Project Overview
Flight Handling Qualities Assessment for
Bo-105 Helicopter
Author: Shamaz Khan, Supervisor: Prof G. Padfield
Flight Science and Technology Lab (FS&T), University of Liverpool
Abstract
The concept of Handling Qualities arose as the product of both the early aircraft design and subsequent
augmentation systems. In the early stages of design, the configuration will form the base of the aircraft stability
and manoeuvrability. The aim of the project was to assess the feasibility of using a Bo105 aircraft for AntiSubmarine Warfare (ASW) missions. This has been conducted by first assessing the capabilities of the ‘bare
airframe’ Bo105 and then assessing the feasibility of upgrading the aircraft to reduce pilot workload and
increase safety during missions. Offline analysis was carried out on the Bo105 model using ART FLIGHTLAB.
The data from the offline tests were analysed and Mission Task Elements (MTEs) were designed in order to
critically assess the handling qualities of the Bo105 for ASW missions. In order to bring consistency to this
subjective analysis, performance standards such as ADS 33 for military rotorcraft have been developed and are
required to be adhered to for airworthiness certification.
Introduction
The aim of the project was to assess the
feasibility of using a Bo105 aircraft for AntiSubmarine Warfare (ASW) missions. This has
been conducted by first assessing the
capabilities of the ‘bare airframe’ Bo105 and
then assessing the feasibility of upgrading the
aircraft to reduce pilot workload and increase
safety during missions. The Bo 105 is a light
utility helicopter system recognized around the
globe for its versatility, performance and
safety record. The helicopter has served, and
continues to do so, in a military and civilian
capacity in nations throughout the world. This
report details initial offline analysis and flight
test results of the ‘bare airframe’ Bo105.
Offline analysis was carried out on the Bo105
model using ART FLIGHTLAB. The data
from the offline tests were analysed and
Mission Task Elements (MTEs) were designed
in order to critically assess the handling
qualities of the Bo105 for ASW missions. The
MTEs were precision hover, emergency pullup, turn to target, decelerating approach and
deck landing. ADS-33 criterion was used for
the MTEs. After the flight test, the predicted
HQRs were compared with pilot assigned
HQRs, based upon the Cooper-Harper scale.
DIPES scale was also used to measure the
pilot workload during the deck landing
manoeuvre.
The predicted and pilot assigned handling
qualities were found to be similar for most
MTEs. The Bo105 consistently exhibited
Handling Qualities Level (HQL) 3 (based on
ADS-33 definitions/boundaries). The handling
qualities of the ‘bare airframe’ were poor, with
large amounts of inter-axis cross coupling and
issue regarding sensitivity of the control
system. The simulation fidelity during the
flight test caused problems for the test pilot
with false motion cues and inaccurate visual
cues.
After the offline and online analysis, it has
been found that the Bo105 ‘bare airframe’ is
not suitable for ASW missions. Modifications
need to be carried out to the helicopter’s
1
control system in order to comply with ADS33 standards. Currently, the Bo105 has a rate
command system, and in order for it to
complete missions in Degraded Visual
Environments (DVE), the control system
needs to be upgraded. Upgrades should
incorporate Translational Rate Command
(TRC), Position Hold (PH), Rate Command
Directional Hold (RCDH) and Rate Command
Height Hold (RCHH) systems. Other upgrades
recommended include feedback control to
provide stability, and a Hover-Hold system to
significantly reduce pilot workload.
Description of Test Aircraft and Mission
profile
When introduced in 1970, the helicopter
(Figure 1) incorporated “bold innovations”,
including a hingeless rotor system, plastic
blades and twin turbines (Flight International,
1978). It was designed to be an all round
helicopter, for every situation. To enhance its
capabilities, MBB designed over 40 accessory
kits (floats, winches, searchlights) specifically
for the helicopter. Due to fluctuation in the
German economy during production of the
MBB Bo105, the original retail price is
difficult to ‘pinpoint’.
However, this is
estimated as originally DB1.25 Million
(£320,000 in 1978 (Flight International, 1978),
£2,010,900 in 2008 RPI, £3,153,965 in 2008
AVE (Measuring Worth, 2009).
again maintained the stability of the rotor
system during flight, where articulated
systems may cause problems. Following the
successes in both the civilian and military
situations, the Bo105 was proven to have all
round capabilities. It then became “The Multipurpose” helicopter. For use on oil rigs, the
size of the helicopter was important (to ensure
safety in landing). The rotor also allows
‘touchdown’ to be made almost anywhere.
The landing gear is also the strongest of all
helicopters (in its class), beneficial to landings
in ‘rough’ seas on a heaving landing deck.
