# Basic Rule of Thumb

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RC design

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• By

S. M. Anwarul Aziz Lecturer AIB. PRO Runway 32.

• Outline

Components of an Aircraft

Basic Definitions

Rules of Thumb for RC Aircrafts (Method-1)

Rules of Thumb for RC Aircrafts (Method-2)

Rules of Thumb for RC Aircrafts (Method-3)

• Components of an aircraft

3

• Basic Definitions

Aspect Ratio, AR

AR =

=

Glider = 7 - 10

Trainer = 5 - 7

Fighter = 3 - 5 4

Weight of the aircraft divided by the area of the wing.

e.g. Boeing 787 : Weight = 228,000 kg

Wing Area = 325 m2

= 701.54 kg/m2

= 70.154 gm/cm2

Thrust to Weight Ratio

Thrust provided by powerplant divided by weight of the aircraft

e.g. Boeing 787 : Max Thrust = 57,084.6 kg

Weight = 228,000 kg

T/W Ratio = 0.25 5

• Rules of Thumb (Method 1)

1. Estimating Weight

3. Wing Area and Other Wing Parameters

4. Empennage Design

5. Fuse Length

6. Wing and Empennage Position

7. Control Surface Sizing

8. Required Thrust 6

• 1. Estimating Weight

Estimate a weight for your RC.

As a beginner, it is a good idea to start with a low weight.

e.g. Model Weight, W = 900 grams

7

Glider = 10 oz/ft2 = 3.05 kg/m2= 0.305 gm/cm2

Trainer = 15 oz/ft2 = 4.58 kg/m2 = 0.458 gm/cm2

Fighter = 20 oz/ft2 = 6.10 kg/m2 = 0.610 gm/cm2

** We will go for a Trainer in this session. 8

• 3. Wing Area and Other Wing Parameters

Get Wing AREA (S) from Model Weight (W) and Wing Loading (/)

Choose Aspect Ratio (AR) according to your Aircraft type [i.e. Glider, Trainer, Fighter]

Get Wing SPAN (b) and Wing CHORD (C) from Aspect Ratio (AR) and Wing AREA (S)

9

• 3. Wing Area and Other Wing Parameters (cont) Model Weight, W = 900 grams

So, Wing Area, S = 900

0.458 = 1965.07 cm2

Let, AR = 6 [as, AR for Trainer = 5 7]

=

= 6

Wing Span, b = 6 1965.07 = 108.58 cm

Wing Chord, C =

=

1965.07

108.58 = 18.10 cm

10

• 4. Empennage Design

Get Horizontal Tail AREA (SHT) and Vertical Tail AREA (SVT) from the following approximations:

Horizontal Tail AREA, SHT = 20 25% of Wing AREA (S)

Take Aspect Ratio (AR) 3 or 4

Get Horizontal Tail SPAN (bHT) and Horizontal Tail CHORD (CHT) from Aspect Ratio (AR) and AREA (SHT)

Vertical Tail AREA, SVT = 7 11% of Wing AREA (S)

11

• 4. Empennage Design (cont)

Wing Area, S = 1965.07 cm2

So, SHT = 22% of S [SHT = 20 25% of S] SHT = 1965.07 x 22% = 432.32 cm

2

Let, AR = 3

=

= 3

HT Span, bHT = 3 432.32 = 32.01 cm

HT Chord, CHT =

=

432.32

32.01 = 13.51 cm

And, SVT = 9% of S [SHT = 7 11% of S] SVT = 1965.07 x 9% = 176.86 cm

2

12

• 5. Fuse Length

Calculate Fuse Length from the following approximation:

Fuse Length = 75% of Wing SPAN (b)

Fuse Height = 10 15% of Fuse Length

e.g. Wing Span, b = 108.58 cm

So, Fuse Length = 75% of b

Fuse Length = 108.58 x 75% = 81.44 cm

13

• 6. Wing and Empennage Position

Wing position and Horizontal Tail position may be found from the following approximations:

Wing leading edge to Propeller or,

The NOSE LENGTH = 1 1.5 times the Wing Chord (C)

Wing trailing edge to the Elevator = 2 3 times the Wing Chord (C)

14

• 6. Wing and Empennage Position (cont)

Wing Chord, C = 18.10 cm

Wing leading edge to Propeller or,

The NOSE LENGTH = 1 X 18.10 cm = 18.10 cm

Wing trailing edge to the Elevator

= 2 X 18.10 cm = 36.20 cm

15

• 16

Sum

min

g U

p

• Summing Up

17

• 7. Control Surface Sizing

Calculate Control Surface Area as follows:

Aileron Area= 2 x

of Wing Area

Elevator Area =

of HT Area

18

• 8. Required Thrust

Get a Motor based on Estimated weight of your RC and your Aircraft type.

Assume motor efficiency = 80 90%

So, Thrust Required for a:

Trainer type = 1.10 X Estimated weight of RC

Fighter type = 2.30 X Estimated weight of RC

e.g. Model Weight = 900 grams

Motor Required = 1.10 x 900 = 990 grams 19

Powerplant should be placed as such that, we get

2 3o Right Thrust

2 3o Down Thrust

Better to place the wing at a 3 4o incident.

20

• Rules of Thumb (Method 2)

1. Available Thrust

2. Estimating Weight

4. Wing Area and Other Wing Parameters

5. Empennage Design

6. Fuse Length

7. Wing and Empennage Position

8. Control Surface Sizing 21

• Summing Up

Thrust for Trainer type = 1.10 X Est. Weight of RC

Choose Aspect Ratio (AR) according to your Aircraft type [i.e. Glider, Trainer, Fighter]

Get Wing SPAN (b) and Wing CHORD (C) from Aspect Ratio (AR) and Wing AREA (S)

Horizontal Tail AREA, SHT = 20 25% of Wing AREA (S) 22

• Summing Up

Take Aspect Ratio (AR) 3 or 4

Get HT SPAN (bHT) and HT CHORD (CHT) from AR and SHT

Vertical Tail AREA, SVT = 7 11% of Wing AREA (S)

Fuse Length = 75% of Wing SPAN (b)

The NOSE LENGTH = 1 1.5 times the Wing Chord (C)

Wing trailing edge to Elevator = 2 3 times the Wing Chord (C)

Aileron Area = 1/16 of Wing Area

Elevator Area = 1/4 of HT Area

23

• Rules of Thumb (Method 3)