International Journal of Research in Engineering and Technology (IJRET) Vol. 2, No. 6, 2013 ISSN 2277 – 4378
Flight Control System for Aircraft Wings
and Tail Strike Avoidance during
Takeoff and Landing
Ashish Kumar, Affrin Pinhero, Cibi Vishnu Chinnasamy, Rajeev.J, Darshan Kumar.J, and V.R. Sanal Kumar
angles of incidence relative to a runway during both takeoff
and landing segments of flight. If the angle becomes large
enough while the aircraft is close to the ground, the aft or tail
portion of the craft may contact the runway surface. Such
contact is sometimes referred to as a tailstrike and is generally
sought to be avoided. For this reason and others,
manufacturers recommend pitch rates and speeds at which
takeoff and landing maneuvers are to be performed. In
practice, however, variations in both can be expected due to
differing pilot techniques and weather conditions. In some
instances, takeoff and landing speeds are increased to provide
additional aft body margin and thus reduce the probability of
tail contact in the event of a large variation in airspeed or pitch
rate. Increasing scheduled takeoff or landing speeds is not an
optimal arrangement, since it introduces a performance penalty
[2].
Abstract—An algorithm has been developed for prohibiting the
likelihood of an aircraft wingtip-to-ground contact and tailstrike
during the takeoff and landing using an advanced flight control
system. This flight control system (FCS) includes both roll rate and
pitch-command control devices for altering the aircraft’s pitch and
roll attitudes in accordance with the runway topography and weather
conditions. The proposed FCS accounts for the various rotations and
movements of the rotation centers by considering both the height of
the aircraft wings and aft body relative to the runway and the rate at
which the wings-tips and the tail-tip are actually approaching the
runway during the roll and pitch commands respectively. The
improvement includes the realistic prediction of the height of the
wings-tip and tail-tip from the ground with the help of closed loop
guidance system, using the proximity sensors mapping technique,
during takeoff and landing maneuvers. This FCS is very vital for the
safe takeoff and landing where the visibility is limited and the pilot's
judgment can lead to errors.
Keywords—Aircraft wingtip-to-ground
system, Flight control system, Tailstrike.
contact,
Autopilot
I. INTRODUCTION
T
HE present paper is an improvement to an aircraft flight
control system that reduces the likelihood of aircraft
wingtip-to-ground contact and the tail strikes during
takeoff and landing maneuvers [1]. The landing and the takeoff are the most difficult part of a flight journey; especially
during the unexpected conditions such as rainstorm and foggy
situations, the landing as well as the take-off of an aircraft
becomes a very perilous task [1-15]. Aircraft can achieve high
Ashish Kumar, and Affrin Pinhero are undergraduate students of
Electronics and Communication Engineering and with Sasurie Academy of
Engineering Coimbatore-641653, affiliated to Anna University Chennai,
Tamil
Nadu,
India
(e-mail:
ashish.kumar716@gmail.com,
affrin.pinhero@gmail.com; Phone:+91-8714158927,+91-9995926684).
Cibi Vishnu Chinnasamy is an undergraduate student of Electronics and
Instrumentation Engineering, Kumaraguru College of Technology,
Coimbatore – 641 049, Tamil Nadu, India (e-mail: cibivishnu7@gmail.com).
Rajeev. J is an undergraduate student of Aeronautical Engineering,
Kumaraguru College of Technology, Coimbatore – 641 049, Tamil Nadu,
India (e-mail: jayasrj58@gmail.com).
Darshan Kumar. J is currently Assistant Professor and with Department of
Aeronautical Engineering, Kumaraguru College of Technology, Coimbatore –
641 049, Tamil Nadu, India (email: darshankct@yahoo.in).
V. R. Sanal Kumar is Professor and Aerospace Scientist, and currently with
Department of Aeronautical Engineering, Kumaraguru College of
Technology, Coimbatore – 641 049, Tamil Nadu, India (Corresponding
Author, Phone:+91-9388679565; email id: vr_sanalkumar@yahoo.co.in).
