Helix (xem hình ) xoắn là một đường cong tạo ra bởi một điểm di chuyển trên một hình trụ với khoảng cách nó transverses song song với trục của tỷ lệ thuận với góc quay quanh trục xi lanh: x = a cos y tội lỗi = a z = k = bán kính của hình trụ, độ dốc = 2πk. | 46 Aeronautical Engineer s Data Book The parametric form of the equation is x a secỡ y b tanỡ where 0 s the eccenteric angle. The equation of the tangent at x1 y1 is xx _ yy1 1. a2 b Sine Wave see Figure y a sin bx c y a cos bx c a sin bx c where c c n 2 y m sin bx n cos bx a sin bx c where a Vm2 n2 c tan-1 n m . Fig. Sine wave Helix see Figure A helix is a curve generated by a point moving on a cylinder with the distance it transverses parallel to the axis of the cylinder being proportional to the angle of rotation about the axis x a cos Ỡ y a sin Ỡ z kb where a radius of cylinder 2nk pitch. Fundamental dimensions and units 47 z À y Fig. Helix Useful references and standards For links to The Reference Desk - a website containing over 6000 on-line units conversions calculators - go to ramsdale EngZone United States Metric Association go to http hillger This site contains links to over 20 units-related sites. For guidance on correct units usage go to http hillger Standards 1. ASTM IEEE SI 10 1997 Use of the SI system of units replaces ASTM E380 and IEEE 268 . 2. Taylor . Guide for the use of the International System of units SI 1995. NIST special publication No 8111. 48 Aeronautical Engineer s Data Book 3. Federal Standard 376B 1993 Preferred Metric Units for general use by the Federal Government. General Services Administration Washington DC .
