Problem 1 (20 Pts, 10 Min): For the More Unusual

8/14/2019 Problem 1 (20 Pts, 10 Min): For the More Unusual

1/29

1)

Problem 1 (20 pts, 10 min):

For the more unusual aircraft features listed below, do the following:

Explain conceptually whether the feature has a stable or unstable

contribution and for which axis (roll, pitch, or yaw)

Pick a similar feature which has the opposite effect and explain conceptually

why this feature has the opposite contribution

a) Forward-swept wings

b) CanardsNote: Conceptually means use no equations. Diagrams are acceptable.

2)

a) An airplane at trim conditions steadily consumes its fuel, increasing xcg. Whatimpact does this have on the static stability of the plane?

Points: 2

b) Eventually the cg reaches and crosses the neutral point, sketch the Cmvsalpha curve for xcg = xnp and xcg


2/29

4. A nose left yaw moment results from ___________ deflection of the ______________.

5. For an aircraft to be statically stable the ____ must be located ______ of theaerodynamic center.

Estimated time: 5~10 minutes

4)

12 Minutes: 25 Pts.

Q: Given a positive rudder deflection, would you need a positive or negative aileron

deflection to maintain a trim for yaw while creating a roll moment. Why?

5)

Time: 10 min.

Points: 20/100

Q ) Knowing that the Lateral and Directional forces/moments are coupled,

explain the motion an aircraft would experience from a negative rudder

deflection. Why?

6)

Estimated Time: 10 minutes

Estimated Points: 20 points

Question: If a plane has a positive aileron deflection what is the required

rudder deflection (positive or negative) to combat the adverse yaw

generated? Why?

7)

A Boeing 747 is near JFK International Airport.

Scenario 1: The aircraft is at cruise and trimmed. There is a sudden wind gustwhichcreates a nose up motion. The pilot needs to pull back slightly on the yoke tomaintain level flight. The reacting moment is larger than the motion created by thewind gust. Is the aerodynamic center fore or aft of the center of gravity?

PTS: 6

Time: 3 min

Scenario 2: The 747 experiences adverse yaw in a turn whichcreates a nose-rightmoment. Is the right aileron deflecting positive or negative?

PTS: 4

Time: 2 min

8)

Your team is commissioned to build a new fighter jet that has high maneuverability.Which of the following lines on the graph would be most similar to yours? Explain.


3/29

A positive velocity vector your new plane. You want to stabilize the jet with yourrudder. Would the r>0 or r


4/29


5/29

PART II. (5 points) Are there any deflection(s) that are assumed to be equal andopposite? Hint: Are there any blank(s) above (besides a + or -) that can bedescribed by more than one effect?

11)

Calculate the longitudinal moment,

M

, of an airplane in terms of

cgx

,

cgz

,

, AC wx

,

,AC tx

,

, AC wz

,

,AC tz

,

wL

,

tL

,

wD

,

tD

,

,

wi

,

ti

,

,

, AC wM

,

,AC tM

.

Time: 15 minutesPoints: 25

Assumptions:

t wD D


6/29

12)

Time: 10 minutes

Value: 10 points

1.) Is r for the dashed line greater than, equal to, or less than zero? Explain yourchoice in terms of the trailing edge of the rudder.

13)

Prove the following aircraft wing configuration is lateral-directionally unstable:

14)

Figure 1

From Figure 1 above, which of the following is true?

(A) Plane 1 has nose-up motion generating nose-down moment

(B) Plane 2 has nose-up motion generating nose-up moment

Cm

r=


7/29

(C)Plane 1 has nose-down moment generated from nose-up motion

(D)Plane 2 has nose-up moment generated from nose-down motion

(E) Both planes have nose-down motion generating nose-down moment

(F) Both planes have nose-down motion generating nose-up moment

(G)None of the above

15)

Q: You work for a company designing and analyzing high performanceexperimental aircraft. A brand new statically stable experimental aircraft has just

been designed. This aircraft has canards forward of the center of gravity, forwardswept wings behind the center of gravity, and also utilizes a twin vertical ruddersystem. You are to determine its response to a) a gust causing a nose-updisturbance, and b) a nose-left disturbance.

16)

(30 pts)12-15 minutes

The coefficient of lift for an aircraft is given as:

SV

L

Sq

LC

L2

2

1

==

The tail efficiency parameter, t, is given as:

2

==

w

t

w

t

tV

V

q

q

Assume the total lift for the aircraft includes lift components from the wing andhorizontal tail.

