Article citation information:
Świątoniowski, A., Szostak, J., Chodorowska, D. Repair technology of the
composite wing of a light-plane damaged during an aircraft crash. Scientific Journal of
Andrzej ŚWIĄTONIOWSKI[1],
Janusz SZOSTAK[2],
Dorota CHODOROWSKA[3]
REPAIR TECHNOLOGY OF THE
COMPOSITE WING OF A LIGHT PLANE DAMAGED DURING AN AIRCRAFT CRASH
Summary. The increasing use of composite structures in
aircraft constructions has made it necessary to develop repair methods that
will restore the component’s original design strength without compromising its
structural integrity. In this paper,
the complex repair technology of the composite wing of a light plane, which was
damaged during an aircraft crash, is described. The applied repair scheme should meet all the original design
requirements for the plane structure.
Keywords: light plane; composites; damage
repair; wing.
1.
INTRODUCTION
In Poland in recent years, following the experience of
other countries in the EU, it has been observed that sporting activities based
on the use of ultralight (UL) planes have been developing rapidly.
In accordance with the Ordinance of the Minister of Transport, Construction and
Maritime Economy of 26 March 2013, the class
of UL planes is constituted in terms of machines intended to be used by
amateur pilots, of which the stall speed or minimum horizontal flying speed in
the landing configuration should not exceed 65 km/h, while the take-off weight
should not exceed
In accordance with the available data, there are
currently more than 2,000 UL-class planes registered in Poland, of which the
vast majority are mostly made from composite materials [1]. Alongside the
increase in the number of planes in operation is the rise in the number of
breakdowns.
Apart from ever more complex plane constructions, this
situation makes it necessary to develop repair technologies in order to restore
the initial structure of the construction, as well as its design strength. This
issue is becoming more significant, particularly with regard to the difference
between the technological level represented by the manufacturers of the planes
of this type and that represented by the original equipment manufacturers
(OEMs), as well as the methods applied in the course of repairing
and operating them, especially as far as composite structures are
concerned [2].
As a result, taking into consideration the still
unsatisfactory level of the standardization of these methods, there is a need
to collect the experience connected with them and generalize the data in
question as far as possible.
2.
IDENTIFICATION OF DAMAGE
TO THE PLANE CONSTRUCTION AFTER A BREAKDOWN
In the course of an emergency
landing of a two-seat UL plane (a low-wing monoplane), its structure
sustained major damage.
The damage in question affected the front part of the
fuselage (manufactured entirely of fibreglass and carbon
fibres with the application of “sandwich” technology
and possessing a honeycomb structure core), the front undercarriage and
the wings on a 9 m wingspan. The left wing, of which 1,760 mm was burnt
together with the main spar, and the aileron could no longer be repaired (Fig.
1).
Fig. 1. View of the fragments of
the left wing of a UL plane burnt in an aircraft crash involving another UL
plane (irreparable)
The reason for this was
that it was impossible to reconstruct the main spar in such a way that its
initial design strength would be restored.
After a detailed
analysis, however, it was found that such a repair may be conducted on the right
wing, in which the boom ribs were broken, while the Fowler flap protracting
mechanism, which contained the right high-lift device, as well as the end of
the wing, was destroyed.
3. REPAIR TECHNOLOGY OF THE WING
3.1 Construction of the
wing
The section of the construction of
the wing is presented in Figure 2.
A wing, made entirely of
carbon fibres, has a rectangular
outline with trapezoidal endings, the final parts of which are winglets. In the
rear part of the wing, there is an electrically controlled high-lift Fowler flap[4], which is able to move on aluminium rollers fastened to the boom
ribs. In the wing, there is an also a 39-litre fuel tank.
3.2 Description of the wing repair
The objective of the
repair to the right aerofoil of the plane was to restore its initial structure
and rigidity of it, together with the ability to carry design loads, while
simultaneously maintaining aerodynamic parameters and restrictions, which
result from the mass balance.
Fulfilling those
requirements results in adopting the algorithm of subsequent operations in the
way presented in Figure 3.
