Auto-towing a Glider

Launching a glider is normally accomplished through one of three methods: Aero-tow, Winch-tow, or Auto-tow.  I’ve done all three, and all three have distinct advantages and disadvantages.  I chose to launch at Casey Aviation via the Auto-tow method for several reasons, and have become one of only a few in the USA who are currently actively doing it.  Since the Auto-tow method is so rarely used, I thought I’d write step-by-step instructions to help anyone else who might find it interesting to try.

Why Auto-launch? I chose Auto-launch because it is almost certainly the cheapest way to get a glider in the air, and I did not need to get the glider very high to accomplish my primary mission of providing engine-out training to PA-46 Malibu/Mirage/Matrix pilots during initial/recurrent training. I only need to get to 800‘AGL, and the Auto-launch does a super job of getting me that high.  Because I did not want to invest capital expenditure into the start of this phase of Casey Aviation, I went with the cheapest method that accomplished the job.  Since just about everyone has a vehicle large enough to pull a glider, the initial investment is not high.  I invested less than $1,000 to get all of the required items to launch, and I probably could do it for even less than that if I had known what I was doing from the start.

Social network: Before you even think about Auto-launching, let me underscore an aspect of gliding that is absolutely critical…you must have a network of interested and passionate helpers! I cannot over-emphasize the importance of having others around to help.  Gliding is a naturally social activity, and the auto-launch method demands others to help out.  I’ve been blessed to have many at my home airport that are interested and many have devoted untold hours to making this happen.  You will need help too!

Essential equipment: You’ll need some equipment to make it happen.  Here’s a list that we found essential.

  1. Tow vehicle: We decided to use any full-sized truck with a square-receptacle hitch on the back.  An 8-cyl engine does work best, but a 6-cyl works just fine.  With a  full-sized truck, you will not need any additional weight in the back of the truck.  In fact, the truck hardly even notices the glider during launch, and the back of the truck is not lifted at all with a Schweizer 2-33 glider.
  2. Reel: I went to the local hardware store and found a reel that was used to hold a large amount of wire.  It has an inside diameter of about 10” and the outer edges are about 2’ in diameter.  If in doubt about the size needed, go for the larger size as it makes it easier to roll up the rope at the end of the launching.  Our first attempts to roll up the rope was with a garden-hose reel.  This did work, but it required 650 cranks of the handle, and that it entirely too much for anyone to accomplish repeatedly.  The rope weighs a lot and the friction of the rope on the ground increases the force required to move it to about 20 lbs of pressure.  Don’t think you’ll do this on your own…you’ll need a mechanical device.  We made a wooden bracing system and attached a home-made device so a drill could be used to roll up the rope.  This worked minimally, at best.  Find the guy in your group of glider friends who is mechanically minded and have him come up with a device that works, but plan to over-build.

    Rope reel with electric motor…all home-designed and home-made

    We ended up with a nice mechanical device that has an electric motor, and it works super (thanks to Robert Gatewood!)  We use electricity powered by the batteries in the golf cart.

  3. Emergency release: I am not convinced this is absolutely required because the SGS-2-33 has a tow hook the will release the rope if backwards tension is applied.  However, we decided that a release on the truck was a good idea, and it does make it much easier to deal with the rope while launching (more on that later).  I bought my release from www.wingsandwheels.com for $100 as a rebuilt model.  It works great.
  4. Rope:  I bought 1,500 feet of pre-stretched 2,000 lbs tensile strength rope from www.wingsandwheels.com for $320 and it is working fine.  However, I have since discovered that the electric companies use a rope to run the electric lines on the power poles, and it comes in very long lengths.  It is flatter and works super and is $170 for 3000’.  I’d go with the cheapest I could find as the rope will become quite dirty, scuffed, and ugly after just a few tows.
  5. Weak link: You’ll want to add a weak link on the rope, and I recommend using 1/4” nylon rope from and hardware store.  I use a few metal rings at the attach points, again provided by www.wingsandwheels.com
  6. Communication devices:  We’ve used two radios or one radio and one set of walkie-talkies.  It was kind of nice using the walkie-talkies because others cannot hear the side banter.  Whatever you use, the both the truck and glider must have a method to communicate.