1. Derive an expression for the total lift coefficient, CL, in terms of the coefficientsCLw and CLt.

2. Decompose the expression for CL to find an expression for the total lift-curveslope, CL. Clearly indicate any assumptions made.

17)

(24 points total of 100 pt test, 18 minutes total)

Given:

a) An aircraft with the horizontal stabilizer forward of the wing (canards).b) The aircraft has a negative static marginc) Canard Airfoil is symmetric


8/29

d) it=0Considering longitudinal static stability Find:

a) Draw a moment-arm diagram (2pts, 2 min)

b) Compute the moment: (2 pts, 2 min)

c) The Taylor series expansion for the moment coefficient (2 pts, 2 min)

d) Given the result in c, draw on the graph the effect of a positive and a negative on and explain your result (6 pts, 6 min)

e) Given the result in c, draw on the graph the effect of alpha on Cm. Explain youresult, and comment on whether a canard is stabilizing or destabilizing. (4 pts, 2min)

f) Given the information above, what passive design consideration (i.e. not active

control) could be implemented to help improve longitudinal static stability? (8 pts, 4

min)

18)Worth total of 8 pts and should take no longer 5 minutes to complete!


9/29

Figure 1

Effect of ih on Cm vs Alpha

ih=? ih=0ih= ?

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Alpha

Cm

Figure 2


10/29

(Problem 1) For the following problem, please refer to Figures 1 and 2:

(a) (3pts) Correctly label

X

,

hi+

,

wi+

on Figure 1

(b) (1pt) If the F 16 had a positive

5

incidence angle of the horizontal

stabilizer, label the correct line in Figure 2(c) (4pts) Knowing that

1.0=mC

and

5=hi

, determine the total aircraft

pitching moment coefficient

19)

Initially, an airplane flying at trim hits a wind gust causing a nose disturbance in the

+ direction.

A) (3 pts) The center of gravity is located AFT of the aerodynamic center, how

will this disturbance affect the stability of this airplane. Explain.

B) (3 pts) The center of gravity is located BEFORE of the aerodynamic center,

how will this disturbance affect the stability of this airplane. Explain.

C) (8 pts) The + direction is replaced with a + direction, should Cnincrease or

decrease to keep stability? How does the position of center of gravity affect

the stability in this case? Explain.

20)

Consider an aircraft employing two rear-mounted jet engines that is statically stablein a longitudinal sense. Assume that the two engines are mounted near the tail ofthe aircraft and that their net thrust acts only in the axial direction of the fuselage

along the line passing through the center of gravity of the aircraft so that itproduces no moment. Now suppose that the aircraft designers have decided toelevate the engine mounts with respect to the center of gravity. Determine thethrust contribution to the aircraft pitching moment and sketch it as a function of .On the same plot, sketch the CM- curves of the original and modified aircraft.Describe the relationship between these two curves and how the height of theengine mount affects it.

21)

Explain the effects of a forward swept wing under a nose left disturbance as they

relate to longitudinal stability. How could forward swept wings be beneficial to aspecified aircraft?


11/29

Center ofGravity

22)A) Indicate if, for the following conditions, the aircraft component is stabilizing or

destabilizing:

Component Condition StaticallyStabilizing?

Wings

The aircrafts center of gravity is

fore of the airfoils aerodynamic

center

WingsThe aircrafts center of gravity is aft

of the airfoils aerodynamic center

FuselageThe aircrafts center of gravity is

fore of the components

aerodynamic center

Horizontal Tail

The components aerodynamic

center is aft of the aircrafts center

of gravity

Vertical Tail

The components aerodynamic

center is fore of the aircrafts center

of gravity

B) A prototype aircraft is designed to incorporate wings with negative sweepand a center of gravity that is fore of the airfoils aerodynamic center. Will the

wings be statically stabilizing with respect to pitch? With respect to yaw?

Explain.

23)

A four-engine airplane is flying at trim when a bird enters the inlet of the far engine

on the right wing, causing immediate engine failure. (15 minutes, 30 points)

(a) What immediate effect does the engine failure have on the airplanes static

stability with respect to roll and yaw motion? Why?

(b) To bring the airplane back to trim, would the pilot want a positive or negative

aileron deflection, and also a positive or negative rudder deflection? Why?

AerodynamicCenter


12/29

(c) How does the aileron deflection affect the input needed for the rudder

deflection?

Assume no structural damage other than engine failure.

