---
title: Particle Filter - non-Gaussian distribution
tags: wiki
disqus: hackmd
---
Drags of Fixed-wing UAVs
===

1. Force magnitude in order
- form drag>friction drag>Induced drag
2. Friction drag: boundary Layer Formation、Viscous Forces、Laminar and Turbulent Flow、Surface Roughness
3. form drag 由separation產生
4. 有vortex可以產生turbulence（因為氣流速度快，跟機翼前緣比，壓降少），減少form drag
5. 

[golf ball turbulence](https://www.youtube.com/watch?v=fcjaxC-e8oY)
5. 低雷諾數比較不容易有turbulence(<500000)
6. Wing tips減少induced drag

**Takeaway: form drag>friction drag>Induced drag**

## 1. [Lift to drag](Lift#^5eaaa2) ratio L/D

- Induced drag is defined below:
$$C_D = C_{D0} + k C_L^2 \\
C_D = C_{D0} + \frac{C_L^2}{\pi e AR} \\
C_D $$

$$= 0.173 \\
\frac{L}{D} = \frac{C_L}{C_D} = \frac{1.7}{0.173} = 9.78$$
The definition of $e$:

**Takeaway: Drag is a function of lift、AR、AOA.**

## 2. For a cambered wing, the minimum drag $C_{Dmin}$ occurs at some positive lift $C_{Lmin}$ drag.

## 3. Formdrag:
Viscous separation drag is also called "form drag" and depends upon the location of the separation point on the body.

## 4. Energy, Drag, and [[Lift]]
The energy required to produce these vortices is extracted from the wing as a drag force and is proportional to the square of the lift (see Sec. 12.6)

## 5. [[Laminar flow]] induces less drag
If an airfoil is designed to maintain a lot of laminar flow, it will have substantially less drag, as long as it is operating near its design lift coefficient.

## Parasite Drag

$$C_{D_0} = C_{fe} \frac{S_{wet}}{S_{ref}}$$