CA1299908C

CA1299908C - Aircraft runway grooved surface

Info

Publication number: CA1299908C
Application number: CA000590312A
Authority: CA
Inventors: Ronald A.W. Clarke
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-02-10
Filing date: 1989-02-07
Publication date: 1992-05-05
Anticipated expiration: 2009-05-05
Also published as: GB2214958A; GB8803086D0; GB2214958B; AU4031789A; WO1989007689A1

Abstract

Abstract of the Disclosure AIRCRAFT RUNWAY WITH GROOVED SURFACE

A manner of providing grooves in the surface of an aircraft runway is described. The grooves are of skewed Y-shape in cross-section, having a steeply-sloping face and a gently-sloping face. The grooves face in opposite directions at the two ends of the runway, each groove is orientated so that the gently-sloping face is toward the adjacent end of the runway. A benefit of the arrangement is to combine a resistance to aqua-planing upon landing at high speeds on a wet runway, at one end of the runway, with a good friction grip between the and runway for emergency braking at the other end of the runway. This benefit is present when the runway is used in either direction.

Description

~Z99908 AIRCRAFT RUNWAY WITH GROOVED SURFACE

This invention relates to a manner of arranging grooves in the surface of a runway.

In order to prevent the onset of aqua-planing of aircraft tires when the aircraft is landing at high speed on a wet runway, the top surface of the runway may be provided with water run-off ~rooves.

THE PRIOR ART

Hitherto, such grooves have qenerally been cut by a saw.
However, saw cut grooves are very costly to produce, and are only marginally ef~ective.

saw cut grooves can be reasonably effective at preventing aqua-planlng when the groves are new, and clean. But saw cut grooves, belng narrow, tend not to be self-cleanlng, and have to be swept. When the runway is asphalt, the edges of a sawn groove tend to curl over ln hot weather. Another disadvantage of sawn grooves is that the sawlng operatlon, in addition to its cost, 15 unhealthy due to the dust created.

A tire will aqua-plane if the water cannot escape quickly enough from the contact patch. The invention is concerned ~X99908 with providing as llttle resistance as posslble to the rapid movement of large quantities of water along the grooves.
Saw cut grooves, even though expensive, are only marglnally effective in conducting large quantities of water away rapidly from a fast-moving tire. tTo make a saw-cut qroove wide enough to conduct the water away adequately and rapldly would be even more expensive.) The grooves used in the invention are aimed at removing more water, more quickly, and thus at deferring the onset of aqua-planlng, but without undue expense.

In US patent no 3791699 (CLARK) 12 Feb 74 there is shown a machine for producing grooves in concrete and asphalt. The grooves as produced by the machine are also shown. The process by which material is broken and removed in this machine has come to be known as the "reflex-percussive!' process. In this process, the concrete is struck with repeated blows, each blow beinq delivered with a heavy hammer, but the hammer is withdrawn forclbly from the surface of the concrete immediately after the blow is dellvered, before the hammer can naturally bounce off the surface. The effect is that the concrete is sub~ect to tensile forces in the area of the blow, due to the movement of the impact-induced shockwave~ within the material. The concrete is broken, not by crushing or cuttlng, but by tensile stresses. Concrete and asphalt of course have guite a weak resistance to tensile stresses, while being strongly resistant to compressive and abrasive stresses.

i299908 Grooves may be cut in ~soft) asphalt by the reflex-percusslon process, but slnce the process works by the reflection of shock waves within the material, the process is better on harder materials. The improvement due to the reflex-percu~slon process, compared wlth other processes such as sawing, therefore i4 even more marked when the groove is in concrete than when lt ls ln asphalt. On the other hand, concrete lespecially poorly laid concrete) sometimes can have a comparatively soft layer on its upper surface, which breaks into flakes upon impact. In this case, it would be difficult to form a clean groove in the concrete by the reflex-percussion process. The guallty of concrete used for aircraft runways, however, is generally hlgh. In asphalt, too, recent lmprovements ln reflex-percussion techniques have made it possible to produce uniform, clean, grooves economically.

A cross-section of the grooves produced by the machine are shown in Fig 3 of '699. The as-formed groove may be described as having a skewed V-shape. The groove has two faces, a gently sloping face and a steeply sloping face.
The invention makes use of the skewed V-shape grooves. The skewed V-shaped groove is open, and clear: the groove conveys water away laterally at good flow rates (so that the grooves may be widely spaced, for economy when forming the grooves); and the groove tends to be self-cleanlng. The skewed V-shaped groove is not so deep as to damage the i - ~299908 runway ~tructure, nor so deep as to be liable to cave in.

