# Aerodynamics Questions

THE BOOK REFERRED AND ALL THE FIGURES ARE FROM

Materials Dole, C. E., & Lewis, J. E. (2000). Flight theory and aerodynamics (2nd ed.). New York, NY: Wiley & Sons.

ISBN: 978-0471370062

1. Find Ground Speed for an Aircraft in a 200 KTAS climb with a climb angle of 20 deg (assume no wind).

Ground speed $V_g = V*cos(\alpha) = 200*cos(20) = 188 KGS$

2. According to the universal gas law,

a) temperature changes do not affect density or pressure.

b) pressure is proportional to changes in temperature but not density.

c) density is always constant with either temperature or pressure changes.

d) density in proportional to pressure changes and inversely proportional to temperature changes.

The universal gas law can be written as

$P*V = \nu*R*T$

or equivalent for density

$rho = P*\mu/(R*T)$

$\nu$ is the number of gas moles, $mu$ is the molecular weight

From the above equation one can say that

density in proportional to pressure changes and inversely proportional to temperature changes.

3.What is the density of the air (slugs/ft3) at 20,000 ft on a standard day?

At 20000 ft the density ratio from table 2.1 is sigma = 0.5328

The density of air at sea level on a standard day is $\rho(0) = 0.002377 slugs/ft^2$

$\sigma = \rho(20000 ft)/\rho(0)$

$\rho(20000 ft) = \sigma*\rho(0) = 0.5328*0.002377 =0.001266 slugs/ft^3$

4. Mach number is defined as:

d) Equivalent airspeed of the aircraft divided by the local speed of sound.

5. According to Boundary Layer theory, What parameters are used in determining the Reynolds Number?

a) Free Stream Velocity

b) Distance downstream

c) kinematic viscosity

d) all of the above

6. How does decreasing camber on an airfoil affect CL max and Stall AOA?

a) Stall AOA increases, CL max increases.

b) Stall AOA decreases, CL max increases.

c) Stall AOA increases, CL max decreases.

d) Stall AOA decreases, CL max decreases

7. Find Parasite Drag (Dp) of aircraft at Stall speed.

Weight (W)= 20,000lb

Wing Ares (S)=200 $ft^2$

Altitude=5,000 ft

CLmax=1.5

Temperature – Standard

Drag coefficient (Cdp) = 0.02

$D_p = C_dp*q*S$

$q = \sigma*V_k^2/295$   or

$C_l =W/(q*S)$

$q = W/(C_l*S) = 20000/(1.5*200) =66.67$

$D_p =0.02*66.67*200 = 266.68 lb = 269 lb$

8. According to Bernoulli’s Theory, as airspeed increases, static pressure:

a) decreases

b) increases

c) stays the same

d) increases with velocity squared

Bernoulli equation is

$P + \rho*g*h + \rho*v^2/2 = constant$

P is the static pressure,

$\rho*g*h$ is the position pressure

As the airspeed v increases the static pressure P decreases if position pressure is the same.

9. What is the Stall Angle of Attack for the aircraft depicted in Figure 4.1 from the textbook?

From the figure 4.1 the stall angle is 14 degree (At CL max)

a. where structural failure will occur if exceeded

11. What is Maneuvering Speed (VA) of the aircraft with 1 g stall speed of 120 KEAS if the Limit Load Factor (LLF) is 6.0 g?

$V_a = V_s(6g) = V_s(1g) *\sqrt{G} = 120*\sqrt{6} = 294 KEAS$

12. A 4.5 g level coordinated turn will result in what AOB?

$G = 1/cos(\phi)$

$\phi = arccos(1/G) = arccos(1/4.5) =arccos(0.222)$

$\phi = 77 deg$

13. Given T-38 Thrust Available/ Thrust Required Curve Figure 6.11. Weight 10,000 lbs. What is the approximate Maximum Range Speed (VBR) with 100 Kt Headwind?

Max range airspeed V(BR) is where the tangent line draw from the origin intersects the graph from figure 6.11

V(BR) = 250 KTAS +100 Kt headwind = 350 KTAS

14. Given T-38 Thrust Available/ Thrust Required Curve Figure 6.11. Weight 10,000 lbs. What is the Best Angle of Climb (AOC) and Best Climb Angle Airspeed (VX) at 100% RPM?

a) 0.342 deg, 270 KTAS

b) 19.9 deg, 245 KTAS

c)  0.127 deg, 265 KTAS

d) 7.3 deg, 245 KTAS

Climb angle occurs at (Ta-Tr) max . From figure 6.11 Ta(100% rpm) = 4200 lb

Tr min = 830 lb

angle of climb is $sin(\gamma) = (Tr-Ta)/W =(4200-830)/10000 =0.337$

$\gamma =19.7 deg$