Remote Control Airplane Design 

and Construction

June 16, 2015

Alfred A. Gates, Ph.D., P.E.

Department of Engineering

Central Connecticut State University

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Remote Control Airplane Terminology

Conventional Remote Control Airplane

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Remote Control Airplane Electronics

Radio Control 

Receiver

RC Aircraft Servos

Motor

Electronic Speed 

Controller (ESC)

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LoPo Battery
Brushless Motors Basics

• Motor max current capability must be less than ESC 

max current capability

• Motor max current capability must be less than max 

Lipo battery current discharge 

• High KV rating = Low Torque and High RPM

– High speed flight, slow acceleration 

– (Use smaller diameter and pitch props)

• Low KV rating = High Torque and Low RPM

– Low speed flight heavy lifting (Muticopters)

– Higher acceleration 

– (Use larger diameter and pitch props)

Alfred A. Gates, Ph.D.,P.E., © 5
Brushless Motors Basics

• Motor efficiency: The percent efficiency goes 

into power to the propeller. The remainder 

goes into generating heat.

• Example 85% efficiency, 85% power goes to 

the propeller thrust, 15% power goes into 

generating heat. If the motor is large and the 

power demand is high the soldered wires 

could be melted.

• Always go with high efficiency.

Alfred A. Gates, Ph.D.,P.E., © 6
Max Current Draw From Motor < ESC and < Battery

Max current draw 

from motor is

20A

Max continuous 

current is 25A

Max continuous 

current 1.8A X 30C 

= 54A

950KV X 11.1V = 10545 RMP

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Acceptable/no fires
No load max RPM capability

11500KV X 3.7V /Cell (3S cells) = 127,650 RPM

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RPM Estimation From KV, Max RPM, Low Torque

Max no load RPM = motor KV rating X Voltage/cell X Number of cells
RPM Estimation from KV, High Torque

Alfred A. Gates, Ph.D.,P.E., © 9

360KV * 3.7V/Cell * 6S/Cell = 7,992 RPM

Put a big propeller on this (15 inch)

Max thrust 2080 grams (4.6 Lb) 14.7Amps, 6S Lipo

Propeller size 15 inches
Alfred A. Gates, Ph.D.,P.E., © 10

• Max power 14.7 A X 3.7V/Cell * 6S/ Cell = 14.7A * 22.2V = 326.4W 

• 326.4W X 6 motors in a Hexcopter = 1951 W ( 2.6 Hp)

• Flight time = (Battery amps pr hr)5000mah/(14.7A *6)* 60min/hr = 3.4 min

• Lifting capability = 2080g X 6 motors /454 g/Lb = 27Lb for 3.4 min

• 27 pounds for 3.4 min
Lipo Batteries

• Must be charged with a Lipo charger.

• Min voltage must not go below 3.2V/ cell.

• ESC are programed to cut power to the motor at 

3.2V/ cell.

• Must be disconnected from circuit when not 

used.

• Must be stored in a cool place.

• The can be damaged due to freezing.

• They can explode if shorted out. They will 

definitely catch on fire.

Alfred A. Gates, Ph.D.,P.E., © 11
Alfred A. Gates, Ph.D.,P.E., © 12

Lipo Batteries
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1800 Mah X 1A/1000Ma X 11.1V = 20 Watt hr 

This battery can produce 20 Watts for 1 hr

C rating the battery can produce 30 times the amperage or power 

30C X 1800Mah X 1A/1000Ma = 54 Amps

How long will this battery last at discharge rate of 54 Amps

(1800 Mah X1A/1000Ma) /54Amps = .033hr X 60min/hr = 2 min 

3S battery pack (3 cells at 3.7Volts/ cell) = 11.1 volts

Power output for 2 min = 54Amps X 11.1 Volts = 599. Watts (.8hp)
Alfred A. Gates, Ph.D.,P.E., © 14

ESC regulates the amperage/power being applied to the electric motor

Controlled by the receiver.

This one can send 25Amps to motor at 4S X 3.7V = 370 Watts

It says it can only send 250 Watts = .33 hp

746Watts = 1hp

Electronic Speed Controller
Flying Wing

Pusher

Canard 

Elevons

RC Airplane Types

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Starship Enterprise

Free Remote Control Airplane Plans

http://www.rcfoam.com/stpg.php?page_id=free_rc_airplane_plans

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Remote Control Airplanes with Elevons

Elevons replace elevator and aileron by electronic mixing

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Location of motor

Elevator

Rudder

Aileron

Cg

CL Horizontal

Stabilizer

CL Wing

Canard

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Additional Types of Planes

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Rules of Thumb

• Center of lift (Center of Pressure, Aerodynamic Center): Point at 

which all of the lift force can be applied on an aircraft. Function of 

airfoil and geometry. [Fixed does not change] 

• Center of gravity (Center of Mass): Point at which all of the weight 

can be applied on an aircraft and it will balance. [Can be changed 

by moving battery]

• Center of gravity, Cg, behind center of lift, Cl, airplane can stall/ Spin 

and not recover. (Spin into the ground)

• Center of gravity, Cg, in front of center of lift, Cl, airplane will be 

controllable and can recover from stalls/spins.

