Expedient runway surfacing with post tensioning system for expeditionary airfields

A portable airfield runway having an anchoring and tensioning system is crised of a plurality of fiberglass reinforced plastic panels anchored with earth anchors at each end of the runway and uses self-contained hydraulic tensioning and load maintenance units to maintain constant tension on the runway while allowing for both expansion/contraction due to temperature and dynamic aircraft braking loads.

This invention relates to co-pending U.S. patent application Ser. No. 
631,954 filed July 17, 1984 by Preston S. Springston and Richard L. 
Claxton for PREFABRICATED PANELS FOR RAPID RUNWAY REPAIR AND EXPEDIENT 
AIRFIELD SURFACING, and commonly assigned. 
BACKGROUND OF THE INVENTION 
This invention relates to runway surfacing, and particularly to a runway 
formed from a plurality of interconnected portable fiberglass reinforced 
polyester mat panels in conjunction with earth anchors and hydraulic 
tensioning system. 
Currently there are a variety of portable airfield landing mats in the 
prior art literature. However, most such mats are for lightweight 
aircraft, helicopters and VTO aircraft, and are unsuitable for heavy 
aircraft. One matting presently in use for surfacing of expeditionary 
airfields and for rapid runway repair consists of extruded aluminum 
planks. The aluminum matting planks, however, are difficult to produce and 
are expensive, and also present a bump profile which causes overstressing 
of critical components of aircraft which must traverse bomb craters in 
runways surfaced over with such matting. Other landing mats involve 
complex laminar and/or mechanical structures which are also difficult and 
expensive to produce, and do not provide anchoring with a constant tension 
on the runway while allowing for expansion/contraction. 
SUMMARY OF THE INVENTION 
The present invention is a portable airfield landing mat and anchoring and 
tension system for commercial and military use in the expedient surfacing 
of forward area airfields. The invention comprises a panel which can be 
linked with others to form airfield runways and also to form a protective 
and trafficable cover over backfilled bomb craters in conventional 
airfield pavements. The invention has further utility as a relocatable 
surfacing for runways and parking aprons of V/STOL forward operating 
facilities and taxiways and parking aprons of expeditionary air bases and 
expeditionary airfields. 
The portable panels each consist of a fiberglass reinforced plastic 
composite mat. The panels are connected together with bolts to form 
airfield surfacing and pavement repair. A self-contained, closed hydraulic 
tension and load maintenance device which maintains a nearly constant 
tension on the runway while allowing for expansion/contraction along with 
deadman type earth anchors provide the necessary reaction force at each 
runway end.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The expedient airfield runway of this invention has three primary 
components: fiberglass reinforced polyester panels 10, hydraulic 
tensioning units 12, and earth anchors 14, as shown in FIG. 1. A typical 
fiberglass reinforced panel (i.e., plastic composite matting panel) is 
shown in FIG. 2 and is further reinforced along its edges with cloth or 
woven aramid fibers. Runway panel composition fabrication and assembly are 
fully disclosed and discussed in aforementioned U.S. patent application 
Ser. No. 631,954. The fiberglass matting panels 10 are readily field 
assembled to form a runway taxiway or parking apron. The hydraulic 
tensioning units 12 are connected along panel edges at one or opposite 
ends of the assembled runway, and are used in conjunction with earth 
anchors, as shown in FIG. 1, for post tensioning of a fiberglass 
reinforced panel surfaced runway. 
A single tensioning unit 12 is shown in the schematic of FIG. 3 and is 
composed of a dual acting hydraulic cylinder 17 (having a 12 inch stroke, 
for example), a flow control valve with integral check valve 19, and a 
bladder type accumulator 20. One end of the tensioning unit 12 is 
connected to an edge of the runway mat via a steel rod 22 and the other 
end connected to an earth anchor via steel rod 24. A deadman earth anchor 
14 is shown in FIG. 1, however, other suitable earth anchors can be used, 
and two alternate earth anchors are shown in FIGS. 4a and 4b, by way of 
example. 
