drag and weight. Use the output as a design guide, not a final rule.
Practical Building Advice
Always leave extra strength near the wing root, landing gear, and motor mount. Check prop clearance before choosing wheel size. Test glide over soft grass if the model is light enough. Measure final weight after covering, wiring, and paint. Recheck the center of gravity with the actual battery installed. Small changes can shift handling. Record each flight. Then adjust throws, expo, prop size, and battery position with care. Keep notes on failures too. Broken parts reveal stress points. Better logs make the next airframe lighter, safer, and easier to trim well.
FAQs
1. What is wing loading?
Wing loading is aircraft weight divided by wing area. Lower values usually make takeoff, landing, and slow flight easier.
2. What is a good CG position?
Many RC airplanes start near 25% to 33% of mean aerodynamic chord. Confirm with your airframe plan and test carefully.
3. How much power does a trainer need?
A basic trainer may fly well around 200 to 300 watts per kilogram. Heavier or aerobatic models need more reserve.
4. Why is stall speed important?
Stall speed helps estimate safe landing and turning speed. A lower stall speed gives more time to react.
5. Does battery capacity equal flight time?
Not directly. Flight time depends on usable capacity and average current draw. High throttle use can reduce time quickly.
6. What is tail volume?
Tail volume compares stabilizer size and tail arm against wing size. It gives a quick guide for pitch stability.
7. Should ESC rating exceed max current?
Yes. Use a safe margin above expected maximum current. Extra headroom helps reduce overheating and sudden power loss.
8. Can this replace flight testing?
No. It is a design guide. Always inspect the model, check balance, range test, and fly cautiously first.