• Center of gravity, Cg, too far in front of center of lift, Cl, airplane will 

nose dive. Elevator will not be able to cause a balancing moment.

• If the fin is too small for an airplane it will barrel roll in a turn and 

spin out of control with a Cg in front of the CL.

Alfred A. Gates, Ph.D.,P.E., © 20
Cg Range For Controllability

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Center of lift does not change

(function of geometry)

Elevator

Max FWD position

If further forward 

the elevator will not 

be able to lift the 

nose of the aircraft 

up

Max AFT position if further 

back, at slow speeds the 

aircraft will become 

uncontrollable and unable 

to regain control 
Terminology

Alfred A. Gates, Ph.D.,P.E., © 22
Center of gravity, Cg, behind center of lift, Cl, 

airplane can stall/ spin and not recover.

Adjust Cg with battery position

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1⁄4 to 1/3 chord length back from leading edge
Lift

• Increase in airspeed over top of wing creates a vacuum 

• Decease in airspeed on bottom of wing creates 

increase in pressure. 

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Typically the body and wing creates lift.

The front of the aircraft creates lift.

The air will accelerate over the canopy 

reducing the pressure

Top of wing must be 

smooth to prevent flow 

separation/ stall
Wing Angle of Attack

Desired quality is a wing 

that can fly at a high angle 

of attack. Smoother wings 

can handle a higher angle 

of attack.

Alfred A. Gates, Ph.D.,P.E., © 25

• Increase angle of attack causes deflection of 

air and increase in vacuum.
Sharpe edge 

will cause stall 

at a low angle 

of attack

Rounded leading 

edge will cause 

stall at a higher 

angle of attack

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Flat Plate

Round corners to increase stall angel of attack

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This type of wing is used for this week
Rules of Thumb, Preflight Testing

First Test Flight

• Cg is in proper location. Check by balancing on fingers

• Motor thrust line is neutral. Check by holding airplane vertical and running 

motor. Only should feel torque.

• Control surfaces move correct direction with motor off. Check by moving 

them.

• Control surfaces move aircraft is correct direction with motor on and 

holding aircraft. Check by holding airplane vertical and running motor and 

cycling control surfaces.

• Servos motor, receiver, ESC and battery are secure and will not move.

• Aircraft glides nose down and does not settle

• Aircraft settling means it will stall

• Glide test

Demonstration

Alfred A. Gates, Ph.D.,P.E., © 28
Rules of Thumb, Flight Testing

• Glide with no power (provided the aircraft is light 

and the landing area is soft, tall grass is ideal)

– The aircraft should glide nose low

• Glide at a low power setting straight and land 

– Slight climb slight turns

– Check

• Fly at altitude, 75ft, to check slow and normal 

flight, stall, stall turns. 

– Land and check electronics

Alfred A. Gates, Ph.D.,P.E., © 29
Computing Cg of Design

Flying Wing CG calculator

https://danielhubert.wordpress.com/rc-project-help/dollar-wing/

Aircraft CG calculator

http://www.instructables.com/id/Introduction-65/step5/Find-the-Center-of-GravityCG-with-the-Static-Marg/

RC Foam Aircraft Plans

http://www.pic2fly.com/RC+Foam+Plans.html

http://betterfly.ca/RC_plan_F_pusher.html

Alfred A. Gates, Ph.D.,P.E., © 30
Remote Control Airplanes VTOL

• Use foam building insulation, 1⁄4 to 3/8 inch TK

• Flat plate design

• Types

– Flying wing

– Pusher

– Conventional

– Different

Alfred A. Gates, Ph.D.,P.E., © 31

Cg range was unknown so the gild test was 

used to determine the Cg
Remote Control Airplane Building

• Monday design only, Tuesday design and cut 

out on foam board.

• Cutting foam board with box cutter

• Control surfaces

• Gluing on spars

• Music wires

• Servos

• Cut foam board and glue on spars and body.

Alfred A. Gates, Ph.D.,P.E., © 32
Draw Plans on 3/8 thick building insulation foam

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Note:

Balsa leading edge is 

not required. 

Sand the foam leading 

edge. 

Sand Leading Edge

Alfred A. Gates, Ph.D.,P.E., © 34
Cut out Rudder, servo holes, assembly slots, and make elevons out of balsawood 

or foam balsawood is better. If you use the foam you can use strong duct tape as 

a hinge. Once side of the elevons and rudder must be sanded to a 45 degree 

angle so the surface can move in two directions.

