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International Forum on Aeroelasticity and Structural Dynamics
IFASD 2019
9-13 June 2019, Savannah, Georgia, USA
SMALL SCALE FLYING DEMONSTRATION OF
SEMI AEROELASTIC HINGED WING TIPS
Thomas Wilson, James Kirk, John Hobday & Andrea Castrichini
Airbus Operations Ltd, United Kingdom
thomas.wilson@airbus.com
james-graham.kirk@airbus.com
john.hobday@airbus.com
andrea.a.castrichini@airbus.com
Keywords: Aeroelastic, flutter, load alleviation, gusts, manoeuvres, hinged / folding wing tips,
semi aeroelastic hinge, flying demonstrator, flight testing, AlbatrossONE
Abstract: The primary purpose of a hinged wing tip on an airliner aircraft is to allow an
aerodynamically efficient high aspect ratio wing to enter an airport gate of standard dimensions.
There exists a potential opportunity to allow a wing tip to move in flight to alleviate the loads
and achieve a lower wing weight – or enable the wing span to be maximised. This technology
has become known as the “Semi Aeroelastic Hinge”. This paper will present the AlbatrossONE
Semi Aeroelastic Hinge small scale demonstrator aircraft and the results from the wind tunnel
tests and the first flight tests.
1. INTRODUCTION
Folding wings have long been a reality in naval aviation to allow fixed wing aircraft to be stored
in confined spaces on aircraft carriers. The concept of applying the same technology to large
civil aircraft is not new, and now the industry is developing a long range aircraft that will
include a wing span extension of the order of 7m with the objective of achieving a performance
improvement via a reduction in induced drag, but will be able to access the standard 65m gate
thanks to a folding mechanism. However, wing weight increases for such an aircraft can be
expected due to the longer wing, the folding mechanism, and above all the reinforcement of the
existing wing to resist the higher bending loads from the greater span.
It has been recognised that the hinge associated with folding a wing tip on the ground could in
principle also be used in flight for the purpose of load alleviation, thus enabling a wing span
increase and drag improvement with a much lower increase in loads and weight. Moreover
although many possibilities exist for realising a hinged, load alleviating wing tip, the path
favoured by researchers at Airbus is to exploit the key property of an ideal hinge, which it
simply that is does not transmit bending moment [1 & 2]. By combining the free hinge with a
lock and a clutched actuator, an active / passive / adaptive system is envisaged whereby the
wing tip can be released in response to a severe gust or manoeuvre, but then “recovered” to its
planar position afterwards to continue efficient flight. This technology has become known as
the “Semi Aeroelastic Hinge”.
Much theoretical work has been done to understand the basic physics of a freely folding wing tip
[1 & 3-7], including how the orientation of hinge axis – the “flare angle”, see figure 1 – can be
used to avoid flutter [1 & 4] and the levels of load alleviation that appear to be achievable,
approaching 20% in terms of wing root bending moment [1 & 4]. In addition the inherent static
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and dynamic stability of a freely folding wing tip (with a flared hinge), when behaving as a single
degree of freedom, has been verified by wind tunnel tests at the University of Bristol [8].
Figure 1: Definition of the hinge flare angle
The next step was to demonstrate the Semi Aeroelastic Hinge with a small scale flying
demonstrator, known as “AlbatrossONE” which is shown in figure 2. This paper will present
the details of the aircraft and the results from the wind tunnel tests and the first flight tests.
Figure 2: AlbatrossONE, Semi Aeroelastic Hinge Demonstrator
© Airbus Operations Ltd, 2019
© Airbus Operations Ltd, 2019
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2. EXPECTED FINDINGS FROM THE FLYING DEMONSTRATOR
AlbatrossONE is intended to be a basic proof of concept demonstrator for the Semi Aeroelastic
Hinge technology. So although the aircraft is geometrically scaled to represent a possible future
full scale aircraft, it is not dynamically scaled for either handling qualities and/or aeroelasticity
in terms of mass and stiffness properties, nor of course will it fly in the Mach range that airliner
aircraft are designed for. Therefore the aircraft is intended to provide a qualitative rather than a
quantitative demonstration of the various aspects of physical behaviour associated with the semi
aeroelastic hinge concept, including:
Near-linear variation of the symmetric and anti-symmetric wing tip flapping mode
frequencies with airspeed. Figure 3 gives an example of this predicted behaviour for a full
scale A321-like aircraft with wing tip extensions [4].
