Select parameter and/or step value from drop-down menu at top left corner of display or change any text-box data value and hit 'Enter' (more info below)


 

First obtain reliable data on sail CL and CD, fuselage drag, tire drag and expected sailing conditions to get realistic velocity predictions.

Good reference material to have on hand -

  • Standard Handbook for Mechanical Engineers - McGraw-Hill
  • Fundamentals of Vehicle Dynamics - SAE
  • Theory of Wing Sections - Dover

    •  

    The Mathcad program Single.mcd and JavaSingle are based on a landyacht performance equation developed by Tom Speer (www.tspeer.com):

    This equation adds up the forces acting on a landyacht. When the forces are in equilibrium (thrust equals drag), the maximum speed at a particular heading has been reached. JavaSingle uses the equation to determine top speed for all headings from 0 to 180 degrees, then displays the results as a color coded polar plot.

    A case study: the Iron Duck

    With data from the NALSA website and selected reference material, JavaSingle is able to correctly calculate the Iron Duck's top speed, plus produce a detailed report on the yacht's performance.

    However, to be useful, a velocity prediction program will need to identify modifications that improve performance.

    -- Fun facts --
    Iron Duck may have developed 86 hp on it's record breaking run!
    thrust lbs x velocity mph / 375 = horsepower
    278.4 lbs x 116.7 mph / 375 = 86.63 hp

    Enter yacht data from below or select the Iron Duck option from drop-down menu at top left corner of display to set JavaSingle to the correct parameters.

    Fire up JavaSingle and take a shot at the record!

    Yacht data -
    · Fastest pilot: Bob Schumacher: 116.7 mph, March 20, 1999
    · Probable wind speed during the fastest runs: 25-30 mph
    · General Configuration: Asymmetric, port tack favored
    · Length: 39'
    · Wheel base: 30'
    · Width: 23'
    · Track (outside of tires): 22'
    · Frontal area -- 23 sqft 
    · Weight: 1600 lbs
    · Moderate aerodynamic hold-down from the axles
    · Wing span: 23'
    · Wing area : 71 sqft
    · Aspect ratio: 7.45
    · Wing section: NACA 0014.5
    · Wing chord/profile: 3.33' with elliptical top 5'
    · Side Tires: 14" wheel, 23" diameter: very sticky dirt track tires or high performance street tires
    · Tire pressure: 35 to 50 psi
    · Tire life: ½ to 2 days
    · Location: Ivanpah Dry Lake - Primm, NV - Altitude - 2700'


    Step parameter

    Wind speed -- 25 to 30
    Plot -- 10 steps


    Wing lift and drag
    Theory of Wing Sections contains wind tunnel data and equations necessary to determine the oswald efficiency, max CL and CD input values.

    Wing section -- NACA 0014.5
    Wing span -- 23'
    Wing area -- 71 sqft
    Wing aspect ratio -- (span ^ 2 / area) -- 7.45

    Altitude -- 2700'
    Wing area -- 71 sqft
    Aspect ratio -- 7.45
    Wing max CL -- 1.2
    Wing CD-- .01

    Wing profile -- elliptical top 5'

    Wings with a oswald efficiency equal to 1 have a elliptical lift distribution and will produce the minimum induced drag for a given wing section and span.

    Oswald efficiency -- .9


    Tire rolling resistance
    Using tire performance graphs and formulas found in Fundamentals of Vehicle Dynamics, obtain a ball-park figure on rolling resistance coefficients for breakout friction, speed effect and side force effect.

    Vehicle weight - 1600 lbs
    plus moderate aerodynamic hold-down from the axles - 200 lbs ?
    Gross weight -- 1800 lbs

    Values from an empirical formula developed at The Institute of Technology in Stuttgart for passenger car tires on concrete - 50 psi
    Breakout friction-- .008
    Target rolling coefficient at max speed -- (3.24 x .0025 x (top speed mph / 100) ^ 2.5) -- .012
    Rolling coeff -- .0085

    Experimental data on a 7.30x14 tubeless tire - lateral acceleration .6 G
    Target sideforce coefficient at max sideforce -- .07
    Sideforce coeff -- .00068

    Target total rolling resistance coefficient at top speed -- .09


    Fuselage sideforce and drag
    Automobile aerodynamic force formulas obtained from Fundamentals of Vehicle Dynamics and data from the Standard Handbook for Mechanical Engineers are used to estimate fuselage sideforce and drag effects.

    Frontal area -- 23 sqft

    Lift (fuselage sideforce)
    The fuselage lift coefficient grows nearly linearly for the first 20 to 30 degrees of relative wind angle. For motor vehicles, the slope of the gradient ranges from .06/deg for vans to .035/deg for sedans. A reasonable value for a streamline fuselage like the Iron Duck may be around .015/deg.
    Frontal CL / deg -- .015

    Drag
    A drag coefficient of .12 would be a conservative value for a vehicle with a well streamlined fuselage, wheel fairings and airfoil rear axle.
    Frontal CD -- .12


    Heading calc -- 1°
    Speed scale -- 120 mph