Flight Testing of the Stability of a Jetstream 31
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Embry-Riddle Aeronautical University *
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413
Subject
Aerospace Engineering
Date
Jan 9, 2024
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Uploaded by ProfessorFog18854
Flight Testing of the Stability of a Jetstream
31
AE 413: Stability and Control
Spring 2023
Name 1
Name 2
Name 3
Submitted on ______
1
[Abstract]
I.
Nomenclature
β
=
Angle of sideslip
AoSS
=
Angle of sideslip
ζ
=
Rudder deflection ξ
=
Aileron deflection
α
=
Angle of attack
IAS
=
Indicated airspeed
δ
=
Control deflection
AHRS
=
Attitude, Heading, Reference System.
T/O
=
Take-off
U/C
=
Undercarriage
KIAS
=
Knots Indicated Airspeed
II.
Longitudinal Static Stability
A.
Flight Test Method
The pilot should identify a stable region of the atmosphere (ie. with minimal turbulence) at a suitable altitude at
which to conduct the test. The pilot should accelerate to 145 knots, flaps up, gear up (clean configuration), and set
the elevator trim tab such that zero force is felt on the control column/stick (ie. trim the aircraft in a cruise). Once on
condition, we will record the first data point noting: elevator angle, elevator trim tab angle, airspeed, and fuel
quantity. Next, while maintaining the same power setting, the pilot will reduce the airspeed by 10 knot increments
(135 and 125 knots) using the elevator, and trim out the control force using the trim tab. Once on condition, we will
record the same parameters as above. This will be repeated for increases in airspeed by 10 knot increments (155 and
165 knots). Once on condition, we will note the same parameters as above. We will repeat the entire test 3 more
times for varying CG positions.
B.
LSS Analysis
Q1. Calculate the total mass of the aircraft for each test. This should include the aircraft empty mass, total mass of
the passengers, and the average fuel load. Q2. Calculate the total moment based on the passenger weights, and the moment arms given in Section 6. Q3. Calculate the CG position (%¯c) for each test using the formula below and confirm that the tests were
conducted within the published CG limits for the Jetstream (16 – 37 %¯c).
CG
(
%
´
c
)
=
(
Σmx
Σ m
−
5.149
1.717
)
×
100
Q4. Convert airspeed into appropriate units so that C
L
may be calculated for each data point using the equation
below
C
L
=
2
m g
0
ρ
0
V
2
S
W
Q5. Plot elevator deflection angle (y-axis) vs. CL (x-axis) for each test. Fit a straight line through the point (0, 1) for
each data set. Q6. Plot the gradients of the straight line fits in Q5 (y-axis) vs. CG position (x-axis) for each test. Fit a straight line
through the data points. 2
Q7. Extrapolate the straight line in Q6 to estimate the ‘stick fixed’ neutral point in (
%
´
c
)
Q8. Plot elevator trim tab deflection angle (y-axis) vs. CL (x-axis) for each test. Fit a straight line through the point
(0, -3.7) for each data set. Q9. Plot the gradients of the straight line fits in Q8 (y-axis) vs. CG position (x-axis) for each test. Fit a straight line
through the data points.
Q10. Extrapolate the straight line in Q9 to estimate the ‘stick free’ neutral point in (
%
´
c
). Q11. Suggest a safe aft CG limit for the aircraft based on this test and explain your decision. Discuss the difference
between the stick fixed and stick free neutral points and why they are different in the case of the Jetstream 31.
III.
Longitudinal Maneuver Stability
A.
LMS Flight Test Method
The pilot should identify a stable region of the atmosphere (ie. with minimal turbulence) at a suitable altitude at
which to conduct the test. The pilot should accelerate to 160 knots, flaps up, gear up (clean configuration), and set
the elevator trim tab to neutral (centered). Once on condition, we will record the first data point noting: elevator
angle, elevator link force, normal acceleration (g), airspeed, and fuel quantity. Next, while maintaining the same
power setting, and without re-trimming, the pilot will perform steady turns, incrementally increasing the bank angle
up to 60◦ . Once on condition, we will record elevator angle, elevator link force, normal acceleration (g). Once
complete, the pilot will release the controls, and at datum speed, we will record the elevator link force. We will
repeat the entire test 3 more times for varying CG positions.
