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

Air Force Developmental Education (DE)

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%)

Air Force Developmental Education (DE)

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%?)

Air Force Developmental Education (DE)

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%

Air Force Developmental Education (DE)

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%

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%

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%

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%

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%

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!!!