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  #1  
Old 09-21-2010, 10:48 AM
fdmurphy44 fdmurphy44 is offline
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Default Aerotow Simulation

Nice link to a video of simulated aerotowing and boxing the wake. This is what USHPA is taking a close look at for signing off aspiring A.T. pilots. I like the references made and the picture the glider pilot should see in relation to the tug and horizon. Note the "Sweet Spot", getting to high or low on the D-Fly creates problems with climb and speed control for the tug. Again, note the "Sweet Spot".

http://ihanglide.com/aerotow/

Thanks to Tracy and Lisa at DFSC
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Old 09-21-2010, 11:59 AM
John Alden John Alden is offline
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I'd like a discusion of the sweet spot. The sweet spot will vary from tug to tug depending upon the tugs climb rate. The stronger the tug, the faster the climb rate, the lower the towed pilot can be and still be safe. If the tug is climbing slow and enters a faster wind gradient with the hang glider low, guess what; big line slack. A faster climb rate gets the hang glider into the faster wind gradient sooner so there is less of a problem. I would question whether or not the sweet spot depicted in the animation is the sweet spot we all want to use behind our Dragonfly. For lighter pilots on faster gliders it's probably OK.
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Old 09-21-2010, 01:26 PM
fdmurphy44 fdmurphy44 is offline
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John, when you refer to a faster wind gradient, are you talking about verticle air movement, specifically lift? If so, in all but the sharpest shots of lift, I always speed up some until the glider is also in the lift. There are days when the air is so textured that my reaction time, combined with the bullits, can allow some slack in the line. I would agree that the Fly is a slow climber, especially with the larger pilot/wing combinations and positioning could be slightly different behind the tug. My point was to help with what the picture should look like from the glider pilots perspective and to reiterate the limitations of the tug when the glider pilot gets much above or below the tug. Safety at both ends of the line is always the primary concern. Not looking to compromise anyones safety here.
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Old 09-21-2010, 03:01 PM
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RickM RickM is offline
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I would say that position is about where I try to stay, although slightly higher does make you feel better able to deal with sudden tow plane climb. Higher does make it a bit tougher on the tug pilot and staying in the sweet spot probably gives you a quicker tow. I think it's easier to get slack in the line if you are high on a tow. If you are low and the tug hits lift, the tug it still flying away from your position. If you are high and the the angle of the tug increases in lift, the distance between you can decrease some as it climbs to your height.

Towing the tandems is a challenge. You can usually avoid slack in the tow line by towing faster, but that cuts down on the climb that is already marginal.

Isn't doing a tandem "box the wake" exercise already a requirement for an aerotow rating?
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Old 09-21-2010, 06:16 PM
Paul Farina Paul Farina is offline
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Quote:
Originally Posted by RickM View Post
I would say that position is about where I try to stay, although slightly higher does make you feel better able to deal with sudden tow plane climb. Higher does make it a bit tougher on the tug pilot and staying in the sweet spot probably gives you a quicker tow. I think it's easier to get slack in the line if you are high on a tow. If you are low and the tug hits lift, the tug it still flying away from your position. If you are high and the the angle of the tug increases in lift, the distance between you can decrease some as it climbs to your height.

Towing the tandems is a challenge. You can usually avoid slack in the tow line by towing faster, but that cuts down on the climb that is already marginal.

Isn't doing a tandem "box the wake" exercise already a requirement for an aerotow rating?
Tracy always asks you to put his tug wheels on the horizon. This is exactly what Rick describes as his "feel better" position. This has always been my goal too, however it's not a very perfect world.
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Old 09-21-2010, 09:38 PM
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CHassan CHassan is offline
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STracy tells you to keep their tugs much higher than wheels on the horion. My personal thought is keeping the tug, rope, and glider flying along on the same path is the sweet spot. A higher climb rate equals a lower position behind the tug.
Having towed behind a very heavy, fast tug (Kolb) and a very light, slow tug (Qucksilver) only a day apart I can saw a very big difference. With the qucksiliver I kept him on the horizon until we hit a thermal. Then all hell broke lose and I couldn't keep up with him. He hit the thermal and was 100' above me before I hit it. The tow line draped behind me and I was going to release but then I hit the thermal as he fell out the other side. The tow line quickly went tight and I was off tow when the link broke.
The kolb doesn't climb any faster than the fly, but with its weight it would blow thru the thermals with minimal amonts of change. While I had to work to work to keep him wheels on the horizon.
Between the two I would pick the kolb, and did pass up a tow with the qucksilver on the final day of the comp.

Again. My thought is keep the tug, rope, and glider flying along the same path.

Another thing to think of is rope length. To short and you get very little room for error before you lock out. To long and it makes the tow harder because the tug and glider are not in the same air and always chasing each other.

I'm no tug pilot but those are my thoughts.
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Old 09-22-2010, 06:45 AM
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Larry Huffman Larry Huffman is offline
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All good points. When I was at Cloud Nine I spoke to Tracy about the position he preferred. The worse place to be is very high above the tug on tow. This can be dangerous for the tug pilot and what Tracy is trying to prevent. By staying down it gives the pilot being towed an advantage to prevent getting too high. I learned this in the early days flying gliders too large for me and having tons of bar pressure.

I've also towed behind many tugs. Several different trikes, Dragon flies with different engines, Quicksilver MX, older KOlb, and a couple I can't remember. I have always tried to keep the tug pilots seat on the horizon but keeping the wheels there works too. For me watching the tugs attitude and trying to maintain proper line tension is what works best.

Larry
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Old 09-22-2010, 09:32 AM
John Alden John Alden is offline
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I love hearing all the differing experiences and ideas being expressed. I also love towing behind Tracy's tugs, wheels on the horizon and two minutes later you're off the line. I also love the animation link and think that everyone who aero tows should study it. I think we all agree that the sweet spot as depicted in the animation is not nessessarily the ideal position for all tug-pilot/glider combinations but is certainly a position to strive for most of the time. Frank, the wind gradient that most concerns me if the glider is low is a horizontal gradient as when climbing into a wind aloft. In that situation a low glider behind a tug with a slow climb rate will find itself sinking big time. Thats the kind of situation that the tandem glider could easily get into and why a slightly higher position (wing on the horizon) is what I prefer during initial climb out. Even though it's not the best position for the tugs climb rate, if it's tolerable for the tug pilot I think it's safer all around. And that's the point; keeping the whole operation as safe as possible.
And yes Rick, doing the pattern depicted in the animation is required for an aero tow sign off. In fact the new rules require that the patern be flown in a tandem glider with a tandem instructor and that's a whole other topic. I think USHPA has caved to presure from aero tow flight parks creating in some situations unnessessary hazard for instructors and expense for students.
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  #9  
Old 09-22-2010, 10:01 AM
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Larry Huffman Larry Huffman is offline
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John I think that Tracy has drawn up the requirements for the tow rating. He told me about him thinking that boxing the wake should be done tandem.

I've towed behind a fair few tug pilots and I usually ask them where they would like me on tow. As long as you aren't too far out most of them don't care.

Larry
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  #10  
Old 09-22-2010, 04:42 PM
Paul Farina Paul Farina is offline
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another thing i like to do is:
keep eyes on tug ALL the time, anticipate it's movement, then mimick it's flight path in real time, not waiting.
of course, nobody screws around with their harness, or instruments on tow, right?
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