C.
LMS Analysis
Q1. Using your calculations from the LSS analysis, update the total mass and total moment of the aircraft for the 4
longitudinal maneuver tests with the new average fuel loads
. The passenger masses and seating positions are the
same as in the LSS tests. Test
Total Mass (kg)
Total moment
(Nm)
1
6652.9468
361168.4435
2
6626.766
373821.4771
3
6667.8866
365675.435
4
6606.6724
367757.9437
Q2. Calculate the CG position (
%
´
c
) for each longitudinal maneuver stability test, based on the updated values
for total mass and total moment from Q1, using the formula below. Confirm that the tests were conducted within the
published CG limits for the Jetstream (
16
−
37%
´
c
¿
.
CG
(
%
´
c
)
=
(
Σmx
Σ m
−
5.149
1.717
)
×
100
Test
Center of Gravity
(%c)
1
22.41361675
2
35.02277765
3
25.70439898
4
30.59252951
3
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Q3. Plot elevator deflection angle (y-axis) vs. normal acceleration (g) (x-axis) for each test. Fit a straight line
through the point (0, 2.5) for each data set. 0.8
1
1.2
1.4
1.6
1.8
2
2.2
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
Elevator deflection angle vs normal acceleration
Normal Acceleration (g)
Elevator deflection angle/degrees
Q4. Plot the gradients of the straight-line fits in Q3 (y-axis) vs. CG position (x-axis) for each test. Fit a straight line
through the data points. 20
22
24
26
28
30
32
34
36
-6
-5
-4
-3
-2
-1
0
Change in elevation deflection angle with normal acceleration vs CG position
CG Position [%]
dη/dg
Q5. Extrapolate the straight line in Q4 to estimate the ‘stick fixed’ maneuver point in (
%
´
c
). Based on the figure above, the stick fixed maneuver point is at approximately 51% of the cord.
Q6. Calculate the stick force (
P
η
) at each point using the equation. P
η
=
0.256
(
P
L
−
P
L
SR
)
4
where P
L
is the elevator link force and P
L
SR
is the elevator link force stick released (ie. Test 1 stick forces
will all be calculated using the same value of P
L
SR
, Test 2 stick forces will all be calculated using the same value
of P
L
SR
, etc.)
Test
Stick force (N)
1
21.00659
32.08474
44.34586
58.92122
114.1092
2
-12.5094
-3.94445
1.270784
19.71661
54.71283
3
5.380352
19.38714
33.2032
55.34182
92.39629
4
2.345984
8.610304
21.52858
43.31674
67.88685
Q7. Plot stick force (y-axis) vs. normal acceleration (g) (x-axis) for each test. Fit a straight line through the point (0,
-84) for each data set. 0.8
1
1.2
1.4
1.6
1.8
2
2.2
-20
0
20
40
60
80
100
120
140
Stick force vs normal acceleration
Normal Acceleration (g)
Stick force[Pη] (N)
5
Q8. Plot the gradients of the straight-line fits in Q7 (y-axis) vs. CG position (x-axis) for each test. Fit a straight line
through the data points. 20
22
24
26
28
30
32
34
36
0
20
40
60
80
100
120
Change in stick force with normal acceleration vs CG position
CG position (%)
dPη/dg
Q9. Extrapolate the straight line in Q8 to estimate the ‘stick free’ maneuver point in (%
´
c
). Based on the figure above the stick free maneuver point is at approximately 72% cord.
Q10. What is the stick force per g at the CG limits of Jetstream (ie. at 16%
´
c
and 37%
´
c
)? Comment
generally on how the aircraft would feel from a pilot’s point of view with a forward vs. aft CG position.
At 16% chord the stick for per g is approximately 110N/g and at 37% chord the stick force per g is approximately
70N/g.
IV. Lateral-Directional Stability – Steady Heading Sideslips
A.