Figure 3: Frequency versus airspeed for hinge flare angles of 15o, 25o and 35o
Static and dynamic stability of the free wing tip [8].
The increase of the free wing tip fold angle – the “coasting angle” – with aircraft angle of
attack.
Reduction of the wing loads when the wing tip is free to fold. Figure 4 gives an example of
this predicted behaviour for a full scale A321-like aircraft with wing tip extensions [4].
Near immediate reduction in wing loads when the hinge is released, including consequent
aircraft pitch-up response [10]. Moreover the elevator compensation will be demonstrated.
Demonstration of using an actuator to recover the wing tip to its planar position.
Avoidance of separated flow at high aircraft incidence when the wing tip is coasting.
No contact between the wing tips and the ground when the aircraft lands with freely hinged
wing tips [11].
Reduction in roll damping when the wing tips are free to fold. Figure 5 gives an example of
this predicted behaviour for a full scale A321-like aircraft [4].
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Figure 4: Gust and manoeuvre wing loads for fixed (black) versus free (red) hinged wing tip
Figure 5: Steady roll rate ‘bookcase’ simulation for unit aileron deflection for 45m and 50m
wings with fixed and free hinged wing tips, plus a 35m wing without wing tip
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3. AIRCRAFT OBJECTIVES
Although the Semi Aeroelastic Hinge offers the potential to improve the fuel efficiency of an
aircraft there are significant technical challenges posed by allowing a wing tip to flap freely and
the necessity to be able to return the wing tip to a planar position after a gust encounter for
continued efficient flight. Therefore the overall objective is essentially to show that the Semi
Aeroelastric Hinge is a serious proposition based on sound physical principles.
In terms of detailed objectives the AlbatrossONE aircraft is intended to demonstrate that the
wing aspect ratio of an Airbus-like aircraft could be approximately doubled without the usual
detrimental impact on loads and handling qualities thanks to semi aeroelastically hinged wing
tips. This demonstration will cover physical effects described in section 2, and also the main
functions of the system including the in-flight “release” and “recovery” of the wing tips. These
objectives are shown diagrammatically in figure 6.
Figure 6: AlbatrossONE objectives
4. DESIGN AND MANUFACTURE
The wing of AlbatrossONE is based on a generic short range aircraft, and is approximately 1:14
scale. The wing has five wing tip configurations:
A 2.6m wing span with no wing tips, equivalent to a 35m wing span.
A 3.2m wing span with fixed (i.e. locked) wing tips, equivalent to a 45m wing span.
A 3.2m wing span with the wing tips free to rotate about their hinges.
A 3.7m wing span with fixed (i.e. locked) wing tips, equivalent to a 52m wing span.
A 3.7m wing span with the wing tips free to rotate about their hinges.
Note that the aspect ratios of the three wing spans are approximately 9, 14 and 18. The wing
section is a PSU-90-125WL sailplane aerofoil: 12.5% max thickness at 35.1% chord, 2% max
camber at 54.4% chord. The flaps are connected to the wing via dropped hinges. The wing tip
hinge flare angle is approximately 15 degrees.
The fuselage is based on the Airbus A321, as are the horizontal tailplane (HTP) and vertical
tailplane (VTP) but oversized by 10% in the linear dimensions to increase directional stability.
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The wing skins are constructed with Carbon Fibre Reinforced Plastic (CFRP) stiffened with
Rohacell foam. The spars are constructed from plywood wrapped in CRFP. The mid and outer
wings are detachable from the inner wing with the attachments constructed in titanium with the
additive layered manufacturing (ALM) technique. The landing gear attachments and the wing
hinges are also constructed in titanium. The landing gears are fabricated from aluminium (with
water as the working fluid to provide the required damping), with a pneumatic braking system.
