Taildragger groudloop technique

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orion

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How To Groundloop Your Taildragger

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

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 maneuver, 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” attached, but rather are rated on the International HC* scale. *Holy Cow.

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 maneuver really came into its own during the Golden Era of the Groundloop which was when the cross-wind landing was invented. Previous to this, circular landing fields were the norm and the pilot simply eye-balled the windsock, and landed into wind. However, it was soon discovered that a short, straight landing strip could be plowed out, and now there would be lots of room for hangars, clubhouse, and an expansive 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 maneuver is started in a cross-wind; 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 maneuver 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 5MPH 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 enjoys a longer arm to really accelerate things once the maneuver starts. If the airplane 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) Cross-wind Landings and Take-offs. 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, heck, wasn’t that about lesson 5 on your Private License? 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 of all, 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 cross-wind, 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 blow-out can be the start of a dazzling Groundloop.

Avoid the hassle of taking off those trouble some wheel-pants 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 caliper 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 an 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 tire, 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 the tower talks to you on the roll-out, 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.

TECHNIQUE (HOW-TO)

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-taxiing in a cross-wind and you want a Groundloop... you guessed it- do nothing.

Taxi with abandon. As a pilot, you are a free-spirited individual, and this can be best displayed by a carefree jaunt down the taxiway. Just let go of the stick and use the hands-free time to organize your maps 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 brushes off some rubber, but everybody does it and it looks cool. If you get rolling quickly, any cross-wind 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 fanning the rudders through 500 feet, and keep it going until you’ve cleared the runway. The fanning technique is to let the airplane know who’s boss. Get the plane 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 fanning the rudder to cool the tail-wheel assembly. Taxi in as you taxied out.

VARIATIONS

45-Degree Overland Express - This one is best done at about 40 MPH. The airplane 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.

90-Degree Quick Turn with Prop Curl - Use the same technique as above, except at about 20 MPH. When you stomp on the downwind brake, also shove the stick forward. Even though you are traveling slower, 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 MPH 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 maneuvering the tail-wheel over an obstacle. For a more dramatic Curl, hold the stick forward and add a burst of power.

Pitts Special Twin Arcs - Start the Groundloop from the roll-out at about 25 MPH. Remove all cross-wind inputs and allow the airplane 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 concise 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 days flying.

180-Degree Pirouette with back-track - This one is best attempted in a light high-wing with narrow bungee landing gear, a Cub will do. The maneuver 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 weather-cocking started in the usual manner. Move aileron out-of-wind and push the stick forward to get weight off the tail. 20 MPH is fine. As the up-wind wing rises, the center of gravity swings as a pendulum toward the lower wing. About the time the down-going wing smacks the runway, the center 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 center 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 brake completed a full 180-degree turn, and fast-taxi back to the button.

Groundloop with Bunt. - This is certainly one of the more dramatic figures in the Groundloop family. You’ll want to be traveling a little faster to get this one. Say 35 MPH. 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, cross-wind take-offs, landings and ground-handling. Sounds pretty easy to me.

Enjoy your spin-around!!!
 

cgwendling

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Very Funny!
Wish me luck, I am going to attempt my first one tomorrow in a close coupled, high wing, bungee corded J-3.:ban:
Although I think the owner/CFI will probably have a different agenda.:rolleyes:
 

Topaz

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Heh. Very nice.

My sole experience with this manuver was many years ago, since I've been flying nose-draggers pretty much exclusively since we sold the plane involved.

I was about seventeen when my dad bought a 1941 Aeronca 11AC Super Chief. When we bought the plane, it was really tough to start - and since it had to be hand-propped, we have the genesis of this story. Turns out the previous owner had let gas sit in the tank for years, and varnish had formed on the finger screen. Pity we didn't figure that out until later...

On an early attempt to start the plane, he had me in the cockpit (I'd already soloed a Tomahawk by this point) and was pulling the prop through himself. We kept futzing with the carb, trying to get the thing to fire, me adjusting the throttle in an attempt to get some gas to the cylinders.