Getting Started:  From when we get to the airport, here’s what we do to Auto-tow.

  • Get the Glider:
  • We arrive and pull the glider from the hangar to the runway via a 30’ tow rope and a golf cart.  You’ll need a minimum of two people to do this part of the job.

  • Lay out the rope: The key to this maneuver is to drive the truck slowly and steadily.  If the driver is sporadic in controlling speed, the spool of rope will behave just like a bait-cast fishing reel and you’ll have a massive bird nest in seconds.  We lay the rope out on one side of the runway in case an airplane needs to use the runway.  Once about 50’ of rope is on the ground, you won’t need anyone to hold the rope as the truck drives.
  • Position the glider: Move the glider into position on the runway making sure to have the radio tuned to the local unicom frequency.  The pilots then get into the glider and prepare for launch.
  • Connect the rope: Hook up the rope to the truck and position the truck on the runway centerline.  Once everyone is ready (including the glider and its occupants) connect the towrope to the glider.

The actual tow: Truck driver duties…

  • Initial acceleration: It is best to use the CG hook for auto-towing because it does not pull the nose down excessively during launch. Whereas the CG hook is longitudinally nearer the CG of the glider than the nose hook, it is not vertically nearer the CG.  By this, I mean that the CG hook is mounted on the bottom of the glider, well below the CG (which is normally somewhere near a foot above and in front of the main wheel).  So, if the auto accelerates quickly at first, a nose-up force is placed on the glider which results in a hard impact of the tail against the ground.  To counter this, the initial acceleration (up to about 20mph) must be gradual, much like the initial acceleration from a green light signal at an intersection.  Once enough speed is obtained to allow control of the pitch axis via the elevator, the tail can be controlled so it doesn’t hit the ground.
  • Burst speed: After the initial acceleration to about 20mph, the rate of acceleration must increase rapidly to the target speed.  Once the target speed is obtained, the tow vehicle must maintain that speed until braking is required so as not run off the end of the runway.  For the SGS-2-33, the target speed is 55mph, and any headwind is subtracted from that number.  For instance, if there is 10 knots of headwind, the target speed would be 45mph.
  • Ground safety considerations: The biggest safety consideration for the vehicle is to continue the pull regardless of the glider’s position.  In case of a rope break, the vehicle needs to be out of the way.  So, if a rope break does occur, the vehicle does the exact same action as if the rope did not break…continue to the end of the runway at the prescribed speed.  If a safety observer is available, the best place for this person is in the back of the truck where clear sight of the glider is available.  If the safety observer is in the back of the truck, we like for this person to be responsible for the truck’s rope release, in case a rope emergency occurs.