The HTP and VTP are made from Rohacell foam wrapped in CFRP. Lastly the fuselage is built
from a fibre glass shell supported by plywood frames. The structure is sized to 2.5g / -1g vertical
acceleration, with an ultimate factor of 3. Figure 7 shows the wing limit load static test.
The overall weight of the aircraft is approximately 19Kg, which is under the UK Civil Aviation
Authority (CAA) limit of 20Kg, above which the aircraft has to be certified. Other relevant CAA
regulations include a maximum altitude of 400ft and a maximum line-of-sight distance from the
pilot of 500m.
The aircraft is powered by two electric ducted fan motors, which each provide approximately
50N of maximum thrust and a power of 2.7kW. Two 22.5v lipo batteries allow an estimated
maximum flight endurance of 10 minutes. The cruise speed of the aircraft is 25m/s and the
maximum rated speed is 40m/s.
Figure 7: Wing limit load static test
It is important to reiterate that AlbatrossONE has not been designed so that it necessarily has the
physical properties of the full size aircraft, other than the wing tip hinge not passing bending
© Airbus Operations Ltd, 2019
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moment when released. Therefore the aircraft behaviour, and the handling qualities, loads, static
aeroelastic and dynamic aeroelastic characteristics related to the free wing tips in particular, can
be considered to be only representative of the full size aircraft in a qualitative sense.
Finally note that the name, AlbatrossONE, has been chosen for two reasons. Firstly the wing
span and aspect ratio of the largest Albatrosses approach 3.7m and 18, respectively. Secondly
the Semi Aeroelastic Hinge concept is superficially analogous to the biomechanics of the
Albatross. Albatrosses are able to travel distances of hundreds of kilometres through gliding and
“dynamic soaring” flight, and consequently they must maintain spread-wing posture for
prolonged periods of time. This is achieved, in part, by a locking mechanism at the shoulder
comprised of a sheet of tendons [9]. Simply put, for efficient gliding flight the Albatross locks
its shoulder, and when it needs to flap its wings (for propulsion, rapid manoeuvres, responding
to turbulence, etc) it unlocks its shoulder.
5. CONTROL SYSTEM
The aircraft is piloted remotely. The pilot and co-pilot control the aircraft via two ground radio
transmitters, which are linked to three radio receivers on the aircraft: Transmitter #1 is linked to
receivers #1 and #2, and transmitter #2 is linked to receiver #3. With transmitter #1 the pilot
commands the primary flight controls: Ailerons, elevators, rudder, “throttle”, main landing gear
brakes and nose wheel steering. The controls are partitioned into two independent blocks so that
the aircraft can still be controlled should one of the on board receivers fail. With transmitter #2
the co-pilot commands the emergency parachute and the folding wing tip hinge release and
recovery mechanism (not yet installed on the aircraft). The parachute can only be safely deployed
above 150ft and it is intended to be used in case of a total loss of control of the aircraft, or a
failure of transmitter #1 or receivers #1 and #2. If there is a failure of both transmitters or all
three receivers then the aircraft automatically enters a shallow spiral dive in order to ensure that
it comes down within the operational area. The control system is schematically shown in figure
8.
Figure 8: Aircraft control system
6. FLIGHT TEST INSTRUMENTATION
The aircraft is equipped with flight test instrumentation (FTI). For the research aspects of the
project the key instruments are the strain gauges and the aircraft accelerometers, which allow the
wing loading to be correlated with the aircraft load factor. There are four strain gauges on each
wing, located at approximately 10% (wing root), 35%, 55%, and 75% (inboard of hinge) of the
semi span (based on the 3.2m / 45m span), which were calibrated prior to each flight by applying
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a known load to the wing. The aircraft accelerometer is located close to the centre of gravity.