Just as I pushed it forward to about 3/4 open, the engine caught, and immediately jumped to that power. Those big, soft, rough-field tires had no problem jumping the chocks and my dad did a lovely dive off to the left to avoid becoming one with the blades. I think the Russian judge might have given him a lower score based on his landing, though. ;-)

Given the choice between trying to get the engine shut down and ramming the hangar in front of me, I stomped on the right pedal and headed off down the taxiway towards the active runway, Continental in full song.

By the time I got the engine shut down, I was doing about 15-20mph and was getting (in a seventeen-year-old's-mind) perilously close to the runway. I stomped on the left peddle, and was rewarded with a lovely 180deg. groundloop, although I think I lost points because the wingtip didn't actually touch the ground. But for a few inches, I almost left my mark.

After the turn the plane and the prop stopped spinning. I wished I could've said the same for my stomach!

Eventually we got the plane running well and I loved the beast, but dad had to sell it for some reason I can't remember. Wish I had it today!
 
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Johnny luvs Biplanes

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Orion
You forgot the easiest way to perform ground-looping displays: Just try and manouvere a skeg equipped biplane with no brakes on a hard surface. Further enhancements can be made by having a lovely narrow track undercarriage/big wheels and close coupled!
The artistary that can be performed with this configuration is astounding and world class.
How I will enjoy this when my Flitzer is built!
Cheers
John (Groundloop champion in the making)
 

Chester

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Orion,

Thanks for that great insite into taildragger flying. As I've always been a nosewheel driver, not pilot, I look forward to the days when I too can start practicing this fine maneuver.
 

Starman

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AIRCRAFT - The aircraft can be prepared in a variety of ways to ensure consistently good Groundloops. First of all, 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.
Just reiterating this for a friend. Toe-in causes ground loops, toe-out makes them much less likely
 

Starman

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This is the physics of it as I see it.

Lets say the plane, for whatever reason, presses more on the right wheel. If the right wheel is toed in it will make the airplane move to the left, starting the deviation andthrowing even more weight onto the right wheel, worsening the tipping and looping tendency.

However, if the right wheel is toed out then when the weight presses on the right side it will tend to move the plane to the right, removing the load from that wheel and transferring it more to the left which will tend to pull the plane away from the ground loop.
 

Joe Fisher

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30 or more years ago I saw a Cessna 172 ground loop. The middle eastern pilot came in really hot and tried to force the airplane to the ground with elevator. The nose wheel bounced the airplane a cupple times then with only the nose wheel in contact with the runway and probably 50mph speed the airplane turned 90 to the left.The right main wheel contacted the runway and slammed the right wing to the runway and bent the wing at the strut about 20 deg. up.The pilot insisted that the airplane was defective.This happened at a fly in breakfast and there were at least 50 witnesses.
 

BBerson

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30 or more years ago I saw a Cessna 172 ground loop. The middle eastern pilot came in really hot and tried to force the airplane to the ground with elevator. The nose wheel bounced the airplane a cupple times then with only the nose wheel in contact with the runway and probably 50mph speed the airplane turned 90 to the left.The right main wheel contacted the runway and slammed the right wing to the runway and bent the wing at the strut about 20 deg. up.The pilot insisted that the airplane was defective.This happened at a fly in breakfast and there were at least 50 witnesses.
Yep, riding on the noeswheel only is called "wheelbarrowing". The airplane is very unstable with the weight on the nosewheel. Probably worse than any taildragger because the nosewheel is much further in front of the CG and that makes it unstable.

Keeps repair shops busy, I have rebuilt a few myself.
BB
 

PTAirco

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OK, I'll try to explain the concept of it:

You're rolling along the ground, let's say tail up to remove any influence of the tailwheel. The wheels are toed in. Now the airplane's nose begins to deviate to the left, let's say. The toe-in on the left wheel is now diminishing and reducing the resistance the wheel has with the ground. The right wheel's toe-in is now increasing and with it its drag against the ground. You now have more drag on the right wheel than the left which will cause the right side of the airplane to slow down and the nose to swing back into line.

With toe-out, as soon as the nose starts to swing to the left, as above, the left wheel's drag increases as its toe-out increases, while the right wheel's drag is decreasing, making the nose swing even harder to the left.

