Note: Descriptions are shown in the official language in which they were submitted.
10~4S~6
Thi~ rent;Lon re:Lates to a meth~d of pro~ctiJIg pred~
erlllinec~ sllrface regions of an aircraft and to an aircraft s~rf-lce
reg:ion incorpo~atig sllch protection.
-Lt i.9 k210Wn that certain surface regions of an aircraft~
for example the leading edgeR of the wing~, tha englne air intake~,
the leading ~dge~ o~ the tail structure, helicopter rotor blade~
airscre~3, engine compressor blades, and guide vanes, are subjec-.
in use to surface erosion and to impact dam~ge5 by rain, airborn~
~and, and ice ~nd the like. These ~urface r~.gionq may incorporate
electrical heating devLces to facilitate de-icing during ~light~
and of course the preservation of the mechanic~l, and where app~
ropriato electrical integrity of these regiorls i4 of great imp~
ortance. It is known to protect ouch ~urface r0gions a~ainst
~i erosion and impact damage by providin~ the surface rsgion witha synthetic resin covering, for ex~mple a covering of a polyura~
th,ne or neoprene material. Such co~erings ar0 quit2ble for
3 relati~ely low speed app`lication~, for example up to an ~pprox-
imate maximum of 450 miles per hour~ this fig~lre repres6nti3lg ~he
v~locity component normal to the ~urface in que~tionO In order
to provide surface erosion protection for higher speed aircraft~
for e~ample aircraft c~pable of entering supersQnic speed rang~s,
it has in the past been proposed to provide protective layers~
o~ stainles3 ~teel or nickol. The synthetic resin group of
materials provjde protection by virtue o~ their resili~nce ~nd
toughness~ l~hile t'lemet~llic coatig3 ment~oned a~ford protectiou
by virtue o~ their hardness. The syrrthetic resi~ Inaterials
~u~fer from t~e ~isad~rantage that i-lleir usef`lllne~ is limited
.
-2- ~ ~
s
lO9'1S26
~o rclatively low sp~ )p]i~ltions, whi]e ~le prev;ously-
ploposed layers of llicliel or stainlcss steel, while bc;ng suit-
a})le for a w;~e specd r~nge, are both extremely difficult and
e~t)^eille]y expensive to produce. ~loreover, even thougll the pro-
~-ective metallic ]ayers are extreme]y thin, it is extremely
difficult al~d expens;ve to rorm them accurately to the complex
surface shapes involved.
It is an object of the present invention to provide a
method of pro~cecting surface regions of an aircraft, and an air-
craft surface region so protected, in a simple and convenient
r,lanner .
A metllod of protecting a surface region of an aircraftin accordance with the invention, includes starting with a sneet
or sheecs of a super-plastic alloy engaging the sheet or sheets
of super-plastic alloy, with the surface region to be protected,
shaping the sheet or sheets of ~uper-plastic alloy at a tempera-
ture such that the super plastic properties of the alloy are
exhibited to follow the surface contours of the surface region
to be protected, and securing the protective layer of super-
plastic alloy so formed to said surface region~
In this specification, by the term super-plastic alloy,
the applicants mean a super-plastic metal alloy.
Desirably the formed layer is secured to said surface
reyion by means of an acihesive.
Conveniently the adhesive is applied to the surface
region to be protected and/or the sheet or sheets of alloy prior
to the shaping of the sheet or sheets.
1094SZ~; -
Convellientl~- the ~31leet or ~h~et~ are preform~-l to th~
general .shap~ of the surface region ~nd are finally sh~ped in
situ so as to conform to the s~rface contours p~cul-iar tG the
actual surf~ce region~
The invention further resides in an aircraft ~urface regicr
having seGUred thereto a protectivs laye~ of a super-plastic
alloy.
In one aspect of the inventior., the aircraft surface reg-Gn
incorporates heat~r structure and the protective layer of .5uper-
, plastic alloy overlie~ the hoater structure.
3 In a further aspect of the invention the aircraft ~urface
region incorporates ~trengthening fibre3 in its con~truction
` for example carbon filaments.
:~ In a furth~r aspectt the invention re~ides .in a protective
shoe of a s~per~pla~tic alloy which is shaped 'o fit onto a
.' predetermined aircraft surface region, said shoe being intended
finally to be shaped in 9itU 90 as completely to follow the
surface contours pecu~ar to the surf2ce region for ~hich it
defines the protecti~e layer.
Conveniently the prefoxmed shoe i~lcorporate~ a heater
structure 50 that the p~otective shoe and the he~ter structurs
can be applied to the prede~rmined surface region in the
;
same operation.