Other important instruments for both the research and aircraft safety include the pitot tube (for
airspeed), the alpha and beta vanes on the nose of the aircraft, the barometer (for altitude) and
the battery voltage. For the wind tunnel tests (see section 7.) the wing tip was equipped with an
accelerometer, however for technical reasons that was not available for the first flight tests. A
full list of the FTI can be seen in figure 9.
The data from the FTI was processed and recorded by a set of Arduino computers stacked in the
“black box” and by an off-the-shelf Pixhawk computer which can be commonly found in
recreational radio controlled aircraft and drones. A telemetry system allowed the data to be
viewed live at the ground station during the flights.
In addition to the FTI listed in figure 9 a video camera was mounted at the top of the VTP in
order to visually track the movements of the wing tips. A video camera was also used to film the
aircraft from the ground. In addition an anemometer was used to assess the latest wind speed and
direction at the airfield.
Figure 9: Flight test instrumentation
7. WIND TUNNEL TESTS
Prior to flight testing a wind tunnel test campaign was performed with the following objectives:
1. To check that the flapping frequency of the free wing tips (“45m” and “52m”) are well
separated from the first wing bending frequency of the wing for the operational airspeed
range. By ensuring this frequency separation the wing tip flapping mode and the wing
bending mode are not able to couple and cause flutter. A subsidiary objective is to check that
the evolution of wing tip flapping frequency with airspeed is more or less linear as predicted
by the models for the full size aircraft [4].
2. To check the range in the “coasting” (or fold) angle of the free wing tips (“45m” and “52m”)
for the operational ranges of airspeed and aircraft angle of attack.
© Airbus Operations Ltd, 2019
© Airbus Operations Ltd, 2019
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Regarding the first objective it is worth noting that for a full size aircraft it is effectively not
possible to avoid a coalescence between the flapping and bending modes. However the
coalescence can be shifted to a higher airspeed by adjusting the wing tip hinge flare angle, which
results in extra aerodynamic damping that can stabilise the flutter mechanism [4].
The test campaign was performed in the Airbus 12ft by 10ft low speed wind tunnel in Filton,
UK. The interface between the inner wing and the detachable mid / outer wing provided an ideal
anchor point to the wall of the wind tunnel, such that only the mid and outer part of the left wing
was tested, plus both the 45m and 52m wing tips – figure 10 shows the wing installed in the wind
tunnel. The anchor point allowed the wing angle of attack to be adjusted. A length of string was
tied to a bracket on the underside of the wing tip, passed through the wing and the tunnel wall,
and then pulled and released in order to provide the dynamic excitation for the first part of the
test. An accelerometer was installed in the wing tip in order to measure the acceleration time
history. For the second part of the test the wing tip coasting angle was recorded with a camera.
Figure 10: Wind tunnel test
The results from the first part of the test are shown in figures 11 and 12. Figure 11 provides an
example result from the case with an airspeed of 18m/s and aircraft angle of attack of 4 degs. In
both the acceleration time history and Fourier transform it can be seen that the response is
dominated by the wing tip flapping frequency at approximately 3.5Hz. The wing bending
frequency is at over 30Hz indicating a large frequency separation. Figure 12 gives the frequency
of the flapping mode for both the 45m and 52m wing tips for the full range of airspeeds. The
maximum frequency is less than 6Hz. However it should be noted that the first wing bending
mode frequency of the full wing connected to the fuselage is approximately 15Hz rather than the
30Hz measured for the shortened wing in the wind tunnel. Nevertheless the frequency separation
is still more than 9Hz indicating that the wing tip flapping mode cannot couple with the first wing
bending to cause flutter. Figure 12 also shows that the wing tip flapping frequencies for the 52m
wing tip are lower than for the 45m wing tip, which is as expected and due to the greater inertia
of the 52m tip. Also as expected is the clear increase of the flapping frequency with airspeed.
© Airbus Operations Ltd, 2019
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The trend is not as linear as previous modelling for the full size aircraft has predicted [4] (note
the apparent “dog leg” at 18m/s), but this is likely to be due to scatter in the results since the
acceleration time histories were minimally processed in order to confirm there is no flutter risk.
