AeroTow Details 

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All you ever wanted to know about aerotowing.


INTRODUCTION

Aerotowing is a system in which an ultralight aircraft, called a “tug,” tows you and the glider aloft. To launch, your glider sits on a specially designed rolling cart. The cart supports your glider at the correct attitude for liftoff, and stabilizes it until you reach flying speed. You will already be prone before you begin rolling, making failure to hook in almost impossible. The ground crew will connect you and your glider to the tow line (the tow line any be anywhere from 150-200 feet). Then, after a signal from the ground crew, the tug accelerates, and as soon as you have enough airspeed (a few seconds), you rise smoothly from the cart. You then essentially fly in formation with the tug until it’s time to release.

EQUIPMENT

Besides the cart, you will also need a V-pull bridle and a release mechanism. The V-pull  bridle is a piece of line such as Spectra or polypropylene which connects to both of your shoulder straps, and to a point on your glider’s keel. There are two parts to the aerotow bridle system: the "long part" and the "short part". One end of the "short part" connects to one harness shoulder loop and the other end to the other harness shoulder loop. When attached properly it would form a "v" if you pull the center of the line away from you. The "long part" has a loop in both ends and the "v" part connecting the shoulders slides through the "long part" so that the long part is in the middle of the "v." The "long part" then passes through a ring at the end of the tow line, joining the glider to the tug and the other end is secured, via a weak link, to a (primary) release mechanism which, in turn, is attached to a specific point on the keel of the glider. Thus the tug pulls the pilot and glider evenly, resulting in a more natural-feeling control pressure.

The "release" actuator looks like a bicycle brake lever and is Velcro-mounted on the lower control frame. When you squeeze that lever an attached cable actuates the primary release at the keel attachment point. The "long part" of the bridle is then free to run through the ring on the tow rope and you and the glider are left in free flight. A weak link connects the long V-pull bridle to the release, providing a safe limit on the tow force. If you fail to maintain the correct tow position (centered, with the wheels of the tug on the horizon), the weak link will break before you can get into too much trouble.

A "secondary release" is a simple "hook & barrel release" attached to your harness shoulder loop. One side of the short "v" bridle is attached to the "secondary release," so in the event the "primary release" fails the pilot merely slides the hook barrel back and the tow line is released.

LAUNCHING OFF THE CART

The ground crew will assist you. After you have done a preflight inspection of your gear, place your glider on the cart, hook in, and a hang check. Check that both the cart wheels have enough air – a flat tire will cause the cart to steer in that direction. Your angle of attack should be high relative to the ground. While in the prone position, ensure that there is nothing to tangle or get stuck on the wheels or frame of the cart (cords which may be dangling from the control bar or the harness). Hold onto the cart string with your thumbs, Or if your club is lucky enough to have a T-Dolly there is a solid bar to grasp right under your base tube. The string or solid bar will hold you and the glider securely on the cart when you begin your takeoff roll.

The ground crew will attach the bridle through the aerotow ring and then to the release mechanism. The tug will move forward to take up the slack in the tow line. You will feel it pull you forward, but you should resist and hold your bar position just aft of minimum sink. When you are all set, the ground crew will give a signal and the tug will accelerate.

While rolling on the cart prior to lift off make any necessary lateral corrections to steer the cart. FLY THE GLIDER WHILE IT’S ON THE CART. You’ll feel the speed pick up and the glider will begin to fly. YOU WILL LIFT OFF BEFORE THE TUG DOES. If one wing lifts prematurely while you are still on the cart, quickly make the necessary correction so that you rise with your wings level. When the feel the cart just start to want to lift off the ground, specifically, you’ll feel the weight of the cart on the string, let go of the string or bar, and let the glider rise up 10-15 feet. This should allow you to have enough speed if the weak link should break and puts you in a position to land should that happen. If the weak link breaks when you are still on cart, simply hold on to the string until you roll to a stop.