SHSS Flight Test Methods
The pilot should identify a stable region of the atmosphere (ie. with minimal turbulence) at a suitable altitude at
which to conduct the test. The pilot should accelerate to 120 knots, flaps up, gear up (clean configuration). Once on
condition, we will record the first data point noting: aileron angle, rudder angle, bank angle, sideslip angle, airspeed,
fuel quantity. The pilot then incrementally yaws the aircraft using the rudder and ‘checks’ with aileron to maintain a
steady sideslip. Once on condition, we will record aileron angle, rudder angle, bank angle, sideslip angle. We will
repeat the process for 3 port sideslip angles and 3 starboard sideslip angles. Then, the whole test is repeated for
another aircraft configuration, in this case, with the undercarriage down at the same datum speed.
D.
SHSS Analysis
Q1. Plot sideslip angle (x-axis) vs. rudder deflection angle (y-axis) for both sets of data: cruise configuration and
undercarriage (U/C) down. 6
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-10
-5
0
5
10
15
20
-10
-5
0
5
10
15
12
0C
R
AoSS (Degree)
Rudder Defecton (Degrees)
Q2. Plot an appropriate trend line through both sets of data and confirm, with justification, that the aircraft exhibits
directional stability in both configurations.
Q3. Do your trend lines pass through the origin? ie. Does a neutral rudder deflection yield zero sideslip? If not,
explain the reason for this. Neither trendline for the cruise nor undercarriage down conditions pass through the origin demonstrating that with a
neutral rudder the Jetstream 31 will still have an AOSS of between approximately 0.5
−
1
°
. This is due to
several factors such as the Jetstream 31 having co-rotating propellers creating a positive yaw moment and the
undercarriage down condition produces considerably more drag. In the UC down condition the propellers must
generate more thrust to maintain the same IAS resulting in a stronger propeller slipstream over the inboard wing
portion .
Q4. Plot sideslip angle (x-axis) vs. aileron deflection angle (y-axis) for both sets of data: cruise configuration and
undercarriage (U/C) down. -10
-5
0
5
10
15
20
-2
-1
0
1
2
3
4
AoSS (Degree)
Aileron Defecton (Degree)
7
Q5. Plot an appropriate trend line through both sets of data and confirm, with justification, that the aircraft exhibits
lateral stability in both configurations. Q6. Comment on the effect of the U/C down configuration on the gradients of the trend lines for both graphs
(sideslip angle (x-axis) vs. rudder deflection angle (y-axis) and sideslip angle (x-axis) vs. aileron deflection angle (y-
axis)). What is the reason for this effect, and is it what we expect? Q7. Plot sideslip angle (x-axis) vs. roll (bank) angle (y-axis) for both set of data: cruise configuration and
undercarriage (U/C) down. -10
-5
0
5
10
15
20
-6
-4
-2
0
2
4
6
AoSS (Degree)
Roll Angle (Degree)
Q8. Consider a cross wind landing. If the cross wind induces a sideslip angle of +10◦ , approximately what bank
angle should the aircraft be flown at (in the U/C down configuration) to offset the cross wind? Is this likely to cause
a problem with wing strike considering that the Jetstream has positive dihedral angle?
V.
Conclusion
[Conclusion] Appendices
A.
Passenger Weights and Seating Locations
Test 1
Seat A
Seat B
Seat C
Test 2
Seat A
Seat B
Seat C
Row 1
76
85
105
Row 1
X
X
X
Row 2
68
68
69
Row 2
52
61
62
Row 3
63
65
67
Row 3
63
68
X
Row 4
60
60
58
Row 4
75
71
70
Row 5
57
52
85
Row 5
76
75
80
8
Row 6
X
X
X
Row 6
85
85
94
CO
X
X
X
CO
85
X
X
Test 3
Seat A
Seat B
Seat C
Test 4
Seat A
Seat B
Seat C
Row 1
60
61
49
Row 1
54
54
X
Row 2
61
61
62
Row 2
58
58
58
Row 3
70
67
64
Row 3
61
65
65
Row 4
70
70
70
Row 4
72
67
X
Row 5
75
82
X
Row 5
72
78
78
Row 6
X
X
X
Row 6
80
90
X
CO
75
X
X
CO
75
X
X
E.
