Aircraft Tie Down Knot - Another company, Carolina North Manufacturing, claims that their 3/8-inch rope ratchet, with a load limit of 250 pounds, is perfect for securing aircraft. Even with a 1/2-inch ratchet, at a load limit of 500 pounds, there is not enough strength if a fierce microburst blows up.
Portables and DIYsSelf-installed or portable tiedown anchors come in three types, screw auger, helical plate auger and stake. All are dependent on geology. Anchors that hold in clay might pull from sand. None will get through rock or hold much in soupy mud.
Aircraft Tie Down Knot
One system that takes advantage of this principle is Fly-Ties-not to be confused with Fly-Tyes. The company markets excellent stake type anchors. This system includes a Delrin plastic hub for each tie down point (three in all).
Each hub has three symmetrically spaced holes which receive an 18-inch stainless steel stake driven into the ground outwardly. The tiedown ropes (not provided), are secured to the forged-steel eyebolts integral to each hub. Then, when its time to break camp, the stakes are pulled with a special tool (included).
If you are looking for polyester rope locally, we suggest a marine outlet, not a hardware store, unless it is a coastal outlet. Inquire about polyester/Dacron rope and ask about the tensile strength for the 1/2-inch variety.
Dacron is the Dupont trade name for generic polyester rope. Helical plate augers also screw into the ground, but because of their greater surface area, they take a better bite. Sportys Pilot Shop lists two helical plate types.
Their 15-inch, portable model withstood 400 to 600 pounds of pull during evaluation tests and their 4-foot, permanent model, withstood 4000 to 5000 pounds during tests, more than enough to hold your average light aircraft. Stake type anchors are merely pounded into place and can't be expected to hold much unless the stake is large and driven deep.
(Also, driving the stake at an angle and placing it so the tiedown rope can be angled improves holding.) Our ramp tour revealed that many owners use nylon rope or webbing and some use gasp-manila rope.
Nylon is strong when new, loses a little strength when wet but isnt as abrasion resistant as polyester, an important characteristic for tiedowns. Manila is half as strong as nylon but has poor weather resistance and will rot in no time.
Its simply the worst choice. Polypropylene is strong and light but gets stiff in the cold and has virtually no UV resistance, so it loses strength rapidly. Then, 6 inches of sand, followed by 6 inches of gravel, is poured and packed around the shaft.
After that, concrete is shoveled in and smoothed out with the ground ring sticking up just above it. Finally, a beveled edge is formed around the circumference. If frost heave is a problem, extend the concrete below the frost line.
RecommendationsWe don't think owners should spend much money or time worrying about tiedowns. On the other hand, if you're going to bother to tie down, do it right. That means using serviceable polyester rope or, if you prefer nylon, change it more often.
Absent any mechanical damage or chemical degradation, polyester should last two to three years. We recommend avoiding S-hooks, tension tighteners, ratchets and other gimmicks that serve only to reduce the ropes basic strength by introducing unknown tensile weaknesses that grow worse due to weathering.
Simply whip the ends of the rope, as shown in the drawing, and use good knots. There it is, in FAR 23.415 (c), which says the tie-down attachment fittings and the surrounding structure must be designed for limit load conditions resulting from wind speeds up to 65 knots horizontally from any direction for the weight determined to be critical for
tie-down. It should be easy to knot and should hold a knot well while securing an aircraft in high winds, for it is important that the rope be capable of being snugged up and remaining that way.
But by far, the most significant wear factor is the weather. Strong sunlight, extreme dryness, petroleum products, moisture, mildew and rot sharply reduce the strength of the tie down rope in a short time. Also With This ArticleClick here to view the tiedown checklist.Click here to view the tiedown sins.Click here to view “Do the Math: A Lotta Lift.”Click here to view the tiedown illustrations.Click here to view the tiedown addresses.
The best polyester product we found is American Cordages three-strand twist/SSR-1200 (1/2-inch), a combination of filament polyester and the company's proprietary Ultra Blue fibers, providing an average tensile rating of 7200 pounds. (See the address box.)
Nylon webbing is a popular tiedown choice but its weakness is the fastening devices that allow it to be snugged up. And snug is important, says rope expert McKenna: Rope loves tension. If the rope is loose, it is subject to shock loading and the more it moves around, the weaker it gets, the more it notes.
Although we know a little about rope, you can imagine there are experts who know everything and our man is Hank McKenna, of Tension Technology International, an independent consulting group who knows rope inside out and recommends the right cordage for everything.
McKenna counts among his clients the likes of Exxon and Mobil-whose supertankers dare not suffer a snapped mooring line. For example, one cordage manufacturer we contacted reported a tensile rating of 4400 pounds for their three-strand twist, 1/2-inch polyester and 6200 pounds for their three-strand twist, 1/2-inch nylon.
For quality polyester, tensile strength of nylon and polyester should be essentially identical. If you're a claims adjustor for Avemco, here's a nightmare: A microburst sweeps through Oshkosh in the middle of the EAA convention, chewing up everything in its path, which happens to be oh, maybe 10 percent of the insured general aviation fleet.
Secure .gov websites use HTTPS A lock ( LockA locked padlock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites. As a rule of thumb, the tiedown anchors and ropes ought to be capable of carrying about a 5000-pound load, allowing for knots and other degradation.
But considering the poor condition of many tiedown ropes we examined on a recent ramp survey, we doubt if many are even close to that value. (No, a cinder block on the tail ring isnt enough.) Over time, the aircraft tiedown ring picks up a little corrosion and some fatigue, so it loses strength.
