1) Aircraft: F/A­18 Hornet (Blue Angels)
2) Aircraft Gross Weight: 66,000 lbs
3) Aircraft Wing Area: 500 sq. ft.
4) Positive Limit Load Factor: 7.5 G's
5) Negative Limit Load Factor: ­3 G's
6) Max speed: 1.8 Mach (you need to convert this to knots TAS)
7) Cl = 1.5 Exercise 7: Maneuvering & High Speed Flight
For this week’s assignment you will research a historic or current fighter type aircraft of
your choice (options for historic fighter jets include, but are not limited to: Me262, P-59, MiG15, F-86, Hawker Hunter, Saab 29, F-8, Mirage III, MiG-21, MiG-23, Su-7, Electric Lightning,
Electric Canberra, F-104, F-105, F-4, F-5, A-6, A-7, Saab Draken, Super Etendard, MiG-25,
Saab Viggen, F-14, and many more).
As previously mentioned and in contrast to formal research for other work in your
academic program at ERAU, Wikipedia may be used as a starting point for this
assignment. However, DO NOT USE PROPRIETARY OR CLASSIFIED INFORMATION even
if you happen to have access in your line of work.
Notice also that NASA has some great additional information at:
http://www.hq.nasa.gov/pao/History/SP-468/contents.htm.
1. Selected Aircraft:
2. Aircraft Gross Weight [lbs]:
3. Aircraft Wing Area [ft2]:
4. Positive Limit Load Factor (LLF - i.e. the max positive G) for your aircraft:
5. Negative LLF (i.e. the max negative G) for your aircraft:
6. Maximum Speed [kts] of your aircraft. If given as Mach number, convert by using Eq. 17.2
relationships with a sea level speed of sound of 661 kts.
For simplification, assume the CLmax for your aircraft was 1.5 (unless you can find a
different CLmax in your research). A. Find the Stall Speed [kts] at 1G under sea level standard conditions for your aircraft (similar
to all of our previous stall speed work, simply apply the lift equation in its stall speed form from
page 44 to the above data):
B. Find the corresponding Stall Speeds for 2G, 3G, 4G, and so on for your selected aircraft (up
to the positive load limit from 4. above), using the relationship of Eq. 14.5. You can use the table
below to track your results.
C. Add the corresponding Stall Speeds for -1G, -2G, and so on for your selected aircraft (up to
the negative load limit from 5. above) to your table. Assume that your fighter wing has
symmetrical airfoil characteristics, i.e. that the negative maximum CL value is equal but
opposite to the positive one. (Feel free to use specific airfoil data for your aircraft, but please
make sure to use the correct maximum positive and negative Lift Coefficients in the correct
places, i.e. CLmax in the 10
positive part and highest negative CL in the negative part of the table
and curve, and indicate your changes to the given example.)
9
Explanation: Making the assumption of symmetry simplifies your work, since the stall curve in
8
the negative part of Lthe V-G diagram becomes a mirror image of the positive side. Notice also
O of7 Eq. 14.5 won’t work with negative values; however, if using the Gthat the simplified form
dependent stall equation
A 6in the middle of page 222, it becomes obvious that negative signs
cancel out between D
the negative G and the negative CLmax, and Stall Speeds can actually be
calculated in the same way
5 as for positive G, reducing your workload on the negative side to
only one calculationFof the
`4 stall speed at the negative LLF, if not a whole number.)
A 3
C
D. Track your resultsT in the
2 V-G diagram below by properly labeling speeds at intercept points.
Add also horizontal lines for positive and negative load limits on top and bottom and a vertical
O 1
line on the right for the upper speed limit of your aircraft at sea level from 6. above. (Essentially
R 0
you are re-constructing the
V-G diagram by appropriately labeling it for your aircraft. Notice that
the shape of the diagram
and
the G-dependent curve relationship is essentially universal and
G -1 will change from aircraft to aircraft. Make sure to reference book Fig.
just the applicable speeds
14.8 for comparison.) -2
-3
G VS
(kts) -4
-5 PLL:
10
9
8
7
6
5
4
3
2
1 EAS (kts): 0
-1
-2
-3
-4
-5
NLL: E. Find the Ultimate Load Factor (ULF) based on your aircraft’s Positive Limiting Load Factor
(LLF). (For the relationship between LLF and ULF, see book discussion p. 226 and Fig. 14.9):
F. Find the Positive Ultimate Limit Load [lbs] based on the ULF in E. above and the Gross
Weight from 2.?
G. Explain how limit load factors change with changes in aircraft weight. Support your answer
with formula work and/or calculation example.
H. What is the Maneuvering Speed [kts] for your aircraft?
I. At the Maneuvering Speed and associated load factor, find the Turn Radius ‘r’ [ft] and the
Rate of Turn (ROT) [deg/s].
I) Use Eq. 14.3 to find bank angle ‘’ for that load factor (i.e. G). (Remember to check
that your calculator is in the proper trigonometric mode when building the arccos).
II) With bank angle from I) above and maneuvering speed from H., use Eq. 14.15 to find
turn radius ‘r’. find III) With bank angle from I) above and maneuvering speed from H., use Eq. 14.16 to
ROT. (Make sure to use the formula that already utilizes speed in kts and gives results in
degree per second). J. For your selected aircraft, describe the different features that are incorporated into the design
to allow high-speed and/or supersonic flight. Explain how those design features enhance the
high-speed performance, and name additional features not incorporated in your aircraft, but
available to designers of supersonic aircraft. K. Using Fig. 14.10 from Flight Theory and Aerodynamics, find the Bank Angle for a standard
rate (3 deg/s) turn at your aircraft’s maneuvering speed. (This last assignment is again designed
to review some of the diagram reading skills required for your final exam; therefor, please make
sure to fully understand how to extract the correct information and review book, lecture, and/or
tutorials as necessary. You can use the below diagram copy to visualize your solution path by
adding the appropriate lines, either via electronic means, e.g. insert line feature in Word or
Acrobat, or through printout, drawing, and scanning methods.) From: Dole, C. E. & Lewis, J. E. (2000). Flight Theory and Aerodynamics. New York, NY: John
Wiley & Sons Inc.

 

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