stability and control evaluation of the lancair 360 mkii€¦ · 06.09.2013 · substantially...
TRANSCRIPT
-
Stability and Control Evaluation of
the Lancair 360 MKII
C. Zavatson
9-6-2013, revA
-
Stability and Control Evaluation of the Lancair 360 MKII
2
1 Contents
2 Introduction .......................................................................................................................................... 4
3 Objective and Test Approach ................................................................................................................ 4
4 Test aircraft ........................................................................................................................................... 4
5 Instrumentation .................................................................................................................................... 5
5.1 Airspeed ........................................................................................................................................ 5
5.2 Pressure Altitude ........................................................................................................................... 5
5.3 Angle of Attack/Angle of Side Slip ................................................................................................ 5
5.4 Manifold Pressure ......................................................................................................................... 5
5.5 OAT ................................................................................................................................................ 5
5.6 Elevator Position ........................................................................................................................... 6
5.7 Flap Position .................................................................................................................................. 6
5.8 Aircraft Weight and Center of Gravity .......................................................................................... 6
5.9 Stick Force ..................................................................................................................................... 6
6 CG Locations and Neutral Points........................................................................................................... 6
7 Results ................................................................................................................................................... 9
7.1 Short and Long Period Modes ....................................................................................................... 9
7.2 Stick Force Gradients and Control Effectiveness ........................................................................ 11
8 Handling Qualities ............................................................................................................................... 15
9 Conclusion ........................................................................................................................................... 15
10 Works Cited ......................................................................................................................................... 15
-
Stability and Control Evaluation of the Lancair 360 MKII
3
Table 1, Parameters affected by Configuration Change ............................................................................... 7
Table 2, Period and Damping Ratio .............................................................................................................. 9
Figure 1, Configuration Neutral Points ......................................................................................................... 7
Figure 2, NLF(1)-0215F Section Lift Coefficient, Flaps +10 (Somers, 1981) .................................................. 8
Figure 3, Lift Curve Slopes, Cruise, Landing Configurations .......................................................................... 8
Figure 4, Short Period Mode, Cruise, FWD CG ............................................................................................ 10
Figure 5, Phugoid, Cruise, FWD CG ............................................................................................................. 10
Figure 6, Phugoid, Landing, AFT CG ............................................................................................................ 11
Figure 7, Stick Force Gradient, Cruise ......................................................................................................... 12
Figure 8, Stick Force Gradient, Landing Configuration ............................................................................... 12
Figure 9, Airspeed Sensitivity to Stick Force ............................................................................................... 13
Figure 10, Elevator Deflection with Stick Force .......................................................................................... 13
Figure 11, Elevator Effectiveness, Landing ................................................................................................. 14
Figure 12, Angle of Attack Sensitivity to Stick Force ................................................................................... 14
-
Stability and Control Evaluation of the Lancair 360 MKII
4
2 Introduction
The Lancair 320/360 is an all composite homebuilt aircraft first introduced in the late
1980’s. It is a two-seat side-by-side layout, low wing design with retractable landing
gear. The design took advantage of the NLF(1)-0215F airfoil and good aerodynamics
to achieve exceptional performance (~1.1 kt/hp). The design went through an
evolutionary process during its production life. Two changes were made that had a
significant impact on handling qualities: Lengthening of the engine mount and
increasing both the area and aspect ratio of the horizontal stabilizer – designated as
MKII. Numerous other changes primarily affected utility and construction of the aircraft
and not necessarily performance or stability and control.
While not designed for aerobatics, the aircraft is known to be very responsive and have
a light feel.
3 Objective and Test Approach
The goal was to evaluate the basic longitudinal stability and control of the Lancair 360
MKII. Examined were the stick free short and long period modes, as well as, speed
stability. Four different configurations were tested: Two CG locations at 20% and 9%
static margin in each of two flight configurations, cruise and landing.