(Manchester, 2007). The cost of the Bo105
aircraft is significantly less than the cost of
other ASW helicopters, which can cost
upwards of $56 million (AW-101 Merlin).
It would therefore be of significant
economical advantage if the Bo105 aircraft
could be upgraded to perform ASW
missions. The Bo105, with its hingeless rotor
and size, provides agility to surpass the larger
traditional ASW aircraft. However, systems
may need to be incorporated into the aircraft to
rival those available to the military ASW
aircraft.
Operational Flight Envelope
Figure 2 shows the Ship Helicopter Operating
Limit (SHOL) envelope provided for use in
the ASW mission. The figure is taken from
the point of view of the ship, heading at 0°.
From 0-60° the wind speed is 50kts, between
60 and 90° the wind speed is 30kts, and
between 90 and 180° the wind speed is 20kts.
The limits given by the SHOL define the safe
operating conditions for the helicopter during
Ship-Helicopter operations.
Figure 1: Bo-105 Helicopter
With the heavy hingeless rotor, the helicopter
was tolerant to rough weather conditions. This
2
140kts. This performance is expected at a
cruise height greater than 250ft. In order for
safe operations, the Torque margin within
normal operating conditions is specified as
10%. The primary choice of frigate for the
proposed ASW missions would be a ship
similar to a Type-23 frigate, as operated by the
Royal Navy (Figure 3).
Figure 2: SHOL for ASW mission
An important consideration with the SHOL
limits involves the boundaries between the
different levels of wind speed. As shown in
Figure 3.5, the operating limit changes from
50 knots to 30 knots. Therefore, the tolerance
of the task becomes an issue. If the aircraft
changes heading by ± 5 degrees and is
operating at 58˚, it will be outside of safe
operating limits in a wind of 50kts. However,
if the tolerance of heading is ± 2˚, it will be
within safe operating limits in a wind on 50kts.
With this in mind, the operational envelope of
the aircraft within the SHOL will increase with
heading tolerance. In many situations,
considered less common (50kt winds), the
handling qualities required for safe flight may
degrade to Level 2. In these situations, it is
reasonable to assume the pilot will be able to
deal with moderate handling deficiencies.
When the aircraft is flying within this
envelope, control margins should be 10%.
This means when the pilot is making
inputs into the system, there should be
10% of the control range remaining. If the
pilot needs to correct the aircraft’s position
because of a gust, or change in wind they
would need that extra travel (margin) to
allow them to achieve this. For example,
if the maximum range of the cyclic
longitudinal
stick
is
10
inches,
longitudinally the pilot must only use ±4
inches of travel for safe operating limits,
giving the desired 10% margin.
Operational requirements for the proposed
ASW missions require a cruise speed of
Figure 3: Type-23 Frigate (Armada de Chile, 2009)
The task for Bo105 is to perform missions for
ASW (Anti Submarine Warfare). During
maritime operations, a number of acoustic
sensors are used to detect submarines. The
helicopter is required to take-off quickly from
a frigate out at sea and rapidly approach a
designated ‘target’. Upon arrival, the Bo105
must lower a sonar device below the water,
whilst hovering at low altitude, to ‘pinpoint’
the location of the submarine. Upon
completion of this task the helicopter must
then return to the mother frigate, and land on
the rear deck. The procedure for performing
this task involves a hover to the side of the
ship followed by sidestep and vertical
manoeuvre.
Mission Task Elements
The Hover MTE was designed in order to
investigate the capabilities of the helicopter for
precision station holding. This was identified
as a critical part of an ASW mission whilst
dipping a sonar in order to search/find
submarines. The manoeuvre was to be
performed using a ‘hover’ board, similar to the
board used for defined ADS-33 MTEs, with
the arrangement shown in Figure 4.
The vertical pull-up MTE was designed in
order to assess the helicopter’s response to an
aggressive collective input. This was likened
to the situation where the pilot would be
3
required to aggressively ‘pull out’ of a
manoeuvre in an emergency or unexpected
situation. Relating the task to the mission, the
most likely event of this occurring is during a
deck landing in adverse weather conditions.
The manoeuvre was to be performed using the
hover board arrangement shown in Figure 5.
Other defined manoeuvres were Turn to target,
Decelerating Approach and Deck Landing.
Figure 4: Arrangement for Hover MTE (AVSCOM, 2000)
initial understanding into the dynamic
response of the aircraft. It was also conducted
first in order to come to initial conclusions on
expected pilot workload through the speed
range of the Bo105. It was important that the
model was correctly linearised from trim for
the stability analysis.
With the model
linearised, the aircraft states and ‘modes of
motion’ could be analysed using Eigen Value
analysis. Solutions of the states were plotted
in the S-plane, to show the location of the
stability modes. ADS-33 defines boundaries
for the Phugoid, Dutch Roll and Spiral
stability modes based on experience and
testing.
