High Speed: FINAL 4040

Question 1

An aircraft’s critical mach number is the speed at which airflow somewhere on the aircraft starts to exceed mach one
true
false

Answer 1

true

Question 2

How does the coefficient of parasitic drag act in the subsonic speed regime?

It is characterized by a gradual increase until reaching a velocity of approximately 50% of the critical mach number, then it decreases.

It is characterized by a gradual increase as velocity increases

It is characterized by a gradual decrease as velocity increases

It is basically a constant

Answer 2

it is basically a constant

Question 3

The dividing line between the subsonic and transsonic speed regimes is the critical mach number of the aircraft
true
false

Answer 3

true

Question 4

How does the coefficient of parasitic drag act in the transsonic speed regime?

It rapidly increases shortly after passing the critical mach number and levels again when all of the airflow is supersonic.

It rapidly increases shortly after passing the critical mach number and level approximately at mach one.

It rapidly increases shortly after passing the critical mach number and peaks approximately at mach one. It then decreases to a point where it is well below its peak but well above its level at subsonic speeds.

It rapidly increases shortly after passing the critical mach number and peaks approximately at mach one. It then decreases to a point where it is below its level at subsonic speeds.

Answer 4

It rapidly increases shortly after passing the critical mach number and peaks approximately at mach one. It then decreases to a point where it is well below its peak but well above its level at subsonic speeds.

Question 5

How does the coefficient of parasitic drag act in the supersonic and hypersonic regimes

The coefficient of drag increases throughout the supersonic regime and then is basically a constant in the hypersonic regime.

The coefficient of drag decreases in the supersonic regime and then once again increases entering the hypersonic regime.

The coefficient of drag is basically a constant throughout the supersonic and hypersonic regimes.

The coefficient of drag is basically a constant in the supersonic regime and then once again starts to increase throughout the hypersonic regime.

Answer 5

The coefficient of drag is basically a constant in the supersonic regime and then once again starts to increase throughout the hypersonic regime.

Question 6

The airflow behind a normal shockwave is always supersonic
true
false

Answer 6

false

Question 7

What are the two ways shockwaves create drag.

Boundary Drag

Shockwave drag

Mach Stall

Transsonic drag

Answer 7

shockwave drag
mach stall

Question 8

Mach stall is characterized by boundary layer separation under certain conditions. Match those conditions with their proper descriptors.
True Airspeed
Angle of attack

Answer 8

high
small

Question 9

How do you minimize the effects of increased drag on aircraft as it flies at high mach numbers?

Put winglets on its wings

Streamline the shape of its fuselage

Design the aircraft with fanjet engines

Design the aircraft with a high MCR airspeed

Answer 9

Design the aircraft with a high MCR airspeed

Question 10

What are some of the ways that one can increase MCR?

Increase wing dihedral

Use a wing with low camber

Decrease the wing’s chord

Add an aerodynamic twist to the wings

Increase the wing’s thickness

Use a supercritical wing

Lower a wing’s thickness/chord ratio

Use swept wings

Answer 10

use a wing with low camber
use a supercritical wing
lower a wing’s thickness/chord ratio
use swept winds

Question 11

Swept wing aircraft have the following disadvantages.

Trailing edge controls are less effective

The have a greater tendency to experience mach stall

For the same wing area and aspect ratio, swept wings have more mass

There is a strong tendency for the wingtips to stall first

They increase the amount of parasitic drag generated by the aircraft

Answer 11

Trailing edge controls are less effective

For the same wing area and aspect ratio, swept wings have more mass

There is a strong tendency for the wingtips to stall first

Question 12

What problem does a high speed, subsonic aircraft encounter as it climbs higher in altitude?

Due to decreased air density, laminar flow of air on the wings tends to detach

Parasitic drag increases

Stall speeds decrease

They get caught in “coffin corner”

Answer 12

They get caught in “coffin corner”

Question 13

In supersonic flight, normal shockwaves _________.

Double in size

Disappear

Detach from the wings

Double in number

Answer 13

Disappear

Question 14

In supersonic flight, shockwaves become oblique.
true
false

Answer 14

true

Question 15

Above Mach 1.0, there are _______ pair of shockwaves.
1
2
3
4

Answer 15

2

Question 16

The airflow behind a normal shockwave is ___________. The airflow behind an oblique shockwave is _________.

Subsonic / subsonic

Subsonic / supersonic

Supersonic / Supersonic

Supersonic / Subsonic

Answer 16

Subsonic / supersonic

Question 17

The primary drag problem with supersonic flight is _______________.

the bow wave ahead of the wing.

the trailing oblique shockwave.

the normal shockwave

induced drag

Answer 17

the bow wave ahead of the wing.

Question 18

The problem with using a supersonic wing for such things as airliners is that ____________.

They have a very low crosswind limitation.

they cause instability around the longitudinal axis of the aircraft.

they have high stall speeds, thus necessitate long runways.

their large wingspan limits the number of gates at airports.

Answer 18

they have high stall speeds, thus necessitate long runways.

Question 19

In supersonic flight, the aerodynamic center of the wing ________________.

Doesn’t move

moves to the 75% chord point

moves to the 25% chord point

moves to the 50% chord point

Answer 19

moves to the 50% chord point

Question 20

In order for swept wings to be effective in supersonic flight, they must be swept back at least to the mach angle.
true
false

Answer 20

true

Question 21

Mach tuck is the tendency of an aircraft to pitch _________ when transitioning from subsonic to supersonic speed.
up
down

Answer 21

down

Question 22

When an aircraft goes supersonic, movement of the aerodynamic center increases ___________.

yaw stability

longitudinal stability

lateral stability

both yaw and lateral stability

Answer 22

longitudinal stability

Question 23

A high bypass (fan jet) engine is the most efficient engine for supersonic flight.
true
false

Answer 23

false

Question 24

Which of these statements is true concerning jet engines and supersonic flight?

Jet compressors are very efficient when the incoming airflow is supersonic.

Compressors are not efficient with supersonic air, therefore the airflow must be slowed to subsonic speed.

Designing a jet diffuser so that an oblique shockwave forms is a good way to slow the airflow down.

Answer 24

Compressors are not efficient with supersonic air, therefore the airflow must be slowed to subsonic speed.