I'd like to design a flying wing that could lift about 16oz of cargo.

Is there a way to calculate if the a/c design I come up with will create enough lift to haul it up ?

I'm guessing I need to know how much lift the wing will create ?


(Sorry thats such a basic question)


Digsy

given enough speed, you can create the lift you want. The questions you need to know,

1. What's the maximum lift coefficient of the airfoil that you will use? (flying wings use symmetrical or reflexed airfoils that don't generally lift as much as highly cambered ones do)

2. What will it weigh including the payload?

3. What are the dimensions of the wing?

4. What power are you going to use? (thrust must overcome drag or the plane won't be able to climb)

The lift equation is, (from Andy Lennon's book, applicable to models)

Lift (oz) = Lift Coefficient x relative density x velocity^2 x Wing Area / 3519

Relative Density = 1 at sea level, 0.8616 at 5000 ft, 0.7384 at 10000 ft

Digsy

There are some basic parameters you have to take into account, these are:

1.Airfoil you are using in your wing, this parameter will give you lift and drag coeficients required to make calculations in therms of weight required to sustain (Cl)

2.Speed you intend to fly or minimun stall speed desired to control the aircraft (MPH)

3.Wing area for your specific planform of aircraft (flying wing) (square inches)

4.Finally, you will need density ration from you intend to fly against standard atmosphere density (sigma)

The weight you have to sustain, plus aircraft weight will be the same lift the wing should be developing in order to be able to have an straight and level flight in other words, to fly in static equilibrium.

Equation to be solved is then:

L = (Cl x Sigma x Speed squared x wing area) / (3519)

Cl, is the lift coeficient at any particular angle of atack you choose, usually the most critical one or Clmax at stall AOA
3519, is a number used as factor if you use units as above mentioned
L, will be the total lift or weight (oz) you can sustain with that conditions of wing area, speed and density ratio

So...if you know your weight, you should then vary your speed, your wing area, your airfoil (Cl) or the density ratio to fly at the specific weigth you want to.

Internet provide several web sites where you can find aerodynamic theory to help you make this calculations.

There's a fancy equation but you can cheat and do what I do.

Go to Foilsim at http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html and load in the size of wing you think you want to use. The measurements are in feet so be prepared to figure out the decimal equivalents. Then select the lift coefficient readout and set the angle of attack to match the readily available lift coefficient of the airfoil you want to use. Typically this is about .7 to .8 for a Clark Y flat bottomed type and about .5 to .6 for a symetrical airfoil. If you chose something with more camber you may be able to set the angle of attack to achieve as much as a Cl of 1. Now switch the readout to lift in pounds. Then start reducing the speed until the lift matches the expected weight of your total model. That will be the lowest practical speed you can use. It'll fly slower but it'll be near the stall.

If you build a larger and lighter model there is no reason a .15 to .25 cannot easily lift an extra pound along with a 2.5 lb model on a 500 to 600 sq inch area wing. Speeds will be low and it won't have a vertical climb but it'll fly nicely. Adding a one pound payload to a 40 size model is no biggie at all as long as your model is not grossly overweight to begin with.

Thanks

Would the velocity be in mph and the wing area in sq inches ?


Thanks,
Digsy