Cruise configuration is defined as: Wide open throttle (WOT), 2480rpm, 7,500 ft
pressure altitude, flaps and landing gear retracted.
Landing configuration is defined as: Full flaps, landing gear extended, 15” manifold
pressure, 90 KIAS.
4 Test aircraft
The aircraft used in this study was a Lancair 360 MKII, N91CZ. The aircraft engine
was a stock Lycoming O-360-A1A rated at 180 hp. External modifications to this aircraft
include changes to the cowling inlets to accept a plenum type cooling system and a
change to the landing gear doors. These modifications have previously shown to
substantially reduce aircraft drag (Zavatson C. J., Cooling Drag, 2007), but were not
expected to significantly affect the stability and control test results.
The aircraft had a two axis autopilot installed. The pitch axis was disabled during
testing. The autopilot was used in the roll axis to maintain wings-level for all test points.
Using the autopilot for lateral control avoided any unintended stick inputs in the pitch
axis.
-
Stability and Control Evaluation of the Lancair 360 MKII
5
5 Instrumentation
An airborne data acquisition system was installed in the aircraft. Data was recorded on
an SD card via a stand-alone DATAQ DI-710 data logger. Engine speed, outside air
temperature, fuel quantity and stick force were manually noted at each test point or
series of test points. All other parameters were recorded at 20 Hz by the data logger.
The following parameters were recorded during test flights:
1. Dynamic Pressure (Airspeed)
2. Static Pressure (Altitude)
3. Angle of Attack
4. Angle of Side Slip
5. Elevator Position
6. Control Stick Input Force
7. Flap Position
8. Outside Air Temperature
9. Manifold Pressure
10. Engine Speed
11. Fuel Quantity
5.1 Airspeed
A +/-1 psi differential pressure transducer, Omega part # PX139-001D4V, was used to
capture dynamic pressure. The unit was calibrated using a manometer. The low range
of the transducer provides excellent resolution to a fraction of a knot.
5.2 Pressure Altitude
Pressure altitude was measured using a 15 psia pressure transducer, Omega part #
PX139-015A4V. This unit was also calibrated via manometer to 14,000’.
5.3 Angle of Attack/Angle of Side Slip
Angle of attack and side slip were measured using an “alpha/beta” probe mounted to
the left wingtip of the aircraft. Non-contact sensors AS5162 by AMS captured angular
position of the vanes to 12-bit resolution.
5.4 Manifold Pressure
Manifold pressure was measured with a 15 psia pressure transducer Omega part #
PX139-015A4V. This transducer was also calibrated via manometer.
5.5 OAT
OAT was captured by a thermo couple (TC) probe behind the rear spar of the
wing. Previous testing identified this location to be very accurate in capturing stagnation
temperature across the entire speed envelope of the aircraft. (Zavatson C. J.,
-
Stability and Control Evaluation of the Lancair 360 MKII
6
Experimental Evalutation of Cruise Flap Deflection on Total Aircraft Drag using the
NLF(1)-0215F, 2013)
5.6 Elevator Position
Elevator control from the pilot control stick to the elevator is via pushrods and rod end
bearings. This results in a very solid and responsive control system with minimal lash
or hysteresis. A 3 inch linear potentiometer, Panasonic PP1045SB, was used to
measure elevator position by following the movements of one of the primary
pushrods.
5.7 Flap Position
The flap is operated via an electric linear actuator. It is capable of continuous travel
between full up and full down positions. The flap can be stopped at any intermediate
position. There are no detents. A 100 mm linear potentiometer, ALPS
RSA0N11S9A0K, was used to measure flap position by mounting an arm to the flap
torque tube.
5.8 Aircraft Weight and Center of Gravity
Prior to each test flight, the weight and CG were verified by weighing the ready-to-fly
aircraft at each wheel position. The pilot was weighed just prior to entering the aircraft.
A calibrated fuel flow transducer and totalizer tracked fuel burn throughout the flight.
This information is used to determine aircraft weight and CG at each test point.