Epoxy hinge tape

Onto wing and 

elevon

Alfred A. Gates, Ph.D.,P.E., © 35
Cut out wings and body

Better to glue balsa sheet as spar onto wing

Sand Leading Edge

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Make the front and the 

rear of the balsawood 

smooth. Sharp edges 

will disrupt the air flow 

and decrease the critical 

angle of attack.
Lipo Battery Servo Receiver (RX) Electronic Speed Controller (ESC) Motor

Alfred A. Gates, Ph.D.,P.E., © 37

Can use Velcro to secure ESC, Receiver and Battery to Aircraft

Verify CG first with battery placement
Bend music wire as control rods Install control rods and foam supports

Alfred A. Gates, Ph.D.,P.E., © 38
Anything can Fly

• Need to have correct control surfaces and 

movement

• Need to have enough power

• Need to have acceptable Cg, Cl locations

Alfred A. Gates, Ph.D.,P.E., © 39
Will It Fly

• Foam Missile

• FWD Swept Wing

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All that is needed is: 

• Cg is in the proper location

• Thrust line is on axis of aircraft

• Control surfaces move enough 

to direct pitch, roll and yaw
Stall Speed Estimation

• Lift Force = Aircraft Weight

• Lift = (1/2) Lift Coefficient X Air density 

Velocity2 X Wing Area

Alfred A. Gates, Ph.D.,P.E., © 41
http://en.wikipedia.org/wiki/Airfoil

Alfred A. Gates, Ph.D.,P.E., © 42

We are using a flat plate

Cl approx. .6 to 1
Stall Speed Estimation

• Air density at sea level = 1.29 Kg/m3

• Coefficient of lift, CL = .6 for a flat plate at 6-8 

degrees angle of attach.

• V = Velocity airplane

• A = Perpendicular wing area

Alfred A. Gates, Ph.D.,P.E., © 43
Stall Speed Estimation Example

Solving for minimum airspeed to keep the aircraft in flight

WA: Wing area 36inch X 8inch = 288 in2 = .1858 m2

AD: Air density = 1.29 Kg/m3

CL = .6 , flat plate at 6 to 8 degrees 

V: Stall speed, unknown

Wt: Aircraft weight = 300grams = .3 kg, .66Lb

1Lb = 454g

Lift = Weight = 1⁄2 CL (AD) (WA) V2

Solve for minimum velocity

V =[ Wt *2/(CL (AD) WA) ]1/2

V = [.3Kg * 9.81 m/s2 *2/(.6*1.29 Kg/m^3*.1858m2)] 1/2 = 6.39 m/s = 21 ft/s = 14.53 MPH

Vmin

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Stall Speed Estimation

Applied to a micro UAV

V min

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L

C
http://wright.nasa.gov/airplane/drageq.html

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Parasitic Frontal area

Angel of attack
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Power is required to over 

come the total drag.

Example

Dependent on airflow type

Laminar or turbulent Form Drag coefficients for shapes
Alfred A. Gates, Ph.D.,P.E., © 48

V = 14.5Mph

This example 

does not 

include 

calculating 

the propeller 

thrust force 

and efficiency

Best possible

t = 8.88W/hr/34.1W * 60min

Blockage Area

Aircraft Body

Aircraft Wing Surface area Due to wing angle of attack
Alfred A. Gates, Ph.D.,P.E., © 49

V = 20Mph

This example 

does not include 

calculating the 

propeller thrust 

force and 

efficiency

Best possible
Stall Speed Estimation Example

Adding 100 grams of More Batteries

WA: Wing area 36inch X 8inch = 288 in2 = .1858 m2

AD: Air density = 1.29 Kg/m3

CL = .6 , flat plate at 6 degrees

V: Stall speed, unknown

Wt: Aircraft weight = 300grams + 100grams of more batteries 

= 100grams = .400 kg, .88Lb

1Lb = 454g

Lift = Weight = 1⁄2 CL (AD) (WA) V2

Solve for minimum velocity (Stall)

V =[ Wt *2/(CL (AD) WA) ]1/2

AD : Air density, WA: Wing Area

V = [.36Kg * 9.81 m/s2 *2/(.6*1.29 Kg/m3*.1858m^2)]1/2 = 6.39 m/s = 21 ft/s = 16.7 MPH

Vmin

Alfred A. Gates, Ph.D.,P.E., © 50
Alfred A. Gates, Ph.D.,P.E., © 51 V = 16.8 Mph Time = 30.5min for 3 batteries

There will 

be a point 

at which the 

number of 

batteries 

will decrees 

the time of 

flight. Due 

to the drag

At a higher 

velocity 

required to 

keep the 

aircraft aloft 

and motor 

required

This example 

does not 

include 

calculating 

the propeller 

thrust force 

and 

efficiency

Best possible