LSS Flight Test Data
Test 1
Elevator deflection angle (°)
Elevator trim tab deflection angle (°)
Altitude (ft)
IAS (knots)
OAT (°C)
Fuel (kg)
-3.503
6.252
6165
146
1
685.46
-4.22
7.147
6347
135
0
683.036
-5.037
9.191
6477
125
0
680.612
-3.113
5.426
5910
156
-1
676.976
-2.73
4.554
5348
164
0
672.431
Test 2
-0.809
3.003
6147
144
2
609.096
-0.806
2.321
5888
155
0
604.248
-0.265
1.358
5476
165
1
600.006
-0.905
3.764
5865
136
1
594.855
-1.108
4.482
6065
125
1
592.431
Test 3
-3.104
5.883
6582
145
-1
740.612
-3.725
7.186
6634
135
-1
738.491
-4.207
8.217
6687
126
-2
736.37
-2.672
4.512
6104
155
-2
733.643
-2.013
3.546
5661
163
-1
730.613
Test 4
-1.794
4.012
5056
146
3
589.398
-2.2
5.712
5332
134
2
587.58
-2.988
7.121
5552
125
2
585.762
-1.453
3.441
5058
156
1
582.732
-0.872
2.003
4796
165
1
580.914
F.
LMS Flight Test Data
Test 1
Elevator deflection Elevator link force Normal Accel Fuel 9
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angle (°)
(N)
(g)
(kg)
-3.004
-173.084
1.088
669.40
1
Alt (ft)
5200
-3.857
-129.81
1.261
668.18
9
OAT (°C)
3
-4.25
-81.915
1.252
666.06
8
IAS (knots)
161
-5.54
-24.98
1.351
664.85
6
-7.91
190.598
1.991
661.22
Link force, stick released (N)
-
255.
1
Test 2
-0.535
-301.51
1.067
580.00
8
Alt (ft)
6100
-0.777
-268.053
1.139
578.79
6
OAT (°C)
0
-0.989
-247.681
1.224
575.76
6
IAS (knots)
161
-1.771
-175.627
1.474
574.25
1
-3.112
-38.923
1.901
570.00
9
Link force, stick released (N)
-
252.
6
Test 3
-1.879
-224.542
1.022
724.85
6
Alt (ft)
5500
-2.963
-169.828
1.125
723.64
4
OAT (°C)
1
-3.704
-115.859
1.305
722.43
2
IAS (knots)
160
-4.445
-29.38
1.538
720.00
8
-6.581
115.364
1.978
718.49
3
Link force, stick released (N)
-
245.
6
Test 4
-1.118
-251.858
1.004
575.15
7
Alt (ft)
5000
-1.485
-227.388
1.05
573.94
5
OAT (°C)
1
-2.395
-176.926
1.258
572.73
3
IAS (knots)
161
-3.134
-91.816
1.543
571.21
8
-4.251
4.161
1.86
570.30
9
Link force, stick released (N)
-261
G.
SHSS Flight Test Data
Config.
Cruise
Datum Speed (kts) 120
10
Fuel (kg)
555
Altitude (ft)
7000
Aileron Deflection Angle (°)
Rudder Deflection Angle (°)
Sideslip Angle (°)
Roll (Bank) Angle (°)
1.057
2.736
3.26
0.291
-0.17
6.679
8.641
1.879
-0.051
9.117
12.122
3.181
-1.531
11.737
15.367
4.081
2.197
-1.003
-1.835
-1.494
2.395
-3.637
-4.791
-2.67
3.342
-5.64
-7.382
-3.318
Config.
U/C down
Datum Speed (kts) 120
Fuel (kg)
540
Altitude (ft)
7000
Aileron Deflection Angle (°)
Rudder Deflection Angle (°)
Sideslip Angle (°)
Roll (Bank) Angle (°)
0.803
2.816
3.644
0.154
-0.126
6.867
9.179
2.802
-0.217
8.553
11.856
3.554
-0.75
10.299
15.209
4.614
1.678
0.197
-0.598
-1.472
2.407
-1.311
-2.467
-2.296
2.75
-3.326
-5.551
-3.84
11