Fig. 1 Aircraft estimated flight path and headings with respect to the
approach centreline (Not to scale). Inset (a) Low wing aircraft,
(b) Demonstrating a typical wingtip strike during landing phase,
(c) Demonstrating a typical tailstrike.
Wing-strike is the contact between an aircraft's wing and the
ground during takeoff or landing, most often as a complication
of a crosswind landing. Unexpected gusts of wind may cause
an aircraft to roll to one side or the other during landing,
whether they are performing a crosswind landing or not. The
risk for wing-strike primarily depends on the angle of the line
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International Journal of Research in Engineering and Technology (IJRET) Vol. 2, No. 6, 2013 ISSN 2277 – 4378
between the tip of the wing and the landing gear. The position
of the landing gear, when calculating that line, should be at the
point that it is maximally compressed, for example if the
aircraft comes down off center and with its weight entirely on
the downwind gear. The maximum safe angle would be
slightly less than that angle - at that angle, the wing will
probably hit the runway. High wing aircraft, where the wing is
located on top of the fuselage, are configured more safely from
a wing strike perspective. Low wing aircraft have the wing
closer to the ground (see inset Fig.1(a)). Dynamic flexing of
the wing due to landing touchdown loads can also cause wingstrikes (see inset
Fig. 1(b)). These are reported in the open
literature [2-15].
Of late Harjeev Singh Anand et al., [1] made an attempt to
develop an algorithm for aircraft tail strike avoidance during
the takeoff and landing with the help of laser proximity
sensors. The scope of this connected paper is further extended
owing to the fact that more laser proximity sensors are
recommended for fixing at various locations of the aircraft for
estimating the height of the wings-tip, tail tip and other parts of
the aircraft with ground for ensuring a smooth takeoff and
landing. Literature review further reveals that of late a Spanish
MD-83 passenger plane suffered a wing tip strike upon landing
at Kandahar, Afghanistan on January 24, 2012 [3]. The
Spanish accident investigation agency CIAIAC published the
final report of their investigation into the causes of this
accident at Kandahar.
The investigation report reveals that the en route part of the
flight SWT094 with 86 passengers onboard was uneventful.
Kandahar approach cleared them for an RNAV (GPS)
approach to runway 05. It is reported that the precision
approach path indicator (PAPI) was out of service and as a
result Pilot only had visual references to the runway and above
the ground during the final part of the approach. During the
short final phase the captain corrected a deviation from the
runway centreline by adjusting the flight path from right to left
(see Fig.1). Note that the touchdown speed was 122 knots,
which was below V ref as well as the target speed. The wing
had contacted the ground some 20 m prior to the threshold,
resulting in five threshold lights being destroyed by the
aircraft. The Civil Aviation Accident and Incident
Investigation Commission (CIAIAC) concluded that the
accident was “likely caused by the failure to observe the
company’s operating procedures and not executing a goaround when the approach was clearly not stabilized.
Lufthansa wing-strike in Hamburg reported some time in
2008 also triggered a serious concern in the airlines industry
for remedial measures. While the German federal agency for
flight accident investigation BFU states that a combination of
circumstances led to the wing-strike during an abortive
Fig.2 Reported Wingtip strike of a Spanish Airline: Damaged right
wing of MD-83 seen from the front.
landing attempt in strong crosswinds, it determined that the
aircraft switched from 'flight' mode to 'ground' mode at a
critical moment, even though it was still technically airborne.
Just after the touchdown the aircraft lost contact with the
runway, and in the gusting wind conditions banked 23° left.
Both pilots reacted with full right sidestick, and up to 14° right
rudder, but the limited control authority meant they were
unable to counter the bank enough to avoid the wing-tip strike.
We inferred that, had the flight control system been advanced
with more sensors for online correction of flight attitude these
types of accidents would have been avoided.
A tail strike can occur with any type of aircraft during
takeoff or landing, although long aircraft may be more prone
to tail strike, because tail strike occurrence is directly related
to pitch attitude versus aircraft geometry and main landing
gear status (see inset Fig. 1(c)). In some instances, takeoff and
landing speeds are increased to provide additional aft body
margin and thus reduce the probability of tail contact in the
event of a large variation in airspeed or pitch rate [2].
