Aero 315 Happy Studying

If a wing with a 5 m chord uses a NACA 0008 airfoil section, what is the wing's maximum thickness in centimeters? (10.3)

40 cm

Which of the following statements is FALSE? (6.1)

Bernoulli's equation can be used at all subsonic speeds

Bernoulli's Equation requires what five assumptions? (6.1)

Body forces can be ignored, steady, inviscid, incompressible and along a streamline

A NACA 2421 airfoil is being tested in a wind tunnel at an angle of attack of 6 degrees in test section conditions that produce a chord-based Reynolds number for the airfoil model of 8,900,000. The airfoil spans the entire test section, so the flow around it is 2-dimensional. What lift coefficient will this airfoil generate in these conditions? (11.4)

Cl = 0.8

If you were designing a helicopter to land on the top of Mount Everest, and you did some research to find out what the atmospheric conditions were there, what step of the Engineering Method would you be accomplishing?

Collecting Info

The continuity equation is a statement of which principle of physics? (5.2)

Conservation of mass

Solve this problem using the lift coefficient, Cl = l/(qS). An airfoil with an planform S = 2m2 is tested in a wind tunnel at sea level at a velocity V = 8 m/s in the test section. If the lift coefficient is equal 1.1, how much lift is generated? (11.4)

D. 86.24 N

When a gas is Perfect, or Ideal, what properties can be related in an equation?

Density, temperature, and pressure

The decrease in lift and increase in drag of a wing relative to an airfoil is caused by what phenomenon? (15.2)

Downwash due to wingtip vortices

What is pressure drag? (9.5)

Drag due to separation --- flow separation causes a low pressure wake behind the object which sucks the object back. This is pressure drag.

Which of the following statements about pitot-static systems is FALSE? (7.3)

Dynamic Pressure is equal to the Static Pressure at a stagnation point -- Dyn P = 0 at stag point (Pt = Ps here)

True or False: afterburners are a fuel-efficient way of increasing thrust. (22.3)

False

An aircraft is doing a loop. At the moment when it is traveling straight up, the _______ must be equal to 90º. (21.1)

Flight path angle Answer Feedback: Correct, because the Flight Path Angle is defined as the angle between the horizon and the aircraft reference line.

Where does an adverse pressure gradient occur on an airfoil? (9.2)

Near or after the point of maximum thickness.... Correct!! The adverse pressure gradient starts approximately at the point of max thickness. After this pt the air is slowing down and the pressure increases with distance.

Which of the following assumptions is NOT necessary when using the continuity equation? (5.5)

No nuclear reactions

According to the Airfoil Lab packet, the density, ρ, used in the manometer equation, P2 - P1 = - ρ g (h2 - h1) , is the density of the air, oil or water? (12.1)

Oil

Which of the following statements is true about the Airfoil Lab? (12.3)

Part A is Individual Effort only and must be turned in prior to the lab.

The standard atmosphere was built using these three relations:

Perfect gas, hydrostatic equation, and an empirical temperature profile

Which of the following is a correct description of an airfoil? an airfoil is... (10.1)

a cross-section of a wing with dimensions of chord and thickness, or an airfoil is a constant-chord wing section with the same cross-section shape which spans an entire wind tunnel test section so that the flow around it is 2-dimensional

What correctly describes one of the influences World War I had on aviation?

The large number of trained pilots and inexpensive surplus military aircraft available in the US after the war led to a vast expansion of aviation activities, enterprises, and public awareness

Lift acts perpendicular to which vector? (21.2)

The relative wind (velocity vector).