24)

Consider the representative wing figure and the seven numbered circles, assign thecorrect abbreviation to each circle and describe the abbreviation below. Velocity (V)is already noted on the sketch.

Note: Circle #7 indicates the intersection of the two aerodynamic forces on the

wing where the moment about this point is independent of the angle of attack.

Part A

Part B

If a positive aileron deflection was applied to the right wing of an aircraft, what

would happen to the values of 1 and 2 (the circles in the sketch) on the left wing?

Explain.

25)

Worth 15 pts (Approximately 10 minutes)

Question:

For what range of Cm, does static stability dependupon? Why?

26)

16 points


13/29

A new test aircraft has a Cm vs. curve like that shown below. This plane is then

modified with some new device that adds lift near the front of the plane. (a) Show

how the plot below would change and explain why. Then, while flying, the plane

experiences engine failure very briefly in its turbofan hanging off the right wing.

After regaining full power, the plan continues to yaw at an increasing rate. (b) Now

considering the brief asymmetry in thrust, discuss the type of lateral stability

demonstrated and draw a plot for Cn vs. .

27)

Re-label the empty plots at the bottom of the page.

i) Label the axes with the corresponding directions of the moments (nose-up

moment, nose-left moment, etc.).

ii) For Plane A and Plane B, designate whether they are stable or unstable.


14/29

28)

The two graphs below represent an aircraft flying at trim conditions when issuddenly is hit by a wind gust as shown below. In the graphs, the solid dot locatedin the body of the aircraft represents the aerodynamic center, while the encircled Xrefers to the center of gravity. Sketch in each graph, the resultant pitch moment.Explain.


15/29

29)

Question: ( 5 pts total, 3 minutes )

i) What is the condition for required for static stability? What does this mean about ?(1pt)ii) Draw a graph of vs. (2 pts)iii) Describe how the plane moments react to increases in . (2 pts)

30)

During lecture, it was mentioned on a number of occasions that there is not alwaysa right answer, but some answers are certainly better than others when it comes

to designing for stability and control aspects of an aircraft. In this sense, stabilityand control design can be viewed somewhat as an art, where past experience playsa vital role to understanding and creating a system that responds pleasingly.Please give/explain both a theoretical example and a real-world example of thisconcept as explained in class.

31)

Q. (5 pts, 5 minutes)

Flight envelope is the plot of flight speed vs. flight altitude. Show the rough

sketch of flight envelope, and explain what flight envelope and plot line represents.Explain why flight envelopes become these shapes.

Some kinds of aircraft (F-16 etc) have circle regions in the inside of their flight

envelope. What is the name of these regions?

32)


16/29

Time: 5min

Credit: 10points

Say that you are flying along in the F-15 pictured above. You encounter awind gust that induces a negative roll moment. The airplane goes to correct itselfby having +a right and a -a left.You suddenly realize that the ailerons are notresponding. Is there anything that you can do to stabilize your aircraft? If so, what?

33)

1a.) Draw an aircraft with a body fixed frame coordinate system (1 pt.) and label

and define the following letters/symbols (1 pt. each):

, r, L, u

1b.) Name three control systems that could be modified or added onto an aircraft to

increase its static stability. Do these control systems ensure dynamic stability? (2

pts. each)

1c.) If a Cessna-182 is flying straight and level at 4000 ft above ground level (AGL)

and undergoes a strong wind gust that causes the nose of the aircraft to rise

rapidly, what should the pilot do to bring the aircraft back to a straight and level

trim condition? Explain what is happening during the correction. (20 pts.)

34)

As discussed in class, the over effect of a wing (on most aircraft) is destabilizingbecause the aerodynamic center is in front of the center of gravity in most cases.

Using a canard (a horizontal control surface in front of the wings) would cause even

greater static instability. Derive the pitch moment equation for a canard and

describe why it is indeed destabilizing and suggest a way to correct/mend this

situation.

35)


17/29

1) (18 points/14 minutes) Based on what was learned in class, answer thefollowing two part question about the effects of canards on static stability.

a.)(9 points) Suppose the aircraft manufacturer Eurofighter is thinking

of increasing the planformarea(Sc) of the canards (while keeping all

other geometries constant and assuming the canards aerodynamic

center does not move) on their Typhoon aircraft in order to enhance its

maneuverability. What effect would these changes have on the static

stability of the aircraft?

b.)(9 points) Assume that the canards have control surfaces similar to

elevators on a horizontal tail. A deflection of an elevator is denoted

e,likewise a deflection of the canards control surfaces will be denoted

c. If the canards control surface is deflected by c during trim

conditions, what effect would this have on the aircraft?