The boundaries give predicted
handling qualities levels, which can be
referenced to actual flight test ratings awarded.
Figure 6 shows the root locus of the isolated
Phugoid mode with respect to forward speed
(only shown for 1 of the 2 repeated roots). The
Phugoid of the Bo105 was found to be
unstable from 0 to 120 knots. Interestingly
however, it was suggested that the handling
qualities concerning the longitudinal stability
of the Bo105 would improve in the region of
low speed forward flight.
Figure 6: Root Locus of Phugoid of Bo105 with respect
to forward speed
Figure 5: Arrangement for Emergency Pull-up MTE
[adapted from (AVSCOM, 2000)]
Bare Airframe Stability Assessment
The Quantification of the stability of the
aircraft was conducted prior to any other
testing of the Bo105 ‘bare airframe’ to gain
In terms of ADS-33 boundaries and predicted
handling qualities levels for the lateral
stability, problems were identified for hover
and low speed flight, where the Dutch roll
mode was found to be within Level 2
boundaries.
This was due to the low
frequency (0.5 rad/s) and low damping (0.4) of
4
the mode. Unlike the Phugoid mode, the
Dutch roll is stable for the speed range of the
Bo105. This means that, if the pilot was to
make a perturbation in the lateral axis of the
Bo105, eventually the oscillatory contribution
to lateral motion would decay and, assuming
other axis remain fixed, the helicopter would
return to trim.
However, looking at the results obtained,
(Figure 7) it was believed that the low
frequency of the mode in Hover would cause
the pilot significant workload due to slow
oscillations. This was also believed to be of
major importance during tasks which required
stabilised precision, such as the hover MTE
defined
Figure 7: Root Locus of Dutch Roll mode with respect to
forward flight speed
It was found that both pitch quickness and roll
quickness in forward flight fell within Level 1
ADS-33 Target Acquisition and Tracking
boundaries.
These were found to be
significantly ‘quicker’ than required. At hover
and low speeds, the roll quickness (Figure 8)
was found to be within Level 1 for Target
Acquisition and Tracking ADS-33 boundaries.
Therefore, at this stage with no upgrades to the
Bo105, the roll and pitch quickness’ were
Level 1 for all ADS-33 requirements.
Figure 8: Roll Quickness for Bo105 ‘bare airframe’
against ADS-33 Target Acquisition and Tracking
In order to find the quickness’ of all axes in
offline analysis, step control inputs were
made, varying the time of the step input. The
Bo105 uses a rate command system. When a
control input is made, a rate in the primary
axis causes the attitude of the axis to alter.
When the input is ‘released’ and the controls
return to the original positions, the rate starts
to reduce and will return to zero as the
helicopter returns to a trim position (if the
helicopter has the necessary stability).
Large yaw rates and heading changes can be
achieved with pedal deflections. Due to this, it
was recognised that if, when the control input
was ‘released’ and returned zero rate quickly,
quickness would be significantly increased. In
order to quantify this quickness, doublet
control inputs were made to add ‘synthetic
damping’ to the axis. Results for both step and
doublet inputs for yaw quickness during hover
are shown in Figure 9. As expected, the yaw
quickness increased to Level 1 with the use of
doublet inputs. This suggests that the Bo105
has capabilities for high yaw quickness and, in
order to achieve this, damping must be
increased within the axis. For the response for
step inputs, the yaw quickness was found to be
within Level 2 for all test points.
5
However, for moderate aggression tasks, the
control power was found to be Level 1 at
higher speeds and Level 2 at lower speeds.
For aggressive manoeuvres, the low speeds (0,
10, 20, 30 and 40 kts) were found to be Level
3 according to ADS-33 criteria
Figure 9: Yaw Quickness of Bo105 ‘bare airframe’
plotted against ADS-33 Target Acquisition and Tracking
Tasks
With an increase of forward speed, the yaw
quickness was found to improve as a result of
increased damping. Figure 10 shows the
results for computation with a step input and
doublet input at 40kts
Figure 11: Large Amplitude Roll rate for Bo105 at hover
and low speeds
However, for roll control power at high
speeds, this was not found to be the case.
Results are shown in Figure 4.11. For all
levels of aggressiveness, the high speed roll
control power was found to be within Level 1
boundaries
Figure 10: Yaw Quickness of Bo105 'bare airframe'
plotted against ADS-33 Target Tracking boundaries for
40 kts
The large amplitude roll rate change was
measured for the Bo105 in hover and at low
and high forward speeds. Results for roll
control power for hover/low speed flight are
shown in Figure 11. Results are shown plotted
against criteria defined in ADS-33 for
different levels of aggressiveness.
