|Line 1:||Line 1:|
From www.wallaby.com description of Aerotowing:
Latest revision as of 19:02, 28 August 2007
From Wallaby Ranch's description of Aerotowing:
Aerotowing is a system in which an ultralight aircraft (called an aerotug, or just a "tug") tows you and your glider aloft. For launch, your glider sits on a specially designed rolling cart. This 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. (Your harness should remain unzipped, however, in case you have to land immediately, due to weak link failure, rope break, etc.) An assistant will connect you and your glider to a 150 foot long tow line. Then, at a signal from the ground crew, the tug accelerates, and as soon as you have enough airspeed (a couple of seconds), you rise smoothly from the cart. You then essentially fly in formation with the tug until it's time to release. The tug pilot will try to drop you off in the best thermal he can find upwind.
Besides the cart, you will also need a V-pull and a release. The V-pull is a piece of Spectra line which connects to both of your shoulder straps, and to a point on your glider's keel. The bridle of the V-pull passes through a ring at the end of the tow line, joining the glider to the tug. Thus the tug pulls the pilot and glider evenly, resulting in a more natural-feeling control pressure. The release handle is Velcro-mounted on the lower control frame. When you release, the bridle feeds through the ring on the tow rope and you and the glider are left in free flight. A weak link connects the V-pull 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 Ranch Hand will assist you. After you have done a preflight inspection of your glider and gear, place your glider on the cart, hook in, and do a hang check. Your angle of attack should be high relative to the ground. While in the prone position, ensure that there is nothing to get tangled on the wheels or frame of the cart (VG cord, zipper pull cords, loose straps, etc.). Do not zip up the harness; be ready to execute a quick landing if necessary. Hold onto the cart string with one finger of each hand. The string will hold you and the glider securely on the cart when you begin your takeoff roll.
At this point you should stay prone and wait for the tug. Your vario, helmet, and gloves should be on, your V-pull and weak link laid in front of you. The tug should never have to wait. A glider and pilot pointing into the wind on a cart at launch is the signal to the pilot and staff you are fully prepared to tow. The only thing left is the attachment of the tow line. This is the Ranch definition of READY.
A Ranch Hand will attach the bridle through the aerotow ring and then to the release mechanism. The tug will move forward to take up 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. Hold your arms firm to overcome the initial cart drag and resist the tendency of the tow line to pull you through the control bar. When you are all set, the ground crew will give a signal and the tug will accelerate. You'll feel the speed pick up and the glider will begin to fly. YOU WILL LIFT OFF BEFORE THE TUG DOES. FLY AS SOON AS YOU HAVE FLYING SPEED. If one wing lifts prematurely while you are still on the cart, correct it so that you rise with your wings level. Just when you feel that the cart wants to lift off the ground, let go of the string, and let the glider rise 10 to 15 feet. This position gives you enough time to land if the weak link breaks. (If a weak link does break while you are still on the cart, simply hold on to the cart string until you roll to a stop.) When the tug climbs up through your altitude, do whatever it takes (push out or pull in, maybe even aggressively) to match the tug's climb rate.
Flying Under Tow
Watch the tug and control your pitch so that you climb with it. Always try to KEEP THE WHEELS OF THE TUG ON THE HORIZON! Do not ever take your eyes off the tug during the tow. While being aerotowed, tug position is everything. Unlike in free-flight, you must forget about bar position and bar pressure, and focus on only one thing: tug position. Do whatever it takes to keep the tug's wheels on the horizon throughout the tow. (If the sky is hazy, approximate the horizon.). The tug controls airspeed. Pulling in too much under tow will cause the glider to go down, possibly into the wake of the tug. Towing too high behind the tug will 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 control inputs and the glider's response to them. You must learn to anticipate this. If you hold the correction too long, you will overshoot the ideal position and then have to make the opposite input. You will make it much easier on yourself if you keep the tug's wheels on the horizon.