A discussion of the performance of grooves formed by reflex percussion, and having a skewed v-shape, ls glven ln the report: Modifled ~eflex-Percusslve Grooves for Runways, by S K Agrawal, publlshed by the US Federal Avlatlon Administration, April 1984, ref DoT/FAA/PM-89/8 and DOT/ FAA/ Cl' - 13 4 / 7 .

BRIEF DESCRIPTION OF THE INVENTION

The invention is concerned with the manner of placinq grooves on an aircraft runway. In the invention, the grooves lie transversely across the runway, and are asymmetrical, or skewed, when vlewed in cross-section along the length of the groove.

The invention, in its broadest aspect, lies in the fact that some of the skewed grooves lie facing one end of the runway, and some lie facinq the opposite end of the runway.

A runway has a Near end and a Far end, and in the invention it ls preferred that the grooves that lle towards the Near end all lle faclng ln the same dlrectlon as each other, and the grooves that lle towards the Far end all lle facing in the opposite direction.

-` 1299908 Preferably, in the lnventlon, the groove~ have the skewed V-shape as illustrated in US-3791699.

Preferably, in the inventlon, in a Near portlon of the runway, being a portlon whlch ls close to the Near end of the runway, the grooves are orlentated ~uch that, of the two surfaces of the groove, the surface whlch lles close~t to the said Near end of the runway is the steeply-sloping surface.

Preferably, ln the invention, in a Far portion of the runway, being a portion whlch ls close to the Far end of the runway, the grooves are orientated such that, of the two groove surfaces, the surface which lies closest to the said Far end is the steeply sloping surface.

Preferably, ln the lnventlon, the sald portlons are spaced apart on the runway, and are so arranged that the sald Near portlon ls the portlon of the runway at whlch an alrcraft, upon landing at the Near end of the runway, touches down and decelerates to taxilng speeds. The Far portion ls the portion of the runway in which an aircraft would be undergolng heavy braklng, at low speeds, in an emergency such as an aborted take-off.

It ls recognised in the invention that, for touchdown at high speeds, what is required of the grooves is that they convey the water away quickly, and leave large dry areas in the contact patch, which wlll lead to a good resi~tance to aqua-planing. On the other hand, it is recognised that, for emergency braking in an aborted take off, the requirement is for the grooves to give a good tire-to-runway adhe~ion. It is recognised that the oppositely-orientated grooves of the invention can contribute to these requirements, in both directions of use of the runway.

Normally, the two portions will be symmetrically arranged as the two halves of the length of the runway.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

In order to further describe the invention, an example of an actual runway which has been provided with grooves according to the invention, will now be described, with reference to the accompanying drawings, in which:

Fig 1 shows a grooved runway, which incorporates the invention;

Fig 2 is a close-u~ of the surface of the runway of Fig 1, showing the disposltlon of the grooves;

Flg 3 ls a plan vlew of an alrcraft tlre landing onto the grooves from the "right" direction;

~299908 Fig 4 is a plan view of' an airora~t tire landing onto the grooves fro~ the "wrong' direction; and Fig 5 is a side elevation corresponding to Fig 3; and Fig 6 is a side elevation oorresponding to Fig 4.

The aircraft runway 1 in Fig 1 co~prise a strip o~ concrete 2.
The runway has a Near end 3N and a Far end 3F.

Extending over the Near portion of the runwaY, which is the portion 4N from the end 3N to halfway along the runwaY, the top surf'ace 5 of the oonorete 2 is eguipped with grooves 6N.

The grooves 6N run transversely across the concrete. As shown in Fig 1, the grooves extend at right angles to the line of the runway. On a runway, it would usually not be allowed for the grooves to be set at an angle to the line of the runway, because such angled grooves ~ight cause an aircraft to veer to the side of' the runway under critical conditions.

At the Far end 3F of the runway, the top surface 5 o~ the concrete 2 is equipped with grooves 6F.

One of the Near end grooves 6N and one of the Far end grooves 6F are shown in Fig 2. The grooves 6 are identical, except that, in accordance with the invention, the grooves 6F face in the opposite direction to the grooves 6N.
Bl~.