The
differences in aggressiveness cause differences
in the predicted handling qualities rating
relating to the control power. For limited
aggression manoeuvres, at all low speeds, the
control power was found to be Level 1.
Figure 12: Roll Control Power for the Bo105 at high
speeds
Bandwidth and phase delay are important
parameters for the response of aircraft control
systems. The two parameters are related to the
transfer function between the desired control
input and the vehicle response. The bandwidth
of a rotorcraft is the frequency beyond which
closed loop stability is threatened. It is defined
as the highest frequency at which the pilot can
double his gain or allow a 135 degree phase
6
Target Acquisition & Tracking
0.4
Yaw Rate for Step Input at 0 kts
0.03
0.025
0.02
Yaw Rate rad/sec
lag between control input and aircraft attitude
response without loss of stability. If the gain
bandwidth is sufficiently lower than the phase
bandwidth the aircraft is more prone to pilot
induced oscillations (PIOs).
0.015
0.01
0.005
0
0.35
LEVEL 3
-0.005
0.3
-0.01
0
1
2
3
LEVEL 2
4
5
Simulation Time (s)
6
7
8
9
Fig 14 : Yaw rate following a Step input in Collective
0.2
LEVEL 1

p
(sec)
0.25
0.15
0.05
0
0
0.5
1
1.5
2

BW 
2.5
3
3.5
4
4.5
5
(rad/sec)
Figure 13: Yaw control bandwidth for Bo105 'bare
airframe' plotted against ADS-33 Target Acquisition
and Tracking Boundaries
It was found for all speeds analysed that the
phase delay was approximately zero.
Bandwidth was found to fall within Level 3
(Figure 13) and Level 2 at 20 knots for target
acquisition and tracking and all other MTE’s
respectively. The pitch bandwidth for hover
was found to be within Level 1 for both target
and tracking along with all other MTEs. This
was also the case for roll bandwidth at low and
high speed. This allows for high frequency
inputs in these axes without concern for
instability in the system.
All single rotor ‘bare airframe’ helicopters
using a tail rotor will be subject to yaw due to
an input into collective pitch. For an anticlockwise rotor (as for the Bo105), the applied
Torque acts in the clockwise direction. This
forces the helicopter to yaw to the right. The
yaw response for an abrupt step input was
examined for range of different speeds,
between 0 and 120 knots. It was found during
the tests that changes to pitch and roll attitudes
remained small and there were no
objectionable yaw oscillations following an
input in collective (step or ramp inputs in both
directions).
Figures 14 and 15 show the response to
collective input in hover. ADS-33 defines a
limit of maximum yaw rate excursions of 5°/s
following an abrupt collective input. It also
defines more detailed limits on the ratio of
yaw rate to vertical velocity.
Climb Rate for Step Input at 0 kts
0.2
0.15
0.1
Climb Rate (ft/s)
0 Kts
10 Kts
20 Kts
30 Kts
40 Kts
0.1
0.05
0
-0.05
-0.1
-0.15
0
1
2
3
4
5
Simulation Time (s)
6
7
8
9
Fig 15 : Climb Rate following a Step input in Collective
Overall Predicted Assessment
With offline analysis conducted before Online
piloted assessment, results could be used
assign ‘Predicted’ Handling Qualities Levels
for the MTEs. The offline analysis allowed
deficiencies to be determined by using ADS33 requirements. Each MTE designed has a
different set of criteria. These criteria include
tolerances, aggressiveness and flight mode.
Through
countless
flight
tests
and
investigations, ADS-33 criteria have been
developed for different ‘types’ of task.
Hover
7
Handling Qualities levels for the Hover MTE
are shown in Figures 16 and 17. The task was
defined as a low aggression task. This led to
HQL 1 for the control power within the lateral
and longitudinal axes. In hover, the stability
of the aircraft was found to be Level’s 2 and 3
for Lateral and Longitudinal axes respectively.
These HQLs were due to the low frequency
Dutch roll mode and unstable Phugoid. As
shown in Figure 16, the bandwidth of the
lateral axis (yaw) was found to be HQL 3,
suggesting poor handling qualities for the
precision hover task. Quickness’ for lateral
and longitudinal axes were found to be Level 2
and 1 respectively. Overall, due to deficiencies
for small amplitude high-frequency lateral
control inputs and small amplitude low
frequency open loop response, the task
received a Predicted Handling Qualities Level
3.
