Platform towing /risk mitigation / accident

[curious]

It sounds like you are practicing for an insanity defense instead of an incompetence defense.

:silent:

[Free]

As facts don't appear to be forthcoming anytime soon it looks like speculation and supposition is all we got.

In other news... It has finally warmed up in Missouri..

[Bill Cummings]

Lets speculate then.
As a thirty four and a half year, towing experience, pilot I know what a lockout is.
I often smirk when I hear of a center of mass lockout.
Unless you have used a Moyes stainless steel towbar, towing from the base tube, you really have know concept of what a lockout REALLY is.
That said, you can loose control while under tow, center of mass, for a host of reasons. All of the reasons are more forgiving with center of mass towing.

Rules of thumb like, while towing in a crosswind point your gliders nose at the tow vehicle, work with a constant wind vector throughout the ascension to release altitude.

If you pay attention you will see your towline with a slight “S” curve, look to it on days when you are towing through vector changes, with accompanying shears, that will require you to not have your nose pointed at the tow vehicle during a crosswind tow. I would guess that about better than 90% of the tow pilots have never thought past the, “Point you gliders nose at the tow vehicle while towing in a crosswind,” --rule of thumb.
In that situation you will find yourself constantly dropping a wing to the same side until you simply have to pin off.
Why? ---You are not towing in the “Sweet Spot.”
Why? ---because you don’t yet know how to read the rope and put yourself in the, “Sweet Spot,”
Why? --Because you are pointed at the truck and not the relative wind while crabbing down the tow road to the downwind side of the tow vehicle.

You can only figure this out (being in the sweet spot) once you embrace the fact that the rule of thumb only works in an air steady state situation. (How many time will we find that happening while towing?)

And another thing, -- darn it!-- What is with all the Youtube video’s of experienced tow people dashing out from under the glider and paying out rope until the tow vehicle has a fifteen degree angle on the tow line to the ground?

If you want to do that use a rope to the keel so it won’t wallow and tip stall because of too much angle of attack. (AOA).

Center of mass (to the pilot only) works best if you keep the pilot anywhere from about thirty five degrees to forty five degrees angle to the surface.

The argument that you want to tow the pilot ahead and not down does not hold up especially if you have a low airtime tow pilot on the line. The trim feel will not be there. It will stall a tip easy with a low airtime pilot.
Sure, a long time tow pilot can hold in on the base tube to keep it from stalling a tip while towing with a poor angle. But why?

Fly the correct angle on the towline and tow up at trim. Safety should win out
over efficiency all the time.

It’s late. More later on being in the sweet spot while towing.

This post is only to point out how to avoid loss of control while towing and is not related to Terry’s accident since I don’t know what his control problem was

[Bill Cummings]

When towing:
Where will I find the sweet spot? How big will it be? Does it change in size for any reason?

The towing sweet spot will be found downwind of the tow vehicle of course.
If the wind is right smack dab down the center of the runway/tow road being in the sweet spot is straight forward. Just stay directly behind the truck.

The sweet spot will be very narrow right after platform launching. In other words if you get just a little to the left or right of the tow vehicle with a short rope to the tow vehicle you can find yourself locked out in no time at all.

The more towline/rope that you have between the tow vehicle and your glider the wider, left and right, the sweet spot will be.

When you increase the towline tension the sweet spot narrows.

At times a spool with too much rope on it will allow the towline to dig in and prevent the spool/reel from paying out rope. This will increase you line tension and narrow your sweet spot.
A warped disc brake can drag and change the line tension.
If a rag or glove blows in between the chain and sprocket of you rewind or in between your pulley and belt of a rewind this can lock up the winch/reel.
If the chain climbs a worn sprocket it can lock up the winch.
If you splash through a big puddle on the dirt road and get dirt on the disc that will increase your line tension by causing more friction between the disc and brake pads. Believe me there are many more things that can happen to increase the line tension and reduce the size of the sweet spot that you were enjoying.