In Equation 4.14, what does the e represent? (15.3)

The span efficiency factor

What relationship should you expect to see between the overall static pressure on the top versus the bottom of the airfoil at 0 degrees AoA? (12.2)

The static pressure on the bottom will be higher than the static pressure on the top

Which of the following is NOT a characteristic of a wing compared with an airfoil with the same dimensions? (14.2)

The wing has more skin friction drag

You just got into your F-22 Squadron and you get to do a flyby of the Academy (7,000 ft std day). You decide to kick it up a notch and do the fly-by at 610 KIAS (emphasis on INDICATED). You figure that the speed of sound is about 645 KTAS (emphasis on TRUE) that day anyway, so what's the big deal? If the position error for the F-22 is -5 knots and the f correction factor is 0.977, will this be a mistake? (7.6)

This is a bad idea since my true air speed will be approximately 675 knots. Breaking the sound barrier over USAFA might just get me in trouble

If a wing is producing zero lift, then its total drag is the same as a 2-D airfoil. (15.2)

True

If we know the dynamic pressure and the density, then we can find the velocity of the flow. (7.3)

True

If you have a tailwind with an unchanged indicated airspeed, what happens to your true airspeed? (7.7)

True airspeed doesn't change

What would be the best engine choice if you were designing an aircraft that will be operating primarily at 300 KTAS and 30,000 feet (Hint: Refer to Figure 5.4)? (22.4)

Turboprop Answer Feedback: Correct. Turboprops are a better choice at low speeds (think C-130).

Why does cool, dry air get more viscous as it warms up? (8.2)

Viscosity of air results from transfer of momentum, and since molecules in hotter air have higher velocity, they transfer more momentum

As we fly closer and closer to the speed of sound, we have to take into account a new type of drag that we have previously neglected. This drag is due to the flow separation induced by shock waves. What type of drag is this? (19.7)

Wave drag

If an aircraft is in SLUF and we know the weight of the aircraft, W, the wing area, S, the density and velocity, what else must we know to determine the coefficient of lift of the aircraft? (21.7)

We need no additional information

What is an adverse pressure gradient? (9.2)

Where pressure increases with distance downstream

We do not have a leading-edge pressure port on the airfoil/wing. However, we have a pitot probe inserted in the tunnel. Can we use this to estimate the leading-edge pressure? If not, why not (12.2)

Yes, the pitot probe measures total free stream pressure. The leading edge of the airfoil is a stagnation point and its static pressure will be the free stream total pressure

Since there is more drag on a whole aircraft than only on a wing, how does the Oswald efficiency factor, e0, compare to the span efficiency factor? (18.5)

e0 is less than e

How does a standard altimeter work

It is a simple pressure gauge calibrated in units of altitude instead of pressure

Which of the following statements about jet engines is true? (22.1)

Jet engines make thrust by pushing air out the back of the engine at a higher speed than the speed at which the air came in the front. Answer Feedback: Correct. Jet engines create thrust by the exit velocity being greater than the inlet velocity.

Which of the following definitions of Mach number is correct? (19.1)

Mach number is the ratio of true airspeed to the speed of sound.

What is the NACA designation of the airfoil/wing we will use in the Airfoil Lab? Is it symmetric or cambered? (12.1)

NACA 2415, cambered

Given sea level standard day conditions, a wind tunnel has an inlet area of 10.5 square ft and a test section area of 2.7 square feet. This allows the air that goes through the inlet at 250 ft/s to accelerate to 2,950 ft/sec in the test section. What is the density in the test section? (5.7)

NOT 2.38x10-3 slugs/ft^3

What would be considered by the USAF to be a valid reason for designing a new aircraft?

National Security requires that we have the newest aircraft in the world

What is the zero lift AOA for a airfoil NACA 4412? (11.2)

-4º

On a hot summer day, you are standing inside a cabin looking at a manometer that compares the outside air and inside air pressures. The outside thermometer reads 95 deg F and the fluid in the manometer is water. The fluid level in the manometer inside the cabin is 30 inches lower than it is outside the cabin. If the pressure altitude in the cabin is 10,000 ft, what is the density of the air outside? (4.4) Hint: Use Manometer Equation to find the pressure outside, then the perfect gas law to find the density.