FIG. 4a illustrates a cross plate earth anchor 25 positioned in a slot in 
the ground which is then backfilled. Steel rod 24 from a tensioning unit 
12 connects to the rod of anchor 25. The earth anchor of FIG. 4b uses a 
tubular shaft with tines 26 having an adapter plug 27 and take-up bolt 
assembly which is used to fasten a connection means to steel rod 24 of the 
tensioning unit. Tines 26 of the tubular shaft are secured in the ground 
with a grout 28. Other suitable earth anchors can also be used with the 
present system. 
This invention may be used in conjunction with soil stabilization either by 
conventional chemical stabilizers, e.g., lime, cement, asphalt, or by 
mechanical means such as soil grid reinforcement or a lower membrane 
placed in the subgrade for soil reinforcement. With soil 
stabilization/reinforcement the invention can be used for surfacing of 
runways for use by medium weight and cargo aircraft. 
The airfield surface of the present invention is installed as follows: the 
runway ground surface 29 is compacted and graded. Then the fiberglass 
reinforced panels 10 are assembled on the runway ground surface 29 and 
bolted together. A number of earth anchors 14 are installed at suitable 
intervals along each end of the runway (a typical 72.times.900 ft STOL 
runway requires eight evenly spaced earth anchors and hydraulic units at 
each runway end). Boxes containing the hydraulic tensioning units 12 are 
set just below the grade of runway ground surface 29 between respective 
ground anchors and the runway end (see FIG. 1). Steel rods 22 having 
threaded ends and a turnbuckle 30 are connected to the edge of matting 10 
by suitable means such as shackles, bolts, etc. (not shown). The opposite 
end of the tensioning units are connected to the earth anchors 14. 
The runway is then tensioned by adjusting each hydraulic tension unit as 
follows. Accumulator 20 is precharged with 1600 psi of nitrogen 32, for 
example; a bladder within the accumulator separates nitrogen 32 from 
hydraulic fluid. Hydraulic fluid is pumped into the system at quick 
disconnect coupling 35 to an hydraulic fluid pressure of 1600 psi, for 
example. Slack is removed from the steel tensioning rods 22 and 24 and the 
hydraulic piston 36 is positioned properly by means of turnbuckle 30. 
Depending upon the time of day (i.e., runway expansion condition) the 
system is pumped with hydraulic fluid to one of the pressures indicated in 
FIG. 5 which shows piston position at 150 degrees F., 100 degrees F., and 
50 degrees F. for a 12 inch hydraulic cylinder. Each tensioning unit 12 is 
adjusted per the foregoing procedure starting with those units at the 
runway centerline and proceeding outward in a symmetrical fashion to those 
at the runway edge. Each end of the runway is tensioned concurrently. The 
system is now ready for operation. 
Once in operation the system performs as follows: The fiberglass reinforced 
panels 10 matting distributes aircraft wheel loads to the underlying 
subgrade thereby affording long traffic life. The tension units 12 system 
maintains tension on the runway within prescribed bounds. For a 
72.times.900 ft STOL runway each end has an applied tension of between 
56,000 and 72,000 lb, for example, depending upon ambient conditions. This 
tension prevents warping of the runway as a result of 
expansion/contraction and prevents the development of a matting bow wave 
ahead of the landing gear of braking aircraft. 
A tension unit 12 operates as follows: Runway expansion causes the cylinder 
piston 36, FIG. 3, to retract thereby increasing cylinder 17 volume. 
System pressure is maintained by accumulator 20 which forces additional 
pressurized hydraulic fluid into the system accompanied by a slight drop 
in gas pressure and fluid pressure, and, consequently, runway tension. 
Runway contraction causes piston 36 to be withdrawn from cylinder 17 
thereby reducing cylinder 17 volume. Hydraulic fluid is forced into 
accumulator 20 compressing the nitrogen gas 32 thereby resulting in a 
slight rise in system pressure, and, consequently, runway tension. A flow 
control valve with integral check valve 19 permits unrestricted relatively 
slow (quasi static) flow of fluid resulting from runway 
expansion/contraction. An aircraft braking on the runway, however, will 
produce a very short term dynamic effect. The flow control valve 19 will 
allow only minimal by-pass of fluid under such a dynamic shock loading 
condition. The fluid being noncompressible, the aircraft braking forces in 
the matting will be transmitted directly from the matting 10, through the 
tension unit 12, and to the anchor system 14. 
Obviously many modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that within the scope of the appended claims the invention may be 
practiced otherwise than as specifically described.