5.9 Stick Force
Stick force was applied to the control stick using a spring scale.
6 CG Locations and Neutral Points
Prior testing and analysis has confirmed the stick fixed neutral point in cruise to be 0.46.
(Zavatson C. J., 2013) The same analytical model was used to determine the center of
gravity locations for the static margins to be used for this evaluation, 0.20 and 0.09.
The corresponding CG positions are 28.9” and 33.4” aft of the firewall. The aft CG
location was achieved by use of sand bags secured in the rear of the baggage
compartment behind the pilot/passengers seats.
Flight test data verified the stick fixed neutral of point 0.47 in the landing configuration.
Figure 1 shows the neutral point derivation for both cruise and landing configurations
from test data. The neutral point moved rearward approximately 0.5” in the landing
configuration.
The lift curve slope decreases with flap deflection. Figure 2 is adapted from NASA TP-
1865 and shows the reduction in the two dimensional Clα curve once flow separation
occurs on the upper surface of the simple flap. Full flap deflection will produce flow
-
Stability and Control Evaluation of the Lancair 360 MKII
7
separation at all angles of attack and therefore a reduction of the lift curve slope for the
flapped region of the wing. The net lift curve slope for both cruise and landing
configurations were extracted from test data and are presented in Figure 3.
Full flap deflection also yields an increase in downwash derivative, dε/dα, which is
effectively balanced by the reduced lift curve slope of the wing. Table 1 summarizes the
key parameters affected by the configuration change from cruise to landing.
Figure 1, Configuration Neutral Points
Table 1, Parameters affected by Configuration Change
-1.59, 33.40
-3.28, 28.90
-2.97, 33.00
-5.69, 29.20
27
29
31
33
35
37
39
-6 -5 -4 -3 -2 -1 0 1
Loca
tio
n A
ft o
f D
atu
m (
in )
dδe /dCL
Flaps Extended, +40 degFlaps Retracted, -7 deg
Ne
utr
al P
oin
t
CLa Cma dԐ/dα hn
Cruise, WOT 0.096 -0.0321 0.40 0.46
Landing, 15" MP 0.068 -0.0250 0.52 0.47
-
Stability and Control Evaluation of the Lancair 360 MKII
8
Figure 2, NLF(1)-0215F Section Lift Coefficient, Flaps +10 (Somers, 1981)
Figure 3, Lift Curve Slopes, Cruise, Landing Configurations
y = 0.0536x
y = 0.1025x
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
-15 -10 -5 0 5 10 15
Lift
Co
effi
cie
nt,
Cl
Angle of Attack, α
+ 10 deg Flaps
y = 0.0955x
y = 0.0679x
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
-5 0 5 10 15
Lift
Co
effi
cie
nt
(CL)
Angle of Attack (deg)
AFT CG-Lndg ConfigAFT CG-Cruise Config
-
Stability and Control Evaluation of the Lancair 360 MKII
9
7 Results
7.1 Short and Long Period Modes
Dynamic response of both the short and long period modes were measured in all four
aircraft configurations. Table 2 summarizes the period and damping ratios for all
configurations. For all short period tests, doublet pulses were input by the pilot both in
push-pull and pull-push directions. Angle of attack was used to evaluate the period and
damping ratio. Only a single cycle is obtained before the amplitude of the disturbance
drops into the noise level of the signal. (Figure 4)
Airspeed was used to evaluate period and damping ratio for the long period or phugoid.
In the cruise configuration a pitch up to roughly a 30 knot speed delta was used. This
provided a reasonable margin to Vne on the first descending cycle. In the landing
configuration, speeds were bounded by the maximum full flap extension speed of 100
KIAS and stall speed of 61 KIAS. A pitch up to a 10 knot airspeed reduction was used
to initiate the long period mode in the landing configuration.
