10 - How to do a ground loop

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Hello folks,

Damien O'Reilly sent this. He and I both thought it made amusing reading while making a few very valid points.

Remember, there are only two types of tailwheel pilot. Those who have executed a groundloop, and those who are going to...

Keep the oily side down!

Yours,

Bob Grimstead
SABC Safety Committee

HOW TO GROUNDLOOP YOUR TAILDRAGGER

Judging by how frequently it is performed, the Groundloop is indeed a popular aerobatic manoeuvre. The Groundloop is an extreme low-level figure that is highly acrobatic in nature, and it can be executed in many exciting variations. It is customarily performed as the last figure in an aerobatic sequence, but I have also seen the Groundloop attempted as a preliminary or warm-up manoeuvre.

It is rarely scored however, because it is most often performed out of the Judges' line-of-sight. Also, the Groundloop is categorized as a surprise manoeuvre, and therefore nobody is really prepared when it is executed.

In fact, the figure is not considered genuine unless Judges, spectators and the pilot-in-command are all surprised! The many interesting and dynamic variations do not have a Degree of Difficulty or "K" factor attached, but rather are rated on the International HC (Holy Cow) scale.

HISTORICAL PERSPECTIVE

The Groundloop is one of the earliest recorded aerobatic figures. It was performed on virtually all of the taildraggers dating back to Aviation's infancy. The manoeuvre really came into its own during the Golden Era of the Groundloop, which was when the crosswind landing was invented. Before this, circular landing fields were the norm, so the pilot simply observed the windsock and landed into wind. However, it was soon discovered that a short, straight landing strip could be ploughed out, and now there would be lots of room for hangars, clubhouse, and an expensive cocktail lounge. Once everyone saw how much fun this new land-use concept generated, it was adopted internationally. The daily Groundloop displays were an instant hit, and helped cast the new idea in tarmac.

ANALYSIS

Most Groundloops are weathercocking-related phenomena. This means that at least one main wheel must be touching the earth, and a wind is blowing. Traditionally, the manoeuvre is started in a crosswind; during the landing roll-out the tail is allowed to be blown down-wind. At this point, there are a variety of options that can be exercised depending on your inputs, and the manoeuvre can take off in almost any direction, and finish in a variety of attitudes. Groundloops that occur under calm conditions are more rare, and require vigorous control inputs, so you really have to work at it to get a decent one.

Groundloops can be generated anywhere from 5 knots to flying speed. When executed at high speed, the figure covers more territory and generally spawns the most interesting variations. High-wing taildraggers probably Ground loop the best because the upwind wing is more exposed to the breeze. The high-wing also has a higher centre of gravity to really accelerate things once the manoeuvre starts. If the aeroplane is designed with the wheels forming a small triangle (short-coupled), and in the hands of the right pilot, this could be a Groundlooping champion.

ESSENTIAL BACKGROUND KNOWLEDGE

Avoid the study of the following subjects: a) Crosswind take-offs and landings. b) Ground-handling in winds. Avoid seeking instruction on these subjects, for it will greatly reduce your chances of producing a truly World-Class Groundloop. Also, you might want to have a good line ready in case someone raises one of these subjects in conversation: "Cross-wind landings, wasn't that about lesson 5 on your PPL? I'm way beyond that!

PREPARATION

To be successful, we must prepare both pilot and aircraft.

PILOT

To perform good Groundloops, the best preparation is no preparation.

AIRCRAFT

The aircraft can be prepared in a variety of ways to ensure consistently good Groundloops. First, the main wheels should be shimmed to a toe-in condition. If the wheels are adjusted to track straight ahead or are shimmed slightly toe-out, the tracking will be too stable to assist your attempts at Groundlooping. Keep the tire pressures different from one another. If you know the direction of the crosswind, reduce the pressure on the up-wind tire before going flying. And remember, it isn't necessary to change the tires until you can see the second ply of fabric showing; a blowout can be the start of a dazzling Groundloop.

Avoid the hassle of taking off those troublesome spats by putting a drop of Loc-tite on the screws. Now you have a good excuse not to inspect the brakes. So, when the brake fails on one side or the calliper pinches through a rusted disc, you will enjoy a splendid Groundloop.

At the back end, you can start by loosening the fitting that holds the tail-wheel spring to the fuselage. Just back the nuts off a few turns. Also back off the nut that attaches the tail-wheel casting to the spring. Now, slack off the steering springs a couple of links so the chains sag. And while you're at it, cut off that lock wire that some conscientious Engineer installed in case the chains break. From time to time, they break on landing and produce a thrilling, and rakish Cramer-like lurch. Fantastic! These simple mods will produce a delightfully loose rear-end that feels like it's on ball bearings.

The little tail-wheel is best left alone; over time, it becomes worn into interesting cone-shape by the effects of slipstream, P-factor and gyroscopic effect. These left-turning forces create more wear on the starboard side of the tyre, and soon you have a beautifully unstable little demon back there to really help you out.

Install the push-to-talk switch in a remote area of the cockpit. When someone talks to you on the rollout, you can look down into the cockpit to locate the button, and when you look up, you may be treated to the wonderful green-and-blue kaleidoscope of rotation about the vertical axis.

VENUE

Whatever you do, be sure never to land on the grass. A soft, low-friction surface like grass will almost never allow a proper Groundloop, even in a strong crosswind. Gravel is almost as bad. Particularly when the wind is calm, be sure to land on a hard-surfaced runway.

