Aero Engineering 315 Lesson 25 Performance— Power Required and Power Available.

Aero Engineering 315

Lesson 25

Performance—Power Required and

Power Available

Air Force Developmental Education (DE) —formerly known as Professional Military Education (PME)

Step 1: Aerospace Basic Course (ASBC)Maxwell AFB, AL – six weeks All second lieutenants (first year of service) In-residence program Ungraded course/no DG program Airpower history/theory/operations, communication

skills, leadership/problem solving/teambuilding Physical training, obstacle course Wargame

Air Force Developmental Education (DE)

Step 2: Squadron Officer School (SOS)Captains (4-7 years of service) Offered via correspondence (after pin-on), in-residence Competitive selection for in-residence (75%+,

alternates) In-residence program: Maxwell AFB, AL – five weeks

Graded course/DG program (overall performance) Airpower history/theory/operations, communication

skills, officership/problem solving/teambuilding MC tests, graded briefings, graded position paper Physical training, volleyball, flickerball, Project X Wargame Flight competition


Step 3: Intermediate Developmental Education (IDE)—formerly known as Intermediate Service School (ISS) Majors Multiple options

Air Command and Staff College (ACSC)—offered via correspondence/seminar (after selection), in-residence

In-residence program: Maxwell AFB, AL – 10 months Graded course/DG program (academic

performance) Softball

Advanced academic degree (e.g. AFIT) Advanced Study of Air Mobility (ASAM) Air Force Intern Program (AFIP) Sister service/foreign schools

IDE in-residence candidacy determined by O-4 promotion board (~30%)


Step 4: Senior Developmental Education (SDE)—formerly known as Senior Service School (SSS) Lieutenant colonels Multiple options

Air War College (AWC)—offered via correspondence (after selection), in-residence

In-residence program: Maxwell AFB, AL – 1 year Industrial College of the Armed Forces (ICAF) – 1 year Various fellowship programs National War College/sister service schools/foreign schools

SDE in-residence candidacy determined by O-5 promotion board (~20%?)


Why do I care?

Without SOS (IPZ): 0% selection!Without SOS (IPZ): 0% selection!

Selection Rate (CY02B)Selection Rate (CY02B)

PRF BPZ IPZ APZ

DP n/a 100% 100%

P n/a 79.8% 4.3%

Total n/a 92.6% 7.8%


Selection Rate (CY02)Selection Rate (CY02)

PRF BPZ IPZ APZ

DP 39.9% 99.9% 94.87%

P 0.3% 40.8% 0.6%

Total 4.6% 71.7% 3.7%


PRF BPZ IPZ APZ

DP 39.9% 99.9% 94.87%

P 0.3% 40.8% 0.6%

Total 4.6% 71.7% 3.7%

PRF BPZ IPZ APZ

DP 39.9% 99.9% 94.87%

P 0.3% 40.8% 0.6%

Total 4.6% 71.7% 3.7%

Without ISS (IPZ): 0% selection!Without ISS (IPZ): 0% selection!Selection Rate (CY02)Selection Rate (CY02)

PRF BPZ IPZ APZDP 17% 98.6% 77.8%

P 0.1% 26.3% 0.1%

Total 2.9% 45.9% 0.8%



P 0.1% 26.3% 0.1%

Total 2.9% 45.9% 0.8%



P 0.1% 26.3% 0.1%

Total 2.9% 45.9% 0.8%

Without SSS (IPZ): 2% selection!Without SSS (IPZ): 2% selection!

AdditionalExample: T-38

At Sea Level:

1. What is (L/D)MAX for 8,000 lb?

2. What is the Parasite Drag at (L/D)MAX for 8,000 lb?

3. For W=8,000 lb, what Mach range can I achieve using reverse command on the throttle (i.e. back side of curve)?

Power req’d & available objectives Sketch power required (PR) & power available curves for

a turbojet aircraft State the slope of a power available curve (TA ) Find min drag point on power required curve

From a T-38 chart find PR, min PR, excess power, max excess power, max and min Mach

Know relationship between induced & parasite drag at min PR

From a drag polar calculate velocity for min PR

Sketch TR and PR changes with wt, alt & configuration Know how parameters & velocities change with wt, alt

& config Min drag, (L/D)max, and min PR

Thrust vs. Power vs. a Pickup

What is Power?