With enough time anything that can go wrong probably will. But we can all adopt procedures the will answer all of the known probabilities.

I have noticed operations that have strayed from good procedures.

Things that can be done to mitigate things that Murphy will throw at you follow.
I don’t think accelerating through the launch window speed is a good idea.
At my altitude my launch speed with no wind is a steady 32 miles per hour (double surface glider not a Falcon.) At that speed and not hooked to the towline I can launch and climb to 30 to 50 feet behind the truck, round off the climb and land on the road again as the truck goes away still at 32 mph. The Sweet Spot never even enters the equation.
Hooked to the towline I prefer to launch with low tension. Just enough to keep the winch from back lashing. When I stop climbing the preset tension is allowed to be applied to the towline. For the low tension launch I am almost totally in free flight. The towline has very little affect on me. Once the preset tension is applied I now have to concern myself with staying in the sweet spot. Which will be much broader with all the line I have pulled off of the winch/reel.
Accelerating through the launch window can have me launching with too much speed if I miss the release the first time with some rigs. I prefer to radio to the tow vehicle, “Clear!” Have them trip the nose release. Then when I see that I’m free of the nose release I rock back anytime and launch. You need hand holds for this to keep you in the launch yokes.

It 12:02 am here in Minnesota so I’ll try to finish this after my road trip.
(second try first attempt didn't work.)

[SamKellner]

The sweet spot will be very narrow right after platform launching. In other words if you get just a little to the left or right of the tow vehicle with a short rope to the tow vehicle you can find yourself locked out in no time at all.

OK Bill,

Say a pilot is in this position, "to the right or left", just after platform launch.

Now, one of the bits of advice I was given, by email, before I ever PL towed, was " don't try to out fly the vehicle".

Say in addition to being "to the right or left", say the pilot "trys to outfly the vehicle", and that reduces the climb.

A pilot being in this position would be on the fringe of the "sweet spot", if that, I'd say.

How would this effect the chances of a lockout or loss of control?

Thanks for the help.

[Bill Cummings]

Only have a few minutes here in Topeka.
When a pilot overflies the vehicle they are usually holding on too much speed. This high speed can induce adverse yaw. PIO will exacerbate the loss of control.
Pushing out to slow down will pull more line off of the winch and stop the adverse yaw.
The loss of control can be more a result of over speed and not so much out of the sweet spot in the situation you describe.
Once the adverse yaw gets you way off to the side then the lock out will not be preventable. Release is then the next thing to do.
Did I stay on track with your question?
I may be off line for a while------

[Bill Cummings]

Continuing 11/02/2012-----

This will be somewhat of a review and slightly reworded from my earlier post with added detail with my goal being more clarity.

Earlier I said, “Hooked to the towline I prefer to launch with low tension.”

A ball park method of selecting the lower line tension for platform launching has me reducing the brake pressure until I can trudge away from the winch with the towline over my shoulder. That is usually enough brake pressure (or resistance) to keep the winch/reel from back lashing if tension should come off of the towline for any reason. A weaklink break may leave the pilot free of tow but any freewheeling of the winch/reel could backlash the winch so badly that several hatchet knots are tied into the towline. (For those of you that don’t know already a hatchet knot is a knot that is more easily removed with a hatchet.)

If your winch/reel is smoothly paying out with a high degree of regularity you will not be surprised by a sudden increase in towline tension and the sweet spot narrowing to spit you into a lock out.

A crisp launch with a low tension tow to about 50’ agl is safer than launching at higher maximum set tow tension. Increase the tension once you have about 100’ of line out. For platform towing try to keep the glider around 35 to 45 degrees of angle behind the tow vehicle. When hooked only to the pilot that is the desirable angle for towing. If the angle is less that would be more like static towing when a “V” bridle would be desirable to be towing the pilot closer to pitch trim. To tow from the pilot only, a low angle does not have the pilot towing in pitch trim. The pilot will have to hold the bar in to keep from wallowing around during the climb out. (Experienced pilots would not have too much of a problem with a low/poor tow angle but a low airtime tow pilot will tip stall and lock out.)