No aircraft manual I have ever seen has ever advocated toe-out. A Maule for example, specifies 3/8" to 1/2" toe-in as measured across the front and back centerline of the tire tread. I challenge anyone to show me an example of a manufacturer specifying toe-out on a taildragger, it may specify zero, but never toe-out. Aircraft manufacturers are not stupid and are hardly likely to overlook something so obvious, since the beginning of aviation.

By the way, your car has toe-in on the front wheels for the same reason - go play with the tie rods and toe-out the wheels and see what happens.( It is more readily obvious with a car without power steering.)

I think this is a typical case of an urban myth in the making.
 

davidb

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Cool, the debate continues. I'm putting my money on you PTAirco. I'm not a taildragger pilot yet. I think I understand why a tail dragger has the tendency to ground loop, but what is the usual trigger? Slow reaction to the deviation onset seems to allow the fully developed loop, but what is the start cause? I mean is it usually gusty crosswinds, quartering tailwinds, landing in a drift or crab, or something else?

OK, I'll try to explain the concept of it:

You're rolling along the ground, let's say tail up to remove any influence of the tailwheel. The wheels are toed in. Now the airplane's nose begins to deviate to the left, let's say. The toe-in on the left wheel is now diminishing and reducing the resistance the wheel has with the ground. The right wheel's toe-in is now increasing and with it its drag against the ground. You now have more drag on the right wheel than the left which will cause the right side of the airplane to slow down and the nose to swing back into line.

With toe-out, as soon as the nose starts to swing to the left, as above, the left wheel's drag increases as its toe-out increases, while the right wheel's drag is decreasing, making the nose swing even harder to the left.

No aircraft manual I have ever seen has ever advocated toe-out. A Maule for example, specifies 3/8" to 1/2" toe-in as measured across the front and back centerline of the tire tread. I challenge anyone to show me an example of a manufacturer specifying toe-out on a taildragger, it may specify zero, but never toe-out. Aircraft manufacturers are not stupid and are hardly likely to overlook something so obvious, since the beginning of aviation.

By the way, your car has toe-in on the front wheels for the same reason - go play with the tie rods and toe-out the wheels and see what happens.( It is more readily obvious with a car without power steering.)

I think this is a typical case of an urban myth in the making.
 

PTAirco

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Cool, the debate continues. I'm putting my money on you PTAirco. I'm not a taildragger pilot yet. I think I understand why a tail dragger has the tendency to ground loop, but what is the usual trigger? Slow reaction to the deviation onset seems to allow the fully developed loop, but what is the start cause? I mean is it usually gusty crosswinds, quartering tailwinds, landing in a drift or crab, or something else?
The intial cause can be many things,; landing with any amount of yaw is probably the most common cause. I suppose a gust could hit you just at the wrong time, a wheel could hit a minor obstruction and the pilot over corrects etc.

If you boil it all down, whatever causes the onset of a groundloop, when it becomes inevitable is when the momentum of the CG swinging out of line overcomes your ability to force a correction, whether through rudder or brake or steering inputs. As long as the deviation is small, the force required to correct it is small, like the small force produced by the drag of toed-in wheels for example. Let the CG move far enough out of line and forcexdistance does its thing and you'll run out of available options to correct it.

Once a groundloop gets going all the toe-in/toe-out debate is moot - neither will have much effect compared to the force produced by the aircraft's swinging mass. But it does help the aircraft to track straight while everything is under control.

All the groundloops I have seen personally have been towards the end of the landing roll, when the speed is relatively low and the tail has just settled.

And just to throw fuel on the fire - I am getting very interested in the castoring wheel arrangement found in Helios and Cessna 195s; They will swivel up to about 20 degrees out of line. Up to that degree, it's as if a crosswind didn't exist. I talked to people who have flown them and those who get familiar love the system, a smaller number didn't.
 

dirtstrip

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Toe out helps bring the high wing down on a taildragger increasing stability. Example crosswind landing. Wing low on upwind side, touchdown upwind wheel first. The slightly toe out roll of that wheel helps to add down pressure to that gear strut as it tries to roll forward, tracking under the pressure exerted by low wing's aileron, increasing traction and control for the upwind wheel during the cross wind landing. As correction is continued through roll out the toe out roll of that wheel forces the high wing to come down. Toe in, under that same situation, will cause the upwind wheel to roll away from the lower wing and decreasing traction and control by lessening down pressure on the gear and increasing chance of wing strike or at the very least, over correcting for the wind during rollout which sets up conditions for the ground loop.
Cars on the other hand, ground loop best in reverse with an over correction, similar to tail wheel steering.
 