The wing repair was
commenced by cutting out a fragment from its bottom shell plating, which was
120 mm on each side of the damaged rib no. 1, in order that it could be cut out
with the application of a rotary saw.
This operation was
repeated on ribs nos. 2 and 3 (Fig. 4), although there was an additional
difficulty due to the fact that those ribs constituted the side panels of the
fuel tank, which was inseparably connected to the construction of the wing, as
show in Figure 5.
After removing the
remnants of the cut-out ribs and grinding down the layer of the old adhesive,
it was ascertained whether the new ribs could be located in their proper places
in the structure of a wing, as well as whether there was sufficient
clearance value to make it possible to correct the ribs’ arrangement if that
was needed.
Fig.
2. Construction of the wing
Fig. 3. Algorithm of the
subsequent wing repair operations: (1) identifying the kind and scope of the
damage; (2) irreparable damage; (3) taking the aerofoil out of service; (4)
making a decision concerning the kind of repair; (5) together with the
producer (or an OEM), establishing the repair scope and technology, as well as
approving the repair; (6) determining the provisional repair scope; (7)
establishing and accepting the provisional repair quality; (8) performing
the provisional (airfield) repair in the period before handing the item over to
a specialized workshop; (9) performing a permanent comprehensive repair in
accordance with the adopted guidelines and the conditions of the producer; (10)
controlling the quality of the performed repair; (11) putting the aerofoil
into service again and mounting it on the plane
After finishing that
work, a Fowler flap was mounted and fitted to the ribs in such a way as to
guarantee its seamless movement on the rollers.
Subsequently, after the
wing and ribs shell plating have holes drilled into them, these elements were
initially joined with the application of connectors (so-called “hefts”). Once again,
the control of the flap movement’s seamlessness was performed, together with
that of the dimensions of the slot between the flap and the wing shell plating.
Finally, the flap and the ribs were dismounted.
Fig.
4. View of the wing in the course of repair work
Fig. 5. Fragment of a
fuel tank constituting the inseparable part of the wing construction
Subsequently, the parts
along the rib edges, which were previously prepared and degreased with the
application of acetone, while epoxy resin, thickened beforehand with cotton
flakes, was applied to the places where they join the wing shell plating, were
clamped with “hefts” after the application of adhesive. Any excessive quantity
of the adhesive was also removed.
The high-lift device was
fitted again and it was ascertained that the flaps could move seamlessly, which
confirmed that the resin had dried and that the positions of the ribs, mounted
with the use of the adhesive, were correct.
After gelling, the flap
was dismounted. In the places of connection between the ribs and the wing shell
plating, angle sections made of composite, based upon carbon fibre, were laminated
in [3] in order to strengthen the connection.
The side surfaces of
ribs nos. 2 and 3, constituting the side surfaces of the fuel tank (Fig. 5),
were subjected to lamination. For that purpose, a composite based upon a fibre
made of S-type glass, impregnated with epoxy resin, whose tensile strength
amounts to 
= 882 MPa, and fuel resistant was applied. This step was
also repeated on the remaining surface of the tank, with the surface in
question subsequently covered with the TAPOX 2-k Epoxy sealant, made by Fertan.
The subsequent stage of
the work involved making the new fragments of the wing shell plating.
For that purpose, in the
place of connection between the old and new elements of the wing shell plating
(at a width of 40 mm), the layer of the composite made of carbon fibre was
removed, as was the Nomex[5].
The purpose here was to make it possible to conduct “overlap”
fastening with the adhesive of the new shell plating bands, which were adjusted
to the holes cut out of the wing (Fig. 6).
The new fragment of the
fuselage shell plating, which was situated where the fuel tank was, was
additionally painted with the TAPOX 2-k Epoxy sealant.
In the course of the
work, particular attention was devoted to removing the excessive quantity of
the adhesive (flashes) in the place of connection between the shell plating
(Fig. 6), which, after the resin has dried, facilitates grinding and preparing
60 mm surface bands, on which the strengthening elements of those edges
are laminated.
Subsequently, the
surfaces being joined with the application of the adhesive were cleaned, then
filled with the first layer of putty to cover the larger uneven areas, while
defects on the surfaces were repaired.