Each groove 6 has a steeply sloplng face 8, and a gently sloping face 9. The sloping faces 8,9 meet at the base 10 of the groove 6. The steeply sloplng facc 8 intersects w1th the top surface 5 at lntersection 12, whlle the gently sloping face 9 intersects with the top surface 5 at intersection 14.

The groove 6 as shown is a skewed V-shaped groove, in cross-section. As shown, the intersection of the two faces 8,9 at the base 10 of the groove is a right angle. The steeply slopinq face 8 lles at an angle of 70 degrees to the (horizontal) top surface 5, and the gently sloping surface 9 lies at an angle of 20 degrees to the top surface. As shown, the external corner at the "steep" intersection 12 is quite sharp (ie the radius of the corner is small).

The arrangement of the grooves is such that, in each portion 4 of the runway, it is the steeply sloping face 8 of the groove 6 which lies nearest to the respective end 3 of the runway.

The wheel 18 of the aircraft, as it touches down, engages the top surface 5 of the runway, and then rolls over the transverse grooves.

Flg~ 3 and ~ ~how the wheel runnlng over the same surface at the same speed, where the grooves in the surface are the same depth and width, and the same spacing. The difference ~29~908 g between Flg 3 and Fig 9 lles ln the dlrectlon from whlch the wheel "attacks" the groove. Fig 3 shows an aircraft on landing, attacking the grooves from the correct dlrectlon, in accordance with the invention. Fig 9 shows the wheel attacking the grooves from the "wronq" directlon, accordlng to the preferred feature of the invention.

The shading in Figs 3 and 9 illustrates the much lmproved wheel-to-ground contact area when the wheel attacks the groove in the steeply-sloping-face-first orientatlon.
Numeral 20 indicates the contact patch or footprint of the tlre on the surface. 21 is the direction of motion of the landing aircraft. 23 is the bow-wave that builds up in front of the wheel. 25 is the forwardly and sidewardly directed splash or spray from the high speed passage of the wheel, and 27 is the after-splash of water being shed from the wheel as it breaks contact.

The dark shadlng 29 indlcates a zone of good wheel-to-ground contact, from which water has been (virtually completely) eliminated, so that the wheel is running on dry surface in that zone. The lighter shading 30 indicates a zone in which the water has not been completely squeezed out, and marks the start of aqua-planing.

It may be seen that in the "wrong" orientation of Fig 4, traces of water tend to be led into the area 39 between successive grooves to a greater extent than in the "right"

orientation shown in Fig 3.

The dif~erence between the Fig 3 and Fig 4 conditions is highly dependent on speed. If speeds are slow, most of the contact patch is dry, even in the Flg 4 condltlon. on the other hand, if speeds are hiqh, the water can encroach into zone 39 even in the Fig 3 condition. The difference between the Fig 3 contact and the Fig 9 contact, at different speeds of th~ tlLe, th~refoL~ would not nece~aLlly b~ tll~ ~ame that illustrated.

The following explanations are proposed, as to why the "right" (Fig 3) orientation of the grooves should be so much better than the "wrong" ~Fig 4) orientation at alleviating the onset of aqua-planing.

It is noticeable that in the Fig 3 orientation, the bow-wave 23 in front of the tire is considerably reduced in depth and extent, compared with the bow-wave in Fig 4. The smaller the bow-wave, the less bulk of water has to be cleared to create a dry contact patch. In Fig 3, the water which is projected forwards and downwards by the onrushing tire, and which strikes the ground in front of the tire, tends to strlke the gently-sloping surface 9, and to bounce well forwards and clear of the tire; while by contrast, in Fig 9, water which is pro~ected forwards and downwards tends to strike the steeply sloping face 8, and therefore tends to be reflected back into the path of the oncoming tire. This is `- ~299908 a possible explanation why the bow-wave ln Flg 3 should be smaller than the bow wave in Fig 4. And, the larger the bow wave, the more water has be thrust aside by the tire, and therefore the lower the speed at which aqua-planing sets ln.

