Avit 421 Block 1 Exam

The atmospheric pressure at 60,000 feet is approximately _____ psi.

1

What is the thickness of a normal shockwave?

1/10,000th of an inch

The atmospheric pressure at sea level is approximately ______ pounds per square inch (in2/psi).

15

The atmospheric pressure at 20,000 feet is approximately _____ psi.

7

Refer to the following illustration (shown below) of a subsonic airfoil. Identify the area of maximum velocity airflow.

B (top of curve)

Lift can be explained through the equations built by _______.

Both Bernoulli and Newton

Refer to the following illustration (shown below) of a subsonic airfoil. Where is the adverse pressure gradient?

D (the top back side)

True/False: According to our classroom discussions, the relative wind is parallel and opposite to the lift vector.

False

True/False: The forward stagnation region is characterized by a region of slow moving air, reduced dynamic pressure, increased static pressure, and low drag.

False

What should you do if you need to send a text message during class?

If you need to respond to a text message, quietly leave the classroom.

Low Supersonic flow is considered to be:

Mach 1.2 to Mach 3.0

Transonic flow is considered to be:

Mcrit (which is approximately Mach .75) to Mach 1.2

According to the Equal Transit Time/Longer Path theory (Fred and Barny), airfoils are shaped with the upper surface longer than the bottom. The air molecules have farther to travel over the top of the airfoil than along the bottom. In order for these air molecules to meet up at the trailing edge, the molecules going over the top of the wing must travel faster than the molecules moving under the wing. Therefore the air molecules must move faster over the top of the wing to meet molecules at the training edge that have gone underneath. Question: Is this Equal Transit Time/Longer Path theory (Fred and Barny) correct?

No

What should you do if you receive a text message on your cell phone?

Quietly leave the classroom; if you need to respond to a text message.

Where is Professor Ullrich's office?

Ryan Room 221

Name the possible affects to the airflow as it passes through a shockwave.

Static pressure, density, and temperature all increase.

What is Professor Ullrich's policy concerning portable electronic device (PED) use in class?

Stow all PEDs during class, and put the ringer on vibrate

Which of the following factors affect the speed of sound the most? (Assume the speed of sound in the earth's atmosphere.)

Temperature

Why is a bow wave sometimes termed a "Detached" shockwave?

The forward stagnation region causes the bow wave to separate from the leading edge.

Identify Professor Ullrich's office hours.

There are no formal office hours, however you can make an appointment via Starfish, or make and appointment before/after class.

Explain the term "adverse pressure gradient."?

This is an area of increasing static pressure and decreasing velocity.

According to our classroom discussions, the airflow behind a normal shock wave is ALWAYS subsonic.

True

True/False: Bernoulli's equations also partially explain lift: an increase in air velocity creates a rise in dynamic pressure and a decrease in static pressure.

True

True/False: Newton's 3rd Law of Motion partially explains lift: air is deflected downward by the wing and the corresponding reaction deflects the wing upward.

True

True/False: Normal shock waves do not change the flow direction.

True

True/False: Normal shock waves form perpendicular to the airflow.

True

True/False: When we study subsonic airflow, we assume incompressible flow. The air molecules are not compressed.

True

Does the movement of air behave like fluid?

Yes

Will attendance be taken every class period?

Yes

Can I sign in if I am tardy?

Yes, however it is the student's responsibility to sign in before departing class.

Subsonic flow is considered to be:

Zero to Mcrit which is approximately Mach .75

If the surface has a bullet shaped leading edge, the drag is reduced from approximately 5 drag units down to _______ drag units.

about 1

How will I get credit for "Participation Points"?

attend class AND sign the attendance sheet (arrive & sign)

Which of the following is a characteristic of an airfoil optimized for slow-speed, subsonic flight?

blunt and rounded leading edge

The angle-of-attack is measured between the

chord line and relative wind.

How can we reduce skin friction drag?

clean design and keeping the aircraft clean and polished

If the surface area is cut in half, what happens to the drag?

drag is cut in half

If the surface area of an object is doubled, what happens to the drag?

drag is doubled

What happens to the drag of an object when the speed is doubled?

drag is increased by a factor of 4

The lift vector is perpendicular to ____________.

drag vector, relative wind, and flight path

Why does the coefficient of parasite drag increase at Mcrit?

due to the creation of wave drag

As the (static) air pressure falls, the temperature _______ and the density _______.

falls, falls

How can we reduce induced drag?

fly faster

When airflow is accelerated, the dynamic pressure _______.

increases

If the trailing part of the surface also has a bullet shape, the drag is reduced from approximately 5 drag units down to _______ drag units.

less than 1

What happens to the lift when an airfoil is stalled?

lift is decreased

What causes wing vortex drag?

low static pressure above the wing and high static pressure below the wing

How do we get air molecules to flow from high static pressure to low static pressure?

nothing, this happens naturally

Explain Skin friction drag.

skin friction drag: - is also called surface friction drag - is characterized by the air molecules clinging to the surface of the aircraft - decreases when the speed is increased

When airflow is accelerated, the _______ pressure decreases.

static

According to Bernoulli, total pressure is a combination of

static and dynamic

The use of flaps during landing resulting in a _______ approach angle, a ______ view of the landing area, and a _______ landing speed.

steeper, better, lower

Describe the differences between the leading edge and trailing edge:

the leading edge is blunt and rounded and the trailing edge is sharp

Which of the following two drawings (shown below) more accurately reflects high transonic flight ... lets assume .95 Mach?

the top drawing (shock wave is broken at wing)

Discuss the differences between the bottom of the airfoil vs the top of the airfoil:

the top of the airfoil is curved and the bottom is often flat