Figure 17: Hover MTE Predicted H.Q. Longitudinal Axis
Colour
Predicted
HQL
offline analysis)
(from
HQL 3 – Major Deficiencies
HQL 2 – Deficiencies
HQL
1
Deficiencies
–
Negligible
Emergency Procedure
Figure 16: Hover MTE Predicted H.Q. Lateral Axis
Handling Qualities Levels for Emergency
Pull-up are shown in Figures 18 and 19. The
manoeuvre was designated as high aggression.
This was due it being an assessment of a
possible ‘emergency situation’. The task also
required the pilot to stabilise at the end,
making the requirements for the task both high
frequency/low amplitude inputs and low
frequency/high amplitude inputs. The low
stability of Levels 2 and 3 for lateral and
longitudinal motion respectively was due to
the poor Dutch roll and Phugoid
characteristics at low speeds. For the
quickness, laterally the roll and yaw were
found to be Levels 1 and 2 respectively.
Overall, the aircraft was found to have severe
deficiencies in all different aspects of the
testing, with the exception of the quickness
(found to be Level 2 in the lateral axis).
Because of this, the MTE was assigned
Predicted Handling Qualities Level 3.
8
lateral axis was shown to have a number of
deficiencies for the high aggression task. Roll
control power was found to be Level 3 for
high aggression manoeuvres. Although roll
quickness was found to be Level 1, yaw
quickness was found to be Level 2 during
hover. Again, yaw bandwidth was found to
represent Level 3 handling qualities,
suggesting the possibility for problems during
the stabilisation of the manoeuvre. As a result,
and the presence of Level 3 findings in both
the lateral and longitudinal axes, the MTE was
assigned Predicted Handling Qualities Level
3
Figure 18: Emergency Pull-up MTE Predicted H.Q.
Lateral Axis
Figure 20: Turn to Target MTE Predicted H.Q. Lateral
Axis
Figure 19: Emergency Pull-up MTE Predicted H.Q.
Longitudinal Axis
Turn To Target
Predicted Handling Qualities Levels from
offline analysis are shown in Figures 20 and
21. The manoeuvre was designated as high
aggression. Not only was the task high
aggression but it also required stabilisation at
the end by the pilot. This combines both low
frequency large amplitude and high frequency
low small amplitude control inputs.
Deficiencies in the longitudinal axis were
found to result from the open loop stability
and the unstable Phugoid mode. However, the
Figure 21: Turn to Target MTE Predicted H.Q.
Longitudinal Axis
9
Piloted Assessments and Results
ADS-33
defines
Degraded
Visual
Environments (DVE) – Figure 21 in terms
of ‘Useable Cue Environment’ (UCE).
Pilots control aircraft by using visual aids
available
to
them
through
the
environment.
For Good Visual
Environments (GVE), the pilot will be able
to judge their performance by using
exterior cues. However, when flying in
DVE, the horizon may not be visible (i.e.
due to fog). In this case, their ‘cues’ are
degraded and, they must judge their
performance using alternative methods
(i.e. avionics). This becomes a major issue
when performance is desired with relation
to the environment.
If the pilot has no visual cues, they will
have to rely on other cues such as motion
cues. The UCE must be determined by
pilots before attempting actual Mission
Task Elements (MTEs) for each
environment. This is done by performing
various low-speed/hover MTEs (Padfield,
1995).
It uses the combination of
translational rate Visual Cue Ratings (VCR)
and Attitude Visual Cue Ratings (VCR).
For the purpose of the MTEs designed
incorporating DVE, an estimated UCE
(based upon experience) was assigned by
the test pilot. This gave an appreciation of
the environment and how restricted the
‘pilot cueing environment’ was due to the
DVE. The three MTEs incorporating DVE
were Precision Hover, Emergency Pull-up
and Deck Landing. For these tasks, based
on the environment, the pilot awarded
Translational and Attitude VCRs. These
were plotted using Figure 21, and UCE 3
(estimate) was found for all tests
incorporating DVE.
This rating is
important when upgrading the helicopter.
ADS-33 defines control systems which
must be implemented for operations in
different UCEs.
Results from the Precision Hover and
Deck Landing test are only shown here.
Both missions were performed under GVE
and DVE conditions.
Precision Hover
The test pilot completed both a test and
evaluation run of the Precision Hover MTE.
This task was performed in DVE to simulate
operations at sea, with limited pilot cueing.
Fog was used to simulate the conditions, with
the visibility set at 100 m. The main problem
encountered by the pilot during the task was
the lack of longitudinal and lateral cues to
judge his location. The unstable longitudinal
motion of the aircraft and the low frequency
lateral oscillations made it necessary to apply
control inputs to stabilise the motion
constantly. The control inputs made from the
hover trim positions are shown in Figure 22.
Constantly pressing the trim tab button recentred the control stick, reducing the physical
workload of the pilot by eliminating any
control stick forces applied.
