After last weeks tows, we noticed that the tow hook being at the nose of the glider, quickly overpowered the elevator action, bringing down the nose, and stopping the climb. The result of this, was a mild climb angle until the glider got close to 70 meters (With a 200 meter rope) where the climb rate tapered off to nothing.
To improve on this, we decided to take the idea from larger gliders and change the tow hook anchor point closer to the C.G. of the plane. Since I learned (way too long ago..) to fly gliders on the venerable Schweizer_SGS_2-33, my thought was to place the tow hook, somewhere close to the mid point between the nose and the wheel (The wheel being at the C.G.)
To place the hook, Juan drilled tow holes on behind the skid and then used a larger diameter tube slit in half to use as reinforcements at both sides of the the bottom tube.
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With this new setting we still use the paraglider release line, but now connected closer to the C.G. and with the added security of an auto release feature. (If the glider ever moves ahead of the rope, the line releases automatically)
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With all the changes now in place, we moved the glider to the runway an connected to 200 meters of rope. The wind was about 10 KPH , so we told the car driver to tow 10 KPH slower (40 KPH) and to be extra "steady" on the run as I expected the glider to be a bit more "nimble" since the rope would not have as much leverage to keep it straight as when towed from the nose.
First tow went perfect. The wind was aligned with the runway and the glider got in the air pretty much as when towed from the nose. The change came when I gained altitude and increase the pitch to climb faster. It was clear that the elevator had a lot more authority over he plane. Once I was 30 meters over the ground I increased the pitch even more and the plane went straight up !
I know that when towing is hard to notice the G's you are really putting on the plane, so I was watching closely the speed indicator to make sure not to exceed VNE (~ 45MPH)
Within seconds I was at 100 meters and the car downstairs still had runway to keep towing. From my limited experience on auto tow I keep reminding myself that controlling the speed is counter intuitive. if you pull the stick, the glider speeds up , to lower the speed (and climb rate) you have to push the nose down.
All in all the tow seemed to me pretty straight forward. most of the ride, I kept the stick close to the middle, pushing forward every so often when the speed tried to creep up.
I released at 120 meters, which I consider is as much as I am going to get from a 200 meter rope. (about 60% of the length of the rope)
Next flight we increased the rope, but did not gained as much altitude. I believe the wind above went down when I got above the heights of the mountains surrounding the runway. (Our runway sits on a venturi created by the mountains on each side)
I did a third tow, and again with no much difference in height .. max for the day 120 meters.
Now, a word of caution..
After my test flight with the new hook connection, (I felt everything was fine) my friends who the previous weeks have been flying the glider just fine, now had quite a bit of trouble keeping it flying straight. One deviated from side to side of the runway until he finally got control of it... The other one released almost immediately because he felt he lacked control.
We are still trying to figure out if it was that to me it "felt" fine, because of my previous glider experience (About 20 years) or if the wind changed in some way. In any case, we are moving the hook back to the nose until everyone gets more experience with the glider.
