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Aerospace Model Aerofoil project

  1. Aug 25, 2008 #1
    Hi there,

    I am testing a model aero foil that I have built for an A-Level project. I mad the aerofoil out of polystyrene and have set it up so that it can go vertically up and down in from of a fan. I was hoping to investuigate how the angle of attack and different aerofoils affect the amount of lift produced but so far I have only suceeded in getting the lightest aerofoil to stay up, and I haven't been able hang any weights from it. I am very worried that this project will not work at all.

    I was just wondering what sort of air speeds will I need to get a reasonable lift that I could measure in this manner or is this project not possible within a high school environment? or is their any simpler way for me to measure the list of an aerofoil?

    I would really appreciate any help with this

  2. jcsd
  3. Aug 26, 2008 #2

    Working with a normal household fan and working with a windtunnel are two very different things. A wind tunnel uses the fan to generate the wind speed, but it is also ducted at the same time to give you a more stable air flow. A fan on it's own will give you an unstable airflow over your aerofoil. Maybe you could try making a wind tunnel, but this will probably take more time and effort than the actual project.

    What sizes or aerofoils are you making? Maybe you could add a sketch or some photos to your next post. What equipment do you have available?

    A good way to measure the lift force generated by an aerofoil is to attach it via a thin rod to a mass scale (which would be attached to the top or bottom of your windtunnel). A change in value on the mass scale will indicate the lift generated, using F=mg.

    If you are comparing aerofoils at the same airspeed, then you can have any speed you want as the results will be comparable in terms of percentages of lift between models. If you want realistic results (ie. scale results that are compared to actual wings on aircraft) then your speeds will have to increase as your model gets smaller.
  4. Aug 26, 2008 #3
    Thanks for your reply. I have attached two images one is of the setup at the moment (left hand thumb nail) and one is my interpretation of your proposed modified setup (right hand thumb nail.)

    Your idea of attaching the aerofoil by a ridgid pole to a balance is really useful. This should allow me to get more sensitive continious data instead of the discrete data that I would collected if my way worked properly.

    I originally did want to build a wind tunnel to test my design as I appreciate that there are going to be many problems with non uniformity of the flow. I have considered many designs for a wind tunnel but any design like a Baals wind tunnel is far beyiond the scope of the work that I am doing. I have found designs on the internet of a that house the aerofoil in a box with a matrix of narrow tubes at the front of the boxto halp stabalise the flow but I am not of the effectiveness of this design.

    I was planning to attempt this stage once I had some readings for the aerofoil.
    Having the aerofoil supported by just one rod will make this loads easier.

    If you have any ideas of a simple windtunnel or if this setup will work I would be very grateful. I am looking forward to testing out htese ideas and will let you know how I get on.

    Attached Files:

  5. Aug 26, 2008 #4
    just a quick link to sub sonic windtunnels (I'm assuming you'l be working in the subsonic region, it will definitely make things easier for you)

    note the size of the tunnel in comparison to the model. This is important to reduce affects that the tunnel has on the flow over the model. Your tunnel diameter should be quite a bit larger than your test piece. You could just try ducting the flow from your fan (by using cardboard boxes or something) and maybe add vanes later to try to stabilise the flow.
  6. Aug 26, 2008 #5
    first off, the fan was a good idea. but total rubbish if you want any sort of useful results

    if you have access to a car, you have access to a wind tunnel with relatively uniform cross sectional flow properties. basically you're going to do the thing with your hand out the window, where the air lifts your hand up and down.

    take your airfoil. mount it on a rigid, but light pole. if you can get a 1/4" diameter pipe used for electrical conduit, that would work well - but it needs to be at least 5 feet long i would think. fix a sturdy mount location in the car (this will be your hinge location)

    basically you're going to create lift on one end with a large moment arm, and measure the force at the other end of the rod with a smaller moment arm. the ratio of the moment arms multiplied by the measured force should be the lift created.

    when you have this contraption created you should have a 4 foot-ish pole with a styrofoam airfoil sticking out the car window, and 1 foot of pole sticking in the car in contact with a scale.

    remember that the center of lift (for simplicity's sake in names), will be right in the center (spanwise) of the wing, and thus your moment arm will be from the center of the wing to fulcrum. the other moment arm being from the fulcrum to the contact point with the scale.
  7. Aug 27, 2008 #6
    Great idea, ufortunatly this is for coursework and the project must be completed in the lab.
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