Power and Work

For aircraft

Power =

and Work =

therefore Power = Force x Distance/Time

or Power = Force x Velocity

PA = TAV

PR = TRV = DV

Work / Time

Force x Distance

V

P

PR

PA (DRY)

VMAXPRMIN

VMIN

Slope = rise/run = PA/V = TA

Note: curve steepens at high velocities

VPRMIN

Power Required and Power Available versus Velocity

V

P

PR for a given V

Slope = (PR/V)MIN

= TRMIN = DMIN

VTRMIN = VDMIN

VPRMIN

The slope of a line from the origin to any point on the PR curve is rise/run or PR/V = TR. So the point where the slope is minimized is the point of TRMIN

or DMIN.

VPRMIN < VTRMIN

If this slope = TR,where is TR,MIN ?

T-38 Power Chart from Supplemental Data

Sea Level

PR for M= 0.8= 2.15x106 ft-lbs/sec

= 2.5x105 ft-lbs/sec At 0.325 Mach

Min PR, W=8000 lbs

Min Power Required using Drag Polar

So, at min PR : 3 x Parasite Drag = Drag due to Lift

so: CD = CD,0 + CD,i = 4 CD,0 = 4 k CL2/3

Solving for CL:

Thus: 3CD,0 = CD,i or 3CD,0= k CL2

CL = (3CD,0 /k)1/2

TR = ½ V2 S CD,0 + 2 kW2 / ( V2 S)

PR = TR x V = ½ V3 S CD,0 + 2 kW2 / ( V S)

dPR /dV = 3 ( ½ V2 S CD,0) - 2 kW2 / ( V2 S) = 0

At Minimum PR

Example: T-37 againUsing CD = 0.02 + 0.057CL

2 (from whole aircraft lesson), S = 184 ft2 and W = 6,000 lb @ SL

Find V @ PRMIN

CL = (3CD,0 /k)1/2 (at PRmin )

L = 6,000 lbs = (3CD,0 /k)1/2 ½ V2 S

so V = (12,000 / (3CD,0 /k)1/2 S ) 1/2

CL = (3•0.02/0.057)½ = 1.026V = 163.5 ft/s

V

P

PR

PA (DRY)

PX

Excess Power

For a given velocity,

say V 1

PX = Excess Power= PA – PR (@ V1)

V1

V

P

PR

PA (DRY)

PXMAX

VPXMAX

Maximum Excess Power

Line parallel to PA and tangent to PR

Configuration Changes

V

TTR

TA

V

P

PR

PA

“Dirty configuration” – increases CDo

SV21

kWCSV

2

1T

2

2

0,D2

R

Weight Changes

V

TTR

TA

V

P

PR

PA

Increasing Weight

SV21

kWCSV

2

1T

2

2

0,D2

R

Altitude Changes

V

T TR

TA

Increasing Altitude(Decreasing )

Less Parasite Drag

More Dragfrom Lift

SV21

kWCSV

2

1T

2

2

0,D2

R

TA = TSLSL

Altitude Changes

P

PR

PA

V

Increasing Altitude(Decreasing )

Parameter Changes

CD0 W h

Dmin

VDmin

Vmax

Vmin

PRmin

VPRmin

L/D max

T & PA

A little

A little

TAS

TAS

TAS

Next Lesson (26)…

Fighter Design Project Prior to class

Read Handout! In Class

Finish PR and PA material Discuss fighter design project Ask questions!!!

Aero Engineering 315 Lesson 25 Performance— Power Required and Power Available.

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Transcript of Aero Engineering 315 Lesson 25 Performance— Power Required and Power Available.