Revised byGreg Holt

ASE 167M Lecture One

Aircraft SystemsFlight 1 Briefing

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Today’s lecture

• Pitot-static systems• Bernoulli’s equation• Airspeed definitions• Flight Instruments• Flight control systems• Flight 1 briefing

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Pitot-Static Systems• Essential requirements in the measurement of a/c performance

are: (1) state of atmosphere and (2) relative motion betweenthe a/c and the air mass ⇒ air data systems

• Of the primary flight instruments (Altimeter, airspeed, VVI,compass, turn coordinator), the first three use the Pitot-staticsystem

• The Pitot-static systems, drive instruments (movement of apointer mechanically) that use difference between static andtotal pressure, or just static pressure (independent of electricalpower supply)

• System includes a pitot tube for measuring impact (ram)pressure, and static ports for measuring barometric staticpressure.

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Pitot-Static Systems (2)

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Bernoulli’s Equation• Total pressure at a given point is that which would exist if

the flow were slowed down isentropically to zero.• Assumptions?

– Isentropic– Incompressible

• Derived from Newton’s 2nd Law (F = ma)

( )

21

2

12 1 21 . 12 T

P P V

P V P const along streamline

ρ

ρ

− =

+ = =

Static Pressure

Dynamic Pressure

Total Pressure

PT

P

Static Port

Pitot TubeFlowV1,P1V2=0

P2

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Airspeed Definitions• True Airspeed: Solve (1) for V:

– Keep– P and ρ are corrected for at flight condition

• Calibrated Airspeed:– Speed read on a perfect airspeed indicator (i.e. no instrument error

and true static pressure)– Corrections may be particular to a/c and instruments– Take into account position errors

Vtrue =2 PT − P( )

ρ⇒ Function of 2 variables

)Atmosphere StandardLevel(Seaslρρ =

. .calibrated indicated posit instV V V V= + ∆ + ∆

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Airspeed Definitions (2)• Equivalent Airspeed

– Corrected for compressibility effects– Corrected for altitude/density changes– For incompressible flow we use

– We will assume:

• Indicated Airspeed– As measured by airspeed indicator– We will assume:

( )22 21 12 2

Tsl equiv cal true

sl sl

P Pq V V V V

ρ ρρ ρρ ρ−

= = ⇒ = =

equiv calV V=

trueindicated VV =

1

02 1 11

( 1.4 )

truep ppV

p

ratio of specific heats for air

γγγ

γ ρ

γ γ

−

− ⇒ = + − −

⇒ =

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Airspeed Definitions (3)• white arc

– flap operating range– stall speed (with full flaps + landing

gear – landing configuration) tomax. flap operating speed

• green arc– normal operating range– stall speed (power-off in clean

configuration) to caution range• yellow arc

– caution range• red line

– never exceed speed

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Altimeter• Measures the weight of the air above

the A/C ⇒ fly at a constant pressurelevel

• Pressure typically decreases, in thelower atmosphere, by a known amountwith altitude.(standard lapse rate)

≈ - 1.00”Hg/1000 ft

• Static pressure readings are comparedto a table of pressures to calculatealtitude

0 /

0

0 0

1R g

T pHp

β

β

− = −

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Vertical Velocity Indicator (VVI)

• Rate of static pressurechange is measured to givean indication of rate ofaltitude change.

• System exhibits a 4-8 seconddelay before steady statereading is accurate.

• Shows Trend (immediateindication) and rate(stabilized) of climb

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Example Problem• Altimeter and airspeed indicator read 8000 ft.

and 120 mph, respectively. Assume that allinstruments are perfect.

• A pitot-static tube measures the dynamicpressure.– What is the true airspeed?

• Assume the a/c flies at the same altitude andenters an area of lower pressure.– What happens to the altimeter reading?– What happens to the airspeed indicator reading?– What happens to the VVI reading?

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Example Solution (1)• True Airspeed

mphVft

slugft

slug

mphVV

ftslugft

slug

true

SLcaltrue

ft

SL

4.135

00186.0

00237.0120

00186.0

00237.0

3

3

38000

3

=

==

=

=

ρρ

ρ

ρ

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Example Solution (2)• (altitude) As the altitude increases, static

pressure decreases. Therefore, the altimeter willshow an increase.

• (airspeed) Assuming constant density, there willbe no change in the airspeed indication as thedynamic pressure measured by the pitot-statictube will not change.

• (VVI) The static pressure will appear to havedecreased with time; therefore, the VVI will showa climbing rate.

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Gyroscopic Systems• Attitude indicator, heading indicator, and turn &

slip indicator or turn coordinator.• These devices exploit two properties: (1) rigidity

and (2) precession which are based upon theconservation of angular momentum.– Rigidity is the property which resists any force

tending to change the plane of rotation of the rotor.– Precession is the actual change in the direction of the

plane of the rotation under the influence of an appliedforce.