-4-
10~ ~52~
Preferal-ly the alloy from which ih~ prot0ctive Layer i~
formed .i9 that kno~.~ as:
~ 'SP~ alloy" rnanufacturcd by the Imperial S~lting Comp~ny
Lim.ited;
or is a two~pha~e aAuatornary alloy having a fine grain micro-
structure stable at t,he te~perature of a super~pla~tic deformation
consist.ill~ of zinc within thc range 70-~2/-' by weight and
aluminium 30-18~ by wei~ht to which is added up to 0025,~o by
- weight of magnesium and up to 2~ by woigh.t of one of the elerllents
copper~ nickel and silver.
In the accompanying drawings 9
~ igura t i9 a cross-~ectional r~pre3ent~tio~ of p~rt of an
aircraft wing in accordanco with one eæample of th~ pr~ent
' invention~
:. ~igure 2 i9 a ~iew similar to ~lgure 1 of a modificationt
; and
Figure 3 i~ a diagrammatic repre~entation o~ an aircraft.
i, .
Referring^ to thc drawing~ the wing includes an out~r skin
11 which defil~es the airfoil shape of the ~ring. The de~irabi.~it~
of protecting wing surfaces and other surface regions of the
airfra~le again~t erosion and impact damage by rain~ and air-
borne ~and and ice~ is well known. For example~ the leading
e~ge surface~ of wlng~, tail structure~ and erlgine air i~ntake~
g~i~ vane~ and compressor blade~ and the leaaing edges of
h~licopter rotor blades are su~ceptible to erosion and i~act
dam~ge by ~a.in9 and airborne ice and ~nd, and thAus it ~
~ S ~
.
109452~
desirable to take steps to preserve the mechanical integrity
of these re~ions, and also, of course, their electrical inte-
grity in the event that they are provided with surface heaters
for de-icing. Moreover where the component, for example a
helicopter rotor blade, is formed from a material reinforced
with fibres, i.e. carbon filaments, then clearly their integrity
must also be protected. Thus in accordance with the present
invention such surface regions are provided with an outer
protective layer, the layer 12 in the drawing, formed from a
sheet or sheets of super-plastic alloy having the super--plastic
properties found in many binary zinc/aluminium alloys but not
having their susceptibility of moisture attack. This reduction
is susceptibility to moisture attack is of course important
where protection against rain erosion is one of the requirements.
Tests made on aircraft parts filled with surface protection
layers of the super-plastic alloy as described hereinafter show
a good resistance to erosion under conditions of impact by
rain, hail and sand.
A further benefit of using such super-plastic alloys
to produce the protective outer layer is that as a result of
the super-plastic properties sheets of alloy can be worked
easily to follow accurately the surface contours peculiar to the
actual airfoil or other surface region of the airframe on which
the sheet or sheets are secured.
The sheet or sheets of super-plastic alloy are
- relatively thin, of the order of 0.010 - 0.030 inches, the
thickness chosen being consistent with need for the layer to
be thick enough to prevent the impact shock of rain, ice and
said from damaging
-
~O~`~S~6
the adlle~ . bo~ bet~een t:lla la~-er ~nd the surface being
protected ~where all adhes:ive is u~ed) but thin anougll to Iceep
the weight of the layer within acceptable limitsO
In o~er to apply such a protective layer t2 to a predet~
errnincd ~urface re~ion 11 of the airframe ~e~er~l alternative
procedures are po~sible, for e~ample; ~he airframe component is
detached and the predQterrnined surface region and/or,sheet or
sheets of the ~uper plastic ~lloy are coated with an expoxy resin
adhesi~e 13. The sh00t or sheet~ of alloy are the~ pressed ontv
the predeter~ined surface region ~o that they generally f~low
the sh~ptng thereof. Thereafter9 the components tog0ther with
the sheet or sheets of alloy are rai~ed to the temperature of
superpla~tlc defor~nation of the alloy at which ~emperature t'ne
super plastic properties ~ the alloy are e~hibited, i~ an ove~
and the sheet or sheets of ~lloy are then shaped to inti7nately
follow the predetermin~ surface regi.Gn, using the surface
region itself as the former. Tho shaping ~orce is applted to
the sheet or 3heet~ of alloy by engaging with the outer surface
o~ the ~heet or sheets one or more air bag~, and thGn ir.flatin~
the air b~s to apply pressure to the sheet or shsets 90 as to
~chie~e a u~iform fi~al t~}ickness o~ adhe~i~e over the whols o`
the sheet or sheets. Alternati~rely the airfran~e compo~e~t
carrying the ~heet or ~heet~ raised to the temperature of s~ita'ote
plas~c de.ormatio~ can be placed in an impervious flexible baæ
~hlcb i5 then e~acuated 50 that external air pres~ure pres~es
the ~heet or ~heet~ o, alloy to ~ollo~ intimately the .~.~hapir~
o~ the predetermine~d sllrface re~ion of the air~rams componellt.