Figure 21: Useable Cue Environment Definition
(AVSCOM, 2000)
10



Figure 22: Control Deflections from Trim
during Hover MTE
Also shown in Figure 23 are the relatively
small deflections applied in the cyclic control
stick. The pilot commented that the responses
were sharp, leading to over-control of the
aircraft. The longitudinal drift was found to be
greater than the lateral drift which was
suggested to be the case by the pilot during the
test. However, the pilot was able to remain
within the required height tolerances during
the complete manoeuvre. Due to the inability
to maintain position within tolerances and due
to the frequency of control inputs required, the
pilot awarded a HQR 7 for the Precision
Hover Task.
Figure 22: Position of Bo105 during Hover MTE
Deck Landing Manoeuvre
Three different situations were tested;
Airwake of 20 Kts Green-45, ship
foward speed of 12 Kts, Sea State 6,
GVE
No Airwake, No ship motion, No Sea
State, GVE
Airwake of 20 Kts Green-45, ship
forward speed of 12 Kts, Sea State 6,
DVE (100 m visibility)
These three tests were conducted with time not
a factor (pilot attempt in his own time).
Figures 23 and 24 shows the resulting
helicopter motion during all three tasks. The
graphs show the end of the manoeuvre, when
the pilot was required to perform a sidestep to
a position above the deck and then perform a
vertical manoeuvre to land on the deck.
The pilot commented that, whilst alongside the
ship the task required him to make large,
frequent and erratic control inputs ((as shown
in the trace). Not only did this lead to
uncomfortable motion within the simulator, it
led to inaccuracies within the task. The pilot
also commented that, due to the high workload
involved in simply landing on the deck, he had
insufficient spare capacity to perform the
landing within the required tolerances.
However, when hovering above the ship, the
pilot commented that workload reduced, with
the airwake having a less significant affect on
task performance.
The motion of the aircraft within the air wake
may have been disorientating for the pilot,
leading to the inaccurate control inputs. For
the task the pilot awarded both a CooperHarper Rating and a DIPES rating. The pilot
has during his career performed deck landing
trials and, as a result his experience would
differ from the average test pilot. Therefore,
when awarding a DIPES rating, the pilot gave
both his rating and that expected for an
‘average squadron pilot’.
Due to the high intolerable workload and the
opinion that the aircraft was at the limit of
controllability, the pilot awarded a HQR 7.
He awarded a DIPES rating of 4
11
(P,T,R,D,Y,A,V,H,F,L) and a DIPES of 4.5
for the ‘average’ test pilot.
The opinion of the pilot was of complete
contrast once the airwake was disabled and the
ship motion was stopped. Following the need
to make large control inputs to stabilise, the
pilot could not make gentle ‘calculated’
control inputs. The resulting motion is shown
in Figure 23 and Figure 24.
Figure 23: Heave Axis Response and Collective Input
during all Deck Landing MTEs
The final deck landing MTE was conducted in
a Degraded Visual Environment with Sea
State 6. The DVE was so severe that, the only
horizontal reference available to the pilot was
the ship.
similar for the Air wake and no air wake tasks.
However, inputs made during DVE do not
reflect these. An example is the large drop in
collective applied by the pilot, shown in
Figure 24. This may be an indication that the
ship motion made the pilot believe that he was
too high during the task.
Large reduction in collective could cause the
pilot to crash the aircraft into the ship or even
into the turbulent seas. From the offline
analysis of the Bo105, it has been found that
collective to yaw coupling is an issue. With
this in mind, when performing an aggressive
reduction in collective, the aircraft could yaw
significantly, disorientating the pilot in DVE
and, again causing catastrophic results. With
the cueing very poor, workload very high and
the pilot unsure of his position, HQR 9 was
awarded. He pilot felt he had no choice due to
the significant danger involved in performing
the task. The pilot also suggested that, if the
task had been attempted in 10 seconds, it
would have been practically ‘impossible’ to
achieve and extremely unsafe (would never be
attempted in the real world). The pilot
awarded
a
DIPES
rating
of
5
(P,T,R,D,Y,A,V,H,F,L) suggesting that task
workload was completely unacceptable for
deck operations.
Simulation Limitations
MTEs were performed in HELIFLIGHT-R a
6DoF simulator based at the University of
Liverpool, Flight Science lab (Figure 25).