The three most common mistakes for pilots new to aerotowing are: The pilot comes off the cart and rises too quickly above the tug, breaking the weak link. The pilot fails to anticipate the tug's quick climb-out after launch, gets low, and then doesn't push out far enough to climb up. Remember: it is almost impossible to stall under aerotow. The induced thrust vector makes the glider trim at a higher attitude. It is OK to push way out; you will climb, not stall. Over-controlling and over-correcting. Make only small, relaxed, conservative movements and corrections. 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, and not a stall. Stay with the tug using pitch input. If you are low, PUSH OUT!
Early Aerotowing Flights
AT is different than free flight, and indeed than any other form of towing. Again, it is DIFFERENT. Not difficult, just new. So even if you are a Hang IV, you will need some transition time. During your first few AT flights you should fly in smooth and stable air on one of our easy-to-aerotow gliders. Taking a tandem flight is the ideal way to familiarize yourself with AT. Some of the world's best pilots have done this and been glad they did. For experienced hang glider pilots, the first solo always goes more smoothly after first taking a tandem, and this may save you some embarrassment. When you begin to fly in more active air, the tug gains and loses altitude as it encounters thermals or sink. Try to anticipate these changes and stay in position by pushing out and pulling in appropriately (always keeping the wheels of the tug on the horizon). Relaxing and executing short, smooth movements will make the tow much easier. The tug pilot will generally signal for you to release in the first good thermal OR at 2,500 feet, whichever comes first.
Turns on Tow
It is especially important to remain in position behind the tug during turns. Wait, let the tug turn first, then follow, allowing the tug to draw you into the turn. Otherwise you may accelerate towards the outside of the turn like a water-skier "cracking the ship" behind a boat, and a lockout could occur. Getting too far inside of the tug's turn, on the other hand, will cause you to descend, slow down, and put slack in the line. In this case, pushing out and leveling your wings will allow the glider to pivot back into position. As always, early anticipation is the key. You don't want to turn more or less than the tug; just do whatever it takes to stay "tangent to the same arc".
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 angel of attack while under tow and the sudden loss of energy upon release. Regain airspeed and land normally. Wheels are highly recommended. They increase your landing options, and never hurt anybody.
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. If all else fails, the tug pilot will release the tow rope at his end (see below). Looking away from the tug, adjusting your harness, vario, etc., can cause an inadvertent release. You may release from tow at any time, if you feel things are not going well. 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 (this may occur as a result of flying too high so that you pull the tug into a dive, a lockout, or some kind of tug problem), the rope will lie over the control bar and trail behind you. Remember: you may not be able to see it. If you have enough altitude, fly it back and drop it over the landing field. 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.
Some gliders have less directional stability than others during AT. These gliders have a tendency to oscillate from side to side on tow, especially when flown by pilots with less aerotowing experience. This is pilot-induced, but can be controlled and even eliminated through early anticipation and appropriate control inputs. Hint: try not to correct for yaw, only for pitch. Don't concern yourself with the exact orientation of the glider's airframe; the glider is happy to tow at a skewed angle. Hang glider pilots new to AT tend to over-control in roll and under-control in pitch. To prevent or stop an oscillation, relax and remain still and centered on the bar. Make gentle pitch corrections. Ignore yaw. Think smooth happy thoughts and the oscillations will cease. If you feel like you are losing control, however, simply release and fly your glider normally. Do not try to save some crazy situation; if in doubt, release. After your flight, ask for helpful follow-up instruction from the Ranch staff.
While towing, watch the tug pilot. He will give you signals to guide your flight. If you keep the wheels of the tug on the horizon, you will only see the release signal. All signals are given with his left arm.
Tug Pilot Signals to Hang Glider Pilot MOVE HIGHER - Tug pilot's arm held bent at the elbow, with hand up. You must push out and climb. MOVE LOWER - Tug pilot's arm held bent at the elbow, with hand down. You must pull in and descend. RELEASE! - Tug pilot's arm waved up and down. You must release immediately. 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 the Ranch. The Ranch is usually behind you or else straight down. 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 Ranch.
