[Bill Cummings]

Creep in weak-link strength.

Some things that can cause creep in weak-link strength.
If the problem is at the winch/reel the remedy is not of necessity at the weak-link.

Did you know that as you pull more line off of the winch/reel a simple payout system will increase the line tension as the rope diameter on the drum gets smaller?

This is understood by the long time platform tow pilots but for those that haven’t stopped to think it through yet I have come up with this analogy that has worked for me in the past.

Let’s say your winch/reel doesn’t have any towline on it yet.
Let’s say your winch/reel axle is now visible because there is no towline on it.
Let’s set (SET not say) the brake pressure so that the brake pads hold the caliper so that you cannot turn the winch/reel without a pipe wrench on the axle.
Depending where we grab the pipe wrench handle either down close to the pipe wrench jaws at the axle or at the other end of the pipe wrench handle away from the pipe wrench jaws, which choice will make it easier to turn the winch/reel against the brake pads?
If you said it would be easier to turn the winch/reel by grabbing the pipe wrench handle at the end farthest from the jaws you are now on the same page as the long time platform tow pilots.

Put your first layer of towline on the axle one wrap deep. If you pull until the winch will turn it will be hard to turn the winch/reel against the brake. Once you have all four thousand feet of towline on the winch/reel the top wraps will be farther from the axle and it will be easier to pull the line off against the brake. Kind of like grabbing the pipe wrench higher up on the handle.

Pretend your significant other bought you a brand new winch/reel and four thousand feet of towline. Wow! Are we going to get high or what? Probably not right away. Your troubles await you!

If your towline is wrapped snugly around the drum with each wrap against the previous wrap it will payout with a minimum of abrasion. This assumes that the line is coming off of the drum perpendicularly. Coming off at an angle will cause abrasion while increasing the tension above your desired setting.

If the line is wrapped loosely with many layers deep the line will dig into the wraps which will increase line tension from friction and possibly nest stopping payout.
This can cause a weak-link to break.
In this situation the problem is not at the weak-link.
Remember that not only does the digging in of the line cause more friction against the towline creating more line tension for the pilot but the line is being pulled out from a smaller diameter as was discussed earlier. Two things that increase the tension to the pilot. A double whammy for weak-links.

Pulling off at an angle gives you the triple tension whammy. Any one or combination of whammies will break a proper, safe, weak-link.

Once a winch/reel momentarily stops paying out there is also a fourth tension whammy called inertia. Depending on the weight and size of the drum this inertia can be just a little or a lot.

If you are using towline with a low stretch value the inertia issue is magnified.
What do you think? Should we name this, inertial, shock load, tension increasing, whammy # five?

We once splashed through a mud puddle putting mud on the brake rotor. The mud dried and left grit to embed itself into the brake pads. For many more tow ups we had the winch/reel paying out line with too much line tension due to the increased friction against the brake rotor.

Is the problem the weak-link or one of several other causes or maybe a combination of causes?

Whatever the cause “weak-link creep,” usually ends up becoming the fix which in turn has you approaching the edge of the safety envelope in the direction of unpreventable stalls when tow tension is lost.

We should be asking ourselves these questions:
1) If I’m low during platform towing and the truck is dashing out ahead of me would I be better off, should the payout freeze up, with me being at 45 degrees to tow or 25 degrees to tow?
2) If I was safer static towing with a climb restricting bridle to the keel to handle low angles of tow am I now immune from low angle hazards while platform towing without a climb restricting bridle?
3) If I should have a payout lock up would I be better off with the platform rig maintaining me with enough airspeed/energy to land to either side of the runway/road or have the rig steadily accelerating away from me? (Be careful here with this answer.)
4) If I have a 5,000’ runway should I have 4,000’ of towline on the winch/reel?
5) Does higher tow tension narrow the distance that I can be to left or right and downwind of my platform rig?
6) Will too much line on my winch/reel cause excessive line abrasion and/or nesting?
7) What length of towline is simply too much for the winch/reel that I’m using.
8) Is it easier to find myself, “locked out over the top” at low towline angles or high towline angles while platform towing.
9) Did I attempt to fix the payout problem at the winch/reel or did I fudge with, “Weak-link creep?”
10) If my weak-link breaks will I more likely be able to prevent a stall?

[Bob Kuczewski]

How does this look Bill?

Assuming that the braking mechanism does not change as the line is paid out ...

spool_diameter_s.gif (94.49 KiB) Viewed 5806 times

[Bill Cummings]

spot on Bob

[Bob Kuczewski]

Thanks!!

There's a great program called "Blender" that lets you make realistic 3-D drawings and animations like this one. I am hoping it will be very helpful in developing the training manual. It's free software and you can download a copy at blender.org.

There's also a web site for Blender artists (blenderartists.org) which shows off all the cool things people have done with Blender. Some of the images there are very difficult to tell if they're real or not.

Blender isn't an easy program to use, but if anyone is interested, I'm thinking we could start a working group of people who want to learn it together. Please contact me if you'd like to give it a try. There are also lots of tutorials available on line.

Here are a few pictures from blenderartists.org that I found today. Remember, none of these are real photographs!

SanctuaryRisingOverlook.jpg (151.43 KiB) Viewed 5744 times

mercedes_rendu_final3.jpg (63.66 KiB) Viewed 5744 times

Gamepad05.jpg (32.09 KiB) Viewed 5744 times

Nessie_Prefers_No_Fishing.jpg (51.14 KiB) Viewed 5744 times

The talent of those real artists puts my little spool diagram to shame!!    

