# Iteration 4: Propulsion Weight

## Contents

# Iteration 4: Propulsion Weight#

```
from unyt import km, m, mm, inch, g, kg, hr, minute, s, degree, radian, volt
import numpy as np
from matplotlib import pyplot as plt
from math import pi as Ļ
%matplotlib inline
```

```
rpm = minute**-1
```

```
Ļ = 1.225*kg/m**3 # air density
Ī¼inf = 1.81e-5*kg/(m*s) # viscosity of air
```

Goals:

Use more accurate weight estimate with new power system components

## Initial Design#

```
b = 3050*mm # wingspan
c = 230*mm # chord
```

```
S = b*c # wing area
AR = b**2/S
```

```
AR
```

```
unyt_quantity(13.26086957, '(dimensionless)')
```

## Weight Estimate#

Weight estimate increased from 2340 to 3047 (increased weight of battery, ESC, motor, and future expansion + added prop weight estimate).

```
W = 3047*g # weight
```

## Airfoil Selection#

Cruise speed lowered from 45 to 30.

```
V = 30*km/hr # cruise speed
```

```
CL = (2*W)/(Ļ*V**2*S)
```

```
Re = (Ļ*V*c)/Ī¼inf
round(Re.to_value(), -3)
```

```
130000.0
```

From bottom left up: Blue = 50,000 Orange = 100,000 Green = 200,000

```
Ī±0 = -3.75*degree
ClĪ± = 1.05
e = 0.8
```

```
CLĪ± = ClĪ±/(1+(ClĪ±/(Ļ*e*AR)))
```

```
CL_unitless = CL.to_value('s**2/m')
```

```
Ī± = Ī±0+((CL_unitless/CLĪ±)*radian)
Ī±
```

```
unyt_quantity(1.99785477, 'degree')
```

By increasing the weight our cruise angle of attack increased to 2Ā° which is a lot closer to the optimal. Thatās a nice consequence.

```
CLmax = 1.4*s**2/m
Vstall = np.sqrt((2*W)/(Ļ*S*CLmax))
print(f"Cruise speed: {V.to('m/s'):.2f}, Stall speed: {Vstall:.2f}")
```

```
Cruise speed: 8.33 m/s, Stall speed: 2.25 m/s
```

Worse than the 1.97 m/s of iteration 3 but still OK.

## Wing Loading and Thrust to Weight Ratio#

```
WCL = W/(S**(3/2))
print(f"Wing loading: {WCL.to('kg/m**3'):.2f}")
```

```
Wing loading: 5.19 kg/m**3
```

Type of Aircraft |
WCL (kg/m^3) |
---|---|

Gliders |
under 4 |

Trainers |
5-7 |

Sport Aerobatic |
8-10 |

Racers |
11-13 |

Scale |
over 15 |

This could probably be a bit lower. Although my eventual vision is more like a glider-with-enough-power-for-autonomous-takeoffs type design, so I guess itās not surprising I wonāt have the most incredible glide slope.

```
TtoW = 1.1
T = TtoW*W
print(f"Required thrust: {T.to('kg'):.2f}")
```

```
Required thrust: 3.35 kg
```

## Propulsion system#

Refer back to iteration 3 for kv and prop pitch Y estimates as we did not change the airspeed, so the required kv ratings and pitch Y estimates stay the same.

Increasing the weight did increase the required thrust from 2.6 to 3.35kg.

### Propulsion system component selection#

Looking back at the options I outlined in iteration 3, I couldnāt find anything which can sustain the 3.35kg required thrust. I decided to forgo that requirement. A 16x10 inch prop at full throttle may not be sustainable continuously for the `PROPDRIVE v2 4258 500KV`

, but I think itāll be fine because:

This would only occur at takeoff

The manufacturer published the 16x10 test results so at least itās not

*completely*fatal to run it like thatrcplanes.onlineās excellent Electric Motor & Prop Combo Estimator indicates the 16x10/500Kv/6S combination should be able to generate 3.5kg of thrust @ 46.7A (below the Propdriveās 60A max). I probably chose a bunch of paramters wrong, but still, it indicates the current draw will not be completely ludicrous.

In conclusion, I will be keeping the selction I made in iteration 3:

Motor: `PROPDRIVE v2 4258 500KV Brushless Outrunner Motor`

- ā¬46.10

Prop: `TGS Precision Sport Propeller 17x10`

- ā¬6.14 * 3 = ā¬18.42

ESC: `YEP 80A (2~6S) SBEC`

- ā¬43.49

Battery: `Turnigy nano-tech 4000mAh 6S 35~70C`

- ā¬63.39

Total power system: ā¬171.40