As the tug climbs up through your altitude, do whatever it takes (pushout or pull in, maybe even aggressively) to match the tug’s ascent. To reduce the possibility of pilot induced oscillations make short sliding bumps to steer left and right. Do not leave your weight shifted left or right for too long!

PILOT UNDER TOW

Watch the tug and control your pitch so that you climb with it.

If you are towing behind a Moyes-Bailey Dragonfly always try to KEEP THE WHEELS OF THE TUG ON THE HORIZON! When towing behind a Trike always try to KEEP THE WINGS OF THE TUG ON THE HORIZON! Do not ever take your eyes off the tug during the tow. Unlike the free flight, while being aerotowed tug position is everything. Pay no attention to bar position and bar pressure, focus on only one thing, tug position. Do whatever it takes to keep the tug’s wheels or wings on the horizon throughout the tow. (If the sky is hazy, approximate the horizon).

Remember: The tug controls airspeed.

Pulling in too much under tow will merely cause the glider to go down, possibly into the wake of the tug. And cause you to feel a lot of bar pressure.

Pushing out too much will merely cause you to towing too high behind and, again cause you uncomfortable bar pressure.

If you get above or below the ideal position, it is important to make a pitch correction right away. There is a lag in time between tug control inputs and the glider’s response to them; learn to anticipate this. If you hold the correction too long you will overshoot the ideal position and then have to make the opposition input. You will make it much easier on yourself if you keep the tug’s wheels or wings on the horizon.

MOST COMMON AEROTOW MISTAKES

1. Pilot coming off the cart and rising too quickly above the tug, breaking the weak link.

2. Pilot not anticipating the tug’s quick climb-out after launch, getting low and then not pushing out far enough to climb up

3. Over-controlling and over-correcting. Make small, relaxed, conservative movements and corrections.

4. Most students seem to want to undercontrol in pitch

Remember. . .

It is almost impossible to stall under aerotow. The induced thrust vector makes the glider trim at a higher attitude. It is okay to push way out; you will climb, not stall. Should you find yourself low behind the tug, you may need to actually push out on the control bar forcefully, resulting in a “past normal” bar position that in non-towing situations would lead to a stall. However, because of the “pull” of the tow line, this action will result in a CLIMB, not a stall. Stay with the tug using pitch. If you are low, PUSH OUT.

TURNS ON TOW

When the tug begins to turn, relax, and wait for the turn to begin. DO NOT begin to turn as soon as the tug does, or you will wind up inside the turn. Just like a water skier who gets inside the boat’s turn, you will slow down and sink. Instead, let the tug pull you around. Once you feel the tug pulling you into the turn, make a short sliding bump to establish your own turn, roughly matching the tug’s bank angle (amount of “tilt”). Don’t be anxious or impatient on tow: this makes it seem much more difficult than it really is. Let the tug and glider do the work. The fewer and smaller your movements, the easier it will be to follow the tug. Early recognition and compensation are the keys here. By anticipating and correcting early, you avoid the need for large control inputs.

Remember . . .

1. Wait for the tug to pull you into the turn, then follow

2. Match the tug’s rate of turn with smooth sliding “bumps” on the bar to the left and right

Helpful Hint. . .

You will find that good towing technique is often more about not doing things than doing things; a hang glider pilot with a lot of aerotow experience moves the control bar less on the tow than an inexperienced one. Correct EARLY, correct LESS

WEAK LINK FAILURES

The pilot is responsible for inspecting the weak link well before the tug arrives. Any fraying indicates that it’s time to replace the weak link. The weak link is designed to act as a fuse, breaking the circuit when overloaded. In an excessive out-of-position situation, the weak link will snap before the control authority of the glider would be lost. If you should have a weak link failure close to the ground it will be important to immediately lower the nose of the glider, due to the relatively high angle of attack while under tow and the sudden loss of energy upon release. Regain airspeed and land normally. Wheel landings are highly recommended.