36)

(20 points)

A statically stable plane with a wingspan, b, is blown at an angle off course by a

gust, giving it a negative yaw. If the coefficient of force in the y direction is known,determine the moment coefficient required to bring the aircraft back to trim.

37)

Worth: (10 pts) Time: (5 minutes)


18/29

Look at the following CM vs. and CN vs. curves:

(A) CM

Plane 1

Plane 2

(B) CN

Plane 1

Plane 2

For each case, determine whether each of the aircraft is considered statically stableor unstable. Explain your answer

38)5 points(3 mins)

The wings on an airplane are located aft of the cg. If a wind gust hits the plane while flying attrim, what effects on stability and Cm,w does it have?

39)

This will take probably 7-13 minutes to solve this question in details)

1) What does the term adverse yaw means physically? And now, using

your basic knowledge in stability, explain how you would maintain the

aircraft stable, and by doing so, what motion you will be creating? (Your

answer can be described with words or with well labeled schematic).

(10pts, 5pt each section)


19/29

40)

Problem is worth 10/100 Estimated time: 5 min.

You are sitting copilot in a WWII era plane flying at trim and soon the pilot needs to

increase altitude. Knowing that you do not want a CM>.006 for the risk of stall,

calculate the deflection (e)of the elevator that will increase your altitude as quickly

as possible. Is epositive or negative, explain your answer.

CMe= .01 where units are in meters.

41)

Given is a line with arbitrary slope L1, and another line L2 with the same slope but alower y-intercept on a Cnvs Beta graph. If L1 has a delta aileron of 0, is the deltaaileron for L2 positive or negative?

42)

Question:

When considering a first order approximation for the momentcoefficients of an airplane, which of the following terms (Cmo,Cno, Clo) of this approximation are typically assumed to be zero?Explain.

43)

Suppose you have an aircraft made with aero elastic materials at the tail. At

a greater speed, the tail generates more drag causing the tail to stretch back in thenegative x direction. Assume that the cg and the wings stay at the same point withthe cg being aft of ac. Will this stretch make the airplane unstable? How will thisaffect its static margin?

44)

Potential Question:

Define adverse yaw and explain the aerodynamic forces that cause it. Also, givean example a way to aerodynamically counteract adverse yaw.

Estimation of time and points:

This question should not take more than seven or eight minutes to complete if thestudent understands the concept. The time needed is largely for writing.

Because adverse yaw is an important concept in flight dynamics, the questionshould be worth slightly more than is proportional to the time it takes to answer.


20/29

Therefore, the question should be worth twenty points because it should takebetween fourteen and sixteen percent of the allowed fifty minutes.

45)

Creative Test Question - 10 pts. 5 min.

During the design phase of an aircraft,static stability is achieved with thehorizontal stabilizer mounted to thefuselage at the base of the verticalstabilizer.

Due to an interference with theengines, which affectedmaneuverability, the mountingposition of the horizontal stabilizerwas changed to the top of the vertical

stabilizer (Note the vertical stabilizerextend upward from the fuselage, inthe negative direction).

Before (Looking at Aft End) :

After (Looking at Aft End) :


21/29

Dw,left

Homework #1 ProblemsEAS4400

Dimensions of the horizontal stabilizer were kept the same. This induced apitch moment on the aircraft due to the drag of the horizontal stabilizer.

What is the sign of the pitch moment, CM ? Also, what is the sign of theelevator deflection, e , you would use to counteract the induced pitchmoment, and regain static stability?

46)

Question: If an aircraft is statically stable and a disturbance creates a CM>0,conceptually explain why the locations of the center of gravity (CG) and theaerodynamic center (AC), with respect to each other, are critical to the staticstability of the aircraft?

47)

Given a statically stable aircraft with swept wings and flying at low Machnumber, complete the graph below. Explain.

48)

Anaircraft

was


22/29


tested at different cg locations to find the neutral point. The data wastabulated:

Xcg e,trim CL,trim

Forward CG 1020 212 4

Arf CG 2022 318 5

CG @ NP ?28 1

28 10

(a) Plot e,trim vs. CL,trimand show all CG curves

(10 pts)

(b) What is the location of Neutral Point?