The Actual Tow: Glider operations… 

  • Stick position: The glider pilot should hold full-forward elevator position to counteract the tail-strike that may occur.  As soon as elevator authority is obtained, the elevator should be controlled to maintain a slightly nose-up attitude.  This position will be held for only a few seconds before the glider will leave the ground and then the pilot should use elevator position to maintain the proper pitch attitude.
  • Below 200’: Below 200’ is the critical time for the glider.  If a rope were to break, the only option is to land straight ahead.  An extremely high pitch attitude can be dangerous so low to the ground, so the pitch attitude should be limited to about 10 degrees nose up.  The rate of acceleration will not be high below 200’ and the tension on the rope will be minimal…and this is good for if we do have a rope break, we want a nose-low attitude to be available to give the glider pilot options.  So, the rate of increase in nose-up attitude should be minimal through 200’.
  • After 200’: Once 200’ is obtained, the goal of the glider pilot is to get as much altitude as quickly as possible without exceeding glider limitations.  On the SGS-2-33, the ground launch max airspeed is 69mph.  At 200’ the glider will be at about 50mph.  Above 200’, the pitch attitude should be held so the desired airspeed is obtained.  I shoot right for 69mph.  The difference between flying a glider under tow and not under tow is in the response to the pitch attitude.  When under tow, if the nose is raised, the airspeed will increase, not decrease as normally expected.  Pitch angles of 45 degrees positive nose-up are common on climb-out.
  • Water-skiing simile: If you have ever water skied behind a boat, you will understand the towing of a glider.  If a boat travels through the water at 30 mph, then the skier is going 30mph if behind the boat.  With the boat going straight ahead, if the skier maneuvers to the right or left of the boat, the forces acting on the skier increase exponentially.  The skier must lean away from the boat, the speed increases, and the forces required go way up.  The limiting angle for the skier is either the slippage of the ski’s on the water or the ability of the skier to hold onto the rope.
  • This same phenomenon occurs with the glider.  As the glider pitches up and increases the angle between the movement of the auto and the movement of the glider, the forces acting upon it go way up.  The limiting factor is either the strength of the rope (just like the hand-strength of the skier) or a tail-stall (just like slippage of the skier on the water).  If the max tow speed of the glider is not exceeded, then the tail will stall before structural limits on the glider are achieved (just like Va in an airplane).
  • Top of the climb: When the top of the climb is approached (about 900’ AGL with a 1,500ft rope on a 5,000ft runway with a SGS-2-33) the pilot must pitch the nose forward to lessen the release forces.  The glider will be at a high pitch angle, so high that a stall will soon occur if the nose is not pushed forward soon after rope release.  I begin the nose forward attitude before releasing the rope, simply to lessen these forces.    Once released, the glider will usually obtain another 100’ of climb before the inertia is expended.  Then, the hunt for a thermal begins.  When the pilot wants to return to the airport, we always land with a tailwind so the glider ends up where it originally began and does not have to be repositioned via the golf-cart.  If the wind are greater than 10kts, then I might re-think landing with a tailwind, but the SGS-2-33 glider lands in a very short distance, so it is no big deal on a long runway.  My biggest challenge is setting up the right approach so as to land so there is ground handling required.

Giving love to the ground guys:  One of the quickest ways to cast a huge wet blanket on your un-hired (but passionate) help is to release the rope and have it float far from the runway.  The amount of work required to dig out a rope that has floated into the weeds, fence, or forest is exponentially more difficult the further the rope strays from the runway.  The pilot has complete control over the fall of the rope, and he must fly wisely to have it hit pavement.  First, a small wind will affect the rope greatly.  A lot of rudder must be applied into the wind so the glider will divert upwind.  Note your position when you release the first time so you can bracket your release on subsequent launches.  Secondly, don’t release the rope late.  The later you release, the more the rope will bundle up in a big mess.  If you release slightly early, then the auto will naturally begin to stretch out the rope, leaving it in a long and wavy pattern, but it be much neater than if you were to release late.  I usually look down every now an then while towing and note the position of the truck.  When it begins to brake, the climb is effectively over and rope release should follow shortly.
Ground guys go to work: When the rope is released, the glider has the fun part, but the ground guys get to go to work.  At the end of the runway, we stop the truck and disconnect the rope.  We drop that end of the rope in place and drive the truck to the other end of the rope.  We then reconnect the rope and drive it back to the starting point at the beginning of the runway.  There are several good reasons why we do this.  First, if the truck simply turns around, then the rope will begin to twist excessively.  Second, this limits the amount of distance the rope has to abrate against the ground.  The friction of the ground is the greatest detriment to the health of the rope, so tow it as little as possible.  We drive the truck on one side of the runway so the grand majority of the runway is available for other airplanes.  Once the rope is back at the launch end of the runway, the rope is disconnected from the truck again.  The truck then drives back to the rope and prepares for another launch.

Call me: Got questions?  Call me.  This is far easier to explain verbally than write.  I’ll share all the knowledge I have, and I’m gaining knowledge all the time.  Remember, gliding is a social sport!

About Joe Casey

ATP, CFI, CFII, MEI, CFI-G Commercial Pilot - SE, ME, Rotorcraft, Glider US Army AH-64 Pilot and UH-60 Instructor Pilot and Instrument Flight Examiner
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