Asked by HAITHAM AL SATAI
on 8 Jun 2019

I'm trying to find the lift force to what I have here in the system that shown below in the attached picture. I found some parameters to solve the equation of the left, but I couldn't find the air velocity. How could I find this velocity?. Could anyone help me with this matter, please?.

%The given aircraft characteristics are defined below

m= 4.6; % Aircraft Mass [kg]

S= 0.85; % Wing surface [m^2]

k= 0.0095; % Induced drag parameter

Cd0=0.118; % Zero-lift drag coefficient

alpha=2.75; % Angle of attack[deg]

p0=945.15; % Air pressure[hPa]

rho=1.225; %Air density of (ISA)standard[kg/m^3]

alpha0 = -4; % zero lift angle of attack (Found from given graph)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%Q1:How much is the lift force?

%The lift force can be found by the below equation:

L=(1/2)*rho*(v^2)*S*CL

The system

Answer by PIYUSH AGGARWAL
on 9 Jun 2019

Accepted Answer

As per your diagram , the aircraft experiences T (I guess its forward propelling/throtelling force)and D (backward drag force) in the horizontal direction (x). You need the velocity to apply this equation :-

L=(1/2)*rho*(v^2)*S*CL

A possible solution maybe :-

(T-D)/m = A = Gives you the acceleration of aircraft in positive x direction.

If T and D are not time varying forces then velocity calculation will be pretty straight forward :-

v = u + A*t

where t is time lapsed from the initial point till now and u the velocity at initial time

If these forces are not constant you have to go for integration:-

HAITHAM AL SATAI
on 11 Jun 2019

PIYUSH AGGARWAL
on 11 Jun 2019

@HAITHAM AL SATAI :) Anytime. Look I don't know much about areodynamics but the solution which I told you was based on pretty basic mechanics only. There must be some formulae for calculating Drag Force D and Throttle T, as for the initial velocity u and time t, you are the observer of the frame of reference so you must be knowing the time interval length and initial states of the system such as velocity (u) before hand.

Drag Force D:- refer this link

I can see that Drag also depends on velocity, So you have a differential equation of the type where force is proportional to velocity squared.

Or I can say the derivative of velocity wrt time depens on Velocity squared. So you will have to rearrange terms, Bring similar terms together on one side and then integrate both the sides. Pretty much how you solve the basic diff eqns.

Well in ideal case if the aircraft needs to move with constant speed/velocity , T = D.

HAITHAM AL SATAI
on 11 Jun 2019

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