high tow vs low tow

On Thursday, February 28, 2019 at 12:35:13 AM UTC-8, Martin Gregorie wrote:
On Wed, 27 Feb 2019 18:12:56 -0800, Tom BravoMike wrote:

I have always believed the wake basically goes DOWN behind the tow
plane, being compressed, i.e. heavier, air, and/or maybe for other
reasons. I don't remember feeling any wake turbulence just following the
tow plane at the same height, climbing or level flight.

Its caused by a wing generating lift. If you assume that the wake's
downward angle is 1/3 of the wing's AOA you won't be far wrong.

So maybe 2 to 3 degrees from a towplane, a 1:20 to 1:30 slope, 2 or 3 metres at the end of a 60m towrope.

What is the more controlling factor, is the tow plane is continuously climbing up and away from the wash. Leaving the wash behind if you will.

At say 60 knots, and 10 knots climb..that is a 1 in 6 angle.....giving the glider pilot the impression that the wash is dropping...but really the glider and towplane are climbing compared to the wash.

I've done many "level" (not climbing) tows. The wash essentially comes straight back. To fly outside of the wash, the glider must be either above the tow plane, or below it.


Cookie






reasons. I don't remember feeling any wake turbulence just following the
tow plane at the same height, climbing or level flight.

Its caused by a wing generating lift. If you assume that the wake's
downward angle is 1/3 of the wing's AOA you won't be far wrong.


--
Martin | martin at
Gregorie | gregorie dot org

On Thursday, February 28, 2019 at 12:45:49 AM UTC-5, Surge wrote:
On Monday, 25 February 2019 15:28:09 UTC+2, Tango Eight wrote:
Chris Rollings:
Being in low-tow when that happens
simple makes the sunsequent event take about half a second longer - not
enough extra time to greatly increase the chance of releasing before the
critical point."

So low tow does offer more time to react to a tug upset.
From the info at hand it appears that a tug upset occurs over a duration of about 3 to 4 seconds. An additional 0.5 seconds on 4 seconds is a 12.5% increase.
Why throw a free 12.5% additional safety margin away?

I think we have two distinct types of events to consider, that differ in their causes, effects and kinetics.

In the case of "kiting" accidents, what does the towplane in is the *pitch of the glider*, not the pitch of the tow rope. It's the acceleration of the glider that produces the dangerous deceleration of the tow plane. We think that beyond a critical (glider) pitch of about 30 degrees, the situation is not recoverable. I don't think low tow buys you much in this scenario.

In "distraction" events, the glider remains below the critical pitch, the situation remains recoverable much longer, the problem is caused when the glider drifts so far out of position that the angle of the rope becomes a problem for the tug. Or it may turn into a kiting event.

Here's the order of priorities for prevention of both types of problems:

1. PIC that maintains situational awareness and positive control, all the time.
2. Rope of reasonable length. We find that 200 - 225' works well. Longer gets to be a problem for recovery at our airport.
3. Tow position probably improves margin in distraction scenario.

I have reservations about using low tow at our club because a PTT below 200' means something is going to get bent with high probability (it's roughly a ten second window of time between able to land straight ahead and able to make a safe 180). On a 225' rope, low tow is about 30 feet lower than high tow, why throw away 15%? :-)

best,
Evan

Put simply, kiting accidents just don’t happen on low tow. The only time I’ve ever seen a tug upset was a glider that had to use high tow
fortunately, the glider released immediately and landed ahead. Again, to be simple, the tug is at all times visible to the glider pilot, it cannot disappear
under the nose, a feature unique to low tow. As for the small height gain, I have the opposite view, being lower gives a better chance of straight ahead landings.
I can’t recall a single accident caused by an upset in low tow. I stay as low as possible after lift off, and wait for the tug to climb above me and stay there.
As my glider has winch hook only, I would not risk the tug pilots life by doing high tows. All I’m seeing is spurious arguments in favour of high tow, that put the risk on the tow pilot not the glider pilot.
I’d rather crash myself than kill an thuggish, but that’s just me.