All long period, as well as, short period tests exhibited stable behavior. The aft CG
increased the duration of the short period mode for both landing and cruise
configurations. In the landing configuration, the long period was nearly half of that in
cruise, 30/32 vs. 56 seconds. Damping ratios were only minimally affected by the
configuration changes. In the landing configuration, the short period was slightly more
damped than in cruise with forward CG while the phugoid was slightly more damped
with an aft CG. The results show positive dynamic stability in all configurations tested.
Representative short and long period responses are shown in Figure 4 through Figure
6. Figure 4 is the short period response for the forward CG in cruise. The first two
(large) peaks are driven by the doublet input. The next two peaks are the stick free
response of the aircraft. Note that airspeed remains unchanged throughout the event.
Figure 5 shows the long period response for the cruise condition with forward CG and
Figure 6 shows the long period response in the landing configuration with the aft CG.
Table 2, Period and Damping Ratio
Period Periodsec sec
FWD CG 0.9 0.35 56 0.15
AFT CG 1.3 0.50 56 0.10
Short Period Phugoid
Cruise Confguration
ζ ζ Period Periodsec sec
FWD CG 1.8 0.44 30 0.15
AFT CG 4.1 0.50 32 0.14
ζ ζ
Short Period Phugoid
Landing Configuration
-
Stability and Control Evaluation of the Lancair 360 MKII
10
Figure 4, Short Period Mode, Cruise, FWD CG
Figure 5, Phugoid, Cruise, FWD CG
180
182
184
186
188
190
192
194
196
198
200
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
870 871 872 873 874 875 876 877
Air
spe
ed
(K
IAS)
AO
A(d
eg)
Time (sec)
AOA
Airspeed
150
160
170
180
190
200
210
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
715 765 815 865 915
Air
spe
ed
(K
IAS)
AO
A (
de
g)
Time (sec)
AOA
Airspeed
-
Stability and Control Evaluation of the Lancair 360 MKII
11
Figure 6, Phugoid, Landing, AFT CG
7.2 Stick Force Gradients and Control Effectiveness
In each of the four configurations, the airspeed deviation from trim speed for a given
stick force input was recorded. The forward CG position was tested through a range of
+/-500g (+/- 1.1 lb). The aft CG test was limited to +/-250g (0.55 lb) since the aircraft is
more responsive with the aft CG position. Airspeed, elevator position and angle of
attack were examined as a function of stick force, as well as, the relationship between
elevator deflection and angle of attack.
Figure 7 and Figure 8 show the stick force gradients for the cruise and landing
configurations respectively. In the cruise condition, the curves are nearly linear over the
speed range tested. Figure 9 shows all four configurations together. Figure 11 shows
elevator effectiveness or angle of attack for a given elevator input. Control effectiveness
increases with the rearward CG movement.
In the landing configuration, the pitch response per unit force increases as airspeed
reduces. The forward CG position produced a second order increase in angle of attack
while the aft CG position produces a third order increase in angle of attack with respect
to stick force (Figure 12). The increase is smooth through to stall speed and stability
remains positive throughout. In the forward CG configuration, approximately 1 lb of
stick force was required to reach the stall speed of 61 KIAS from a stabilized 90 KIAS.
70
75
80
85
90
95
100
-4
-2
0
2
4
6
8
10
2000 2010 2020 2030 2040 2050 2060 2070
Air
spe
ed
(K
IAS)
AO
A(d
eg)
Time(sec)
AOA
Airspeed
-
Stability and Control Evaluation of the Lancair 360 MKII
12
With the aft CG, 0.5 lbs of force was required to reach stall speed – half that of the
forward CG.
Total elevator (and stick movement) is very small in cruise, spanning no more than 0.5
degrees (Figure 10). These small deflections require minimal lash in the control
system. In the landing configurations elevator movement is larger for the same force
input, spanning nearly 3 degrees.
