Funny you should post about this idea....
Been doing just that, just last week...here are some pics of Richard Ng's stock power system Apprentice aerotowing his vintage Raven flying wing sailplane just last week in Little Rock at the SMALL Steps 2010 event. (GREAT event!) I am the big guy at the far right in the first pic, flying his Apprentice for the tow.
I also dug out a very old piggyback rack for launching small gliders from the back of a glow R/C model, rebuilt it and did some piggybacking as well. Piggybacking is much easier than aerotowing, with small models. A servo in the rack releases rubber bands that hold the glider to the top of the rack. As Richard had the stock AR500 RX and has already added flaps to the Apprentice, we used a y harness to hook in the piggyback release servo and simply activated the flaps to release the payload. Note the deployed flaps in the pictures of the piggyback gliders being released.
For towing, we opted for no release on the towplane. However, if you do not have a towplane release, you really ought to use a weak link of 4-6lb monofilament for the towline, which is what we did. That way, if the glider release fails, you can do a break-away and still escape the towplane. Our towline was made from some 12lb test Spiderwire, with a metalized mylar streamer on the glider end, for visual confirmation of glider release.
We left the piggyback rack on top during the tow...pics also included of the Apprentice piggybacking my Alula and a old Klingberg Rocket Wing, with an Estes D12P motor that ignites in mid air, using a brushed ESC as the ignition source.
The stock power system is only good for a couple of pounds of glider on tow. Weight and drag on tow it more of an issue than size actually is.....but it is not only that. No matter the power, when the weight of the glider gets to be a good portion of the mass of the towplane, the glider starts steering the towplane a little too much.
It hardly knows the Alula and rack are on top, with the stock power system. The stock landing gear was not quite up to the heavier Rocket wing, and it needed a hand launch for that one...
We are going to pump up the Apprentice with a better motor and a 4S pack here soon making at least 50-75% more watts, for somewhat heavier gliders and a quicker tow or piggyback to altitude...
Richard also flies this Apprentice as a float plane...it is one awesome multi purpose model!
We worked it pretty hard for three days at SMALL....
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