Cart Shopping Cart My Store Account Orders Downloads Shopping Cart Remove item Thumbnail image Product Price Quantity Subtotal × 12. Weight Control - Aircraft Design Problem $20.00 12. Weight Control - Aircraft Design Problem quantity $20.00 × 1. Weight Economy $20.00 1. Weight Economy quantity $20.00 × 25. The Effect of Overload and Unbalance on Long Range Operation $20.00 25. The Effect of Overload and Unbalance on Long Range Operation quantity $20.00 Coupon: Apply coupon Update cart Available coupons (Click to apply). Cart totals Subtotal $60.00 Tax $0.00 Total $60.00 Proceed to checkout