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Homework Help: Airplane Airspeed

  1. Nov 6, 2014 #1
    1. The problem statement, all variables and given/known data
    For monoplane of Clark Y wing, 36-feet by 6-feet, with 3.8 sq ft. equivalent flat plate area, what should be the airspeed for minimum Horsepower when fuel has been burned so that the total weight is 1800 lb?

    2. Relevant equations
    Wing Area = 36 x 6 = 216
    Weight = Lift
    Weight = Max. Coefficient of lift × (density at sea level/2) × wing area × (Minimum Airspeed)^2

    ○ Gasoline consumption
    HPreq/V = W/375 × (((Coefficient of Drag) + (1.28Ae/ wing area))/Coeffcient of Lift)

    3. The attempt at a solution
    Clark Y wing
    Wing span = 36; wing chord = 6
    Wing area = 216
    Ae = 3.8 sq. ft
    W = 1800 lbs

    Reqd: Airspeed

    From the formula
    W = Max. Coefficient of Lift × (density at sslc/2) × (Wing area) × (Minimum Airspeed)^2

    Since, the problem stated that the wing is Clark Wing, Max. Coefficient of Lift of the airfoil selection is 1.56.

    By substituting the given data,

    Minimum Airspeed = 67.03 ft/s

    My question is, does my answer correct? What is the relevant of the equivalent flat plate area on the problem?

    Thank you..
  2. jcsd
  3. Nov 11, 2014 #2
    Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Nov 11, 2014 #3


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    Homework Helper

    I assume that is how you're supposed to calculate the coefficient of drag. Not sure if that includes the drag related to the fuselage.

    Max coefficient of lift occurs at a specific angle of attack, and the angle of attack required for a specific amount of lift decreases as the aircraft speed increases. It's more likely that what you're looking for is the speed that corresponds to the lowest amount of drag for the amount of lift required which equals the weight of the aircraft. Using a Cessna 172/182 as an example, looks like the longest range speed is around 65 to 70 knots, which is slower than the best glide ratio speed which is closer to 80 knots. Since longest range is affected by engine and propeller efficiency, I don't know if it is the same as the speed of lowest power output (thrust (equals drag) times air speed). Also the stated speed of 65 to 70 knots was posted by another person as opposed to the article that mentioned best glide ratio speed was around 80 knots.
    Last edited: Nov 12, 2014
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