Some over built winches come with a pivoting winch that can display the line tension on a gauge that the pilot is experiencing as it is paying out line. These can be helpful for towing up students but experienced pilots should be in Pilot In Command mode. The tow driver should almost completely ignore the pressure gauge. Let the pilot do the commanding. Why?-- you might ask--- after all isn’t constant pressure a basic rule of towing? For students I would agree with constant pressure and to keep your eye on the gauge.

As you tow up you will have to be correcting all the time to stay in the sweet spot. If your left wing gets higher due to a thermal you could be heading for a lock out. If you pull in the bar to relieve some tension momentarily to make a roll correction you don’t want the driver to give you the tension back until you have your glider responding to your control input. The driver bringing you back up to prearranged protocol line tension could be serving you toward the lock out you were trying to avoid.
Rather than the driver deciding what the pilot needs while looking at a pressure gauge at the bottom of the towline it is safer for the pilot in command to tell the driver what is needed. A good driver should always give more credence to the pilot in command over a pressure gauge. (Don’t forget we are not talking about student pilots here.)

So now you have some suggestions that may help you stay in the sweet spot. Let’s back up and cover some logistical suggestions that will help you arrive in the sweet spot.

Good towing procedures should include towing in such a fashion that at any second you will be ready and have the room to maneuver (with enough glider energy --aka, airspeed) in the event of a weaklink break, line break, premature release, truck emergency stopping, (dog, deer, or kid running in front.)

If your platform tow rig does not have a nose over stop on it to catch the glider I can almost guarantee that at some point you will install one. For sure after the horse has left the barn ---so to speak. This can manifest itself from extreme glider damage to great bodily injury. Mistakes or oversights like this have been learned several times already by different tow operators.

Hand holds under the base tube are a must. If you haven’t found the need for hand holds yet ---you will. I know of bodily injury and with another tow club of severe damage to a glider due to lack of hand holds.

When your hands are not there to hold the base tube into the launching yokes you need bar safeties on each side of the base tube for times such as crosswinds and thermals. Not a WalMart cinch straps where you drape a strap over each side of the base tube, hook to the anchor points, and draw the straps tight through a the buckles. That is way too slow. Releasing the buckles to get slack in the straps so that you can unhook the ends of the straps from their anchor points to undrape the straps takes too long. You need something very fast to secure and free up your base tube. Make a simple push/pull type of bar safety on each side.

I don’t at all like a winch/reel that does not allow for pressure changes by the winch operator while the tow is in progress. As pilot in command, by means of a radio, I want to be the person that calls for more tension or less tension, more speed or less speed. I’m not saying that this will be the same for student pilots. The scenario I am describing is for experienced tow pilots.
As pilot in command this necessitates good radio communication. Totally unacceptable would be a transmission that carries with it a lot of air noise that masks the voice of the pilot. Take the time to do what ever is necessary to reduce air noise in the microphone of the pilots radio. You can uses wind socks or order a high impedance microphone or do both. With a low impedance microphone the completely wrong thing to do is get up close to and yell into the microphone. Actually moving the microphone away from your mouth and speaking softly is the answer. You have to keep air from moving across the microphone. Otherwise you come out distorted on the radio in the tow vehicle.

Do your air noise suppression tests on the ground from a bike, motorcycle, convertible, boat or on a windy launch before platform launching and towing.

A check list should be waterproofed and mounted just ahead and under the base tube when the glider is sitting on the launch platform. The driver should be following along as the pilot does his check list to make sure the pilot doesn’t loose his place and skip over a step on the check list.

Use only procedural radio transmissions before and during launch. No cutesy or really cool radio chatter. Stick to the procedural script so there will be no confusion or misunderstanding on the part of the driver/winch operator.

If you loose radio communications ---- "Bag it and Drag it!”