Standardization in Slack Rope Recovery?

On Tuesday, February 2, 2016 at 11:31:22 PM UTC-5, Surge wrote:
Where I fly only low position aerotows are performed and even in turbulent conditions with glass gliders, rope slack doesn't seem to be much of a problem.

Are high position aerotows more prone to developing rope slack?

I would say yes, it's a lot easier to let the nose drop and accelerate, thus causing slack.
In low tow, an easy way to get slack is to turn inside the towplane.

At our field, almost all our tows are low tow. I mostly do high tow at contests, training and checkrides.

On Tuesday, February 2, 2016 at 11:31:22 PM UTC-5, Surge wrote:
Where I fly only low position aerotows are performed and even in turbulent conditions with glass gliders, rope slack doesn't seem to be much of a problem.

Are high position aerotows more prone to developing rope slack?

Where we fly low tow is the standard procedure. We rarely, if ever, get significant slack during tow, even in early training. We have to go out of our way to teach slack rope procedures.
To get slack you most commonly are coming down from a somewhat too high position that is not likely in low tow.
UH

The best way to demonstrate slack rope recovery is to take your BFR on a wave day with rotor in the pattern. Scenario based BFR.

I once took a very instructive BFR with Marty Eiler at Cal City. Needless to say, with lots of wave/rotor flying, Marty had plenty of experience in what actually works in real slack rope situations. He chuckled at the yaw the nose at the last moment stuff, encouraging me to try it and see how it made matters worse.

His technique is to stay a bit off to one side, high if possible, and make sure the glider is banked toward to towplane with nose low and pointing towards the towplane as the slack comes out.

The key is to avoid a kiting attitutde. This makes absolute sense. Think about rope coming taut with the glider nose up and banked away in a kite attitude, vs. nose down and banked toward the tug. The kite is going to be a lot rougher.

When the rope pulls the glider, you don't want that to raise the glider's angle of attack, so the lift force fights the rope. Ideally, the rope pull should lower the glider's angle of attack, and the lift force should be somewhat in the direction of the rope. The key point is the glider's attitude when rope comes out, not relative motion.

The yaw at the last minute idea, beyond being very hard to do (especially bouncing around in rotor), will typically leave the glider slightly banked away from the towplane, unless you're very very good and also banking the other way at the same time. It also points the glider away from the tug. Trying to speed up at the last minute means you get lower and lower. Any amount of last minute maneuvering is going to be very hard to do in the real situation of extreme turbulence. Holding a good attitude is easier.

After a lot of subsequent experimentation I haven't found a better technique, at least one that I can perform reliably.

John Cochrane BB

When the rope pulls the glider, you don't want that to raise the glider's angle of attack, so the lift force fights the rope. Ideally, the rope pull should lower the glider's angle of attack, and the lift force should be somewhat in the direction of the rope. The key point is the glider's attitude when rope comes out, not relative motion.

Interesting technique John, this does sound a little familiar to the "Freeze it, fix it, face it method," perhaps just explained a bit better. The one thing i don't understand is the line above...Wouldn't a nose-low situation with towplane-induced pulling the nose up cause an increase in AOA, not a decrease? I can, however, see that configuration helping from a total energy perspective, but not sure that attributing the additional "cushion" to an AOA change, as much as preventing a dive on the towplane.

Not trying to argue or disprove, just clarify... Thanks for the technique, i will have to try it out this spring.

Chris

On Saturday, February 6, 2016 at 7:57:42 PM UTC+3, John Cochrane wrote:
His technique is to stay a bit off to one side, high if possible, and make sure the glider is banked toward to towplane with nose low and pointing towards the towplane as the slack comes out.

That's largely what I do.

I think the key is that if you're getting slack rope developing it's because you're going faster than the towplane.

The amount of slack that develops is the integral (sorry) of your excess speed and the amount of time you have the excess speed.

I don't like to throw away energy by slipping or using the brakes. It should be a very rare thing indeed.

Much better to store the energy by climbing. You can then get most of the speed back by descending, lessening the jolt as the rope comes tight.

The sooner you start to climb the less slack accumulates.

It doesn't matter how high you are above the tow plane as long as the rope is slack. So you've got 150 ft of altitude above the towplane and 150 ft below the towplane to play with. That's a lot.

Also 150 feet to the side. Most people seem to forget this. You can bring out the slack when *you* want to by flying out to the side, and turning back as it's about to come tight. And with no risk whatsoever of a tug upset. If you get the slack out while you're out to the side, turning back into the middle gives you more more rope. It means that you can have no jolt even if you're going considerably slower than the towplane at that point.

So, yes, a combination of higher (to store energy that you can turn back into speed) and to one side (for visibility, to take out the slack early, and to "put back" a controlled amount of slack as needed to eliminate the jolt..

Both descending and coming back from the side help you to match speeds.

The big big key is to concentrate on controlling the amount of bowing in the rope and the trend in the amount of bowing, not at the actual speeds and positions.