_ 7 ~-
:10~526
~ ere it is necessar~r to restx:;ct the temperature to which
the aircraft surf~ce reglon i~ heat0dr the sheet or sheets of
super~plastic al].oy can be heated~ separat~ from the surface
region9 to a suital)le te~perature in exces.q of the ideal forming
temperat~r~ and Call then raidly be applied to and shap~d on tne
cold surf~ce region. As a further pracaution.a heat in3ulating
layer can be introduced between the hot ~heet or sheets and the
surfa~0 region9 the insulati.~g layer being-in place of and of a
thickneYs equal to, the adhesiv0 layer. The sheet or sheets ~r0
then shaped to the Aurface region, th~ sheet or sheets t~en being
remo~ed to permit the insulatine~ layer to be replaced by a layer
of adhesi~et ~ol~owing which tha sheet or sh~et~ will be replaced
so as to be adhesively bonded to the ~urface region. As is me~-
tionèd later, the aricraft region m~y require to be provided
with a heat~r for use in aircraft de~icing. The heater layer
may act a~ a heat insulating layer during sh~ping of the sheet
or sheets of super-plastic alloy9 but of course in this situation
the insul.atln.g layer defined by the heat~r will be left in situ
and the sheet or ~heets will be adhesively bonded in positio~
co~ering the heater layer. As a still further ~lternative
the aircraft surface regioll can temp.orarily be pro~ided with
a cooling ar~angement to prevent ov~rh~a$ing of the surface
or sheets
region, during fitting of the sheet/o~ super~plastic alloy.
~, ,
` As a furth~r alternative where a series of thaoretically
j identical qurraces are to b2 protected, for example tha leading
; èdg6s of the wings of a flight cf identical air~raft then a
pl~r~lity Gf protecti~e 3hoes each formed from a sheet or ~heets
of 3uper-pla~tic al.Loy cnn be prGduced using a for!ner which is
.
~ 8 --
- 10~S26
idcnt:ical in sh.-lpe to the tllooretj.cal leading edge sh~pe of
the aircraft of the fl:~gllt. It will be recofj^nised however that
eac}l aircraft irl the flig~t will be slightly different from tne
other~ since it i.f3 individually constrllctecl and so although eaol
leadirlg edgs has tha same theoretical ~hape lt will ,n fact havG
surff~tce colltour3, minor a~perities and the like ~hich do not
m~teria].ly affect it.s airfoil performarce, peculiar to itqelf~
Thus each protective shos will fit anyone oi` the leading ~dges
of the aircraft of the flight but none wi.ll follow accurat~ly the
peculi.ar surface contours. It is vital that the protcctive
layer does follo~ the contours of t~ surface it is to pro~.ect
in order ~hat t.he layer of adhesive securing the layer to the
surff~ce ~s of even thickness and so exhibits conf3tanft ~dhesive
properties over the whole area, it being recognised that for
optimum adhesiva bond strength, many adhesive must be present
in a lay-er of predetermined thicknes3 accurate to 0.1 Mm,
Additionally failure of the layer to follow local peculiarities
in the surface could result in a void between the layer and the
surface which would be an inherent weakness in the co~posite
structure. Such in~erent weakness would rapidly give rise tG
failure of the protective layer, under the extremely hig~ impact
forces of even sMall particles at sonic velocitiesO It is kno~.in
that such a weakness would give rise to failure of the previously
known nichel or stainless steel protective layers under the same
operating condltions. Al.so, wherc heater layers are incorporete~
then suoh voids would retract ~rofn lheir performance an~ m`'ght
give rise to fa_lure due to overheating
- 9 ~
. , ", ~ ~ . ~ , . . .
109~526
Since the pro-tective layer is th.n7 it is ~ependent for
its mechanical. :integrity on the adhesive boIld and thus protec~ e
laycr t7~US t conform accurately to the surface to be protected to
ensure optimuln adhesive bond stren~th. I~lUS al.though a ~tc,ck
of preforl,led identical shoes can be retained, in many cases each
shoe muC-it be subject to final shaping operatior in situ on th3
actual surface to be protected. It will be understood th~t when
using a preformed shoe the adhesive can be applied to the surface
and/ol~ the shoe. The final shaping operation of the shoe ~ill
be perf`ormed at the temperature of plastic de~formation of the a
and may involve either of the techniques described above. I~
will be understood that the intimate cnrrelation in sh~pe can
be achie~ed with relative ease by virtue of the super-plasticity.