Fig. 6. Shell plating
mounting operation with the application of the adhesive, as well as the view
of the right wing after its new fragment was mounted with the use of the
adhesive
Mounting work was concluded by
ascertaining the tightness of the fuel tank[6].
Having reconstructed the wing in
such a way, it was then soaked in a furnace for a period of 16 h and at a
temperature of 56 oC.
After the repair was completed as described above, it was
possible to commence the subsequent stage of the work, which was the
initial mounting (the so-called
semi-mounting) of the wing.
This stage consisted of joining
separate parts and sub-assemblies of the wing in order to ascertain the
correctness of fitting and mounting, as well as the functioning of the control
systems.
The initial mounting included the
following activities (in the order given):
- mounting
the aileron after previously covering the fittings with a lubricant and
securing the pin with locking pins, followed by connecting its control
system inside a wing
- ascertaining
the correctness of mounting the aileron by controlling the clearance
values, as well as the seamlessness and easiness of the movement of the
entire system
- mounting
the end of the wing, together with the navigation lights, as well as
installing electric cables to them
- installing
the dynamic air pipe to the pitot tube
- mounting
a rotameter on the tank mounting, together with connecting electrical
cables to it
- mounting
the fuel pipe, which feeds fuel from the tank to the engine, the fuel cap
and the special fuel in the lowest point of the tank
- mounting
the electrical mechanism of protracting a Fowler flap from the wing and
mounting the flap itself, as well as connecting the mechanism and the flap
- ascertaining
the correctness of mounting the flap by controlling clearance values, as well
as its seamless protraction
The wing prepared in
such a way was initially mounted on the fuselage, after which the correctness
and seamlessness of the functioning of the system was checked, followed by
closing the main pins of the wing, as well as the auxiliary pins (front and
rear). The dimension of the slot between the wing and the fuselage was also
checked. The control systems were connected to the instrumental panel in the
fuselage.
Afterwards, the wing was
dismounted and handed over for lacquering. In order to limit the increase
in the mass resulting from the repair, the old lacquer was grounded. The
surfaces being repaired were filled with putty, then painted with a filling
primer. Finally, the wing was painted with an acryl lacquer. The entire
preparation process for the painting, as well as the painting itself, was
conducted manually.
After concluding the
painting process, the wing was again mounted on the fuselage in the course
of the final plane mounting.
The following were also
performed:
- mounting
the plane anchoring handle
- controlling
the tightness of the fuel tank when it is 100% filled
- mounting
the peephole cover on the wing
- installing
a special “platform” for standing on the wing, together with the call
signs of the plane, which were cut out of high-quality decorative foil
The assembled airframe
was set in the position for horizontal flight, the purpose of which was to
level the airframe, which involved checking its geometry in accordance with the levelling
sheets at our disposal. Afterwards, with the use of a special protractor, the inclination
angles of the ailerons and the flaps were checked, regulating their inclination
values on pushers or limiters in the control system.
4. SUMMARY
Upon the basis of the experiences
collected in the course of repairing the wing of an UL airframe with a
composite structure, it is possible to indicate that what seems to be the essential
problem is the assessment of the character of damage and the possibility of
removing it, so as to restore the design parameters of the structure in full.
Such an assessment is relevant in terms of both technical (the selection of
repair technology) and financial aspects. It is possible to estimate that, as
in the described case of using conventional methods of repairing composite
structures, the cost of restoring the structure of the right aerofoil alone
constitutes approximately 35-45% of the purchase cost of a new element.
However, this is dependent upon the degree of damage. This paper describes all
the processes for repairing a plane, commencing with its delivery to the
workshop to inspecting the entire airframe, repairing the airframe
sub-assemblies, painting the plane, and mounting the airframe for the purpose
of conducting tests on the ground and in the air.
After checking the geometry of the
plane in such a way, we may be sure that the plane will be flying as it should,
will maintain its handling qualities.
References
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DOI: 10.1016/j.paerosci.2013.03.003.
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Received 17.01.2016; accepted in revised form 30.05.2016
Scientific Journal of Silesian
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