II. METHODOLOGY
It is generally understood that the rate at which the aft body
approaches the runway is a function of both the rotation rate of
the aircraft and the movement of the center of rotation relative
to the runway. As the wing begins to generate lift and the
aircraft begins to climb away from the runway, the motion of
the aft body toward the runway becomes a function of the
motion of the rotation rate of the aircraft and the motion of the
center of rotation relative to the runway. During this period,
the center of rotation moves from the landing gear to the center
of gravity of the airplane. In addition to this movement, the
center of gravity of the airplane begins to move away from the
runway as it lifts off. It is during this segment of the rotation,
just at or just after liftoff, that many takeoff tailstrikes can
occur. By ignoring the motion of the center of rotation,
inventions based on pitch and pitch rate alone limit the
performance of the aircraft in some situations and provide only
limited protection in others [2].
The present paper is an improvement to an aircraft flight
control system that reduces the likelihood of aircraft tailstrikes.
The flight control system includes a pitch command provided
to a pitch control device for altering the aircraft’s pitch
attitude. The improvement is a system of altering the pitch and
roll commands to avoid an aircraft wings-tip to ground contact
and tailstrike using feedback signals various proximity sensors.
The selection of a suitable proximity sensor and the fixing the
same at the proper location of aircraft are critical for avoiding
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International Journal of Research in Engineering and Technology (IJRET) Vol. 2, No. 6, 2013 ISSN 2277 – 4378
the wing-tip-to-ground contact and tailstrike. A sensor (also
called detector) is a converter that measures a physical
quantity and converts it into a signal which can be read by an
observer or by an (today mostly electronic) instrument. A
sensor with high response time and high resolution and high
dynamic characteristic is ideal for distance measurement
between the ground and the aircraft. This sensor is integrated
with the autopilot and auto throttle system. The primary aim of
using the sensor is to prevent wingtip strike and tailstrike by
continuously monitoring the tip clearance with ground and
maintain a safer clearance height through a feedback
governing system.
In order to minimize the wingtip and tail strike accidents,
laser proximity sensors with high response time and high
resolution and high dynamic characteristic could be
implemented near the wingtip and tail of the aircraft. It may be
noted that in most of the cases fixing the proximity sensors at
the tip of the wing or the tail are difficult. It is recommended
to fix the sensors where the aerodynamic tip effects are
negligible. Admittedly, a prior prediction of the tip clearance
is extremely difficult in a dynamic system with online variable
inputs, such as variable acceleration and non-linear rotation
and roll rates. Therefore a separate subroutine ASHISH has
been developed to estimate the exact tip clearance from the
ground in both the static and the dynamic conditions. The
instantaneous positions of various sensors are declared with
the time dependent 3D coordinate system. Location of the
sensors from the tip will be different for different aircraft.
Therefore sensor location (x s , y s , z s ) is estimated using the
aerial distance from the wing tip or tail location (x t , y t , z t )
where likelihood strike can occur with ground during takeoff
and landing. All sensors are integrated with the autopilot and
the auto throttle system. The suitably calibrated sensors with
3D computational model will predict the actual distance
between the ground and the tip (wing or tail) of any aircraft
whatever maybe the orientation of the sensor during the
takeoff and landing. Figure 3 shows the schematic block
diagram of an aircraft wingtip and tailstrike avoidance system.
The improvement in the present paper includes determining
online the safe height of wingtip and tail from the ground
during takeoff and landing using an algorithm. Nose-down
pitch command and appropriate roll rate are also incorporated
to avoid wingtip-to-ground contact and tailstrike during
takeoff and landing. The effect of proper Take-off speed is
important when runway lengths and landing distances are
critical.
Fig.3 A schematic block diagram of the flight control system.