Another possible explanation may be offerred as to why the Fig 3 orientation is more resistant to aqua-planing than the Fig 4. With the skewed grooves, the tire tends to exert a higher pressure on the runway surface in the region of the steep corner 12, than in the region of the gentle corner 14.
Therefore, it would be expected that the last place where water could intrude would be into the area immediately contiguous with the steep corner, ie the strip 36. This is borne out in Fig 4, where although water has intruded in other areas of the contact patch, that strip rernains dry.
In Fig 3, water is squeezed out, and the water film broken, by the increased contact pressure in the strip 36.
Therefore a barrier is created, which prevents water from in front of the tire from entering the zone of contact 34. In Fig 4, on the other hand, there is no such barrier to a wedge of water driving into the contact area from in front of the tlre. In Flg 9, the barrier, le the strip 36, ls ineffective, because the strip is located where water is in any event tending to leave the zone 34, whereas in Fig 3, the strip is effectlve, because the strip ls located where water from the bow wave is seeking to enter the zone 34.

If this explanation is accurate, it is important that the steep corner 12 be sharp. If the corner 12 starts to acqulre a larger radius, or if the corner ls rounded due to wear, or if the corner is pltted by spalling, during the formation of the groove, the local lncrease in the contact pressure might not take place, and that may allow the water to start to enter the zone 34. For that reason, grooves ln concrete are generally more efficient and longer lasting than grooves in asphalt. Concrete can retaln a better sharp edge than asphalt. Concrete that has a hard matrlx wlll provide a cleaner edge than concrete with a soft matrix: the concrete used for runways invariably has a hard matrix. On the other hand, the invention may be applied equally to asphalt runways, especially if the grooves are formed as follows.

It may be noted that with conventional processes for forming grooves, even with the conventional reflex-percussive process, it is difflcult, economically, to obtain an edge that is reliably sharp. As surmised above, lt is the sharpness of the edge 12 that is the important factor in creating the high contact-pressure barrier to the wedge of water. An a)paral:us for forming the grooves in such a way that the as-formed corner 12 is sharp, is described and claimed in our co-pendlng patent application, entltled:
APPARATUS FOR FORMING GROOVES IN CONCRETE ETC SURFACES. It 15 therefore preferred, in the present lnventlon, to form the grooves by means of the apparatus as described ln the said co-pending patent application.

~299908 The apparatus described therein is aimed at producing a groove ln whlch the steep corner 12 ls free of plttlrlg arlcl spalling. Concrete ls not qenerally homogeneous, but consists of hard pebbles set ln a relatlvely soft matrlx, and the apparatus is aimed at providlng a clean edge especially in the case where a pebble lies partially across the line of the corner. The pebble can be cut without any tearing out of the pebble, nor of the matrix.

The angle at which the groove is skewed is important. If the steep corner 12 were to have an angle 38 of less than about 50 degrees, the concentrated tire-contact pressure in the strip 36 might be lost, and water might start to enter the zone 34. If the steep corner 12 were to have an angle 38 of more than about 70 degrees, on the other hand, the corner 12 would not be so well supported structurally, and might become vulnerable to being chipped. The an~le of the gentle corner 14 is not so important, nor is it particularly important, from the point of view of the anti-aqua-planing performance of the groove, that the base of the groove be a right angle. It is important that the groove be not so deep as to weaken the concrete, nor too shallow that the water cannot be conducted away properly. A groove depth of about 6 mm has been found effective. The groove spacing is also important: when the grooves have the dimensions shown, they should preferably be set at a pitch of about 75 mm.

~299908 It is preferred that every one of the grooves be set to face in the correct direction, as set out in the inventlon.
However, it would not matter if the occaslonal groove were to face the other way. It is usually speclfied that runway grooves must lie at right angles to the llne of the runway, wlthln qulte close tolerance~.

As mentioned, it is recognised for the above described reasons that an aircraft landing at high speed on a runway should attack the grooves as shown in Fig 3. On the other hand, it is recognised in the invention that the Fig 3 orientation of the groove is not advantageous under other conditions. At low speeds, it has been found that dlfferent effects predominate, leading to different performance reguirements. At low speeds, aqua-planing is not a concern, but at low speeds the requirement for heavy braking can arise, and of course the closer the aircraft gets to the end of the runway, the more it must be ensured that heavy braking can be applied, without the aircraft skidding or otherwise losing ~ontrol. The requirement for heavy braking can occur due to an aborted take-off, or other emergency.

It has been found that, under emergency braking conditions, the highest coefflcient of frictlon at low speeds between the tire and the runway surface, wet or dry, arises when the tire atta~ks the grooves in the Fig 4 mode. Thi~ may be explained ln that a tlre which is undergoing heavy braking tends to dig into the steep corners 12. There is a - lS -mechanlcal lnteractlon, or cog-wheel type of enga~ement, of the tire with the grooves, much more in the Fig 4 mode than in the Fig 3 mode.