[Bill Cummings]

Platform pay out winch/reels will always need a line splice at some point in the PL operation.
Using a hollow center towline is a must for smooth splices.
Many pilots know how to fid the line into the center of the towline to make a nice splice.
Here is a suggestion that will almost always stop future line breaks at one end of the splice or the other.

After making your splice feed both ends back outside the hollow towline and cut the ends at an angle. Next unbraid the end and cut the end into a long taper. Last pull the end back inside the hollow towline.
When done correctly you will not be able to drag the splice through your fingers and know where the end of the splice is. This will stop line breaks right at the ends of the splice.

For sure don’t allow a hard melted end to remain inside the hollow towline. A melted hard end will practically guarantee a line break exactly at the hard melted end of the splice.
Strive for LLoonngg tapering splice ends.
I have done many break tests on splices and have found this to be worth the extra time it takes to make long tapering splice ends.

[Bob Kuczewski]

I'd like to make an animation of that process, but I think it may be beyond my skills!!!     

[Bill Cummings]

How many pilots out there are flying a hang glider that is ten or more years old?
A show of hands please! Wow! That many of you!!
Do you remember or still have a glider where the lower nose wire keyhole tang was/is secured by a rubber retainer?

This new (at the time) idea didn’t pass muster with me and I used a stainless steel safety ring that I put through the keyhole after it was fastened to the anchor post. I used a safety ring at the underside nose wire keyhole tang and at the haul back keyhole tang. The safety ring made it impossible for the keyhole tang to become unattached from the anchor post bolt for whatever reason that might come along.

I never had one become unattached but I heard of it happening several different times at the nose plate and once at the haul back anchor.

The haul back keyhole tang of Darren Fox’s hang glider was only around the haul back anchor and not seated into the anchor posts slot. It became unattached and the wing partially folded up and dove Darren into a tree at Chelan Butte, WA (so I’m told).
If Darren had used a safety ring to secure the keyhole haul back tang I’m quite sure he would have realized the glider was not set up correctly.

Two separate events had the keyhole tang becoming unattached at the nose plate while launching from a platform truck. The nose release rope crowded the keyhole tang off of the nose plate anchor post but not making itself evident until just after the nose release was activated at 30 miles per hour. (OUCH!)

Two other key hole tangs became unattached at the nose plate in the hands of the people giving a nose assist at a foot launch sites. These were caught before launching. (This may have occurred more than the two times that I heard about.)

I’d be willing to bet that the pilots that saw their gliders come apart on launch suffered a huge blow to their confidence level.

For platform towing this is definitely an important preflight consideration with older model hang gliders.

[Bill Cummings]

Platform Launching hand holds are a MUST!
GLV Ground Launch Vehicle as in an aero-towing launch dolly, in general, have adequate hand holds since it is not much of a problem to lift the dolly’s front wheels off the ground once sufficient air speed has been attained.

If the launch dolly weighed more than it does there would come a time where the current hand holds in use now would be stripped through your grasp.

With this in mind you should be able to understand that the current launch dolly hand holds installed onto a truck platform launching rig would be more easily stripped from your grasp than hand holds that are fastened on both sides of your hands.

Ridged hand holds are alright as long as they are designed not to snag any low hanging cords, lines or wires.

Although you may not be able to lift a two hundred and fifty pound bar bell off the floor it is quite possible that you could easily do it with your hands and two police officers lifting you by your upper arms. (Caution, this his may be confused with resistance.)

Greater resistance is exactly the goal when platform towing.

Rather than allow a thermal under one wing to rock you out of the platform launching yokes into a banking turn you want a better grasp on the truck hand holds than the launch dolly style hand holds would provide.

Since it is harder to hold your body position forward while reaching for a nose release lever the better release method is to have both hands around the base tube and also around the hand holds when the nose release is activated.

Next you can swing back to trim position or slightly behind and launch at your FIXED launch airspeed. This airspeed needs to be enough that without a towline you could launch, round off, get vertical, and land on the left or right side of your road or runway.
You can even land on the road as the truck goes away at your FIXED launch speed.

Allow your fingers to be stripped clean of the hand holds without having the palms of you hands ever leaving contact with the base tube/control bar.

The act of nose releasing can be done by the driver or observer when you say, “Clear,” over your radio that is set to constant transmit or by yourself with a one finger button or lever.

There are some pilots that believe that once the nose is released it is impossible not to launch. This is not true! --If you pick the correct, FIXED, launch airspeed.

Just to be clear --I’m going against the way platform launching is being taught throughout the United States.
I’m advocating, “Go to cruise and hold.” This is a safer procedure than ---
“Go to cruise and accelerate.”

The reason why is because if the platform rig, especially over land, is accelerating at launch time to a speed well above what is needed for the hang glider to clear the platform launch vehicle the pilot is trusting that the payout system will not lock up and fail to payout line.
If the winch/reel would fail to pay out line you would be static towing too fast near the ground and the procedure has the tow vehicle accelerating. This wouldn’t be the best practice. (And it will at some point fail to pay out.)

You can always command, “accelerate,” over your constant transmission radio once you are safely away from the PL rig and the ground.

Never trust that a payout winch/reel will work flawlessly due to its precision engineering and spotless history.

Your loved ones continued happiness will be better served due to your lack of trust and you having adopted procedures that holds the answer for the rare yet inevitable occurrences.