(Extra Credit)

(a question in (b) part is probably to fail +80% of students, unless the middle

step is incorporated. Therefore, it was chosen to be as Extra Credit)

49)

The lateral roll static stability Cl is giving by the equation Cl=Cl dihedral+Cl wing+Cl wing sweep+Cl r

Explain how does Cl dihedral or the wing geometric dihedral angle

contribute to overall Cl?

50)

It is often seen at airports, airplanes descending with the nose away from xwhen landing. In this case, the nose points in the direction of the incomingwind, while the center of gravity of the airplane stays in the same direction asx. Explain why the airplane is positioned that way.

51)

A plane is affected by a nose up disturbance. Because it is stable, it returnsto trim flight. Roughly sketch the plane on the graph below. (5 points, 3minutes)Cm


23/29


For the Cmvalue that makes this plane statically stable, what needs to be

true physically on the airplane? Reference Xcg and Xac and consider only the

wings of the airplane. (15 points, 15 minutes)

52)

Given:

A C-17, seen in figure 1, has a T-Tail configuration. While in flight the pilotproduces a +e deflection on the elevators. This action causes each elevatorto produce a lift force (whether positive or negative), as well as a resultantdrag force. The forces act a distance x behind the center of gravity of theplane, a distance y to the left or right (depending on the elevator) of thecenter of gravity, and a distance z above the center of gravity of the airplane.

Figure 1: C-17 in flight.

Find:

a) Define the body-fixed coordinate system; write out where the positivedirections of the axes are with respect to the plane. (1 pt)

b) Draw out the airplane and identify the wings, rudders, ailerons, verticaltail, and horizontal tail. (1 pt)

c) Draw the rudder, elevators, and ailerons, and identify what way theymust rotate to produce +r, +e, and +a motions. (3 pts)

d) Following the alphabetical-order naming convention given on thesecond day of class, name the lift and drag forces action on eachelevator (use l and r subscripts to denote force on left or rightelevator.) (1 pt)

e) Identify the directions of each of the forces in part d), with respect tothe axes in part a). (3 pts)

f) Using the same naming conventions mentioned in part d), name themoments produced by the lift and drag forces on each elevator. (1 pt)

g) Identify if the moments above are roll, pitch, or yaw moments, andabout what axis they act. (3 pts)


24/29


h) Leaving the answers in terms of distances x, y, z, and the forces frompart d), find the values of the individual moments produced by eachelevator. (10 pts)

i) Calculate the net roll, pitch, and yaw moments caused by theelevators. (2 pts)

j) During flight the left elevator is frozen shut by ice build-up. As thishappens, begins his descent in preparation for landing. When tries toactuate the elevators, only the right one moves. In order to decreasehis elevation, does he cause a +de or e motion? (1 pt)

k) Find the net roll pitch and yaw moments on the airplane from themotion in part j) given that only the right elevator moves. Whatdeflections in the ailerons and rudder, a and r (positive or negative)are needed to cancel out these moments? (4 pts)

53)

15 PointsEstimated Time: 5-10 minutes

After a positive rudder deflection, what should be the sign of the left aileron

deflection for a directionally stable aircraft with conventional ailerons(adverse yaw); such that the Cn- curve remains unchanged (assumingaileron deflection is the only component of Cn that is changed). Essentiallyhow would the aileron-rudder interconnect deflect the left aileron tocompensate for a positive rudder deflection?

Assume: First-order (i.e. a and r are independent of )Equal but opposite deflection of the ailerons

54)

Derive the relationship between canards (horizontal lifting surfaces ahead ofthe wings) and the pitch moment coefficient CMAssume the canards areefficient and symmetric. Also assume that linearized equations of motion andsmall angle approximations are valid. How do canards affect longitudinalstatic stability?

55)

Point Allocation: 20pts

Time to solve:

Part 1: no more than 3 minutes

Part 2: No more than 5 minutes

Part 1


25/29


The graph below shows the relationship between the moment coefficient

(Cm) to the angle of attack (). The trim condition for a C-17 is shown. In

reference to the longitudinal axis, draw the appropriate curve that satisfies

stability and provide an explanation for your choice using the graph as a

reference. Mathematically, what does this type of stability imply?

Part2

A positive acts on an aircraft. On what side of the aircraft is the velocity

hitting? Would a positive or negative C n trim the aircraft and why? Name

the two features of an aircraft spoken about in class that correctly return an

aircraft back to trim when a positive exists and explain how they do so.

56)

A plane is flying at trim with a positive . Using statics, show how wingsdestabilize an airplane. Assume small angle approximations, the airfoil isefficient and 1st order linear approximations for simplicity. Write all additionalassumptions.