GLIDER RELEASE FAILURE

If your release fails to operate or the V-bridle hangs up (extremely unlikely) you have several options:

Use the secondary release

Cut the V-pull/bridle with a knife

If you are high above the ground push out sharply to snap the weak link

Remember. . .

If all else fails, the tug pilot will release the tow rope at the tug end. Generally the weak link will fail before any situation can develop to a critical point. However it is better to recognize a less- than-ideal situation and release intentionally before tow line tension builds to the point of a weak link failure.

FLYING WITH THE TOW ROPE

If you are released by the tug pilot and left with the tow rope there are a couple of thing you can do, and a few reasons why you got the rope in the first place.

Why you'd get the rope - Why would the tug pilot release you:

1. If the tug had an emergency situation, such as a engine out.

2. If on launch you getting high on the tug, this pulls up on the tail of the tug and puts the tug into a dive the tug pilot will release you immediately because the tug and the pilot are not in jeopardy

3. If the pilot is in or on his way to a lockout situation

4. If the tug pilot sees the pilot is in distress and cannot release for whatever reason

5. If the weak link on the tug breaks for the rope breaks

These are the most common reasons the pilot will be left flying with the rope

Now that you have the rope, what to do with it:

1. If you are low or the ground or any objects, release it immediately. You do not want it dragging and possibly hooking on anything. Since the rope will be over the top of your basetube, if it get tangle up in an object, the consequence could be extreme.

2. If you are high and you the rope and there is nothing to hit, you can fly back over the landing area, drop it in the field.

3. So people had wadded it up and stuffed down the front of their harness. Be careful doing because when you go upright to land the rope would possible come loose and fall down out of the bottom of your harness, causing problems.

Remember. . .

You may not be able to see it, but if you have enough altitude, fly the rope back over the landing field and drop it. If you are low, release the rope immediately. Do not land with the tow rope still dangling if you can possibly avoid it ! If you must land with the rope, do so over an open area.

OSCILLATIONS

This is generally pilot induced (called PIO - Pilot Induced Oscillation), but can be controlled and even eliminated through appropriate control inputs. Don’t be concerned with the exact orientation of the glider’s airframe behind the tug – the glider is happy to tow at a skewed angle. To prevent or stop oscillation, relax and remain still and centered on the bar. Make gentle correction. Ignore yaw. If you feel like you are losing control, however, simply hit your aerotow release and fly normally. Don’t try to save a bad situation, if in doubt, just release and we'll figure out how to fix the problem.

Hint. . .

Do not correct for yaw. Make bumping corrections. Don’t leave your weight shifted too long.

Remember:

You already know how to fly, so if you're PIOing it's the aerotowing that's the problem - release immediately. Trying to hang on generally makes things worse.

SIGNALS

While towing, watch the tug pilot. They will give you signals to guide your flight. If you keep the wheels or wings of the tug on the horizon, staying in a good position behind the tug, the only signal you will see from the tug pilot if the "release" signal. If you are out of position the signals below will be given to the pilot by the tug pilot with their left hand.

TUG PILOT SIGNALS TO HANG GLIDER PILOT TO:

GET HIGHER

Tug pilot’s arm held bent at the elbow, pointing up.

Pilot Action: push out and climb

GET LOWER

Tug pilot’s arm held bent at the elbow, pointing down.

Pilot Action: pull in and descend

RELEASE !

Tug pilot’s arm waving in an up and down motion.

Pilot Action: you must release immediately.

Remember. . .

The tug pilot does not need any signal from the hang glider pilot when to release. The hang glider pilot can release at any time, there is no consequence to the tug pilot for that action. However, when the tug pilot "waves you off" (gives you the signal to release) you absolutely must release, right then, regardless of your altitude or your position - you must release.

AFTER RELEASE

When flying behind the tug, you are concentrating on alignment. This may cause you to lose your ground reference. The tug will never tow you beyond gliding range of its landing zone. As soon as you release you should locate the landing field. Look at the tug, the pilot will most likely make a bee line for the land zone. Otherwise, ENJOY.