PTAirco

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Toe out helps bring the high wing down on a taildragger increasing stability. Example crosswind landing. Wing low on upwind side, touchdown upwind wheel first. The slightly toe out roll of that wheel helps to add down pressure to that gear strut as it tries to roll forward, tracking under the pressure exerted by low wing's aileron, increasing traction and control for the upwind wheel during the cross wind landing. As correction is continued through roll out the toe out roll of that wheel forces the high wing to come down. Toe in, under that same situation, will cause the upwind wheel to roll away from the lower wing and decreasing traction and control by lessening down pressure on the gear and increasing chance of wing strike or at the very least, over correcting for the wind during rollout which sets up conditions for the ground loop.
Cars on the other hand, ground loop best in reverse with an over correction, similar to tail wheel steering.

If only one wheel is on the ground, toe-in or toe out is immaterial. On one wheel an airplane behaves like a wheelbarrow - it will go in any direction with equal effort. Toe-in or out is a measured relative to both wheels and it only really affects the airplane while both wheels are on the ground.

I still fail to see how every aircraft manufacturer has got it wrong to this day.
 

davidb

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Once a groundloop gets going all the toe-in/toe-out debate is moot - neither will have much effect compared to the force produced by the aircraft's swinging mass. But it does help the aircraft to track straight while everything is under control.
I think what you just said above might be key to the whole debate. If you are tracking straight and constantly putting in small corrections to go straight then the toe-in will provide a better, more stable platform making it easier to stay straight. Once the "looping" motion starts for whatever reason, seems like proper/timely rudder input will outweigh any toe-in/out effects.

Can both camps agree on just the above statements or do the toe-out guys think toe-out helps the aircraft track straight when everything is under control? I have no taildragger time but I'm building one. Right now I'm going for zero to slight toe-in as that is what the designer suggests--until the next guy chimes in.;)
 

Topaz

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>>> Warning - Humorous content <<<

Personally, I can't understand why you guys feel the need for so many wheels in the first place. One, right in the center, does just fine for me! :gig:
 

dirtstrip

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Sometimes we like to substitute ourselves or our limited experience for real authority on a subject. I am no different. For the benefit of those that are now forming opinions on the matter, I am attaching the experience of EAA builders and the real world observations of time honored authorities who are more experienced in the debate of toe in vs. toe out. The great majority of these people will be older pilots who never "transitioned to tailwheel" but instead, began their flying in one.

The article begins on page three.
http://www.eaahighriver.org/Newsletters/200901_EAA_CHAPTER1410_NEWS.pdf
 

Dan Thomas

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No aircraft manual I have ever seen has ever advocated toe-out. A Maule for example, specifies 3/8" to 1/2" toe-in as measured across the front and back centerline of the tire tread. I challenge anyone to show me an example of a manufacturer specifying toe-out on a taildragger, it may specify zero, but never toe-out. Aircraft manufacturers are not stupid and are hardly likely to overlook something so obvious, since the beginning of aviation.

By the way, your car has toe-in on the front wheels for the same reason - go play with the tie rods and toe-out the wheels and see what happens.( It is more readily obvious with a car without power steering.)

I think this is a typical case of an urban myth in the making.
I flew an Aeronca with the mains toed in. It was a bear. Once we straightened things it was much better.

Most front-wheel drive cars call for toe-out. The wheels pulling forward draw them inward so they're straight when driving. Rear wheel drive will spec a bit of toe-in, which becomes straight once the rolling friction is factored in.

If Maule specifies toe-in, it may be that the wheels straighten under load and friction. What sort of gear legs are they using now? Rod-or leaf-type gear will change alignment a lot under various loads. The Cessna 180/185 manual, for instance, calls for 0.12" toe-in with the cabin and tanks empty; under load, the wheels will come to zero toe-in/toe-out.

Dan
 
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