Where the shaping operation is parformed ~ith the adhesive
in situ-then it i~ of course a requirement of the adh,sive that
it has a sufficien.tly long curing time to permit the alloy and
component to be raised to the correct temperature~ and tc permi.t
the sheet or sheets of alloy to be for~cd to the correct shape
before the adhesive cures to a point at which relative move~ent
between the sheet and the aircraft component is prevented~ In
the event that a suitable adhesive is not available then it will
be understood that the sheet or shoe of alloy could be finally
shaped on thc actual surface but without adhesive present, the
sheet or shoe then bein~ rernoved to permit application of the
adhe,ive in temperature co~lditions s~iited to the adhesivs and
t~e sheet er shoe then being ~rep~acsc so as to be secured by
the adhe-sive. In such a te,chnique ~ spacar repr¢sentin~ the
adhesive layar ma~- be interposad betwean the alloy a~d th~ sur~
- 10 --
.. ... ~................................................. . . ..
10~526
face duri~ i~inal sln~Li3-g of ~,he alloy so as to eJl.'.UJ:e eVCntl~al
confoLinity be~weell ~he alloy and the surface whcn the spaccr is
replaced by the aclhesive.
Some airfr~ime surface regions inCOLpOrate heater struc-
tures 14 for de--iciny t]le surfaces in use. It is of course irnpor-
tant to preserve the electrica] integrity as well as the mechani-
cal inteyrity of such surface regions and thus such surface
regions can be protected by sheets or shoes of super-plastic
alloy as described above. It is envisaged -that in some
instanccs, for example he]icopte ~-otor blades, it may be
desirable ~o incorporate a heater into the protective alloy
shoe prior to the application of the shoe to the surface to
be protected. In such cases the alloy shoe may be preformed
to the general surface shape and may then have a heater struc-
ture 14 bonded on to its aircraft surface engaging face prior
to fitting the shoe to the surface. It will of course be neces-
- sary for the heater structure to be sufficiently flexible to
conform to the surface contours of the airframe surface during
the final shaping operation to ensure an even, void free thick-
ness of adhesive. Various epoxy resin adhesives can be used and
also phenolic resin adhesives and acrylic resin adhesives can be
used if desired. I~here complex surface shapes are involved the
heater structure 14 rnay be fitted to the surface prior to the
- application of the sheets of alloy. In such cases the assembly
of the sheets of alloy to the aircraft surface will be as des-
cribed previously.
The adhesives used may obviously be painted or sprayed
in liquid form or may be applied in the form of a paste or a
prepared film.
109 ~5Z6
A su~t,able supor~pl~stic a110y is "SPZ all~" manufac~tl~ed
by the Imp~rial Smelting Company Limited. The e~act form1~1~t~on
of this alloy is not known to us. Ho~evars it io belia~e~ that
the alloy is definable as "two-phase quzJcernary alloy havi~3:
a fine grain micro3tructure stabl0 at t;he temp~ature of 5upe~
plastic deformation9 consisting of ~illC within the range 70~,h
by weight and aluminiurn 30~1 8~o by weight to which i~ added up
to 0. 25~/o by weight of m~gnesium and up to 2.000,b by weight of one
of the elements copper, nickel and silver~" and that many alloys
within this definition may ~e suitable.
Reference is made herein to "the temperature of super-
plastic deformation". It is to be understood that thi~ t~mp-
erature is i~ practic~ a rang~ of tomperatures althou~h a
particular te-nperature within the range may prove preferable in
practice. ~or e~ample super plastic deformation of` a suitabl6
alloy can take place between approximately 150 C and 260 C but
it i8 desirabLe in some applications in order to match the qual-
i$ies o~ the adhesive used, the nature of the airframe regisn,
and/or the degree o~ forming requirsd~ to perform the final
shaping necessitating super-plastic deformation at the minim~lrn
temperature at which pcrmanent de~ormation of the layer of` alloy
can be en~ured. It will be u~derstood that the protecti-~e layer
may be applied to the a~rcraft component wl1ich has the surface
to be protected either while the component is on the aircraft
or where po~sible while 1;he component i9 detached from tne
aircraft.
~ 12 _
las~sz6
It ~ e recogni.sec~ at the ~hapin~ of` the protGctive
layer t;o accuratoly conform to the contours peculiar to the
act~ ur~ace to be protect;ed i.s a desideratu!n which is
virtu~.lly in~po.~-~i b].e to achi~ve in practice u~inD the previou~ly
known non-~uper-plas l;ic metal protective member