The take-off speeds specified in the aircraft flight handbook
is generally the minimum safe speeds at which the aircraft can
be landed. Often during foggy situations, where the visibility is
limited, the pilot's judgment on take-off and landing
parameters is very vital. If there is an error in the judgment,
then there is a chance of tail-strike to occur. The effect of
touch down velocity and the vehicle orientation are also very
important; and if the pilot commits any mistake while landing
or if his judgement is erroneous then the flight may either
crash land or overshoot depending on whether the aircraft is
aligned with the runway or not, and also the vertical distance
between the aircraft and the ground determines a perfect touch
down at correct marker position. Also if the main wheels are
not in an axial plane with the ground, non-uniform wheels
touchdown occurs leading to one sided landing, which might
cause tire burst due to excess stress on one wheel. Thus all
these factors must be properly calibrated for an easy
touchdown.
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International Journal of Research in Engineering and Technology (IJRET) Vol. 2, No. 6, 2013 ISSN 2277 – 4378
Fig. 5 A schematic block diagram highlighting the takeoff phase
without wingtip strike and tailstrike.
Fig. 4 A schematic block diagram highlighting the prerequisites for
takeoff and landing operations without any wingtip-to-ground contact
and/or tailstrike.
Figure 4 shows the schematic block diagram highlighting
the takeoff phase without wingtip strike and tailstrike after
considering the aerodynamics parameters pertaining to lift
force calculation. Note that tail strikes on landing generally
cause more damage than takeoff tail strikes because the tail
may strike the runway before the main gear, damaging the aft
pressure bulkhead. Admittedly, many operational and human
factors are involved in tail strikes at takeoff. Analysis of inservice events highlighted that the following factors may
reduce, when combined, the tail clearance margin (i.e. distance
between the aircraft tail and the ground) at takeoff, such as (i)
early rotation, (ii) rotation technique, (iii) thrust / weight ratio,
(iv) slats / flaps configuration, (v) erroneous CG position and
trim setting, (vi) crosswind, (vii) shock absorber oleo inflation.
Figures 5 & 6 show schematic block diagrams highlighting
the takeoff and landing operation and its functionalities
without any wingtip-to-ground contact and/or tailstrike using
close loop command controller system. Note that takeoff speed
is the key safety element for takeoff, and it enables the pilot
with situational awareness and decision-making in this very
dynamic situation. The use of erroneous takeoff speeds can
lead to tail strikes, high-speed rejected takeoffs or initial climb
with degraded performance. Therefore development of an
algorithm for a smooth takeoff phase is inevitable in the light
of recent reported accidents [1, 3].
Fig. 6 A schematic block diagram of the flight control system
prohibiting aircraft wings and tail strikes using close loop command
controller.
The typical takeoff risk factors reported are (i) mis-trimmed
stabilizer, (ii) improper rotation techniques,
(iii) improper
use of the flight director, (iv) rotation prior to Vr, (v) excessive
initial pitch attitude, (vi) heavy derate/flight control abuse
during gusty/crosswind conditions.
The mis-trimmed
stabilizer usually results from using erroneous data like wrong
weights and incorrect center of gravity (CG). Also the nose up
mis-trim can present problems.
An unstabilized approach is one of the major causes of
wingtip-to-ground contact and tail strike during landing.
Wings strike and tailstrikes are costly but can be prevented
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with proper feedback control system and training. To
overcome the undesirable contacts of aircraft with ground we
propose a flight control system prohibiting aircraft wings and
tailstrike using close loop command controller. We also
recommend to fix laser proximity sensors at various locations
of aircraft with automatic feedback system for correcting the
errors and prohibiting the undesirable strikes during the
takeoff and landing phase of operation.
definitely avoid human errors causing the wing and tail-tip
strikes. The algorithm also considers the total weight of the
aircraft at takeoff, taxiing acceleration, pitch and rolls rates,
local density and lift coefficient with respect to various angles
of attack instantaneously. Therefore computation and
prediction of safe clearance height to avoiding wingtip-toground contact and tail strike will be more accurate. Note that
rotating the aircraft at the appropriate time, proper rate and
correct takeoff speed can avoid the wing and tail strike.
Rotating early means less lift and less aft tail clearance.
