Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Airplane takeoff speed

  1. Mar 23, 2007 #1
    1. A light aircraft has a mass of 2.0x10^3 kg, a wingspan area of 10.0m^2, an upper wing distance of 1.75m, and a lower wing distance of 1.00m. What minimum takeoff speed must the airplane travel to become airborne?

    2. V1= square root of ((2Fw)/(pA(((d2/d1)^2)-1))

    3. How am I supposed to find p and Fw? Which length is d1 and which is d2?
  2. jcsd
  3. Mar 23, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Look at the ratio of d2/d1 and its effect on take off velocity V. Should V decrease as d2/d1 increases? If so then d2 is the longer length. Also d2/d1 > 1, because one does not want to be taking the sqrt of a negative number (argument) in this case.

    Isn't there some discussion of the variables and the equation from the source (text) where the equation was taken?
  4. Mar 23, 2007 #3
    No, it isn't taken out of the textbook. I read through multiple chapters a few times and haven't even found that equation in the book. I was gone the day he went through it too and he told me to ask one of my students for help because theres no time for us to meet outside of class. Every student I asked gave the reply "I just got the answeres from x." So I ask x how to do it. "Oh I just stole y's answers."

    None of them could help explain it.

    edit: Thank you for the answer about d2/d1. I am almost posative you are correct(and now that I look at it I feel silly for having to ask that question :frown: lol...) I gtg eat but i'm gonna try and figure it out again, will post the results and how I got them within the hour.
    Last edited: Mar 23, 2007
  5. Mar 23, 2007 #4
    p is sapposed to be density correct? but how am I sapposed to figure out density from the given information if I can only figure out the volume of the wing and not the entire plane and only the mass of the entire plane is given?

    And why would density matter in the first place?
  6. Mar 24, 2007 #5
    Towely, you can use Bernouilli's equation for ideal fluids (even though air, strictly speaking isn't an ideal fluid) and you also have to take into account that the total force which is "pulling" the jet up must be greater than its weight. I hope that cleared things up a bit. :)

    Hint: pressure = force/ wingspan area , also remember that you have TWO wings.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook