Tying down aircraft
Broomstick,
Truckie's hitch is different. Trucker's hitch - Wikipedia, the free encyclopedia shows the version my dad taught me when I was a kid (no prizes for guessing what he did for a living).
This type of hitch forms a fixed loop on the standing end with the running end passed down and around the restraint point, back up through the loop and finally back to the restraint point to be tied off (although you can tie it off around the knot itself if rope length is limited). All that passing down, around, back up, through the loop & down again forms the pulley and gives a 3:1 mechanical advantage.
If you allow enough room you can form second hitch on the running end to increase mechanical advantag to 9:1, a 3rd hitch on No.2's running end to give 27:1 etc. Need a fair bit of rope & room though.
Truckie's hitch is different. Trucker's hitch - Wikipedia, the free encyclopedia shows the version my dad taught me when I was a kid (no prizes for guessing what he did for a living).
This type of hitch forms a fixed loop on the standing end with the running end passed down and around the restraint point, back up through the loop and finally back to the restraint point to be tied off (although you can tie it off around the knot itself if rope length is limited). All that passing down, around, back up, through the loop & down again forms the pulley and gives a 3:1 mechanical advantage.
If you allow enough room you can form second hitch on the running end to increase mechanical advantag to 9:1, a 3rd hitch on No.2's running end to give 27:1 etc. Need a fair bit of rope & room though.
Last edited by Tinstaafl; 28th Jan 2009 at 18:57.
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I don't like the picture that goes with that Wikipedia article. There is absolutely nothing but the friction of the two half hitches that keeps the upper part intact. Depending on the type of rope and its surface friction, I think that top end will work itself loose very quickly.
If you follow the link to the Animated Knots by Grog website you'll see a variation where the upper part cannot come undone, other than by undoing the whole knot. The top end is then either a slipknot or a noose, or a figure-eight slipknot or noose.
On the other hand, that Grog website suggests that once under tension, you tie the free end of the rope off with two half hitches. I would never do that with anything that's under tension, preferring a slipknot with a double half hitch instead. A plain half hitch that's been under tension is almost impossible to undo. When still under tension - forget it.
If you follow the link to the Animated Knots by Grog website you'll see a variation where the upper part cannot come undone, other than by undoing the whole knot. The top end is then either a slipknot or a noose, or a figure-eight slipknot or noose.
On the other hand, that Grog website suggests that once under tension, you tie the free end of the rope off with two half hitches. I would never do that with anything that's under tension, preferring a slipknot with a double half hitch instead. A plain half hitch that's been under tension is almost impossible to undo. When still under tension - forget it.
Tied properly with sufficient length of the bight through the half-hitches it won't come loose. The tension locks the two half hitches in series. Neither can come undone unless the other is loosened 1st. What tends to happen with slippery ropes like polypro. is that the loop around which the half-hitch is formed slips through. More of a problem if only a single half-hitch is used instead of the two in tandem. An alternative is to add an extra half-twist to form a loop instead a proper half-hitch. That can be done with each half-hitch for a belts-and-braces approach.
My dad & I have secured all manner of loads for travel over outback roads using this knot & it's never come loose if tied correctly. It relies on tension to hold together so if the rope isn't pulled tightly then it can come loose.
My dad & I have secured all manner of loads for travel over outback roads using this knot & it's never come loose if tied correctly. It relies on tension to hold together so if the rope isn't pulled tightly then it can come loose.
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SAS, a bowline is good if you can do, and undo it without tension being applied.
The nice thing about the truckies hitch is that you can apply a lot of tension (three times your own weight, if you do it properly) and then tie it off. But that tension will usually be there (unless you've had a load shift, which is what you're trying to prevent) so it has to be undone under tension as well.
The nice thing about the truckies hitch is that you can apply a lot of tension (three times your own weight, if you do it properly) and then tie it off. But that tension will usually be there (unless you've had a load shift, which is what you're trying to prevent) so it has to be undone under tension as well.
Most of the time for tie-downs I just pull the rope tight without using any fancy knots then use a slipped half-hitch for the 1st knot. That's followed by a 2nd half hitch using the bight just formed to lock the 1st hitch. Both hitches must be snug against the attachment point otherwise all that's formed is a slip knot with room to slip loose. If the bight or running end is long enough to flail around then I use more half-hitches as necessary to secure the loose bits to the standing end.
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Tinslaaf, sounds like the exact same thing I would do.
Fortunately we have chains with carabiners permanently installed at our little corner of the field. Can't do much wrong with those.
Fortunately we have chains with carabiners permanently installed at our little corner of the field. Can't do much wrong with those.
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I like PilotDAR's contributions 
IMHO, the most vulnerable planes are going to be lightweight ones with a low wing loading, and preferably high wing.
A C150 etc gets blown away easily, as do rag/tube taildraggers.
The least vulnerable will be relatively heavy low wing IFR tourers with high wing loading. I never tie down my TB20, though most of the time it is hangared. I carry the screw-in tiedowns but have never yet used them. With chocks, it is almost un-movable. I reckon it would take a 60kt wind to move it at all.
Regarding weights, anything a human can lift is going to be next to useless. A tiedown rope needs to attach firmly to the ground, so either to the rings fixed into a concrete apron, or the type which screws into the soil. There have been a good number of cases of pilots flying away with these tiedowns still attached (not sure how good the preflight check was
).
The rope needs to be tight. It is a bit like a wooden panel fence in strong wind; as soon as there is any play in it, the wind will rapidly rip it apart.
IMHO, the most vulnerable planes are going to be lightweight ones with a low wing loading, and preferably high wing.
A C150 etc gets blown away easily, as do rag/tube taildraggers.
The least vulnerable will be relatively heavy low wing IFR tourers with high wing loading. I never tie down my TB20, though most of the time it is hangared. I carry the screw-in tiedowns but have never yet used them. With chocks, it is almost un-movable. I reckon it would take a 60kt wind to move it at all.
Regarding weights, anything a human can lift is going to be next to useless. A tiedown rope needs to attach firmly to the ground, so either to the rings fixed into a concrete apron, or the type which screws into the soil. There have been a good number of cases of pilots flying away with these tiedowns still attached (not sure how good the preflight check was
).The rope needs to be tight. It is a bit like a wooden panel fence in strong wind; as soon as there is any play in it, the wind will rapidly rip it apart.
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Tying down aircraft
The lower the stall speed the easier they blow away and tail draggers have the added disadvantage of sitting at an angle of attack that helps this to happen.
I used to park my J3 tail to a strong wind with the controls locked, wheels chocked and tail wheel and wings tied down to screw in tie downs.
I used to park my J3 tail to a strong wind with the controls locked, wheels chocked and tail wheel and wings tied down to screw in tie downs.
More on Midshipman's Hitch
This is a excellent, if ignored, knot -- and easy to learn, tie, adjust and untie.
Taut-line hitch - Wikipedia, the free encyclopedia
It's still my favorite knot for tying things down securely. You can tension the rope as you tie it and can even adjust the tension as it will slide like a Prussik; in fact arborists sometimes use it to climb trees. That makes it a knot that professionals are willing to trust with their lives
A good knot or hitch can be untied after being loaded and this hitch does not jam.
I have done several thousand miles with a canoe or two on top of my car at 75+ mph and the hitch has always held in 1/4" nylon laid rope.
While I am quite comfortable doing aerotows in a glider behind laid polypropelene rope, remember that glider tow ropes are done with eye splices as knots in the stuff are not dependable.
Polypropelene rope is not something I would trust to tie down anything worth serious money, but it is adequate for throw bags where you need length and light weight.
Bowlines can be shaken lose as some mountaineering accidents have shown; so, it's not something to trust unattended for a week or so unless seizing is used. It is also difficult to adjust tension with Bowlines.
Taut-line hitch - Wikipedia, the free encyclopedia
It's still my favorite knot for tying things down securely. You can tension the rope as you tie it and can even adjust the tension as it will slide like a Prussik; in fact arborists sometimes use it to climb trees. That makes it a knot that professionals are willing to trust with their lives
A good knot or hitch can be untied after being loaded and this hitch does not jam.
I have done several thousand miles with a canoe or two on top of my car at 75+ mph and the hitch has always held in 1/4" nylon laid rope.
While I am quite comfortable doing aerotows in a glider behind laid polypropelene rope, remember that glider tow ropes are done with eye splices as knots in the stuff are not dependable.
Polypropelene rope is not something I would trust to tie down anything worth serious money, but it is adequate for throw bags where you need length and light weight.
Bowlines can be shaken lose as some mountaineering accidents have shown; so, it's not something to trust unattended for a week or so unless seizing is used. It is also difficult to adjust tension with Bowlines.
I don't think it really matters which is your knot of choice, as long as it will stay taut and non slip until you want it to. The antonovs that blew away in Poland were all tied down to rings set in concrete. I don't know if it was the cables that broke or the tie-downs pulled out of the wings. Point is that sometimes the wind is just so strong that it will blow away hangars, not just aircraft 
I think there's an important qualifier in your statement that should be emphasized, Piper.C, viz. "...as long as it will stay taut and non slip...". There are lots of knots that look good and seem to hold but don't stand up to loading eg a granny knot. Also, as a general rule all knots become a weak point in a rope, some more than others so the type of knot can be important. No good using a 1000lb rope if the knot used breaks at some much lower value.
I found it surprising just how many people couldn't tie an effective knot. That's why I used to make sure my students knew how to tie rope tie-downs simply but adequately.
I found it surprising just how many people couldn't tie an effective knot. That's why I used to make sure my students knew how to tie rope tie-downs simply but adequately.
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Trimming nose down for an aeroplane with tricycle (nosewheel) undercarriage makes a huge difference. When trimmed nose down, with the nose into wind, the upwards force from the tail keeps the nose low, reducing the amount of lift generated by the wings.
I've seen it first hand when we hand strong winds last year - our PA28s were skipping around until we trimmed nose down and locked the control columns forward.
Taildraggers are tricky, though!
I've seen it first hand when we hand strong winds last year - our PA28s were skipping around until we trimmed nose down and locked the control columns forward.
Taildraggers are tricky, though!
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our PA28s were skipping around until we trimmed nose down and locked the control columns forward.
Locking the elevator full-down requires addition brackets or other things which might get lost or misapplied. And it contravenes the advice in the POH, although I don't know how serious that is in this case.
And furthermore, lift is not determined by the position of the elevator, but by the angle of attack of the wings. As long as the wind is not strong enough to lift the nosewheel clear off the ground, or extend the oleo to a sufficient length, it should not matter whether the elevator is trimmed or positioned up or down.
Lift will be affected by elevator position. As wind strength increases tailplane forces will cause the nose to pitch up or down, pivoting around the main gear (nosewheel types). Locking the elevators in a down position will produce a nose down pitching force, which in turn will aid reducing the mainplane's AoA.
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What he said (beat me to it).
The winds in question were 35kt gusting to damn near double that. In other words, the gusts were around PA28 rotate speed! Even with the controls tied back with the seat belt, full nose down trim made a noticeable difference. Our T-.tail Arrow was repeatedly lifting the nose wheel as the tail pushed down - ending up on the tail skid at one point. The trim settled it right down
The winds in question were 35kt gusting to damn near double that. In other words, the gusts were around PA28 rotate speed! Even with the controls tied back with the seat belt, full nose down trim made a noticeable difference. Our T-.tail Arrow was repeatedly lifting the nose wheel as the tail pushed down - ending up on the tail skid at one point. The trim settled it right down