Figure 24: Lateral Axis Response and Lateral Cyclic
Inputs during All Deck Landing MTEs
As this ship was moving in all axes, the
perceived horizon moved. Comparing output
from the three separate tasks, it can be seen
that the test conducted in DVE was performed
differently by the pilot. Control positions are
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were the differences in control system
configuration use in the simulator and the
actual aircraft. This related to the layout of the
panel, the systems used and the Field of View
during the task. The inputs may not have been
exactly 10 inches for a real Bo 105, as was the
case with the simulator. Lack of ‘chin
windows’ during the simulation restricted the
view, making the FOV less than in the actual
Bo105. This could be seen in the hover task, as
the pilot struggled to hold his position with
respect to the ground.
Overall Assessment (Impact on Role)
Figure 25: ART HELIFLIGHT-R 6DoF simulator
During the flight tests there were several
issues that arose relating to the simulation
fidelity. These problems made it difficult for
the pilot to complete all of the MTE’s, and
may have possibly skewed the data retrieved
from the tests. One of the issues identified was
the pilot cueing during an engine failure.
When the engine failed, the Torque meter
became disconnected from the simulation,
causing inaccurate Torque readings to be
displayed. Along with this, audio changes
were not significant enough to ‘warn’ the pilot
of the failure. The pilot therefore took a
couple of seconds longer than usual to notice
and react to the engine failure, meaning he did
not respond as quickly which could impact the
survivability.
Another problem identified
related to the motion cueing provided. The
motion was not able to ‘keep up’ with the
actual simulation during maximum aggression
manouevers. One particular example of this
was with the turn to target MTE. The yaw rate
applied during the MTE led the motion base to
reach maximum travel. Within the simulation
environment, this caused a sudden change in
rate without the pilot making any control
inputs. Even if the pilot was aware of this, it is
likely that his subconscious would believe
something was wrong and apply a method of
control to ‘fix it’. Another problem found
The yaw due to collective cross-coupling was
one of the major deficiencies identified during
the online and offline analysis. The offline
analysis was conducted only for low speeds, as
defined by ADS-33 standards. ADS-33 sets a
limit of maximum yaw rate excursions of 5
degrees per second following an abrupt
collective input, and also sets more complex
limits on the ratio of yaw rate to vertical
velocity. The offline analysis revealed that the
coupling was in Level 3 during the Emergency
Pull-Up manoeuvre and during hover. This
indicates that the yaw-collective crosscoupling is more severe in hover than in
forward flight and reduces as forward airspeed
increases. The aircraft yaw due to coupling
begins in level 3 during hover and improves
with increasing airspeed, reaching Level 2 at
50 knots upwards. This occurs due to the
decrease of yaw rate response of the aircraft as
the speed increases. This shows that the
aircraft has a very strong yaw coupling during
its tactical operating speed which is usually
less than 40 knots. The reason for the presence
of yaw-collective coupling has already been
discussed earlier in this report. As the
application of a collective causes the pitch of
the main rotor blades to change, this in result
changes the torque. Thus the results show, that
the aircraft has objectionable collective-yaw
coupling for the majority of the proposed
mission. Most of the MTEs designed were
performed at low speed; hence this deficiency
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has a major impact for the mission, and as
such is an area that must be improved.
From the offline analysis, it was revealed that
for Bo 105 the pitch response to collective step
is very strong. This causes the speed to reduce
and the nose of the aircraft to pitch up. In
helicopters, pilot can use a combination of
both collective and cyclic to achieve a
combination of a pitch and flight path angle in
forward flight to suit the mission requirements.
Hence, applying cyclic to minimise the pitch
excursions results in a first order height rate
response, with the estimated parameters
dependant on a cyclic control strategy.
During the offline analysis, large amplitude
roll rate changes were observed particularly in
hover, and for low forward speeds. Since the
control power is task dependant, at low speeds
for limited agility manoeuvres, the achievable
roll rate for Bo 105 was found to be in Level 1
criterion.
However,
for
aggressive
manoeuvres, the achievable roll rate dropped
to Level 3.
The increased hub moment capability of the
hingeless rotor transforms into increased
control sensitivity and damping, and hence
greater responsiveness at the expense of
greater sensitivity to extraneous inputs.
During hover and low speeds, the roll
quickness was found to be within Level 1 for
Target Acquisition and Tracking ADS-33
boundaries. The rate at which the helicopter
returns to the trimmed condition is defined by
the damping in the axis. Both the pitch and
roll axes have high levels of damping.
However, this is not the case for the yaw axis
at low speed where very little damping exists
(due to the relatively small tail surface area).
Large yaw rates and heading changes can be
achieved with pedal deflections. The yaw
quickness increased to Level 1 with the use of
doublet inputs. This suggests that the Bo105
has capabilities for high yaw quickness and, in
order to achieve this, damping must be
increased within the axis.
Bandwidth was found to fall within Level 3
and Level 2 at 20 knots for target acquisition
and tracking and all other MTE’s respectively.