0.0014 slugs/ft3

For the same scenario as previous question (NACA 2421 ; Re = 1,900,000) , if the AOA is set such as the coefficient of lift is equal to 1.0, what's the coefficient of drag? (11.2)

0.013

If an aircraft has a k factor of 0.04 and a zero-lift drag coefficient of 0.02 and a lift coefficient of 0.5, what is the coefficient of drag? (18.6)

0.03

Given an aircraft with a wing area of 250 ft², wing span of 50ft, Oswald efficiency factor of 0.80. Calculate the k coefficient for the induced drag. (18.2)

0.0398

A C-130 is flying in standard sea level conditions at a true airspeed of 200 knots. What is its flight Mach number? First, convert true airspeed in knots to feet per second using the conversion factor on page 569 of the textbook. Then, find the speed of sound at sea level in the standard atmosphere on page 564 of the textbook... Finally, divide the true airspeed by the speed of sound and select your answer from the list below by clicking on the appropriate letter: (3.7)

0.3

You are trying to duplicate the flight test conditions of an aircraft in a water tunnel. You know the Reynolds Number in the water tunnel needs to match the Reynolds number in the actual flight test. The aircraft was flying 200 m/sec at 7 km on a standard day. The mean chord of the aircraft is 2 m. (8.7) If the tunnel velocity is 27 m/sec, what is the proper length of the mean chord of the water tunnel model? (density of water is 1,000 kg/m3; viscosity of water is 1.12e-3 N sec/m2)

0.6 meters

On a standard day, if an aircraft with a wing area of 510 ft2 is generating 20,000 lb of lift and is flying at 300 ft/s at an altitude of 16,000 ft, what is the coefficient of lift? (18.1)

0.602

What is the Mach number if your velocity is 800 ft/s and the local speed of sound is 1000 ft/s? Note: M=V/a

0.8

A NACA 2412 airfoil with a 10 ft chord length is tested in a wind tunnel in standard sea level conditions with a velocity equal to 49 ft/s in the test section. What is the coefficient of lift at 6º AOA? (11.2)

0.88

What are the % camber and % thickness of a NACA 1408? (10.3)

1% camber and 8% thick --- (first number is camber and last two are thickness)

An aircraft's instruments measure an air temperature of 15 degC and an air pressure of 83 kPa. What is the air density for these conditions? (Use Equation 2.1)

1.0 kg/m^3

An aircraft's instruments measure an air temperature of 20 degrees C and an air pressure of 95 kPa. What is the air density for these conditions?

1.13 kg/m3

An airfoil NACA 2421 is tested in a wind tunnel with a Reynolds number equal to 1,900,000. What is the lift coefficient for 14º? (11.2)

1.24

Now decode a NACA 4-digit airfoil series code. The NACA 4-digit airfoil series code designates maximum camber in % chord with its first digit, location of maximum camber in tenths of chord with its second digit, and maximum thickness with its last two digits. So, if a NACA 2415 airfoil has a 10-meter chord, calculate its maximum thickness in meters by multiplying the chord length by 15% thicknes... Select the correct answer from the list below by clicking on its associated letter: (10.3)

1.5 meters --- (15%x10)

According to Figure 2.4, at what altitude is the tropopause

11km

From Table B.1 in Appendix B, what is the atmospheric pressure on a standard day at 10,000 ft altitude?

1456 lb/ft^2

Now calculate Equivalent Airspeed from Calibrated Airspeed. Enter the f factor chart in Table B-3 in Appendix B on page 568 of the textbook with the Calibrated Airspeed of 220 knots and the altitude of 14,000 ft. Read the f factor for 225 knots and 15,000 ft, which are the values in the chart closest to the actual value... Then multiply the Calibrated Airspeed (220 KCAS) by f factor to get the Equivalent Airspeed. Choose the correct answer below: (7.6)

218 KEAS

Now try working an ICeT problem. An aircraft flying at 14,000 ft pressure altitude has an indicated airspeed of 225 knots. According to Equation 8, if the position error is -5 knots, what is the aircraft s calibrated airspeed? (7.6)

220 KCAS Answer Feedback: Correct! By the way, KCAS stands for Knots Calibrated Airspeed. Likewise, KIAS stands for Knots Indicated Airspeed, KEAS stands for Knots Equivalent Airspeed, and KTAS stands for Knots True Airspeed.

