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high tow vs low tow



 
 
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  #1  
Old February 25th 19, 06:52 PM posted to rec.aviation.soaring
Charlie M. (UH & 002 owner/pilot)
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Default high tow vs low tow

OK, I will start with.....I am biased to UH, he was one of my early instructors and we have other connections.

The "only" time I see an issue with low tow is with a VERY high wind gradient and someone being waaaayyyyyy too low near the ground.
The relevant airspeed of the tug vs. the glider (especially on a weaker tug) may put the glider in a poor position speed wise.

I will say, I have towed out of our field on very gusty days with, about a 45* cross wind, near gross weight (say, a ASW-20 A or C, so, about 9lbs/sqft.).
Yes, it ''twas sporty down low", why not? Big cross wind, over trees, higher wingloading, etc.

I have had rope breaks and a few TP dumped ropes while low tow, the rope just drops below the glider, try to drop a broken rope over the field on the grass.

As to the towpilots, what I have heard is that low tow allows them to trim a climb in their ship, thus less tiring over a day. High tow is usually outside the trim limits, thus always using your arms to maintain a climb pitch.. Part of this is a correct low tow puts the glider basically on the pitch line from tug spinner and down the rope to the glider...

I remember decades ago in upstate NY at a contest. Summer day, ballast, weak towplane (leaving site and tug out, not trying to slam the site). I started in high tow. We were attempting to do circles close to the field to clear terrain, I ended up in low tow since I was just hanging on. It appeared that it helped climb a bit, but I was not happy.

In general, the "perfect world" done wrong/incorrect still sucks and may be dangerous.

At our place, we teach both.
Other places, we do as they do, but if it gets bad, we may fall back to what we have more time with.

A search on RAS will likely pop up multiple threads with the same basic question, which tow is better?

I guess this discussion is akin to, "what contest rules should we use?", sheesh......
  #2  
Old February 25th 19, 07:30 PM posted to rec.aviation.soaring
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Default high tow vs low tow

I flew at Valley Soaring for a while and did low tow. Worked fine. The only negative I heard was that the glider appears to be lower in the first critical phase of climb so it takes longer to get to the 200' safe 180 turnaround point. But I've also heard that low tow is more efficient because there's less/no trim drag from the towplane using up elevator to keep the tail down and therefore climbs faster. So perhaps it's a wash.

I'll move into low tow on cross-country aerotows if I've briefed the tow pilot or can communicate with him/her because it seems easier to hold position.

Yes, kiting a glider is going to upset the towplane regardless of the tow position. But at least if you're in low tow, you'll feel the wake as you pop up thru it, which provides an alert that might help prevent situations as was described in the NTSB report where the glider pilot may have taken his eye off the towplane for a few seconds.

Chip Bearden
  #3  
Old February 25th 19, 07:55 PM posted to rec.aviation.soaring
Charlie M. (UH & 002 owner/pilot)
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Default high tow vs low tow

To add a tiny bit, some high tow proponents have said, "I want to clear low obstructions, thus I fly high tow....!"
I usually counter with, if the towplane clears, there is typically enough energy for the glider to clear, even from low tow. Also, as Chip stated (and I agree), low tow does not require as much parasitic drag from the towplane tail to maintain a climb angle, thus more efficient. This also means the towplane is marginally higher clearing an obstacle, thus more energy for the sailplane to clear even if too low doing low tow.
Again, big wind gradient can be a negative factor if too low.

We break ground, sit in ground effect (pretty much the most efficient place for any aircraft), let towplane accelerate, break ground, then establish a climb. Once the sight picture looks good, the sailplane starts a climb.
Turbulence from towplane wing wash/vortex is essentially "0" since that does not really form until some climb is done. By the time it starts, the sailplane should be starting up.

As stated before, any method done wrong/incorrect is still poor.
 




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