Figure 7, Stick Force Gradient, Cruise
Figure 8, Stick Force Gradient, Landing Configuration
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
150 160 170 180 190 200 210 220
Stic
k Fo
rce
(lb
), P
ull
= P
os
Airspeed (KIAS)
FWD CG- Cruise Config
AFT CG, Cruise Config
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
60 70 80 90 100 110
Stic
k Fo
rce
(lb
), P
ull
= P
os
Airspeed (KIAS)
FWD CG- Lndg Config
AFT CG, Lndg Config
-
Stability and Control Evaluation of the Lancair 360 MKII
13
Figure 9, Airspeed Sensitivity to Stick Force
Figure 10, Elevator Deflection with Stick Force
50
70
90
110
130
150
170
190
210
230
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
Air
spe
ed
(K
IAS)
Stick Force (lb), pos=pull
FWD CG-Lndg Config
FWD CG-Cruise Config
AFT CG-Lndg Config
AFT CG-Cruise Config
-7
-6
-5
-4
-3
-2
-1
0
1
2
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Elev
ato
r D
efle
ctio
n (
de
g), T
E D
N =
Po
s
Stick Force (lb), pull = pos
FWD-Landing Config
FWD-Cruise Config
AFT-Lndg Config
AFT-Cruise Config
-
Stability and Control Evaluation of the Lancair 360 MKII
14
Figure 11, Elevator Effectiveness, Landing
Figure 12, Angle of Attack Sensitivity to Stick Force
y = -3.15x - 11.78
y = -7.44x - 4.99
-7
-2
3
8
13
18
-8 -6 -4 -2 0 2
An
gle
of
Att
ack
(de
g)
Elevator Deflection (deg)
FWG CG-Lndg ConfigAFT CG-Lndg Config
-4
-2
0
2
4
6
8
10
12
14
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
AO
A (
de
g)
Stick Force (lb), pos=pull
FWD CG-Lndg Config
FWD CG-Cruise Config
AFT CG-Lndg Config
AFT CG-Cruise Config
-
Stability and Control Evaluation of the Lancair 360 MKII
15
8 Handling Qualities
The pilot is an integral part of the aircraft flight control system and one with great
variability in terms of training, skill and proficiency. The FAA is rather hands-off in
setting quantitative standards for acceptable pitch sensitivity of GA aircraft and even
less so in the experimental arena. From FAR-23: “any substantial speed change results in
a stick force clearly perceptible to the pilot.” This leaves room for interpretation, but it also
provides the freedom to increase or reduce stability and handling qualities according to
the mission at hand. High stick force gradients are a guard against inattention,
distraction or inadvertently bumping the control stick (turbulence). Higher stick force
gradients are also a guard against pilot induced oscillation (PIO). Studies have
suggested ranges for stick force gradients suitable for GA. In addition, correlation
between low stick force gradients and accident rates have been shown (Bromfield,
2012). Nonetheless, sub-categories of GA will desire lighter than average stick forces
gradients, aerobatics for example. Light stick force gradients do however require a
control system with low friction, low break-out forces (stiction) and low hysteresis. The
Lancair 360 control system possesses these required attributes.
9 Conclusion
The aircraft exhibited positive static and dynamic stability in every configuration and in
every flight condition tested. Control effectiveness was inversely proportional to static
margin and no discontinuities or other undesirable characteristics were observed. Stick
force gradients were light with a very predictable and consistent response.
10 Works Cited
Bromfield, M. A. (2012). Criteria for Acceptable Stick Force Gradients of a Light Aeroplane. Brunnel
University.
Somers, D. M. (1981). Design an Experimetnal Results for a Falpped Natural-Laminar-Flow Airfoil for
General Aviation Applications. NASA Technical Paper 1865.
Zavatson, C. J. (2007). Cooling Drag. Sport Aviation.
Zavatson, C. J. (2013). Experimental Evalutation of Cruise Flap Deflection on Total Aircraft Drag using the
NLF(1)-0215F.
Zavatson, C. J. (2013). Longitundinal Static Stability of the Lancair 360.