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Gyroscopic Systems (2)

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Attitude Indicators• Universally mounted gyroscope (rotates free in any plane)• Horizon bar is attached to a gyro to remain parallel to natural

horizon (Gyro acts as a pendulum)

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Attitude Indicator (2)

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Heading Indicators• Formerly called the Directional Gyro• Heading indicator is mounted vertically

– Susceptible to precession errors

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Turn Coordinator or Turn-and-SlipIndicator

• Displays rate and quality of turn• Turn rate, bank angle, and velocity related when

performing a coordinated turn• “Step on the ball”

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Flight Control Systems• Elevators

– Horizontal surfaces on tail of a/c that induce pitch• Ailerons

– Horizontal surfaces on wing of a/c that act in oppositedirections to induce roll

• Rudder– Vertical surface on tail of a/c that induces yaw

• Trim Tabs– Supplemental surface on elevators, ailerons, and

rudder than can be used to create “fingertip” yokerequirement under continual control surfacedisplacement

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Flight Control Systems (2)

Flaps

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Flight Control Systems (3)• Flaps

– increase lift– increase drag

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Power Plant Systems (1)• Carburetor : Use Carburetor Heat

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Power Plant Systems (2)• MagnetosTest L and R

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Power Plant Systems (3)• Cowl Flaps

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Power Plant Systems (4)• Propellers

– RPM controls Pitch ofthe propellers

Fuel Flow Control

RPM Control Manifold Pressure

(MP) or Throttle

Control

RPM ControlManifold Pressure (MP)or Throttle Control

Fuel Flow Control

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Lab Schedule

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Flight 1 Briefing• Orientation Flight: Expand cockpit familiarity and

develop the basic concepts for a/c performance• Get the best rate-of-climb and best angle-of-climb

and its respective velocities (Vx and Vy)

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Flight 1 Briefing (2)• In theory we would have to get those

performances at a constant altitude ⇒ wait untilflight #5

• We are going to climb and read R/C for severalaltitudes, velocities and power settings and wewill assume that they were read at H=const.

Read R/C at constant altitude

H=const

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Equations of Motion in a VerticalPlane

• EOM:

( )

( )

0

0

cossin

cos sin

sin cos

x Vh V

gV T D WWg T L W

WVW CT

γγ

ε α γ

γ ε α γ

= = = + − − = + + − = −

&&

&

&

&

PITCH ANGLEO

V

xw – Relative Wind directionxb – x body directionxh – x local horizon direction

γ

α

xb

xw

xh

θ

x

h

E i

k

ANGLE OF ATTACK

FLIGHT PATH ANGLE

L

D

T

W

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Flight 1 Briefing (2)• Record airspeed

and rate of climbdata for climbs anddescents.

• Go to specifiedairspeed, allow timefor VVI to stabilize(to ensure steadystate reading ofdata).

Event MP = Manifold Pressure (“ of Hg)

Rate of Climb (ft/mim)

Airspeed (knots)

Preflight Checklist; RPM = Max ; MP = Max 0 0

Takeoff (Rotate at 75 knots); Raise Landing Gear 0 75

Climb at 100 knots to 2000 ft MSL; Read R/C at 1800 ft; Set RPM = Max; MP = Max

100

Climb at 120 knots to 3000 ft. Read R/C at 2800 ft 120

Climb at 85 knots to 4000 ft. Read R/C at 3800 ft 85

Climb at 70 knots to 5000 ft. Read R/C at 4800 ft 70

Climb at 65 knots to 6000 ft. Read R/C at 5800 ft 65

Level off at 6000 ft. Set autopilot and Stabilize for 1 mim. Read Airspeed 0

Reduce RPM = 2300; MP = 21 “Hg. Read Airspeed after stabilized 0

Reduce RPM = 2000; MP = 20 “Hg. Read Airspeed after stabilized 0

Set RPM = 2400; MP = Max. Read Airspeed after stabilized. 0

Lower ½ flaps. Read Airspeed after stabilized 0

Lower Full flaps. Read Airspeed after stabilized. Raise ½ flaps and then retract all flaps.

0

Set RPM = 1800, MP = 17 “ Hg; adjust pitch for 120 knots descending. Descend to 4000 ft. Read R/C at 4200 ft.

120

Adjust pitch for 100 knots. Descend to 3000 ft. Read R/C at 3100 ft. 100

Adjust pitch for 90 knots. Record R/C, then Lower ½ flaps. 90

Set RPM = 1500; MP = 15 “Hg; Adjust pitch for 80 knots. Descend to 1000 ft MSL. Note R/C

80

Lower Full Flaps. Set RPM = Min., MP = Min. Descend at 80 knots. Read R/C

80

Lower Landing Gear. Continue Descent to landing 80

Accomplish shutdown checklist 0

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Flight 1 Briefing (3)• Plot dh/dt vs. V for 5 points in the flight (Steps 3 to 7). Fit data to

– Use a least squares curve fit (available on most plottingpackages)

• Calculate and from parabolic constants andfrom graphical representation

2210/ VaVaahCR ++== &

maxmax hdtdh &= maxγ

h

x

h max

γ max

x

h

V

x

xb

γ

h

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Flight 1 Briefing (4)• Calculate theoretical max dh/dt by solving:

• Calculate theoretical max γ by solving:

02 21 =+= VaahV

&∂∂

( ) 0sin

sin/

220 =+−=

=

∂∂

==

aVa

Vh

VV

VhCR&

&

∂∂γ

γ

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Flight 1 Briefing (5)• Why does this provide max γ?

– In this a/c -900< γ <900 so thatmax γ = max sin(γ)

– Note that this also has a linear geometricalinterpretation.

( ) mVaaVa

Vh =++== 21

0sin&

γ

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Flight 1 Briefing (7)• Report:

– Answer 4 questions in lab manual, put in eitherDiscussion or Test Results section.

– Plot h vs. x (use intuitive x, since ground distance isnot actually measured).

– Discuss the effects of flaps on the lift and dragcharacteristics of the a/c. What is the purpose offlaps?

And…– look at report requirements on the web and in lab

manual– include every section– Do not hesitate to ask questions …

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Lab Administration• Reports

– Groups of 5– Individual Work and Lab Reports– Due in two weeks

• Look at the website for procedures• Look at the website for Schedule (When

should I fly?)– Fly after a briefing class

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Next Week:The Atmosphere

Computer Project 1

This Week:Flight 1 – Orientation Flight

Report Due: 02/16