What It Takes to Solo
Everyone is different. A conversation with the Ranch staff will determine the individual needs of each pilot. Some pilots will need only the Introduction to Aerotowing, others multiple tandems. Many advanced and master-rated pilots have opted for a tandem as the best way to learn this new skill. Our first and overriding objective is safety. To solo, you must be able to smoothly follow the tug and set up a conservative approach (both without assistance from the tandem instructor.). Tandems to determine solo capability are done in calm and stable conditions. This leaves room for only one variable - the control input of the pilot in command.
Remember: Relax, Hold Still and Keep the Wheels of the Tug on the Horizon!
The Fine Print...
Have fun, relax. Tug position is everything. Check your weak link. Always tie down the glider. Be cool, get a T-shirt. Don't blame the tug pilot if you bomb out. Tow the easiest glider first. Pick up trash. Wheels never hurt anybody. Be ready before the tug gets there. Start to turn where the tug pilot drops you. You are welcome to run a tab. Stay west of US-27. Treat the release with extra care. If the weather is great you'll have a super time; if the weather sucks you'll still have a good time. Chill out. Don't land in the orange grove next door. Tape your Camelback nipple to the tube. Learning is easiest in smooth air. Stay upwind. Avoid the Class B airspace to the east. Let us know what kind of tow you want. Suggestions are welcome. Park gliders in the shade. The thermals are out there. The tug pilot can't put everybody in the world's greatest lift every single time - but he'll try. Use your variometer on tow and get off in lift. Roll the cart by pushing the downtubes. Buy a Lifetime Membership. Cross-Country means to go at least 5 miles; otherwise, land back at the Ranch, please. Help us implement the good ideas. Pick up your glider and move out of the way right after you land. Try to remember to pay - sometimes we forget to ask. Run in all your landings - it works better and it is safer than no-steps. You are responsible for everything in your life. Tell all your friends about us. Remember that we're all here for the same reason: we love to fly. Share in the positive energy of the Ranch lifestyle.
Learning to tow took me by surprise. I read the starter books, the one for the beginner and the one for performance flying, before heading to Wallaby to try towing for the first time. The books were helpful, particularly with the concept of the coordinated turn, but I did not expect towing to require the skills it did, and neither book focused upon the towing issues sufficiently to place me ahead of the curve.
My biggest problem was pilot induced oscillation. In other words, as we were towed I tended to move back and forth because of over corrections. Malcolm told me to loosen up, but it was Mike Barber (he of the distance record fame) who, one morning at breakfast, really cured me of my rigidity, and thus my PIO.
Mike had me grip a couple of salt shakers very tightly, and then asked me to identify which was heavier. I could not tell which shaker was the full one when I was holding the shakers tightly. He then told me to hold them in a relaxed grip. The difference in their weight was immediatly apparent when I relaxed my grip.
It probably seems ridiculous and self evident that too much tension interferes with your ability to distinguish subtleties, but it was a very helpful lesson for me. Once I loosened up I was able to feel the glider's inputs and respond both more quickly and more appropriately, avoiding the oscillations.
For those who have not towed, being towed is a great experience. I loved various parts of it, and genuinely liked the rest. Taking off on the wheels was just plain satisfying. The feeling of the glider gaining lift, and the flying of the glider even prior to lift off was a stone gas.
I also loved it when the tug pilot would give the release signal, the series of events thereafter were gratifying to all the senses. First, just after release you hit the tugs wake. Not always, but almost so. It is necessary to increase the glider's speed by pulling the nose down a little to meet the wake correctly. The wake is akin to the wake of a boat, and it was possible to visualize it while bumpily passing through it.
As part of the post release sequence the tug dives out of the sky, while you hang there. That visual was always fantastic. The sight of the tug spiralling down, followed by the tow rope gave a visual reference of heighth and depth, and just looked way cool. I never tired of the sight.
The flight down was unfailingly fun, but I will not rhapsodise about that, I guess it is kind of a given.