Figure 11: 45m wing tip release acceleration time history (left) and Fourier transform (right) at
airspeed of 18m/s and aircraft angle of attack of 4 degs
Figure 12: Flapping frequency for 45m and 52m wing tips versus airspeed
The results for the second part of the test are shown in figures 13 and 14, where the relationship
between wing tip coasting angle and airspeed and aircraft angle of attack is shown. Figure 13
shows the coasting angles are less for the heaver 52m wing tip, and also that as the airspeed
increases the coasting angle is asymptotic as the weight of the wing tips apparently becomes less
significant. Figure 14 shows the expected increase in coasting angle with aircraft angle of attack.
For low coasting angles the gradient of delta coasting angle to delta angle of attack is
approximately 3 to 1, regardless of the size of the wing tip or the airspeed. At higher angles of
attack the wing tip coasting angle appears to reach a maximum of no more than 45 degs. It is
important to note that this non-linear behaviour is not the wing tip stalling – because of the zero
moment across the hinge the wing tip only needs to generate enough lift to balance its weight
(approximately 100 grams) in terms of hinge moment. Instead as the coasting angle increases the
relationship between coasting angle and angle of attack (as a consequence of the flare angle)
becomes weaker, and the effective side slip due to the flare angle (approximately 15 degs)
becomes dominant. Of course this begs the question as to whether an aircraft in side slip could
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result in the “effective” flare angle changing and affecting the behaviour of the free wing tips,
and in the extreme if the side slip was greater than the flare angle whether the wing tips could
become statically unstable. For this reason for the free hinge flight test cable ties were used to
stop the wing tip coasting angle exceeding 90 degs.
Figure 13: Coasting angle versus airspeed for 45m and 52m wing tips for a range in aircraft
angle of attack
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Figure 14: Coasting angle versus aircraft angle of attack for 45m and 52m wing tips for a range
in airspeed
In addition to the measured data, a number of qualitative observations were made during the wind
tunnel testing:
- Due to the very low turbulence in the wind tunnel the coasting behaviour of the free wing tip
is almost complete steady for moderate aircraft angles of attack.
- If the angle of attack is increased so that the wing goes into stall, the wing tip remains
unstalled and the motion required to maintain zero moment across the hinge is small.
- The force required to pull the wing tip back to its planar position with the string can be high
(for the person pulling), especially for high angles of attack and/or high airspeeds.
- If the wind tunnel is started with the wing tip at a fold angle of approximately 135 degs the
wing tip will “unfurl” once the airspeed becomes sufficiently high.
8. FLIGHT TESTS
Prior to the flight tests a number of ground tests were completed. These included wind tunnel
testing, transmitter / receiver and telemetry tests, engine tests, FTI tests, and limit load static
testing of the wings, wing tips, fuselage, HTP and VTP.
8.1 Flight test philosophy
The philosophy for the flight tests is diagrammatically shown in figure 15. The philosophy was
developed to step through the flight test campaign so that the low risk elements came first and
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the most risky last. Practically this meant ground run tests before flying, including handling,
rejected take-offs and rotations; Flying with fixed wing tips before free wing tips; Flying free
wing tips before attempting to release and then recover the wing tips in flight; And flying with
the 45m wing tips before the 52m wing tips.
Figure 15: Flight test philosophy
After all the ground run tests had been completed, the above philosophy was adapted for the first
phase of flight testing: It was decided to fly twice with the 45m wing tips, fixed and then free.
8.2 Summary of the flight tests
The first two flights were performed on 26th February 2019 at Aston Down airfield in
Gloucestershire, UK. For each flight the aircraft performed a series of left hand circuits, in
“clean” and “high lift” configurations, and including stall tests. The flight time for both flights
was approximately five minutes, and the aircraft stayed below 25m/s and within the operational
area in terms of 500m from the pilot and no more than 400ft altitude. Figure 16 shows images
from the flight tests.
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Figure 16: Images from the flight tests
8.3 Results
The first findings from the flight tests were qualitative:
- The wing tips were statically and dynamically stable throughout the flight.