57)

Aircraft rolling moment acts about the x-axis and may be expressed using therolling moment coefficient. The first order Taylor series expansion is given by:


26/29


Cl=Cl0+Cl+Claa+Clrr

Where the derivative Cl is the lateral stability derivative.

a) What are the four aspects of an aircraft design that primarily influence

Cl?

b) If an aircraft is to have roll static stability, what must be the sign of c

and why?

58)

Pitot TubeA pitot tube is a pressure measurement instrument used to measure fluidflow velocity. The basic pitot tube consists of a tube pointing directly into thefluid flow (Point A). As this tube contains fluid, a pressure can be measured;the moving fluid is brought to rest (stagnates) as there is no outlet to allowflow to continue. This pressure is the stagnation pressure of the fluid (P0),also known as the total pressure or (particularly in aviation) the pitotpressure.

The static pressure is generally measured using the static ports . Point B inthe pitot tube measures static pressure or ambient pressure (P).Static and stagnation pressure can be measured and compared to calculatethe aircrafts airspeed using the incompressible Bernoullis equation given by:

P+12V2+gz=constantAlso the following assumptions must be made to use this equation:

1. Incompressible fluid (low Mach number)2. Along a streamline

Given:If stagnation pressure P0 and static pressure Pcan be measured using

the pitot tube, and also knowing the air density () which is given by theaircrafts altitude, derive an equation to calculate V. State the assumptions.

59)

5 pointsWhat do the acronymsVIAS, VCAS, VEAS, VTAS and KEAS imply, andhow is each one determined?
http://en.wikipedia.org/wiki/Pressure_measurementhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Stagnation_pressurehttp://en.wikipedia.org/wiki/Static_porthttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Stagnation_pressurehttp://en.wikipedia.org/wiki/Static_porthttp://en.wikipedia.org/wiki/Pressure_measurement


27/29


4 points(True or False?): Stability is the tendency of a system to return toequilibrium after disturbance.How can this sentence be altered to include actual physicalphenomenon in flight?

3 points(Complete the Relationship):__________ stability __________ generate __________ stability, but __________

stability __________ generate __________ stability.

1 pointWhat chapter(s) of the book have we gone over?

3 PointsLabel the control surfaces of the airplane.

60)

Figure: d e/dCL versus cg position. Experimental data points for a given airplane.

Problem

a) Using the graph find neutral point xnp. (2pts, 1minute)

b) What is xnp given a mean chord cof 7.5ft? (3pts, 1minute)

c) Find static margin SM at the indicated data point (red circle). (5pts, 2minutes)

d) What can be inferred from static margin in terms of stability? (5pts, 1minutes)

Total: 15 points, 5 minutes

61)

What value of Cn would be desired to obtain directional static stability?Explain your answer.

0 1 2 3 4 5 6 70

1

2

3

4

5

6

7

8

9

10

11

dde/d

CL

Xcg (ft)


28/29


62)

Problem 1 (6 min.)Directions: Please complete the following True/False section representing Tfor True and F for False.[12 pts.] Each question is worth 2 points.

1) ___ _ For the first-order approximation, elevators are independent of

the angle of attack.2) ___ _ Perturbation does not generate pitch moment when the angle ofattack changes.

3) ___ _ Thewings and horizontal tail are both stabilizing.4) ___ _ There is an instability if xcg is aft xnp.5) ___ _ Canards are good at low speeds but not good at high speeds.6) ___ _ If e>0, then CM>0.

Problem 2 (5 min)Directions: Complete the plot below and determine which plane is staticallystable. Note that the [6 pts.] numbers on the graph are of noimportance to this problem.

In a recent flight test, the center of gravity of an aircraft was varied by

loading and unloading passengers. With each change in Xcg, the elevator

deflection is measured and the CL is computed, giving the following plot

a) What assumptions can be made about the elevator and for this plot?(5 points)

b) The x-intercept of this plot is referred to as what? (2 points)

c) Draw a plot of Cm vs at this intercept point for all . What is thiscondition referred to? (3 Points)


29/29


d) For an aircraft to be statically stable, where should this point be inrelation to the center of gravity, measuring from the nose of theairplane? Hint: Static Margin. (5 points)

Bonus : Draw a plot of Cm vs. CL for a positive static margin. (5 points)

Documents

Problem 1 (20 Pts, 10 Min): For the More Unusual