In the same way that you don't try to calculate the distance to a ridge you want to cross and your height above it, but just look at how the angle is changing and if you can see more or less stuff beyond the ridge as you get closer.

On Saturday, February 6, 2016 at 11:57:42 AM UTC-5, John Cochrane wrote:
I once took a very instructive BFR with Marty Eiler at Cal City. Needless to say, with lots of wave/rotor flying, Marty had plenty of experience in what actually works in real slack rope situations. He chuckled at the yaw the nose at the last moment stuff, encouraging me to try it and see how it made matters worse.

His technique is to stay a bit off to one side, high if possible, and make sure the glider is banked toward to towplane with nose low and pointing towards the towplane as the slack comes out.

The key is to avoid a kiting attitutde. This makes absolute sense. Think about rope coming taut with the glider nose up and banked away in a kite attitude, vs. nose down and banked toward the tug. The kite is going to be a lot rougher.

When the rope pulls the glider, you don't want that to raise the glider's angle of attack, so the lift force fights the rope. Ideally, the rope pull should lower the glider's angle of attack, and the lift force should be somewhat in the direction of the rope. The key point is the glider's attitude when rope comes out, not relative motion.

The yaw at the last minute idea, beyond being very hard to do (especially bouncing around in rotor), will typically leave the glider slightly banked away from the towplane, unless you're very very good and also banking the other way at the same time. It also points the glider away from the tug. Trying to speed up at the last minute means you get lower and lower. Any amount of last minute maneuvering is going to be very hard to do in the real situation of extreme turbulence. Holding a good attitude is easier.

After a lot of subsequent experimentation I haven't found a better technique, at least one that I can perform reliably.

John Cochrane BB

I don't believe any of us said to, "yaw the nose at the last moment".

It's more of, "Get the nose started to the side (using rudder)" so you:
-avoid the loop
-slow the glider
-sorta maintain relative altitude to the towplane
-maintain sight of the towplane

It should be obvious that yawing inside the turn (if the towplane is turning) does not help at all. So, rudder away from the turn. It does not take much.

When the rope comes tight, it's not a huge swing in either ship, it's just a realignment and a lessening of rope shock.

If all else fails, drop the rope (especially if you lose sight of the towplane).

On 2/3/2016 11:36 AM, son_of_flubber wrote:
The best way to demonstrate slack rope recovery is to take your BFR on a
wave day with rotor in the pattern. Scenario based BFR.


Chortle! Writ with tongue near cheek, I'll guess...

But seriously, this may in fact be as realistic a scenario as Joe Instructor
and Joe Experienced-near-mountains Soaring pilot can devise. In my case I
expect it woulda helped demonstrate the validity of my post-BFR claim, "I
never get slack in the rope!" FWIW, upon the presence of "significant slack"
on gnarly days (gnarly being common in the foothills of the Rockies), I
maintained a slight out-of-turn (if any) heading, yawed "slightly away" from
the tug angle, matching as best as possible the tug's deck angle (slightly
less than his, if I'm higher - the usual case), and wait. Never had a back
release while so doing, & only rarely any appreciable yanks or subsequent
"sympathetic loops" as noticeable in the glider.

Bob W.

On Sunday, February 7, 2016 at 9:16:12 PM UTC-5, BobW wrote:
On 2/3/2016 11:36 AM, son_of_flubber wrote:
The best way to demonstrate slack rope recovery is to take your BFR on a
wave day with rotor in the pattern. Scenario based BFR.


Chortle! Writ with tongue near cheek, I'll guess...

At my last BFR, we did slack rope recovery in rotor, spin recovery, dove through a closing foehn hole, and flew V-approach of 75 K. Plan to do it again in 2016.

On Sunday, January 31, 2016 at 6:29:23 AM UTC-8, LongJourney wrote:
I would like to hear feedback from the instructors here about which method they use, and why?

Any comments?

Thanks,

Jeff

There are many ways of effecting a maneuver or result. Always strive to learn (for the 'applicant'), and always strive to be respectful and open (for the 'teacher'). There is a lot to be said for the 'cooperate and graduate' methodology in a field checkout, but these thread stories reveal more opportunities for learning.

Apologies to the international readers-- the following is a mostly US and mostly high-tow(above the wake) level with the tug scenario.

The yaw-away-from-the-tug method was documented in the Joy of Soaring (in the US) when tugs were lucky to have 150 hp and trainers were mostly 20:1 drag bricks. There really wasn't much option for differential in speed and lots of slack, due to that combination. And in the early 1960's in the US, there wasn't as much wave flying/rotor exposure commonly done.

Training publications have lagged behind the changes of equipment, and developed techniques.

In this century, with tugs believed to be minimal-performance with 180 h.p. and typically 230-235 h.p., and training occurring in (and under 50 hr. pilots buying) 30 and 40:1 or greater sailplanes, it is not uncommon to hear of towing moments gone awry. Minor glider pitch changes make abrupt speed changes. Towing speeds have changed from 55 - 65 mph to glider pilots requesting 70-75 knots.
Trainers might have nose, chin or c.g. hooks. New solos in single-place might have a new tow-mount and no or minimal instruction in the new potential for different glider behavior (ie., no longitudinal stabilization).