- The wing tips “coasted” with no oscillations in calm air, but responded to gusts to maintain
the zero hinge moment condition.
- The wing tip coasting angle tended to be higher in the turns when the angle of attack
increased.
© Airbus Operations Ltd, 2019
© Airbus Operations Ltd, 2019
© Airbus Operations Ltd, 2019
© Airbus Operations Ltd, 2019
© Airbus Operations Ltd, 2019
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- The free wing tips gave the pilots no particular problems with controlling the aircraft.
The strain gauge results at spanwise stations of 35% and 56% are summarised in figure 17. The
plots show the expected positive correlation between bending moment and aircraft load factor,
although there is significant scatter. The scatter is due to the fact that the aircraft is very light and
so gets “buffeted” by small gusts, plus the general the level of unsteadiness was quite high – for
example no attempt was made to achieve totally stable level flight or precisely coordinated turns,
although landing, take-off and stall tests were filtered from the data. Despite the scatter it is clear
that the bending moments at these two spanwise stations are lower for flight 2 than for flight 1,
thus confirming the load alleviation effect.
Figure 17: Bending moment versus aircraft load factor at 35% and 56% span for flight #1 (fixed
wing tip) and flight #2 (free wing tip)
Due to problems with the wing tip accelerometers, which could also be used as inclinometers,
another means was required to record the coasting angles for the free wing tips. This was
achieved by writing software to process the VTP video footage. Figures 18 to 20 show the
results. Figure 18 shows the relationship between wing tip coasting angle (average of left and
right) and aircraft angle of attack, and despite the scatter the data confirms the wind tunnel results
including the geometric non-linear behaviour. Additionally a simple geometric calculation of the
change in coasting angle due to the change in aircraft angle of attack, as defined in equation (1),
shows excellent agreement with the wind tunnel results in the linear region. The time histories of
the left and right wing tips is shown in figure 19. There is a clear asymmetry between the two
wing tips, which is currently not understood, but is possibly due to interference from the cable
ties that were installed at the hinge to prevent the wing tip coasting angle exceeding 90 degs.
Figure 20 is a zoom of the wing tip time histories and displays the response to a gust.
∆θ = tan-1(tan∆α / sinΛ) (1)
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Figure 18: Average of left and right wing tip coasting angles versus aircraft angle of attack for
flight #2, plus wind tunnel result, plus geometry calculation
Figure 19: Left and right wing tip coasting angles versus time for flight #2
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Figure 20: Left and right wing tip coasting angles versus time for flight #2 – zoom showing
response to a gust
9. CONCLUSIONS
The second flight of AlbatrossONE represented the first ever flight of an aircraft with free folding
wing tips, and throughout the flight the wing tips were demonstrated to be both statically and
dynamically stable. The wing load alleviation effect from the free wing tips has been confirmed
through comparing the strain gauge measurements between the two flights. The coasting (free
folding) angle of the wing tips has been shown to have a non-linear relationship with aircraft
angle of attack because the hinge flare angle causes an effective sideslip. And the near linear
variation of wing tip flapping frequency with airspeed was confirmed by the wind tunnel tests.
In general the first flights of AlbatrossONE represent a major step in demonstrating that the Semi
Aeroelastic Hinge technology is a serious proposition.
10. NEXT STEPS
The flight test campaign will be completed with the following elements:
- Identify the roll damping alleviation effect due to freely hinged wing tips.
- Identify the tip stall avoidance effect due to freely hinged wing tips (in flight).
- Fly with the 52m wing tips fixed & free.
- Fly with no wing tips.
- Release the wing tips in flight.
- Recover the wing tips to their planar position in flight.
In addition the mathematical models of AlbatrossONE require significant improvement. The
models (e.g. finite element model, loads model, longitudinal trim and handling qualities model)
that have been developed to date are relatively simple and were created to give the data needed
to produce a conservative design. They are however not adequate for properly understanding the
physical behaviour of the aircraft, and the wing tips in particular (noting the non-linear geometric
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effect as the coasting angle increases). There is much still to learn about the physical behaviour
of free hinged / semi aeroelastic wing tips, and better models allied to the AlbatrossONE flight
test data will enable this.