(D3) A new hypersonic surveillance aircraft is capable of flying at Mach 10 at 100,000 feet (Std Day). At this rate how fast can it transit from Los Angeles to New York (2500 nm)? Hint: First, find the Speed of Sound (in ft/sec), then determine the aircrafts velocity by v = Ma. Then convert to knots (nm/ hour). Now remember velocity is distance per time. Solve for time. Finally convert to minutes.(19.2)

25 minutes

An aircraft flying in standard sea level conditions has a wing area of 300 ft2, CLmax of 1.2, and weight of 30,000 lb. What is its stall speed for these conditions? Work this problem using the equation definition of lift coefficient, solved for velocity, which is Equation 5.18. Assume SLUF so L = W and substitute the value of CLmax = 1.2 for the CL in the equation, then the velocity you calculate will be the stall speed.

265 ft/s.

Now calculate the True Airspeed from Equation 3.10. Find the density for 14,000 ft and sea level in the Standard Atmosphere Table (on page 564 of the textbook... Then multiply the Equivalent Airspeed by the square root of the ratio of the sea level density divided by the density at altitude to get the True Airspeed. (7.6)

270 KTAS

The wing of the F-16 has a span of 30 feet and a wing area of 300 square feet. What is its aspect ratio? Aspect ratio is an indication of how long and slender or short and stubby a wing is. It is defined as AR = b²/S where b is the wing span and S is the wing reference planform area, sometimes just called wing are... So, square the F-16's 30-foot span and divide by the wing area. Select the correct answer from the list below: (14.1)

3

An F-16 generating 30,000 lbs of lift has a dynamic pressure is 134 lb/ft2. The zero-lift drag coefficient for the F-16 is 0.019 and it has a k of 0.117. With a wing area of 300 ft2, what is the drag on this aircraft? (18.6)

3,382 lbs

If an airplane with a turbojet engine produces 10,000 lbs of thrust at sea level, how much thrust will it produce at 30,000 feet (assume Std Day)? See Equation 5.11. (22.5)

3,750 lbs

The flow over your car's sunroof is not freestream velocity because the car disturbs the air. If you are moving 70 mph down the freeway at sea level standard conditions, and the velocity increases by 23% as it moves over the car, compute the resulting drop in static pressure over the top of your car? (i.e. calculate the pressure at point 2 and subtract from the pressure at point 1) Assume all of the Bernoulli assumptions apply. (6.3)

6.43 lb/ft2

Referring to Figure 5.14a in the book, what is the minimum velocity this aircraft can fly at in SLUF? (23.4)

70 kts

A manometer is filled with water. On the first side, the pressure is standard sea level pressure (P1 = 101325 kPa). The second side is open to the room. The fluid is 50cm higher on the second side than the first side. What is the pressure in the room? Note: The density of water is 1000kg/m^3. Use Equation 2.3

96425 Pa

A stream tube is defined as _________________? (5.1)

A collection of streamlines

Which of the following is an advantage of a laminar boundary layer over a turbulent one? (8.8)

A laminar boundary layer has less skin friction drag

Which of the following shapes would most likely have less drag if transition to a turbulent boundary layer could be made to occur earlier? (8.8)

A streamlined external fuel tank

In Figure 3.9 in your book, what can you say about the flow properties at points 2a and 2b (on top and bottom of the airfoil, respectively)? (6.3)

According to the continuity equation, the velocity at 2a is faster than 2b

If you were designing an aircraft to fly at M = 0.5 and you wanted the engine with the highest thrust-to-weight ratio, which engine would you choose (Assume that a rocket is not an option)? (Hint: refer to Figure 5.2) (22.4)

Afterburning turbofan

Which of the following assumptions is NOT required to derive the relationships T = D and L = W? (21.3)

