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?
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%
Without SOS (IPZ): 0% selection!
Air Force Developmental Education (DE)
Selection Rate (CY02)
PRF
BPZ
IPZ
APZ
39.9%
99.9%
94.87%
P
0.3%
40.8%
0.6%
Total
4.6%
71.7%
3.7%
DP
Selection Rate (CY02)
Without ISS (IPZ): 0% selection!
PRF
DP
BPZ
17%
IPZ
98.6%
APZ
77.8%
P
0.1%
26.3%
0.1%
Total
2.9%
45.9%
0.8%
Without SSS (IPZ): 2% selection!
Additional
Example: 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
Power = Work / Time
 For
and
Work = Force x Distance
therefore
Power = Force x Distance/Time
or
Power = Force x Velocity
aircraft
PA = TAV
PR = TRV = DV
Power Required and Power Available versus Velocity
PR
P
Note: curve steepens at
high velocities
PA (DRY)
Slope = rise/run = PA/V = TA
VMAX
PRMIN
VMIN
VPR
MIN
V
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.
P
VPR
MIN
PR for a given V
< VTR
MIN
If this slope = TR,
where is TR,MIN ?
VPR
MIN
Slope = (PR/V)MIN
= TRMIN = DMIN
VTR
MIN
= VDMIN
V
T-38 Power Chart from
Supplemental Data
Sea Level
PR for M= 0.8
= 2.15x106 ft-lbs/sec
Min PR, W=8000 lbs
= 2.5x105 ft-lbs/sec
At 0.325 Mach
Min Power Required using Drag Polar
TR = ½ r V2 S CD,0 + 2 kW2 / (r V2 S)
PR = TR x V = ½ r V3 S CD,0 + 2 kW2 / (r V S)
dPR /dV = 3 ( ½ r V2 S CD,0) - 2 kW2 / (r V2 S) = 0
So, at min PR : 3 x Parasite Drag = Drag due to Lift
Thus: 3CD,0 = CD,i
or
3CD,0= k CL2
so: CD = CD,0 + CD,i = 4 CD,0 = 4 k CL2/3
Solving for CL:CL = (3CD,0 /k)1/2
At Minimum PR
Example: T-37 again
Using CD = 0.02 + 0.057CL2 (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 r V2 S
so V = (12,000 / (3CD,0 /k)1/2 r S ) 1/2
CL = (3•0.02/0.057)½ = 1.026
V = 163.5 ft/s
Excess Power
P
PA (DRY)
PX = Excess Power
= PA – PR (@ V1)
PX
PR
V1
V
Maximum Excess Power
P
PA (DRY)
Line parallel to PA and
tangent to PR
PXMAX
PR
VPX
MAX
V
Configuration Changes
“Dirty configuration” – increases CDo
1
TR  r V 2 S C D ,0
2

kW 2
1
rV 2 S
2
T
PA
P
TR
TA
PR
V
V
Weight Changes
Increasing Weight
1
TR  r V 2 S C D ,0
2

kW 2
1
rV 2 S
2
P
T
PA
TR
TA
PR
V
V
Altitude Changes
Increasing Altitude
1
TR  r V 2 S C D ,0 
(Decreasing r)
2
T
kW 2
1
rV 2 S
2
TR
TA
r
TA = TSL r
SL
Less Parasite Drag
More Drag
from Lift
V
Altitude Changes
Increasing Altitude
(Decreasing r)
P
PA
PR
V
Parameter Changes
CD0
Dmin
VDmin
Vmax
Vmin
PRmin
VPRmin
L/D max
T & PA
W
h
TAS
A little
A little
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!!!