TECHNIQUE

Once the pilot and aircraft are prepared, it's a little like shooting fish in a barrel; there's really nothing to it. There are several things you can do to get the Groundloop going, but really, the best thing to do is nothing. Just let it happen. If you are landing or fast-taxying in a crosswind and you want a Groundloop... you guessed it – just do nothing.

Taxi with abandon. As a pilot, you are a free-spirited individual, and this can be best displayed by a carefree high-speed jaunt along the taxiway. Just let go of the stick and use the hands-free time to organize your charts and sequence cards. If the tail-wheel comes off the ground, you're going a little fast. Maybe you'll want to use the time to put on your seatbelt, polish the inside of the canopy, re-tie your shoelaces or perhaps light up a smoke. Taildraggers have the right-of-way, so you won't have to stop suddenly.

When cleared for take-off, start bringing the power up as you swing out on to the runway. Of course, you'll want to shove the stick forward quickly to get that tail up (you can't get it up too soon). If the plane will fly at 50, hold it on until 65. This technique spreads out the landing gear and scrubs off some rubber, but everybody does it and it looks cool. If you get rolling quickly, any crosswind won't matter. Now rotate as you would a 767. Haul straight back and blaze into the blue.

On the approach, keep it low and fast. If the airplane lands at 50, cross the fence at 100. It's best not to have a planned touchdown point because that can interfere with the free-spirited nature of the flying event. Start pedalling the rudders through 500 feet, and keep it going until you've cleared the runway. The pedalling technique is to let the aeroplane know who's boss. Get down to the runway as soon as possible, and force it to land with plenty of forward stick. The fast-landing method is good for all weather conditions, especially quartering tail-winds. Once the plane is firmly on the ground, let go of the stick, but keep pedalling the rudder to cool the tail-wheel assembly. Taxi in as you taxied out.

VARIATIONS

1. The 45-Degree Overland Express.

    This one is best done at about 40 knots. The aeroplane is allowed to weathercock slightly, the upwind wing and wheel are allowed to rise about 30 degrees and the plane swings into wind. At 45 degrees off the runway heading, sharp downwind brake, full aft stick and aileron into wind are added to stop the Groundloop. The plane is now headed off overland. This is useful for taking a short cut to the washrooms after a long flight.

2. The 90-Degree Quick Turn with Prop Curl.

    Use the same technique as above, except at about 20 knots. When you stomp on the downwind brake, also shove the stick forward. Even though you are travelling more slowly, the gyroscopic effect of shoving the stick forward will give you that extra 45 degrees of rotation. The tail will rise briskly. As soon as the prop touches the runway, pull hard back on the stick and apply both brakes. This was how the original Q-Tip Propeller was invented. If you've done it just right, you'll probably have a much more efficient prop.

    The Prop Curl can also be done straight ahead. Taxi at about 10 knots while tucking in your shirt or cleaning your sunglasses. Keep your hands off the stick and slam on the brakes. Voila! Also, try this while manoeuvring the tail-wheel over an obstacle. For a more dramatic Curl, hold the stick forward and add a burst of power.

3. The Pitts Special Twin Arcs.

    Start the Groundloop from the rollout at about 25 knots. Remove all crosswind inputs and allow the aeroplane to weathercock. Move the stick forward to at least neutral to lighten the tail-wheel and reduce its directional control. The little biplane will rise up on the downwind wheel and begin a precise pirouette. The downwind wing-tip will hit the runway and begin scribing an arc of red butyrate, Dacron and plywood. Without hesitation slam in full upwind aileron, as if to attempt to lift the lower wing. The downwind aileron will shoot down and describe a beautiful red arc parallel to that made by the wing-tip. Pull the stick full back, push full downwind brake with full rudder and a burst of power to erect the plane. These little red arcs are very artistic and will attract a good crowd in the evening following the day's flying.

4. The 180-Degree Pirouette with backtrack

    This one is best attempted in a light high-wing aeroplane with narrow bungee landing gear. A Cub will do nicely. The manoeuvre works best in a quartering tail wind. This figure looks difficult, but is really pretty simple. It works best if the pilot does not interfere.

    Get the weathercocking started in the usual manner. Move the ailerons out-of-wind and push the stick forward to get the weight off the tail. 20 knots is fine. As the up-wind wing rises, the centre of gravity swings as a pendulum toward the lower wing. About the time the down-going wing smacks the runway, the centre of gravity will have swung to the outside of the downwind wheel. Apply this brake hard. Now it's as if you had two upwind wheels because the centre of gravity has migrated outside via centrifugal force. So now it wouldn't matter which brake you applied, the effect would be to increase the rotation of the Groundloop. The wing-tip smacks off the tarmac, the brakes complete a full 180-degree turn, and you can fast-taxi back to the numbers.

5. The Groundloop with Bunt.

    This is certainly one of the more dramatic figures in the Groundloop family. You'll want to be travelling a little faster to get this one – around 35 knots is good. The figure should start slowly then get faster and tighter as rotation sets in. A dry runway is necessary, and a quartering tail-wind from the left is best. Once rotation starts, shove in full down-wind stick and full forward elevator. This will really tighten up the rotation. Now add full brakes and full power. The tail will shoot upwards and the airplane will do a kind of shoulder roll right on to its back. This is really low-level inverted, and you should ensure that your belts are very tight. This figure should be reserved for the last flight of the day.

CONCLUSION

The Groundloop has been around for almost a century and I'm sure it will be with us forever. And to keep it alive, all we have to do is be a little complacent, a little cock-sure and in a little hurry. Most important, one needs a thorough misunderstanding of weathercocking, crosswind take-offs, landings and ground handling. Sounds pretty easy to me.