Angle of attack = 0

The Reynolds number is a non-dimensional parameter that illustrates the relative magnitude of the momentum of the flow versus viscous force of the fluid. Flow A has a Reynolds number of 1,000,000. Flow B has a Reynolds number of 10,000? What conclusions can you draw? (8.7)

Flow A has a greater ratio of momentum forces to viscous forces

What is Thrust Specific Fuel Consumption (TSFC)? (22.2)

Fuel flow (lbs/hr) required to produce a pound of thrust (lbs)

If you were designing an aircraft to fly at M = 0.8, what would be the most fuel efficient engine you could choose? (Hint: refer to Figure 5.3 and lower TSFC is better...) (22.4)

High-bypass turbofan

The airspeed indicator in the cockpit of an aircraft provides what type of velocity? (7.4)

Indicated

Which of the following is NOT a type of drag that is present in the drag polar of a finite wing? (15.6)

Interstitial drag

The most important aspect of dimensionless parameters is their value in establishing

Similarity

Viscosity of air in the boundary layer creates a drag force known as: (8.5)

Skin friction drag

When utilizing the Continuity Equation (Compressible form), what assumptions must be made?

Steady, one-dimensional, area is perpendicular to the airflow

SLUF stands for: (21.3

Straight, Level, Unaccelerated Flight

Why can streamlines be treated as material boundaries when they form the walls of a stream tube? Can't air just flow across the streamline since they are not really a material surface? (5.1)

Streamlines are defined as lines everywhere tangent to the local velocity vector. So, even though a streamline is not material, air can't flow across it

If an aircraft is in SLUF, then the equations of motion simplify to: (21.2)

T = D and L = W

What are the four fundamental flow properties that define the condition of a fluid?

Temperature, Density, Velocity, and Pressure

If two airfoils have the same chord length but one is a NACA 2408 and the other is a NACA 1408, which will create more lift at zero angle of attack? (11.4)

The NACA 2408 will create more lift than the NACA 1408 because the NACA 2408 has more camber

Which statement describes the flow over an airfoil (refer to figure 3.9 in your book, assume the flow is 1D at station 1)? (6.4)

The Total Pressure will be the same everywhere in the flowfield

You are designing an aircraft to fly slowly at high altitude, so you want to minimize induced drag. Which of the following statements best describes the likely shape of the wing you will design? (14.4)

The best wing for this mission will have a very high aspect ratio, like the wing on the U-2

Refer to Fig.3.17 in your textbook. What is happening at the transition point? (8.3)

The flow changes from laminar to turbulent

Critical Mach number is the freestream Mach number (19.4)

at which local Mach number first equals 1 somewhere around the body.

Which of the following statements about an airfoil is true? (10.1)

he flow around an airfoil is by definition 2-dimensional

Wingtip vortices are the main contributor to changes in the behavior of a wing as opposed to an airfoil. Since a wing is finite, ___________ air on the bottom of the wing is allowed to flow around the wing-tip to the top. Due to this circulation, the wing creates _______ lift and ______ drag than a 2-D airfoil of the same size. (14.2)

high-pressure, less, more

When comparing the lift curve of a 3-D wing with an airfoil of the same NACA 2412 profile, the wing will have a _______________ stall angle-of-attack and ______________ max lift coefficient vs. the 2-D airfoil. (14.7)

higher, lower

The symbol CDo stands for?

parasite drag coefficient

Because many of aerodynamic principles are based on Reynolds number, matching the Reynolds number can matter more than matching scale or velocity for many effects. We use this principle with a water tunnel where the increased density allows _____________ models to be tested at lower _____________ while still matching real-world results. (8.7)

smaller, velocities

Which of the air and aircraft properties define the air's speed of sound and the aircraft's Mach number? (3.6/3.7)

temperature and aircraft velocity

What's the name given to the equation for an aircraft's coefficient of drag as a function of the coefficient of lift? (18.2)

the drag polar

In order for flow to separate, (9.3)

the flow must be in an adverse pressure gradient