The pitch bandwidth for hover was found to be
within Level 1 for both target and tracking
along with all other MTE’s. This was also the
case for roll bandwidth at low and high speed.
This allows for high frequency inputs in these
axes without concern for instability in the
system.
Conclusions and Recommendations







Through analysis using ADS-33
standards, the Bo105 ‘bare airframe’
has been found to be not suitable for
Anti-Submarine Warfare missions.
The helicopter consistently exhibited
Level 3 performance during the online
and offline analysis.
Deficiencies identified in offline
analysis were found to have an impact
on the workload during the simulated
flight test. From the offline analysis,
the yaw quickness was identified as a
deficiency. During the flight test, the
pilot did not manage to perform the
turn-to-target task to the desired
specifications.
The yaw due to collective cross
coupling effects was found to be
strong for the Bo 105 ‘bare airframe’
The Degraded Visual Environment
(DVE) used for online simulation had
an adverse effect on the outcome of
some of the tasks (Emergency Pull-Up
manoeuvre, Hover, Deck Landing).
There was a certain amount of nonlinearity in the pedal control present in
the Bo 105 model. During the
decelerating approach task, the pilot
used to full right pedal for majority of
the task duration.
During the flight test, it was noticed
that the yaw response was very
sensitive.
During the flight test, the pilot
complained about the over sensitivity
14

of the pitch, roll and yaw response.
Steady state was reached quickly.
Torque response of the Bo 105 was
found to be slow following application
of collective. The pilot found the
heave axis to be the easiest to control
The Bo 105 has oscillatory Dutch Roll
and Phugoid stability modes. The
Dutch
Roll
handling qualities
improved with speed, falling within
Level 1 boundaries for forward flight
above 20kts. The Phugoid was found
to be unstable for the entire speed
range (0-120kts).
Recommendations
It has been found, through the use of online
and offline simulation, that the Bo105 ‘bare
airframe’ is not suitable for Anti-submarine
Warfare missions. Therefore, if the aircraft is
to be used for these missions, various upgrades
must be made to the aircraft. The feasibility of
the upgrades is dependent both on cost and
complexity.
During online simulation, the evaluating test
pilot gave an estimate for the UCE for DVE
tasks as UCE 3. This represents the poorest
possible level of cueing for the pilot and, as a
result requires the largest amount of control
responses to be available to the pilot. Table 1
outlines control response types required for
environments of different UCE.
The requirements suggest that, in order for
successful operations in ASW missions in
DVE, TRC, RCDH, RCHH and PH must be
implemented to the Bo105 control system.
The ‘bare airframe’ Bo105 consists of only a
RC system, currently suitable for operations
involving a UCE 1.
Table 1: Response Types Required for UCEs Outlined by
ADS-33 (ADS-33, year)
UCE
UCE 3
UCE 2
UCE 1
RC
ACAH
RCDH
RCHH
PH
TRC
Response Types in hover/low
speed flight
TRC + RCDH + RCHH + PH
ACAH + RCDH + RCHH + PH
RC
Rate Command
Attitude Command Attitude Hold (roll and
pitch)
Rate Command, Direction Hold (yaw)
Rate Command, Height Hold (heave)
Position Hold (horizontal plane)
Translational Rate Command
The final consideration is to go beyond the
requirements of ADS-33 and incorporate a
Hover-Hold system to significantly reduce
pilot workload during ASW missions. A
Hover-Hold system would allow the pilot to
efficiently hold his station before, during and
after MTEs. For example, the precision hover
task could be completed using the Hover-Hold
system, resulting in very desirable handling
qualities.
Works Cited
Armada de Chile. (2009). Chilean Navy Fleet.
Retrieved 12 1, 2009, from Armada de Chile:
La marina de todos los chilenos:
http://www.armada.cl/prontus_armada/site/
edic/base/port/inicio.html
AVSCOM. (2000). Aeronautical Design
Standard (ADS-33E) - Handling Qualities for
Military Helicopters. US Army AVSCOM.
Flight International. (1978). 11th March 1978.
Flight , 685.
Manchester, E. (2007). Hovering Over the
Artic. verticalmag.com.
Measuring Worth. (2009). Convertion of GBP.
Retrieved 12 1, 2009, from Measuring Worth:
www.measuringworth.com/
15
Padfield, G. (1995). Helicopter Flight
Dynamics. Blackwells.
Acknowledgements
This paper provides the summary of the Flight
Handling Qualities report, to assess and
upgrade the handling qualities of Bo-105
helicopter suitable for Anti-Submarine
warfare. Special thanks to Bo-105 team,
Supervisor Dr Mark White for his support, and
Prof G Padfield for always being there.
This is project overview, not the published
paper.
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