Aerodynamic Speed

  • Thread starter Jones1987
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Hi guys,

Problem I'm having is, I need to obtain speed.. I'm not sure how I go about this. I need this to obtain my Wing Lift and Wing Drag.

So I'm not sure if I use a set speed of my choosing, or if there is a way to calculate the speed.

This is the equation I'm using:

Lift = 1/2 density * (v^2) * (Platform Area) * CL
 

Answers and Replies

  • #2
boneh3ad
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V is just the air velocity. You should know this already. No calculation is necessary.
 
  • #3
SteamKing
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I feel the need The need! for speed.
 
  • #4
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What do you know about the problem?

Density should be known. Assuming you have a wing geometry you know the area, and you should know the weight and for steady level flight Lift=Weight. So you are left with v and CL. You can choose a speed and determine the CL and hence angle of attack necessary assuming you have the data for your wing or you know how to estimate/calculate CL.
 
  • #5
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What do you know about the problem?

Density should be known. Assuming you have a wing geometry you know the area, and you should know the weight and for steady level flight Lift=Weight. So you are left with v and CL. You can choose a speed and determine the CL and hence angle of attack necessary assuming you have the data for your wing or you know how to estimate/calculate CL.
Density and area we have from the material and total area of the wing. I've seen this Lift = Weight before but I don't understand? If the weight of the total aircraft is 10kg, then lift is equal to 10kN of force?

We have CL values as I am using already made airfoils. I did question if you give your own v value, however me and my design buddy have come out with some chronic results...
 
  • #6
boneh3ad
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Weight is not measure in kilograms. That is your first problem. Weight is measured in Newtons, as it is a force.

What are you actually trying to determine here? Is the ultimate goal to find the air velocity or the lift?
 
  • #7
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What exactly are you trying to do? Are you designing an airplane or testing airfoils?

Lift = weight applies for steady level flight. If lift is equal to weight then there is no net vertical force on the aircraft so you will not accelerate in the vertical direction. If you are climbing then lift > weight. And 10kg is mass, to get weight multiply by the gravitational constant.

Force = mass x (9.81 m/s^2)

Of course you pick your own velocity, at least that is the idea. When you are flying a plane whether it be a small remote controlled plane or a large passenger jet the pilot controls the throttle. So when the force from the propulsion system is equal to the drag of the aircraft you will reach a steady speed and at that speed there will be once value of CL ( angle of attack) that will set lift equal to weight and then you will be in steady level flight.
 
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The aim is to choose an airfoil which suits the needs for our aircraft to fly. It needs to carry a specific weight for x amount of time. So currently, testing airfoils is the objective to attach to a fuselage and to analysing the different outcomes of a variety of airfoils.

So I assumed you would choose your own v values, but my friend was adamant you needed to know the v value from another source. This is where the confusion has come from.

We have the density, the area and the CL, so we need to work out the Lift. But now you have explained v is purely a value of our choice, it has cleared up one of the problems.
 
  • #9
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Are you taking into account the fact that your wing lift coefficient at a a given angle of attack will be less than the airfoil's lift coefficient at that same angle of attack due to the downwash from the tip vortices.
 
  • #10
boneh3ad
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If you are testing like that, then you supply your own V. You pick a V, tune your wind tunnel or CFD code to that V and see what happens.
 

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