11. ACKNOWLEDGEMENTS
Many thanks to all the colleagues who have worked on or supported this topic recently, including
Andy Dyer, Alex Fordham, Manuel Taramona Perez, Thomas Maierhofer, Rob Buckley,
Raymond (Hao Chen) Yu, Alvaro Azabal, Kirsty Mon Williams, John Yorke, Colin Atwell, Mike
Bishop, Hagen Christian Hagens, Jan-Niklas Garbers, Sylwia Kozlowska, Ed Wheatcroft,
Carmine Valente, Patrick Metcalfe, Reece King, Paul Kealy, Anna Delmas, Jessica Kiraly,
Joshua Robson, Abdul Rehman, Kushal Agarwal, Andy McCarthy, Med Evans, Ciaran O'Rourke
and Simon Galpin all at Airbus, plus Jonathan Cooper at the University of Bristol, and Mudassir
Lone and Gaetan Dussart at Cranfield University.
12. REFERENCES
[1] Aeroelastic Behaviour of Hinged Wing Tips; T. Wilson, M. Herring & A. Azabal, Airbus;
A. Castrichini & J. Cooper, University of Bristol; and R. Ajaj, University of Southampton;
IFASD 2017
[2] An aircraft wing with a moveable wing tip device for load alleviation, patent application
GB2546246A; T. Wilson, M. Herring, J. Pattinson, J. Cooper, A. Castrichini, R. Ajaj, H.
Dhoru, July 2017
[3] Preliminary Investigation of Use of Flexible Folding Wing-Tips for Static and Dynamic
Loads Alleviation; A. Castrichini, V. Siddaramaiah, D. Calderon, J. Cooper, T. Wilson, Y.
Lemmens, Aeronautical Journal - New Series, published online 21 Nov. 2016, Doi:
10.1017/aer.2016.108
[4] Aeroelastic Behaviour of Hinged Wing Tips; T. Wilson, M. Herring & A. Azabal, Airbus;
A. Castrichini & J. Cooper, University of Bristol; and R. Ajaj, University of Southampton;
RAeS 5th Aerospace Structures Design Conference, 2016
[5] Nonlinear Folding Wing-Tips for Gust Loads Alleviation; Castrichini, A., Hodigere
Siddaramaiah, V., Calderon, D., Cooper, J., Wilson, T. & Lemmens, Y.; Journal of
Aircraft”, published online 17 Feb 2016. Doi: http://dx.doi.org/10.2514/1.C033474
[6] High fidelity simulation of the folding wing tip, J. Pattinson, M. Herring & T. Wilson
Airbus Group Innovations/ Airbus, IFASD 2015
[7] Nonlinear Negative Stiffness Wing-Tip Spring Device for Gust Loads Alleviation;
Castrichini, A., Cooper, J. E., Wilson, T., Carrella, A. & Lemmens, Y; Journal of Aircraft,
published online 9 Nov. 2016. Doi: 10.2514/1.C033887
[8] Wind Tunnel Testing of Folding Wing-Tip Devices for Gust Loads Alleviation; R. Cheung,
A. Castrichini, D. Rezgui & J.E. Cooper, University of Bristol; and T. Wilson, Airbus;
IFASD 2017
[9] Anatomy and histochemistry of spread‐wing posture in birds. 3. Immunohistochemistry of
flight muscles and the “shoulder lock” in albatrosses; Ron A. Meyers & Eric F. Stakebake,
Journal or Morphology 2004
[10] The Dynamic Release of the Semi Aeroelastic Hinge Wing-Tip Device; A. Castrichini &
T. Wilson; And J., University of Bristol; RAeS 6th Aerospace Structures Design
Conference, 2018
[11] Non-Linear Aeroelastic Behaviour of Hinged Wing Tips; T. Wilson & A. Castrichini,
Airbus; J. Paterson & R. Arribas, formerly Imperial College London; RAeS 6th Aerospace
Structures Design Conference, 2018
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