When a tire is rolling, but undergoing heavy braklng, the observed rotational speed of the tire ls considerably slower than would be expected in theory, ie from a theoretical computation using the linear speed of the aircraft and the radius of the tire. A tire under braking in fact undergoes a controlled slippage: and the more heavily braked the tire, the greater the slippage. The slippage can be stated as a percentage of the actual rotational speed compared to the computed rotational speed. It ls important that the slippage be prevented from exceeding the percentage limits that the surface can support, because that would lead to skidding. By arranging that the heavily braked tire attacks the grooves in the Fig 4 manner, the tire can undergo a larger percentage slip before skidding. It should be noted that this improvement to the low-speed heavy-braking performance of the surface, caused by orientating the grooves correctly, happens whether the surface is wet or dry, although the tendency is that the "wet" performance is improved more than the "dry" performance.

To summarize, it is recognised in the invention that when an aircraft is landing at high speed, the grooves should face in one direction, to avoid aqua-planing in the wet, but that when the aircraft is travelling at low speeds under heavy lZ99908 braking, the grooves should face in the other d~rectlon, to avoid premature wheel-lock.

Ill the invention, it is recognised that even if a runway were to be used to land and take off alrcraft only ever ln the one direction, it would be advantageous to provide the oppositely facing groove arrangement of the invention, the grooves at the Near end being set for maximum resistance to high-speed aquaplaning during landing, while the grooves at the Far end are set for the maximum coefficient of friction under heavy braking at low speeds.

It will be appreciated that a runway that is provlded with grooves set according to the invention in fact is equally effective to protect both landings and aborted take-offs in both directions.

Claims

CLAIM 1. An aircraft runway, having grooves formed in its upper surface, wherein:

the grooves lie transversely across the width of the runway;

the grooves are asymmetrical, when viewed in cross section along the line of the groove, each groove having a steeply sloping surface and a gently sloping surface;

and some of the grooves lie with the steeply sloping surface facing towards one end of the runway, and others of the grooves lie with the steeply sloping surface facing towards the opposite end of the runway.
CLAIM 2. Runway of claim 1, wherein a substantial number of the grooves that lie towards one end of the runway face in one direction, and a substantial number of the grooves that lie towards the other end of the runway face in the opposite direction.
CLAIM 3. An aircraft runway, having grooves formed in its upper surface, wherein:

the runway has two ends, a Near end and a Far end;

a Near portion of the runway is the portion extending from a point close to the Near end of the runway, to a point remote from the Near end;

a Far portion of the runway is the portion extending from a point close to the Far end of the runway, to a point remote from the Far end;

the grooves are in the surface of the runway and extend over both portions, the grooves in the Near portion being termed the Near grooves, and the grooves in the Far portion being termed the Far grooves;

the grooves in both portions are of skewed V-shape in cross-section;

each groove includes a respective steeply-sloping face, and a respective gently sloping face;

wherein the steeply-sloping faces of the Near grooves lie closer than the corresponding gently-sloping faces of the Near grooves to the Near end;

and wherein the steeply-sloping faces of the Far grooves lie closer than the corresponding gently-sloping faces of the Far grooves to the Far end.
CLAIM 4. Runway of claim 3, wherein each of the two portions extends from the respective end of the runway, to halfway along the runway.
CLAIM 5. Runway of claim 3, wherein each groove includes a steep corner, which is the corner or intersection between the steeply-sloping face and the surface of the runway; and wherein the said steep corner is, in substance, sharp.
CLAIM 6. Runway of claim 3, wherein the angle of the steeply sloping surface of the grooves in both portions to the surface of the runway is approximately 70 degrees.
CLAIM 7. Runway of claim 6, wherein the angle of the gently sloping surface of the grooves in both portions to the surface of the runway is approximately 20 degrees.
CLAIM 8. Runway of claim 3, wherein, in the Near portion, there is substantially no groove of skewed V-shape, of which the steeply-sloping face lies closer than the gently-sloping face to the Near end;

and wherein, in the Far portion, there is substantially no groove of skewed V-shape, of which the steeply-sloping face lies closer than the gently-sloping face to the Far end.