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Sometimes we do 'Dual Tows' where we aerotow two gliders with one towplane. This might be done to ferry two gliders to a different site to operate for a camp or similar, or just to launch two gliders on a long tow to save time.
Special tow ropes are used for dual tows. The special rings used on the towplane ends of the rope are described in the MOAP. There is a short rope and a long rope. The short rope is the normal length, around fifty meters. The long rope is thirty meters longer, so around eighty meters.
The leading glider pilot and wingrunner do a more normal launch, so the trailing glider should get the more experienced pilot and wing runner.
Lay out the ropes first in a narrow 'V' so that the gliders can be placed in the correct position and the towplane taxied to the point of the 'V'. This will reduce the time taken to take up the slack wen you're ready to launch.
The gliders are set out seperated longitudinally by thirty meters and horizontally so the wingtips are on the centerline, so approx 20 meters.
The long rope may pass under the wingtip of the lead glider. This will happen whatever you do, so don't think you need the gliders so far apart that the rope doesn't go under the wing.
Clearly the lead glider doesn't want to drop the inside wing and risk collecting the rope. If a wing goes down you really want it the be the outside wing. If there is a crosswind you want the lead glider on the downwind side.
Wing runners are on the outer wingtips. The trailing glider wing runner can see both gliders and the towplane, so they control the launch.
When both gliders are ready, the trailing wing runner gives the take up slack signal. As the ropes come tight the gliders will want to swing inwards toward the towplane. Especially the lead glider as the rope angle is greater. The wing runners can resist this, but not much. The glider can't stop this with the rudder, because there is no airflow yet.
This swinging in is reduced by having the cables laid out first with the lead glider closer to the centerline and the trailing glider more offset. The gliders positioned so that both ropes come tight close to the same time reduces taxy time for the towplane dragging one glider forward while it tries to swing in.
When the tow ropes are tight, the trailing wing runner checks for traffic and gives the 'all out'.
As the gliders start moving they will take longer than usual to get up to speed. The lead wing runner must be able to run until the ailerons are working. The lead wingrunner needs to run further than usual and will need to exit to the side promptly once the glider has aileron control to clear the trailing glider. The trailing wingrunner also needs to be ready for a longer run.
The combination will accelerate slower than usual. The pilots will need to have agreed an abort point. If the combination is not in the air by the abort point, the trailing glider releases first and turns away, then the leading glider.
Once the combination gets airbourne, the leading glider moves into the normal high tow position directly in line with the towplane just above the towplane slipstream. The trailing glider moves into the low tow position directly in line with the towplane and just below the slipstream.
As the towplane is hauling more load it will climb at a flatter than usual angle. This means the slipstream is at a flatter angle than usual, so the gliders also should be positioned at that flatter angle. The trailing glider shouldn't be extremely low, rather just below the normal position and just clear of the slipstream turbulence.
When the combination reaches the release point, the lead glider releases first and turns away as normal. The trailing glider can hang on for a bit to ensure seperation, move up to the normal high tow position, and release and turn away as normal.
Briefing prepared by Phil Plane.
This work is licensed under a Creative Commons Attribution 4.0 International License