Low tow isn't common in Italy, and in the EU as far as I know. We practice the low-tow position during basic training, then it's at the pilot's discretion. Occasionally during the season I use it for a minute or so, and every time I make my first flight on a new type.

What's the standard low-tow procedure? Do you still take-off in the high-tow position then transition to low-tow at a given altitude?
Or do you watch the towplane climb, then start climbing when "it looks about right"? the latter seems scary to me (as I've never done it).

Thanks!

Aldo Cernezzi

Low tow is.....sailplane breaks ground, stays close to ground (since close ground effect basically negates the sailplane drag), let towplane accelerate, lift off, when towplane "looks about right" follow it up.

This is the short version.

Having, taught newbs for both, low tow seems easier and safer.

There is ALWAYS the outlier where, "I think high tow would have been better".
To me, sorta like, "I won't wear seat belts because I knew of a case where they were thrown free in a crash and survived because they didn't wear seat belts".

I stick with low tow, but teach and fly both.

As I stated before, this is a "no win" conversation.

On Wednesday, February 27, 2019 at 9:30:18 AM UTC-8, Dan Marotta wrote:
While I agree that "slow is slow", I think it's much better to be in
high tow position and be able to sink to low tow if the tug gets too
slow.Â* I've been dangling on the end of a slow rope with a full load and
had to start dumping while on tow.Â* It's not comfortable.

Of course that proper thing is to not get slow and I blame this on an
inexperienced tuggie who strives for a good climb rate at the expense of
the glider.

On 2/27/2019 6:52 AM, wrote:
On Wednesday, February 27, 2019 at 7:45:46 AM UTC-5, Tango Eight wrote:
On Tuesday, February 26, 2019 at 10:16:56 PM UTC-5, Ramy wrote:
Sounds to me that this method of staying low in ground effect for low tow position will increase the time we spend in the dangerous zone below 200 feet, in addition to transitioning through the wake while low and slow. Personally I prefer to spend as less time as possible down low, and would rather transition to low tow position at safe altitude and safe speed. Especially at high density altitude such as we have in the west, fully ballasted combined with not so powerful towplane, the last thing I would want is to purposely stay in ground effect at the end of the runway while the tow plane slowly climbs higher. I never tried this, so maybe it is not as bad as i think it is.

Ramy
One reason I will never do this in a ballasted glider is wind shear.

Low tow increases the glider pilot's vulnerability to a slow tow.

best,
Evan
If excessively low on tow wind shear can be a factor. Properly flown, my experience is that it is not.
Possibly you can explain your second contention. Slow is slow no matter which position you are in.
UH

--
Dan, 5J

I received my glider training in Minden. Some of you might have heard rotor can be a real thing there. From day one I was conditioned, if I ever lost sight of tow plane to release immediately, and I have! Other than training the only low tow I have been in was back in the 90's we (local not Minden) had a string of very poorly (not) trained tow pilots. It was so bad pilots were making signs that said "Fast tow". To this day there are no radios in the local tugs I was flying a loaded ASW-24 and was so slow and low that the tow rope was basically just inched in front of the leading edge (CG Hook). Thank goodness for the Nixon/Murray water system, dumps fast. Since this tow pilot was towing away from field low and slow, I to wait until I thought I could make it back to airport before I released. On the ground I spoke to the tuggie. He had no clue gliders carried water ballast. I held up a sign that said I had water ballast before the tow he thought that was drinking water! That same day he towed a 1-26 at 70 knots straight away from airport with no mind of return to airport for the 1-26 driver. Since I got back into gliding our tow pilots are some of the best pilots of anything I have ever met! Perhaps all this boils down to improper initial training. If I was sleeping, dreaming of being on tow, and in the dream lost sight of tow plane, I would still be pulling for that release. Of course I don't mess with anything else on tow because I have been trained while flying tow, that is the only thing you should be doing!

In Minden before each training session we briefed the tow and we briefed immediate release if lost sight. It was much more than cursory, or something we mentioned a few times, it was part of every before flight emergency procedure spoken outloud.