But the ring isn't the problem, the ropes and anchors are. Nicely packaged in a PVC tube and weighing 6 pounds, the kit sells for $139.95, plus $12.50 shipping, and is guaranteed for one year, money back.
Bruce Roberts, the company president, says that in tensile load tests of Fly-Ties in light soil, the soil failed at 10,000 pounds while the FlyTies came through unscathed. High WearThe ideal tiedown rope must have several properties.
It has to resist the brutal chafing generated by pilots and line crew as they feed, pull and yank it through hundreds of tiedown rings a year at a busy FBO or even a fraction of that at an owners personal tiedown spot.
Screw augers are nothing more than the K-9 anchors available at the local pet store-or pilot shop-and consumers in both markets will quickly dismiss these galvanized corkscrews as lightweight, at best. While they may satisfy the tiedown rules at air shows, they offer little beyond that, although these hold better than we expected in our pull out tests.
Worse yet, S-hooks formed of wire stock that are often used with webbing and occasionally rope will almost certainly bend before good rope or webbing snaps, a fact not noted by the manufacturers who sell such hardware.
Sportys, for example, sells a pre-cut tiedown whose S-hooks are rated for 990 pounds. In our view, if the anchor and tiedown ring will hold more, the S-hook is then the weak link. In our pull test, the S-hook actually held 1,000 pounds, bettering Sportys claims.
Because the tiedown rings of most general aviation aircraft will not pass a rope more than 3/4-inch in diameter, this is the upper limit of rope size. Because 3/4-inch rope is more difficult to knot, 1/2-inch rope is considered the ideal.
Even as they're shelling out $20 each for those screw auger portable tiedowns, most OSH goers know these devices are just for show. There's no way those flimsy stakes will hold against a gale, right? Right, although you could get lucky and have enough camping junk on top of the wing to spoil the lift.
The typical permanent tiedown on a paved ramp is installed so snowplows can pass freely, with the ground rings simply recessed below ramp level. This is easily accomplished by auguring a 12 X 24-inch hole, centering a 4-foot, helical-plate, tiedown anchor in the hole, and boring it into the ground until the ring is just below ramp level.
Portable anchors are required for off-airport adventures, air shows, and fly-ins. We can tell you that the security of both permanent anchors and the portable variety varies all over the map. And just because a tiedown area appears to be permanent, it doesn't mean the anchors are.
But more on that later, too. First, lets talk rope. There are two elements in an aircraft tiedown system: The anchor points and some flexible cord, rope, webbing or chain to secure the aircraft to the anchors.
At airports, the anchors are usually permanent, and the flexible member is usually rope. Similarly, use rope instead of webbing and forget about chain or cable, both of which are difficult to keep taut and mercilessly beat the tiedown ring when passed through for fastening.
For portable tiedowns, use the K-9-type augers only if you don't care about whether the airplane will survive a blow. Otherwise, we like the Fly-Tie system, which is expensive but well designed. For permanent tiedowns, Sportys helical (four-foot) installed as described is sufficient to anchor the Queen Mary and, at $17, its a good value.
Power washing flushes out the grit and restores the operation, and West says the company has provided first-rate product support. But Fly-Tyes are hardly low maintenance. When we visited Martin State to examine this system, not a single one was working on the transient ramp.
Some webbing was twisted and abandoned above ground while other units were jammed below ground. Fly-Tyes were subjected to a dynamometer test where 5,000 pounds of tension couldn't budge them, so the inertial reel seemed robust.
However, at $800 to $1200 per tiedown, this is an expensive system. As for the placement dimensions, the two wing anchors should be 20 feet apart, and the tail anchor should be 20 feet behind them to accommodate a wide range of airplane sizes.
Were quite certain that ropes and tiedown rings will give it up long before such an anchor will pull free. For more than five decades, active and dedicated aircraft owners and pilots have turned to AVIATION CONSUMER to answer their most important buying questions.
This website contains many older reviews. Unless otherwise noted, these reviews carry product pricing from the time of the original review. Sixty-five knots? You read that right. When it left the factory, that chintzy little tie-down ring was theoretically capable of understanding the lift generated by that much wind.
Depending on how heavy the empty airplane is and whether it has a tail or a nosedragger, the load can be considerable. (See the sidebar link below.) We also found an intriguing permanent tiedown system made by Fly-Tye, LLC.
Its distinguished by nylon webbing that retracts into the ground on an inertia reel, disappearing entirely except for the bitter end, which has a stainless steel swivel hook for the aircraft tiedown ring. Because it flushes with the ramp, this system does not present any snags for snowplows.
Although it appears to be exceptionally well made, it has a significant weakness. Jake West, the airport manager at Martin State Airport in Baltimore, which has Fly-Tyes on the transient ramp, told us that sand used during the winter jams the inertia reel mechanism.
Although few of us think much about tiedown anchors and ropes, if they are going to bother to lash the airplane down in the first place, its worth doing it with the best materials which, in the aviation scheme of things, are dirt cheap.
Heres an analysis of whats admittedly a dull subject: Tiedowns. In McKenna's estimation, the right rope for aircraft tiedowns is a no-brainer: Three-strand polyester. It meets all the weather resistance and knot-holding criteria and its strong.
But, says McKenna, get the right stuff. If you buy a good grade of polyester rope, it should be virtually the same strength as nylon. Unfortunately, there's a lot of low-grade polyester in the consumer market, says McKenna.
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