Gliders are a fascinating aspect of our RC hobby. There are several different types that fill unique places in the soaring world. The launch methods vary with the types of gliders flown. Hand launched, discus, and slope gliders are simply thrown or flung into the air by hand. Hi-start or bungee launching uses just that: a bungee to sling your flying machine heavenward. Winches are also used, as are power pods and an assortment of motor configurations with folding props, and so on. Some are carried piggy-back on powered planes. And some are pulled behind powered aircraft on a towline.
Welcome to the world of aerotowing!
I live a few miles from the Mountain Valley Airport in Tehachapi, CA. Mountain Valley is home to a glider school and lots of glider flying. Most days from our RC field you can watch the full scale operations in full swing as glider after glider is towed into the sky. I used to watch them and wonder how it would be to duplicate their methods in RC. I got bit by the bug as they say…
I am by no means an authority on aerotowing. I just got excited about it and decided to give it a try. My purpose in this blog is to spark your interest and to demonstrate that it is very doable. At the end of the blog I will point you to some sources for information and equipment.
To do this with RC there are some differences from the full scale procedures. For instance, the full scale tow plane usually has the towline attached at the rear of the plane down by the tail wheel. The full scale glider pilot has the advantage of sitting directly behind the tow plane where he can see what is going on. In RC, with depth perception being what it is, and your perspective changing constantly as the aircraft duo circles the field you won’t have this nicety. It seems to work much better to put the towline anchor point up on top of the tow plane just aft of the CG. This way, if the glider deviates from the heading of the tow plane it won’t pull the tail of the tug with it. I think that could get pretty erratic, but you’re welcome to try!
My tow plane is a tattered old Sig Kadet LT-40 with an O.S. .46FX and 12X5 APC prop. The towline is attached to a homemade release that sticks out of the top of the wing just aft of the CG. It has a servo mounted to the bottom of the wing to activate it. This is an emergency feature, as normally you would only release the line at the glider end. However, should things go badly, you can release it here, and save the tow plane. It looks like this…
The towline is 75 feet of #18 premium braided mason twine from Home Depot. It comes in neon colors! I use an 8” loop of 60 lb mono at the tug end attached with a heavy fishing swivel and a 12 lb mono weak link. At the glider end I have another 8” loop of 60 lb mono attached with a heavy fishing swivel and an 8 lb mono weak link. The mono and swivels are all available at any fishing store. I also have a neon ribbon tied on just in front of the swivel setup. It is there for visibility. Here are some pictures of the line setup…
The glider is my own scratch built design. It was designed to be a somewhat retro looking glider. It is 4 channel control (ail.,ele.,rud.,split flaps). It also has a servo-actuated release in the nose. All servos are Hitec HS-85BB. Airfoil is SD6060. Span is 72″, area is 567 sq. in. Completed weight is 51 oz. There are wire skids in the tail and wingtips. It was a great project! It is too heavy to be much of a thermal ship; however the design is robust, and the main objective was the towing experience rather than lots of gliding. And here is the glider…
Operations are pretty straight forward. Be courteous to others using the runway, and make sure to communicate your plans. Line up the tow plane and glider at the start of the runway, facing into the wind. Hook up the towline, and stretch it out so it is straight. Make sure that the line is lying on TOP of the horizontal stab on the tow plane. Start the engine on the tow plane. Tow and glider pilots should be in close enough proximity to communicate well.
Take off normally and climb straight ahead. If it is really windy (and we have wind most of the time), we will just climb as high as we can comfortably see, straight into the wind and release before any turns are made. If the wind is low, circling the field is really fun. I like to get some space under me before turning. After gaining sufficient altitude, make a big oval or figure eight, maintaining a steady climb until release. Make your turns gradual. No abrupt maneuvers here!
The glider pilot will be holding some up elevator and keeping the wings level. Don’t try to bank the glider; let the towline pull it around the turn. Keep those wings level! You don’t want to get inside the tow plane in the turn. If you do, the line will slack and then jerk, and it becomes increasingly difficult to get back on course. This usually results in a broken weak link, and you will both need to land and try again. (This is the reason for the weak link; it will save you heartache and rebuilds.) Staying to the outside and above the tow plane seems to work best. When you get to the position where you want to release, preferably heading into the wind, just announce your intentions and flip the switch. If you turn out as you come off the line, it will look just like the big boys do!
That about sums up my experience with aerotowing this past summer. I hope you decide to get in on the fun! Hobby King sells the release that I used in my glider. Horizon Hobbies/Parkzone has a KA8 with an optional release that may be a good way to get started. There are several others on the market also. http://www.rcaerotowing.com/ is an excellent resource for ideas and product sources. Of course, I am a proponent of building, and this is a great project to do your own designing and building. Drop me a note, as I will be glad to answer questions where I can, and would love to see your aerotowing project! Now go tow a glider!
Interested in scratchbuilding? See the glider building slideshow here… SCRATCHBUILDING
I would like to thank all of the local RC Guys who have helped and cheered this effort. Also my lovely wife for the wonderful photography. You have all helped to make this project a success!