Whenever the aircraft exceeds the safe clearance height the
sensors will swiftly detect and map the attitude of the aircraft
and the algorithm will activate for pitch and roll corrections in
accordance with the correct takeoff speed and touch down
velocity. It is important to note that prudent selection of
locations for fixing the high-response time sensors lucratively
is important for the accurate surface clearance mapping of
ground/runway and the aircraft. Rotating at the proper rate and
direction is very important for avoiding wing and tail strike
and one should not rotate the aircraft at an excessive rate or to
an excessive attitude. When a last minute-change occurs,
takeoff speeds are sometimes modified and that will be
automatically updated by the algorithm. It is recommended to
get the correct takeoff weight for the aircraft for a better
performance prediction and safe maneuvers.
A. Development of an Algorithm
An effort has been taken for developing an algorithm after
considering all the input variables including aerodynamics and
local environmental data causing the wingtip-to-ground
contact and tail strike. It may be noted that properly calibrated
laser proximity sensors will be continuously monitoring and
maintaining the safe wingtip and tail clearance height with the
help of automated feedback system using the subroutine. The
proposed sensor is evidently having fast response for
correcting the aircraft rotation and climb rate to avoid the wing
and tail strike. Algorithm will also evaluate the safe taxing
acceleration; take off velocity, rate of climb, based on the total
weight of the aircraft, local air density, lift coefficient and
frontal area corresponding to the angle of attack set by the
Pilot. The wings tip heights and tailtip height from the ground
will be continuously computing with the help of a subroutine
ASHISH specifically developed using the moving boundary
computation in any dynamic situation of the aircraft based on
the landing or takeoff ground / run way surface mapping. The
sequence of operations and functionalities are shown in the
flow charts (see Figs. 3-6).
IV. CONCLUDING REMARKS
While accident investigations can provide a wealth of
information to improve safety, accidents are fortunately rare.
Incidents should be investigated in more depth. More finely
grained data for example by airline or by geo-graphic region
would be useful and that is a subject of topical interest.
Additionally, one should perform correlation analyses between
the accidents, incidents, and enforcement actions. Here we
were stymied by several limiting factors, both in terms of the
data itself, and in terms of the nature of aviation safety.
Nevertheless, based on the available information on hand, we
proposed that the commissioning of an additional lucrative
feedback control system using latest high-response proximity
sensors, for detecting and ensuring the minimum wingtip and
tail clearance can definitely avoid wing and tail strikes. It is
well known that an unstabilized approach is the biggest single
cause of tail strike during landing. We conjectured that both
undesirable wingtip-to-ground contact and tailstrikes can be
reduced by flight control system with online close loop
feedback command controller. Commissioning multiple
proximity sensors at the proper locations will meet the desired
task for wing and tail strikes avoidance of any aircraft. We
concluded that the schematic block diagram of the flight
control system presented through this paper prohibiting the
aircraft wings and tail strikes using close loop command
controller is a viable option for the wing and tail strike
avoidance of aircraft during takeoff and landing.
III. RESULTS AND DISCUSSION
In this paper an attempt has been made to develop an
algorithm for aircraft wings and tailstrike avoidance during the
takeoff and landing with the help of the flight control system
by invoking the operation of a close loop command controller.
In many situations, for takeoff speed calculations, have errors
crept in estimating the total weight of the aircraft. This is
particularly true when a last minute change occurs in cargo
loading, or when time pressure and workload are high.
Therefore, calculated speeds will be much lower than
expected, and will lead to: Tail strikes, “heavy aircraft”
sensation, and high-speed rejected takeoffs. But in our
algorithm, as seen in Fig. 6, we have taken in to account all
last minute changes of the total weight using calibrated
specially designed load cells, which are attached to the landing
gears. The computation of the minimum safe clearance is done
using analytical expressions based on the ground level data
base and the aircraft attitude during the takeoff / landing. Note
that takeoff speeds and runway distance calculations are based
on specific configurations with lift coefficient data base on
different angles of attack, and taxing acceleration. Any change
in the parameters of these configurations will invalidate the
takeoff speeds and taxiing distance.
The commissioning of laser proximity sensors with close
loop guidance system with command controller in any aircraft
proposed through this paper, as shown in Figs. 3-6, can
ACKNOWLEDGMENT
The authors would like to thank Management of
Kumaraguru College of Technology and Sasurie Academy of
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Engineering, Coimbatore, India for their extensive support of
this joint research work.
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