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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)
Additional Considerations 2
Components of an aircraft
3
Basic Definitions
Aspect Ratio, AR
AR =
=
Glider = 7 - 10
Trainer = 5 - 7
Fighter = 3 - 5 4
Basic Definitions (cont) Wing Loading
Weight of the aircraft divided by the area of the wing.
e.g. Boeing 787 : Weight = 228,000 kg
Wing Area = 325 m2
Wing Loading =
= 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
2. Wing Loading Calculations
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
2. Wing Loading Calculations
Pick a Wing Loading for your Aircraft type:
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)
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3. Wing Area and Other Wing Parameters (cont) Model Weight, W = 900 grams
Wing Loading (/) = 0.458 gm/cm2
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
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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
Additional Considerations
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
3. Wing Loading Calculations
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
Pick a Wing Loading for your Aircraft type: Trainer = 0.458 gm/cm2
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)
Download full plans from Internet.
http://www.parkjets.com/free-plans
http://www.flyelectric.ukgateway.net/
http://www.flitetest.com/
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