Question

What is critical Mach number? An aircraft design exhibits excessive transonic wave drag and an unacceptably low Mcrit. Brainstorm five ways to change the design to improve these characteristics.

What is aspect ratio? Why do supersonic fighters have small aspect ratio?

(by typing please to help me understand)

Answer 1

Critical mach number:-critical mach number is defined as the lowest mach number at which aircraft Or airfighter reaches its maximum speed, it reaches about the speed of sound but do not cross that value.

Critical mach number can be determined by equation two pressure coefficient (Cp)min and Cp, cr

when M(infinity) >Mcr the airfoil will have increase in drag coefficient, and critical mach number determines when it will happen.

Critical mach number is denoted by Mcr or Mcrit.

Mach number is the ratio of flow velocity to the velocity of sound in that locality

Design modification to improve excessive transonic wave drag.

1.Modification in the design features of wing section by the definition using profile shape function it will improve and minimize excessive transonic wave drag.

2.The design should be maintained to produce higher lift coefficient which improves excessive transonic wave drag.

3.Design features should include comparable measurement between pressure distribution for initial and optimized wing geometry that also cause minimization and improvement in excessive transonic wave drag.

4.use of antishock bodies in design features results in minimization of excessive transonic wave drag

5.Excessive transonic wave drag can be reduced by fuselage waisted

Improvement in unacceptably low Mcrit

1.Modification in sweep can increase Mcrit. Higher sweep can be useful to maintain higher Mcrit

2.lowering of camber will also obtained high Mcrit.

3.Design of wing should be thicker in order to obtain high Mcrit

4.By the use of supercritical wings it will increase Mcrit

5.pressure Coefficient should be kept minimum for higher Mcrit

Aspect Ratio:-

Aspect ratio is defined as the ratio of span of wing to mean chord of wing.

AR= span of wing/mean chord of wing

Supersonic fighters have lower aspect ratio because it is important to obtain longer chord because at same surface area the mean chord will be smaller. Longer mean chord will be obtained by lower aspect ratio. Also lower aspect ratio provide higher rolling rate and increase in swift manoevrability which is important features for supersonic fighters.