I find the most likely scenario for pilots to develop inadvertent slack line to be 1) a distraction when the tug turns (delaying their glider's heading change) or 2) turbulence. The glider pilot then typically makes a move that creates slack.

In a delayed turn, the glider flies a differing arc than the tug, with a resultant increase in speed and a climb from increased lift. The increased glider attitude increases rope tension and reduces the excess thrust of the tug, which usually makes climb rate. The tug pilot changes his stick pressure aft to counteract the trim change of his lifting tail (mostly subconsciously).

When the glider pilot notices the deviation they abruptly bank to "return to center" and drop the nose to level the path to the tug. At that moment, the glider releases line tension. The nose-up trim in the tug and gain in excess-thrust means he gets 'extra' rate of climb while trying to maintain normal tow speed. The glider and tug are differing in intention, closing separation, and creating increasing slack line.

It is now up to the glider pilot to 'do something' to remove slack.

Yet, if he achieved centerline position, the slack is under his nose and not visible. Yawing could allow sight of more of the rope, the changing of the bow. Yawing decelerates the glider relative to the tug and 'removes slack'. Yawing/slipping on tow is the only technique discussed in (US) training literature.

Meanwhile, the tug continues climbing, marching away from the glider. The bigger the bow, the more differential speed at the moment of tensioning and greater likelihood of a rope break or a grumpy tow pilot. If the glider pilot notices the tugs climb, he also climbs -- increasing drag, AoA, differential speed, being more draggy to accel, adding a yaw .... and making for a big yank at the tensioning.

Thank you to John Cochrane and Bill Tisdale for continuing to cross-pollinate the techniques we taught at Cal City for two decades. Perhaps this more simple recipe will clarify the teaching of position recovery and slack line management.

When faced with slack line:
1) parallel the tug, 2) stay a smidge above the tug, 3) watch the rope and bow (below and alongside you) for tensioning, 4) match speed.
As the rope tightens - gently lower the nose and yaw toward the tug -- to make the acceleration moment as easy as possible, and you will have minimal/no secondary slack. When tension is normal, return to position. Repeat as necessary. Recall from the boxing-the-wake exercise that a slight bow is normal for an off-centerline towing position.

The same technique works in low tow position, yet the bow is above the glider ( yikes - my least favorite place). To not break a rope, the critical point is to match the speed of the tug, by accelerating the glider to slow the disappearance of the bow as it is coming tight.

Yes, even students can be taught to do this smoothly, with knowledge and confidence -- even from bows of slack that have made high-time pilots 'wet their pants'.

Why not just release, you ask? Usually, I see the distracted out-of-position kite occur on the first turn on departure to cross-wind leg. I don't really want the customer/renter releasing here in a PT3.
Maybe this slack occurred from some punch-you-around rotor, and you'd like to get to the laminar lift. Maybe this slack happened during a long aero-retrieve and you aren't in range of the destination. Maybe if you just bail-off, you'll be at the back of the launch queue. I'd like to tow until I choose to release.

Please note - none of this says to stay attached if you lost sight of the tug. All of this works when you are managing your position relative to the tug that you can see.

Turbulence and Big Lift:
When the tug punches up in lift - go up THEN. Don't wait. Take some of his energy/climb rate by tensioning the line with higher pitch attitude in the glider. He won't get quite so much higher than you. If he falls in a hole of sink, ease a little forward stick. By accelerating the glider, you make it easier for him to transition the hole and have less differential in climb rates.

Yawing:
Yes, you can/should yaw on tow to maintain enough tension to not allow a rope to back-release from a c.g. hook. Yawing/slipping is easier and a smaller scale correction than opening and closing spoilers (which the tug pilot doesn't appreciate).

I write this not to "have you do it my way", but to share with more detail the technique I teach and have found to be effective in romping big conditions or for pilot whoopsies. Not every CFIG has same the range of experience or site social tolerances. Have a touch of empathy for their situations, too.

If you are a CFIG -- do NOT surprise your tug driver by trying to teach this without a preflight detailed briefing. The time of slack line flight by the glider might be interpreted as a release by the tug driver. Ask your tugpilot to maintain normal speed and steady heading while practicing slack recoveries. Begin with only small deviations. The awkward phase of learning smooth recoveries includes a few yo-yo practices. A proper rope will break before hurting a sound towplane. (Be in reach of home.) A smooth slack recovery is imperceptible to the tug. Towpilots perform a huge service to soaring. Don't scare them or disrespect them.

And Tisdale's comments about awareness of the rings and their potential path, if you choose to release are very pertinent. A bowed, released line will stream AFT of your glider, with potential to tangle/touch or damage the sailplane.
Private questions always welcomed.
Soar safely,
Cindy B